Journal of Animal Ecology

Anthropogenic changes to the environment, including altered food resource availability, influence host physiology, behaviour, and population dynamics, which can have strong downstream consequences on wildlife disease dynamics. Additionally, some individuals within a population contribute disproportionately to infection as super-shedders of infection, but the extent to which food availability alters the likelihood of super-shedding and overall parasite infection patterns is poorly understood. We conducted a three-year field experiment in southern Finland to investigate how food supplementation and parasite removal affect nematode infection measures and the relationship between nematode infection and fitness of wild bank voles (Clethrionomys glareolus). Using a factorial design across 12 populations, we manipulated food availability and administered anthelmintic treatments to assess effects on nematode infection status, intensity, and two measures of super-shedding (abundance super-shedding, intensity super-shedding). We also examined parasite impacts on host fitness, including apparent survival probability and reproductive status. Food supplementation did not affect likelihood of infection, intensity or intensity super-shedding, but did reduce the likelihood of abundance super-shedding, suggesting an effect of food availability on infection heterogeneity. We also identified an interaction between nematode infection status and host age on fitness. Notably, infected younger individuals had reduced survival and reproduction, but infected older individuals had greater survival and reproduction compared to their uninfected counterparts. Our study provides novel empirical evidence on how anthropogenic changes in food availability can influence parasite transmission dynamics and the fitness consequences of these sub-lethal parasites in a wildlife system.

Parasites occur in every ecosystem, although their dispersal is often constrained by the availability of hosts or vectors. Here, we explore how variation in parasite life history traits, particularly transmission strategy, may influence their distributions. Specifically, we test whether a variety of parasites ad-here to the rules of island biogeography, and whether their distributions vary with transmission strategy. We utilised broad-spectrum parasite detection from existing Whole Genome Sequence (WGS) data to characterise parasites with varying transmission strategies from the blood of a passerine bird, the silvereye (Zosterops lateralis), sampled across 25 islands in the South Pacific and from five of the states in mainland Australia. Overall, parasite richness was higher on mainland Australia compared to islands and decreased with distance of islands from the Australian continent. However, these patterns were dependent on transmission strategy. For parasites transmitted by flying insect vectors, richness decreased on islands compared to the mainland. However, increasing isolation from the mainland among islands had little further impact. On the other hand, richness of directly transmitted parasites and those requiring another intermediate host declined sharply with increasing distance from the mainland. While islands may act as an initial barrier to colonisation for parasites relying on flying insect vectors, their highly dispersive vectors may subsequently reduce the impact of increasing isolation distance on richness. Our work underscores the importance of considering parasite life-histories and their transmission strategies for understanding the processes that shape parasite communities on islands.

Parental care can shape post-fledging behaviour through provisioning, guidance and social information, yet its absence may alter how young birds establish space use and habitat preferences. We tested the consequences of absent parental care by comparing, hand-reared juvenile herring gulls released without parents with wild, parent-reared conspecifics, focusing on the first two months after fledging. Wild juveniles frequently revisited their natal nest during the first month, whereas hand-reared birds rarely returned to the release site; revisits declined in both groups by the second month but remained more common in wild birds. Wild juveniles used smaller ranges that subsequently expanded, while hand-reared birds began with larger ranges that later contracted, leading to convergence. Contrary to expectation, wild juveniles occurred in areas with higher human population density than hand-reared birds. Habitat use also differed between groups and changed over time. Early on, wild juveniles concentrated activity in anthropogenic and marine habitats, whereas hand-reared birds used rural green habitats more. Later, both groups shifted away from marine areas towards rural green habitats, reducing but not eliminating between-group differences. Short-term survival, did not differ between hand-reared and wild juveniles, indicating that parental care primarily reshaped early space use and habitat choice rather than immediate survival.

