Journal of Animal Ecology最新文献

Understanding differences in life-history outcomes under variable abiotic conditions is essential for understanding species coexistence. At middle elevations, a mosaic of available sets of abiotic conditions could allow highland and lowland species of the same ecological guild to overlap. Therefore, these sites are excellent to study the influence of abiotic conditions on life history and, thus, spatial overlap patterns of competing species. To test differences in life-history outcomes, we selected a pair of closely related lacertids, Iberolacerta horvathi and Podarcis muralis, with an overlapping geographical range but a contrasting elevational distribution. To assess how abiotic and biotic factors contribute to the realized niches of both species, we first built dynamic energy budget (DEB) models for each species based on available functional and life-history data. Then, we used a mechanistic modelling framework (NicheMapR) to simulate the microclimatic conditions at 15 study sites across an elevational gradient and performed whole life-cycle simulations for both species to compare egg development times, lifespans, reproductive years, mean yearly basking and foraging times and yearly fecundity in syntopy and allotopy along the elevational gradient. Our simulations show that the variability of abiotic conditions along an elevational gradient affects life-history traits of both species. We found strong effects of species and elevation on life-history outcomes such as longevity, activity and fecundity. We also observed the effects of syntopy/allotopy on egg development times, activity and reproductive output. In addition, we found a significant interplay between elevation and species impacting fecundity where occupying higher elevation habitats resulted in a more pronounced reduction in fecundity in P. muralis. Furthermore, using two different thermal preferences for spring and summer, we show that some physiological and reproductive traits change with seasonal changes in thermal preferences. Based on our simulations, we conclude that the intermediate elevations that harbour the majority of syntopic populations exhibit high environmental variability that is likely facilitating species coexistence. Since our model predictions support that the current elevational distribution of the species is not only affected by abiotic factors, this suggests that past historical contingencies might have also played a significant role. Our study provides a framework using mechanistic models to understand current distribution patterns of two interacting species by comparing life-history differences between species based on responses to changing abiotic conditions along an elevation gradient.

Recurring events like migrations are an important part of the biological cycles of species. Understanding the factors influencing the timing of such events is crucial for determining how species face the pervasive consequences of climate change in highly seasonal environments. Relying on data from 406 GPS-collared Alpine ibex Capra ibex monitored across 17 populations, we investigated the environmental and individual drivers of short-distance migrations in this mountain ungulate. We found that vegetation phenology, including spring growth and autumn senescence, along with snow dynamics-snowmelt in spring, onset of snow cover in autumn-were the main drivers of the timing of migration. In spring, ibex migration timing was synchronized with the peak of vegetation green-up, but more in males than in females. Specifically, a peak of green-up occurring 10 days later delayed migration by 6.4 days for males and 2.7 days for females. This led to increased differences in migration timing between sexes when the peak of green-up occurred early or late in the season. In addition, ibex delayed migration timing when the length of the spring season was longer and when the date of snowmelt on ibex summer ranges occurred later. Similarly, in autumn, prolonged vegetation senescence and delayed onset of snow cover led to later migration. Overall, we observed a high degree of behavioural plasticity, with individuals responding to inter-annual variations in vegetation and snow phenology, even though the extent of these adjustments in migration dates was lower than the magnitude of the interannual changes in environmental conditions. Nonetheless, females could be less plastic than males in their timing of spring migration, likely due to the parturition period following migration forcing them to trade off foraging needs with predation risk. As the identified drivers of ibex migration are known to be and will continue to be largely impacted by climate change, the capacity of ibex to respond to such rapid changes could differ between sexes.

Intraspecific trait variation (ITV) is an increasingly important aspect of biodiversity and can provide a more complete perspective on how abiotic and biotic processes affect individuals, species' niches and ultimately community-level structure than traditional uses of trait means. Body size serves as a proxy for a suite of traits that govern species' niches. Distributions of co-occurring species body sizes can inform niche overlap, relate to species richness and uncover mechanistic drivers of diversity. We leveraged individual-level body size (length) in freshwater fishes and environmental data from the National Ecological Observatory Network (NEON) for 17 lakes and streams in the contiguous United States to explore how abiotic and biotic factors influence fish species richness and trait distributions of body size. We calculated key abiotic (climate, productivity, land use) and biotic (phylogenetic diversity, trait diversity, community-level overlap of trait probability densities) variables for each site to test hypotheses about drivers of ITV in body size and fish diversity. Abiotic variables were consistently important in explaining variation in fish body size and species richness across sites. In particular, productivity (as chlorophyll) was a key variable in explaining variation in body size trait richness, evenness and divergence, as well as species richness. This study yields new insights into continental-scale patterns of freshwater fishes, possible only by leveraging the paired high frequency, in situ abiotic data and individual-level traits collected by NEON.

