Functional Ecology

The seasonal forms of the temperate butterfly Araschnia levana (Nymphalidae: Nymphalinae) differ in morphology (weight, wing area, and wing loading) and colouration. Spring individuals are predominantly orange with higher weight per wing area, (i.e. wing loading) while summer individuals are black with a white stripe and have lower wing loading. However, it remains unclear if and how these seasonal differences affect heating and cooling dynamics. We compared thermal responses of seasonal forms, focusing on the roles of morphology and colouration. Further, we assessed whether live butterflies heat and cool differently from dead individuals to detect the presence of active thermoregulation. Morphology and colouration influenced the thermal dynamics of the thorax and wings as expected from heat-transfer principles, but we found no evidence of active thermoregulation on the thorax. Based on aligned temperature curves, seasonal forms showed similar thermal dynamics. This similarity was driven by morphology and colouration, with larger wing area accelerating thermal change and higher body weight (or wing loading) reducing it, thereby masking underlying form-specific patterns. After accounting for significant morphological differences between forms, the thorax of spring individuals heated and cooled faster than that of summer ones. This trend suggests form-specific optimisation of thermal performance, likely as a response to temperate climates. Thermal responses differ between forms in ways not directly explained by the polyphenism itself, potentially reflecting a broader trait of multivoltine ectotherms to cope with seasonal temperature changes.

Stingless bees are key pollinators in tropical ecosystems, yet their ecological dynamics remain poorly understood in highly seasonal environments such as the seasonally dry tropical forests of Ecuador. These ecosystems experience pronounced climatic seasonality, with sharp transitions between dry and wet periods that strongly affect floral resource availability. Understanding interspecific competition and niche partitioning in such systems is critical, particularly given the global decline of pollinators. We investigated resource use and niche dynamics in two native stingless bees, Melipona mimetica and Scaptotrigona sp., by quantifying pollen, nectar, and resin collection across seasons. Log-linear models were used to test the effects of species, season, and their interaction on resource use, while non-metric multidimensional scaling (NMDS) assessed niche overlap. Contrary to the expectation that niche overlap increases under resource scarcity, we found greater overlap during the wet season, when resources are more abundant. This suggests that both species converge on high-quality floral resources during peak availability, reflecting an adaptive response to strong environmental seasonality. Pollen use remained stable across seasons, consistent with generalist foraging behavior. In contrast, nectar collection increased significantly during the wet season, while resin exhibited a shared seasonal peak, likely associated with synchronized nest construction or maintenance. These findings reveal context-dependent competition dynamics and highlight the role of environmental seasonality in shaping pollinator interactions. Our study provides new insights into the ecology of threatened stingless bees and contributes to their conservation in tropical dry forest ecosystems.

Winter survival in dormant animals depends on conserving finite energy reserves, yet winter temperatures fluctuate around shifting means. In ectotherms, metabolic rate increases exponentially with temperature, so thermal variability is expected to accelerate energy loss, with important consequences for overwinter survival and population persistence under climate change. However, it remains unclear whether dormant ectotherms can compensate physiologically for thermal variability. We overwintered Bombus impatiens queens under constant (2, 3, 4{degrees}C) or variable (2 {+/-} 6{degrees}C or 4 {+/-} 6{degrees}C) regimes for six weeks, then measured metabolic rates across a range of temperatures. The temperature dependence of metabolic rate shifted in response to thermal experience, but the direction of compensation depended on mean temperature: variability centered on 2{degrees}C elevated metabolic rate and increased thermal sensitivity relative to all other conditions, whereas variability centered on 4{degrees}C reduced metabolic rate and dampened thermal sensitivity relative to constant 4{degrees}C. We used these metabolic responses to simulate rates of lipid depletion and found that survival trajectories echoed physiological shifts: experiencing variability around 2{degrees}C would reduce subsequent survival time, whereas experiencing variability around 4{degrees}C would preserve subsequent survival even under variable future conditions. Thus, identical thermal variance produced opposite energetic outcomes depending on the mean temperature around which fluctuations occurred. Integrating both temperature means and variability is, therefore, essential for predicting overwintering survival in a changing world.