Climate change and anthropogenic pressures are reshaping marine food webs, altering prey availability and affecting top predators. The European Shag (Gulosus aristotelis), a coastal demersal seabird, provides a valuable model for examining environmentally mediated dietary variation, given its trophic plasticity and capacity to adjust prey use according to local availability, while also allowing assessment of potential demographic consequences. This study investigated spatial and temporal variation in diet at two Portuguese colonies (Berlengas and Arrabida) between 2016 and 2024 and assessed long-term reproductive productivity at Berlengas. A total of 468 regurgitated pellets were analysed, and diet composition was quantified using the Index of Relative Importance (IRI). Generalised additive models were applied to assess environmental, spatial, and period-specific effects on diet composition, while reproductive productivity was modelled in relation to prey biomass. Diet variation was primarily explained by environmental predictors, including sea surface temperature, chlorophyll-a concentration, and zooplankton, whereas year per se had no significant effect, indicating environmentally mediated bottom-up effects. Spatial differences between colonies reflected contrasting prey field structures, and period-specific patterns suggested increased specialisation during breeding. Higher biomass of sandeels (Ammodytidae) was positively associated with reproductive output, whereas shifts toward lower-energy prey were associated with reduced productivity. These findings demonstrate that environmentally driven dietary change has measurable demographic consequences, underscoring the importance of bottom-up processes in shaping seabird population dynamics and informing conservation strategies under ongoing climate change.

Cross-Fostering, i.e., the exchange of eggs or hatchlings, is a widely used technique, to disentangle genetic from environmental effects or to manipulate the clutch size. In most bird species, this manipulation is easily accepted by the social parents, leading to the conclusion that fostering has no detrimental effect. Using a dataset of four cohorts (N=298) of zebra finches (Taeniopygia castanotis), in which we fostered routinely a single egg into another nest of zebra finches, we explored potential short- and long-time effects of fostering. Noteworthy, these experiments were not designed to test this hypothesis. The objective of the egg fostering experiments was to test for parental recognition (Caspers et al. 2017) and mate choice decisions (Goluke 2018). Consequently, the aim of the present study is purely explorative. Our study confirmed previous findings that fostering has no short-term effects on the morphology and growth rates of the chicks, neither in males nor in females. However, we found that fostering has a sex-specific long-term effect. Females originating from fostered eggs had a significantly reduced lifespan compared to those from non-fostered eggs. Conversely, the lifespan of fostered males was similar to that of non-fostered males. All birds were housed in large groups, experiencing the same conditions after nutritional independence (day 35). Therefore, we can only speculate that fostering might result in early developmental stress, which may affect the individual fitness of females later in life, ultimately leading to shorter lifespans.

Understanding habitat association of animals and how they change through ontogeny is critical to predict the likely effects of habitat change on populations. We investigated how fine scale habitat associations of three common coral reef damselfish species changed among life-stages on reefs surrounding Lizard Island, northern Great Barrier Reef. All three species showed distinct habitat selection at settlement, however the degree to which these initial associations changed through ontogeny were species specific. Pomacentrus amboinensis associated with sandy areas throughout all life-stages; Pomacentrus chrysurus settled to areas with high cover of sand and rubble, but displayed no clear habitat preferences as juveniles or adults. Pomacentrus moluccensis settled to areas with high cover of fine branching corals before shifting to areas with relatively high cover of soft corals as adults. We also compared two different approaches to estimate habitat selection; one that quantified the benthic composition within the approximate home range of individuals versus a more widely used approach of recording a single point underneath the focal individual when they were first observed. Although results were broadly similar, the benthic composition approach revealed details that was overlooked using the single point method. Decreases in the availability of any of these preferred benthic habitats may adversely affect future populations, therefore understanding habitat associations and their transitions among life stages will be crucial in predicting future reef fish communities under ongoing coral loss and habitat change. This will require to systematically study a broader range of species, integrating relevant spatial and temporal scales.

