Journal of Animal Ecology最新文献

Growing evidence suggests that organisms with narrow niche requirements are particularly disadvantaged in small habitat patches, typical of fragmented landscapes. However, the mechanisms behind this relationship remain unclear. Dietary specialists may be particularly constrained by the availability of their food resources as habitat area shrinks. For herbivorous insects, host plants may be filtered out of small habitat fragments by neutral sampling processes and deterministic plant community shifts due to altered microclimates, edge effects and browsing by ungulates. We examined the relationship between forest fragment area and the abundance of dietary-specialist and dietary-generalist larval Lepidoptera (caterpillars) and their host plants in the northeastern USA. We surveyed caterpillars and their host plants over 3 years in equal-sized plots within 32 forest fragments varying in area between 3 and 1014 ha. We tested whether the abundances and species richness of dietary specialists increased more than those of dietary generalists with increasing fragment area and, if so, whether the difference could be explained by reduced host plant availability or increased browsing by white-tailed deer (Odocoileus virginianus). The overall abundance of dietary specialists was positively related to fragment area; the relationship was substantially weaker for dietary generalists. There was notable variation among species within diet breadth groups, however. There was no effect of fragment area on the diversity of dietary-specialist or dietary-generalist caterpillars. Deer activity was not related to the abundances of either dietary-generalist or dietary-specialist caterpillars. Plant community composition was strongly associated with fragment area. Larger fragments were more likely to include host plants for both dietary-specialist and dietary-generalist caterpillars. Deer activity was correlated with decreased host plant availability for both groups, with a slightly stronger impact on host plants of dietary specialists. Although dietary specialists were more likely to lack host plants in fragments, the relationship between fragment area and host availability did not depend on caterpillar diet breadth. This study provides further evidence that decreasing patch area disproportionately impacts specialist consumers. Because this relationship was derived from equal-sized plots, it is robust to some criticisms levelled at fragmentation research. The mechanisms for specialist consumer declines, however, remain elusive.

Uniparental incubating birds must resolve the trade-off between self-maintenance and incubation. This balance manifests through diverse incubation behaviours that vary significantly among species and geographic regions. However, limited research has examined the variability of incubation behaviours across species and regions. Using Bayesian phylogenetic mixed models, we investigated how three incubation behaviours (off-bout frequency, off-bout duration and incubation constancy) vary with latitude across 201 uniparental incubating bird species. Our findings reveal distinct incubation strategies adopted by uniparental birds across latitudes. Species at lower latitudes exhibit fewer off-bouts and, meanwhile, have longer off-bout durations. Conversely, those at higher latitudes exhibit more frequent but shorter off-bouts. Notably, a clear latitude-dependent pattern emerges in incubation constancy, with higher latitudes showing greater incubation constancy. Additionally, smaller-bodied birds tend to take more frequent off-bouts. Significant variations in off-bout frequency were observed across different habitats. Herbivorous species, in particular, show higher incubation constancy compared to omnivorous and carnivorous birds. These findings offer valuable insights into the association of latitudinal variation with the evolutionary dynamics of life histories in uniparental incubating birds.

Billions of animals undertake migratory journeys every year, with powerful consequences for ecosystem dynamics. Key behaviours that enable successful migration are often guided by the visual system. The amount and quality of information that animals can extract from visual scenes are directly related to structural eye size-larger eyes can house larger pupils, enhancing light-gathering capacity and vision by improving visual acuity and contrast sensitivity. Migration should exert strong demands on individual visual performance, for example via foraging, antipredator benefits or navigational requirements. Yet, it remains elusive whether variations in eye morphology and corresponding visual capabilities are associated with migratory propensity. Here, we capitalize upon intra-population variation in migratory propensity (also known as partial migration) in roach, a common freshwater fish, to directly test for migration-associated variation in image-forming eyes within a species. In a multi-year field study tracking the migration decisions of over 2000 individuals in two different lake systems, we found that relative pupil size was positively associated with individual migration propensity. Computational simulations of the visual ecology associated with the observed differences in pupil size show that migrants have an extended visual detection range and that the performance gain is most pronounced for viewing small targets (e.g. planktonic prey) under low-light conditions. These results suggest that the larger pupils of migrants represent an adaptation for increased foraging efficiency to aid in the accumulation of critical pre-migratory energy reserves. Together, our anatomical and functional findings provide new perspectives on visual system design in relation to individual-level migratory decision-making.

