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Social entities are linked and interdependent through shared members, a phenomenon described as niche overlap. Using archival data on yearly affiliations of International Communication Association (ICA) members with divisions and interest groups over a 9-year period, this study conducts a longitudinal network analysis to examine the formation mechanisms of intra-organizational niche overlap among organizational subunits. The results of the temporal exponential random graph model suggest the absence of dominant ICA subunits whose topic areas are broad enough to integrate different specializations through membership overlap. Triadic closure facilitates the sharing of members among three subunits, leading to a cohesive internal structure and limited brokerage opportunities. Subunits with smaller membership sizes are more likely to have membership overlap, particularly with larger subunits. Positive affinity relations between subunits, characterized by the sharing of scarce resources within the organization, contribute to the formation of membership overlap. [ABSTRACT FROM AUTHOR]

The study is to explore the dynamics of community structure, diversity, interspecific relationships and stability during naturalized developmental vegetation restoration which realized by natural interaction between plantation and native trees without human's involvement. The naturalized developmental restored forests in Baxianshan National Reserve were divided into three typical stages (i.e. Pinus tabulaeformis forest stage, mixed forest stage and near-natural forest stage) according to the ratio of P. tabulaeformis coverage to arbor layer, and the zonal natural secondary forests for control. According to the data of each wood gauge, we focused on the dynamics of community in terms of structure, diversity and stability. We found that, (i) The composition of dominant populations kept stable since the mixed forests stage and the α -diversity increased with restoration; (ii) The diameter class structure of tree layer exhibited a tendency of bell-shaped type toward inverted J-type, indicating an active regenerating and developmental status; (iii) Niche width of dominant populations such as Juglans mandshurica , Quercus mongolica , Quercus variabilis and Tilia amurensis increased during restoration, while that of Quercus dentata population decreased after playing a pioneer role; (iv) The proportion of negative association and high niche overlapped population pairs (>0.5) both decreased with restoration. In summary, naturalized developmental restoration has promoted the actively developing and regenerating of populations and improved the healthy restoration of plantation community. The status and interrelationships of populations were still being adjusted. The results provide a reference for revealing the dynamic characteristics of vegetation community development in naturalized developmental restoration of plantations. [ABSTRACT FROM AUTHOR]

Major hypotheses on sex evolution predict that resource abundance and heterogeneity should either select for or against sexual reproduction. However, seldom have these predictions been explicitly tested in the field. Here, we investigated this question using soil oribatid mites, a diverse and abundant group of soil arthropods whose local communities can be dominated by either sexual or asexual species. First, we refined theoretical predictions by addressing how the effects of resource abundance, heterogeneity and abiotic conditions could modify each other. Then, we estimated the strength of selection for sexual species in local communities while controlling for phylogeny and neutral processes (ecological drift and dispersal), and tested its relation to resource and abiotic gradients. We show that sexual species tended to be favoured with increasing litter amount, a measure of basal resource abundance. Further, there was some evidence that this response occurred mainly under higher tree species richness, a measure of basal resource heterogeneity. This response to resources is unlikely to reflect niche partitioning between reproductive modes, as sexual and asexual species overlapped in trophic niche according to a comparative analysis using literature data on stable isotope ratios. Rather, these findings are consistent with the hypothesis that sex facilitates adaptation by breaking unfavourable genetic associations, an advantage that should increase with effective population size when many loci are under selection and, thus, with resource abundance. [ABSTRACT FROM AUTHOR]

Modern North American carnivorous mammal assemblages consist of species from a single clade: the Carnivora. Carnivorans once coexisted with members of other meat-eating clades, including the creodonts (Hyaenodontida and Oxyaenida). Creodonts, however, went extinct in North America during the late Eocene and early Oligocene, potentially due to niche overlap and resource competition with contemporary carnivorans. In this study, we employ a community ecology approach to understand whether the dietary niches of coexisting creodonts and carnivorans overlapped during the late Eocene (Chadronian North American Land Mammal Age), a time when creodonts were dwindling and carnivorans were diversifying. We quantify niche overlap based on inferences of diet from carnassial tooth shape estimated using Orientation Patch Count, Dirichlet's Normal Surface Energy, and linear dental measurements as well as from body mass for all species in the Calf Creek Local Fauna of Cypress Hills, Saskatchewan (Treaty 4 land). Although creodonts and carnivorans shared characteristics of their carnassial tooth shape, suggesting similar chewing mechanics and feeding habits, we find that marked differences in body size likely facilitated niche partitioning, at least between the largest creodonts and carnivorans. Calculations of prey focus masses and prey mass spectra indicate that only the smallest creodont may have experienced significant competition for prey with the coeval carnivorans. We suggest that the ultimate extinction of creodonts from North America during the late Eocene and Oligocene was unlikely to have been driven by factors related to niche overlap with carnivorans. [ABSTRACT FROM AUTHOR]

