Resource Gradients Research Articles

Selection of Vegetation Greenness by Nyala Antelopes on a Resource Productivity Gradient

Geographic gradients in plant productivity can present foraging large herbivores with varying resource levels across the range of a population, to which individuals can demonstrate varying intensity of selection. To investigate individually-specific responses of nyala antelopes (Tragelaphus angasii ) to vegetation greenness, we monitored the landscape use of eight telemetry-collared adult females, half at the wetter end and half at the drier end of Hluhluwe–iMfolozi Park, South Africa. We used remotely-sensed greenness as an index for plant productivity and data on canopy structure, and we compared the strength of selection for greenness between animals having different greenness averages within their home ranges. We found a decreasing pattern between home-range average greenness and strength of selection, which depended on season and presence of tree canopies. Animals in low-greenness home ranges tended to have stronger positive selection in closed-canopy vegetation in the dry season; those in high-greenness home ranges tended to have the stronger negative selection in open-canopy vegetation in the wet season. Our study emphasizes the possibility that a spatial resource gradient on a landscape might provide a valuable model of temporal change in a resource and an indication of potential for foraging animals to adapt to those changes.

The success of alien plants in an arid ecosystem: Structural equation modeling reveals hidden effects of soil resources

AbstractThe diversity of a native community is not the sole driving factor determining the success of an invader; abiotic factors can also play a role, making it important to understand their contributions in modifying the expected outcome of biotic and abiotic resistance to invasion. In order to test the contributions of native diversity, relatedness between native and alien plants, and abiotic factors in resisting alien invasion, we used a trait–environment data set of 33 alien‐ and 130 native plants in 166 invaded plots, covering a gradient of soil resources in Saint‐Katherine‐Protectorate, an arid‐protected area in Egypt. We measured the native diversity components as predictors of native biotic resistance. We quantified the success of alien plants based on their abundance and their performance traits. Additionally, we calculated the mean functional and phylogenetic distance between aliens and natives in each plot. We tested all plausible influences of native diversity components, relatedness, and soil resources on alien abundance and performance first using mixed‐effects models and second with a structural equation model (SEM). Mixed‐effect models revealed that, in the resource‐rich environments, alien abundance increased even though native plants were more productive, but alien performance decreased. SEM direct pathways revealed that native communities with high functional dispersion and richness and high mean‐weighted performance traits repelled alien plants by lowering their success. Simultaneously, in line with mixed‐effect models results, the effect of soil resources on alien success was found to be indirect, being mediated by the mean functional and phylogenetic distance between aliens and natives: The success of alien plants increased in resource‐rich environments when they were dissimilar to the natives, while it decreased for aliens similar to natives in resource‐limited environments. Our findings provide new insights on native community resistance to invasion, with resistance being higher in resource‐limited environments and when aliens are functionally and phylogenetically similar to resident natives.

Competition drives the evolution of emergent neutrality in the dietary niches of mammalian herbivores

The coexistence of multiple species competing for a finite set of resources is a widely debated topic in community ecology. Species with strongly overlapping niches are expected to drive each other towards exclusion, but such species may also coexist if they have similar competitive abilities. This compromise can lead to a peculiar pattern of clumped coexistence, where multiple species share similar niches, leaving gaps open in the theoretically available niche space. Large mammal herbivores may be a good example of this, where species' dietary niches clump as either grazers, browsers, or intermediate-feeders, rather than being continuously distributed over the resource gradient. Here, we develop a model of such emergent neutrality amongst species competing for a set of predefined resources each distributed along a finite niche axis. The model is commensurate with stable isotope niches, thus allowing us to compare its predictions with empirical evidence for changes in community niche structure over evolutionary time. We present stable carbon and oxygen isotope evidence for six discontinuous Late Quaternary assemblages from the central interior of South Africa, demonstrating the emergence of a clumped niche structure from an initial pattern of strongly overlapping diets. We show that species tend to cluster on parts of the niche axis where resource availability is highest, mirroring the proliferation of grazer species as landscapes became more grass-dominated. However, the presence of competition means that species’ niches continue to differentiate, explaining the persistence of browser and intermediate-feeder species even in these open, predominantly treeless landscapes. These results highlight that species interactions are a necessary factor for robust inferences about the evolutionary dynamics of palaeocommunities.