Large herbivores at northern latitudes often forage on agricultural farmland. In these populations, the presence of both resident and migrant individuals (termed partial migration) is common, but how migrants and residents differ in their selection of farmland is not well-understood. Higher access to farmland may provide benefits to residents compensating for not following the 'green wave' of emerging vegetation such as migrants. According to sexual segregation theory, males and females differ in body-size-related nutritional needs and risk sensitivity associated with farmland. Yet, how the sexes differ in the selection of farmland through an annual cycle remains unclear. We quantified seasonal variation in the selection of farmland by partially migratory red deer (Cervus elaphus) at broad, landscape scale and at fine, within-home range scale using 16 years of data (2005-2020) from 329 females and 115 males in Norway. We tested predictions related to the partial migration and sexual segregation theories using resource selection functions. We predicted higher selection for farmland by residents than by migrants, and higher selection by females than by males due to higher nutritional needs, but that higher perceived predation risk would impact their diurnal selection patterns. The time spent on farmland was higher in winter (14%-18%) than in summer (8%-14%). Residents selected farmland more than migrants mainly at broad, landscape scale, while differences were smaller and less consistent at a fine, within-home range scale. Females showed higher broad-scale selection for farmland in winter, whereas males showed higher selection in summer. At a fine, within-home range scale, females selected farmland more in summer during darkness, whereas sex differences were small otherwise. The fine-scale selection of farmland was markedly higher during low-light conditions than in daylight. A high population density index was correlated with high broad-scale selection of farmland, i.e. high farmland availability in the home ranges, whereas the effect of the density index was weak at a fine, within-home range scale. Our study emphasises how hypotheses deriving from the theories of partial migration and sexual segregation can improve our understanding of ungulates' selection of farmland. The higher selection by residents during summer highlights the importance of retaining landscape connectivity, allowing for migration and reducing pressure on local resources.

Invited Research Highlight: Matthews, A. E., Trevelline, B. K., Wijeratne, A. J., & Boves, T. J. (2024). Picky eaters: Selective microbial diet of avian ectosymbionts. Journal of Animal Ecology. Trophic interactions such as herbivory and predation are crucial regulators of ecological communities, yet few examples exist for these processes within host-associated microbiomes. In a recent study, Matthews et al. (2024) looked for evidence of selective microbial predation of bacteria and fungi by microscopic mites on the feathers of wild Prothonotary warblers (Protonotaria citrea). The authors quantified the bacterial and fungal diet of commensal feather mites and compared this with the composition of microbial communities living directly on the feather. They found that, despite a large variety of microbes to choose from, mites strongly preferred to eat a small number of bacterial and fungal genera. Some of these selectively enriched taxa are known keratin-degraders, suggesting that mites may protect feathers by selectively consuming harmful microbes. This study presents a rare example of a trophic interaction within the microscopic ecosystem of the feather that may act as an important force shaping microbial communities in ways that benefit the host, providing an overlooked mechanism by which symbioses between birds and mites could evolve.

Climate change is altering the seasonal timing of biological events across the tree of life. Phenological asynchrony has the potential to hasten population declines and disrupt ecosystem function. However, we lack broad comparisons of the degree of sensitivity to common phenological cues across multiple trophic levels. Overcoming the complexity of integrating data across trophic levels is essential for identifying spatial locations and species for which mismatches are most likely to occur. Here, we synthesized over 15 years of data across three trophic levels to estimate the timing of four interacting phenological events in eastern North America: the green-up of forest canopy trees, emergence of adult Lepidoptera and arrival and subsequent breeding of migratory birds. We next quantified the magnitude of phenological shift per one unit change of springtime temperature accumulation as measured by accumulated growing degree days (GDD). We expected trophic responses to spring temperature accumulation to be related to physiology, thus predicting a weaker response of birds to GDD than that of insects and plants. We found that insect and plant phenology indeed had similarly strong sensitivity to GDD, while bird phenology had lower sensitivity. We also found that vegetation green-up and bird arrival were more sensitive to GDD in higher latitudes, but the timing of bird breeding was less sensitive to GDD in higher latitudes. Migratory bird species with slow migration pace, early arrivals and more northerly wintering grounds shifted their arrival the most. Across Eastern Temperate Forests, the similar responses of vegetation green-up and Lepidoptera emergence to temperature shifts support the use of remotely sensed green-up to track how the timing of bird food resources is shifting in response to climate change. Our results indicate that, across our plant-insect-bird system, the bird-insect phenological link has a greater potential for phenological mismatch than the insect-plant link, with a higher risk of decoupling at higher latitudes.