Three species of Rattus , Norway rat (R. norvergicus), black rat (R. rattus) and Asian house rat (R. tanezumi) are currently known to occur in South Africa. The latter two species are cryptic and form part of the Rattus rattus species complex. Historically, R. norvegicus has been reported to occur along the coast and in urban centres, R. rattus is widespread in most urban areas, except in the drier areas, while R. tanezumi was only recorded to occur in the country (and Africa) ca. 15 years ago, and its distribution remains unknown. The aim of this study was to predict the potential distribution of R. tanezumi in South Africa and assess how it overlaps with that of R. norvegicus and R. rattus using species distribution modelling. Rattus tanezumi was predicted to mainly occur in most inland urban areas and along the coast. The distribution of R. rattus was as expected, in contrast, the predicted range of R. norvegicus was not restricted to the coast but also included inland urban areas. All three species showed broad potential distributional ranges that overlapped extensively indicating that their establishment and spread may be influenced by similar factors such as proximity to urban areas and a wet and moderate climate. These results allow insights into assessing their risk of establishment and for formulating appropriate intervention strategies for their management and control. [ABSTRACT FROM AUTHOR]

European honey bees have been introduced across the globe and may compete with native bees for floral resources. Compounding effects of urbanization and introduced species on native bees are, however, unclear. Here, we investigated how honey bee abundance and foraging patterns related to those of native bee abundance and diversity in residential gardens and native vegetation remnants for 2 years in urbanized areas of the Southwest Australian biodiversity hotspot and assessed how niche overlap influenced these relationships. Honey bees did not overtly suppress native bee abundance; however, complex relationships emerged when analysing these relationships according to body size, time of day and floral resource levels. Native bee richness was positively correlated with overall honeybee abundance in the first year, but negatively correlated in the second year, and varied with body size. Native bees that had higher resource overlap with honey bees were negatively associated with honey bee abundance, and resource overlap between honey bees and native bees was higher in residential gardens. Relationships with honey bees varied between native bee taxa, reflecting adaptations to different flora, plus specialization. Thus, competition with introduced bees varies by species and location, mediated by dietary breadth and overlap and by other life-history traits of individual bee species. [ABSTRACT FROM AUTHOR]

We assessed genetic differentiation and habitat suitability for Homopus areolatus during current and Last Glacial Maximum (LGM) conditions. The ND4 locus retrieved two monophyletic mtDNA clades with lower diversity in clade 1, in the west, than in clade 2, in the south-east. Clade 1 showed a north–south and clade 2 a west-to-east genetic divergence, and the clades co-occur in the syntaxis zone of the Cape Fold Mountains. The clades occupy distinct niches with limited overlap. Rainfall seasonality contributed most to habitat suitability, with clade 1 being restricted to winter rainfall and clade 2 to all-year rainfall regions. Precipitation variables contributed 90% and 60%, respectively, to habitat suitability of clades 1 and 2, with temperature, particularly mean temperature of the driest quarter, being of greater importance for clade 2 than clade 1. Suitable habitat shrank from the LGM to current conditions, probably due to reduced rainfall in the west and higher temperatures in most regions. We conclude that patterns of genetic divergence are strongly associated with ecological niche divergence of H. areolatus clades. More studies are needed to assess the taxonomic status of clade 1, particularly in view of its shrinking habitat due to climate change and anthropogenic factors. [ABSTRACT FROM AUTHOR]

Bird plumage is often very colorful and can communicate the quality of the bearer to conspecifics. These plumage-based signals of quality are composed of multiple pigments (e.g. melanin and carotenoids). Therefore, sex and age classes, which often show marked differences in plumage coloration, may have different dietary needs for the different plumage components and this might promote preferences for different dietary niches at different molting stages. However, no study has addressed the role that changes in niche use play in the expression of multiple component plumage signals in birds. We used stable isotope analysis to test the hypothesis that niche use is related to age and sex and to differently cultured plumage patches, yellow carotenoid-based and black melanin-based, in great tits Parus major. We recorded high niche overlap between plumage patches, although δ15N was higher in black than yellow plumage. Niche overlap was relatively low for age classes and relatively high for sex classes, and age classes showed a contrasting pattern of niche overlap between carotenoid- and melanin-based plumages. Moreover, δ13C, but not δ15N, had a significant negative relationship with carotenoid-based plumage, which was only apparent in juveniles. Taken together, our results demonstrate that niche use had a moderate influence on plumage coloration characteristics of great tit individuals, mostly associated with δ13C rather than with δ15N and with age rather than with sex. Therefore, our study is significant because it confirms the relevance of niche use during ornament production in free-living birds. [ABSTRACT FROM AUTHOR]

