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Secondary cavity-nesting species must find natural cavities or artificial nest boxes to reproduce. Cavities are often limited, which results in intense interference competition among species that rely on them. Nest site shortages may exclude subordinate individuals from cavities and force them to adopt alternative reproductive tactics such as laying eggs in the nests of conspecifics or in the nests of other species. The Prothonotary Warbler (Protonotaria citrea) is a secondary cavity-nesting bird that opportunistically parasitizes conspecifics that has never been recorded parasitizing heterospecifics. Here, we report brood parasitism of a House Wren (Troglodytes aedon) nest by a Prothonotary Warbler and the subsequent fledging of a warbler from this nest This is the first observation of interspecific brood parasitism for the Prothonotary Warbler and the first instance of interspecific brood parasitism by any New World warbler species. Received 19 January 2024. Accepted 17 June 2024. Key words: cavity nest, House Wren, Troglodytes aedon. (Spanish)--Especies que anidan en cavidades secundarias deben encontrar cavidades naturales o cajas nido artificiales para reproducirse. Las cavidades son usualmente limitadas, lo que resulta en una intensa competencia por interferencia entre especies que dependen de ellas. La escasez de sitios de anidamiento puede excluir individuos subordinados de las cavidades y obligarlos a adoptar estrategias reproductivas alternativas como poner huevos en nidos de conespecificos o en nidos de otras especies. La reinita Protonotaria citrea es una ave que anida en cavidades secundarias que parasita oportunisticamente a conespecificos pero que nunca ha sido grabada parasitando a heteroespecificos. Aqui reportamos parasitismo de nidada en un nido de saltapared Troglodytes aedon por una reinita Protonotaria citrea y el subsecuente emancipamiento de una reinita de ese nido. Esta es la primera observacion de parasitismo de nidada interespecifico por la reinita Protonotaria citrea y la primera instancia de parasitismo de nidada interespecifico por alguna especie de reinita del Nuevo Mundo. Palabras clave: nido en cavidad, saltapared, Troglodytes aedon., Secondary cavity-nesting bird species must find old woodpecker nests, natural cavities within trees, or artificial nest boxes to reproduce. These cavities are often limited, which results in competition for available [...]

Salmonid populations are often regulated by territorial competition among juveniles for food and space. In the canonical view, salmonid territories are spaced horizontally across the river bottom in a two-dimensional mosaic. However, some juveniles instead feed in tight, three-dimensional (3-D) social groups. To investigate whether territoriality is possible within such groups, we applied a new concept--the momentary home range--to quantify the size, exclusivity, and temporal dynamics of 3-D space use by juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Chena River, AK. Individual strategies spanned a broad continuum of exclusivity and stationarity. However, some of the largest, most dominant fish in each group aggressively defended stationary, exclusive feeding spaces and thus were unambiguously territorial. Transient floaters entered and left the group quickly. A majority of fish were not aggressive but nevertheless occupied exclusive, stationary spaces that probably function as territories with regard to resource distribution and population regulation. The presence of territoriality within social groups, in a 3-D configuration, expands the known domain of this important behavior. Key words: territoriality, home range, Chinook salmon, schooling, salmonids, drift foraging, Introduction Patterns of space use are among the most fundamental relationships between animals and their environment, and competition for space strongly affects population dynamics in many species (Adams 2001). For [...]

We examined the performance of sweetgum (Liquidambar styraciflua L.), cherrybark oak (Quercus pagoda Raf.), and loblolly pine (Pinus taeda L.) in two-species pine-hardwood mixtures (sweetgum : loblolly pine and cherrybark oak : loblolly pine) at various planting densities (1482-1976 trees per hectare (TPH)) over 23 years in northern Louisiana, USA. Species were planted in alternating rows with hardwood establishment occurring 1 year prior to loblolly pine. Mixtures were also compared to loblolly pine monocultures at a common density (1482 TPH) to assess whether mixing improved productivity. Sweetgum exerted more competitive pressure on loblolly pine than cherrybark oak. At final measurement, sweetgum survival statistically exceeded that of loblolly pine across mixture density. Moreover, sweetgum cumulative basal area and volume growth nearly tripled that of loblolly pine in balanced high-density mixtures (1976 TPH, 50 pine : 50 hardwood). In contrast, cherrybark oak basal area and volume growth did not significantly exceed loblolly pine at any density. At a common density (1482 TPH), loblolly pine monoculture cumulative basal area and volume significantly exceeded those of mixtures with sweetgum and cherrybark oak by 19% and 24%, respectively. Collectively, these results indicate that growing loblolly pine in mixture with these two species did not produce complementary interactions and negatively affected stand-level growth. Key words: overyielding, loblolly pine, cherrybark oak, sweetgum, interspecific competition, mixed stands Nous avons examine la performance du copalme d'Amerique (Liquidambar styraciflua L.), du chene a feuilles en pagode (Quercus pagoda Raf.) et du pin a encens (Pinus taeda L.) dans des melanges de pins et de feuillus a deux especes (copalme d'Amerique : pin a encens et chene a feuilles en pagode : pin a encens) a diverses densites de plantation (1482 a 1976 TPH) pendant 23 ans dans le nord de la Louisiane, aux Etats-Unis. Les especes ont ete plantees en rangs alternes, l'etablissement des feuillus ayant lieu un an avant celui des pins a encens. Les melanges ont egalement ete compares aux monocultures de pin a encens a une densite commune (1482 TPH) pour evaluer si le melange ameliorait la productivite. Le copalme d'Amerique a exerce une plus grande pression concurrentielle sur le pin a encens que le chene a feuilles en pagode. Lors de la mesure finale, la survie du copalme d'Amerique a statistiquement depasse celle du pin a encens, quelle que soit la densite du melange. De plus, la croissance cumulative de la zone basale et du volume du copalme d'Amerique a presque triple par rapport a celle du pin a encens dans les melanges equilibres a haute densite (1976 TPH, 50 pins : 50 feuillus). En revanche, la croissance de la surface terriere et du volume du chene a feuilles en pagode n'a pas depasse de maniere significative celle du pin a encens, quelle que soit la densite. A une densite commune (1482 TPH), la zone basale et le volume cumules de la monoculture du pin a encens ont depasse de maniere significative ceux des melanges avec le copalme d'Amerique et le chene a feuilles en pagode de 19% et 24%, respectivement. Collectivement, ces resultats indiquent que la culture du pin a encens en melange avec ces deux especes n'a pas produit d'interactions complementaires et a affecte negativement la croissance au niveau du peuplement. [Traduit par la Redaction] Mots-cles : rendement excessif, pin a encens, chene a feuilles en pagode, copalme d'Amerique, competition interspecifique, peuplements mixtes, Introduction Maintaining productive forests is a global priority. Historically, monocultures have been established to maximize forest productivity (Rubilar et al. 2018). However, concerns over declining biodiversity, enhanced risk of species-specific [...]

Effect of neighbor tree competition on crown shape of Korean pine plantation in Northeast China was studied. A total of 48 trees aged 7-58 years were felled, and all living branches were measured. A novel neighbor competition index that considered the overlap length between subject tree and neighbor tree crowns was created and incorporated into crown shape model. The effects of neighboring competition on crown shape, largest crown radius, and inflection point were analyzed. A dummy variable approach was used to detect crown asymmetry. The crown length index (CLI) of the subject tree was selected as the best neighbor competition index, and the mean square error reduction compared with that of the basic model was 2.0% after incorporating CLI. Crown radius displayed differences in the four cardinal directions and followed the order north > west > south > east. The crown radius in four directions for different ages decreased with increasing CLI and the difference increased with increasing tree age. The competition index, which considers horizontal and vertical competition effects, can significantly improve the performance of crown shape model. Both of inflection point and largest crown radius increased with increasing of CLI; however, the Pearson correlation coefficient was not significant (P > 0.05). Key words: crown radius, crown length index, modified Kozak equation, crown asymmetry, branch analysis L'etude a porte sur l'effet de la concurrence entre arbres voisins sur la forme de la couronne d'une plantation de pins coreens dans le nord-est de la Chine. Au total, 48 arbres ages de 7 a 58 ans ont ete abattus, et toutes les branches vivantes ont ete mesurees. Nous avons cree un nouvel indice de competition entre voisins, qui prend en compte la longueur de chevauchement entre les couronnes de l'arbre sujet et de l'arbre voisin, et nous l'avons integre au modele de forme de couronne. Les effets de la competition des voisins sur la forme de la couronne, le plus grand rayon de la couronne et le point d'inflexion ont ete analyses. L'analyse a utilise une approche par variable muette pour detecter l'asymetrie des couronnes. L'indice de longueur de couronne (ILC) de l'arbre concerne a ete selectionne comme le meilleur indice de competition entre voisins, et la reduction de l'erreur quadratique moyenne par rapport a celle du modele de base etait de 2,0 % apres l'incorporation de l'ILC. Le rayon de la couronne presente des differences dans les quatre directions cardinales et suit l'ordre suivant : nord > ouest > sud > est. Le rayon de la couronne dans les quatre directions pour differents ages a diminue avec l'augmentation de l'ILC et la difference a augmente avec l'age de l'arbre. L'indice de competition, qui prend en compte les effets de la concurrence horizontale et verticale, peut ameliorer considerablement les performances du modele de forme de couronne. Le point d'inflexion et le plus grand rayon de la couronne augmentent avec l'augmentation de l'ILC; cependant, le coefficient de correlation de Pearson n'est pas significatif (P > 0,05). [Traduit par la Redaction] Mots-cles: rayon de la couronne, indice de longueur de couronne, equation de Kozak modifiee, asymetrie de la couronne, analyse des branches, Introduction The crown shape of an individual tree plays an important role in determining tree growth and forest productivity (Valentine et al. 2012) and has a strong functional relationship with [...]

