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The article explores the phenomenon of "dear enemy effects" in the stoplight parrotfish, Sparisoma viride. Dear enemy effects refer to the tendency of territory holders to act less aggressively towards their neighbors compared to strangers. The study observed territorial interactions between male parrotfish and neighboring males or nonterritorial "floaters." The results showed that territorial males were more likely to engage in escalated chases with floaters than with neighbors. The study suggests that the dear enemy effect may be influenced by the defense of food resources and the presence of females. The findings contribute to understanding the mechanisms underlying territoriality in parrotfish and its role in population regulation and ecosystem functioning. [Extracted from the article]

In Amazonian streams, damming caused by road construction changes the system's hydrological dynamics and biological communities. We tested whether the degree of specialization in fish (Bryconops giacopinii) individuals is higher in pristine stream environments with intact ecological conditions than in streams dammed due to the construction of a highway in the Amazon rainforest. To achieve this, stomach content data and stable isotopes (δ13C and δ15N) in tissues with varying isotopic incorporation rates (liver, muscle, and caudal fin) were used to assess the variation in consumption of different prey over time. The indices within‐individual component (WIC)/total niche width (TNW) and individual specialization were employed to compare the degree of individual specialization between pristine and dammed streams. The condition factor and stomach repletion of sampled individuals were used to infer the intensity of intraspecific competition in the investigated streams. The species B. giacopinii, typically considered a trophic generalist, has been shown to be, in fact, a heterogeneous collection of specialist and generalist individuals. Contrary to our expectations, a higher degree of individual specialization was detected in streams dammed by the highway. In dammed streams, where intraspecific competition was more intense, individuals with narrower niches exhibited poorer body conditions than those with broader niches. This suggests that individuals adopting more restricted diets may have lower fitness, indicating that individual specialization may not necessarily be beneficial for individuals. Our results support the notion that intraspecific competition is an important mechanism underlying individual specialization in natural populations. Our results suggest that environmental characteristics (e.g., resource breadth and predictability) and competition for food resources interact in complex ways to determine the degree of individual specialization in natural populations. [ABSTRACT FROM AUTHOR]

Aim: Wallacea is a global biodiversity hotspot and Sulawesi is the largest island in this region, notable for a high proportion of endemic species. The Wakatobi archipelago, off the southeastern peninsular arm of Sulawesi, is home to several endemic bird species. Although islands are known to influence the morphology of their resident species, competitive interactions also exert strong influences on morphology. Here, we consider the contributions of both islands and competitors on two morphological traits of two bird species in a small passerine guild found on the Wakatobi islands. Location: Wakatobi archipelago, Sulawesi Tenggara, Indonesia. Taxon: Wakatobi White‐eye (Zosterops flavissimus) and Wakatobi Sunbird (Cinnyris infrenatus). Methods: Working with morphological measures (from netting studies), population density metrics (from transect surveys) and fundamental data from islands (area, distance from mainland and elevation), we investigated (by means of multiple linear regression) which terms best explained variation in the body size and bill size of two small passerine birds endemic to the Wakatobi islands. Results: Both island metrics and competitor presence/density were useful in describing the variation in body size of both bird species. However, only competitor presence/density was useful in describing variation in bill size of the birds. The best models describing variation in these traits included terms representing both interspecific and intraspecific competition. Main Conclusions: Our findings indicate that simple island metrics may be useful in predicting some of the variation in some functional traits of island species. However, in this example, simple island metrics were insufficient to explain the full variation in body size of endemic birds across the Wakatobi archipelago and were of no use in predicting the variation in their bill size. As bill morphology frequently dictates diet and feeding niche, it is a trait which may determine population divergence and speciation. If simple island metrics fail to describe such diversification, it is surely important to capture that information in other ways. [ABSTRACT FROM AUTHOR]

Interspecific competition is an important factor in the population dynamics and geographical distribution of insect populations. Fall armyworm (FAW), Spodoptera frugiperda, an invasive species, and the Asian corn borer (ACB), Ostrinia furnacalis, a native pest species are major pests on maize in China, posing a threat to maize yield and grain quality. A series of laboratory, greenhouse, and field experiments were conducted to elucidate the competitive interactions between FAW and ACB. In the laboratory experiments, FAW exhibited aggressive behaviors more frequently when compared with ACB, while the latter species exhibited defense behaviors more frequently. Higher intraspecific competition was recorded in the FAW conspecific rather than in ACB, particularly in the 6th larval stage. FAW had a higher interspecific competitive advantage through intraguild predation over ACB, resulting in partial or complete displacement ACB when initially the ratio of the 2 species was 1 : 1. The interspecific competition also had significantly influenced on the population parameters, defensive enzymes, and nutrient of these 2 species. Competitive interaction proved that the response of superoxide, catalase, and soluble protein in FAW were significantly increased, whereas the total sugar content in both species was substantially decreased. Survival rate, and the plant damage that co‐infested by both species varied significantly among the sequential combinations under greenhouse and field conditions. FAW consistently exhibited stronger intraspecific aggression than ACB under laboratory and field conditions when co‐existing on the same feeding guild. These findings contribute to efforts toward the improvement of integrated pest management programs for FAW, in decision making for invasive and native pests' management strategies to reduce the high risks of FAW and ACB outbreaks. [ABSTRACT FROM AUTHOR]

Aim: Invasive plants may evolve a suite of distinctive traits during spread in the new range. Among these traits, dispersal ability is an important trait determining the invasion speed of exotic plants. There is evidence that higher dispersal ability is favoured at the invasion front, where population density may be low. However, no study has explicitly tested how planting density in a common garden affects the dispersal ability of invasive plants. Location: Hainan island of China. Methods: In this study, using 27 populations of an invasive plant, Mikania micrantha, which is expanding its range on Hainan island of China, we examine how three dispersal‐related traits (i.e. dispersal ability, fruit mass, and pappus radius) change with distance from invasion centre and field population density, and how planting density in a common garden affects dispersal traits. Results: Dispersal traits did not change with distance from the invasion centre and field population cover either in the natural environment or in the common garden. In the common garden, increasing planting density from one to five plants per pot increased fruit mass and decreased dispersal ability, indicating that the effect of density on dispersal traits could not be detected in the field. The relationship between dispersal ability in the natural environment and that in the common garden was positive but significant only under the five plants per pot treatment, possibly because dispersal traits in natural conditions were selected under high‐density growth conditions. Main Conclusions: Our results indicate that increasing population density may increase fruit mass and reduce the dispersal ability of range‐expanding invasive plants. We suggest that further studies exploring the patterns of dispersal traits in range‐expanding invasive plants in a common garden should consider intraspecific competition. [ABSTRACT FROM AUTHOR]

Territorial defence depends on highly interrelated factors such as food abundance and conspecific density. We used Dupont's Lark Chersophilus duponti as a model species to evaluate the response of a territorial bird to a foreign male playback, examining how conspecific density, habitat quality and male body condition impact responses. The study was conducted in central Spain with variable male density. Response (yes/no), latency time, distance to the playback speaker, and the number of songs and other vocalizations were monitored for 5 min. Habitat quality was estimated using BlueNDVI vegetation index extracted from high‐resolution drone imagery, which is a proxy for arthropod prey biomass. Conspecific density (Kernel Density Estimator) and male body condition were calculated to assess their effect on response and intensity. We applied generalized linear mixed models (GLMMs) to determine which factors predicted the response and its intensity. There was a greater response probability in areas with a higher density of conspecifics and in areas of poorer habitat quality (i.e. lower BlueNDVI values). In contrast, latency time was longer in areas with lower conspecific density. Intrasexual communication (singing and calling rates) increased with habitat quality. Intraspecific communication (other vocalizations) increased in poorer quality habitats and at a higher density of conspecifics. Body condition was not related to any variables. Our results suggest that male density, sometimes used as an indicator of an area being well conserved for the species, may reflect areas of poorer habitat quality occupied by unpaired floater males, whereas paired territorial males would occupy and defend higher quality areas, leading to lower density. [ABSTRACT FROM AUTHOR]

