Journal of Animal Ecology最新文献

Social interactions among conspecifics can have significant fitness implications, but how social behaviours develop in wild animals remains poorly understood. Here, we examine the intrinsic drivers of a social behaviour, communal winter roosting, in red kites Milvus milvus. In this species, communal roosting is a facultative behaviour, and the mechanisms underlying its emergence at the individual and population levels are unclear. Through longitudinal GPS tracking of 635 bird-winters from 216 red kites, we derived multi-year roosting histories to investigate (i) which individual characteristics associate with the decision to join communal roosts, (ii) how these patterns change across life stages and (iii) whether roost composition reflects assortative associations among breeding pairs or kin. Based on 33,930 nights across six consecutive winters on the breeding grounds, we identified red kites from our tagged sample joining communal roosts on average 38% of the time. Males occurred more at communal roosts than females, but in both sexes this probability drastically decreased with age and additionally decreased once they started breeding. These ontogenetic changes in communal roosting behaviour were driven by behavioural plasticity at the individual level rather than selective mortality. Red kites displayed assortative behaviour both in communal and non-communal roosting contexts. Breeding pairs showed the strongest affiliation, roosting more often together than expected by chance in non-communal roosting sites, when in proximity to their breeding territory. In contrast, sibling and parent-offspring dyads were rare, and roosting less frequently together than expected by chance within communal roosts. Overall, our results show that the structure of communal roosts in the red kite is shaped by the age, sex and social relationships of individuals. The influence of these factors may stem from trade-offs across various life history stages, driven by changes in the net benefits associated with foraging, territory and mate prospecting, as well as territory maintenance throughout an individual's life.

The traits that are important for adaptation may exhibit genetic correlation due to pleiotropy or as a result of linkage. Understanding the genetic architecture of such correlations is important for predicting the selection response of populations. Exploration in fishes is a behavioural trait by which individuals may find habitats with better foraging and growth opportunities that subsequently improve their fitness. For example, in Atlantic salmon (Salmo salar), all individuals originate in spawning rivers where females lay eggs, but some juveniles migrate to small tributaries which are not spawning areas but provide favourable habitat patches for young salmon. The increased growth in these nursery streams may facilitate earlier sexual maturation, implying a potential pleiotropy between exploration and maturation traits. In this study, by sampling juveniles from two wild populations in the large Teno River catchment in northernmost Fennoscandia, we tested the genetic association between exploration behaviour in nursery streams across four SNPs that span a 70-kb long genomic region with a major effect on age at maturity variation. Three of these SNPs are missense mutations in the vgll3 and akap11 genes, and one SNP tags a putative regulatory region with the strongest association with the age-at-maturity trait. We show that the exploration behaviour was linked to the genomic region in one of the two studied populations. However, the genetic association was substantial in the missense SNP located in the akap11 gene, which is farthest away from the vgll3 SNPs and previously ruled out as being causally linked to the age at maturity. We also detected a marginal interaction effect between SNPs in the vgll3 gene and akap11, indicating a potentially complex genetic architecture underlying the trait variation. Our results suggest that exploration and age at maturity are co-inherited within the same haplotype block, but we find no evidence for direct causality via pleiotropy in the region. These two traits may form a coadapted trait complex that may be instrumental in local adaptation processes.

Climate warming has been associated with widespread body size declines in many vertebrate taxa, but relatively little is known about possible climate warming induced shifts in trait heritabilities. The main goal of the study was to investigate how changing food availability affects evolutionary potential of four traits related to nestlings' body size. We used long-term, pedigree structured data of two woodland passerines living in the boreal zone, the Willow Tit (Poecile montanus) and the Great Tit (Parus major), to study how food availability for their nestlings has changed in time, how this has influenced their morphological traits (viz. wing, tail & tarsus length & body mass) and their heritabilities and evolvabilities. This was done by assessing heritabilities under varying food availabilities using random regression animal models. We found that caterpillar food availability had increased over the 25-year-long study period and that this was accompanied by increases of nestlings' body mass, but not other morphological traits. All traits were heritable in both species, but additive genetic variance, heritability and evolvability were affected by food availability only in the case of the wing length, being higher under low food availability (the Great Tit) or higher under low and high food availability (the Willow Tit). We conclude that changes in food availability seem to have limited influence on evolutionary potential of body size traits in these two passerine birds.