Species can alleviate competition by reducing diet overlap. Non-native coyotes (Canis latrans Say, 1823) and historically native gray foxes (Urocyon cinereoargenteus (Schreber, 1775)) have expanded their ranges and may compete with native red foxes (Vulpes vulpes (Linnaeus, 1758)). To examine potential competition among canids in Maine, USA, we compared [[delta].sup.13]C and [[delta].sup.15]N from muscle and hair samples to assess relative resource use, and we compared frequency of occurrence of prey items from stomach contents to assess diets. For these species, red foxes consumed anthropogenically based foods the most in fall and early winter, gray foxes consumed anthropogenically based foods the most in summer, and coyotes consumed anthropogenically based foods the least in all seasons. Coyotes held the highest relative trophic position in fall and early winter, red foxes held the highest relative trophic position in summer, and gray foxes held the lowest relative trophic position. Based on stomach contents, gray foxes had the broadest diet and consumed the most plants, and coyotes had the narrowest diet. Red foxes were the only species to show isotopic niche overlap with both potential competitors across seasons. Thus, they may be most susceptible to competitive exclusion among these canids, with implications for community dynamics as ranges shift due to human activity. Key words: Canis latrans, coexistence, competition, coyote, diet analysis, red fox, gray fox, stable isotopes, Urocyon cinereoargenteus, Vulpes vulpes. Certaines espèces peuvent limiter leur concurrence en réduisant le chevauchement de leurs régimes alimentaires. Les coyotes (Canis latrans Say, 1823) non indigènes et les renards gris (Urocyon cinereoargenteus (Schreber, 1775)) historiquement indigènes ont élargi leurs aires de répartition et pourraient être en concurrence avec des renards roux (Vulpes vulpes (Linnaeus, 1758)) indigènes. Afin d'examiner la concurrence potentielle entre canidés dans le Maine (Etats-Unis), nous avons comparé le [[delta].sup.13]C et le [[delta].sup.15]N d'échantillons de muscle et de poil afin d'évaluer l'utilisation relative des ressources et nous avons comparé la fréquence de présence d'éléments de proies dans les contenus stomacaux pour évaluer les régimes alimentaires de ces canidés. De ces espèces, les renards roux sont ceux qui consomment le plus d'aliments d'origine humaine à l'automne et au début de l'hiver, les renards gris en consommant le plus en été et les coyotes en consommant le moins toutes les saisons. Les coyotes occupent la position trophique relative la plus élevée à l'automne et au début de l'hiver, les renards roux l'occupant à l'été et les renards gris occupant la position trophique relative la plus basse. À la lumière des contenus stomacaux, les renards gris présentent le régime alimentaire le plus large et consomment le plus de plantes et les coyotes présentent le régime alimentaire le plus étroit. Les renards roux constituent la seule espèce dont la niche isotopique chevauche celles de ses deux concurrents potentiels toutes les saisons et pourraient donc constituer, de ces canidés, l'espèce la plus susceptible de subir une exclusion concurrentielle, avec des conséquences sur la dynamique des communautés au fil des modifications des aires de répartition causées par l'activité humaine. [Traduit par la Rédaction] Mots-clés : Canis latrans, coexistence, concurrence, coyote, analyse du régime alimentaire, renard roux, renard gris, isotopes stables, Urocyon cinereoargenteus, Vulpes vulpes., Introduction To reduce costs of competition and promote coexistence, species may partition resources by choosing different prey items and adjusting diets seasonally (Palomares and Caro 1999; Neale and Sacks 2001). [...]

One of the causes of nest failure in woodpeckers is competition for nest sites among cavity-nesting bird species, expressed through aggressive interactions. Here I report a case of mortal aggression by an adult White-fronted Woodpecker (Melanerpes cactorum) toward nestlings of the White-barred Piculet (Picumnus cirratus), presumably caused by interference competition, in the dry Chaco woodlands of northwestern Argentina. The woodpecker killed 2 piculet nestlings but did not consume or remove them to feed its own nestlings. The attack could have been motivated by territorial defense, and to reduce competition for nest sites, since the piculet nest was within the territory of the woodpecker, and near its active nest and one of its most consumed sap trees. The observations described here provide new ethological information about the levels of aggression of the White-fronted Woodpecker, and suggests that interspecific competition likely could constitute one of the causes of nest failure among Neotropical woodpeckers. Received 6 February 2019. Accepted 4 February 2020. Key words: cavity-nesting birds, interspecific interference competition, nest failure Una de las causas del fracaso de nidos en pájaros carpinteros es la competencia por los sitios de anidación entre especies de aves que anidan en cavidades, expresada a través de interacciones agresivas. En este trabajo reporto un caso de agresión mortal de un adulto de carpintero de los cardones (Melanerpes cactorum) hacia pichones de carpinterito común (Picumnus cirratus), presumiblemente causado por competencia por interferencia, en los bosques secos del Chaco del noroeste de Argentina. El carpintero de los cardones mató a dos pichones, pero no los consumió ni los removió para alimentar a sus propios pichones. El ataque podría haber sido por defensa territorial y para reducir la competencia por los sitios de anidación, ya que el nido del carpinterito común estaba dentro del territorio del carpintero de los cardones, cerca de su nido activo y de uno de los árboles para consumo de savia más utilizados. Las observaciones descritas en este trabajo proporcionan nueva información etológica sobre los niveles de agresión del carpintero de los cardones y sugieren que la competencia interespecífica podría constituir una de las causas de fracaso de nidos entre los pájaros carpinteros neotropicales. Palabras clave: aves que anidan en cavidades, competencia por interferencia interespecífica, fracaso de nidos, One of the causes of nesting failure in cavity-nesting bird species is the competition for nest sites expressed through aggressive interactions (Nilsson 1984, Paclik et al. 2009). Considered a case [...]

Bare sandy flats at and below low tide level of the Wadden Sea (eastern North Sea, European Atlantic) were observed in 2020 to have been invaded by an introduced grass-like alga, Vaucheria cf. velutina (Xanthophyceae). A dense algal turf accumulated and stabilized mud, where resident seniors of the lugworm Arenicola marina had reworked rippled sand. Algae and worms were incompatible. Initially, rising patches with algal turf alternated with bare pits where lugworms crowded. Their bioturbation inhibited young algae, while the felt of established algal rhizoids clogged feeding funnels of worm burrows. Eventually, a mosaic pattern of competitors gave way to a coherent algal turf without lugworms. Concomitantly, a rich small-sized benthic fauna took advantage of the novel algal turf. This exotic Vaucheria may have the potential for drastically altering the ecological web at the lower shore., Author(s): Karsten Reise [sup.1] , Dagmar Lackschewitz [sup.1] , K. Mathias Wegner [sup.1] Author Affiliations: (1) grid.10894.34, 0000 0001 1033 7684, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine [...]

The purpose of this study was to update rainbow trout (Oncorhynchus mykiss) invasion status, delineate factors that increase the invasion probability, and quantify habitat overlap between invasive rainbow trout and native Atlantic salmon (Salmo salar) and brook trout (Salvelinus fontinalis) on Prince Edward Island, Canada. Analysis of landscape-level variables in 26 watersheds (14 with and 12 without rainbow trout) demonstrated that watershed slope, percent agricultural land use, and distance to the nearest rainbow trout population significantly increased the probability of rainbow trout establishment. Two independent reach-level fish community surveys were conducted by electrofishing in combination with habitat surveys. Reaches with rainbow trout had higher stream slope, Atlantic salmon were found in wider reaches with larger substrate, and brook trout were typically dominant in headwater reaches with finer substrate. Findings at multiple ecological scales illustrated that rainbow trout invasion success is positively influenced by the presence of high-slope habitat. Habitat separation of the three salmonid species indicates that competition with introduced rainbow trout may not be the most significant threat to native salmonid populations. Le but de l'etude etait d'actualiser l'etat des envahissements de truites arc-en-ciel (Oncorhynchus mykiss), circonscrire les facteurs qui accroissent la probabilite d'envahissement et quantifier le chevauchement d'habitats entre la truite arc-en-ciel envahissante et le saumon atlantique (Salmo salar) et l'omble de fontaine (Salvelinus fontinalis), deux especes indigenes, dans l'lle du Prince Edouard (Canada). L'analyse de variables du paysage dans 26 bassins versants (14 avec des truites arc-en-ciel et 12 sans) demontre que la pente du bassin versant, la proportion de sols agricoles et la distance par rapport a la population de truites arc-en-ciel la plus proche accroissent significativement la probabilite d'etablissement de truites arc-en-ciel. Deux releves independants des communautes de poissons a l'echelle du tronqon ont ete menes par peche electrique de concert avec des inventaires des habitats. Les tronqons comptant des truites arc-en-ciel avaient des pentes plus fortes, les saumons atlantiques se trouvaient dans des tronqons plus larges presentant un substrat plus grossier et les ombles de fontaine etaient typiquement dominants dans les tronqons d'amont caracterises par un substrat plus fin. Des observations a differentes echelles ecologiques indiquent que le succes d'envahissement des truites arc-en-ciel est positivement influence par la presence d'habitats de forte pente. La separation des habitats des trois especes de salmonides indique que la concurrence avec des truites arc-en-ciel introduites pourrait ne pas etre la plus grande menace pour les populations de salmonides indigenes. [Traduit par la Redaction], Introduction The global stocking of rainbow trout (Oncorhynchus mykiss) makes them among the most ubiquitously introduced fish species (Fausch et al. 2001; Marchetti et al. 2004; Crawford and Muir 2008). [...]

