Functional Ecology

The timing of reproductive processes can influence how mating interactions shape reproductive strategies. We examined how female age correlates with receptivity and preference in the jumping spider Habronattus formosus, a system characterized by elaborate male courtship and strong female choice. To test how receptivity changes across the post-maturation period, we paired females of different ages with males and quantified male courtship displays and mating outcomes. Females were not receptive immediately after maturation and instead exhibited receptivity primarily 2-3 weeks after maturation. We further found that the full male courtship predicted mating success in older females, whereas only the second stage of the courtship predicted success in younger females. The delay in female receptivity is consistent with expectations for strong female choice systems, where females may have a greater opportunity to evaluate male courtship before mating. These results highlight the importance of age-dependent changes in female reproductive state and suggest that the timing of receptivity may shape how different components of male courtship influence mating success.

While mutualistic symbioses with nitrogen-fixing bacteria enable plants to access fixed nitrogen, they also require substantial carbon investment. Under carbon limitation, such as shading, shifts in biomass allocation can decouple symbiotic investment from leaf and root growth, potentially compromising plant nitrogen status. Because shading shifts biomass allocation toward light acquisition, it could influence nitrogen fixing symbiosis in two opposing ways. If nodulation remains coupled to leaves rather than roots, nitrogen status should be maintained despite reduced root growth. Alternatively, if root growth constrains nodulation, nitrogen status should decline. We tested these hypotheses by manipulating light availability (full sunlight vs. 50% shade) and quantifying biomass allocation and symbiotic nodulation. Under shading, plants allocated proportionally more biomass to shoots than to roots and invested less biomass in root nodules. Relationships between nodulation and leaf or root biomass differed between treatments but converged with increasing plant size, although shaded plants never attained the root biomass observed in full sunlight. Leaf nitrogen concentration was maintained under shading because nodulation remained coupled to leaf investment despite reduced root allocation. These findings highlight that, under carbon limitation, maintaining leaf and nodule coupling enables plants to reduce nodule investment without compromising the nitrogen benefits of symbiosis.

The impacts of a changing abiotic environment on fitness and performance arise not only from low tolerance to new environmental conditions, but also from changes in the abundance and interaction intensity with other species. The strength of the interaction may itself depend on how well each species performs across environments, but there is a dearth of studies investigating how intrinsic fitness and interaction intensity covary across an abiotic environmental gradient. We addressed this question in a hypersaline consumer-resource system: the microalga Dunaliella spp. grazed by the brine shrimp Artemia franciscana. We exposed four Dunaliella strains to a range of salinities above seawater, with or without brine shrimps, and tracked their population sizes over time and the survival of their predators, to estimate basic parameters of a Lotka-Volterra model. We found that the intrinsic growth rate of algae, the survival rate of predators, and the per-capita predation rate, all varied with salinity and algal strain. Significant interactions between strain and salinity further revealed that these ecological responses to salinity are evolvable. Together with correlations between demographic parameters across salinity, this suggests that predation may influence the evolution of salinity tolerance curves, blurring the line between the fundamental and realized niches.

The exchange of energy and organisms across habitat boundaries links aquatic and terrestrial ecosystems and sustains ecosystem functioning. Although disturbance may disrupt these linkages, the mechanisms at play remain poorly understood. Here, we investigated the extent to which flow intermittency may disrupt riparian-aquatic ecosystem linkages by altering consumer communities in the recipient ecosystem or by altering resource quality in the donor ecosystem. We ran an experiment in an intermittent river network in California, focusing on a critical forest-to-river subsidy (organic matter in the form of leaf litter), its transformation, and its reciprocal benefit (aquatic insect production). Using three riparian species (willow, cottonwood, and oak) at sites spanning a gradient of flow permanence, we quantified intraspecific plasticity in leaf traits (specific leaf area, nitrogen and phosphorus concentrations, and {delta}13C), measured decomposition rates, and estimated the secondary production of aquatic shredders (Plecoptera). Across all leaf species, decomposition rates were 16-36% lower at intermittent than perennial sites, an effect largely driven by intraspecific leaf trait plasticity rather than changes in consumer abundance. At high flow intermittency, willow experienced water stress (enriched {delta}13C) and reduced specific leaf area, while cottonwood showed primarily stoichiometric responses (reduced leaf nitrogen and phosphorus). Despite these divergent strategies, all species produced lower-quality litter at intermittent sites. Variance partitioning confirmed that initial litter quality uniquely explained 51.5% of variation in decomposition rates, more than double the contribution of invertebrate community metrics; and structural equation modeling revealed that both leaf traits and stonefly (Plecoptera) secondary production significantly predicted decomposition rates, with leaf traits exerting the stronger effect. Notably, stonefly secondary production was 37-98% lower at intermittent sites across leaf species. Because these insects later emerge as terrestrial adults, they provide a significant energy flux to riparian predators, and, thus, impoverished litter quality suppresses the reciprocal transfer of energy back to terrestrial food webs. As drought intensifies globally, the decoupling of terrestrial-aquatic linkages may begin in the riparian canopy.