Resource partitioning is considered a key factor in alleviating competitive interactions, enabling coexistence among consumer species. However, most studies have focused on resource partitioning between species, ignoring the potentially critical role of intraspecific variation in resource use. We investigated floral resource partitioning across species, colonies, and individuals in a species‐rich bumblebee community in the diversification center of bumblebees. We used a total of 10,598 bumblebees belonging to 13 species across 5 years in the Hengduan Mountains of southwest China. First, we evaluated the influence of a comprehensive set of floral traits, including both those related to attractiveness (flower color and shape) and rewards (pollen, sugar ratio, nectar volume, sugar concentration, and amino acid content) on resource partitioning at the species level in bumblebee–plant networks. Then, we explored intraspecific resource partitioning on the colony and individual levels. Our results suggest that bumblebee species differ substantially in their use of the available floral resources, and that this mainly depends on flower attractiveness (floral color and shape). Interestingly, we also detected floral resource partitioning at the colony level within all commonest bumblebee species evaluated. In general, floral resource partitioning between bumblebee individuals decreased with species‐ and individual‐level variation in body size (intertegular span). These results suggest that bumblebee species may coexist via the flexibility in their preferences for specific floral traits, which filters up to support the co‐occurrence of high numbers of species and individuals in this global hotspot of species richness. [ABSTRACT FROM AUTHOR]

Asexual organisms are ubiquitous. While being members of a single species with the same ecological requirements, multiple asexual genotypes within a species are often found in a single habitat. Niche partitioning in time and space among genotypes has been proposed to explain this phenomenon. However, it is not clear whether these different genotypes co‐occur in the long term.Therefore, we examined the population dynamics of two asexual Daphnia cf. pulex genotypes (JPN1 and JPN2) over 9 years in a small mountain lake. These two genotypes consistently occurred in the same seasons and layers, suggesting that niche partitioning cannot explain their long‐term co‐occurrence. The abundance of JPN1 was typically higher in most years. However, the abundance of dormant eggs in lake sediments was at the same level between the genotypes.Results of a laboratory experiment showed that JPN1 competitively excluded JPN2. However, many JPN2 individuals produced dormant eggs before JPN1 competitively excluded them from the experiment. Furthermore, the competitively inferior JPN2 produced dormant eggs abundantly in the medium containing a crowding cue from JPN1 while no such trend was observed for JPN1.These results showed that a competitively inferior asexual genotype could maintain a population with a competitively superior genotype for a long period of time because it had the ability to detect an increase in competitors and produce dormant eggs each year before being competitively eliminated.Based on these results, we suggest that the variation in genotype‐specific response in dormant egg production to environmental change plays a key role in the long‐term co‐occurrence of different asexual genotypes in single habitats. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

The Skellam model describes discrete‐time population dynamics of a single species assuming uniform (i.e., random or Poissonian) individual distribution and intraspecific contest competition. Apart from studies on individual‐based models derived from first principles it has been rarely applied in ecological research although in specific situations it may be more appropriate than, for instance, the frequently used Ricker model, which is derived assuming scramble competition among the individuals. In this article, we offer an insight into the first principles underlying the Skellam model and provide an alternative parameterization of the model in terms of two commonly used parameters: intrinsic rate of population increase and carrying capacity. We also provide guidelines and software for fitting the Skellam model to discrete population time series data. In light of these findings, the Skellam model may be a useful alternative for a range of purposes where it has been earlier overlooked. [ABSTRACT FROM AUTHOR]

Summary: The Jornada Basin Long‐Term Ecological Research Site (JRN‐LTER, or JRN) is a semiarid grassland–shrubland in southern New Mexico, USA. The role of intraspecific competition in constraining shrub growth and establishment at the JRN and in arid systems, in general, is an important question in dryland studies.Using information on shrub distributions and growth habits at the JRN, we present a novel landscape‐scale (c. 1 ha) metric (the 'competition index', CI), which quantifies the potential intensity of competitive interactions. We map and compare the intensity of honey mesquite (Prosopis glandulosa, Torr.) competition spatially and temporally across the JRN‐LTER, investigating associations of CI with shrub distribution, density, and soil types.The CI metric shows strong correlation with values of percent cover. Mapping CI across the Jornada Basin shows that high‐intensity intraspecific competition is not prevalent, with few locations where intense competition is likely to be limiting further honey mesquite expansion.Comparison of CI among physiographic provinces shows differences in average CI values associated with geomorphology, topography, and soil type, suggesting that edaphic conditions may impose important constraints on honey mesquite and growth. However, declining and negative growth rates with increasing CI suggest that intraspecific competition constrains growth rates when CI increases above c. 0.5. [ABSTRACT FROM AUTHOR]

Territoriality is a behavioural adaptation resulting from intraspecific competition and reflects the strategy of how individuals share limited resources in the environment. As a consequence, territorial contests and levels of aggressiveness are strongly influenced by population density.The positive relationship between population density and the intensity of intraspecific competition may appear straightforward. However, empirical evidence regarding this association remains inconclusive. This ambiguity may be attributed to studies that have predominantly focussed on specific fight‐associated traits while overlooking potential interactions between multiple phenotypic characteristics and population dynamics.To examine the effects of population density and other ecological factors on the variation in fight behaviour as well as fight‐associated morphology and performance. We conducted population surveys and behavioural experiments using the Swinhoe's tree lizard across eight populations.Our findings revealed that males from higher density populations tended to engage in less intense fights and exhibited a weaker resident advantage in fights, which coincided with our findings on lower rates of injuries, weaker bite forces and smaller body sizes (and vice versa). Male‐specific variation in fight behaviour, morphology and performance along a density gradient suggests different evolutionary equilibria in territoriality influenced by local costs and benefits.Our study supports the significant role of negative density dependence as a fundamental regulator of eco‐evolutionary dynamics. The observed phenotypic variation emphasizes the importance of ecological and social factors in shaping ontogenetic growth and life‐history strategies. Our findings provide a basis for future investigations into pace‐of‐life syndromes and shed light on how phenotypic adaptation may shape population structure. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Predation is a major evolutionary force determining life‐history traits in prey by direct and indirect mechanisms. This study focuses on life‐history trait variation in crucian carp (Carassius carassius), a species well known for developing a deep body as an inducible morphological defence against predation risk. Here, the authors tested variation in growth and reproductive traits in 15 crucian carp populations in lakes along a predation risk gradient represented by increasingly efficient predator communities. Lakes were located in south‐eastern Norway and were sampled in summer 2018 and 2019. The authors expected crucian carp to attain higher growth rate, larger size, and later age at maturity with increasing predation risk. In the absence of predators, they expected high adult mortality, early maturity and increased reproductive effort caused by strong intraspecific competition. They found that the life‐history traits of crucian carp were clearly related to the presence of piscivores: with increasing predation risk, fish grew in body length and depth and attained larger asymptotic length and size at maturity. This growth was evident at young age, especially in productive lakes with pike, and it suggests that fish quickly outgrew the predation window by reaching a size refuge. Contrary to the authors' predictions, populations had similar age at maturity. High‐predation lakes also presented low density of crucian carp. This suggests that fish from predator lakes may experience high levels of resource availability due to reduced intraspecific competition. Predation regulated life‐history traits in crucian carp populations, where larger size, higher longevity and size at maturity were observed in lakes with large gaped predators. [ABSTRACT FROM AUTHOR]