Competing species and predators can alter the habitat use of animals, but both factors are rarely simultaneously controlled. We studied in experimental enclosures how closely related species, the sibling vole (Microtus levis Miller, 1908) and the field vole (Microtus agrestis (Linnaeus, 1761)), adjust their habitat use when facing either the competing species or simultaneously competition and predation risk. The species responded differently in their proportional use of two habitat types, a low cover (productive but riskier) and a high cover (safer but poorer). When alone, field voles used the low-cover habitat according to availability at low densities, but decreased its use with increasing density. Sibling voles, however, avoided the low-cover habitat in single-species populations. Under interspecific competition, the habitat-use patterns switched between species: sibling voles used the low-cover habitat according to availability, with decreasing use as densities increased. Sibling voles responded to predation risk by showing a stronger density-dependent decrease in the use of low-cover habitat. Field voles, initially using mostly high cover, did not change behaviour under risk of predation. Our results highlight the importance of considering both predation risk and interspecific competition when interpreting patterns of habitat selection among coexisting species. Key words: coexistence, density-dependent habitat use, field vole, Microtus agrestis, Microtus levis, sibling vole. Les especes concurrentes et les predateurs peuvent modifier l'utilisation de l'habitat par les animaux, mais les deux facteurs sont rarement examines simultanement. Nous avons etudie, dans des enclos experimentaux, la modification de l'utilisation d'habitats par deux especes etroitement reliees, le campagnol d'Ondrias (Microtus levis Miller, 1908) et le campagnol agreste (Microtus agrestis (Linnaeus, 1761)), en presence soit de l'espece concurrente ou de risques de concurrence et de predation simultanes. Les deux especes ont presente des reactions differentes en ce qui concerne leur utilisation proportionnelle de deux types d'habitats, un de faible couvert (productif, mais a plus haut risque) et l'autre de couvert plus dense (plus sur, mais plus pauvre). Quand ils etaient seuls, les campagnols agrestes utilisaient l'habitat de plus faible couvert selon sa disponibilite a faibles densites, mais reduisaient leur utilisation de cet habitat a plus grandes densites. Les campagnols d'Ondrias, pour leur part, evitaient l'habitat de faible couvert dans les populations a une seule espece. En situation de concurrence interspecifique, les motifs d'utilisation d'habitats des deux especes s'intervertissaient, les campagnols d'Ondrias utilisant l'habitat de faible couvert selon la disponibilite, cette utilisation diminuant a plus fortes densites. Les campagnols d'Ondrias reagissaient au risque de predation par une plus grande reduction dependante de la densite de leur utilisation de l'habitat a faible couvert. Les campagnols agrestes, qui utilisaient surtout l'habitat a couvert dense initialement, ne changeaient pas de comportement en presence d'un risque de predation. Nos resultats soulignent l'importance de tenir compte du risque de predation et de la concurrence interspecifique au moment d'interpreter les motifs de selection de l'habitat chez des especes qui coexistent. [Traduit par la Redaction] Mots-cles : coexistence, utilisation des habitats dependante de la densite, campagnol agreste, Microtus agrestis, Microtus levis, campagnol d'Ondrias., Introduction Competition for resources is one of the ecological factors known to have a strong impact on animal communities (e.g., Hairston et al. 1960; Gurevitch et al. 1992) and may [...]

The tremendous diversity of species in ecological communities has motivated a century of research into the mechanisms that maintain biodiversity. However, much of this work examines the coexistence of just pairs of competitors. This approach ignores those mechanisms of coexistence that emerge only in diverse competitive networks. Despite the potential for these mechanisms to create conditions under which the loss of one competitor triggers the loss of others, we lack the knowledge needed to judge their importance for coexistence in nature. Progress requires borrowing insight from the study of multitrophic interaction networks, and coupling empirical data to models of competition., Author(s): Jonathan M. Levine (corresponding author) [1]; Jordi Bascompte [2]; Peter B. Adler [3]; Stefano Allesina [4] The goal of ecological research on species coexistence is to explain how the [...]

As global climatic changes increase plant susceptibility to large-scale disturbances such as drought and pathogens, understory responses to these disturbances will become increasingly important to long-term forest dynamics. To better understand understory responses to canopy disturbance, we measured changes in the growth and physiology of the dominant understory shrub, American witch-hazel (Hamamelis virginiana L.), in response to girdling of canopy oaks in a temperate hardwood forest of the northeastern United States. Changes in the growth and physiology of H. virginiana may be important to the regeneration of northeastern temperate forests, as this common shrub largely shapes the microenvironment for seedlings on the forest floor where it occurs. Canopy disturbance by girdling resulted in significant increases in light and soil nitrogen availability. In response to these environmental changes, basal-area growth of H. virginiana increased by an average 334%. This growth increase corresponded to significant increases in foliar nitrogen, respiration, and leaf chlorophyll and carotenoid concentrations. These findings indicate improved environmental conditions and increased growth for this understory shrub following the loss of dominant canopy trees. This study suggests that following large-scale canopy disturbance, H. virginiana and shrubs like it may play an important role in competing for soil N and shading seedlings of regenerating canopy species. Key words: Black Rock Forest, canopy disturbance, foliar chemistry, photosynthesis, respiration. A mesure que les changements climatiques a l'echelle planetaire augmentent la sensibilite des plantes aux perturbations a grande echelle, telles que la secheresse et les agents pathogenes, les reactions du sous-bois face a ces perturbations vont devenir de plus en plus importantes pour la dynamique forestiere a long terme. Dans le but de mieux comprendre les reactions du sous-bois aux perturbations du couvert forestier, nous avons mesure les changements dans la croissance et la physiologie de l'arbuste de sous-bois dominant, l'hamamelis de Virginie (Hamamelis virginiana L.), en reaction a l'annelation des chenes de l'etage dominant dans une foret feuillue temperee du nord-est des Etats-Unis. Les changements dans la croissance et la physiologie de l'hamamelis pourraient avoir des repercussions importantes sur la regeneration des forets temperees du nord-est etant donne l'influence determinante de cet arbuste commun sur le microenvironnement des semis au sol ou il est present. La perturbation du couvert forestier par l'annelation a entraine une augmentation significative de la disponibilite de la lumiere et de l'azote dans le sol. En reaction a ces changements environnementaux, la croissance en surface terriere de l'hamamelis a augmente en moyenne de 334 %. Cette augmentation de croissance correspond a des augmentations significatives de l'azote foliaire, de la respiration et des concentrations de chlorophylle et de carotenoide dans les feuilles. Ces resultats sont un indice de meilleures conditions environnementales et d'une croissance accrue pour cet arbuste de sous-bois a la suite de la perte des arbres de l'etage dominant. Cette etude indique qu'a la suite d'une perturbation a grande echelle du couvert forestier, l'hamamelis et les arbustes semblables pourraient jouer un role important en competitionnant pour l'azote dans le sol et en ombrageant les semis des especes de l'etage dominant qui se regenerent. [Traduit par la Redaction] Mots-cles: foret de Black Rock, perturbation du couvert forestier, chimie foliaire, photosynthese, respiration., Introduction Temperate hardwood forests play an important role in regulating water and nutrients, sequestering carbon (C), and providing habitat for biodiversity. In the United States (US) and southern Canada, many [...]

Understanding how climate affects tree growth is essential for assessing climate change impacts on forests but can be confounded by effects of competition, which strongly influences tree responses to climate. We characterized the joint influences of tree size, competition, and climate on diameter growth using hierarchical Bayesian methods applied to permanent sample plot data from the montane forests of Mount Rainier National Park, Washington State, USA, which are mostly comprised of Abies amabilis Douglas ex Forbes, Tsuga heterophylla (Raf.) Sarg., Pseudotsuga menziesii (Mirb.) Franco, and Thuja plicata Donn ex D. Don. Individual growth was sensitive to climate under low but not high competition, likely because tree ability to increase growth under more favorable climates (generally greater energy availability) was constrained by competition, with important variation among species. Thus, climate change will likely increase individual growth most in uncrowded stands with lower competition. However, crowded stands have more and (or) larger trees, conferring greater capacity for aggregate absolute growth increases. Due to these contrasting effects, our models predicted that climate change will lead to greater stand-scale growth increases in stands with medium compared with low crowding but similar increases in stands with medium and high crowding. Thus, competition will mediate the impacts of climate change on individual- and stand-scale growth in important but complex ways. Key words: climate change, competition, Pacific Northwest, stand structure, water balance. Il est essentiel de comprendre comment le climat influence la croissance des arbres pour evaluer les impacts des changements climatiques sur la croissance des forets, mais les effets du climat peuvent etre confondus avec ceux de la competition qui influence grandement la reaction des arbres au climat. Nous avons caracterise l'influence conjointe de la taille des arbres, de la competition et du climat sur la croissance en diametre a l'aide de methodes hierarchiques bayesiennes appliquees a des donnees provenant de placettes echantillons permanentes dans les forets montagnardes du parc national du mont Rainier dans l'Etat de Washington, aux Etats-Unis. Ces forets sont surtout composees d'Abies amabilis Douglas ex Forbes, de Tsuga heterophylla (Raf.) Sarg., de Pseudotsuga menziesii (Mirb.) Franco et de Thuja plicata Donn ex D. Don. La croissance des arbres individuels etait sensible au climat lorsque la competition etait faible mais pas lorsqu'elle etait forte, probablement parce que la capacite des arbres a augmenter leur croissance sous des climats plus favorables (generalement plus de disponibilite d'energie) etait limitee par la competition et la variation entre les especes etait importante. Ainsi, les changements climatiques augmenteront probablement davantage la croissance des arbres individuels dans les peuplements plus ouverts ou la competition est faible. Cependant, les peuplements denses comportent plus d'arbres ou des arbres plus gros, ce qui leur confere une plus grande capacite pour augmenter leur croissance totale absolue. A cause de ces effets contrastes, nos modeles prevoient une plus grande augmentation de la croissance due aux changements climatiques dans les peuplements de densite moyenne que de densite faible, mais des augmentations similaires dans les peuplements de densites moyenne et forte. Par consequent, la competition va conditionner les impacts des changements climatiques sur la croissance des arbres et des peuplements, et ce, de facon importante mais complexe. [Traduit par la Redaction] Mots-cles: changements climatiques, competition, region du Nord-Ouest du Pacifique, structure des peuplements, bilan hydrique., Introduction Understanding the relationship between tree growth and climate is essential for assessing the impacts of climate change on forests, but it is confounded by the effects of competition on [...]