The diversity of species responses to environmental change (response diversity) is a key mechanism of ecological stability. However, anticipating where strong or weak stabilizing responses emerge is challenging because species responses can depend on the local community and the specific stability metric. Whether species traits can consistently inform on how species respond to disturbances, enabling less context-dependent predictions, remains an open question. To address this gap, we use microcosm experiments on marine phytoplankton to test how response diversity supports multiple aspects of community stability under pulse temperature changes, testing both an increase (heatwave) and a decrease in temperature (coldspell). We then map species traits to their responses in a community to identify which traits modulate and predict species' sensitivities. Fundamental response diversity, based on the diversity of species responses to temperature measured in isolation, was a weak predictor of community stability, and relationships differed between disturbances (i.e., heatwave and coldspell). Instead, species traits were consistent predictors of species responses in communities. Small, fast-growing species were more tolerant and benefited from the disturbance, while large, slow-growing species were less tolerant and decreased in proportion - these patterns were consistent across disturbances and community compositions. These results suggest that strong trait-performance relationships might reduce the importance of response diversity for stability. But these findings also show that general species traits, such as size and growth rate, can predict which species, and how, contribute to community responses, providing an empirical basis to relate species traits to stability outcomes under climate change.

True crabs (Brachyura) are among the most iconic marine arthropods, representing noteworthy examples of morphological and ecological disparity. A striking feature of brachyurans are their anterior pincer-like appendages: chelipeds. These structures showcase a large diversity of morphologies that reflect ecology and overall multifunctionality. Yet, a comprehensive assessment of appendage functional morphology within phylogenetic and ecological trait contexts has never been attempted. By combining 3D geometric morphometrics, finite element analyses, multilocus molecular phylogeny, and ecological trait data for 80 crab species, including three fossil forms, we unveil a complex evolutionary history for crab chelipeds. Despite extreme shape diversity amongst chelipeds, stress distributions are very similar across taxa and hint a many-to-one pattern. High concentrations of chelipeds within constrained morphospace regions associated with peak pinch forces illustrates that brachyuran morphologies optimised for shell crushing may have arisen in the Cretaceous. Deviations from this morphospace highlight the diversification of non-shell-crushing life modes and the influence of sexual selection on appendages. Neither cheliped shape nor pinch force show phylogenetic signal. Together these results indicate that the evolution of cheliped shape is closely associated with, and inferred to have been strongly influenced by, crab ecology, biomechanical needs and sexual selection. SIGNIFICANCE STATEMENTChelipeds, the pincer-like claws of crabs, are among the most morphologically diverse appendages within Arthropoda, yet the evolutionary forces driving this diversity remain poorly understood. By integrating 3D geometric morphometrics, biomechanical modelling, molecular phylogeny, and ecological data across 80 crab species including fossil forms, we demonstrate that cheliped morphology is driven by ecology, biomechanical demands, and sexual selection rather than phylogenetic relatedness. The multifunctionality of these structures produces strong evidence for many-to-one mapping of form to function. Morphologies optimised for durophagy appear to have originated in the Cretaceous, with subsequent diversification into manipulative and sexually selected forms from a morphologically flexible foundation. These findings demonstrate that cheliped diversity reflects a complex interplay between ecological specialisation, biomechanical optimisation, and sexual selection across Brachyura.