Dietary niche separation is often crucial for promoting coexistence of sympatric species sharing similar habitats. In this study, we used cafeteria experiments to explore feeding preferences of two sympatric small herbivores in Hulunber meadow steppe, the narrow-headed vole (Microtus gregalis) and the Daurian pika (Ochotona dauurica), and used microhistological analysis of stomach contents to measure their actual diets and evaluate their niche overlap. To evaluate the effects of scale, we conducted dietary analyses at two commonly documented taxonomic scales of food type categorization: a fine scale based on the species level, and a coarse scale based on a roughly family-level categorization. Niche analysis at the fine and the coarse scales generated qualitatively similar results, although niche overlap was larger at the coarse scale than at the fine scale. In cafeteria experiments, voles and pikas showed similar feeding preference patterns. When foraging in the field, the two species differed in food use and feeding preference, without a significant dietary niche overlap. In the laboratory, both species preferred to eat Leguminosae and Asteraceae species. In the field, pikas still preferred Leguminosae species and voles switched to prefer Liliaceae species. These results suggest the existence of dietary niche partitioning, and competition might have driven the observed niche shift. [ABSTRACT FROM AUTHOR]

Understanding how the climatic niche of species evolved has been a topic of high interest in current theoretical and applied macroecological studies. However, little is known regarding how species traits might influence climatic niche evolution. Here, we evaluated patterns of climatic niche evolution in turtles (tortoises and freshwater turtles) and whether species habitat (terrestrial or aquatic) influences these patterns. We used phylogenetic, climatic and distribution data for 261 species to estimate their climatic niches. Then, we compared whether niche overlap between sister species was higher than between random species pairs and evaluated whether niche optima and rates varied between aquatic and terrestrial species. Sister species had higher values of niche overlap than random species pairs, suggesting phylogenetic climatic niche conservatism in turtles. The climatic niche evolution of the group followed an Ornstein–Uhlenbeck model with different optimum values for aquatic and terrestrial species, but we did not find consistent evidence of differences in their rates of climatic niche evolution. We conclude that phylogenetic climatic niche conservatism occurs among turtle species. Furthermore, terrestrial and aquatic species occupy different climatic niches but these seem to have evolved at similar evolutionary rates, reinforcing the importance of habitat in understanding species climatic niches and their evolution. [ABSTRACT FROM AUTHOR]

We investigated the spatial relationships among three phylogenetically related and ecologically convergent moles in Italy: Talpa europaea, Talpa romana and Talpa caeca. The spatial niche of each species was described through environmental predictors of climate, soil moisture and topography. Niche overlap between each species pair was quantified, and niche similarity tests were performed through a randomization procedure. The potential distributions of mole species were modelled through an ensemble forecasting approach, while their actual distributions were derived by using a fixed-radius local convex-hull technique. Talpa europaea and T. caeca exhibited the narrowest and the broadest niche, respectively. The highest values of niche overlap were detected between T. caeca and each of the two large moles T. romana and T. europaea, while the lowest value emerged between the last two. The potential and actual distribution ranges of T. europaea were almost equivalent, whereas T. romana and T. caeca were each restricted to limited portions of their potential distribution. We discuss whether competitive interactions could be responsible for their actual distribution pattern, with T. europaea dominant over the other two and T. caeca occupying the most marginal portion of its niche due to competitive exclusion. This study provides an example of how ecoevolutionary factors may be involved in driving the geographical range of closely related and ecologically convergent taxa. [ABSTRACT FROM AUTHOR]

Numerous works have related phylogeographical patterns of north African Mediterranean biota to Pleistocene climatic oscillations. The application of complementary paleoclimate reconstructions, however, remains scarcely used. North African Daboia vipers comprise two Mediterranean generalist taxa, D. mauritanica and D. deserti, with controversial systematic and range delimitations. We combined phylogeographic and ecological niche analyses to unveil biogeographical scenarios for the evolution of these taxa. Phylogeographic analyses (two mitochondrial gene fragments) resolved a monophyletic lineage, which diverged from D. palaestinae at the Miocene, further structured in seven sublineages with mostly allopatric distributions, six of which endemic to north-west Africa having diversified during the Pleistocene. Paleoclimatic reconstructions (four ecological modelling algorithms) of species ranges for three past periods (Last Inter Glacial, Last Glacial Maximum and Middle Holocene) suggested range contractions during warm periods and range expansions during cold periods. Stable climatic areas mostly fit potential refugia for lineages occurring in Morocco. Niche overlap analyses based on spatial genetic interpolations to delimitate lineages occurrence demonstrated lack of niche divergence among lineages. Our findings support an allopatric diversification process in Daboia driven by Pleistocene climatic oscillations, which should be expected in other Mediterranean generalist species from north Africa. Furthermore, D. deserti is identified as an invalid taxon. [ABSTRACT FROM AUTHOR]