Large herbivore-palm interactions modulate the spatial structure of seedling communities and productivity in Neotropical forests

Top-down control by large herbivores is a well-known driver of plant diversity structure and productivity. Yet, for forest ecosystems the sign and magnitude of herbivore control across resource gradients is not well understood. We conducted a series of replicated large herbivore exclusion experiments in defaunated and non-defaunated Atlantic forests of Brazil to evaluate the effects of large herbivores on tropical plant communities. We hypothesized that the top-down impact of large herbivores on seedling recruitment, species richness, diversity and productivity would change across a natural gradient in the density of a key plant resource, the palm Euterpe edulis, which is thought to act as a foundation species. We found both positive (agonistic) and negative (antagonistic) spatially-structured effects of large herbivores on plant communities driven by an interaction between large herbivores and palm density on non-defaunated sites, but not on defaunated sites. Indeed, through its interaction with large herbivores, palm trees were able to regulate the spatial structure of seedling communities. In the non-defaunated forest, the negative impact of large herbivores on plant recruitment and species richness decreased substantially as palms became more abundant and canopy cover decreased. Furthermore, large herbivores caused a 185% increase but a 194% decrease in aboveground seedling productivity in areas of high and low palm density, respectively. In contrast, in the defaunated forest we did not find any consistent large herbivore impacts on plant recruitment or species richness across the gradient of palm density, and herbivore activity consistently had negative effects on seedling productivity. Analyses using camera trap data indicate that white-lipped peccaries (Tayassu peccari) played a key role in modulating recruitment and seedling productivity, while tapirs (Tapirus terrestris) contributed significantly to an increase in plant diversity, hence playing a functionally complementary role. Our results demonstrate that a key interaction between large forest-dwelling tropical herbivores and their palm resource results in landscape-scale modulation of plant communities through positive and negative spatially-structured feedbacks, and support the view that palms might act as foundation species in tropical forests. Anthropogenic pressures posed by defaunation and illegal palm harvesting in the Neotropics might lead to the functional loss of this interaction and the collapse of the spatial structure along palm density gradients, with cascading effects on the dynamics and productivity of tropical forests.

Interplay of above‐ and belowground resource limitations: a competition–facilitation shift maintains species coexistence

Forest ecosystems are commonly characterised by a hierarchy of resources. During a disturbance of a forest community, increased light availability in the understorey can support competitive interactions at the expense of facilitation. This may overwhelm the role of belowground resource heterogeneity in maintaining species coexistence and so result in biotic homogenisation of a site. We re‐surveyed species composition while estimating interspecific interactions along a microtopographic (moisture) gradient of a temperate swamp forest after increasing the availability of light into the undergrowth. We measured temporal changes in species diversity, compositional dissimilarity measures and functional traits, while belowground resource heterogeneity remained unchanged over time. To explain observed changes in terms of prevailing interspecific interactions, we evaluated temporal changes in the competition–facilitation balance. The productivity of understorey vegetation increased strongly over the five years of the study. This was accompanied by an increase in species diversity and the maintenance of compositional dissimilarity. The relative importance of competitive and facilitative interactions along the microtopographic gradient did not change over time. Rather than an overall biotic homogenisation of a site, we observed a spread of resource acquisitive species within the resource‐rich sites and of stress‐tolerant species within the resource‐limited sites. We have shown that the temporary increase in productivity did not mitigate the effects of belowground resource heterogeneity on plant species turnover, which is likely maintained by contrasting interspecific interactions prevalent in different parts of the resource gradient. This suggests contrasting community assembly processes maintain diversity and productivity even in a local community.

Temporal variation in the niche partitioning of Lake Michigan salmonines as it relates to alewife abundance and size structure

Stable isotope analyses offer a useful means for quantifying ecological niche dimensions, though few studies have examined isotopic response of an ecological community with respect to resource gradients such as fluctuations in prey availability. Stable carbon and nitrogen isotopes were measured for Lake Michigan salmonines and their prey collected from 2014 to 2016. Bayesian ellipse and mixing model analyses were used to quantify isotopic niche characteristics and diets, respectively, among species and years. During the 3-year study period, abundance and size structure of preferred alewife (Alosa pseudoharengus) prey changed substantially and offered an opportunity to explore predator isotopic niche response and diet shifts along a prey resource gradient. Results suggested increased reliance on alewives, especially small alewives, over the study period and were consistent with greater availability of this prey. However, differential use of alewife size classes and alternative prey sources by salmonine predators was apparent, which suggested possible resource partitioning. Characterization of ecological niche overlap using stable isotopes likely requires consideration of shared resource availability as well as specific prey and habitat preferences.