BACKGROUND: Intraspecific competition is shared in the insect world, especially under the condition of limited food and space resources. To avoid intraspecific competition and increase offspring survival, insects have evolved various effective strategies. A widely‐accepted tactic is employing chemical cues, which are frequently utilized as indicators of conspecific colonization. The sweet potato weevil (SPW), Cylas formicarius, is a destructive pest of sweet potatoes. Its larvae bore into sweet potatoes and alter the emission of odors. The present study aimed to investigate whether volatiles associated with SPW larvae feeding influence the behavioral preference of conspecific adults. RESULTS: Volatiles from SPW larvae‐infested sweet potatoes were collected by a head‐space method and analyzed using gas chromatography‐electroantennogram detector (GC‐EAD) and gas chromatography–mass spectrometry (GC–MS). Five compounds eliciting EAD responses from the antennae of both male and female adult SPW were identified from sweet potatoes with the third‐instar larvae, including linalool, citronellol, nerol, geraniol, and ipomeamarone. Four monoterpene alcohols significantly repelled SPW adults from feeding and oviposition at higher doses in the behavioral preference bioassays. Among them, geraniol displayed the strongest repellent activities for SPW feeding and oviposition. These results suggested that SPW larvae could reduce colonization of adult SPWs by inducing monoterpene alcohols, thereby avoiding intraspecific competition. CONCLUSION: The present study demonstrated that volatile monoterpene alcohols induced by SPW larvae are chemical cues of larvae occupation for SPW adults to change their behavioral preference. Unveiling factors that mediate avoidance of intraspecific competition could help develop repellents or oviposition deterrents for SPW control. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Environments experienced by parental plants may potentially influence the performance of their offspring. These effects may also vary depending on the current environment experienced by the offspring. However, whether these transgenerational effects, especially those induced by biotic factors such as competition, can persist for multiple generations has not been tested. Here, we examined intraspecific competition‐induced transgenerational effects across multiple generations using a floating clonal plant Spirodela polyrhiza, by growing three successive generations each under either low or high density. The second‐generation offspring performed better when the first‐generation plants were grown under low than under high density, independently of the density experienced by the second generation. The third‐generation offspring performed better under low than under high density, and the difference was more pronounced when the second‐generation plants were grown under low density. Moreover, the density of the first and second generation interacted to influence the morphology of the third‐generation offspring. These results indicate that competition‐induced transgenerational effects in S. polyrhiza can vary depending on the competition environment of its offspring and that these effects can persist across multiple generations. [ABSTRACT FROM AUTHOR]

Carrying capacity has multiple definitions, but nowadays, it is mainly referred to as the maximum number of individuals of a particular species sustained by the environment. We examined whether multiple populations of two flour beetle species grown under controlled laboratory conditions reach similar asymptotic population sizes when provided with similar amounts of food resources. We demonstrate that the variation in the asymptotic population sizes was considerably larger than that of the initial food resources and that the latter had no significant effect on the former. Our results experimentally contribute to past literature criticizing the carrying capacity concept, demonstrating that there is no single carrying capacity even under strict laboratory conditions. Therefore, we should not expect to often find "carrying capacities" in nature, where resources fluctuate over time, and interspecific interactions are ubiquitous. We suggest that the classic meaning of carrying capacity should be revisited or saved chiefly for didactic purposes. Research Highlights: Carrying capacity is the number of individuals a habitat can support. A study of two flour beetles species challenges this concept. Even when given similar amounts of food, the population sizes varied. The study suggests caution when applying this concept. [ABSTRACT FROM AUTHOR]

Intraspecific competition at the larval stage is an important ecological factor affecting life‐history, adaptation and evolutionary trajectory in holometabolous insects. However, the molecular pathways underpinning these ecological processes are poorly characterized. We reared Drosophila melanogaster at three egg densities (5, 60, and 300 eggs/mL) and sequenced the transcriptomes of pooled third‐instar larvae. We also examined emergence time, egg‐to‐adult viability, adult mass, and adult sex‐ratio at each density. Medium crowding had minor detrimental effects on adult phenotypes compared to low density and yielded 24 differentially expressed genes (DEGs), including several chitinase enzymes. In contrast, high crowding had substantial detrimental effects on adult phenotypes and yielded 2107 DEGs. Among these, upregulated gene sets were enriched in sugar, steroid and amino acid metabolism as well as DNA replication pathways, whereas downregulated gene sets were enriched in ABC transporters, taurine, Toll/Imd signaling, and P450 xenobiotics metabolism pathways. Overall, our findings show that larval crowding has a large consistent effect on several molecular pathways (i.e., core responses) with few pathways displaying density‐specific regulation (i.e., idiosyncratic responses). This provides important insights into how holometabolous insects respond to intraspecific competition during development. [ABSTRACT FROM AUTHOR]

While global patterns in body size evolution in island vertebrates have been described extensively, the ecological processes that generate these patterns are not well understood. Here we used variation among lizard populations occupying an archipelago to test hypotheses about body size evolution. We examined 35 populations of Aegean wall lizards (Podarcis erhardii, Lacertidae), a species widely distributed across the Balkan mainland and hundreds of Aegean islands. We evaluated measures of resource availability (island area and seabird density), intraspecific competition (lizard abundance) and predation risk (presence of rats, carnivorous mammals, vipers, and birds of prey) as possible factors affecting lizard body size. Lizard body size increased with island size overall, as well as with seabird colony density, suggesting a role for increased food resources and especially seabird subsidies in the evolution of body size. Lizards were larger where lizard population density was higher, suggesting a possible role for intraspecific competition in the evolution of body size. In our sample, rats, carnivorous mammals, and vipers did not have obvious effects on lizard body size, and lizards were smaller on islands with resident birds of prey. Males were larger than females on average, yet sexual dimorphism did not vary consistently with measures of resource availability and competition. Overall, our results suggest that local resource levels predict population density and body size in these lizards, and that nesting seabirds in particular can substantially affect lizard body size. [ABSTRACT FROM AUTHOR]

BACKGROUND: Wolbachia infection increases the superparasitism frequency of Trichogramma females and provides an opportunity for horizontal intraspecific transmission. However, superparasitism may lead to interstrain competition between Wolbachia‐infected Trichogramma offspring and their uninfected counterparts. This study investigated the outcome of interstrain intrinsic competition between Wolbachia‐infected thelytokous strain (W) and uninfected bisexual strain (B) of Trichogramma dendrolimi. To determine the developmental rate of both strains, the sizes of immature stages of T. dendrolimi offspring at different times after parasitisation were measured in single parasitism and superparasitism conditions. RESULTS: The results reflect increased superparasitism by Wolbachia‐infected females compared with uninfected females. Trichogramma females did not discriminate between host eggs previously parasitised by either B or W females. When the first oviposition was performed by B females, the B offspring outcompeted W offspring deposited later. Although when W offspring was deposited 8 h earlier than the B offspring, it gained no advantage over B offspring. Regardless of parasitism conditions, differences in the development rate between W and B offspring were not significant. CONCLUSION: The results reconfirmed that W females presented a higher tendency for superparasitism than B females, and showed that B offspring outcompeted W offspring even when the latter was deposited 8 h earlier. The inferiority of Wolbachia‐infected Trichogramma compared with their uninfected counterparts is not due to the developmental delay. This study provides insights into the effects of intrinsic competition on the control efficacy of Wolbachia‐infected Trichogramma against pests in biological control programs. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Marine microorganisms have the potential to disperse widely with few obvious barriers to gene flow. However, among microalgae, several studies have demonstrated that species can be highly genetically structured with limited gene flow among populations, despite hydrographic connectivity. Ecological differentiation and local adaptation have been suggested as drivers of such population structure. Here we tested whether multiple strains from two genetically distinct Baltic Sea populations of the diatom Skeletonema marinoi showed evidence of local adaptation to their local environments: the estuarine Bothnian Sea and the marine Kattegat Sea. We performed reciprocal transplants of multiple strains between culture media based on water from the respective environments, and we also allowed competition between strains of estuarine and marine origin in both salinities. When grown alone, both marine and estuarine strains performed best in the high‐salinity environment, and estuarine strains always grew faster than marine strains. This result suggests local adaptation through countergradient selection, that is, genetic effects counteract environmental effects. However, the higher growth rate of the estuarine strains appears to have a cost in the marine environment and when strains were allowed to compete, marine strains performed better than estuarine strains in the marine environment. Thus, other traits are likely to also affect fitness. We provide evidence that tolerance to pH could be involved and that estuarine strains that are adapted to a more fluctuating pH continue growing at higher pH than marine strains. [ABSTRACT FROM AUTHOR]

Dispersal is a vital component of the life history of nearly all organisms. The ability to disperse determines the distribution and abundance of a species and thus its community dynamic at different sites. The scientific challenge is to design standardized laboratory experiments that not only record the effects of single factors but also include the multicausal nature of dispersal. Here we tested the effect of the environmental factors density, food availability and predation, and the combinations thereof on the dispersal of five free‐living nematode species by performing experiments in two‐patched systems. We hypothesized that emigration is generally positively correlated with the intrinsic rate of natural increase and would decrease with increasing food availability and increase both with the presence of a predator and at higher initial population densities. These predictions were tested both using single‐species tests with laboratory cultures and using intact natural nematode communities to investigate whether environmental factors determine the composition of dispersing species. The results of our study revealed a positive correlation between dispersal and intrinsic growth ability, whereas the studied nematode species differed in their dispersal patterns, both under control conditions and in response to bottom‐up, top‐down, and density‐dependent stimuli. Despite the species‐specific differences in dispersal behavior in response to the environmental factors, the availability of food appeared as the main driver. This was particularly pronounced regarding a natural nematode community. Our experiments emphasize the central role of food availability in spatial structuring nematode communities. [ABSTRACT FROM AUTHOR]