Background and Aims The geographical distributions of species are constrained by their ecological requirements. The aim of this work was to analyse the effects of environmental conditions, historical events and biogeographical constraints on the diversification of the three species of the western Mediterranean shrub genus Stauracanthus, which have a parapatric distribution in the Iberian Peninsula. Methods Ecological niche factor analysis and generalized linear models were used to measure the response of all Stauracanthus species to the environmental gradients and map their potential distributions in the Iberian Peninsula. The bioclimatic niche overlap between the three species was determined by using Schoener's index. The genetic differentiation of the Iberian and northern African populations of Stauracanthus species was characterized with GenalEx. The effects on genetic distances of the most important environmental drivers were assessed through Mantel tests and non-metric multidimensional scaling. Key Results The three Stauracanthus species show remarkably similar responses to climatic conditions. This supports the idea that all members of this recently diversified clade retain common adaptations to climate and consequently high levels of climatic niche overlap. This contrasts with the diverse edaphic requirements of Stauracanthus species. The populations of the S. genistoides-spectabilis clade grow on Miocene and Pliocene finetextured sedimentary soils, whereas S. boivinii, the more genetically distant species, occurs on older and more coarse-textured sedimentary substrates. These patterns of diversification are largely consistent with a stochastic process of geographical range expansion and fragmentation coupled with niche evolution in the context of spatially complex environmental fluctuations. Conclusions: The combined analysis of the distribution, realized environmental niche and phylogeographical relationships of parapatric species proposed in this work allows integration of the biogeographical, ecological and evolutionary processes driving the evolution of species adaptations and how they determine their current geographical ranges. [ABSTRACT FROM AUTHOR]

Temporal niche partitioning may result from interference competition if animals shift their activity patterns to avoid aggressive competitors. If doing so also shifts food sources, it is difficult to distinguish the effects of interference and consumptive competition in selecting for temporal niche shift. Bees compete for pollen and nectar from flowers through both interference and consumptive competition, and some species of bees have evolved nocturnality. Here, we use tropical forest canopy towers to observe bees (the night-flying sweat bees Megalopta genalis and M. centralis [Halictidae], honey bees, and stingless bees [Apidae]) visiting flowers of the balsa tree (Ochroma pyramalidae, Malvaceae). Because Ochroma flowers are open in the late afternoon through the night we can test the relative influence of each competition type on temporal nice. Niche shift due to consumptive competition predicts that Megalopta forage when resources are available: from afternoon into the night. Niche shift due to interference competition predicts that Megalopta forage only in the absence of diurnal bees. We found no overlap between diurnal bees and Megalopta in the evening, and only one instance of overlap in the morning, despite the abundance of pollen and nectar in the late afternoon and evening. This supports the hypothesis that Megalopta are avoiding interference competition, but not the hypothesis that they are limited by consumptive competition. We propose that the release from interference competition enables Megalopta to provision cells quickly, and spend most of their time investing in nest defense. Thus, increases in foraging efficiency directly resulting from temporal shifts to escape interference competitionmay indirectly lead to reduced predation and parasitism. [ABSTRACT FROM AUTHOR]

Many forest bird species require tree cavities for nesting, and share this resource with a diverse community of animals. When cavities are limited, niche overlap can result in interspecific competition, with negative consequences for threatened populations. Vinaceous-breasted Parrots {Amazona vinacea) are endangered cavity nesters endemic to the subtropical Atlantic Forest, where cavities are scarce. We examined nest niche overlap among Vinaceous-breasted Parrots and 9 potential competitors (birds and mammals >140 g, and social insects) in Argentina, considering (1) timing of breeding, (2) characteristics of cavities (depth, entrance diameter, height), trees (diameter at breast height [DBH], species, condition), and habitat (surrounding land use, distance to edge), and (3) interspecific cavity reuse. During 10 breeding seasons we studied nests and roosts, measured their characteristics, and monitored cavities to detect reuse. We used multinomial logistic regression to determine whether the 6 most abundant taxa differed in nest and roost site characteristics. Timing of breeding overlapped for all bird species except the White-eyed Parakeet (Psittacara leucophthalmus). No combination of cavity, tree, and habitat characteristics predicted the taxa that utilized cavities. Moreover, 8 of the 10 taxa reused cavities interspecifically. The high level of overlap in realized nest niche, combined with previous evidence that cavities could limit bird density in our study area, suggest the possibility of interspecific competition for cavities among multiple taxa. Although models did not perform well at classifying cavities by taxon, some characteristics of cavities, trees, and habitat were selected more by Vinaceous-breasted Parrots than by other taxa, and we recommend targeting conservation efforts toward cavities and trees with these characteristics (7-40 cm entrance diameter, >10 m high, DBH >55 cm). We found 62% of Vinaceous-breasted Parrot nests on farms (vs. <50% for other taxa), highlighting the importance of working with local farmers to conserve cavities in anthropogenic habitats as well as in protected areas. [ABSTRACT FROM AUTHOR]