The impacts of increasingly frequent and intense heatwaves on parasitism are an important frontier for understanding disease risk under climate change. These impacts are complex because parasitism arises from multiple interacting host and parasite traits that can vary in thermal sensitivity and among populations adapted to different temperature regimes. Here, we used a lab microcosm experiment to investigate the effects of heatwaves occurring during two different phases of a winter-adapted mosquito host - ciliate parasite interaction, for six pairs of sympatric host and parasite populations sourced from two geographic regions with differing histories of winter heat. We found that because heatwaves allowed mosquito larvae to evade infection, they reduced parasitism and increased survival. An early heatwave during initial parasite attack had stronger effects than a later heatwave occurring after infections had established. We did not find evidence of local adaptation to heatwaves: impacts were consistent regardless of population, and were mechanistically predictable from previously measured thermal performance curves that described lower infection and stronger host defenses at warm constant temperatures. The results suggest that increasingly frequent heatwaves may accelerate geographic shifts in parasitism, and demonstrate how fundamental host - parasite thermal biology links to the impacts of extreme temperature events.

The energetic demands of courtship are central to sexual selection, but their magnitude and temporal variation remain poorly quantified in many signalling systems. We used closed-chamber respirometry and low-light video analysis to estimate courtship-associated metabolic rates in males of the bioluminescent ostracod Photeros sp. EGD. Low-activity metabolic rate varied strongly across the diel cycle: in small vessels that constrained movement, individually measured males consumed significantly more oxygen at night than during the day. We then compared oxygen consumption across vessels that differed in opportunities for movement and courtship. Metabolic rates were highest in large vessels that permitted bioluminescent courtship displays, intermediate in medium vessels that allowed swimming but not full displays, and lowest in small vessels that constrained movement. Oxygen consumption in large vessels at night was approximately 500% of small-vessel daytime rates, 280% of small-vessel nighttime rates, and 160% of medium-vessel nighttime rates. Because measurements integrated oxygen use over multi-hour intervals, these values represent time-averaged metabolic demand rather than instantaneous costs of individual light pulses or display trains. Video analyses suggested a positive association between signalling rate and oxygen consumption, although this relationship was not statistically supported in our large-vessel dataset, which had low statistical power. Together, these results show that male Photeros undergo strong diel shifts in metabolic state and that the whole-animal performance required to construct bioluminescent courtship displays may often impose substantial energetic demands.

One of the most intuitive ideas in ecology is that diversity at lower trophic levels in food webs provides niches to support diversity at higher trophic levels. This accumulation of diversity can be limited by survival of species in the landscape, but revealing these limits has been challenging. We analyze spatial turnover in a hyperdiverse parasitoid-caterpillar-plant food web across 75,000 km2 of continuous lowland rainforest in Papua New Guinea. Species turnover across sites is higher in parasitoids than in their caterpillar hosts. Furthermore, turnover of interactions is also higher in parasitoid-caterpillar than caterpillar-plant networks. Spatial turnover thus amplifies upwards across trophic levels, forcing parasitoids to live closer to spatial persistence limits. Consequently, progressing rainforest fragmentation can especially endanger parasitoids.

O_LIThermal performance curves (TPCs) predict species vulnerability to climate change, but standard respirometry assumes that measured oxygen consumption reflects physiological state. Sessile invertebrates that retract their tentacles and contract under thermal stress violate this assumption, with unmeasured consequences for thermal limit estimates. C_LIO_LIWe tested this behavioral confound in an undescribed cold-water intertidal anemone (Urticina sp.) in the Northwest Atlantic by integrating a negative binomial encounter-rate regression, a maximum entropy species distribution model (both from effort-corrected iNaturalist data), and closed-chamber respirometry across seven temperatures (1-30{degrees}C, 18 individuals, 126 trials). C_LIO_LIThe strongest distributional predictors were cloud cover and coastal urbanization, with a weaker association with winter minimum SST; direct evidence for warm-edge thermal limitation came from the experiment. Anemone expansion state (scored 0-1 from fully closed to fully expanded) was variable and without a clear trend across the coldest treatments but declined above 20{degrees}C before collapsing at the 30{degrees}C treatment, which proved lethal to all individuals. C_LIO_LIStandard TPC models extrapolated the thermal maximum far beyond the lethal bracket ([~]74{degrees}C symmetric Gaussian; 45.9{degrees}C asymmetric). A Bayesian multiplicative model that separated physiology from behavior showed that physiology continued to track temperature while expansion state declined above 20{degrees}C; a fully expanded anemone respired about twice as fast as a fully closed one at the same temperature. The decline in measured respiration is therefore both behavioral and physiological, and disentangling the two requires recording expansion state alongside oxygen consumption. C_LIO_LIBecause a closed anemone cannot feed or exchange gases, the ecologically relevant thermal limit is the temperature at which the animal can no longer maintain its normal expanded posture, not a curve-fitted thermal maximum. That behavioral threshold leaves warm-edge populations within a few degrees of functional thermal failure. C_LIO_LIFuture thermal physiology studies of organisms capable of modulating oxygen consumption through behavior should incorporate quantitative behavioral covariates to separate physiological from behavioral components of the metabolic response. C_LI