Farmed anguillid eels are frequently stocked into natural fresh waters to enhance eel resources, but little is known about what happens to these eels or their interactions with wild eels after stocking. A recent study observed a depressed survival and growth rate of farmed Japanese eels when they were reared with wild eels, which indicated that wild eels might interfere with the survival and growth of farmed‐and‐stocked eels through intraspecific competition. To contribute to improving eel stocking efficiency, the growth of farmed‐and‐stocked Japanese eels was compared among four rivers with different wild eel densities using mark‐and‐recapture studies. Based on the 2‐year recapture survey after stocking, it was found that the density of the farmed‐and‐stocked eels was not significantly different among rivers. The daily growth rates of farmed‐and‐stocked eels in the rivers with lower wild eel density were significantly higher than those of the eels stocked into the rivers with higher wild eel density. The farmed‐and‐stocked eels moved significantly greater distances downstream than wild eels that showed sedentary behaviour. This and previous studies indicate that significant questions remain about the effectiveness of stocking farmed eels into water bodies where naturally recruited wild eels are present. [ABSTRACT FROM AUTHOR]

Predation is widely regarded as an important selective force in the evolution and maintenance of dermal armour; yet, the basic premise that predation and armour are strongly linked to each other has proven to be difficult to assess.In this concept, I put forward the fighting‐advantage hypothesis, the view that aggressive interactions with conspecifics, not predation, might have been a key selective pressure in the evolution of dermal armour.Considering intraspecific competition as a potential explanation could not only reveal previously overlooked aspects of the functional and evolutionary significance of dermal armour, but also advance the emerging field of biomimetics in which such knowledge forms the starting point of technological innovation. [ABSTRACT FROM AUTHOR]

The incidence and causality of inverse size‐dependent phenology was investigated for spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae), in part due to large sample size [>22000 feral females with known body size (wing area) and timing of emergence/occurrence]. Data collected in three Canadian provinces (New Brunswick, Nova Scotia, Quebec) between 1976 and 2019 included a wide array of sampling procedures grouped along gradients of reproductive classes. (1) For resident females of local origin (collected as pupae and allowed to emerge in the laboratory), body size declined over time at seven of seven sites, indicative of inverse size‐dependent timing of emergence. (2) Females foraging on trees (collected by fogging host trees or with sweep nets) exhibited declines in body size over time at five of five sites. (3) For behaviorally active females collected at traps (malaise, light, and canopy traps), inverse size‐dependent phenology of flight was observed at 20 of 23 combination of trap types/sites; partition of variance indicated limited variation in body size as a function of trap type, thus all inflight females were pooled in subsequent analyses. (4) In contrast to other sampling procedures, dead females collected on drop trays exhibited size‐dependent timing of mortality at only one of five sites. The article includes first body size measurements of migrant females captured in the troposphere with a kite balloon; as with other sampling procedures, body size decreased during the interval of sampling. Ongoing studies combining measurements of body size and dry weight of females (wing load) aim at inferring consequences of inverse size‐dependent phenology on reproduction and migration of budworms, including linkages with population dynamics. [ABSTRACT FROM AUTHOR]

Cannibalism, the act of preying on and consuming a conspecific, is taxonomically widespread, and putatively important in the wild, particularly in teleost fishes. Nonetheless, most studies of cannibalism in fishes have been performed in the laboratory. Here, we test four predictions for the evolution of cannibalism by conducting one of the largest assessments of cannibalism in the wild to date coupled with a mesocosm experiment. Focusing on mosquitofishes and guppies, we examined 17 species (11,946 individuals) across 189 populations in the wild, spanning both native and invasive ranges and including disparate types of habitats. We found cannibalism to be quite rare in the wild: most populations and species showed no evidence of cannibalism, and the prevalence of cannibalism was typically less than 5% within populations when it occurred. Most victims were juveniles (94%; only half of these appeared to have been newborn offspring), with the remaining 6% of victims being adult males. Females exhibited more cannibalism than males, but this was only partially explained by their larger body size, suggesting greater energetic requirements of reproduction likely play a role as well. We found no evidence that dispersal‐limited environments had a lower prevalence of cannibalism, but prevalence was greater in populations with higher conspecific densities, suggesting that more intense resource competition drives cannibalistic behavior. Supporting this conclusion, our mesocosm experiment revealed that cannibalism prevalence increased with higher conspecific density and lower resource levels but was not associated with juvenile density or strongly influenced by predation risk. We suggest that cannibalism in livebearing fishes is rare in the wild because preying on conspecifics is energetically costly and only becomes worth the effort when competition for other food is intense. Due to the artificially reduced cost of capturing conspecifics within confined spaces, cannibalism in captive settings can be much more frequent. [ABSTRACT FROM AUTHOR]

Eutrophication is believed to promote plant invasion, resulting in high growth performances of invasive plants and, therefore, the great potential for growth‐induced intraspecific competition for light. Current hypotheses predict how eutrophication promotes plant invasion but fail to explain how great invasiveness is maintained under eutrophic conditions. In diverse native communities, co‐occurring plants of varying sizes can avoid light competition by exploiting light complementarily; however, whether this mechanism applies to intraspecific competition in invasive plant populations remains unknown. Using a 2‐year field nitrogen (N)‐enrichment experiment on one of the global invasive plants, Spartina alterniflora, we found that the plasticity of light use reduced intraspecific competition and increased biomass production in S. alterniflora. This plasticity effect was enhanced when S. alterniflora had no nutrient limitations. In the N‐enrichment treatments, the height difference among S. alterniflora ramets increased as light intensity decreased under the canopy. Compared with ambient N, under N enrichment, shorter individuals increased their light‐use efficiency and specific leaf area in response to the reduced light intensity under the canopy. However, such ecophysiological plasticity was not found for taller individuals. Our findings revealed that the light‐use plasticity of short individuals can be envisaged as a novel mechanism by which an invasive plant alleviates intraspecific competition and increases its invasiveness, challenging the prevailing perspective that the invasiveness of exotic plants is constrained by intraspecific competition. [ABSTRACT FROM AUTHOR]

In many animal species, sexually mature individuals may skip breeding opportunities despite a likely negative impact on fitness. In spatio‐temporally heterogeneous environments, habitat selection theory predicts that individuals select habitats where fitness prospects are maximized. Individuals are attracted to high‐quality habitat patches where they compete for high‐quality breeding sites. Since failures in contests to secure a site may prevent individuals from breeding, we hypothesized that attraction to and competition for high‐quality habitats could shape breeding propensity.Under this hypothesis, we predicted the two following associations between breeding propensity and two key population features. (1) When mean habitat quality in the population increases in multiple patches such that availability of high‐quality sites increases across the population, the resulting decrease in competition should positively affect breeding propensity. (2) When the number of individuals increases in the population, the resulting increase in competitors should negatively affect breeding propensity (negative density dependence).Using long‐term data from kittiwakes Rissa tridactyla, we checked the prerequisite of prediction (1), that availability of high‐quality sites is positively associated with current mean habitat quality in the population (represented by breeding success). We then applied integrated population modelling to quantify annual fluctuations in population mean breeding success, breeding propensity and number of individuals by breeding status (pre‐breeders, breeders, skippers and immigrants), and tested our predictions.Our results showed that breeding propensity acts as an important driver of population growth. As expected, breeding propensity was positively associated with preceding mean habitat quality in the population, and negatively with the number of competitors. These relationships varied depending on breeding status, which likely reflects status dependence in competitive ability.These findings highlight the importance of competition for high‐quality breeding sites in shaping breeding propensity. Thereby, we draw attention towards alternative and complementary explanations to more standard considerations regarding the energetic cost of reproduction, and point to possible side effects of habitat selection behaviours on individual life histories and population dynamics. [ABSTRACT FROM AUTHOR]

