Determinantes de los ensambles de arbustos del Desierto Costero de Atacama
Species coexistence depends on two non-mutually exclusive assembly processes, the abiotic filter and biotic interactions. The influence of these two processes varies according to the spatial scale, being abiotic filter (e.g., aridity and environmental heterogeneity) more relevant at large spatial sc...
| Autor: | |
|---|---|
| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2019 |
| País: | Chile |
| OAI Identifier: | oai:repositorio.anid.cl:10533/241972 |
| Acceso en línea: | https://hdl.handle.net/10533/241972 |
| Access Level: | acceso abierto |
| Palabra clave: | Ciencias Naturales Otras Ciencias Naturales Ecología |
| Sumario: | Species coexistence depends on two non-mutually exclusive assembly processes, the abiotic filter and biotic interactions. The influence of these two processes varies according to the spatial scale, being abiotic filter (e.g., aridity and environmental heterogeneity) more relevant at large spatial scales; conversely, the effect of biotic interactions (competition and facilitation) is greater at small scales (i.e., among neighbors). The abiotic environment promotes the convergence of traits of species (i.e., species are more similar to each other); meanwhile, competition (limiting similarity) promotes the divergence of traits (i.e., the species are less similar to each other). Facilitation as well as environmental heterogeneity also promote trait divergence, while competition can lead to trait convergence through the exclusion of less competitive species. Furthermore, the influence of biotic interactions varies as a function of environmental changes along gradients. In this sense, the stress dominance hypothesis (SDH) states that, in more benign places, competition dominates, while the abiotic environment is greater in more stressful places. Conversely, the stress gradient hypothesis (SGH) predicts that as stress levels increase, the effect of competition decreases, with facilitation being the dominant process in the places of greatest stress. The assembly processes determine the functional structure of the assemblages (i.e., diversity and average of the traits at the community level), the spatial aggregation patterns of the species, the way of using the resources (i.e., ecological strategies) and, the trait variation patterns at the intra- and inter-specific level; therefore, by determining the patterns of variation of the aforementioned factors at different spatial scales and along gradients, the dominant assembly processes can be inferred. Arid ecosystems are an ideal study system to study assembly processes, since the scarcity, variation and seasonality of water determine all the biological processes of plant species. In this thesis, I evaluated how the abiotic filter (aridity and environmental heterogeneity) and biotic interactions (competition and facilitation) determine the phenotypic structure of shrub assemblages at different spatial scales, in four sites distributed along an aridity gradient in the Coastal Atacama Desert. For this, throughout the gradient, the ecological strategies of shrubs at plant level were determined (Chapter 1), the relative contribution of inter- and intra-specific variability on the functional structure of shrubs at different spatial scales was evaluated. (Chapter 2) and, using null models, the main processes determining shrub assemblages at two spatial scales were inferred (Chapter 3). The results indicate that the increase in aridity, together with the variability and seasonality of rainfall along the gradient, promoted a rapid use of resources and determined the changes in the functional structure of the shrub assemblies, mediated fundamentally by the species turnover (i.e., due to interspecific variation). On the other hand, at the local scale (between different habitats within a particular site), the effect of heterogeneity on plant assemblages was greater in sites with intermediate aridity levels, promoting the aggregation of different species in the best microenvironments. Finally, at the neighborhood scale, the effect of biotic factors (competition and facilitation) was negligible, however, trends indicate that competition either through limiting similarity or by the exclusion of weaker competitors are the dominant assembly process at this scale. The findings of this study generally indicate that the relevance of the abiotic filter and biotic interactions on the assemblies vary with the spatial scale. Conducting experiments could more definitively confirm the findings of this study. |
|---|