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...

Ecosystem engineering - the physical modification of habitats by organisms - has been proposed as an important mechanism for maintaining high species richness at the landscape scale by increasing habitat heterogeneity. Dams built by beaver (Castor canadensis) dramatically alter riparian landscapes throughout much of North America. In the central Adirondacks, New York, USA, ecosystem engineering by beaver leads to the formation of extensive wetland habitat capable of supporting herbaceous plant species not found elsewhere in the riparian zone. We show that by increasing habitat heterogeneity, beaver increase the number of species of herbaceous plants in the riparian zone by over 33% at a scale that encompasses both beaver-modified patches and patches with no history of beaver occupation. We suggest that ecosystem engineers will increase species richness at the landscape scale whenever there are species present in a landscape that are restricted to engineered habitats during at least some stages of their life cycle.

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Ecological stoichiometry offers a framework for predicting how animal species vary in recycling nutrients, thus providing a mechanism for how animal species identity mediates ecosystem processes. Here we show that variation in the rates and ratios at which 28 vertebrate species (fish, amphibians) recycled nitrogen (N) and phosphorus (P) in a tropical stream supports stoichiometry theory. Mass‐specific P excretion rate varied 10‐fold among taxa and was negatively related to animal body P content. In addition, the N : P ratio excreted was negatively related to body N : P. Body mass (negatively related to excretion rates) explained additional variance in these excretion parameters. Body P content and P excretion varied much more among taxonomic families than among species within families, suggesting that familial composition may strongly influence ecosystem‐wide nutrient cycling. Interspecific variation in nutrient recycling, mediated by phylogenetic constraints on stoichiometry and allometry, illustrates a strong linkage between species identity and ecosystem function.

Prochilodus mariae (Characiformes: Prochilodontidae) is a detritivorous fish distributed throughout the Orinoco river basin of South America. Spectacular migrations of these fishes occur at the end of the rainy season into the Andean foothills. Prochilodus ingest large quantities of sediments and may thereby modify habitats in neotropical streams. The major objectives of this study were (1) to explore experimentally the importance of Prochilodus in structuring a tropical stream in the Venezuelan Andean piedmont, and (2) to determine whether there was sufficient ecological redundancy in a diverse and abundant assemblage of epibenthic fishes to compensate for the removal of Prochilodus. Community structure was compared among three experimental treatments: (1) Prochilodus exclusion, (2) Prochilodus enclosure, and (3) the natural fish assemblage. Selective exclusion of Prochilodus resulted in striking changes in community structure as measured by patterns of sediment accrual and the composition of algal and invertebrate assemblages. Highly significant increases in total dry mass and in ash—free dry mass of sediments accruing on stream—bottom substrates were observed almost immediately following the exclusion of Prochilodus. Moreover, the composition of algal and invertebrate assemblages was significantly modified by Prochilodus. Taxa such as diatoms were reduced in number when Prochilodus was present; in contrast, Prochilodus appeared to facilitate nitrogen—fixing cyanobacteria. Total invertebrate densities were greatest in the Prochilodus removal treatment; however, a variety of responses to the experimental treatments was observed among different taxa analyzed individually, including density reductions, increases, and no measurable effects. This study suggests that the detritivore Prochilodus is a functionally dominant species in Andean foothill streams via sediment—processing activities. Moreover, it provides little evidence to support the notion that strongly interacting species are limited to simple systems with few food web components.