Unlike modern mammalian communities, terrestrial Paleozoic and Mesozoic vertebrate systems were characterized by carnivore faunas that were as diverse as their herbivore faunas. The comparatively narrow food base available to carnivores in these paleosystems raises the possibility that predator-prey interactions contributed to unstable ecosystems by driving populations to extinction. Here, we develop a model of predator-prey interactions based on diversity, abundance and body size patterns observed in the Permo-Triassic vertebrate fossil record of the Karoo Basin, South Africa. Our simulations reflect empirical evidence that despite relatively high carnivore: herbivore species ratios, herbivore abundances were sufficient for carnivores to maintain required intake levels through most of the Karoo sequence. However, high mortality rates amongst herbivore populations, even accounting for birth rates of different-sized species, are predicted for assemblages immediately preceding the end-Guadalupian and end-Permian mass extinctions, as well as in the Middle Triassic when archosaurs replaced therapsids as the dominant terrestrial fauna. These results suggest that high rates of herbivore mortality could have played an important role in biodiversity declines leading up to each of these turnover events. Such declines would have made the systems especially vulnerable to subsequent stochastic events and environmental perturbations, culminating in large-scale extinctions. [ABSTRACT FROM AUTHOR]

Studies on niche evolution allow us to establish how species niches have changed over time and to identify how long-term evolutionary processes have led to present-day species distributions. Here, we investigate the patterns of climatic niche evolution in Tynanthus ( Bignonieae, Bignoniaceae), a genus of narrowly distributed species. We test the hypothesis that niche conservatism has played an important role in the history of this group of Neotropical lianas. We perform univariate and multivariate comparisons between climatic niches of species and associated environmental data with information on phylogenetic relationships. We encountered considerable divergence in niches among species, indicating that niche conservatism in climatic variables does not seem to have played a key role in the history of the genus. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179, 95-109. [ABSTRACT FROM AUTHOR]

The impact of ecological factors on natural hybridization is of widespread interest. Here, we asked whether climate niche influences hybridization between the two closely related plant species Myriophyllum sibiricum and M. spicatum. Eight microsatellite loci and two chloroplast fragments were used to investigate the occurrence of hybridization between these two species in two co-occurring regions: north-east China ( NEC) and the Qinghai-Tibetan Plateau ( QTP). The climate niches of the species were quantified by principal component analysis with bioclimatic data, and niche comparisons were performed between the two species in each region. Reciprocal hybridization was observed, and M. sibiricum was favoured as the maternal species. Furthermore, hybrids were rare in NEC but common in the QTP. Accordingly, in NEC, the two species were climatically distinct, and hybrids only occurred in the narrow geographical or ecological transition zone, whereas in the QTP, obvious niche overlaps were found for the two species, and hybrids occurred in multiple contact zones. This association between hybridization pattern and climate niche similarity suggests that the level of hybridization was promoted by niche overlap. Compared with the parental species, similar climate niches were found for the hybrid populations in the QTP, indicating that other environmental factors rather than climate were important for hybrid persistence. Our findings highlight the significance of climate niche with respect to hybridization patterns in plants. [ABSTRACT FROM AUTHOR]

Species' partitioning of resources remains one of the most integral components for understanding community assembly. Analysis of stable carbon and nitrogen isotopes in animal tissues has the potential to help resolve patterns of partitioning because these proxies represent the individual's diet and trophic niche, respectively. Using free-ranging rodents in a southern African savanna as a model community, we find that syntopic species within habitats occupy distinct isotope niches. Moreover, species with strongly overlapping isotope niches did not overlap in their spatial distribution patterns, suggesting an underlying effect of competitive exclusion. Niche conservatism appears to characterize the behaviour of most species in our sample - with little or no observed changes across habitats - with the exception of one species, Mastomys coucha. This species displayed a generalist distribution, being found in similar abundances across a variety of habitats. This spatial pattern was coupled with a generalist isotope niche that shifted across habitats, likely in response to changes in species composition over the same spatial gradient. The case for M. coucha supports contentions that past competition effects played a significant evolutionary role in shaping community structures of today, including the absence of strong interspecific niche overlaps within particular habitats. Our study highlights the value of stable isotope approaches to help resolve key questions in community ecology, and moreover introduces novel analytical approaches to quantifying isotope niche breadths and niche overlaps that are easily comparable with traditional metrices. [ABSTRACT FROM AUTHOR]