Fishing pressure can have strong impacts on fish populations, driving declines in abundance and, occasionally, changing life history traits. However, much of our current understanding of these phenomena derives from studies conducted decades or even centuries after the onset of fishing. Newly established fisheries provide an excellent opportunity to understand this critical early phase. Temporal trends in catch data and life history traits of the cyprinid fish Rastrineobola argentea (Pellegrin), now the target of a burgeoning artisanal fishery in Lake Nabugabo, Uganda, were analysed. Results showed that the R. argentea fishery intensified and became more selective during the first decade since its establishment (2008–2019), while catch‐per‐unit‐effort of R. argentea (fisheries‐independent abundance) at repeatedly sampled sites in the lake decreased over this same time period. Size‐adjusted egg volume and ovary mass increased significantly over the time period, which may reflect a density‐dependent response to a fisheries‐induced population decline. [ABSTRACT FROM AUTHOR]

1. Food choice may change depending on sex, age, and physiological condition due to nutritional requirements or because of mechanisms that promote food recognition. Among dung beetles, some species are attracted to both carrion and dung, but why males and females are more attracted to either resource remains unclear. This study aimed to investigate whether body size, physiological condition (body dry mass, lipid mass, muscle mass) and age (young, mature, old) affect resource attraction in males and females of two species of dung beetles, Dichotomius iannuzziae and D. gilletti. 2. This study was carried out in remnants of Atlantic Forest in Brazil. To evaluate resource attraction, pitfall traps baited with feces or carrion were installed in the remnants, and the beetles were categorized according to sex and age. Furthermore, beetles' physiological condition and body size were measured. 3. Population structure of D. iannuzziae differed according to bait type. Males of D. iannuzziae were more attracted to feces than carrion across all age classes. The same occurred among conspecific mature females, suggesting a sex‐specific reproductive preference for feces. Contrastingly, D. gilletti resource attraction did not vary with sex or age. For both species, neither body size nor physiological condition defined resource attraction, indicating that compensatory feeding due to nutrient requirements is unlikely. 4. Due to the changes in food quality and quantity as a consequence of forest loss, mammal extinction and landscape transformation, it is critical to understand how wild species respond to different scenarios of food availability. [ABSTRACT FROM AUTHOR]

Generalist species dominate urban ecosystems. The success of urban generalists is often related to a plastic diet and feeding traits that allow them to take advantage of a variety of food resources provided by humans in cities. The classification of a species as a generalist is commonly based on mean estimates of diet‐ and feeding‐related traits. However, there is increasing evidence that a generalist population can consist of individual specialists. In such cases, estimates based on mean can hide important individual variation that can explain trophic ecology and the success of urban dwellers. Here, we focus on guppies, Poecilia reticulata, a widespread alien fish species which has invaded both urban and non‐urban systems, to explore the effect of urbanization on individual diet and feeding morphology (cranium shape). Our results show that guppies in urban and non‐urban populations are not individual specialists, having a similar generalist diet despite the high population density. However, there is important individual variation in cranium shape which allow urban guppies to feed more efficiently on highly nutritious food. Our data suggest that individual variation in feeding efficiency can be a critical overlooked trait that facilitates the success of urban generalists. [ABSTRACT FROM AUTHOR]

Competition and metabolism should be linked. Intraspecific variation in metabolic rates and, hence, resource demands covary with competitive ability. The effects of metabolism on conspecific interactions, however, have mostly been studied under laboratory conditions. We used a trait‐specific response‐surface design to test for the effects of metabolism on pairwise interactions of the marine colonial invertebrate, Bugula neritina in the field. Specifically, we compared the performance (survival, growth, and reproduction) of focal individuals, both in the presence and absence of a neighbor colony, both of which had their metabolic phenotype characterized. Survival of focal colonies depended on the metabolic phenotype of the neighboring individual, and on the combination of both the focal and neighbor colony metabolic phenotypes that were present. Surprisingly, we found pervasive effects of neighbor metabolic phenotypes on focal colony growth and reproduction, although the sign and strength of these effects showed strong microenvironmental variability. Overall, we find that the metabolic phenotype changes the strength of competitive interactions, but these effects are highly contingent on local conditions. We suggest future studies explore how variation in metabolic rate affects organisms beyond the focal organism alone, particularly under field conditions. [ABSTRACT FROM AUTHOR]

Determining influences of predation and competition on community dynamics is particularly challenging in coral reef systems where interspecific interactions between many predator and prey species play out in patchy landscapes. We used ~1000 stereo‐baited remote underwater video deployments (stereo‐BRUVs) to assess the relative abundance and analysed the behaviour of two size classes of mesopredatory teleosts (lutajnids, serranids, lethrinids) in the presence and absence of larger predators (mesopredatory and apex carcharhinids). For mesopredatory teleosts, the presence of sharks did not influence the abundance, time of arrival in vicinity of the stereo‐BRUVs, the probability of feeding on bait or the delay to feeding. Instead, the number of similar‐sized competitors and surrounding habitat features were the strongest drivers of these behavioural metrics. We suggest that for most fishes, the predatory threat posed by highly mobile species such as sharks is likely to be sporadic and transitory, whereas competition is ubiquitous and ever present, particularly for schooling taxa. Ultimately, it is likely that both processes interact to determine behavioural phenotypes as individuals that are inferior competitors can be displaced from safe habitats or prohibited from access to resources and will be more susceptible to predation. Future studies should consider the relative effects of both processes and the degree to which each can be shaped by habitat when investigating trophic dynamics that regulate marine communities. [ABSTRACT FROM AUTHOR]

While it is universally recognised that environmental factors can cause phenotypic trait variation via phenotypic plasticity, the extent to which causal processes operate in the reverse direction has received less consideration. In fact individuals are often active agents in determining the environments, and hence the selective regimes, they experience. There are several important mechanisms by which this can occur, including habitat selection and niche construction, that are expected to result in phenotype–environment correlations (i.e. non‐random assortment of phenotypes across heterogeneous environments). Here we highlight an additional mechanism – intraspecific competition for preferred environments – that may be widespread, and has implications for phenotypic evolution that are currently underappreciated. Under this mechanism, variation among individuals in traits determining their competitive ability leads to phenotype–environment correlation; more competitive phenotypes are able to acquire better patches. Based on a concise review of the empirical evidence we argue that competition‐induced phenotype–environment correlations are likely to be common in natural populations before highlighting the major implications of this for studies of natural selection and microevolution. We focus particularly on two central issues. First, competition‐induced phenotype–environment correlation leads to the expectation that positive feedback loops will amplify phenotypic and fitness variation among competing individuals. As a result of being able to acquire a better environment, winners gain more resources and even better phenotypes – at the expense of losers. The distinction between individual quality and environmental quality that is commonly made by researchers in evolutionary ecology thus becomes untenable. Second, if differences among individuals in competitive ability are underpinned by heritable traits, competition results in both genotype–environment correlations and an expectation of indirect genetic effects (IGEs) on resource‐dependent life‐history traits. Theory tells us that these IGEs will act as (partial) constraints, reducing the amount of genetic variance available to facilitate evolutionary adaptation. Failure to recognise this will lead to systematic overestimation of the adaptive potential of populations. To understand the importance of these issues for ecological and evolutionary processes in natural populations we therefore need to identify and quantify competition‐induced phenotype–environment correlations in our study systems. We conclude that both fundamental and applied research will benefit from an improved understanding of when and how social competition causes non‐random distribution of phenotypes, and genotypes, across heterogeneous environments. [ABSTRACT FROM AUTHOR]

Fluidity of a given membrane decreases at lower ambient temperatures, whereas it rises at increasing temperatures, which is achieved through changes in membrane lipid composition. In consistence with homeoviscous adaptation theory, lower temperatures result in increased tissue concentrations of polyunsaturated fatty acids (PUFAs) in Daphnia magna, suggesting a higher PUFA requirement at lower temperatures. However, so far homeoviscous adaptation has been suggested for single or geographically separated Daphnia genotypes only. Here, we investigated changes in relative fatty acid (FA) tissue concentrations in response to a lower temperature (15°C) within a D. magna population. We determined juvenile growth rates (JGR) and FA patterns of 14 genotypes that were grown on Chlamydomonas klinobasis at 15°C and 20°C. We report significant differences of JGR and the relative body content of various FAs between genotypes at either temperature and between temperatures. Based on slopes of reaction norms, we found genotype‐specific changes in FA profiles between temperatures suggesting that genotypes have different strategies to cope with changing temperatures. In a hierarchical clustering analysis, we grouped genotypes according to differences in direction and magnitude of changes in relative FA content, which resulted in three clusters of genotypes following different patterns of changes in FA composition. These patterns suggest a lower importance of the PUFA eicosapentaenoic acid (EPA, C20:5ω3) than previously assumed. We calculated an unsaturation index (UI) as a proxy for membrane fluidity at 15°C, and we neither found significant differences for this UI nor for fitness, measured as JGR, between the three genotype clusters. We conclude that these three genotype clusters represent different physiological solutions to temperature changes by altering the relative share of different FAs, but that their phenotypes converge with respect to membrane fluidity and JGR. These clusters will be subjected to different degrees of PUFA limitation when sharing the same diet. [ABSTRACT FROM AUTHOR]