Island endemic birds are under greater threat than their mainland counterparts. Sedentary living and historically reduced predation may affect island bird sociality and inform their conservation and management. However, detailed studies on their sociality are uncommon. The federally- endangered koloa maoli (Anas wyvilliana, Hawaiian duck, or koloa) is primarily threatened by hybridization with feral mallards and avian botulism outbreaks. We used capture-mark-recapture and genetic data on koloa on the island of Kaua i, a stronghold of remaining koloa, to construct social networks and examine their associations (inferred from co-occurrence in traps) and spatial genetic structure. Information on associations might shed light on preferences for or against mallards and hybrids, and inform planned translocation efforts. Microgeographic spatial genetic structuring where relatedness among individuals scales with geographic distance is a potential liability for maintaining koloa genetic diversity, and would particularly be detrimental during highly localized outbreaks of botulism that could result in the removal of entire lineages. While we found persistent social associations among adult koloa, they were not apparently influenced by plumage traits or body mass, suggesting a lack of social preference for mallard-like individuals. Importantly, we found no spatial patterns of relatedness within the largest refuge. Therefore, botulism outbreaks remain a demographic threat but are unlikely to remove correlated genetic diversity. There were no sex differences in spatial genetic structure and both sexes moved within a refuge. The lack of spatial genetic structure and the presence of many unrelated conspecifics may enable koloa to limit inbreeding and retain genetic diversity without sex-biased dispersal. In the context of future translocations, our results suggest that translocating koloa captured in the same trap together will reduce disruption of preferred associations while also retaining genetic diversity among translocated individuals. LAY SUMMARYO_LIThe koloa maoli (Hawaiian duck, or koloa) is a federally-endangered, island endemic bird. Like other Hawaiian waterbirds, koloa are threatened by introduced predators and habitat loss, but also specifically by hybridization with feral mallards and localized avian botulism outbreaks. Currently, the island of Kaua i has the largest population of non-admixed koloa. We used capture-mark-recapture and genetic data of koloa at two wetland sites on Kaua i to examine their sociality and spatial genetic structure. C_LIO_LIKoloa formed preferential social associations, but they were not based on plumage traits, body mass or genetic relatedness. C_LIO_LIThere was no spatial genetic structure for males and females within a wetland site. Our results suggested that 1) koloa have no preference for mallard-like plumage that might increase hybrid pairing, 2) localized (within-refuge) botulism outbreaks are unlikely to remove close relatives and unique genetic lineages, and 3) translocation of groups could maintain social associations without limiting genetic diversity. C_LI

Urbanisation is one of the most important forms of human-driven landscape change, altering wildlife populations in unprecedented ways. In terms of behaviour, for example, urbanisation is hypothesised to increase the likelihood of observing urban populations touching, exploring, and solving novel food-related tasks compared to rural areas. However, little is known about the impact of spatiotemporal patterns of urbanisation, particularly historical patterns of change, on these behaviours. We tested this in the worlds most urbanised carnivore, the red fox (Vulpes vulpes), by introducing novel food-related tasks (puzzle feeders) to 284 sites throughout Great Britain. We compared tactile and problem-solving behaviours in rural populations, recently colonised urban populations, and long-established urban populations (>40 years). Foxes from 27.4% of locations touched the tasks, foxes from 12.4% of locations solved them. Urban foxes were more likely to touch tasks compared to rural populations. Exploration time, exploratory diversity, and latency to touch tasks did not significantly differ across urban and rural locations. Urbanisation rate from 1994 to 2020 (26 years) did not significantly predict the likelihood of foxes touching or solving tasks across locations. Older urban populations - particularly from London - spent more time exploring tasks and displayed greater exploratory diversity and higher problem-solving success, despite more recent urban populations being equally likely to touch them. Collectively, our findings suggest that certain population characteristics, such as the likelihood of touching/engaging with novelty, potentially emerge early in urbanisation while other characteristics, such as greater exploratory and innovative behaviours, may emerge after long-term urban exposure across many decades. HighlightsO_LIHistorical impacts of urbanisation on wild animal behaviour are unclear. C_LIO_LIWe tested this with wild red foxes responses to novel food objects. C_LIO_LIUrban foxes were more likely to touch and exploit objects, especially from London. C_LIO_LIOlder urban foxes displayed more exploratory and innovative behaviours. C_LIO_LILength of urban exposure may help predict behavioural responses to novelty. C_LI

Substantial anthropogenic changes to the environment have motivated efforts to quantify temporal trends in population dynamics. While most ecological research has focused on the mean and variance of population density and reproduction, the frequency of these fluctuations through time may also be changing. We analyzed 1,563 datasets of population density and 1,456 datasets of plant reproduction (masting) across the globe. The average frequency of fluctuations increased by [~] 0.5 - 3% per decade within each time series, representing a moderate change (Cohens d {approx} 0.4) over a period of 60 years. We tested four hypothesized mediators of this trend: increased temperature, increased frequency of environmental forcing, increased intrinsic growth rate, and increased distance from a saddle at zero density. Although all hypotheses were rejected, changes in the frequency of environmental forcing and intrinsic growth rate exhibited positive correlations with changes in population fluctuation frequency as expected. Our results suggest that successive peaks in population and masting density fluctuations are becoming closer in time, which may reduce the effectiveness of predator satiation, resilience of food-webs, and the risk of critical transitions, such as population extinction. We suggest some alternative hypotheses for what may underlie this surprising global pattern.