Temporal partitioning of daily activities between species may promote coexistence within animal communities by reducing behavioural interference, particularly when species highly overlap in the use of space and resources. Such a strategy may be used by Alpine chamois ( Rupicapra rupicapra rupicapra) when in the presence of mouflon ( Ovis gmelini musimon × Ovis sp.), an introduced highly gregarious species with a broader ecological niche, overlapping with that of chamois. Using simultaneous monitoring of 29 Global Positioning System-collared chamois and 12 mouflon, we assessed the temporal variation in activity patterns of chamois amongst two subpopulations: one without mouflon and one with mouflon, during January and August, which are the two most extreme periods of spatial overlap of mouflon with chamois distribution. Substantial differences in activity patterns between chamois and mouflon were observed (mean 13.8 ± 10.5% in January and 10.6 ± 11.6% in August). More subtle differences appeared between both subpopulations of chamois and persisted, regardless of the spatial overlap with mouflon (3.2 ± 1.8% in January and 2.6 ± 1.5% in August), thus highlighting that there is no behavioural interference from mouflon on chamois. Our findings suggest that the temporal partitioning of daily activities between chamois and mouflon, although probably a result of species-specific adaptations to environmental conditions, may contribute to their coexistence. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 621-626. [ABSTRACT FROM AUTHOR]

The stable co-existence of individuals of different genotypes and reproductive division of labour within heterogeneous groups are issues of fundamental interest from the viewpoint of evolution. Cellular slime moulds are convenient organisms in which to address both issues. Strains of a species co-occur, as do different species; social groups are often genetically heterogeneous. Intra- and interspecies 1 : 1 mixes of wild isolates of Dictyostelium giganteum and D. purpureum form chimaeric aggregates, following which they segregate to varying extents. Intraspecies aggregates develop in concert and give rise to chimaeric fruiting bodies that usually contain more spores (reproductives) of one component than the other. Reproductive skew and variance in the proportion of reproductives are positively correlated. Interspecies aggregates exhibit almost complete sorting; most spores in a fruiting body come from a single species. Between strains, somatic compatibility correlates weakly with sexual compatibility. It is highest within clones, lower between strains of a species and lowest between strains of different species. Trade-offs among fitness-related traits (between compatible strains), sorting out (between incompatible strains) and avoidance (between species) appear to lie behind coexistence. [ABSTRACT FROM AUTHOR]

Guilds of species that share ecological similarities or recent ancestors are often the basis of studies concerning habitat partitioning. An interesting result of many of these studies is that means of partitioning in one area of sympatry may be different from those in disjunct areas of overlap. Here, we quantified the differences in habitat preference of two forest thrushes in the southern Appalachian Mountains. The Hermit Thrush (Catharus guttatus) has recently expanded its breeding range south along the spine of the Appalachians into the spruce-fir forests of Virginia, North Carolina, and Tennessee. There, it shares breeding habitat with the congeneric Veery (C. fuscescens), previously the only forest thrush breeding in this area. We used several multivariate analyses of habitat variables within both species' territories to understand how these species partition the available habitat and to test if these means of partitioning are similar to those found by other studies. We calculated the niche overlap to be 0.248, indicating that the habitat structures preferred by these two species are highly distinct. Hermit Thrushes generally preferred forest with a high degree of canopy closure, high percent coverage of leaf litter, and low percent cover below 3.0 m. Veery territories generally had a high percent of cover between 0.5 and 3.0 m (i.e., the shrub layer) and less canopy closure than the Hermit Thrush plots. Our data suggest that the Hermit Thrush is expanding south because it is attracted to the maturing of the spruce forests in this region. [ABSTRACT FROM AUTHOR]

Asiatic black bears (Ursus thibetanus) and sun bears (Helarctos malayanus) are ecologically similar and coexist extensively across Southeast Asia. We used foraging signs identified to bear species to examine their food selection and dietary overlap relative to food abundance, nutrition, and phenology in 3 habitats in Thailand. We posited, based on ecological theory, that coexistence of these 2 species would be explained through resource partitioning; our data, however, did not support this hypothesis. We conducted 71 sign transects and recorded 730 bear signs, mainly claw marks on trees that bears climbed for food. Both species fed predominantly on fruit; we documented 93 plant species from 42 families that bears consumed. Insects were of secondary importance. Bears of the 2 species selected fruit trees of the same families and genera in each habitat, especially lipid-rich Lauraceae and Fagaceae, tracking fruiting phenology through time. Diet overlap was high, even during periods of diminished fruit availability. We propose a number of mechanisms that may have promoted coexistence of these 2 species. For example, sun bears consumed proportionately more insects than did black bears; insectivory may help sustain the smaller-sized sun bears in the face of competition over fruits with black bears. Also, competition over fruits was reduced by both species cropping a lower proportion of common fruit trees than rarer fruit trees, thereby leaving a potential surplus for the other species. Furthermore, food resources were generally abundant and available year-round: about half the trees in the forest were potential food trees for bears. Bear populations likely were depressed below carrying capacity by previous hunting; as they recover, more competition for resources and greater niche divergence could ensue. [ABSTRACT FROM AUTHOR]

The article discusses the results of a study that examined the niche partitioning of territorial congeneric species of dragonfly in Northeast Algeria to determine the importance of habitat heterogeneity in promoting co-existence of closely related species. The dragonfly species studied were Orthetrum nitidinerve, Orthetrum chrysostigma and Orthetrum coerulescens anceps. The species' spatial distribution in two different microhabitats is discussed.