Destruction of conspecific and heterospecific eggs and nestlings occurs in several species of passerines. Two main hypotheses have been proposed to explain the adaptiveness of this behavior: as a mechanism to avoid competition or to gain access to reproductive opportunities. In Colombia, Southern House Wrens (Troglodytes aedon musculus) broke eggs and/or killed nestlings of Spectacled Parrotlets (Forpus conspicillatus, 24 cases), Apical Flycatcher (Myiarchis apicalis, one case) and of other House Wrens (four cases). Wrens attacked parrotlet nests in three contexts: 1) wrens took over and used a parrotlet nestbox within their territory, 2) wrens with an active nest attacked a neighboring parrotlet nest, or 3) the attacker was unknown but was inferred to be a wren. Wrens also attacked trial nests with natural and artificial wren eggs that were placed near active wren nests. These observations suggest that infanticidal behavior by wrens at this locality may be driven by competition for nest sites. In contrast, infanticide by House Wrens in Panama has been related to territorial takeover and mate replacement. The context and causes of infanticidal behavior are spatially and temporally variable, both within and between species. Received 28 July 2015. Accepted 4 February 2016. Key words: Apical Flycatcher, House Wren, infanticide, interference competition, Spectacled Parrotlet., Nest destroying or infanticidal behavior, in which birds break eggs and kill nestlings in the nests of other individuals, occurs in several species of passerines. In the 1980s, when studies [...]

In stream-living salmonids, an underlying mechanism for the critical period after emergence has generally been assumed to be size-dependent swimming capacity constraining fry (age-0) to low-velocity habitats with reduced food availability and intense competition. A further plausible mechanism is that intercohort habitat exclusion confines fry to marginal habitats. This possibility was tested using a seminatural stream with 16 test arenas, each comprising one high-velocity, deep habitat and one low-velocity, shallow habitat. We observed groups of newly emerged Atlantic salmon (Salmo salar) fry, either alone or in sympatry with one or two age-1 salmon. Salmon fry used high-velocity areas (42.2 ± 0.4 cm-[s.sup.-1]) most extensively in the absence of intercohort competition, where they obtained more food than in low-velocity areas (3.3 ± 0.3 cm-[s.sup.-1]), even though foraging efficiency was lower (though not significantly so). In sympatry with older cohorts, fry increased their use of the low-velocity habitat, with a reduced foraging activity, suggesting that strong older cohorts in natural populations may have the potential to influence the strength of the recruiting cohort by negative density dependence due to interference competition for habitat. Il a generalement ete presume que, chez les salmonides vivant dans les cours d'eau, le fait que les alevins (0 an) sont limites par leur capacite natatoire dependante de la taille a des habitats de faible velocite caracterises par une faible disponibilite de nourriture et une concurrence intense constituait un mecanisme sous-jacent pour la periode critique apres l'emergence. Un autre mecanisme plausible veut que l'exclusion inter-cohorte de l'habitat confine les alevins a des habitats marginaux. Cette possibilite a ete verifiee en utilisant un cours d'eau semi-naturel comptant 16 arenes d'essai comprenant chacune un habitat d'eau profonde de forte velocite et un habitat peu profond de faible velocite. Nous avons observe des groupes d'alevins de saumon atlantique (Salmo salar) nouvellement emerges, seuls ou en sympatrie avec un ou deux saumons d'un an. Les alevins utilisaient les zones de forte velocite (42,2 ± 0,4 cm*[s.sup.-1]) plus intensement en l'absence de concurrence inter-cohorte, ou ils y obtenaient plus de nourriture que dans les zones de faible velocite (3,3 ± 0,3 cm*[s.sup.-1]), meme si l'efficacite d'approvisionnement y etait plus faible (mais pas significativement). En sympatrie avec des cohortes plus vieilles, les alevins faisaient un usage accru de l'habitat de faible velocite et reduisaient leur activite d'approvisionnement, ce qui donne a penser que les cohortes fortes plus vieilles dans les populations naturelles pourraient influencer la force de la cohorte qui recrute par une dependance negative sur la densite decoulant de la concurrence pour l'habitat. [Traduit par la Redaction], Introduction In an environment with limited food supply, growth of organisms may be associated with increased per capita demands, resulting in a progressive reduction in their total number. Such progressive, [...]

Interspecific competition among secondary cavity nesters can involve physical conflicts between individuals, which may lead to serious injuries or death. Here we report a case of aggression by a pair of Chilean Swallows (Tachycineta meyeni) towards a nestling of the Thorn-tailed Rayadito (Aphrastura spinicauda) in the sub-Antarctic forests of Chile. This aggression caused the displacement of the breeding rayaditos from an occupied nest box and it appears, nestling mortality. Since levels of aggression among cavity nesters depend on the synchrony of their breeding phenologies, further research is needed to study the prevalence of nest usurpation by Chilean Swallows and its relation to the degree of breeding synchrony with other cavity nesters inhabiting the sub-Antarctic forests. Received 13 May 2014. Accepted 23 October 2014. Key words: Aphrastura spinicauda, interspecific aggression, nest box, nest-site competition, nestling mortality, Tachycineta meyeni., Nest-site availability is a key limiting factor in bird populations, especially for secondary cavity nesters, which cannot excavate their own cavities and therefore must rely on existing holes produced by [...]

Competition between native and invasive species may bring about a suite of ecological and evolutionary outcomes, including local extirpations. In the Laurentian Great Lakes, competition for food may explain the dramatic decline of Diporeia spp. amphipods following the introduction of dreissenid mussels. This hypothesis has not been confirmed, in part because dreissenids and Diporeia appear to co-exist and flourish in other systems, including the Finger Lakes of New York. We used carbon, nitrogen, hydrogen, and oxygen stable isotope ratios to examine resource use by Diporeia from three spatially distinct populations (Lake Michigan, Lake Superior, and Cayuga Lake), dreissenids from areas where they co-occur with Diporeia (Lake Michigan and Cayuga Lake), and Diporeia from Lake Michigan collected before and after dreissenid invasion (1986-2009). Our results suggest that dreissenids may affect resource use by Diporeia in areas of co-occurrence, but the extent to which those effects are positive or negative is unclear. Terrestrial inputs may provide an important subsidy for Diporeia populations in small systems but may not be substantial enough in the Great Lakes to ensure that both taxa thrive. La concurrence entre especes indigenes et envahissantes peut entrainer une serie de changements ecologiques et evolutifs, dont la disparition locale de certaines especes. Dans les Grands Lacs laurentiens, la concurrence pour la nourriture pourrait expliquer l'importante diminution de l'abondance des amphipodes Diporeia spp. apres l'introduction de moules de la famille des dreissenides. Cette hypothese n'a toutefois pas ete confirmee, notamment parce que les dreissenides et les Diporeia semblent bien coexister dans d'autres systemes, dont les Finger Lakes de l'Etat de New York. Nous avons utilise les rapports d'isotopes stables du carbone, de l'azote, de l'hydrogene et de l'oxygene pour examiner l'utilisation des ressources par les Diporeia de trois populations distinctes dans l'espace (les lacs Michigan, Superieur et Cayuga), les dreissenides de regions ou des Diporeia sont egalement presents (les lacs Michigan et Cayuga) et des Diporeia du lac Michigan preleves avant et apres l'invasion de dreissenides (1986-2009). Nos resultats donnent a penser que les dreissenides pourraient avoir une incidence sur l'utilisation des ressources par les Diporeia dans les regions ou les deux groupes coexistent, bien que la mesure dans laquelle ses effets sont positifs ou negatifs demeure incertaine. Des apports de source terrestre pourraient fournir un important subside aux populations de Diporeia dans de petits systemes, mais ne pas etre suffisamment importants pour assurer le succes des deux taxons dans les Grands Lacs. [Traduit par la Redaction], Introduction Accidental or intentional introductions of non-native species can have dire ecological and economic consequences to freshwater ecosystems. In North America, the offshore benthic macroinvertebrate communities of deep, glaciated lakes [...]

Thinning treatments to accelerate coastal redwood forest stand development are in wide application, but managers have yet to identify prescriptions that might best promote Sequoia sempervirens (Lamb. ex D. Don) Endl. (redwood) growth. The creation of successful thinning prescriptions would be aided by identifying the underlying mechanisms governing how individual tree growth responds to competitive environments in coastal redwood forests. We created a spatially explicit individual-based model of tree competition and growth parameterized using surveys of upland redwood forests at Redwood National Park, California. We modeled competition for overstory trees (stems ≥ 20 cm stem diameter at breast height, 1.37 m (dbh)) as growth reductions arising from sizes, distances, and species identity of competitor trees. Our model explained up to half of the variation in individual tree growth, suggesting that neighborhood crowding is an important determinant of growth in this forest type. We used our model to simulate the effects of novel thinning prescriptions (e.g., 40% stand basal area removal) for redwood forest restoration, concluding that these treatments could lead to substantial growth releases, particularly for S. sempervirens. The results of this study, along with continued improvements to our model, will help to determine spacing and species composition that best encourage growth. Key words: forest dynamics, Sequoia sempervirens, spatial pattern, tree growth. Les traitements d'eclaircie visant a accelerer le developpement des peuplements de sequoia cotier (Sequoia sempervirens (Lamb. ex D. Don) Endl.) sont largement appliques, mais les amenagistes n'ont pas encore identifie les modalites qui optimiseraient la croissance du sequoia. La mise au point de prescriptions adequates seraient facilitee par l'identification des mecanismes qui determinent la reaction de croissance des arbres a leur environnement competitif dans les forets de sequoia cotier. Nous avons parametre un modele de croissance et de competition spatialement explicite a l'echelle de l'arbre a partir d'inventaires de forets bien drainees de sequoia du parc national de Sequoia en Californie. Nous avons modelise la competition des arbres dominants (arbres d'au moins 20 cm de DHP) en termes de reduction de croissance causee par des arbres concurrents selon leur taille, leur distance et leur espece. Notre modele explique jusqu'il 50 % de la variation de la croissance des arbres individuels, ce qui indique que la concurrence des arbres voisins est un facteur important de la croissance dans ce type forestier. Nous avons utilise notre modele pour simuler les effets de nouvelles modalites d'eclaircie (p. ex.: prelevement de 40 % de la surface terriere du peuplement) pour restaurer les forets de sequoia, ce qui nous a permis de conclure que ces traitements peuvent engendrer des reactions de croissance substantielles, particulierement dans le cas de S. sempervirens. Les resultats de cette etude, de meme que les ameliorations continues apportees a notre modele, devraient aider a determiner l'espacement et la composition en especes qui favorisent une meilleure croissance. [Traduit par la Redaction] Mots-cles: dynamique forestiere, Sequoia sempervirens, patron spatial, croissance des arbres., Introduction A primary challenge in conserving coastal redwood ecosystems is the restoration of degraded forests. The need for action is clear: over 90% of coastal redwood forests have been logged [...]