Empirical survival model for European beech (Fagus sylvatica L.) seedlings in response to interactive resource gradients and (a-) biotic conditions within an experimental canopy gap study

The success of beech regeneration depends on resource availabilities, which are both heterogeneously distributed in forests and influenced by climate change impacts such as drought and heat waves. To ensure beech regeneration success in the future, it is therefore of great interest to understand the influences of different resource availabilities and their potentially interactive effects on beech seedling survival. In an experimental canopy gap study, we investigated the effects of direct (DIRSF) and diffuse (DIFFSF) solar radiation, soil fertility, groundwater influence, micro-site elevation, vegetation and root competition of overstorey trees on the survival of beech seedlings two years after planting in 2017. The inverse of fine root densities found for overstorey beech (BGRB) and oak (BGRO) was interpreted here as an approximation of the availability of below ground resources, mainly soil water. A logistic model demonstrated positive and interactive effects of DIFFSF, BGRB and soil fertility, emphasizing the complementary resource use pattern of beech seedlings. DIRSF showed a negative effect on survival that was enhanced on groundwater-dominated and higher elevated micro-sites and linked to intensified water limitation. The initial stature of seedlings, the presence and biomass of vegetation and BGRO had no significant effects on beech seedling survival. The unexpected extend to which DIFFSF affected beech seedling survival, the given significance of complementary effects of DIFFSF, BGRB and soil fertility, as well as found interactive effects of DIRSF are discussed in the context of the 2018/19 drought event. Our results suggest that silvicultural measures, such as the creation of larger gaps, can significantly improve resource availabilities, providing an opportunity to increase survival of beech seedlings in the face of climate change impacts.

Habitat-dependent effects of predatory spiders on prey frogs in a Neotropical wet forest

AbstractIn seasonal wet Neotropical forests, many studies have suggested that species-rich terrestrial frog assemblages are regulated bottom-up by the abundance of leaf litter. However, terrestrial frogs are prey to a diverse community of predators, and no studies have tested for top-down effects of predators on this or other anuran assemblages. Here, we used an extensive field dataset to model the relative contribution of food resources, microhabitat resources and predators towards the occupancy and detection of two frog species (Craugastor bransfordiiandOophaga pumilio) at La Selva, Costa Rica. Frog occupancy was most strongly influenced by predatory spiders and secondarily influenced by the abundance of leaf litter. Predators exerted stronger effects on frogs than food resources, and frogs avoided predators more as leaf litter decreased. Detection probability was elevated when predators were present. We found support for bottom-up effects of leaf litter on the terrestrial frog assemblage, but top-down effects by predators exerted stronger effects on frog occupancy and detection. Because predator avoidance varied along a resource gradient, predator and resource effects appear to be dependent, supporting interactions between top-down and bottom-up mechanisms. Climate-driven decreases in leaf litter may drive decreased availability of frog refugia and increased interactions between frogs and predators.

Spatial patterning of regeneration failure in experimental canopy gaps 15–24 years post-harvest

Gap-based silviculture and legacy-tree retention are strategies that can increase structural and resource heterogeneity while maintaining forest productivity at the stand scale. Nevertheless, areas of delayed regeneration have been noted in openings with some persisting for a decade or more. To better understand the causes of localized recruitment delay and/or near-term failure, we examined spatial patterning of persistent (≥15 years) patches of regeneration failure (≤1 sapling ≥1.37 m tall per 10 m2) at two long-term experimental gap experiments in northern Wisconsin and the Upper Peninsula of Michigan. During the summers of 2018 and 2019, we surveyed 84 harvest-created canopy gaps for areas of failure and mapped 79 individual patches where regeneration had failed to establish and recruit in a total of 52 openings. Spatial attributes of these individual patches were summarized and compared to their location relative to expected within (e.g., north versus south, distance from edge) and between gap (e.g., gap size) gradients in light resource availability. Spatial analyses revealed no significant trends between north and south regions of gaps, which suggests that regeneration failure at the gap scale is likely determined by factors disentangled from expected within-gap light resource gradients. At the site without legacy-tree retention, patches that had failed to regenerate trees occupied 17.3% of the total area in gaps (≥10 m radius) and were located near gap center. In contrast, at the site with legacy trees, only 4.8% of the total area in gaps (≥11 m radius) was occupied by patches of regeneration failure and patches were located near gap edge. Furthermore, increasing gap size was associated with a higher risk of regeneration failure only at the study site without legacy-tree retention. Our results suggest that legacy-tree retention may moderate the spatial extent of regeneration failure, however, further work is needed to clarify their long-term influence on regeneration dynamics within harvest openings.