A combination of observational and experimental methods, in both the laboratory and field, were used to assess niche partitioning between Ceutorhynchus alliariae Brisout and C. roberti Gyllenhal (Coleoptera: Curculionidae), two coexisting shoot-boring weevils on garlic mustard, Alliaria petiolata (M. Bieb.) Cavara and Grande (Brassicaceae). We compared their morphology, oviposition behavior, larval development, distribution, abundance, and attack rates in their sympatric range, and of C. alliariae when found alone and in sympatry with C. roberti. Results indicate only very small differences in the fundamental niches of the two species. Comparison of C. alliariae in the range it occurs alone with the range where it co-occurs with C. roberti revealed some evidence for competition between the two species, i.e., attack levels of C. alliariae were reduced in areas where it co-occurred with C. roberti. However, the study showed no character displacement in regard to adult size or shoot choice of C. alliariae and we found no indication for superiority of either of the two species. Clearly, manipulative experiments would be necessary to unambiguously test for competition between the two species. Our results, based on a subset of niche dimensions known to be important in other systems, suggest that C. aUiariae and C. roberti may present one of the rare cases, in which niche differentiation is not the main mechanism underlying coexistence. [ABSTRACT FROM AUTHOR]

The article presents a study that evaluates the interspecific ecological relationships between Sayornis saya and Eastern phoebes at three scales. It states that the species' habitat varies in several environmental conditions, mainly precipitation, temperature, and vegetation indices. Moreover, it notes that local-scale occurrences concurred with results of ecological niche models.

In communities where strong interspecific competition between native species is lacking, exotic and native species often exhibit intense resource competition resulting in decline of native populations. We examined the potential for interspecific competition for nest sites between co-occurring native Mt. Graham red squirrels (Tamiasciurus hudsonicus grahamensis) and exotic Abert's squirrels (Sciurus aberti) in the Pinaleño Mountains of Arizona. Comparison of nest use between red and Abert's squirrels at different scales (nest, nest tree, and nest site) revealed contrasting results. Competition for nests and nest trees appears unlikely given the dissimilarity in use of nest types and tree characteristics. Abert's squirrels predominately used dreys, whereas red squirrels mostly used cavity nests. Neither squirrel species occupied a nest used by the other species. Nest trees differed in size and species between squirrels for dreys, but not for cavities. Abert's squirrel nest sites were found in a wider range of microhabitats including almost all microhabitats in which red squirrel nest sites were located. Although there was significant overlap, each species showed distinct trends in microhabitat. In general, red squirrel nest sites were characterized as more densely forested areas dominated by corkbark fir (Abies lasiocarpa var. arizonica), whereas Abert's squirrel nest sites were more open and contained greater tree species diversity. Overlap in microhabitat characteristics increases the likelihood of interspecific competition and could increase the vulnerability of red squirrels to extinction. [ABSTRACT FROM AUTHOR]

The introduction of a species into an ecosystem with species already occupying a similar trophic level is predicted to lead to a high degree of niche overlap. The feral pig (Sus scrofa), one of the world's worst invasive species, was introduced to the Pantanal about 200 years ago and is thought to compete with the native white-lipped peccary (Tayassu pecari) and collared peccary (Pecari tajacu). Resource partitioning between the 3 species was examined, including analysis of fruit items and plants in fecal samples as well as encounter rates in different habitats, to help generate hypotheses about competitive interactions among the species. Overlaps in food resources and habitat use between feral pigs and peccaries were found to be lower than expected. In fact, niche overlap was highest between the native species. Results indicate that currently, feral pigs are not a direct threat to the native peccaries in the study area. Differences in morphology and behavior indicate possible mechanisms of niche partitioning between the species. Feral pigs may, nevertheless, impact the wildlife community in other ways as predators of eggs, by destruction of vegetation through rooting, or by functioning as disease reservoirs. Cattle-ranching activities may favor feral pigs and the current anthropogenic changes in the landscape could lead to changes in competitive dynamics between feral pigs and native species. [ABSTRACT FROM AUTHOR]