Common carp Cyprinus carpio is a ubiquitous invasive species that commonly imposes negative effects on aquatic ecosystems. However, research evaluating the effects of carp on native fishes is limited. Carp are highly fecund and larvae and juveniles can be abundant. If age-0 carp use similar prey resources as native fishes, they may compete if food becomes limited. We used traditional diet analysis for samples during Jul. and Aug. 2008 in Brant Lake. Stable isotopes were used for samples collected during Aug. and Sep. 2009 in Brant Lake and Lake Sinai to examine prey resource use by age-0 carp and four native fishes: bluegill Lepomis macrochims, black crappie Pomoxis nigromaculatus, yellow perch Perea flavescens, and orangespotted sunfish Lepomis humilis. Age-0 carp were generally as or more abundant than native fishes. In Jul. Daphnia dominated the diets of all fishes sampled, resulting in high (>60%) dietary overlap ranging from 87-98%. In Aug. Daphnia density in Brant Lake declined and dominant diet prey types shifted for carp (to Trichoptera and Daphnia), yellow perch (to Amphipoda), and the three Centrarchids (to Cyclops and Diaptomus). This diet shift resulted in lower diet overlap between Centrarchids and either carp (, INTRODUCTION Translocation of species outside of their native range often occurs without an adequate understanding of the implications of such introductions on native fauna. Introductions and invasions of nonnative species [...]

Predation and competition are important biotic interactions influencing populations and communities in marine soft sediments. Sea stars are ubiquitous predators with diverse diets that play functionally important roles in the benthos. In this study, we examined the diet and the ecological roles of three sympatric species of the genus Astropecten (A. aranciacus, A. irregularis pentacanthus and A. platyacanthus). The study was performed between March 2010 and February 2011 on the Maresme coast (northwestern Mediterranean Sea). Results showed that their main diet consisted on gastropods and bivalves, such as Glycymeris glycymeris, Callista chione, Gibbula guttadauri and Cyclope neritea. Food competition between species was avoided by partition of prey resources. Intraspecific differences in the dietary compositions between seasons were found, but not between size classes. Ontogenetic patterns of prey size consumption were recognized in the three species. A large diet overlap was detected between A. aranciacus and A. platyacanthus in winter, due to changes in prey availability. Nevertheless, the analysis of the infaunal community composition and stomach contents indicated that food selection was not associated with prey availability., Introduction Marine soft sediments are the most common habitat on earth and are increasingly being subjected to broad-scale anthropogenic disturbances due to, for example, eutrophication, hypoxia, fishing, sedimentation and pollution [...]

Stable coexistence of ecologically similar species is often a complicated phenomenon involving a synergy of biotic and abiotic factors. We investigated competitive interactions and small scale division of space in the closely related vole species Microtus montanus and Microtus longicaudus, which co- occur across the Greater Yellowstone Ecosystem (GYE) in the Rocky Mountains. We directly manipulated in situ populations of these species in two habitat types over three consecutive years. We confirmed previously described habitat associations of the study species: M. montanus was most abundant in open grassy meadows; M. longicaudus was most abundant in ecotonal areas with greater woody vegetation cover. Additionally, removal experiments conducted in both habitat types revealed a habitat-dependent competitive interaction between species: M. montanus excluded M. longicaudus from resource-rich meadows; M. longicaudus was limited to patchy ecotonal habitats that M. montanus was not observed to colonize. We did not observe an effect of the experimental treatment on either species' body mass. The outcome of the asymmetric competition between these species is influenced by local environmental conditions and enables their coexistence in the GYE., INTRODUCTION What enables species that compete for similar resources to persist in the same geographic area for long periods of time? Among rodents, Grant (1972) suggested that competition leads to [...]

In this experiment, competition was observed among native bull trout (Salvelinus confluentus (Suckley, 1859)) and non-native brook trout (Salvelinus fontinalis (Mitchill, 1814)) in artificial streams. In intraspecific competitions, brook trout engaged in territorial interference foraging strategies, and their foraging success was correlated with occupancy of the lead position in the stream. No correlation was apparent for bull trout, most of which engaged in nonterritorial scramble foraging tactics. In interspecific competitions, four stream environments were constructed in which fish density, habitat complexity, and current velocity were altered. Bull trout outcompeted brook trout for food in simple pool habitat devoid of cover when competition was head-to-head (density = 3 fish x [m.sup.-2]) between the species. When competitor number was doubled in this habitat, the two became equal competitors. At this higher density, bull trout again outcompeted brook trout for food when the habitat was changed to a complex riffle with substrate cover. Brook trout were more aggressive towards bull trout than vice versa, and interspecific aggression was decreased by low density, cover, and high stream velocity. Territorial brook trout aggressively interfere with their competitor for access to resources, but the success and intensity of this tactic against bull trout may be mitigated by environmental factors. Key words: invasive species, laboratory stream, behaviour, Oncorhynchus, Salmo, interference competition, exploitative competition. Dans cette experience, la concurrence entre l'omble a tete plate (Salvelinus confluentus (Suckley, 1859)), une espece indigene, et l'omble de fontaine (Salvelinus fontinalis (Mitchill, 1814)), une espece introduite, a ete observee dans des cours d'eau artificiels. La concurrence intraspecifique chez l'omble de fontaine comprenait des strategies territoriales d'interference dans l'approvisionnement, et le succes de l'approvisionnement etait correle a l'occupation de la position de tete dans le cours d'eau. Aucune correlation apparente n'a ete decelee pour l'omble a tete plate, dont la plupart des individus empruntait des strategies d'approvisionnement non territoriales en melee. En ce qui concerne la concurrence entre especes, quatre milieux de cours d'eau ont ete reconstitues dans lesquels la densite de poissons, la complexite de l'habitat et la vitesse du courant variaient. Les ombles a tete plate avaient le dessus sur les ombles de fontaine pour ce qui est de s'approvisionner dans un habitat de mouille simple denue de couverture, dans les cas de confrontation directe (densite = 3 poissons x [m.sup.-2]) d'individus des deux especes. Pour un nombre de poissons deux fois plus grand dans ce meme habitat, les deux especes devenaient des concurrents egaux. A cette plus grande densite, les ombles a tete plate avaient encore le dessus sur les ombles de fontaine en matiere d'alimentation pour un habitat consistant en un banc complexe avec couverture du substrat. Les ombles de fontaine etaient plus agressifs envers les ombles a tete plate que l'inverse, et une faible densite, la presence d'une couverture et une vitesse du courant elevee entramaient une reduction des agressions entre especes. Les ombles de fontaine territoriaux font preuve d'interference agressive envers leurs concurrents pour l'acces aux ressources, mais le succes et l'intensite de cette tactique contre les ombles a tete plate peuvent etre modules par des facteurs du milieu. [Traduit par la Redaction] Mots-cles: espece envahissante, cours d'eau laboratoire, comportement, Oncorhynchus, Salmo, concurrence par interference, concurrence par exploitation., Introduction Competitive interactions between non-native and native fishes can be an important determinant of invasion success, and if non-native species are to propagate and spread, it is often at the [...]

In the study of mechanisms structuring fish communities, mixed competition-predation interactions where large predators feed on prey fish versus those in which small predators compete with prey fish for a shared prey have been the focus of substantial research. We used a long-term data set from a system inhabited by brown trout (Salmo trutta) (predator) and Arctic char (Salvelinus alpinus) (prey) to evaluate whether mixed interspecific interactions were present in this system as suggested in other studies focusing on this species pair. We found no evidence for a negative interspecific density dependence in individual performance in either Arctic char or brown trout. In contrast, a negative intraspecific density dependence was present, especially in Arctic char. Furthermore, large brown trout condition showed a positive response to encounter rate with Arctic char (related to the density of small Arctic char). The most parsimonious interaction module to explain the Arctic char--brown trout interaction patterns in the studied system does therefore not need to include interspecific competition. We suggest that size-structured mixed competition-predation interactions in different systems are realized as being either mainly structured through interspecific predation or by competition depending on species life history characteristics and environmental conditions. Dans l'etude des mecanismes qui structurent les communautes de poissons, les interactions mixtes de concurrencepredation au cours desquelles de grands predateurs se nourrissent de poissons proies alors que des petits predateurs se disputent avec ces derniers des proies communes ont fait l'objet de nombreuses etudes. Nous avons utilise un ensemble de donnees de longue duree portant sur un systeme habite par la truite de mer (Salmo trutta) (predateur) et l'omble chevalier (Salvelinus alpinus) (proie) afin d'evaluer si des interactions interspecifiques mixtes etaient presentes, comme le suggerent d'autres etudes centrees sur cette paire d'especes. Nous n'avons rien note qui indiquerait la presence d'une dependance interspecifique negative de la densite sur le plan de la performance individuelle tant de l'omble chevalier que de la truite de mer. En revanche, il y avait bel et bien une dependance intraspecifique negative de la densite, en particulier chez l'omble chevalier. En outre, l'embonpoint des grandes truites de mer presentait une reaction positive par rapport a la frequence des rencontres avec des ombles chevaliers (reliee a la densite des petits ombles chevaliers). Il n'est donc pas necessaire que le mode d'interaction le plus parcimonieux pouvant expliquer les motifs d'interactions entre ombles chevaliers et truites de mer dans le systeme etudie inclue la concurrence interspecifique. Nous postulons que les interactions mixtes concurrence-predation structurees par la taille dans differents systemes sont principalement structurees par la predation interspecifique ou par la concurrence, selon les caracteristiques des cycles biologiques des especes et les conditions ambiantes. [Traduit par la Redaction], Introduction The density-dependent factors that structure ecological communities are the subject of continuous discussion in ecology. Ecologists in general have been largely focused on studying the relative roles of competition [...]