Human impacted shallow lakes in the Pampean plain are ideal hosts for cyanobacterial harmful blooms

The ecological status of Pampean shallow lakes is evidenced by Cyanobacteria Harmful Blooms impairing these nutrient enriched, turbid and polymictic water bodies spread along the Central Plains of Argentina. Under the premise that shallow lakes are sentinels of global climate and eutrophication, a 3-year research in ten lakes located across a climatic gradient explored which factors drove the dynamics of cyanobacterial assemblages frequently driving to bloom prevalence. Contrarily to what is expected, the effect of seasonal temperature on cyanobacteria was subordinated to both the light environment of the water column, which was on turn highly affected by water level conditions, and to nutrient concentrations. Monthly samplings evidenced that cyanobacterial assemblages presented a broad-scale temporal dynamics mostly reflecting inter-annual growth patterns driven by water level fluctuations. Both species composition and biovolume gradually changed across a gradient of resources and conditions and hence, the scenario in each individual lake was unique with patterns at different temporal and spatial scales. More than 35 filamentous and colonial morphospecies constituted the assemblages of Pampean lakes: nostocaleans and chroococcaleans were inversely correlated in the prevailing interannual 3-cycled patterns.

Contrasting alien effects on native diversity along biotic and abiotic gradients in an arid protected area

Alien impact on native diversity could be a function of both the relatedness of alien species to native community and resources availability. Here, we investigated whether alien plants expand or decrease the functional and phylogenetic space of native plant communities, and how this is affected by alien relatedness to natives and by resources availability. We used a trait-environment dataset of 33 alien and 130 native plants in 83 pairs of invaded and non-invaded plots, covering a gradient of soil resources (organic matter-nitrogen) in Saint-Katherine-Protectorate, Egypt. First, we compared the changes in native composition and calculated alien relatedness to natives within each pair of plots. Second, we tested the effects of resources availability and relatedness on the magnitude of alien impact (defined as a change in native diversity). We found that native composition was phylogenetically less but functionally more diverse in invaded plots compared to non-invaded ones. Moreover, in resources-rich plots, dissimilar aliens to natives significantly increased native diversity, while in resource-limited ones, similar aliens to natives declined native diversity. These results suggest that the assessment of alien impacts in arid-regions is significantly linked to resources-availability and relatedness to natives. Hence, future studies should test the generality of our findings in different environments.

Conditions for the emergence of circumnutations in plant roots.

The plant root system shows remarkably complex behaviors driven by environmental cues and internal dynamics, whose interplay remains largely unknown. A notable example is circumnutation growth movements, which are growth oscillations from side to side of the root apex. Here we describe a model capable of replicating root growth behaviors, which we used to analyze the role of circumnuntations, revealing their emergence I) under gravitropic stress, as a combination of signal propagation and sensitivity to the signal carriers; II) as a result of the interplay between gravitropic and thigmotropic responses; and III) as a behavioral strategy to detect and react to resource gradients. The latter function requires the presence of a hypothetical internal oscillator whose parameters are regulated by the perception of environmental resources.

Rethinking the Plant Economics Spectrum for Annuals: A Multi-Species Study.

The plant economics spectrum hypothesizes a correlation among resource-use related traits along one single axis, which determines species’ growth rates and their ecological filtering along resource gradients. This concept has been mostly investigated and shown in perennial species, but has rarely been tested in annual species. Annuals evade unfavorable seasons as seeds and thus may underlie different constraints, with consequences for interspecific trait-trait, trait-growth, and trait-environment relations. To test the hypotheses of the plant economics spectrum in annual species, we measured twelve resource-use related leaf and root traits in 30 winter annuals from Israel under controlled conditions. Traits and their coordinations were related to species’ growth rates (for 19 species) and their distribution along a steep rainfall gradient. Contrary to the hypotheses of the plant economics spectrum, in the investigated annuals traits were correlated along two independent axes, one of structural traits and one of carbon gain traits. Consequently, species’ growth rates were related to carbon gain traits, but independent from structural traits. Species’ distribution along the rainfall gradient was unexpectedly neither associated with species’ scores along the axes of carbon gain or structural traits nor with growth rate. Nevertheless, root traits were related with species’ distribution, indicating that they are relevant for species’ filtering along rainfall gradients in winter annuals. Overall, our results showed that the functional constraints hypothesized by the plant economics spectrum do not apply to winter annuals, leading to unexpected trait-growth and trait-rainfall relations. Our study thus cautions to generalize trait-based concepts and findings between life-history strategies. To predict responses to global change, trait-based concepts should be explicitly tested for different species groups.