Carnivory has evolved independently at least six times in five angiosperm orders. In spite of these independent origins, there is a remarkable morphological convergence of carnivorous plant traps and physiological convergence of mechanisms for digesting and assimilating prey. These convergent traits have made carnivorous plants model systems for addressing questions in plant molecular genetics, physiology, and evolutionary ecology. New data show that carnivorous plant genera with morphologically complex traps have higher relative rates of gene substitutions than do those with simple sticky traps. This observation suggests two alternative mechanisms for the evolution and diversification of carnivorous plant lineages. The ‘energetics hypothesis’ posits rapid morphological evolution resulting from a few changes in regulatory genes responsible for meeting the high energetic demands of active traps. The ‘predictable prey capture hypothesis’ further posits that complex traps yield more predictable and frequent prey captures. To evaluate these hypotheses, available data on the tempo and mode of carnivorous plant evolution were reviewed; patterns of prey capture by carnivorous plants were analysed; and the energetic costs and benefits of botanical carnivory were re-evaluated. Collectively, the data are more supportive of the energetics hypothesis than the predictable prey capture hypothesis. The energetics hypothesis is consistent with a phenomenological cost–benefit model for the evolution of botanical carnivory, and also accounts for data suggesting that carnivorous plants have leaf construction costs and scaling relationships among leaf traits that are substantially different from those of non-carnivorous plants. [ABSTRACT FROM PUBLISHER]

We report on aspects of the ecology and natural history of 2 species of armadillos commonly found in a cerrado remnant in southeastern Brazil--the naked-tailed armadillo (Cabassous unicinctus) and the 6-banded armadillo (Euphractus sexcinctus). Armadillos were captured in pitfall traps or by hand, double-marked, and the habitat (campo sujo, campo cerrado, and gallery forests), season, and time of capture were recorded. We also recorded the sex and age of all armadillos, and reproductive condition of females. Population densities were estimated as 0.27 and 0.14 individuals/ha for C. unicinctus and E. sexcinctus, respectively. E. sexcinctus did not preferentially use any of the habitats included in the study area, whereas C. unicinctus preferentially used habitats with a more complex vegetation structure, such as gallery forests. C. unicinctus was diurnal and E. sexcinctus was mainly nocturnal. Neither species changed its activity pattern with season, but C. unicinctus was more active in months with decreased abundance of arthropods--the main food resource consumed by this species. Both species of armadillos appeared to reproduce year-round. Differences in habitat use and daily activity between C. unicinctus and E. sexcinctus suggest spatial and temporal displacement between these species. [ABSTRACT FROM AUTHOR]

Analysis of the gut contents of six syntopicCyprinodonspecies from Laguna Chichancanab, Mexico, shows that the supposed basal form,C. beltrani, feeds on detritus and has the longest gut. All other species have significantly shorter guts. WhereasC. simusexclusively ingests detritus despite short gut length, all other species additionally rely on different benthic invertebrates. Each species has developed specific preferences:C. labiosus(amphipods),C. verecundus(bivalves),C. maya(ostracods and gastropods) andC. esconditus(ostracods and chironomid larvae). However, all of them ingest a minimum ofc.40% detritus. According to Schoener's index, pairwise niche overlap varies fromc.40% to over 95% in the species flock. Contrary to this, there is almost no overlap between the members of the flock and the only other native fish species,Gambusia sexradiata, which feeds nearly exclusively on terrestrial arthropods dropping on the water surface. Recently, the cichlid genusOreochromisand the characidAstyanax fasciatusgained access to the lake. The cichlids show moderate to high niche overlap, whereas inA. fasciatusit is low.© 2005 The Linnean Society of London,Biological Journal of the Linnean Society, 2005,85, 125–134. [ABSTRACT FROM AUTHOR]

Ecological speciation can proceed despite genetic interchange when selection counteracts the homogenizing effects of migration. We tested predictions of this divergence-with-gene-flow model in Coeligena helianthea and C. bonapartei , 2 parapatric Andean hummingbirds with marked plumage divergence. We sequenced putatively neutral markers (mitochondrial DNA [mtDNA] and nuclear ultraconserved elements [UCEs]) to examine genetic structure and gene flow, and a candidate gene (MC1R) to assess its role underlying divergence in coloration. We also tested the prediction of Gloger's rule that darker forms occur in more humid environments, and examined morphological variation to assess adaptive mechanisms potentially promoting divergence. Genetic differentiation between species was low in both ND2 and UCEs. Coalescent estimates of migration were consistent with divergence with gene flow, but we cannot reject incomplete lineage sorting reflecting recent speciation as an explanation for patterns of genetic variation. MC1R variation was unrelated to phenotypic differences. Species did not differ in macroclimatic niches but were distinct in morphology. Although we reject adaptation to variation in macroclimatic conditions as a cause of divergence, speciation may have occurred in the face of gene flow driven by other ecological pressures or by sexual selection. Marked phenotypic divergence with no neutral genetic differentiation is remarkable for Neotropical birds, and makes C. helianthea and C. bonapartei an appropriate system in which to search for the genetic basis of species differences employing genomics. [ABSTRACT FROM AUTHOR]