Extensive niche overlap between closely related species generally leads to aggressive interactions and competition. The short-tailed mouse (Mus spretus Lataste, 1883) and the wood mouse (Apodemus sylvaticus (L., 1758)) show a large habitat overlap without aggressive interactions. The present study investigates the existence of food competition between these species, based on an analysis of carbon and nitrogen stable isotopes. An almost exhaustive sample of plants, which were potential food resources, was taken and analyzed to infer the consumed plants in mouse diets. The main result showed that both species had a similar diet composition, consisting exclusively of seeds and fruits. This suggests that no competition for food between these species is apparent, or if it exists it would be minimized by a differential exploitation of resources. In the absence of food and space competition,the short-tailed mouse may be using the presence of the wood mouse as an indicator of habitat food quality. In the case of wood mice, we hypothesize that the level of competition with short-tailed mice may be low because of the abundance of resources and because the wood mice may perceive the smaller short-tailed mouse as being equivalent to a young of their own species. Key words: Murinae, small mammals, short-tailed mouse, Mus spretus, wood mouse, Apodemus sylvaticus, diet overlap, stable isotope analysis. Un chevauchement de niche important entre especes proches aboutit generalement a des interactions agressives et de la competition. La souris a queue courte (Mus spretus Lataste, 1883) et le mulot sylvestre (Apodemus sylvaticus (L., 1758)) presentent un important chevauchement d'habitat avec une absence d'interactions agressives. La presente etude vise a comprendre la competition alimentaire entre ces especes, a partir des isotopes stables du carbone et de l'azote. Un echantillon quasi-exhaustif des plantes pouvant servir de ressources a ete preleve. Le principal resultat est la grande proximite du regime des deux murines, qui consommeraient exclusivement des graines et fruits. Il semblerait donc que la competition alimentaire n'existe pas, ou serait minimisee par une exploitation differente des ressources. En l'absence de competition spatiale et alimentaire, le souris a queue courte tirerait avantage de la presence de mulot sylvestre, utilise comme information sur la qualite alimentaire des habitats. Pour diminuer la competition pour le mulot sylvestre, nous proposons l'hypothese qu'il percoit la petite espece souris a queue courte comme un equivalent jeune par rapport a sa propre espece. Mots-cles : Murinae, micromammiferes, souris a queue courte, Mus spretus, mulot sylvestre, Apodemus sylvaticus, chevauchement alimentaire, isotopes stables., Introduction In southern France, two Murinae, the short-tailed mouse (Mus spretus Lataste, 1883) and the wood mouse (Apodemus sylvaticus (L., 1758)) seem to show a peaceful coexistence that is infrequently [...]

Male mate choice has recently been reported in some animals with male-male competition. In the laboratory, we examined whether males choose their mates based on female quality that was indicated by body size and/or days to prenuptial molt, and the effects of female quality on male-male competition in the hermit crab Pagurus nigrofascia. We collected samples from April to May 2009 at an intertidal shore in Hokkaido, Japan (41°N, 140°E). When a male simultaneously encountered two receptive females in the mate choice experiment, males chose females which require less time to molt. When a male guarding a female with less time to molt was challenged by an intruder, the guarding male defended the female for a longer period and was more likely to win the contest. These results indicate that male P. nigrofascia use time to molt to discriminate between females., Introduction Mate choice and competition for mates are the major processes of sexual selection, and the conventional perspective is that indiscriminate males compete for the attention of choosy females. Although [...]

Secondary forest succession after abandonment of traditional agricultural and silvicultural lands is occurring in many parts of the world. Quercus crispula Blume-Quercus serrata Murray fuelwood stands have so far been artificially maintained in natural Fagus crenata Blume forests, central Japan, by resprouting after cutting. It is known that unmanaged fuelwood stands return to F. crenata dominated stands. This study aimed to examine why the two Quercus species are replaced by F. crenata by investigating seedling morphological and physiological responses of the three species to canopy conditions (forest edge and understory). The two Quercus species allocated more carbon to roots and stored more total nonstructural carbohydrates in roots as compared with F. crenata. Therefore, the two Quercus species allocate more photosyn-thetic production to roots than aboveground growth to maintain sprouting ability. On the contrary, F. crenata increased the light-harvesting efficiency (i.e., low leaf mass per area and high chlorophyll concentration) in the understory and increased height growth at the forest edge by greater allocation to stem. These traits would be beneficial for an increase in survival in the understory and height growth at the forest edge. Therefore, it is suggested that Quercus species in unmanaged stands will be replaced by F. crenata, a competitively superior species. Resume: La succession secondaire de la foret apres l'abandon des terres traditionnellement utilisees pour l'agriculture et la sylviculture est une realite dans plusieurs parties du monde. Les peuplements de Quercus crispula Blume et de Quercus serrata Murray destines au bois de chauffe ont jusqu'a maintenant ete maintenus artificiellement dans les forets naturelles de Fagus crenata Blume, dans le sud du Japon, par la production de rejets apres la coupe. On sait que les peuplements de bois de chauffe non amenages redeviennent des peuplements domines par F. crenata. Cette etude visait a determiner pourquoi les deux especes de Quercus sont remplacees par F. crenata en etudiant les reactions morphologiques et physiologiques des semis des trois especes selon l'aspect de la canopee (bordure de la foret et sous-bois). Les deux especes de Quercus allouaient plus de carbone aux racines et emmagasinaient plus d'hydrates de carbone non structuraux totaux dans les racines comparativement a F. crenata. Par consequent, les deux especes de Quercus allouaient plus de produits de la photosynthese aux racines qu'a la croissance aerienne pour maintenir leur capacite de produire des rejets. A l'inverse, F. crenata augmen- tait son efficacite de capture de la lumiere (c.-a-d. faible masse foliaire par unite de surface et concentration elevee de chlorophylle) en sous-etage et augmentait la croissance en hauteur en bordure de la foret par une plus grande allocation a la tige. Ces caracteristiques devraient etre benefiques pour augmenter la survie en sous-etage et la croissance en hauteur en bordure de la foret. Par consequent, les resultats indiquent que les especes de Quercus seront remplacees par F. crenata, une espece competitivement superieure, dans les peuplements non amenages. [Traduit par la Redaction], Introduction Secondary forest succession after abandonment of traditional agricultural and silvicultural lands is occurring in many parts of the world (Gondard et al. 2001; Vogt et al. 2006; Marin-Spiotta et [...]

We compared the amount and type of acoustic competition experienced by Veeries (Catharus fuscescens) when they sang in the dawn chorus as opposed to when they sang in the dusk chorus. Veery songs tended to be masked more often at dawn than at dusk. Veery songs were masked 2.4 times per 10-song sequence at dawn and 1.2 times per 10-song sequence at dusk. A larger number of species were responsible for masking that occurred at dawn. At least 12 species masked Veery songs in our sample, and all identified species masked at dawn; only seven of the 12 also masked at dusk. These results represent the first empirical data documenting natural differences in acoustic competition at dawn and dusk. Acoustic competition may help explain why, in addition to singing at dawn. Veeries and other thrushes also have a pronounced dusk chorus. Received 7 July 2011. Accepted 22 December 2011., Birds and other animals that use sound to communicate have the challenge of competing acoustically with other sounds in their environment (Bradbury and Vehrencamp 1998, Wiley 2006, Brumm and Naguib [...]