Large terrestrial mammalian herbivores (LMHs) play a critical role in ecosystems, but the effects of these species on belowground zoogeochemistry in forest ecosystems remain poorly understood. This study aimed to investigate the influence of LMHs on belowground processes in forest ecosystems. We synthesize current knowledge on how LMH species composition, physiology and feeding habits influence belowground litter and soil properties in boreal, temperate and tropical forests of the world through a systematic review. Tropical forests host the highest diversity of LMHs, but are the least studied, with most species being threatened frugivorous ruminants and non-ruminants. Temperate and boreal forests are more studied and dominated by ruminant browsers or mixed feeder species. The impact of LMHs shows high variation among forest types, but ruminants (Cervidae) tend to have negative effects on litter and soil properties in temperate and boreal forests, thereby decelerating nutrient cycling. Whereas LMHs non-ruminants (Suidae, Tapiridae and Tayassuidae) positively affect litter and soil properties in temperate and tropical forests. Research on the effects of LMHs on litter and soil properties faces several challenges, including confounding factors, such as biotic and abiotic conditions, high contextual variability influenced by factors, such as forest type, seasonality and experiment time, and there is also a geographical bias, with most studies conducted in temperate forests, while research in tropical forests remains scarce. LMHs are highly threatened by defaunation, which can disrupt ecosystem dynamics, highlighting the need to address research gaps. Long-term studies in tropical forests, particularly in South and Central America, Africa, India and Southeast Asia, are essential to understand the effects of LMHs on belowground properties. While LMHs are hypothesized to reduce nutrient cycling in forest ecosystems, this effect appears to be highly context dependent underscoring the need for further research. Understanding these effects is critical for advancing ecological knowledge and predicting climate change impacts on forest ecosystems. In addition, this can guide trophic restoration efforts and enhance ecosystem resilience.

Diversity in life-history strategies is a key aspect of population resilience. However, the spatial and environmental factors that drive this variation remain poorly understood. In a recent study, Shida and Sato combined year-round surveys of water temperature, prey abundance, growth and life-history traits in masu salmon (Onchorhynchus masou) across a river continuum (i.e. from tributary to mainstem river). The authors show that shifting growth opportunities along the river, influenced by thermal and trophic resources, generate differences in age at maturity while maintaining high within-habitat (alpha) diversity. These findings provide an important example of how spatiotemporal habitat heterogeneity influences phenotypic diversity and highlights the role of both environmental and intrinsic factors shaping the population-level variation in life-history strategies.

Research Highlight: Oli, M., Kenney, A., Boonstra, R., Boutin, S., Murray, D., Jung, T., Hines, J., Krebs, C. (2026). Demographic mechanisms of snowshoe hare population cycles in Yukon, Canada. Journal of Animal Ecology. https://doi.org.10.1111/1365-2656.70169. Ecologists have long been intrigued by cycles in population abundances characterizing the dynamics of some wild species. Abundance may follow surprisingly regular cycles, with an increase phase, a peak phase and then a decline phase of more or less the same length. Predator-induced mortality has long been proposed as the main demographic mechanism inducing population cycles, leading most of cycle theory to consider that population cycles result from survival changes only. In this paper, Oli et al. (2025) assessed how the cycles in population abundance of the snowshoe hare (Lepus americanus) in Yukon, observed during 43 years, are driven by survival or reproductive rates of some specific age classes and how their contributions differ according to the cyclic phase. Thanks to the individual monitoring of more than 7000 snowshoe hares and a state-of-the-art capture-mark-recapture modelling framework, they showed different contributions of age-specific vital rates to the population growth rate, depending on the cyclic phase (increase, peak, decline and low phases) and the breeding period considered (early, mid, late and non-breeding periods). For instance, improved breeding probability, litter size and pre-weaning survival played a major role during the increase phases, whereas lower pre-weaning survival explained population decline. They also highlighted a strong interaction between season and cyclic phases, with, for example, at mid-breeding season, a survival in low phases that is close to the survival observed in increase phases. This led to different life-history strategies over the seasons and the phases: the population had a fast strategy in the early breeding season in the increase phase and a slow strategy in the late breeding season and decline phase, demonstrating a high level of plasticity across phases and seasons. The enigma of population cycles is not fully solved yet, but the study by Oli et al. (2025) clearly contributes to improving our mechanistic understanding of population cycles.