Functional Ecology

Metabolic rate is considered to determine the energetic investment placed into life-history traits, regulating the speed of an organisms life-cycle and forming the so called \"pace-of-life\". However, how metabolic rate and life-history traits co-evolve remains unclear. For instance, the energetic demands of life-history traits, including the number of energy allocation trade-offs, is unlikely to remain constant over ontogeny. Therefore, the predicted coevolution between metabolic rate and life-history could be specific to particular ontogenetic stages, rather than a stable property of an organism. Here, we test the ontogenetic dependency of the coevolution between metabolic rate and the pace of life-history, under strictly standardized conditions using 30 species of killifish, which are either annual species adapted to ephemeral pools or non-annual species inhabiting more permanent waterbodies. Standard metabolic rates were estimated at three ontogenetic stages, together with relevant life-history traits, i.e. growth (juveniles), maturity (young adults), and reproductive rate (reproductive adults). Life-history traits largely followed predicted pace-of-life patterns, with overall faster/higher rates in annual species. The divergences in life-history traits across species tended to increase over ontogeny, being smallest during juvenile growth and largest in reproductive adults. However, associations between life-history strategy and metabolic rate followed a reversed pattern, being strongest in juveniles, but lowest in reproductive adults. Our results are concordant with the number of energetic trade-offs increasing over ontogeny, which results in a stronger covariation between physiology and life-history traits earlier in ontogeny.

The outcome of species competition strongly depends on the traits of the competitors and associated trade-offs, as well as on environmental variability. Here we investigate the relevance of consumer trait variation for species coexistence in a ciliate consumer - microalgal prey system under fluctuating regimes of resource supply. We focus on consumer competition and feeding traits, and specifically on the consumers ability to overcome periods of resource limitation by mixotrophy, i.e. the ability of photosynthetic carbon fixation via algal symbionts in addition to phagotrophy. In a 48-day chemostat experiment, we investigated competitive interactions of different heterotrophic and mixotrophic ciliates of the genera Euplotes and Coleps under different resource regimes, providing prey either continuously or in pulses under constant or fluctuating light, entailing periods of resource depletion in fluctuating environments, but overall providing the same amount of prey and light. Although ultimate competition results remained unaffected, population dynamics of mixotrophic and heterotrophic ciliates were significantly altered by resource supply mode. However, the effects differed among species combinations and changed over time. Whether mixotrophs or heterotrophs dominated in competition strongly depended on the genera of the competing species and thus species-specific differences in the minimum resource requirements that are associated with feeding on shared prey, nutrient uptake, light harvesting and access to additional resources such as bacteria. Potential differences in the curvature of the species resource-dependent growth functions may have further mediated the species-specific responses to the different resource supply modes. In addition, while the presence of a heterotrophic competitor may have a direct negative effect on the growth rate of a mixotrophic species through grazing on a shared prey species, its presence may also have an indirect positive effect on the growth rate of the mixotroph by reducing competition between the autotroph and mixotroph for shared nutrients and light. Our study thus demonstrates that complex trophic interactions determine the outcome of competition, which can only be understood by taking on a multidimensional trait perspective.

Invertebrate herbivores are important and diverse, and their abundance and impacts are expected to undergo unprecedented shifts under climate change. Yet, past studies of invertebrate herbivory have documented a wide variety of responses to changing temperature, making it challenging to predict the direction and magnitude of these shifts. One explanation for these idiosyncratic responses is that changing environmental conditions may drive concurrent changes in plant communities and herbivore traits. Thus, the impacts of changing temperature on herbivory might depend on how temperature combines and interacts with characteristics of plant communities and the herbivores that occupy them. Here, we test this hypothesis by surveying invertebrate herbivory in 220, 0.5 meter-diameter herbaceous plant communities along a 1101-meter elevational gradient. Our results suggest that increasing temperature can drive community-level herbivory via at least three overlapping mechanisms: increasing temperature directly reduced herbivory, indirectly affected herbivory by reducing phylogenetic diversity of the plant community, and indirectly affected herbivory by altering the effects of functional and phylogenetic diversity on herbivory. Consequently, increasing functional diversity of plant communities had a negative effect on herbivory, but only in colder environments while a positive effect of increasing phylogenetic diversity was observed in warmer environments. Moreover, accounting for differences among herbivore feeding guilds considerably improved model fit, because different herbivore feeding guilds varied in their response to temperature and plant community composition. Together, these results highlight the importance of considering both plant and herbivore community context in order to predict how climate change will alter invertebrate herbivory.