Understanding how increasing temperatures influence ectotherm population growth rate is necessary for predicting population persistence. Population growth rate depends on the thermal performance of multiple life-history traits that have different thermal sensitivities. Reproductive traits are considered more thermally sensitive than other life-history traits, such as survival and development rate. Moreover, the thermal sensitivity of reproductive traits can be sex-specific, which may differentially affect population growth. However, research concurrently assessing the sex-specific influence of heat stress on multiple reproductive traits is limited. We investigated the effect of heat stress on pupal survival and reproductive traits in both sexes to determine sex-specific thermal sensitivity and reproductive performance. Individuals of the butterfly Pieris napi were reared at either 22°C or 29°C throughout the larval and pupal stages. The latter temperature reflects the fastest development rate in this population, influencing generation time, a common population growth rate metric. We recorded pupal survival and adult body weight in both sexes. After eclosion, males and females from both treatments were allowed to interact, and mating success, copulation duration, egg production, fertility and male sterility recovery were measured. A subset of mated females was dissected to assess the number and length of fertilising eupyrene and non-fertilising apyrene sperm transferred by males of each treatment. While elevated temperatures reduced pupal survival and resulted in smaller body weights in both sexes, more substantial sex-specific effects on reproductive traits were observed. Mating success was reduced in heat-stressed females but not in males. In contrast, egg production and fertility were unaffected by heat stress in females, while heat-stressed males, despite having longer copulation durations, exhibited near-complete sterility. Male heat-induced sterility was mediated by a disruption to both eupyrene and apyrene sperm production or transfer. Male remating did not recover fertility, suggesting continued negative effects on sperm production. Our results highlight how increasing temperatures affect reproduction, illustrating that temperatures generating optimal performance for non-reproductive traits, like development rate, can negatively and differentially impact sex-specific reproductive fitness. These negative reproductive consequences may impact population persistence, highlighting the necessity to incorporate these findings into future advanced models predicting species' responses to climate warming.

The strength and direction of density-dependent mechanisms acting on individual reproduction and survival may vary across the nested levels of organization social animals live in, such that complex patterns of density dependence shape fitness and population growth. Yet knowledge of such processes of population regulation where individuals are simultaneously subjected to contrasting density effects remains limited. We quantify and contrast density effects on components of individual fitness across two nested levels of organization: the population and the social group, using 45 years of demographic data of rhesus macaques. Our analysis reveals opposing density feedback on individual reproduction and survival across levels of organization and shows that density does not affect all life stages equally. While increased population density reduced female reproduction during maturation, females in larger groups were more likely to reproduce. Infant survival was optimal at intermediate population densities, and monkeys in larger groups showed increased survival. Our work shows that population-level density effects on individual reproduction and survival can be as strong as group-level effects and suggests different roles of the philopatric (i.e. females) and dispersing (i.e. males) sexes on the regulation of individual demographic performance. In this way, our work posits testable mechanistic hypotheses for evaluating density effects on components of individual fitness and highlights the need to explicitly consider the organization and demographic structure of social animals when quantifying individual performance and population dynamics.

Population ecology and biogeography applications often necessitate the transfer of models across spatial and/or temporal dimensions to make predictions outside the bounds of the data used for model fitting. However, ecological data are often spatiotemporally unbalanced such that the spatial or the temporal dimension tends to contain more data than the other. This unbalance frequently leads model transfers to become substitutions, which are predictions to a different dimension than the predictive model was built on. Despite the prevalence of substitutions in ecology, studies validating their performance and their underlying assumptions are scarce. Here, we present a case study demonstrating both space-for-time and time-for-space substitutions (TFSS) using emperor penguins (Aptenodytes forsteri) as the focal species. Using an abundance-based species distribution model (aSDM) of adult emperor penguins in attendance during spring across 50 colonies, we predict long-term annual fluctuations in fledgling abundance and breeding success at a single colony, Pointe Géologie. Subsequently, we construct statistical models from time series of extended counts on Pointe Géologie to predict average colony abundance distribution across 50 colonies. Our analysis reveals that the distance to nearest open water (NOW) exhibits the strongest association with both temporal and spatial data. Space-for-time substitution performance of the aSDM, as measured by the Pearson correlation coefficient, was 0.63 and 0.56 when predicting breeding success and fledgling abundance time series, respectively. Linear regression of fledgling abundance on NOW yields similar TFSS performance when predicting the abundance distribution of emperor penguin colonies with a correlation coefficient of 0.58. We posit that such space-time equivalence arises because: (1) emperor penguin colonies conform to their existing fundamental niche; (2) there is not yet any environmental novelty when comparing the spatial versus temporal variation of distance to the nearest open water; and (3) models of more specific components of life histories, such as fledgling abundance, rather than total population abundance, are more transferable. Identifying these conditions empirically can enhance the qualitative validation of substitutions in cases where direct validation data are lacking.

