Theory suggests evolutionary change can significantly influence and act in tandem with ecological forces via ecological-evolutionary feedbacks. This theory assumes that significant evolutionary change occurs over ecologically relevant timescales and that phenotypes have differential effects on the environment. Here we test the hypothesis that local adaptation causes ecosystem structure and function to diverge. We demonstrate that populations of Trinidadian guppies (Poecilia reticulata), characterized by differences in phenotypic and population-level traits, differ in their impact on ecosystem properties. We report results from a replicated, common garden mesocosm experiment and show that differences between guppy phenotypes result in the divergence of ecosystem structure (algal, invertebrate, and detrital standing stocks) and function (gross primary productivity, leaf decomposition rates, and nutrient flux). These phenotypic effects are further modified by effects of guppy density. We evaluated the generality of these effects by replicating the experiment using guppies derived from two independent origins of the phenotype. Finally, we tested the ability of multiple guppy traits to explain observed differences in the mesocosms. Our findings demonstrate that evolution can significantly affect both ecosystem structure and function. The ecosystem differences reported here are consistent with patterns observed across natural streams and argue that guppies play a significant role in shaping these ecosystems.ecological-evolutionary feedbacks | intraspecific variation | ecosystem function E cosystem ecologists commonly view populations as homogeneous biomass pools in which individuals operate in identical ways to influence nutrient and energy flows (1). Individual organisms can influence ecosystem processes by altering their body size (material storage), changing their consumption and excretion characteristics (material flux) (2), modifying their internal stoichiometry (3), or physically altering their habitat (4, 5). Differences among individuals can, via natural selection, become converted into differences among populations and, hence, in the impact of a locally adapted population on the structure of its ecosystem. Furthermore, empirical evidence suggests the evolution of organismal traits that can affect habitat utilization happens on timescales similar to ecological processes (6). One possible consequence of rapid evolutionary change is that it can change ecological dynamics and set up feedbacks between ecological and evolutionary processes (7-9). Central to this hypothesis is the assumption that phenotypic variation translates into variation in how individuals and populations impact their environment (10).Prior research has already established the links between ecology and evolution. Laboratory studies focused on a model predator-prey interaction demonstrated that evolution of the prey population significantly altered the nature of predator-prey cycles (9). Evidence from natural or seminatural settings have shown t...

Evolution has been shown to be a critical determinant of ecological processes in some systems, but its importance relative to traditional ecological effects is not well known. In addition, almost nothing is known about the role of coevolution in shaping ecosystem function. Here, we experimentally evaluated the relative effects of species invasion (a traditional ecological effect), evolution and coevolution on ecosystem processes in Trinidadian streams. We manipulated the presence and population-of-origin of two common fish species, the guppy (Poecilia reticulata) and the killifish (Rivulus hartii ). We measured epilithic algal biomass and accrual, aquatic invertebrate biomass, and detrital decomposition. Our results show that, for some ecosystem responses, the effects of evolution and coevolution were larger than the effects of species invasion. Guppy evolution in response to alternative predation regimes significantly influenced algal biomass and accrual rates. Guppies from a high-predation site caused an increase in algae relative to guppies from a low-predation site; algae effects were probably shaped by observed divergence in rates of nutrient excretion and algae consumption. Rivulus-guppy coevolution significantly influenced the biomass of aquatic invertebrates. Locally coevolved populations reduced invertebrate biomass relative to non-coevolved populations. These results challenge the general assumption that intraspecific diversity is a less critical determinant of ecosystem function than is interspecific diversity. Given existing evidence for contemporary evolution in these fish species, our findings suggest considerable potential for ecoevolutionary feedbacks to operate as populations adapt to natural or anthropogenic perturbations.

Summary1. Ecological stoichiometry expresses ecological interactions as the balance between multiple elements. It relates the ecological function of organisms to their elemental composition, or their organismal stoichiometry. Organismal stoichiometry is thought to reflect elemental investments in life history and morphology acting in concert with variability in abiotic or environmental conditions, but the relative contribution of these factors to natural variability in organismal stoichiometry is poorly understood. 2. We assessed the relative contribution of stream identity, predation, body size and sex to the organismal stoichiometry of guppies (Poecilia reticulata) in six streams in Trinidad. In this system, guppy life-history phenotype evolves in response to predation. Guppies adapted to highpredation (HP) pressure grow faster, mature earlier, produce fewer and smaller offspring and eat a higher-quality diet than guppies adapted to low-predation (LP) pressure. This pattern of lifehistory evolution is repeated in many rivers encompassing a wide range of abiotic conditions. 3. Organismal stoichiometry of guppies was widely variable, spanning up to $70% of the range of variability reported across freshwater fish taxa. Streams from where guppies were sampled were the most important predictor of organismal stoichiometry. In many cases, guppy populations from sites within the same stream varied as much as from sites in different streams. 4. Surprisingly, predation regime was a minor predictor of % C, C : P and C : N in female guppies, despite its strong correlation with life-history phenotype and other organismal traits in this species. Body size and sex were not significant predictors of organismal stoichiometry. 5. Guppies from HP sites were more stoichiometrically balanced with their diets than guppies from LP sites. The latter appeared to be more vulnerable to phosphorus limitation than the former, suggesting that dietary specialization associated with guppy life-history phenotype may have stoichiometric consequences that can affect guppy physiology and nutrient recycling. 6. Our findings suggest that local environmental conditions are a stronger predictor of organismal stoichiometry than organismal traits. We recommend that future work should explicitly consider correlations between organismal traits and organismal stoichiometry in the context of environmental heterogeneity.

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