Species interactions remain a cornerstone in shaping community dynamics and structure, alongside other factors, such as climate conditions and human activities. Although network structure is known to influence community stability and ecosystem functioning, the roles of top predators in shaping interaction network structure remain obscure. We examined a 5-7-year time series of species detections for mammal communities in multiple protected areas to investigate the association between top predators and interaction network structure. Our findings suggest that abundant species, day-active species and species with wide habitat breadth interact with more species, as did species that were more affected by vehicle disturbance. With increased densities of top predators, interaction networks exhibited greater complexity, with increased connectance, nestedness and average degree. An increased density of mesopredators, such as yellow-throated martens and badgers, was associated with sparser, less nested, but more centralized interaction networks. Top predators reduced the degree of highly interactive species, making them more specialized, and increased the degree of less abundant species, making them more general. In particular, this redistribution of interactions was not driven by direct changes in species density of top predators but seemingly by non-consumptive or indirect effects. Our findings emphasize the pivotal role of the main predators in structuring interactions within northeastern China's mammal communities, with large implications for conservation and management.

Research Highlights: Sasaki, M., Finiguerra, M. & Dam, H.G. (2024). Seasonally variable thermal performance curves prevent adverse effects of heatwaves. Journal of Animal Ecology. https://doi.org/10.1111/1365-2656.14221. Marine heatwaves (MHWs) emerge as a devastating stressor that can have direct and transgenerational effects on marine organisms. However, we know very little about how seasonal variations in thermal performance curves (TPCs) may help marine zooplankton cope with these direct and transgenerational effects of MHWs. In a recent study, Sasaki et al. (2024) combined field observations and simulated laboratory heatwave experiments, uncovering seasonal variations in TPCs for key fitness-related traits, including egg and offspring production, hatching success and survivorship in two ecologically important copepod species Acartia tonsa and A. hudsonica. They discovered that the TPC of A. tonsa was highly seasonally variable, allowing them to maintain their thermal optimum of at least 5°C above the field temperature. The transgenerational effects of parental exposure to MHWs on the offspring were minor. In contrast, the TPC of A. hudsonica was relatively unchanged across seasons, suggesting that this species may be highly vulnerable to MHWs, especially during summer. These findings agree with distinct seasonal abundances of the two species in nature: A. hudsonica is primarily abundant during winter and spring while A. tonsa dominates the summer and fall. These findings enhance our understanding of how seasonal variations in TPCs can determine the vulnerability of marine species to heatwaves through direct and transgenerational effects, which are important for ecological risk assessments of marine ecosystems under a rapidly changing climate.

In many natural systems, animal populations are exposed to increasing levels of stress. Stress levels tend to fluctuate, and long-term increases in average stress levels are often accompanied by greater amplitudes of such fluctuations. Micro-evolutionary adaptation may allow populations to cope with gradually increasing stress levels but may not prevent their extirpation during acute stress events unless adaptation to low stress levels also increases their tolerance to acute stress. We tested this idea, here called 'micro-evolutionary priming', by exposing populations of the monogonont rotifer species Brachionus calyciflorus to four levels of copper stress (control, low, intermediate and high) during a multigenerational selection experiment. Subsequently, in a common garden experiment, we exposed randomly selected subsets of genotypes (clones) of each of these populations to low, intermediate and high copper levels and assessed their population growth performance across multiple generations. Compared to populations with an exposure history to copper, genotypes of control populations suffered strong growth reductions when exposed to intermediate and high levels of copper, mainly as a result of high mortality rates. Remarkably, when exposed to low copper levels, fitness differences between genotypes of control populations and populations adapted to these low levels were very small, whereas the latter strongly outperformed the former at intermediate and high copper levels. These results highlight the potentially strong but hitherto largely ignored impact of micro-evolutionary priming on the performance of populations in a changing environment. We discuss the potential consequences of micro-evolutionary priming for the persistence of populations and the spatial eco-evolutionary dynamics of metapopulations.

Rodents are known to interact with seed plants in three different ways, including predation in situ, scatter hoarding and larder hoarding of seeds. These behaviours span a spectrum from mutualistic seed dispersal to predation, and they are related to species' and environmental characteristics. We used interaction networks to evaluate the structure and drivers of rodent-seed plant interactions, including geography, phylogeny and traits at continental scales. We constructed five aggregated networks, each representing a continent and containing three subnetworks defined by foraging behaviours, tested questions about their network structures and analysed the driving signals shaping rodent-seed plant interactions at network and species levels. Rodent-seed plant networks varied across continents. We found most rodents exhibited a significant propensity for one foraging behaviour and detected significant modular structures in both aggregated networks and subnetworks. We detected significant co-phylogenetic signals between rodents and seed plants. Distance matrix-based regressions on interaction and module dissimilarity of rodents suggest geographical and phylogenetic forces are important in the assembly of rodent-seed plant networks. In addition, multiple species traits correlated with the roles of rodents within aggregated networks; however, the specific traits associated with these roles varied among interaction types. Our results highlight that geography and phylogenetics are dominant in structuring the architecture of rodent-seed plant networks at continental scales and reveal challenges regarding spatial and taxa coverage in rodent-seed plant interactions.