O_LINitrogen (N) is limiting for terrestrial herbivores, particularly over winter. Caribou (Rangifer tarandus) have adapted to seasonal scarcity of N by accruing muscle mass during the growing season when N is more abundant. C_LIO_LINitrogen stored in muscle tissue is then relied upon during winter to compensate for dietary deficits. Once their diet shifts from N-rich vascular plants to N-poor lichen over winter, caribou can lose [~]30% of their muscle mass. As catabolized N is shed in urine on wintering grounds, caribou could act as elemental transport across seasons and landscapes. Furthermore, if deposited N is taken up by lichen or other winter forage, it might enrich the nitrogen-poor winter diet of caribou in the future. C_LIO_LIWe tested this potential transport via three steps. We analysed Cladonia spp. lichen and vascular plants upon which caribou forage across Fogo Island, Newfoundland, using %N content as our metric of forage quality. We then compared seasonal habitat selection responses to forage quality by caribou using integrated step selection analyses. In summer, caribou selected areas with higher vascular plant %N but did not select nor avoid Cladonia quality. In contrast, caribou selected sites with higher quality Cladonia in winter but responded neutrally to vascular plant quality. C_LIO_LIWe compared seasonal distributions of caribou to determine whether nitrogen consumed in summer and deposited in winter would occur in spatially discrete locations. Population-level kernel density estimates for summer and winter in this island herd were mostly non-overlapping, lending credence to the potential landscape effects of N transport. C_LIO_LIWhen viewed together with established seasonal changes in woodland caribou physiology, sociality, and forage preferences, the shifts in habitat selection and seasonal ranges we observe here could serve as an adaptive strategy for caribou to recycle N and mitigate winter nutrient scarcity. C_LI

Migration is widely recognized as a strategy for animals to track seasonally shifting resources. Yet, seasonal and spatial dynamics of migration are challenging to study, particularly for difficult-to-track insects. Among insects, monarch butterflies (Danaus plexippus) have a well-documented fall migration, but spring breeding recolonization remains poorly understood, particularly for the western population. We conducted multi-year surveys across six regions in the western United States to characterize monarch breeding phenology and evaluate three related hypotheses: (i) the successive broods model, with discrete generations shifting activity across the breeding range, (ii) a diffusion-like expansion model with overlapping breeding periods, and (iii) a mid-summer lull model with temporary summer declines in breeding for areas near the overwintering habitat. Monarch immature presence served as an indicator of local breeding activity. Our results do not support the successive broods or mid-summer lull hypotheses. Breeding onset occurred earlier near overwintering areas and gradually expanded north-and eastward, with sustained activity in many regions throughout the season. Termination of breeding also occurred earlier at more distant sites, resulting in longer breeding activity nearer to overwintering habitat. Immature monarch density declined with distance from overwintering areas at onset and termination, suggesting delayed colonization of peripheral regions. Together, these results support a diffusion-like expansion of breeding rather than sequential generational replacement. Western monarchs also do not initiate or terminate breeding in close synchrony with host plant availability, contrary to predictions from resource-tracking theory. These findings highlight fundamental differences between western monarch breeding dynamics and paradigms for eastern monarchs, demonstrating that a single species can employ fundamentally different spatial strategies for recolonizing its breeding range in different regions. More generally, these results distinguish insect migration from systems with direct movements between wintering and breeding habitats, and underscore the value of long-term, landscape-scale monitoring for resolving habitat use across heterogeneous environments.

The relationship between morphology and ecology is mediated by behavior. We explore this relationship by assessing the link between trophic ecology and the use of prey-specific feeding behaviors in a cichlid fish system. Cichlid diversification features repeated transitions between free-moving prey and attached benthic prey, requiring predators to evolve prey-specific approaches to feeding. Using 2000 Hz video, we characterized feeding behavior on an experimental attached benthic prey in seven species of Mesoamerican heroine cichlid spanning three independent transitions to specialized piscivory and two to specialized benthic-feeding ecology. We investigated the effect of feeding ecology on the behavior and kinematics of benthic grazing, a derived, specialized mode of cichlid feeding. Surprisingly, all species readily fed on benthic prey, regardless of their feeding ecology. Nearly all non-benthic species used the same benthic-feeding behaviors as ecological benthic-feeders. Our findings demonstrate an unexpected level of behavioral versatility among cichlid species in exploiting functionally demanding prey outside their typical diets. We propose that this repertoire of latent feeding behaviors supports trophic versatility and facilitates niche diversification. We also show that two benthic-feeding lineages of Neotropical cichlids evolved distinct approaches to benthic feeding, exhibiting the highest and lowest total feeding-strike kinesis, respectively. Together, our findings highlight the importance of behavior in linking morphology and ecology and motivate further study into the diversity and evolutionary context of benthic feeding across the Cichlidae. SUMMARY STATEMENTWe demonstrate that prey-specific feeding behaviors and strike kinematics vary with trophic ecology in heroine cichlids and discuss the potential role of latent feeding behaviors in trophic diversification.