Life history theory provides a framework for understanding how trade-offs generate negative trait associations. Among nestling birds, developmental rate, risk of predation, and lifespan covary, but some associations are only found within species while others are only observed between species. A recent comparative study suggests that allocation trade-offs may be alleviated by disinvestment in ephemeral traits, such as nest-grown feathers, that are quickly replaced. However, direct resource allocation trade-offs cannot be inferred from inter-specific trait-associations without complementary intra-specific studies. Here, we asked whether there is evidence for a within-species allocation trade-off between feather quality and developmental speed in tree swallows (Tachycineta bicolor). Consistent with the idea that ephemeral traits are deprioritized, nest-grown feathers had lower barb density than adult feathers. However, despite substantial variation in fledging age among nestlings, there was no evidence for a negative association between developmental pace and feather quality. Furthermore, accounting for differences in resource availability by considering provisioning rate and a nest predation treatment did not reveal a trade-off that was masked by variation in resources. Our results are most consistent with the idea that the inter-specific association between development and feather quality arises from adaptive specialization, rather than from a direct allocation trade-off.

O_LIInsects are core actors for the balance of many earth ecosystems, as well as an alternative source of food and feed with a low ecological footprint. A comprehensive understanding of their life history requires reliable tools. Body condition constitutes the amount of energy reserves available to a fitness trait after maintenance costs have been accounted for. Body condition is standardly estimated using Body Condition Indexes (BCIs) in vertebrates. In insects the relevance of BCIs is frequently questioned on the basis that they might not accurately reflect neither energy reserves nor fitness.. However, to date no study has tested whether the very concept of body condition is relevant in insects, i.e. whether BCIs accurately reflect the relative energy reserves allocated to fitness traits. C_LIO_LIWe propose that the relevance of using BCIs in insects depends on whether their structural size has a fitness cost. If on the contrary insects only benefit from a larger body size, a simple measurement of body size or mass will predict fitness, but not a BCI. We experimentally manipulated food availability at the larval and adult stage and used total fecundity of females as a fitness proxy of Tenebrio molitor, an important model in physiology, ecology and evolution, and one of the first insects to be considered as a source of food and feed. C_LIO_LIOur results support three key assumptions of the relevance of BCIs in insects: (i) a valid BCI correlated with energy reserves corrected for a given size (i.e. relative energy reserves) and not with absolute measures of energy reserves; (ii) both structural size and body condition positively predict different components of fitness; and, (iii) the effect of body condition was dependent on resource availability, whereby its effect was only apparent and large when food was unrestricted at the larval stage and restricted at the adult stage. C_LIO_LIOverall we demonstrate the relevance of using BCIs in insects. Their use should be generalized to improve fitness readouts in evolution, ecological and physiological studies, as well as improve their husbandry for commercial purposes. C_LI

Ant guards can increase plant fitness by deterring herbivores but may also reduce it by interfering with pollination, hence ant-plant interactions are ideal systems in which to study costs and benefits of mutualisms. While ant impacts on herbivory are well-studied, much less is known about impacts on pollinators and associated consequences for plant mating systems and fitness. We used field experiments to quantify the effect of ant guards on pollinator community composition, frequency and duration of flower visits, and cascading effects on plant mating system and plant fitness in Turnera velutina (Passifloraceae). Although ant patrolling did not affect pollinator community composition or visitation frequency, it decreased pollinator foraging time and flower visit duration. Such behavioural changes resulted in reduced pollen deposition on stigmas, decreasing male fitness whilst increasing outcrossing rates. This study contributes to understanding how non-pollinators, such as these defensive mutualists, can shape plant mating systems.