Animals exhibit a diverse range of sociality from the strictly solitary to the highly social. Different forms of sociality have evolved in response to ecological constraints and selective habitat pressures, which are governed by the energetic and fitness costs to an individual. Uniquely among mammals, the clade of African mole-rats (Bathyergidae and Heterocephalidae) covers three distinct life-history forms of sociality: solitary, social and eusocial species. This variety in social structure makes them a model clade to study how metabolic traits vary between different forms of sociality. Resting metabolic rates (RMR) of seven African mole-rat species, ranging from solitary to eusocial, were measured using open-flow respirometry. Results were combined with published data, enabling the inclusion and statistical analysis of 16 species in total. We identified distinct allometric scaling of RMR, with eusocial species exhibiting a considerably greater rise in RMR with increases in body mass. This is likely attributable to reproductive and behavioural divisions of labour, and mass-dependent colony roles in eusocial species. Phylogenetically-informed analyses further identified that sociality, in addition to select bioclimatic traits - diurnal temperature range ({degrees}C) and isothermality (%) - significantly explain variation in the mass-independent RMR of African mole-rats. These findings elucidate, for the first time, that sociality can be a determinant of RMR, and calls for further study to identify the wider significance of sociality on mammalian metabolism, as well as exploring the allometric scaling of metabolic rate with respect to mammalian sociality.

Mesopredators contribute to food web stability and as such, understanding their trophic ecology can help to predict potential consequences of ongoing ecosystem modification. Here, multi-tissue carbon and nitrogen stable isotope analysis ({delta}13C and {delta}15N) and biochemical blood parameters ({beta}-hydroxybutyrate, glucose, lactate, and osmolality) were used to assess sex, size, spatial and seasonal differences in trophic ecology and condition of southern stingrays, Hypanus americanus, in Bimini, The Bahamas. Stingrays exhibited a dietary preference for molluscs and annelids, with an ontogenetic shift towards lower {delta}13C with increasing body size indicating a shift towards more mangrove associated prey. Nitrogen isotope values showed minimal seasonal changes, but higher {delta}15N values in males indicated foraging at a higher trophic level than females. Blood {beta}-hydroxybutyrate concentrations and osmolality revealed a similar energetic state and condition between sex, size, location and season. Our results advance our understanding of the seasonal trophic ecology of a benthic, marine mesopredator and identify the southern stingray as an important trophic link in seagrass and mangrove habitats in Bimini.

Sexual size dimorphism (SSD), the difference in body size between males and females, typically conforms to Renschs rule across species: SSD increases with body size when males are larger but decreases when females are larger. Although this macroevolutionary pattern has been extensively documented, intraspecific analyses remain rare, yet they are essential for understanding the proximate mechanisms underlying the origin and maintenance of sexual dimorphism. In particular, it remains unclear whether within-species variation in SSD is driven primarily by sex-specific differences in growth rate or in development time. Here, we addressed this question by examining SSD scaling in inbred lines of Drosophila melanogaster from the well-established Drosophila melanogaster Genetic Reference Panel (DGRP) reared under two thermal environments (25 {degrees}C and 28 {degrees}C). Females were consistently larger than males, resulting in pronounced female-biased SSD across different lines of this model insect. Moreover, SSD increased with overall body size, representing a reversal of Renschs rule at the intraspecific level. This scaling pattern was largely explained by higher female growth rates rather than sexual differences in development time. Elevated temperature reduced SSD by decreasing female growth rate while slightly enhancing that of males. Together, our results demonstrate that Renschs rule does not universally apply at intraspecific level and underscore the critical role of growth rate and environmental sensitivity in shaping SSD at the intraspecific level.

Injuries are common in animals and represent a major threat to individual survival. They can result from inter- or intraspecific conflict, predation, or pugnacious prey. Despite their potential ecological and evolutionary importance, injury patterns remain poorly documented in animal populations. To test whether a species feeding ecology or habitat can predict injury patterns, we quantified injury rates and affected body regions among native ant species collected from different habitats in Bavaria, Germany. Specimens were sampled using pitfall traps, which proved to be an efficient method for injury assessment. Injury rates varied substantially among species and genera, ranging from 0% to 38%. Predatory ant species exhibited higher frequencies of leg injuries, whereas omnivorous species were more frequently injured at the antennae. The distribution of injuries likely reflects both foraging ecology and species-specific wound care behaviors, with a high frequency of trochanter injuries potentially indicating prior amputation events to cope with infected leg injuries, as observed in Lasius alienus. Our findings demonstrate that injury propensity and distribution are shaped by feeding habits and behavioral adaptations, providing comparative evidence that the costs and management of injuries vary systematically among ant species. Our study thus highlights injuries as a measurable axis of selection that may have contributed to the emergence of wound care and other forms of social immunity in ants.