O_LIPhenological shifts are a major ecological consequence of climate change, yet studies often focus on single life stages meaning that the potential for carryover effects between life stages remains poorly understood. Failing to account for these effects may lead to inaccurate estimates of phenological shifts, with consequences for predicted synchrony among interacting species. This is especially relevant for temperate systems where climate warming is occurring unevenly across the year. C_LIO_LIHere, we investigated how temperature experienced the previous autumn and winter (during the pupal and egg stage) influences spring phenology in the winter moth (Operophtera brumata), a herbivorous insect with distinct life stages. Using 50 years of local climate data to create five experimental temperature regimes, we first quantified phenotypic plasticity in the duration and temporal variability of pupal and egg development. We then examined how timing of adult moth emergence affects timing of offspring hatching. C_LIO_LIWe found divergent effects of temperature on different life stages; pupal development time was shortest at intermediate temperatures while egg development time decreased linearly with increasing temperature. Furthermore, phenological shifts due to the conditions experienced by the mother were carried over to influence the phenology of her offspring. While this carryover effect was partially compensated during subsequent stages, compensation decreased under warming conditions. C_LIO_LIThese results refine our understanding of the sensitivity of the annual cycle of winter moth phenology to variation in temperature with potential implications for population dynamics and interspecific interactions. Overall, our findings highlight the need to consider the impacts of warming across multiple life stages so that carryover effects can be properly accounted for. Doing so will improve predictions of phenological shifts under future climates. C_LI

Urbanization is a major driver of avian biodiversity loss, primarily through habitat fragmentation and the degradation of food resources, leading to the homogenization of bird communities that are often assumed to share increasingly generalist dietary traits. However, the interaction of urbanization gradients with local habitat features in shaping dietary adjustments remains poorly understood, both at the species and community levels, and it is unclear whether these adjustments reflect prey availability or active food preferences to meet energetic needs. We conducted a study across 25 plots distributed along a controlled urbanization gradient in Montreal, Canada. We quantified habitat variables at both landscape and local scales, sampled arthropod prey guilds, identified insectivorous bird communities using acoustic monitoring, and estimated their potential insectivory from trait-based approaches. In parallel, we assessed realized insectivory using cafeteria experiments offering three types of artificial prey (lepidopteran larvae, spiders, and ants), monitored with custom-built cameras developed specifically for this study to record bird-prey interactions. Along the urbanization gradient, we predicted that (i) functional diversity of bird communities declines and foraging-related traits converge toward more generalist strategies; (ii) profitable arthropod prey availability such as lepidopteran larvae decrease, while other guilds (e.g., Hymenoptera, Araneae) increase; (iii) realized insectivory increasingly diverges from potential insectivory; and (iv) food preferences vary due to both prey availability and active prey selection. We found a strong decline in avian biodiversity and in the availability of high-quality prey along the urbanization gradient, with a convergence toward generalist dietary traits. Yet, the avian biodiversity loss was buffered by canopy cover and tree diversity. Impervious surfaces, canopy cover, local vegetation cover, and lepidopteran abundance were key drivers of the composition of foraging communities observed at cafeterias. Interestingly, realized insectivory exceeded potential insectivory under high local vegetation cover, but the opposite pattern emerged in sparsely vegetated sites. Attack probability on larvae models increased with impervious surfaces, whereas attacks on ants decreased with tree diversity, suggesting active selection of nutritionally profitable prey independent of actual prey availability. Overall, our results highlight the critical role of small, unmanaged vegetation patches, alongside larger and structurally diverse canopy-covered areas, in sustaining avian biodiversity and insectivory functions in cities.