Ecosystem functions such as seed production are the result of a complex interplay between competitive plant-plant interactions and mutualistic pollinator-plant interactions. In this interplay, spatial plant aggregation could work in two different directions: it could increase intra- and interspecific competition, thus reducing seed production; but it could also attract pollinators increasing plant fitness. To shed light on how plant spatial arrangement modulates this balance, we conducted a field study in a Mediterranean annual grassland with three focal plant species with different phenology (Chamaemelum fuscatum (early phenology), Leontodon maroccanus (middle phenology) and Pulicaria paludosa (late phenology)) and a diverse guild of pollinators (flies, bees, beetles, and butterflies). All three species showed spatial aggregation of conspecific individuals. Additionally, we found that the two mechanisms were working simultaneously: crowded neighborhoods reduced individual seed production via plant-plant competition, but they also made individual plants more attractive for some pollinator guilds, increasing visitation rates and plant fitness. The balance between these two forces varied depending on the focal species and the spatial scale considered. Therefore, our results indicate that mutualistic interactions not always effectively compensate for competitive interactions in situations of spatial aggregation of flowering plants, at least in our study system. We highlight the importance of explicitly considering the spatial structure at different spatial scales of multitrophic interactions to better understand individual plant fitness and community dynamics.

Historical resurveys of ecological communities are important for placing the structure of modern ecosystems in context. Rarely, however, are snapshot surveys alone sufficient for providing direct insight into the rates of ecological processes that underlie how communities function, either now or in the past. In this study, I used a statistically-reasoned observational approach to estimate the feeding rates of a New Zealand intertidal predator, Haustrum haustorium, using diet surveys performed at several sites by Robert Paine in 1968-9 and by me in 2004. Comparisons between time periods reveal a remarkable consistency in H. haustoriums prey-specific feeding rates, which contrasts with the changes I observed in prey abundances, H. haustoriums body size distribution, and the proportional contributions of H. haustoriums prey to its apparent diet. Although these results imply accompanying and perhaps adaptive changes in H. haustoriums prey preferences, they are nonetheless anticipated by H. haustoriums high range of variation in prey-specific handling times that dictate not only its maximum possible feeding rates but also the probabilities with which feeding events may be detected during diet surveys. Similarly high variation in detection times (i.e. handling and digestion times) is evident in predator species throughout the animal kingdom. The potential disconnect between a predators apparent diet and its actual feeding rates suggests that much of the temporal and biogeographic variation that is perceived in predator diets and food-web structures may be of less functional consequence than currently assumed.

Global environmental changes generate novel communities. Some species adapt to novel community contexts by demonstrating interaction fidelity, or consistently interacting with the same species, while others demonstrate interaction flexibility, or interacting with whichever partners are available (i.e., rewiring). However, the drivers and benefits of fidelity are unclear. Here, we use data from a large-scale mesocosm experiment to determine whether plant characteristics (e.g., provenance, functional group) and community contexts impact plant interaction fidelity to belowground mutualist and antagonist partners (i.e., root fungi and bacteria), and how this fidelity relates to plant performance. We found that the plant-antagonist relationships exhibited higher fidelity than plant-mutualist relationships with the strength of fidelity depending on a combination of plant characteristics and community context. Conversely, plant-mutualist fidelity impacted plant performance with competing effects depending on plant provenance and aboveground herbivore presence. Our study advances understanding of how species interactions influence plant performance in a changing world. Statement of authorshipAMM, JDT, JMT and DBS designed the concept. All authors contributed to refining the ideas. AM coded the analysis to produce the results with contributions from JDT, DBS, and BBM. HRL and DBS helped AMM with the statistical analysis. LPW, WJA, IAD, and JMT designed the experiment while LPW and WJA conducted the experiment. AMM wrote the first draft of the manuscript with assistance from all authors. IAD, JMT, and JDT obtained funding. All authors contributed to further editing of the manuscript.

