RESUMEN
Animal species often show substantial intraspecific trait variability (ITV), yet evidence for its flexibility across multiple ecological scales remains poorly explored. Gaining this knowledge is essential to better understand the different processes maintaining ITV in nature. Due to their broad geographic ranges, widespread invasive species are expected to display strong phenotypic variations across their distribution. Here, we quantified the scale-dependent patterns of morphological variability among invasive populations of two global freshwater invaders-red swamp crayfish Procambarus clarkii and pumpkinseed sunfish Lepomis gibbosus-both established in American and European lakes. We quantified patterns in body morphology across different ecological (Individual and Population) and spatial scales (Region). We then analyzed the scale-dependency of morphological variations among lake populations that span a diversity of abiotic and biotic conditions. Next, we used stable isotope analyses to test the existence of ecomorphological patterns linking morphology and trophic niche of individuals. We found that trait variations mainly accounted for at the regional and individual levels. We showed that populations of both species strongly differed between United States and Europe whereas habitat characteristics had a relatively minor influence on morphological variations. Stable isotope analyses also revealed that ecomorphological pattern for the trophic position of L. gibbosus was region-dependent, whereas no ecomorphological patterns were observed for P. clarkii. Overall, our study strongly supports the notion that the patterns of phenotypic variability among invasive populations are likely to modulate the ecological impacts of invasive species on recipient ecosystems.
Asunto(s)
Ecosistema , Especies Introducidas , Animales , Astacoidea , Europa (Continente) , LagosRESUMEN
Intraspecific trait variability is now well recognized as a key component of biodiversity explaining how individuals within a species can differentially interact with their environment. To date, however, this concept has rarely been incorporated in the study of biological invasions, despite its provision of new insights into invasive species management. Here, we used an experimental approach to investigate how invasive red swamp crayfish (Procambarus clarkii) derived from geographically close ecosystems can differentially impact prey community structure and relevant ecosystem processes. We also compared the magnitude of the effects induced by invasive species introduction with those induced by intraspecific variability. Our results showed that effects of intraspecific variability can be strong for direct interactions such as resource (e.g., leaf litter, snails) consumption and of similar magnitude to the effects induced by the introduction of the invasive species when considering indirect interactions (e.g., primary production, ecosystem metabolism). Overall, these results highlighted that invasive populations of the same species are not ecologically equivalent, with each population acting differently on their recipient ecosystem.
Asunto(s)
Ecosistema , Especies Introducidas , Animales , Astacoidea , Biodiversidad , Hojas de la PlantaRESUMEN
Environmental changes and ecological disturbances can have large and unpredictable effects on parasite dynamics. Increasing human impacts on freshwater ecosystems through land use may thus modify the distribution and abundance of parasites and have cascading effects on host populations. Here we tested the effects of small-scale riparian forest management on the nematode Cystidicoloides ephemeridarum and its insect intermediate host Ephemera danica in forested streams. We assessed the impacts of harvesting riparian trees on parasite prevalence and abundance concomitantly with host densities. We also looked at upstream and downstream reaches to document potential cascading effects on unaltered stream sections mediated by aerial dispersal of adult mayfly or downstream drift of E. danica larvae. We show that host densities and parasite levels (prevalence and abundance) increased significantly following riparian tree removal. Overall, parasite densities showed a 6- to 66-fold increase in harvested reaches compared to upstream, pristine reaches. Similar effects were also clear downstream of the disturbance. Thus, despite the small extent of riparian forest alteration along the study streams, both parasite and intermediate host were strongly affected. Small-scale riparian forest management may thus have large, unforeseen impacts on some aspects of freshwater ecosystem structure and functioning that are often ignored. Generally, understanding how human perturbations influence parasites is vital when trying to predict overall impacts on ecosystem structure and functioning, and how changes in infection dynamics may further affect host species.
Asunto(s)
Conservación de los Recursos Naturales/métodos , Agricultura Forestal , Bosques , Insectos/parasitología , Nematodos/fisiología , Ríos , Animales , Interacciones Huésped-Parásitos , LarvaRESUMEN
A one-year study of rotavirus prevalence was carried out using electron microscopy in Gabon, equatorial Africa. One hundred fifty-six nonhospitalized diarrheic children up to 10 years of age and 115 age-matched controls were investigated together with diarrheic adults and children over 10 years of age. Rotaviruses were observed only in diarrheic children under 10 years of age (10.2%). Rotaviruses were more prevalent in the dry-season months (19.2% versus 1.3%, P less than .001). Rotaviruses were the most commonly found among all the viral, bacterial, and parasitic agents we detected, with the exception of the coronaviruslike particles, which are the subject of another paper [Sitbon, 1985].