Current climate change leads to longer frequencies and reduced predictability of climatic parameters. Recent studies have highlighted the importance of considering multiple environmental factors, but experimental evidence on how species respond to their combined effect remains scarce. Here, we experimentally manipulated precipitation frequency and predictability and tested how they affect body size, growth, and survival using the common lizard (Zootoca vivipara) as a model species. Longer precipitation frequency negatively affected adult growth and male survival. Predictability influenced body size-dependent survival of yearlings and adults in certain frequency treatments. In yearlings, treatment-induced growth differences compensated for treatment-induced differences in size-dependent survival, resulting in no size differences during reproduction. In adults, treatment-induced differences in size-dependent survival were not compensated for, resulting in body size differences during reproduction among treatments. Consequently, precipitation frequency and predictability had a joint effect on life-history traits. Our results demonstrate that, even without water shortage, small differences in the frequency and predictability of precipitation affect population demography and life-history traits. This indicates that integrating the interactive action of different climatic parameters will be key to understanding and better anticipating future impacts of climate change on species.

Resource competition and parasite exposure both present common density-dependent fitness costs for wild animals. Because launching effective immune responses is costly in terms of resources, parasites fitness costs should be further exacerbated in high-density, resource-depleted areas. To disentangle these relationships, we related density, parasitism, and resource availability to survival and fecundity across lifespan in a long-term study of wild red deer. All fitness measures declined with a combination of parasite count, greater density, and reduced resource availability. Beyond these relationships, as expected, local density and resource scarcity exacerbated survival costs of parasitism in calves, effectively undermining tolerance of infection. However, these synergistic relationships faded in yearlings and then reversed in adults, likely through age-structured selection biases. These findings emphasize that the costs of parasites and resource scarcity can be synergistic and intertwined with density in wild populations, accentuating the value of incorporating resource competition when examining parasite-dependent population regulation.

An organisms life history strategy is an attempt to optimize fitness, given environmental constraints and inherent demographic tradeoffs. As such, life history helps to shape an organisms ecological and evolutionary responses to environmental change. However, life history can also be shaped by the environment, as the organisms demographic rates respond--directly or through tradeoffs--to the new conditions. This feedback between life history and environment remains poorly understood, limiting our ability to predict the outcomes of environmental change. Here, we studied the effects of environmental change - specifically altered pollination services - on four perennial plant species. We conducted a field-based demography experiment that subjected naturally occurring populations of Delphinium nuttallianum, Hydrophyllum fendleri, Potentilla pulcherrima and Erigeron speciosus to three pollination treatments: ambient (control), reduced, or increased pollination. We estimated population growth rate ({lambda}) and 11 metrics describing life history strategy and demographic resilience from an Integral Projection Model we constructed for each species and parameterized with 4-5 years of census data. Although most life history metrics responded idiosyncratically to pollination treatment, we found consistent effects of pollination on generation time, longevity and, in three of four species, recovery time. Specifically, reduced pollination led to increased longevity, generation time, and recovery time, and increased pollination led to the opposite. These changes in life history resemble shifts along the slow-fast continuum; reduced pollination led to slower lives and increased pollination led to faster lives. This is consequential because generation time and longevity influence short- and long-term population dynamics - for example, by affecting demographic stochasticity and sensitivity to environmental stochasticity, or rates of adaptation to novel conditions. Notably, these changes occurred largely independent from changes in population growth. Altogether, our results highlight changes in life history as an important but underappreciated consequence of environmental change.

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

Understanding ecological drivers of reproductive success is crucial to predict whether natural populations can cope with the pace of anthropogenically driven environmental change. In marine ecosystems, this knowledge is difficult to acquire due to the lack of tractable field systems. Here, we took advantage of the nest-brooding behavior of the two-spotted goby Pomatoschistus flavescens, an important planktivorous fish in Scandinavian coastal ecosystems, to study its reproduction across the steep climatic gradient of its natural range. We deployed 360 artificial nests in the field, covering six populations during the breeding season of 2022. We found that climate explained differences among populations in the phenotypes of nest-holding males, and in the impact of both marine growth and parental cannibalism on the broods. In addition, climate affected egg density and diameter. Despite these ecological effects, and although populations differed in average male reproductive success, reproductive success was not influenced by climate. Instead, it was largely determined by competition occurring at the local scale, in particular through the acquisition of high-quality nests, which was itself affected by the relative size of males within the local pool. We propose that the frequency-dependent nature of mating competition may buffer reproductive success against climatic influence in P. flavescens, and discuss the potential generality of such mechanisms and implications for population resilience.