Reproduction in species with parental care involves sustaining a brood of offspring through an energetically demanding period, when shifts in resource availability, weather, predation risk, and parental condition can strongly alter offspring survival. The most extreme outcome is complete brood failure (death of all offspring), which is relatively frequent in many bird species and may occur when conditions cross a viability threshold. Although complete brood failure is important for shaping fitness variation and population dynamics, we have limited understanding of how intra- and interspecific density dependence governs these events, or of how factors such as habitat quality and disease burden contribute to them, because deriving this requires fine-scale, individual-level data collected across generations for multiple overlapping species. Using a dataset totalling 38,509 nesting attempts from great tits (Parus major) and blue tits (Cyanistes caeruleus) in Wytham Woods, Oxford, UK, we examined how brood failure is shaped by local conspecific and heterospecific density, habitat structure, and avian malaria infection for a subset. Complete brood failure was frequent (14.75%), mostly involving chick mortality in the nest consistent with starvation, rather than brood removal by predators. Relationships between density and brood failure were strong but species-specific. Specifically, great tit failure risk was higher in neighbourhoods that remained densely populated across years, whereas blue tit failure risk was lower where annual great tit or combined density was high, but not where annual blue tit density itself was high. This suggests that local overall density reflects continuing constraint for great tits, while local annual density may partly track favourable within-year conditions and settlement patterns for blue tits. In great tits, failure was also more common where oak density was low and farther from the closest river (Thames), while habitat associations were weak in blue tits. Malaria infection was spatially heterogeneous and covaried with density and habitat, but infection status did not significantly explain complete brood failure. Together, these results show that complete brood failure is shaped by spatially structured local ecological context, and how density dependence in these events can differ in direction and timescale between sympatric species.

The shift to terrestrial environments in ancestrally aquatic animals is often associated with key physiological and physical changes, including shifts in respiratory physiology and in some cases, even the evolution of completely novel respiratory structures. Examining how respiration operates across a gradient of submersion states in ancestrally aquatic terrestrial animals may shed light on how complex biological traits shift under different selective regimes. In this work, we begin exploring respiration in terrestrially-adapted land crabs that still use their gills to respire while underwater. We tested the relationship between aquatic respiratory rates, body size, and sex in red devil vampire crabs (Geosesarma hagen) at two ecologically-relevant temperatures. We found small females respire more than small males at 28{degrees}C, while large females respire more than large males at 21{degrees}C. Additionally, body size is a significant factor affecting respiratory rates of both sexes at 21{degrees}C and warmer temperatures significantly increase respiration in small crabs of both sexes. Interactions between these factors also led to emerging trends that can be explained by both physiological rules, such as reproductive investment and surface-to-volume ratios and heat transfer. We also report a temperature coefficient (Q10) of 1.52 for this species, showing an expected 52% change in respiratory and metabolic rate for every 10{degrees}C increase. This work also demonstrates the importance of understanding how and to what extent biological variables like sex and body size interact with abiotic environmental factors when measuring physiological traits in ectothermic invertebrate animals.