Sponges commonly form associations within seagrass meadows, but their potential impact on seagrass productivity and nutrient cycles remains poorly understood. This study investigates the association between the demosponge Chondrilla nucula and the Mediterranean seagrass Posidonia oceanica in two sampling occasions during the plant growth (spring) and senescence (autumn) seasons at a small inlet near Naples, Italy, where the sponge grows conspicuously within the seagrass bed. We found a non-linear relationship between the benthic cover of the sponge and the seagrass, with higher C. nucula cover linked to intermediate P. oceanica cover, suggesting spatial dependence. P. oceanica showed higher net primary production (NPP) in spring, while C. nucula was net heterotrophic in spring but exhibited slightly positive NPP in autumn. NPP remained stable when the two organisms were associated, regardless of the season. C. nucula consistently contributed inorganic nutrients to the association in the form of phosphate, ammonium, and substantial nitrate, recycling nutrients that potentially benefited P. oceanica in its growth season. In return, the seagrass consistently provided dissolved organic carbon, which aided sponge nutrition in spring. These findings suggest reciprocal benefits in the interaction between C. nucula and P. oceanica, with nutrient exchange facilitating a facultative mutualism that potentially supports and stabilizes the productivity of the seagrass ecosystem. SIGNIFICANCE STATEMENTThis study provides a novel exploration of the reciprocal interactions between the demosponge Chondrilla nucula and the Mediterranean seagrass Posidonia oceanica, revealing a facultative mutualism mediated by nutrient exchange. Our findings show a non-linear spatial dependence between sponge and seagrass cover and demonstrate the sponges substantial contributions of inorganic nutrients (phosphate, ammonium and conspicuous nitrate) to the seagrass, particularly during its productive spring season. In return, P. oceanica supplies dissolved organic matter, aiding sponge nutrition. This study uniquely quantifies these reciprocal nutrient exchanges across the plant growth and senescence seasons, demonstrating how such interactions stabilize net primary production and support ecosystem functioning. These insights address a critical gap in understanding the role of sponge-seagrass associations in nutrient cycling, highlighting their significance for the resilience, productivity, and metabolic balance of coastal ecosystems under changing environmental conditions.

Prey must balance the energetic benefits of foraging with avoiding predation risk. This risk-reward trade-off, a cornerstone of behavioural ecology, hinges not only on realized predation risk but also on how prey perceive that risk. We often assume energetically rewarding habitats must be inherently risky because prey often increase their vigilance in these habitats or avoid them altogether. However, our assumption that these antipredator behaviours reflect perceived risk frequently goes untested. We used non-behavioural data to test our assumptions about which habitats prey perceive as risky by pairing observations of habitat use of elk (Cervus canadensis) with their physiological responses measured from faecal hormones: glucocorticoids (GC), which reflect stress from perceived risk and hunger, and triiodothyronine (T3), which increases with energy intake. Elk had lower GC and T3 in the forest, a putatively safer and poorer foraging habitat than cropland, where they produced more T3, indicating foraging. Surprisingly, GC levels were consistent in cropland, even during the daytime when human activity--and putative risk--peaked. This lack of risk responsiveness highlights that physiological responses are a nuanced integration of perceived risk and reward rather than a guaranteed outcome of habitat use. Our study challenges the assumption that high-reward habitats are inherently risky, and that safer habitats limit energy intake, revealing that the assumptions we make about habitats from a behavioural lens may not always be the reality for prey.