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

Aerobic scope defines the energetic margin available for activity beyond maintenance and plays a central role in ecological performance. In many organisms, increasing body size or environmental stress can reduce this margin, a pattern often described as having "little left in the tank". However, species that rely on episodic but intense activity may require sufficient aerobic capacity from early life stages onward, particularly when individuals are relatively large at hatching or birth. Here, we examined the ontogenetic scaling of resting metabolic rate (RMR) and active metabolic rate (AMR) in the giant deep-sea scavenger Bathynomus doederleini across a broad size range (1.7-48.4 g) using intermittent-flow respirometry at 10 {degrees}C. RMR and AMR increased with body mass and exhibited nearly identical scaling exponents, resulting in a size-invariant factorial aerobic scope (median = 2.83). This pattern suggests that aerobic capacity is established early and maintained proportionally with maintenance costs, supporting locomotion and scavenging throughout ontogeny in an energy-limited environment.

The mid-domain effect (MDE) predicts that geometric constraints drive unimodal species richness patterns within bounded gradients. However, the role of this effect in ecological networks is currently unexplored. Here we evaluate the role of the MDE in structuring interaction networks. We combine null-model simulations and empirical analyses of plant-pollinator and ant-plant networks along elevational gradients to assess whether the MDE can drive systematic variation in network structure. Our simulations demonstrated that the MDE alone can generate unimodal/U-shaped patterns in network metrics such as connectance, generality, and vulnerability. However, empirical networks only partially conformed to MDE predictions, with deviations indicating the likely influence of other ecological processes. MDE-based models best explained patterns in network-level specialization and nestedness, while only partially explaining patterns in connectance and generality. Because MDEs can shape interaction networks, MDE null models should be used when quantifying the influence of other ecological processes on network structure.

Habitat complexity (HC) in part determines the diversity, stability, and behavior of food webs and can influence predation according to a wide variety of functional relationships. Many aquatic species provide habitat complexity and are also consumed by other species (e.g., macrophytes, corals, mussels). However, food web theory does not readily account for these species that act as edible habitat complexity (EHC). Here, we combine existing theory on predator-prey interactions, HC, and prey switching to describe the role of EHC in benthic food web models. We dissect feedback loops in each model to demonstrate how self-regulation of the prey species, mediated by species densities and HC, drives that food webs behavior. HC can stabilize predator-prey interactions by coupling prey self-regulation with HC self-regulation. EHC can further stabilize predator-prey interactions across a wide variety of "HC functions" that relate HC to predation rates. Significance StatementHabitat complexity (HC) plays a critical role in trophic interactions, population dynamics, and food web stability. However, little theory exists to describe edible habitat complexity (EHC), where a species is both consumed and confers habitat complexity for other species. We provide a series of models demonstrating how HC and EHC alter the population dynamics and stability of simple aquatic food webs. HC is strongly stabilizing in food webs by providing safety in rarity for prey. EHC provides safety in rarity for both prey and the EHC species because their predators are omnivorous. Given the prevalence of EHC species in aquatic systems (e.g., macrophytes, corals, mussels), our models demonstrate the importance of maintaining EHC species in aquatic systems for stable food webs.

Conspicuous coloration in animals is generally thought to evolve and be maintained through inter- or intraspecific interactions such as mate choice, but this might not always be the case. The sight-line hypothesis proposes that conspicuous light-dark contrast in front of the eyes (hereafter, eyeline) evolves and is maintained due to viability selection, enhancing an individual visual acuity and thus evolutionarily associated with a particular foraging behavior that requires accurate aiming. However, empirical evidence that supports the sight-line hypothesis is virtually absent, with no studies demonstrating the key prediction that the direction of eyelines matters. Here, I tested the sight-line hypothesis using macroevolutionary analyses in terns and allies, which are a suitable study system, because they have variation in facial color patterns, including presence/absence and, if any, various angles of eyelines. They also have a large variation in foraging behavior, including picking, plunge diving, and skimming. As predicted by the sight-line hypothesis, tern lineages that require accurate aiming at foraging (e.g., plunge diving) are more likely to have eyelines. In addition, the evolutionary transition to the state with eyelines and these foraging behaviors was more likely to occur than the reverse transition. Furthermore, as expected by the fact that the direction of travel is upwardly deviated from the direction of the bills during skimming, the eyeline angle from bills was evolutionarily positively associated with the occurrence of skimming behavior. To my knowledge, the current study is the first to demonstrate that the direction of the eyeline matters, thereby strongly supporting the sight-line hypothesis.