Coppice growth on cut stumps in thinned Eucalyptus plantations has the potential to compete with and reduce the growth of retained sawlog crop trees (SCTs). This study examined to what extent SCT growth was reduced by coppice in two stands in southeastern Australia: (i) a Eucalyptus globulus Labill. plantation thinned at age 10 years and (ii) a slower growing Eucalyptus tricarpa L.A.S. Johnson & K. Hill (syn. Eucalyptus sideroxylon subsp. tricarpa L.A.S. Johnson) plantation thinned at age 62 years. After 5 years, thinning E. globulus from 850 to 400 trees * [ha.sup.-1] increased the basal area of the largest diameter 200 SCTs * [ha.sup.-1] ([SCT.sub.200]) by 11% when coppice was removed. There was no significant thinning response by [SCT.sub.200] when coppice was retained. After 10 years, thinning E. tricarpa from about 600 to 100 trees * [ha.sup.-1] increased the basal area of the largest diameter 100 SCTs trees * [ha.sup.-1] ([SCT.sub.100]) by about 10% whether coppice was removed or not. At the time of measurement, coppice contributed 17% and 36% of stand sapwood area in thinned E. globulus and E. tricarpa treatments, respectively, and possibly competed with SCTs for water. This study shows the significant competitive effect that coppice can have in thinned eucalypt plantations and the importance of coppice management to the growth of retained trees. Resume: Les rejets de souche qui apparaissent a la suite d'une eclaircie dans les plantations d'Eucalyptus peuvent concurrencer les arbres d'avenir destines au sciage (AAS) et reduire leur croissance. Cette etude vise a determiner l'ampleur de la reduction de croissance des AAS causee par les rejets de souche dans deux peuplements du sudest de l'Australie: (i) une plantation d'Eucalyptus globulus Labill. eclaircie a l'age de 10 ans et (ii) une plantation a croissance plus lente d'Eucalyptus tricarpa L.A.S. Johnson & K. Hill (syn. Eucalyptus sideroxylon subsp. tricarpa L.A.S. Johnson) eclaircie a l'age de 62 ans. Apres 5 ans, l'eclaircie dans la plantation d'E. globulus, qui a reduit le nombre de tiges a l'hectare de 850 a 400, a fait augmenter de 11 % la surface terriere des 200 plus gros AAS a l'hectare ([AAS.sub.200]) lorsque les rejets de souche etaient enleves. Les [AAS.sub.200] n'ont pas eu de reaction significative a l'eclaircie lorsque les rejets de souche etaient conserves. Apres 10 ans, l'eclaircie dans la plantation d'E. tricarpa, qui a reduit le nombre de tiges a l'hectare de 600 a 100, a fait augmenter d'environ 10 % la surface terriere des 100 plus gros AAS a l'hectare ([AAS.sub.100]), que les rejets de souche soient enleves ou non. Au moment de la prise de mesures, les rejets de souche representaient respectivement 17 % et 36 % de la surface d'aubier des peuplements eclaircis d'E. globulus et d'E. tricarpa et concurrencaient possiblement les AAS pour l'eau. Cette etude met en evidence l'effet concurrentiel significatif que les rejets de souche peuvent avoir dans les plantations eclaircies d'eucalyptus et l'importance de l'amenagement des rejets de souche pour la croissance des arbres residuels. [Traduit par la Redaction], Introduction Thinning increases the availability of light, water, and nutrients for retained trees and can increase growth rates of sawlog crop trees (SCTs) in Eucalyptus plantations by as much as [...]

Functions of the major cheliped in pagurid hermit crabs have been studied in fights for shells. The major cheliped often shows sexual size dimorphism, suggesting that sexual selection favors the development of the male major cheliped. The function of the major cheliped in male-male competition was examined in Pagurus nigrofascia collected from April to June 2009 on the intertidal rocky shore in southern Hokkaido, Japan (41°N, 140°E). Sexual size dimorphism of the major cheliped was observed, and precopulatory guarding males had larger major chelipeds than solitary ones. Guarding males used the major cheliped to deter intruders during competitive interactions. Males without a major cheliped were disadvantaged even if they were larger than opponents and had ownership. Cheliped size affected the outcomes of contests between similar sized males. This suggests that the male major cheliped in P. nigrofascia protects mates from competitors and, consequently, enhances male mating success. Sexual selection may favor the development of the major cheliped in male pagurids., Author(s): Chiaki Yasuda [sup.1] , Yutaro Suzuki [sup.1] , Satoshi Wada [sup.1] Author Affiliations: (1) grid.39158.36, 0000000121737691, Laboratory of Marine Biology, Graduate School of Fisheries Science, Hokkaido University, , Minato-cho, [...]

Competition is thought to play a fundamental role in structuring avian communities, yet this has been difficult to quantify and demonstrate in marine ecosystems. We tested for fine-scale competition over foraging space between sympatric pursuit-diving seabirds, Marbled Murrelet (Brachyramphus marmoratus (J.F. Gmelin, 1789)) and Common Murre (Uria aalge (Pontoppidan, 1763)). We simultaneous assessed the effects of inter- and intra-specific competition among these predators, predicting that the larger Common Murres would out-compete the smaller Marbled Murrelets for foraging space. A theodolite was used to map the fine-scale (±2 m) distributions of birds on the water; distance from shore measurements and nearest-neighbour spatial statistics quantified the spatial overlap and segregation between species. Species distributions differed with respect to distance from shore, but overlapped extensively within 1200 m of the shoreline. Nearest-neighbour statistics, assessed with randomization tests, showed Marbled Murrelets foraging farther from Common Murres (mean distances 294 m) than from other Marbled Murrelets (95 m), but groups of Common Murres foraged with similar spacing among conspecifics (266 m) and competitors (186 m). These results suggest avoidance of Common Murres by Marbled Murrelets (interspecific competition) but intraspecifc competition among Common Murres. Avoidance behaviour may minimize the impacts of aggression or competition, but by avoiding Common Murres, the Marbled Murrelets may also be reducing their foraging opportunities. On croit que la competition joue un role fondamental dans la structuration des communautes d'oiseaux, bien qu'il soit difficile de le mesurer et le demontrer dans les ecosystemes marins. Nous avons verifie a echelle fine l'existence de competition pour l'espace de recherche de nourriture chez des oiseaux de mer sympatriques qui font de la plongee de poursuite, le guillemot marbre (Brachyramphus marmoratus (Gmelin, 1789)) et le guillemot marmette (Uria aalge (Pontoppidan, 1763)). Nous avons mesure simultanement les effets de la competition inter- et intra-specifique entre ces predateurs et avons predit que l'espece la plus grande, le guillemot marmette, gagnerait la competition pour l'espace de recherche de nourriture contre le guillemot marbre plus petit. Nous avons cartographie a l' aide d' un theodolite les repartitions a echelle fine (± 2 m) des oiseaux sur l' eau; les distances de la rive et des methodes statistiques basees sur le plus proche voisin ont permis de determiner le chevauchement spatial et la segregation entre les especes. Les repartitions des especes varient en fonction de distance de la rive et se chevauchent considerablement sur les premiers 1200 m a partir de la ligne du rivage. Les statistiques basees sur le plus proche voisin, evaluees par des tests de randomisation, montrent les guillemots marbres s'alimentant plus loin des guillemots marmettes (distance moyenne de 294 m) que des autres guillemots marbres (95 m); cependant, les guillemots marmettes recherchent leur nourriture en maintenant un espacement semblable avec les autres guillemots marmettes (266 m) et avec leurs competiteurs (186 m). Ces resultats indiquent que les guillemots marbres evitent les guillemots marmettes (competition interspecifique), mais qu'il existe une competition intraspecifique entre les guillemots marmettes. Ce comportement d' evitement peut reduire les impacts de l' agression et de la competition, mais, en evitant les guillemots marmettes, les guillemots marbres reduisent peut-etre aussi leurs occasions de se nourrir. [Traduit par la Redaction], Introduction Competition is thought to play a fundamental role in structuring avian communities (MacArthur 1958; Cody 1974; Schoener 1982; Lovette and Hochachka 2006). Nevertheless, mechanisms for competition remain unknown in [...]

We examined the effect of flow regime on the occurrence of interference and exploitative competition in a salmonid species, white-spotted char (Salvelinus leucomaenis). In the lotic treatment, char showed typical consequences of interference competition (i.e., fish aggressively defended their foraging positions, and individuals occupying the most profitable positions grew fastest). In the lentic treatment, however, char behavior was consistent with exploitative competition; fish cruised over a larger area in search of food resources and showed limited aggression and no evidence of a dominance hierarchy. Our results indicate that white-spotted char showed interference competition more commonly than exploitative competition in the lotic habitat and vice versa in the lentic habitat. Resume: Nous examinons leffet du regime decoulement sur la presence de competition dinterference et dexploitation chez une espece de salmonide, lomble a taches blanches (Salvelinus leucomaenis). Dans les conditions experimentales deau courante, les ombles affichent les consequences typiques de la competition dinterference (cest-a-dire que les poissons defendent avec agressivite leurs sites dalimentation, et les individus occupant les sites les plus favorables croissent le plus vite). En revanche, dans des conditions experimentales deau stagnante, les poissons explorent de grandes surfaces en quete de ressources alimentaires, manifestent peu dagressivite et il ny a pas dindication de hierarchie de dominance. Nos resultats indiquent que lomble a taches blanches presente plus communement une competition dinterference qu'une competition dexploitation dans lhabitat lotique et linverse dans lhabitat lenitique. [Traduit par la Redaction], Introduction Interference and exploitative competition are two of the primary modes of competition (Miller 1967). Interference competition is characterized by interindividual interactions (e.g., aggression) that occur when individuals compete for [...]

Ecologists have long recognized the roles of competition and disturbance in shaping ecological communities, and the combinatorial effects of these two factors have been the subject of substantial ecological research. Nevertheless, it is still unclear whether competition remains as an important structuring force in habitats strongly influenced by disturbance. The conventional belief remains that the importance of competition decreases with increasing disturbance, but limited theory suggests otherwise. Using protist communities established in laboratory microcosms, we demonstrate that disturbance does not diminish the importance of competition. Interspecific competition significantly increased rates of species extinction over a broad disturbance gradient, and increasing disturbance intensities increased, rather than decreased, the tempo of competitive exclusion. This community-level pattern is linked to the species-level pattern that interspecific competition led to most frequent extinctions of each species at the highest level of disturbance that the species can tolerate. Consequently, despite a strong tradeoff between competitive ability and disturbance tolerance across the competing species, species diversity generally declined with disturbance. The consistent structuring role of competition throughout the disturbance gradient underscores the need to understand competitive interactions and their consequences even in highly disturbed habitats. competitive interactions | species coexistence | species extinction | species richness doi/ 10.1073/pnas.1000699107

Competitive coexistence in a spatially heterogeneous environment is traditionally attributed to niche differences, but several recent theories have proposed important additional roles for propagule limitation and chance (e.g., neutral theory, stochastic niche theory, spatial storage effect). We tested whether propagule supply and timing of disturbance affected the coexistence of three ecologically similar plants that replace one another with partial overlap along a local soil gradient. We asked -what prevents the species that dominates the most common habitat (Holocarpha virgata, open hillsides) from invading the habitats where the other two species are dominant (Calycadenia pauciflora, rocky hilltops; Hemizonia congesta, clay-rich bottomlands). We added abundant Holocarpha seeds into Calycadenia and Hemizonia habitats that were experimentally disturbed at different times of year. Initial Holocarpha seedling densities in Calycadenia and Hemizonia habitats equaled or exceeded those in unmanipulated Holocarpha habitat, but Holocarpha survival, adult size, and fecundity were much lower outside its own habitat. Holocarpha persisted in Calycadenia and Hemizonia habitats for three years, and springtime disturbance promoted this expansion. However, outside its own habitat Holocarpha showed below-replacement fitness and little competitive effect on the other two species. Our results were most consistent with a deterministic view of spatial niches. Nonetheless, chance events may often cause natural communities to include some transient populations at any given time, leading them to appear 'unsaturated' with species. Key words: Calycadenia pauciflora; competition; disturbance; Hemizonia congesta; Holocarpha virgata; Hutchinsonian niche; neutral theory; seed addition; serpentine, spatial storage effect; stochastic niche; tarweed.