Migration is a well-described behavioural strategy that allows species to track variation in resources and climatic conditions by moving in response to seasonality. A common form is elevational migration, an annual short-distance movement undertaken by many mountain bird species globally. While studies show that the timing of migration may relate to food availability, the mechanisms determining which species migrate remain unclear. Our study investigated if the degree of dietary specialization explains why some high-elevation bird species in seasonal environments migrate downslope for the winter while others remain resident at high altitudes despite the apparent scarcity of their preferred food resources. We mist-netted birds along a 2300-m elevational gradient in the Eastern Himalaya and collected blood and faecal samples from 261 individual birds belonging to 18 species of high-elevation residents (ten) and elevational migrants (eight) in their breeding and wintering ranges. Using stable isotope ratios of carbon and nitrogen in whole blood and faecal DNA metabarcoding, we compared their seasonal trophic levels and dietary niches. Nitrogen isotope ratios showed that residents had a substantially lower trophic position in the winter compared to summer (-0.35 [-0.52, -0.17]), whereas migrants had a slightly higher trophic position in the winter (0.15 [-0.02, 0.32]). This trophic shift in residents was likely due to a decrease in insectivory and an increase in frugivory in the winter. The frequency of key insect orders (Lepidoptera, Hemiptera, and Coleoptera) declined by 20-35% in their winter diets alongside an increase in fruit, particularly from the family Polygonaceae (0.33 [0.18, 0.46]). Additionally, compared with residents, migrants showed greater overlap in their dietary niches between summer and winter (98% vs 80%). Because arthropod abundances in the Himalayas peak at high elevations in the summer and decline in the winter, we suggest that elevational migrants are likely dietary specialists that track resources, while high-elevation residents are dietary generalists that supplement their winter diet with fruit and nectar because of the scarcity of arthropods. These findings indicate that a species dietary specialization is linked to its migratory behaviour, providing a potential mechanistic explanation for how different species solve the challenge of seasonal resource limitation.

Protogynous sex change, where individuals first function as females and later as males, is a key life-history strategy among polygynous reef fishes. In haremic systems, sex change is typically socially regulated, with dominants suppressing subordinates sex change through aggression. Females within a harem form a size-based hierarchy that can remain stable in most species through the threat of eviction. We studied a different situation in the cleaner wrasse Labroides dimidiatus, where larger females have incomplete control, as they spend most of their time alone at their own cleaning territory. We tracked over 400 individuals for 12 months, recording growth, behavior, social organization, and sex change. We confirmed earlier reports that both sexes direct aggression primarily at those ranked immediately below them. However, we observed 30 cases where smaller females outgrew larger ones, revealing hierarchy instability. Of 42 sex change events, 43% occurred in presence of the male, and half of these early sex changers were not the largest female, but individuals overlooked by the male. Fast growth relative to harem-mates and harem switching increased the likelihood of sex change. Local population densities also influenced growth and sex change, with individuals in high-density demes growing faster and changing sex at larger sizes. Our findings reveal flexible sex change dynamics in a system with incomplete social dominance. Such incomplete control and observations that becoming male confers both higher reproductive success and survival highlight the need to expand game-theoretical and life-history frameworks to encompass such strategic flexibility. Lay summaryDominant cleaner wrasse cannot fully control subordinates as individuals occupy distinct core areas. Tracking 400 fish for a year, we found that smaller females could outgrow initially larger ones, and early sex change despite a larger male. Fast growth and harem switching increased the chances of becoming male. Population density also shaped these strategies. Our findings reveal flexible sex change dynamics in a system where becoming male confers both higher reproductive success and survival.