Sexual competition is increasingly recognized as an important selective pressure driving species distributions. However, few studies have investigated the relative importance of interpopulation versus intrapopulation competition in relation to habitat availability and selection.To explain spatial segregation between sexes that often occurs in non‐territorial and central place foragers, such as seabirds, two hypotheses are commonly used. The 'competitive exclusion' hypothesis states that dominant individuals should exclude subordinate individuals through direct competition, whereas the 'niche divergence' hypothesis states that segregation occurs due to past competition and habitat specialization.We tested these hypotheses in two populations of an extreme wide‐ranging and sexually dimorphic seabird, investigating the relative role of intrapopulation and interpopulation competition in influencing sex‐specific distribution and habitat preferences.Using GPS loggers, we tracked 192 wandering albatrosses Diomedea exulans during four consecutive years (2016–2019), from two neighbouring populations in the Southern Ocean (Prince Edward and Crozet archipelagos). We simulated pseudo‐tracks to create a null spatial distribution and used Kernel Density Estimates (KDE) and Resource Selection Functions (RSF) to distinguish the relative importance of within‐ versus between‐population competition.Kernel Density Estimates showed that only intrapopulation sexual segregation was significant for each monitoring year, and that tracks between the two colonies resulted in greater overlap than expected from the null distribution, especially for the females. RSF confirmed these results and highlighted key at‐sea foraging areas, even if the estimated of at‐sea densities were extremely low. These differences in selected areas between sites and sexes were, however, associated with high interannual variability in habitat preferences, with no clear specific preferences per site and sex.Our results suggest that even with low at‐sea population densities, historic intrapopulation competition in wide‐ranging seabirds may have led to sexual dimorphism and niche specialization, favouring the 'niche divergence' hypothesis. In this study, we provide a protocol to study competition within as well as between populations of central place foragers. This is relevant for understanding their distribution patterns and population regulation, which could potentially improve management of threatened populations. [ABSTRACT FROM AUTHOR]

Premise: Plant performance and functional traits vary considerably within species, particularly in response to environmental variation. Plant responses may reflect life‐history trade‐offs, such as between resource acquisition and resource conservation. Larger seeds may buffer young plants from the negative effects of environmental variation, such as limitations in nutrients or water. However, whether seed size plays a similar role in how plants respond to variation in their biotic environment, including competition and soil microbial communities, remains poorly understood. Methods: We used a greenhouse experiment to test the interactive effects of intraspecific competition, the origin of the soil microbial community, and seed size on performance and functional traits in Quercus rubra L. seedlings. Results: Intraspecific variation in seedling traits weakly aligned with a resource acquisition–conservation trade‐off. Across the wide range of initial acorn mass, competition decreased seedling biomass by about 35%. Competition directly decreased the root mass ratio and indirectly increased specific leaf area and specific root length, via the negative effects on total biomass. In contrast, soil microbial communities had minor effects on seedlings, and we found no differences between plants receiving soil originating from a conspecific adult and plants receiving soil originating from a heterospecific adult. Conclusions: Competition is a more important driver of intraspecific variation in young Quercus rubra seedling performance and traits, both directly and by delaying ontogenetic development, than soil microbial communities. Seed size is an important predictor of seedling biomass, but a larger seed does not necessarily buffer seedlings from the effects of competition. [ABSTRACT FROM AUTHOR]

Aim: How plants cope with increases in population density via root plasticity is not well documented, although abiotic environments and plant ontogeny may have important roles in determining root response to density. To investigate how plant root plasticity in response to density varies with soil conditions and growth stages, we conducted a field experiment with an annual herbaceous species (Abutilon theophrasti). Methods: Plants were grown at low, medium, and high densities (13.4, 36.0, and 121.0 plants m−2, respectively), under fertile and infertile soil conditions, and a series of root traits were measured after 30, 50, and 70 days. Results: Root allocation increased, decreased, or canalized in response to density, depending on soil conditions and stages of plant growth, indicating the complex effects of population density, including both competitive and facilitative effects. Main conclusions: Root allocation was promoted by neighbor roots at early stages and in abundant resource availability, due to low‐to‐moderate belowground interactions among smaller plants, leading to facilitation. As plants grew, competition intensified and infertile soil aggravated belowground competition, leading to decreased root allocation in response to density. Root growth may be more likely restricted horizontally rather than vertically by the presence of neighbor, suggesting a spatial orientation effect in their responses to density. We emphasized the importance of considering effects of abiotic conditions and plant growth stages in elucidating the complexity of density effects on root traits. [ABSTRACT FROM AUTHOR]

1. Intraspecific competition for food may affect the development, survival, and fecundity of organisms. However, environmental variation in abiotic conditions can influence resource quality and/or quantity, thereby modifying the strength of intraspecific competition. 2. This study focuses on intraspecific competition among Tanytarsus gracilentus (Chironomidae: Diptera) larvae. In Lake Mývatn, Iceland, T. gracilentus undergoes large population fluctuations, and evidence suggests that these fluctuations are governed by consumer‐resource interactions between the larvae and benthic diatoms. In two experiments, we studied (i) the effects of larval density on individual development and survival, and (ii) how light and nutrients (nitrogen and phosphorus) mediate the strength of intraspecific competition across a density gradient. 3. Survival declined with increasing larval density in both experiments, although not significantly in the first experiment in which we manipulated only density. In the second experiment, enhancement of either light or phosphorus mitigated the negative effect of larval density on survival. In both experiments, density had a negative effect on individual development. In the first experiment, fewer larvae progressed to the final fourth instar at higher densities. In the second experiment, larvae were smaller in high density treatments, and this effect was most pronounced in the treatments without light or phosphorus supplementation. 4. These results highlight the potential for environmental factors to influence the strength of density‐dependent competition. Environmental variation that affects resource quantity or quality may influence the overall dynamics of our study organism and other populations whose dynamics are controlled by consumer‐resource relationships. [ABSTRACT FROM AUTHOR]

Recent reports of the presence of Ambrosia trifida(AT) in areas infested by A. artemisiifolia(AA) in Serbia warn of the impending establishment of a more damaging crop weed. Here, we test the potential competitive effects of these two weed species. We conducted a field competition study in 2016 and 2017 as a replacement series experiment arranged in a split plot, with main plots (20.5 m × 2 m) at total plant densities of 10 and 100 plants/m2, and sub‐plots (3 m × 2 m) at the proportion of AT to AA of 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100. Individual plant biomass (IPB) for AT was lowest when grown in monoculture, while AA reached its highest IPB in its monoculture. With AT < 40%, the AT IPB was larger than (2017) or the same as AA (2016). With AT > 40%, its IPB decreased due to increased intraspecific competition. We obtained the lowest sub‐plot biomass (SPB) of AT + AA in mixtures with 40:60 and 60:40 ratios, and also the highest SPB of other weed species. We show that despite a larger leaf area, AT may not fully replace AA and thus not become a new threat to crops, as it not only suffers from intraspecific competition at high densities, but also from interspecific competition with AA. Therefore, crops may benefit from a stable coexistence of both species as compared to highly dominant AT or AA. Further studies in the presence of crops are needed to confirm this hypothesis. [ABSTRACT FROM AUTHOR]