Tropical montane species are characterized by narrow elevational distributions. Recent perspectives on mechanisms maintaining these restricted distributions have emphasized abiotic processes, bur biotic processes may also play a role in their establishment or maintenance. One historically popular hypothesis, especially for birds, is that interspecific competition constrains ranges of closely related species that 'replace' each other along elevational gradients. Supporting evidence, however, is based on patterns of occurrence and does not reveal potential mechanisms. We experimentally tested a prediction of this hypothesis in two genera of tropical songbirds, Catharus (Turdidae) and Henicorhina (Troglodytidae), in which species have nonoverlapping elevational distributions. Using heterospecific playback trials, we found that individuals at replacement zones showed aggressive territorial behavior in response to songs of congeners. As distance from replacement zones increased, aggression toward congener song decreased, suggesting a learned component to interspecific aggression. Additionally, aggressive responses in Catharus were asymmetric, indicating interspecific dominance. These results provide experimental evidence consistent with the hypothesis that interspecific competitive interactions restrict ranges of Neotropical birds. Our results also underscore the need to consider biotic processes, such as competition, when predicting how species' ranges will shift with climate change. Asymmetric aggression could be particularly important. For example, if warming in montane landscapes allows upslope range expansion by dominant competitors, then high-elevation subordinate species could be forced into progressively smaller mountaintop habitats, jeopardizing viability of their populations. Key words: biotic interactions; climate change; cloud forest; competition; gradient; range limits; species replacement.

Leaving a population without having information about the surrounding areas is highly risky. Candidates for dispersal may reduce these risks by making decisions based on the level of connectivity between patches, e.g., through immigrants. The benefits of information acquisition may vary within a population according to the dispersal cause and the phenotype of the candidate disperser. For instance, kin-based dispersers should be prepared to accept higher dispersal cost than individuals leaving for competition with congeners, and individuals of better condition should better deal with the costs of dispersing. We investigated whether the use of information obtained from immigrants depended on the reason for dispersal and the phenotype of individuals in common lizards (Lacerta vivipara). Dispersal decisions with respect to connection status depended on the cause of dispersal and on body mass. When intraspecific competition was the driving force behind dispersal, the information carried by immigrants allowed candidate dispersers to decrease uncertainty about the success of dispersal. Therefore, larger individuals dispersed when connectivity was low, whereas smaller individuals dispersed when connectivity was high. When kin competition dominated, dispersers did not adjust their dispersal decisions on the basis of information about the existence of surrounding populations, and larger individuals dispersed whatever the connectivity. These results provide support for the hypothesis that kin competition is one of the factors driving colonization. Key words: common lizards; connection; connectivity; immigration; intraspecific competition; kin competition; Lacerta vivipara; natal dispersal; risk decisions; social information.

Sibling Paenibacillus dendritiformis bacterial colonies grown on low-nutrient agar medium mutually inhibit growth through secretion of a lethal factor. Analysis of secretions reveals the presence of subtilisin (a protease) and a 12 kDa protein, termed sibling lethal factor (Slf). Purified subtilisin promotes the growth and expansion of P. dendritiformis colonies, whereas Slf is lethal and lyses P. dendritiformis cells in culture. Slf is encoded by a gene belonging to a large family of bacterial genes of unknown function, and the gene is predicted to encode a protein of approximately 20 kDa, termed dendritiformis sibling bacteriocin. The 20 kDa recombinant protein was produced and found to be inactive, but exposure to subtilisin resulted in cleavage to the active, 12 kDa form. The experimental results, combined with mathematical modeling, show that subtilisin serves to regulate growth of the colony. Below a threshold concentration, subtilisin promotes colony growth and expansion. However, once it exceeds a threshold, as occurs at the interface between competing colonies, Slf is then secreted into the medium to rapidly reduce cell density by lysis of the bacterial cells. The presence of genes encoding homologs of dendritiformis sibling bacteriocin in other bacterial species suggests that this mechanism for self-regulation of colony growth might not be limited to P. dendritiforrnis. bacterial competition | bacterial growth inhibition | growth regulation | Paenibacillus dendritiformis | subtilisin doi/10.1073/pnas.1001062107

Cell competition in the skin promotes tissue youthfulness, but the same process later leads to skin ageing. This finding helps to explain how skin is maintained, and uncovers potential anti-ageing therapeutic targets. Cell competition drives skin youthfulness but also skin ageing., Author(s): Ganna Bilousova, James DeGregori Author Affiliations: Elimination of unfit cells in young and ageing skin Charles Darwin referred[sup.1] to natural selection as 'one general law, leading to the advancement [...]

Keywords: seasonality, photoperiodism, temperature, hormonal regulation, dormancy Abstract Examination of temperate and polar regions of Earth shows that the nonbiological world is exquisitely sensitive to the direct effects of temperature, whereas the biological world is largely organized by light. Herein, we discuss the use of day length by animals at physiological and genetic levels, beginning with a comparative experimental study that shows the preeminent role of light in determining fitness in seasonal environments. Typically, at seasonally appropriate times, light initiates a cascade of physiological events mediating the input and interpretation of day length to the output of specific hormones that ultimately determine whether animals prepare to develop, reproduce, hibernate, enter dormancy, or migrate. The mechanisms that form the basis of seasonal time keeping and their adjustment during climate change are reviewed at the physiological and genetic levels. Future avenues for research are proposed that span basic questions from how animals transition from dependency on tropical cues to temperate cues during range expansions, to more applied questions of species survival and conservation biology during periods of climatic stress.

It is becoming increasingly clear that under natural conditions parasitic infections commonly consist of co-infections with multiple conspecific strains. Multiple-strain infections lead to intraspecific interactions and may have important ecological and evolutionary effects on both hosts and parasites. However, experimental evidence on intraspecific competition or facilitation in infections has been scarce because of the technical challenges of distinguishing and tracking individual co-infecting strains. To overcome this limitation, we engineered transgenic strains of the protozoan parasite Trypanosoma brucei, the causal agent of human African sleeping sickness. Different strains were transfected with fluorescence genes of different colors to make them visually distinguishable in order to investigate the effects of multiple-strain infections on parasite population dynamics and host fitness. We infected mice either with each strain alone or with mixes of two strains. Our results show a strong mutual competitive suppression of co-infecting T. brucei strains very early in infection. This mutual suppression changes within-host parasite dynamics and alleviates the effects of infection on the host. The strength of suppression depends on the density of the co-infecting strain, and differences in life-history traits between the strains determine the consequences of strain--strain competition for the host. Unexpectedly, co-infection with a less virulent strain significantly enhances host survival (+15%). Analysis of the strain dynamics reveals that this is due to the suppression of the density of the more virulent strain (-33%), whose degree of impact ultimately determines the physical condition of the host. The competitive suppression is likely caused by allelopathic interference or by apparent competition mediated by strain-specific immune responses. These findings highlight the importance of intraspecific variation for parasite-parasite and parasite--host interactions. To fully understand parasite and disease dynamics, the genetic diversity of infections must be taken into account. Through changes in parasite dynamics, intraspecific variation may further affect transmission dynamics and select for increased virulence of each strain. The precise mechanisms underlying mutual suppression are not yet understood but may be exploitable to fight this devastating parasite. Our results are therefore not only of basic ecological interest investigating an important form of intraspecific competition, but may also have applied relevance for public health. Key words: Arica; host--parasite interaction; immune-mediated apparent competition; interference competition; intraspecific interaction; intraspecific variation; pathogen; population dynamics; Trypanosoma brucei.

Intraguild competition may be reduced if ecologically similar species segregate temporally. Using data from 1,596 camera-trap photos, we present the 1st quantitative analyses of the activity patterns of Andean cats (Leopardus jacobita), Pampas cats (Leopardus colocolo), culpeos (Lycalopex culpaeus), and pumas (Puma concolor) in high-altitude deserts of the Andes. We compared daily activity patterns for these carnivores with those of mountain vizcachas (Lagidium viscacia), the main prey of Andean cats. Activity patterns of all species were positively skewed toward night. Pampas cats displayed the greatest proportion of nocturnal activity, whereas Andean cats were the most diurnal. Activity of Andean cats differed significantly only from that of Pampas cats; Pampas cats also differed from pumas. Activity of Andean cats was generally similar to that of mountain vizcachas. The dissimilar activity patterns of Andean and Pampas cats support the hypothesis of temporal niche segregation of these felids. Key words: camera trapping, intraguild competition, Lagidium viscacia, Lycalopex culpaeus, Leopardus colocolo, Leopardus jacobita, Puma concolor, South America