Heat tolerance is critical for ectotherms facing environmental temperature variability, yet how it varies across life stages, and whether trade-offs occur between temperature-induced developmental plasticity and heat tolerance, remain unclear, particularly in organisms undergoing metamorphosis which represent 95% of all animal species. We examined how early-life thermal conditions shape growth, development, survival, acclimation capacity, heat tolerance, and energy allocation across ontogeny in the African clawed frog (Xenopus laevis), reared at six constant temperatures (17-32{degrees}C). We tested whether higher developmental temperatures generate trade-offs between accelerated growth and heat tolerance, and the consequences for post-metamorphic resilience to extreme heat. Rearing at 32{degrees}C was lethal before metamorphosis. At non-lethal warm temperatures (17-29{degrees}C), larvae and juveniles simultaneously accelerated development, maintained growth, and enhanced heat tolerance. However, juveniles reared at 29{degrees}C showed reduced survival, elevated corticosterone responses to acute stress, and diminished acclimation capacity, indicating increased energetic demands and constrained metabolic flexibility. These findings show that amphibians can integrate developmental plasticity with plastic adjustments in heat tolerance, but that such strategies incur cumulative physiological costs. By adopting an across-life-stage approach, our study highlights energy-allocation constraints that may limit population persistence under climate warming in species with complex life cycles.

Extreme climatic events impose considerable stress on organisms with consequences for key ecological interactions such as pollination. Because temperature directly affects metabolic processes, heat variations may also importantly influence the nutritional needs and feeding choices of animals. Here, we studied the effects of thermal stress on the nutritional choices and performances of bumblebees, using a 3D nutritional geometry design. At optimal temperature for colony development (30{degrees}C), bees successfully balanced carbohydrate, protein, and lipid collection, at levels beneficial for body weight and survival. Under cold stress (20{degrees}C), bees reduced their overall nutrient collection while selecting proportionally more carbohydrates, thereby prioritizing survival over weight gain. Under heat stress (35{degrees}C), nutrient balancing was disrupted and survival dropped. Notably however, across all temperatures, bees maintained stable lipid collection while flexibly adjusting the amount of carbohydrates and proteins, suggesting strong constraints on lipid regulation. Given the pivotal role of bees for pollination, identifying how their nutritional needs change in response to climatic conditions is of prior importance for food safety and the conservation of terrestrial ecosystems.

Spatial heterogeneity of abiotic resources is essential for species coexistence. Ecological theory often assumes predefined heterogeneity of resources that constrains community dynamics, but the recent developments of meta-ecosystem ecology and zoogeochemistry highlight nutrient patterns could result from the interactions between the activities and movements of organisms and their abiotic environment. Here we investigate the mechanisms by which biotic-abiotic feedbacks could generate nutrient spatial heterogeneity in a simple plant-herbivore occupancy model where populations forage, recycle, and disperse in a homogenous landscape. By systematically varying organisms ranges of foraging and dispersal, and recycling levels, we found that limited dispersal of plants plays a key role on the emergence of nutrient patchiness by favoring small clusters of vegetation that shape their environment through consumption and recycling. However, herbivores could also create nutrient spatial heterogeneity when large foraging and dispersal ranges, and high recycling, allow them to efficiently track plant hot spots and to increase population persistence. Unexpectedly, strong aggregation of herbivore populations did not necessarily result in nutrient clustering. Rather than via recycling, herbivores mainly affected nutrient distribution indirectly, through their top-down impact on plant distribution. When evenly spread in the landscape, herbivore populations with large foraging ranges created areas of strong herbivory pressure unfavorable to plant colonization where nutrient can accumulate. These results can help understand the dynamical feedback between biota and abiotic resources. In a context where human activities alter both nutrient distribution and species abundances, a better understanding of this biotic-abiotic feedback will be key to anticipate the response of ecosystems to current perturbations.