Contemporary organisms in extreme environments can give insight into how species will respond to environmental change. The intertidal forms an environmental gradient where stress increases with tidal height. Here, we explore the contribution of fixed genotypic and plastic environmental effects on thermal tolerance of the intertidal anemone Anthopleura elegantissima and its algal symbionts using a laboratory-based tank experiment. High intertidal anemones had lower baseline symbiont-to-host cell ratios under control conditions, but their symbionts had higher baseline maximum quantum yield compared to low intertidal anemone symbionts, despite identical symbiont communities. High intertidal anemones maintained greater maximum quantum yield and symbiont-to-host cell ratios under heat stress compared to low intertidal anemones, suggesting that high intertidal holobionts have greater thermal tolerance. However, thermal tolerance of clonal anemones acclimatized to different zones was not explained by tidal height alone, indicating emersion duration is not the sole environmental driver of physiological variation. Fixed genotypic effects also influenced physiological baselines, but did not modulate thermal tolerance, demonstrating thermal tolerance is largely driven by environmental history. These results indicate that this symbiosis is highly plastic and may be able to rapidly acclimatize to climate change, defying the convention that symbiotic organisms are more susceptible to environmental stress.

Understanding how endotherms manage energy expenditure at sub-thermoneutral temperatures is crucial for predicting their physiological flexibility and adaptive potential. This study investigated the metabolic responses of captive-bred common waxbills (Estrilda astrild) to decreasing ambient temperatures, with a focus on three questions: whether basal metabolic rate (BMR) predicts standard metabolic rate (SMR), how consistent individual metabolic responses are, and whether waxbills employ cold-induced energy-saving mechanisms. We found that BMR did not reliably predict SMR, underscoring the limits of BMR as a proxy under ecologically relevant conditions. SMR showed moderate repeatability across individuals, but variation was mainly due to baseline metabolic level rather than slope differences in thermal reaction norms. A two-breakpoint model best described the relationship between temperature and metabolic rate, with a marked decline in SMR below ~18.8{degrees}C. This decrease, along with observed reductions in core body temperature in some individuals, reveals an energy-saving strategy involving shallow hypothermia at relatively mild sub-thermoneutral temperatures. These findings suggest that energy-saving mechanisms may be intrinsic to the species rather than purely plastic responses. Overall, our results highlight both the limitations of BMR and the importance of measuring metabolic responses across thermal gradients to detect subtle but ecologically relevant hypometabolic strategies.

Animal stoichiometry affects fundamental processes ranging from organismal physiology to global element cycles. However, it is unknown whether animal stoichiometry follows predictable scaling relationships with body mass and whether adaptation to life on land or water constrains patterns of elemental allocation. To test both interspecific and intraspecific body-size scaling relationships of the nitrogen (N), phosphorus (P), and N:P content of animals, we used a subset of the StoichLife database encompassing 9,933 individual animals (vertebrates and invertebrates) belonging to 1,543 species spanning 10 orders of magnitude of body size from terrestrial, freshwater, and marine realms. Across species, body mass did not explain much variation in %N and %P composition, although the %P of invertebrates decreased with size. The effects of body size on species elemental content were small in comparison to the effects of taxonomy. Body size was a better predictor of intraspecific than interspecific elemental patterns. Between 42 to 45% in intraspecific stoichiometric variation was explained by body size for 27% of vertebrate species and 35% of invertebrate species. Further, differences between organisms inhabiting aquatic and terrestrial realms were observed only in invertebrate interspecific %N, suggesting that the realm does not play an important role in determining elemental allocation of animals. Based on our analysis of the most comprehensive animal stoichiometry database, we conclude that (i) both body size and realm are relatively weak predictors of animal stoichiometry across taxa, and (ii) body size is a good predictor of intraspecific variation in animal elemental content, which is consistent with tissue-scaling relationships that hold broadly across large groups of animals. This research reveals a lack of general scaling patterns in the elemental content across animals and instead points to a large variation in scaling relationships within and among lineages.

Social context can modify the behaviour of animals, influencing how they interact with their environment - potentially cascading to effects on ecosystem functions. However, typical proxies for functions, such as biomass or densities, may not completely capture this behavioural variation. We examined how grouping behaviour of an abundant parrotfish species, Chlorurus sordidus, influences the critical function of herbivory on coral reefs in the Lakshadweep Archipelago and evaluated the role of density-dependence and territorial aggression from competitors in driving group formation in the entire herbivorous fish assemblage. Feeding rates increased with group size and decreased with aggressive encounters, with parrotfish in larger groups consuming about 80% more algae per capita than solitary individuals. Group foragers also benefitted marginally from reduced territorial aggression from competing herbivores. The propensities of herbivores to form groups, and their group sizes were positively density dependent, and, to a lesser extent, were driven by access to resources defended by territorial competitors. Our study highlights the importance of incorporating behavioural variation in assessments and predictive frameworks of ecosystem functioning. As our results indicate, for social animals, key ecosystem functions are particularly sensitive to animal densities and interspecific interactions, especially when individual function varies with social context.