In long‐lived polygynous species, male reproductive success is often monopolized by a few mature dominant individuals. Young males are generally too small to be dominant and may employ alternative tactics; however, little is known about the determinants of reproductive success for young males. Understanding the causes and consequences of variability in early reproductive success may be crucial to assess the strength of sexual selection and possible long‐term trade‐offs among life‐history traits. Selective pressures driven by fluctuating environmental conditions may depend on age class. We evaluated the determinants of reproduction in male bighorn sheep (Ovis canadensis) aged 2–4 years using 30 years of individual‐level data. These young males cannot defend estrous ewes and use alternative mating tactics. We also investigated how the age of first detected reproduction was correlated to lifetime reproductive success and longevity. We found that reproductive success of males aged 3 years was positively correlated to body mass, to the proportion of males aged 2–4 years in the competitor pool, and to the number of females available per adult male. These results suggest that reproductive success depends on both competitive ability and population age–sex structure. None of these variables, however, had significant effects on the reproductive success of males aged 2 or 4 years. Known reproduction before the age of five increased lifetime reproductive success but decreased longevity, suggesting a long‐term survival cost of early reproduction. Our analyses reveal that both individual‐level phenotypic and population‐level demographic variables influence reproductive success by young males and provide a rare assessment of fitness trade‐offs in wild polygynous males. [ABSTRACT FROM AUTHOR]

BACKGROUND: Crop pest management requires an understanding of the complex interactions among species that potentially impact crop yield. In soybean, the velvetbean caterpillar, Anticarsia gemmatalis (Hübner), and the soybean looper, Chrysodeixis includens (Walker), are described as key pests, sharing the same feeding guild. We assessed the intraguild interactions of these species under laboratory conditions. Fitness cost study was conducted to examine the influence of competition on insect development. A video tracking system was used to evaluate behavioral parameters during larval interactions in scenarios with and without food availability. RESULTS: In the fitness cost assay, pupal weight was not significantly affected, regardless of sex. However, larval and pupal survival were influenced by the competition, especially in third versus fifth instar scenarios. We detected 40.00% cannibalism and 46.67% predation when A. gemmatalis and C. includens third instars competed with A. gemmatalis fifth instar, respectively. Distance moved, distance between larvae, body contact (food available) and frequency in food of C. includens larvae were negatively affected by interactions. Anticarsia gemmatalis larvae showed highly active behavior, moving twice or more the distance compared to C. includens larvae, and A. gemmatalis spent more time in body contact with food. CONCLUSION: Our results suggest that A. gemmatalis has a competitive advantage over C. includens. This study provides important information regarding lepidopteran behavior in soybean. We recommended that additional studies are necessary to understand the effects of interactions, especially in field conditions. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

As more and more species face anthropogenic threats, understanding the causes of population declines in vulnerable taxa is essential. However, long‐term datasets, ideal to identify lasting or indirect effects on fitness measures such as those caused by environmental factors, are not always available.Here we use a single year but multi‐population approach on populations with contrasting demographic trends to identify possible drivers and mechanisms of seabird population changes in the north‐east Atlantic, using the Atlantic puffin, a declining species, as a model system.We combine miniature GPS trackers with camera traps and DNA metabarcoding techniques on four populations across the puffins' main breeding range to provide the most comprehensive study of the species' foraging ecology to date.We find that puffins use a dual foraging tactic combining short and long foraging trips in all four populations, but declining populations in southern Iceland and north‐west Norway have much greater foraging ranges, which require more (costly) flight, as well as lower chick‐provisioning frequencies, and a more diverse but likely less energy‐dense diet, than stable populations in northern Iceland and Wales.Together, our findings suggest that the poor productivity of declining puffin populations in the north‐east Atlantic is driven by breeding adults being forced to forage far from the colony, presumably because of low prey availability near colonies, possibly amplified by intraspecific competition. Our results provide valuable information for the conservation of this and other important North‐Atlantic species and highlight the potential of multi‐population approaches to answer important questions about the ecological drivers of population trends. [ABSTRACT FROM AUTHOR]

Dominant species in intercropping experience less resource competition compared with its monoculture. This reduced competition for resources may allow cultivating the dominant species at an increased density in intercropping to obtain greater yield. However, experimental results are inconclusive when the optimal within row density in the sole crop is not well established. Here, we conducted a two‐year experiment to test the hypothesis that optimal within row plant density of dominant species in intercropping would be higher in the intercrop than in the sole crop. We tested three maize densities (3, 4.5, and 6 plants m−1) in both sole maize and two replacement designed intercrops. The row configurations of two intercrops are two rows maize intercropped with four rows peanut (M2P4) and four rows maize intercropped with four rows peanut (M4P4). Peanut was grown at the same plant density of 12 plants m−1 row in both sole crop and intercrops. The results indicated that increasing maize density from the optimal density in monoculture is not worthy of promotion to improve yield in intercropping, which denied our hypothesis. The land equivalent ratios (LER) in the dry year (2017) were higher than the wet year (2016). Maize yields per unit area of the whole intercropping system were highest with densities of 4.5 and 6 plants m−1 row, with no significant difference between these two densities. Maximum maize yields in sole cropping were obtained with maize densities of 6 plants m−1 row. Intercropping provided higher yields at low and intermediate sole crop maize densities, but not at high sole crop maize density. Average land equivalent ratios at 3, 4.5, and 6 plants m−1 of maize were 1.09, 1.04, and 0.95 in 2016, and 1.07, 1.10, and 1.02 in 2017. Our results suggest that intercropping performs better at conditions with less resources than adequate resources. [ABSTRACT FROM AUTHOR]

Plant roots interact with rhizosphere microorganisms to accelerate soil organic matter (SOM) mineralization for nutrient acquisition. Root‐mediated changes in SOM mineralization largely depend on root‐derived carbon (root‐C) input and soil nutrient status. Hence, intraspecific competition over plant development and spatiotemporal variability in the root‐C input and nutrients uptake may modify SOM mineralization. To investigate the effect of intraspecific competition on SOM mineralization at three growth stages (heading, flowering, and ripening), we grew maize (C4 plant) under three planting densities on a C3 soil and determined in situ soil C‐ and N‐mineralization by 13C‐natural abundance and 15N‐pool dilution approaches. From heading to ripening, soil C‐ and N‐mineralization rates exhibit similar unimodal trends and were tightly coupled. The C‐to‐N‐mineralization ratio (0.6 to 2.6) increased with N availability, indicating that an increase in N‐mineralization with N depletion was driven by microorganisms mining N‐rich SOM. With the intraspecific competition, plants increased specific root lengths as an efficient strategy to compete for resources. Root morphologic traits rather than root biomass per se were positively related to C‐ and N‐mineralization. Overall, plant phenology and intraspecific competition controlled the intensity and mechanisms of soil C‐ and N‐ mineralization by the adaptation of root traits and nutrient mining. Soil C‐ and N‐mineralization rates are tightly coupled throughout maize growth stages and dependent on soil N availability. Plant phenology and intraspecific competition govern the intensity and mechanisms of the C‐ and N‐mineralization by the adaptation of root traits and nutrient mining. [ABSTRACT FROM AUTHOR]

When plants compete what influences that interaction? To answer this we measured belowground competition directly, as the simultaneous capture of soil ammonium and nitrate by co‐existing herbaceous perennials, Dactylis glomerata and Plantago lanceolata, under the influence of: species identity; N uptake and biomass of focal and neighbour plants; location (benign lowland versus harsher upland site); N availability (low or high N fertilizer); N ion, ammonium or nitrate production (mineralisation) rate, and competition type (intra‐ or interspecific), as direct effects or pairwise interactions in linear models. We also measured biomass as an indirect proxy for competition. Only three factors influenced both competitive N uptake and biomass production: focal species identity, N ion and the interaction between N ion and neighbour N uptake. Location had little effect on N uptake but a strong influence on biomass production. N uptake increased linearly with biomass only in isolated plants. Our results support the view that measuring resource capture or biomass production tells you different things about how competitors interact with one another and their environment, and that biomass is a longer‐term integrative proxy for the outcomes of multiple separate interactions—such as competition for N—occurring between plants. We tested which of many factors had the strongest effects on competition for nitrogen, and if the same factors influenced competitors' growth. Different factors influenced competition and growth. For complete understanding of plant "competition" more than just biomass responses must be measured. [ABSTRACT FROM AUTHOR]