Range-wide variations in common milkweed traits and their effect on monarch larvae.

Leaf economic spectrum (LES) theory has historically been employed to inform vegetation models of ecosystem processes, but largely neglects intraspecific variation and biotic interactions. We attempt to integrate across environment-plant trait-herbivore interactions within a species at a range-wide scale. We measured traits in 53 populations spanning the range of common milkweed (Asclepias syriaca) and used a common garden to determine the role of environment in driving patterns of intraspecific variation. We used a feeding trial to determine the role of plant traits in monarch (Danaus plexippus) larval development. Trait-trait relationships largely followed interspecific patterns in LES theory and persisted in a common garden when individual traits change. Common milkweed showed intraspecific variation and biogeographic clines in traits. Clines did not persist in a common garden. Larvae ate more and grew larger when fed plants with more nitrogen. A longitudinal environmental gradient in precipitation corresponded to a resource gradient in plant nitrogen, which produces a gradient in larval performance. Biogeographic patterns in common milkweed traits can sometimes be predicted from LES, are largely driven by environmental conditions, and have consequences for monarch larval performance. Changes to nutrient dynamics of landscapes with common milkweed could potentially influence monarch population dynamics. We show how biogeographic trends in intraspecific variation can influence key ecological interactions, especially in common species with large distributions.

Bootstrapped Motion of an Agent on an Adaptive Resource Landscape

We theoretically show that isolated agents that locally and symmetrically consume resources and sense positive resource gradients can generate constant motion via bootstrapped resource gradients in the absence of any externally imposed gradients, and we show a realization of this motion using robots. This self-generated agent motion can be coupled with neighboring agents to act as a spontaneously broken symmetry seed for emergent collective dynamics. We also show that in a sufficiently weak externally imposed gradient, it is possible for an agent to move against an external resource gradient due to the local resource depression on the landscape created by an agent. This counter-intuitive boot-strapped motion against an external gradient is demonstrated with a simple robot system on an light-emitting diode (LED) light-board.

Tree seedling trait optimization and growth in response to local-scale soil and light variability.

At local scales, it has been suggested that high levels of resources lead to increased tree growth via trait optimization (highly peaked trait distribution). However, this contrasts with (1) theories that suggest that trait optimization and high growth occur in the most common resource level and (2) empirical evidence showing that high trait optimization can be also found at low resource levels. This raises the question of how are traits and growth optimized in highly diverse plant communities. Here, we propose a series of hypotheses about how traits and growth are expected to be maximized under different resource levels (low, the most common, and high) in tree seedling communities from a subtropical forest in Puerto Rico, USA. We studied the variation in the distribution of biomass allocation and leaf traits and seedlings growth rate along four resource gradients: light availability (canopy openness) and soil K, Mg, and N content. Our analyses consisted of comparing trait kurtosis (a measurement of trait optimization), community trait means, and relative growth rates at three resource levels (low, common, and high). Trait optimization varied across the three resource levels depending on the type of resource and trait, with leaf traits being optimized under high N and in the most common K and Mg conditions, but not at any of the light levels. Also, seedling growth increased at high-light conditions and high N and K but was not related to trait kurtosis. Our results indicate that local-scale variability of soil fertility and understory light conditions result in shifts in species ecological strategies that increase growth despite a weak trait optimization, suggesting the existence of alternative phenotypes that achieve similar high performance. Uncovering the links between abiotic factors, functional trait diversity and performance is necessary to better predict tree responses to future changes in abiotic conditions.

Cell size influences inorganic carbon acquisition in artificially selected phytoplankton.