Predation is a strong environmental and selective pressure that can favour rapid and plastic shifts in behaviour and escape ability to increase an organisms immediate survival. However, maintaining antipredator responses under repeated predation stress can induce physiological costs to an organism from long-term exposure to elevated cortisol. We know little about how individuals balance this trade-off between short-term survival and longevity, including whether males and females balance this trade-off differently based on life history differences in reproduction, survival, and risk adversity. To assess sex differences in long-term behavioural responses and physiological costs to predation risk, we exposed threespine stickleback (Gasterosteus aculeatus) to visual cues of a live rainbow trout (Oncorhynchus mykiss) predator twice a week for 14 weeks, then measured stickleback antipredator behaviour and swimming performance 5 months later. To quantify potential long-term costs of behavioural adaptation, we measured relative telomere length as a proxy for long-term oxidative damage. We found strong sex specific effects in behaviour and swim endurance: males, but not females, altered their hiding behaviour and had shorter swim endurance in the first trial, suggesting overall lower activity. Surprisingly, we found no evidence for chronic predation shortening telomere length or hindering growth in body length. Overall, these results suggest that plastic responses can be dictated by the different life-history strategies for males and females, and suggest that individuals can maintain long-term changes in antipredator behaviour without costs to their physiological state. HighlightsO_LIChronic predator exposure produced persistent sex differences in space use and swim performance. C_LIO_LIPredator-exposed males altered their hiding strategy and showed reduced swim performance, while females showed no behavioural or performance differences. C_LIO_LIDifferences in swim times were restricted to the first trial and all individuals were exhausted by trial 3. C_LIO_LIRelative telomere length and growth in length did not differ between exposed and unexposed individuals. C_LI

Theory suggests that different components of environmental fluctuations, from daily and seasonal cycles to multidecadal trends, can have distinct and even opposing effects on species abundances and community dynamics, depending on their specific adaptations. But empirical research that deconstructs the influence of these different cycles on communities is lacking. Here, we used long-term biological monitoring data together with flow records of rivers across New Zealand to (i) investigate the role of fast, slow, and seasonal river-flow fluctuations in structuring macroinvertebrate communities; and (ii) to assess whether life-history and mobility traits mediate the response. Using joint species distribution models, we found striking differences in taxon and community responses to the different components of river flow variation. Responses to slow fluctuations were generally stronger and better predicted by traits, while responses to seasonal fluctuations were highly heterogeneous. Fast increases in flow, typical of flooding events, had pervasive negative effects on species abundances, but the severity of impact partly depended on mobility traits. Our results suggest that different ecological mechanisms underpin the response to distinct environmental fluctuations, highlighting the value of jointly considering multiple temporal scales of variation and species functional traits to understand and predict how communities reorganise under fluctuating environmental regimes.

Parasite prevalence varies in time and space. Thus, hosts may escape infection by dispersing out of habitats where parasites are present. However, it is not clear if the advantage of avoiding parasites outweighs the cost of dispersing. Juvenile hosts are expected to be relatively protected from environmentally-transmitted parasites, and we hypothesize that this age bias in transmission could magnify the benefits of juvenile (i.e., natal) dispersal. We tested these ideas in the model nematode Caenorhabditis elegans, a host with discrete life stages and natal dispersal, and its environmentally transmitted microsporidian parasite Nematocida parisii. We found that under standardized exposure conditions, larger C. elegans individuals (corresponding to older life stages) acquired many more parasites than smaller (younger) individuals. We found this same bias during multigeneration epidemics, especially during early stages of the epidemics. We also found that C. elegans dispersal larvae were less likely to be infected and harbored less severe infections than the population mean. We conclude that the early stages of an epidemic can provide young hosts with a window of opportunity to escape infection by dispersing.

The long-standing misconception that the Galapagos petrel (Pterodroma phaeopygia) and the Hawaiian petrel (Pterodroma sandwichensis) were conspecific masked the severe vulnerability of the Galapagos population. By the time its distinct status was recognized, the Galapagos petrel was already in marked decline, primarily due to invasive predators. Consequently, sustained rodent control programs have been implemented on Santa Cruz Island. An unintentional one-year failure in rodent control provided a rare quasi-experimental opportunity to quantify the demographic consequences of the invasive black rat predator. During this year, hatching success declined by [~]35% and breeding success by [~]40% relative to long-term means (66% and 62%, respectively), representing a substantial reproductive collapse. Fledging success exhibited a comparatively modest decline (from a long-term mean of 94% to 86% in 2017), suggesting stage-specific vulnerability. These results support the hypothesis that invasive black rats primarily affect early reproductive stages through egg predation and predation on small chicks, while older chicks surpass a critical size threshold that reduces susceptibility. Across the remaining managed years, reproductive metrics exhibited great stability, demonstrating the petrels resilience against other environmental or climatic stressors. Our findings provide robust empirical evidence that invasive rodent control is the dominant driver of reproductive success in this endangered seabird. The quasi-experimental failure underscored both the effectiveness and the necessity of continuous predator management, highlighting the severe and immediate consequences of even short-term lapses.