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.

Variation in defense traits likely depends on access to different resources and risk from herbivory. Plant defense theories have predicted both positive and negative associations between defense traits and access to resources, but relatively few studies have explored intraspecific variation in defense traits along multiple resource and mammalian herbivory risk gradients. We assessed relationships between herbivory intensity, multiple resources, and plant defense traits using a widely distributed tropical savanna herb, Solanum incanum. As independent measures of risk from large mammal herbivores are rare, we used a satellite-based vegetation index to predict herbivory intensity at the landscape scale. We found that the satellite-based estimate of herbivory intensity was positively associated with browser abundance and total soil P, but negatively associated with rainfall. Intraspecific defense traits too varied substantially across sites (n=43) but only variation in spine density was associated with herbivory intensity and plant resources, such that spine density was positively associated with both rainfall and soil P, but bimodally associated with herbivory intensity. Taken together, it suggests that defenses maybe favored either where resources for defense are abundant under low but still present risk (i.e, at high rainfall sites) or where resource-expensive plant tissue is at high risk (i.e, at high soil P sites). This hints at the possibility of a shift from a resource-associated (bottom-up) to an herbivory-associated (top-down) control of allocation to defenses along an environmental gradient. Additionally, the independent effect of soil P on a carbon-based defense, spine density, suggests potential for resources that are not components of defenses to also influence allocation to defense traits. Thus, our study provides evidence for the influence of multiple drivers, resources, and herbivory intensity, on anti-herbivore defenses and their shifting relative importance on allocation to defenses along an environmental gradient.

Body size has been used thoroughly in arthropod ecology as a reliable trait to assess fitness responses to changes in environmental factors. Among these, spiders represent a large and diverse group, colonizing almost all terrestrial habitats. Here, we propose a review on intraspecific body size variation in arthropods over two main macroecological spatial gradients--latitude and elevation--both of high interest in a global warming context. We found that more species with a direct than with an indirect development present a converse Bergmann cline along both gradients. Focusing on spiders, we propose that life history traits such as voltinism, mobility, and brood care influence intraspecific body size patterns--potentially hiding large-scale patterns. Further, we assessed interspecific sexual size dimorphism (SSD) in spider species. We found that extreme SSD--the most original feature in spider biometry--is influenced by hunting guild rather than phylogeny of spider families, suggesting that ecological factors prevail over evolutionary drivers in shaping SSD.

Individual variation in resource use as well as in the response to competitors has been recognized as playing an important role is species interactions. Still, we have as yet little information on whether such responses have a genetic basis as well as on how they affect each other. Here, we tested whether 20 genetically inbred lines of the spider mite Tetranychus evansi vary in their response to a gradient of cadmium concentration within plants as well as in their propensity to reshape niches when facing interspecific competition along this gradient. In absence of interspecific competitors, most lines were negatively affected by cadmium, albeit often in a non-linear fashion. Morevoer, half of the lines exhibited changes in the curvature of the relationship between number of females and cadmium concentration when facing competition with the congeneric T. urticae. Inbred lines also showed a shallower decay in offspring number along the cadmium gradient in presence of interspecific competition. Our findings provide evidence for large, partly genetic, variation in resource use and in the response to interspecific competition in heterogeneous environments. Moreover, we show that genotype responses to interspecific competition is contingent upon their response to an environmental gradient. Together, our results thus emphasize the importance of considering intraspecific variation in responses to interspecific competition, providing novel insights to link intra- and interspecific levels of biodiversity.

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.