Inter‐ and intraspecific competitive abilities are significant determinants of invasive success and the ecological impact of non‐native plants. We tested two major hypotheses on the competitive ability of invasive species using invasive (Taraxacum officinale) and native (T. platycarpum) dandelions: differential interspecific competitive ability between invasive and native species and the kin recognition of invasive species. We collected seeds from two field sites where the two dandelion species occurred nearby. Plants were grown alone, with kin (plants from the same maternal genotype) or strangers (plants from different populations) of the same species, or with different species in a growth chamber, and the performance at the early developmental stage between species and treatments was compared. The invasive dandelions outcompeted the native dandelions when competing against each other, although no difference between species was detected without competition or with intraspecific competition. Populations of native species responded to interspecific competition differently. The effect of kinship on plant performance differed between the tested populations in both species. A population produced more biomass than the other populations when grown with a stranger, and this trend was manifested more in native species. Our results support the hypothesis that invasive plants have better competitive ability than native plants, which potentially contributes to the establishment and the range expansion of T. officinale in the introduced range. Although kin recognition is expected to evolve in invasive species, the competitive ability of populations rather than kinship seems to affect plant growth of invasive T. officinale under intraspecific competition. [ABSTRACT FROM AUTHOR]

In many animal species, individuals engage in fights with conspecifics over access to limited resources (e.g. mates, food, or shelter). Most theory about these intraspecific fights assumes that damage has an important role in determining the contest winner. Thus, defensive structures that reduce the amount of damage an individual accrues during intraspecific competition should provide a fighting advantage.Examples of such damage‐reducing structures include the dermal shields of goats, the dorsal osteoderms of crocodiles, and the armoured telsons of mantis shrimps. Although numerous studies have identified these defensive structures, no study has investigated whether they influence the outcomes of intraspecific fights.Here we investigated whether inhibiting damage by enhancing an individual's armour influenced fighting behaviour and success in the giant mesquite bug, Thasus neocalifornicus (Insecta: Hemiptera: Coreidae).We found that experimentally manipulated individuals (i.e. those provided with additional armour) were 1.6 times more likely to win a fight when compared to the control. These results demonstrate that damage, and damage‐reducing structures, can influence fighting success.The implications of these results are twofold. First, our results experimentally support a fundamental assumption of most theoretical fighting models: that damage is a fighting cost that can influence contest outcomes. Second, these results highlight the importance of an individual's defensive capacity, and why defence should not be ignored. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Reef‐building corals, like many long‐lived organisms, experience environmental change as a combination of separate but concurrent processes, some of which are gradual yet long‐lasting, while others are more acute but short‐lived. For corals, some chronic environmental stressors, such as rising temperature and ocean acidification, are thought to induce gradual changes in colonies' vital rates. Meanwhile, other environmental changes, such as the intensification of tropical cyclones, change the disturbance regime that corals experience. Here, we use a physiologically structured population model to explore how chronic environmental stressors that impact the vital rates of individual coral colonies interact with the intensity and magnitude of disturbance to affect coral population dynamics and cover. We find that, when disturbances are relatively benign, intraspecific density dependence driven by space competition partially buffers coral populations against gradual changes in vital rates. However, the impact of chronic stressors is amplified in more highly disturbed environments, because disturbance weakens the buffering effect of space competition. We also show that coral cover is more sensitive to changes in colony growth and mortality than to external recruitment, at least in open populations, and that space competition and size structure mediate the extent and pace of coral population recovery following a large‐scale mortality event. Understanding the complex interplay among chronic environmental stressors, mass‐mortality events, and population size structure sharpens our ability to manage and to restore coral‐reef ecosystems in an increasingly disturbed future. [ABSTRACT FROM AUTHOR]

Questions: There is growing evidence on how density‐dependent drivers of plant performance are influenced by habitat heterogeneity such as variation in understorey light availability. How these processes operate in temperate forests still remains an open question, however. We examined the interactive effects of density dependence and light availability on woody seedling mortality across multiple species, two size stages and growth forms. Location: Alluvial old‐growth temperate forest, southeastern Czech Republic. Methods: We mapped seedlings of woody species (≥10 cm tall) and recorded their mortality over a two‐year period on 21 square seedling plots (25 m2) within one large square plot with all trees mapped (≥1 cm diameter at breast height). Seedling mortality was studied using a combined approach of generalised linear mixed models and spatial point pattern analyses. Results: Density‐dependent effects of tree and seedling neighbours influenced seedling mortality at different spatial scales, depending on their size class, growth form and by taxon. Conspecific inhibition raised the mortality of seedlings other than Acer campestre at low light levels, indicating that host‐specific enemies and/or intraspecific competition may be important in unfavourable habitats. While small seedlings experienced conspecific inhibition at low light levels, tall seedlings were additively affected by low‐light conditions and competition with trees. Both conspecific and heterospecific neighbours tended to affect tree seedlings at low light levels, whereas shrub seedlings experienced light‐ and density‐independent mortality. Some negative interspecific interactions indicated ongoing expansion of species like Acer campestre in currently flood‐free habitats. Conclusions: How density‐dependent effects translate into demographic outcomes for woody seedling populations may be largely determined by variation in understorey light availability. Given that seedlings differ in size, growth form and taxa, we also demonstrate that both seedling and tree neighbours may contribute to the strength and spatial variation in density‐dependent effects at seedling neighbourhood scales. [ABSTRACT FROM AUTHOR]

Functional traits are measurable characteristics of an organism that have an impact on its fitness. Variation in functional traits between and among species has been suggested to represent the basis for competition and selection, thus allowing for evolution in natural populations.In freshwater ecosystems, the availability of essential polyunsaturated fatty acids (PUFAs), in particular ω3‐ and ω6‐PUFAs, determines the food quality of phytoplankton for the herbivorous zooplankton Daphnia, an unselective filter feeder. The content of such essential PUFAs in the phytoplankton is thus a functional phytoplankton trait affecting the trophic transfer efficiency and dynamics at the pelagic plant–herbivore interface.In turn, the susceptibility of consumers to become limited by the availability of essential PUFAs is a fitness‐determining trait of Daphnia genotypes, and variability of this herbivore trait may thus affect the daphnids' intrapopulation competition. To estimate the intrapopulation variation in susceptibility, we isolated clonal lines of Daphnia longispina from a natural population and compared the strength of their limitation by dietary PUFA availability via standardised laboratory growth assays. We used a liposome supplementation technique to enrich a PUFA‐poor green alga with essential ω3‐ and ω6‐PUFAs and determined juvenile somatic growth rate of different D. longispina genotypes as a fitness proxy.As expected, D. longispina genotypes that coexisted in a natural population differed markedly in their specific patterns of susceptibility to dietary PUFA availability. On average, the D. longispina population was more strongly susceptible to limitations in the availability of the ω6‐PUFA arachidonic acid (20:4ω6) than to limitations in the availability of ω3‐PUFAs α‐linolenic acid (18:3ω3) and eicosapentaenoic acid (20:5ω3).The ability to cope with PUFA limitation is thus a crucial trait that can probably affect intraspecific competition and Daphnia population structure. Therefore, we suggest that such intrapopulation variation in susceptibility to absence of dietary PUFAs might be one of the driving forces of natural selection and local adaptation among freshwater zooplankton. [ABSTRACT FROM AUTHOR]

We studied the relationship between temperature and the coexistence of great tit Parus major and blue tit Cyanistes caeruleus, breeding in 75 study plots across Europe and North Africa. We expected an advance in laying date and a reduction in clutch size during warmer springs as a general response to climate warming and a delay in laying date and a reduction in clutch size during warmer winters due to density‐dependent effects. As expected, as spring temperature increases laying date advances and as winter temperature increases clutch size is reduced in both species. Density of great tit affected the relationship between winter temperature and laying date in great and blue tit. Specifically, as density of great tit increased and temperature in winter increased both species started to reproduce later. Density of blue tit affected the relationship between spring temperature and blue and great tit laying date. Thus, both species start to reproduce earlier with increasing spring temperature as density of blue tit increases, which was not an expected outcome, since we expected that increasing spring temperature should advance laying date, while increasing density should delay it cancelling each other out. Climate warming and its interaction with density affects clutch size of great tits but not of blue tits. As predicted, great tit clutch size is reduced more with density of blue tits as temperature in winter increases. The relationship between spring temperature and density on clutch size of great tits depends on whether the increase is in density of great tit or blue tit. Therefore, an increase in temperature negatively affected the coexistence of blue and great tits differently in both species. Thus, blue tit clutch size was unaffected by the interaction effect of density with temperature, while great tit clutch size was affected in multiple ways by these interactions terms. [ABSTRACT FROM AUTHOR]