In a wide variety of animals, developmental crowding results in adults with smaller bodies. The crowding effect on body size in Drosophila melanogaster is canonically attributed to heightened competition for nutrition. However, whether other consequences of crowding also contribute to its effect on size remains an open question. We tested the relative contributions of nutritional competition, oxygen availability, and larval-generated metabolites to the crowding effect on size. We found that while nutrition explains most of the variation in body size due to crowding, oxygen also contributes in a sex- and nutrition-dependent manner. We found no evidence that larval-generated chemicals affect body size. These data confirm a widely suspected but untested role of nutrition in producing the crowding effect on size in D. melanogaster, while revealing an unexpected role of oxygen, and raise the possibility that behavior may be a mediator of density-dependent plasticity. Research HighlightsWe found that both nutrition and oxygen mediate the crowding effect on size in Drosophila melanogaster.

The number of chromosome sets per nucleus is a fundamental trait, but why this number is nearly always two for multicellular eukaryotes remains unclear. Chromosomes are made of nucleic acids, which possess abundant phosphorus (P). Therefore, producing new chromosomes, as well as generating new cells and organismal growth, demands substantial phosphorus. Yet, because P is often limiting in nature, P availability could influence the prevalence of diploidy versus polyploidy. Here, we compare growth rates of diploid and triploid Potamopyrgus antipodarum, a freshwater snail, relative to P availability. Because diploid P. antipodarum are obligately sexual while obligately asexual individuals are polyploid, costs associated with sensitivity to P limitation in polyploids could also help explain the maintenance of sexual P. antipodarum. We raised juvenile diploid and triploid snails on either P-adequate or P-deficient diets and found that independent of P availability, juvenile triploid asexual snails grew faster and harbored higher P content as adults than sexual diploid conspecifics. Together, these results suggest life-history advantages of polyploidy or asexual reproduction that exacerbate rather than ameliorate the cost of sex. These outcomes suggest that P availability is unlikely to be a main driver of ploidy polymorphism or the maintenance of sex in P. antipodarum.

Climate change is expected to alter plant populations not only through direct environmental shifts but also via changes in biotic interactions, such as with herbivores and pathogens. As plant species are also expected to differ in their responses to both climate and antagonists, plant responses to both factors are expected to be variable and species-specific. To assess whether interactive effects of climate and antagonists on plant population dynamics are common and whether the strength and direction of plant responses vary across species, we conducted a multi-year field experiment that manipulated realistic climate change and experimentally reduced insect herbivores and fungal pathogens. We measured responses of plant vital rates, such as survivorship, growth, and reproduction across six grassland species. Using Integral Projection Models (IPMs) and Life Table Response Experiments (LTREs), we quantified changes in population growth rate across experimental treatments and the contribution of each vital rate to that observed change. Two of the study species declined so drastically over the course of the experiment that demographic quantification of population growth rates was not possible. From the remaining species, Bromus erectus and Plantago lanceolata show significant interactive responses of climate and antagonist reduction on population growth rates. In contrast, Dianthus carthusianorum and Tragopogon orientalis showed limited responses to experimental treatments. Notably, our results indicate that in some species biotic interactions may amplify the effects of climate change: the presence of plant antagonists exacerbates the negative effects of the future climate treatment on plant population dynamics. Our findings highlight the complexity in predicting plant population responses to climate change and provide insights for grassland management under future environmental conditions.

Arctic and Boreal raptor communities will continue to be affected by borealization and other climate change related processes, providing a challenge for ecologists predicting future sates. However, by using community assembly theory and species traits, future communities may be predictable. In this study, we analyzed variation in reproduction traits as a consequence of diet specialization for 29 raptors, 2 skuas and 3 corvids. We assessed and implemented foraging traits for specialists and generalists into predator-prey models from which successful invasion conditions were derived. Specialist raptors produced larger clutch sizes, had a higher proportion of fledged per clutch and also expressed more variation compared to generalist raptors. These results suggest a relationship between diet specialization and reproductive traits which was also observed within phylogenetic orders. Specialist owls (Strigiformes) produced higher clutch sizes with a larger clutch range compared to generalist owls. The same pattern was observed for falcons (Falconiformes). No clear difference in reproduction was observed for specialist and generalist hawks, kites and eagles (Accipitriformes). Corvids expressed clutch sizes similar to that of specialist raptors while having the lowest proportion of fledged per clutch. Differences in foraging traits between specialists and generalists could be distinguished using functional response curves. A predator-prey model parameterized with foraging trait data showed that a generalist can coexist with a resident specialist if it has access to prey unavailable to the resident specialist. Otherwise, the native specialist outcompetes the invading generalist due to foraging efficiency. The combined empirical and theoretical findings in this study show how diet specialization affects both reproduction and the potential invasion success of raptors.

