Evolution of life history traits can occur rapidly and has the potential to infl uence ecological processes, which can also be shaped by abiotic and biotic factors. Few studies have shown that life history phenotype can aff ect ecological processes as much as commonly studied biotic ecological variables, but currently we do not know how the ecological eff ects of life history phenotype compare in size to the eff ects of abiotic factors, or whether the ecological eff ects of phenotypes are sensitive to variability in abiotic conditions. Using a factorial mesocosm experiment we compared the ecosystem eff ects of guppy Poecilia reticulata life history phenotypes in two light treatments representing a four-fold diff erence in light levels, which was comparable to upstream-downstream diff erences in light availability in Trinidadian streams. Light and phenotype had signifi cant eff ects on similar aspects of ecosystem function. Whereas light had a stronger eff ect on ecosystem structure (algal and invertebrate stocks) than phenotype, phenotype and light had nearly equal eff ects on many ecosystem processes (nutrient recycling, nutrient fl uxes, ecosystem metabolism and leaf litter decomposition). Light had a stronger eff ect on most guppy life history traits and guppy fi tness than diff erences between phenotypes. Th e eff ect of light on these traits was consistent with higher availability of food resources in the high light treatments. Interactions between light and phenotype were weak for the majority of response variables suggesting that abiotic variability did not alter the mechanisms by which phenotypes aff ect ecosystem function. We conclude that subtle phenotypic diff erences in consumers can aff ect ecosystem processes as much as meaningful variability in abiotic factors which until recently were thought to be the primary drivers of ecosystem function in nature. However, despite its eff ects on traits and the ecosystem, light did not alter the eff ect of guppy phenotype on ecosystem function.
Abstract. Chambers are the most common method used to sample soil-atmosphere fluxes of trace gases. Working in tree plantations in Costa Rica and in subtropical forest in Puerto Rico, we performed controlled experiments in order to evaluate whether installation of the chamber bases into the soil affects the soil-atmosphere flux of nitrogen oxides. Installation of chambers severed roots. We found a short-term disturbance effect related to chamber installation. Fluxes of nitrogen oxides increased by as much as a factor of 4 during a period of about 1 month following chamber installation in the soil. Within 6 weeks of chamber base installation, fluxes fell to control levels. Given the timescale of disturbance and recovery, root mortality and decomposition is the most likely cause of the observed effect.
Ecological research has focused on understanding how changes in consumer abundance affects community structure and ecosystem processes. However, there is increasing evidence that evolutionary changes in consumers can also alter community structure and ecosystem processes. Typically, the effects of consumer phenotype on communities and ecosystem processes are measured as net effects that integrate numerous ecological pathways. Here, we analyze new data from experimental manipulations of Trinidadian guppy Poecilia reticulata presence, density and phenotype to examine how effects on the algal community cause changes in gross‐primary production (GPP). We combine analytical tools borrowed from path analysis with experimental exclosures in mesocosms to separate the ecological and evolutionary effects of guppies into direct and indirect components. We show that the evolutionary effects of guppy phenotype act through different ecological pathways than the effects of guppy presence and density on GPP. As reported in previous studies that used a different measure of algal biomass, adding guppies and doubling their densities decreased algal biovolume through direct effects. In contrast to these previously reported results, exchanging guppy phenotypes that live without predators for phenotypes that live with predators did not affect algal biovolume. Instead, guppies from populations that live with predators increased the diversity of algal species and increased GPP compared to guppies that live without predators. These changes in the algal community were driven primarily by guppy phenotypes that live with predators—algal communities in mesocosms without fish were similar to those with guppies from predator‐free locations, but both were different from mesocosms with guppies from populations that live with predators. Changes in the algal community were driven directly by differences in foraging behavior between the two consumer phenotypes. We reconcile these results with our previous findings, thereby enhancing our understanding of the relationship between ecological and evolutionary processes.
L'exploitation de bois d'oeuvre continue à augmenter l'étendue des forêts tropicales surexploitées. Elles ne sont pas économiquement attractives du fait de la perte d'espèces commercialisables et du long délai à prévoir pour leur reconstitution. En dépit de ceci, le bois au sein des forêts intensément parcourues par l'exploitation est à même d'offrir des perspectives de commercialisation, compte tenu de la demande et de l'accès de plus en plus difficile aux zones de forêts intouchées. Dans une forêt jadis surexploitée de Puerto Rico, ont été identifiés des arbres de valeur bien conformés n'ayant pas atteint l'âge de maturité. Ils s'avèrent ubiquistes et se trouvent tout au long des contreforts d'une montagne, indifféremment sur des surfaces concaves ou convexes avec des pentes abruptes ou faibles et protégées ou non des vents dominants. En général, la forte productivité des arbres est la conséquence d'une situation favorable vis-à-vis des arbres concurrents, de l'exposition ou de la taille du houppier. Un quart de ces arbres, en principe en suffisance pour un second prélèvement, sont à l'origine d'une production qui s'avère être le double de celle du reste du peuplement, atteignant ainsi la taille d'exploitabilité en deux fois moins de temps. La valorisation de ce potentiel serait à même d'éviter la conversion inconsidérée des forêts, ainsi parcourues par l'exploitation, à d'autres utilisations des terres. (Résumé d'auteur)
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