Ecosystem engineers shape ecological communities worldwide by modifying the habitats of other taxa. Engineering activities may generate feedbacks that benefit the engineers themselves, though such evidence is sparse. The superb lyrebird (Menura novaehollandiae), a ground-dwelling species of moist eucalypt forests in south-eastern Australia, engineers habitats by extensively modifying litter and soil layers (~155 tonnes/ha/year in suitable habitat) whilst foraging for invertebrates. We examined whether this engineering activity by lyrebirds serves to promote a 'farming' effect on their prey, by increasing the biomass and taxonomic richness of the invertebrates on which they feed and altering the composition of invertebrate communities. We experimentally isolated the effects of engineering (soil/litter modification) from predation effects (on invertebrates) by establishing a manipulative experiment with three treatments: (1) lyrebird-free, fenced exclosures ('control'; no engineering or predation); (2) fenced exclosures with raking ('raked'; engineering effects only); and (3) unfenced plots accessible to lyrebirds ('lyrebird'; engineering and predation effects). Biomass and taxonomic richness of invertebrates were higher in 'raked' treatments compared with 'control' treatments, due to the engineering effects of raking. Biomass and richness were lower in 'lyrebird' treatments, due to predation effects by lyrebirds. Whilst the composition of invertebrate communities showed no significant change due to engineering, it was significantly influenced by predation. Lyrebird foraging actions that mix, turn over, and aerate litter and soil layers create a positive feedback loop that actively replenishes the biomass and diversity of their invertebrate prey, compensating for offtake by predation. These results provide evidence that lyrebirds 'farm' their prey resource. This process of farming by the superb lyrebird operates at a spatial scale that is unprecedented in non-human vertebrates, extending across millions of ha in moist forest ecosystems. The enhanced diversity and biomass of invertebrates generated via lyrebird foraging has potentially far-reaching implications for the structure and function of forest ecosystems; and for the temporal dynamics of forests and their response to disturbance processes, such as wildfire. Reported examples of such positive feedback loops arising from ecosystem engineering activities are scarce, but may be more common than thought and have extensive impacts on ecosystem function.

Theoretical and some empirical evidence suggest that the population dynamics of cooperative breeders (i.e. species with groups including non-reproductive individuals that raise the offspring of dominant breeders) are more likely to exhibit Allee effects at the level of social groups rather than at the population level. However, the extent to which these population dynamics are similar in species where breeding is plural, and group members communally rear their offspring remains unclear. Such species may still be subject to demographic Allee effects at the population-level. Using a 15-year dataset, we examined population and group-level dynamics of communal rearing and colonial Octodon degus to determine whether population- and group-level Allee effects influence population dynamics. We tested whether these effects are contingent on food availability, and whether group size is decoupled from population density, that is implying group-level but not population-level Allee effects. We recorded (i) population-level Allee effects on per capita population growth rate (i.e. demographic) and on per female fecundity rate (i.e. component), (ii) no group-level Allee effects on group per female fecundity, and (iii) that Allee effects detected are more likely whenever food availability is scarce. We further verified that group size is coupled to population density (iv). Our study highlighted how food-mediated cooperation through a colonial setting underlies Allee effects at the population level, and that group-living does not buffer degus against population-level Allee effects. Thus, our findings provide a plausible mechanism underpinning the risk of local extinction in these rodents and potentially in other plurally breeding and colonial species.

Phenotypic variation among individuals scales up when they associate with others, creating variation within and among groups that can shape group-level outcomes such as when and where groups move. While sociality is thought to be a fitness-rewarding behaviour, empirical evidence supporting how it influences individual behaviour and the resulting fitness consequences (e.g. risk experienced) remains limited, especially in the context of human-modified landscapes. Here, we use empirical observations to test whether sociality helps animals cross busy roads. Our data came from free-ranging elk in a population where >75% of the adults were tracked, and in which group size and composition were highly variable. We combined field observations with GPS collar data to quantify four social phenotypes of individuals and groups: dominance (initiation of successful agonistic interactions), social connectedness (number and importance of social connections), social familiarity (frequency of association with group members in the past) and social stability (time since fusion with group members). We then investigated how these four social phenotypes influenced an individual's probability of crossing a major highway and tested if particular social phenotypes made better road crossing decisions (i.e. crossed at lower traffic volume). We found that who is in a group shapes the behaviour of group members around anthropogenic risks. Individuals in groups that were more dominant, more connected, and, to a lesser extent, more familiar had a lower probability of crossing the highway. Individuals that had spent more time with group members had a higher probability of crossing the highway. Importantly, our results suggest that sociality plays a role in safe movements around anthropogenic risks. Individuals in highly connected and familiar groups were less likely to cross the highway at high traffic volumes. Our work provides empirical evidence that sociality influences the movements of group-living individuals through anthropogenic disturbances and helps individuals mitigate the risks associated with such disturbances. Developing a comprehensive understanding of animal sociality in human-modified landscapes is especially important as social behaviours are simultaneously threatened by human disturbances, which could be particularly detrimental for group-living species if those same behaviours help individuals mitigate risks.