Colour and contrast are commonly deployed in anti-predator signals like aposematism or deimatism. In oceans, colour information diminishes with depth, leaving blue bioluminescence the most common visual signal, regardless of function. Bioluminescence can deter predators, but without contrasting colours, how so is largely uncharacterized. Here, we test this by observing fish predators responding to prey that use defensive bioluminescence (Ostracods, Cypridinidae). By manipulating potential chemical defences of prey, and by comparing feeding responses to both luminescent and nonluminescent prey, we show that luminescent prey are unpalatable and use facultative bioluminescence as an aposematic signal. We observed active, luminescent prey secrete bioluminescence only after being attacked. Predatory fishes rarely consumed luminescent prey, especially compared to nonluminescent alternatives. Food treatments revealed that luminescent species may possess some unidentified defence over nonluminescent relatives because fishes also readily ate luminescent prey that had been treated (frozen or boiled), which removed such defences. Over the course of four experimental trials, predators were less likely to consume luminescent prey as their cumulative exposure to anti-predator light displays increased, indicative of learning. Despite their intermittency, temporally dynamic signals like aposematic bioluminescence may be as common and effective as better-studied static coloration, especially in marine ecosystems.

Grasslands are vulnerable to increasing drought with global warming, but process-based models lack the mechanistic knowledge required to predict the magnitude of drought impacts. While a plant hydraulics framework has been successful in advancing process understanding of drought responses in trees, and how drought responses vary across rainfall gradients, similar approaches have rarely been applied to grasses. Here, we quantified the progression of key drought response processes in sixteen dominant perennial grasses (seven C3 and nine C4) with differing climatic origins across eastern Australia. We found that stomatal closure, hydraulic impairment and leaf browning occurred concurrently, in contrast to the progressive sequence typically observed in trees. We also found that drought response traits were not correlated with species climate of origin. The early impairment of leaf hydraulic conductance and leaf browning along with the lack of correlation with climate of origin suggest that grasses may employ fundamentally different strategies to adapt to low water availability than trees. These results highlight the need for grass-specific parameterization of drought responses in process-based models.

Ecological theory states that the geographic ranges and coexistence of species are determined by fundamental and realized niches - the sets of environments where a species intrinsic population growth rate is positive in the absence and presence of competitors, respectively. Yet large-scale tests of niche theory have been hampered by the challenge to obtain sufficient data on demography and competition. Here, we quantify fundamental and realized niches by combining data on variation in fundamental demographic rates, community composition and the abiotic environment across the global geographic ranges of 29 shrub species from the South African Fynbos biome (a global biodiversity hotspot). Estimated pairwise competition coefficients and fundamental-realized niche contrasts reveal multi-scale mechanisms of species coexistence. At small scales, species generally exert stronger competition on themselves than on other species. At biogeographical scales, more competitive species have narrower fundamental niches but are not significantly better dispersed, which provides evidence for a generalist-specialist trade-off rather than a competition-colonization trade-off. Under both present and future climates, interspecific competition more strongly limits the realized niches and geographic ranges of generalist species. The large-scale application of niche theory thus identifies key forces shaping biodiversity and indicates that generalist species may be more strongly impacted by climate change than previously thought.

The Amazon is a mosaic of ecosystems, accounting for 13% of all known species globally, and responsible for providing a variety of ecosystem services, including a key role in global climate regulation. However, 18% of the Amazon forest cover has been lost completely and a further 38% degraded, threatening biodiversity and millions of local livelihoods. Currently, little is known about how this impacts the functioning of ecological communities. Here, we combine an energetic approach with biodiversity metrics to quantify ecosystem functioning in mammal and bird food webs across Amazonia, along a gradient of forest degradation linked to road proximity. We show that even under relatively low disturbance, ecosystem functions shift: carnivory increases closer to roads, driven by generalist species that persist under these conditions, whereas herbivory declines mainly due to reduced herbivore biomass and species richness. This suggests that processes associated with forest degradation can alter energy flow even where biodiversity metrics remain relatively unchanged, highlighting energetic approaches as sensitive indicators of ecosystem disruption.