Cell size influences the rate at which phytoplankton assimilate dissolved inorganic carbon (DIC), but it is unclear whether volume-specific carbon uptake should be greater in smaller or larger cells. On the one hand, Fick's Law predicts smaller cells to have a superior diffusive CO2 supply. On the other, larger cells may have greater scope to invest metabolic energy to upregulate active transport per unit area through CO2 -concentrating mechanisms (CCMs). Previous studies have focused on among-species comparisons, which complicates disentangling the role of cell size from other covarying traits. In this study, we investigated the DIC assimilation of the green alga Dunaliella tertiolecta after using artificial selection to evolve a 9.3-fold difference in cell volume. We compared CO2 affinity, external carbonic anhydrase (CAext ), isotopic signatures (δ13 C) and growth among size-selected lineages. Evolving cells to larger sizes led to an upregulation of CCMs that improved the DIC uptake of this species, with higher CO2 affinity, higher CAext and higher δ13 C. Larger cells also achieved faster growth and higher maximum biovolume densities. We showed that evolutionary shifts in cell size can alter the efficiency of DIC uptake systems to influence the fitness of a phytoplankton species.

Microgeographic divergence of functional responses among salamanders under antagonistic selection from apex predators.

A predator's functional response determines predator-prey interactions by describing the relationship between the number of prey available and the number eaten. Its shape and parameters fundamentally govern the dynamic equilibrium of predator-prey interactions and their joint abundances. Yet, estimates of these key parameters generally assume stasis in space and time and ignore the potential for local adaptation to alter feeding responses and the stability of trophic dynamics. Here, we evaluate if functional responses diverge among populations of spotted salamander (Ambystoma maculatum) larvae that face antagonistic selection on feeding strategies based on their own risk of predation. Common garden experiments revealed that spotted salamander from ponds with varying predation risks differed in their functional responses, suggesting an evolutionary response. Applying mechanistic equations, we discovered that the combined changes in attack rates, handling times and shape of the functional response enhanced feeding rate in environments with high densities of gape-limited predators. We suggest how these parameter changes could alter community equilibria and other emergent properties of food webs. Community ecologists might often need to consider how local evolution at fine scales alters key relationships in ways that alter local diversity patterns, food web dynamics, resource gradients and community responses to disturbance.

Density dependence and habitat heterogeneity regulate seedling survival in a North American temperate forest

Survival and growth of forest tree seedlings are influenced by many abiotic and biotic forces that may vary across space and time. The simultaneous influences of habitat heterogeneity, temporal environmental variability (including disturbance regimes), and biotic interactions are difficult to disentangle, yet understanding the relative importance of these factors for tree seedling dynamics is critical for conservation of forest biodiversity. Most long term, spatially explicit studies of tree seedling ecology have been set in the tropics; much less attention has been given to tree seedlings in temperate forests. We monitored the survival of over 3000 individual seedlings over an eight-year period in a temperate forest in northeast Wisconsin, USA. Results from four seedling censuses demonstrated that both conspecific density and environmental variables significantly affected seedling survival. Higher densities of conspecific trees consistently reduced the probability of seedling survival over time. At the community level, relatively common species were negatively influenced by neighboring conspecific trees and exhibited higher per capita and per basal area mortality. The negative impacts of high conspecific tree density were most pronounced in areas of higher light and moisture, but these interactions varied over time, as did the importance of other abiotic variables. Patterns of less common species were more clearly explained by abiotic variables, with shifting relevance of specific variables according to species abundance. Conspecific negative density dependence, which interacts with resource gradients, and habitat conditions that shift over time are influencing community composition in this northern temperate forest.

Energetic mechanisms for coping with changes in resource availability

Given current anthropogenic alterations to many ecosystems and communities, it is becoming increasingly important to consider whether and how organisms can cope with changing resources. Metabolic rate, because it represents the rate of energy expenditure, may play a key role in mediating the link between resource conditions and performance and thereby how well organisms can persist in the face of environmental change. Here, we focus on the role that energy metabolism plays in determining organismal responses to changes in food availability over both short-term ecological and longer-term evolutionary timescales. Using a meta-analytical approach encompassing multiple species, we find that individuals with a higher metabolic rate grow faster under high food levels but slower once food levels decline, suggesting that the association between metabolism and life-history traits shifts along resource gradients. We also find that organisms can cope with changing resource availability through both phenotypic plasticity and genetically based evolutionary adaptation in their rates of energy metabolism. However, the metabolic rates of individuals within a population and of species within a lineage do not all respond in the same manner to changes in food availability. This diversity of responses suggests that there are benefits but also costs to changes in metabolic rate. It also underscores the need to examine not just the energy budgets of organisms within the context of metabolic rate but also how energy metabolism changes alongside other physiological and behavioural traits in variable environments.