Plant dispersal syndromes and diversity patterns in two Macaronesian archipelagos
- Autores: María Leo
- Directores de la Tesis: Ana Margarida Coelho Dos Santos (dir. tes.)
- Lectura: En la Universidad Autónoma de Madrid ( España ) en 2022
- Idioma: inglés
- Número de páginas: 133
- Títulos paralelos:
- Síndrome de dispersión de plantas y patrones de diversidad en dos archipiélagos macaronésicos
- Tribunal Calificador de la Tesis: Amanda Taylor (presid.), Manuel Ruben Garcia Mateo (secret.), Helena Hespanhol (voc.)
- Programa de doctorado: Programa de Doctorado en Biología por la Universidad Autónoma de Madrid
- Materias:
- Enlaces
- Tesis en acceso abierto en: Biblos-e Archivo
- Resumen
Dispersal is an essential part of the colonization process and the establishment of new populations throughout long and short distances. Dispersal processes are particularly relevant in the context of island biogeography, in which islands are often completely isolated from the mainland and organisms have to get through strong dispersal barriers as the sea. In the case of plants, dispersal is often studied using dispersal syndromes as proxies of species dispersal ability. They can be encompassed into three broad categories according to their main dispersal vector: wind in the case of anemochory; water in the case of hydrochory and animals in the case of zoochory, which in turn can be divided into endozoochory if seeds are ingested and excreted afterwards, or epizoochory if dispersal takes place by external attachment to animals’ fur or feathers.
The main goal of this thesis is to understand the role of dispersal in species distribution patterns, using as a case study the native seed plants of two archipelagos, the Azores and the Canary Islands. In this thesis, within the framework of island biogeography, dispersal syndromes are used to study how small-scale dispersal conditions two attributes of the species niche (size and fill), beta diversity and distribution along geographic and environmental gradients.
The ability of a species to track and fill its environmental niche partially depends on its dispersal ability. At small scales, it is possible that the differences in size of a species’ realized and potential niche and the may be explained by dispersal constrains. The results obtained in this thesis showed that dispersal syndromes have little influence on the climatic niche size of plant species in the Azores, as well as on their ability to track and fill their niches. Only endozoochorous species showed significant differences with the other groups, as they had significantly larger niches than anemochorous and epizoochorous species. Also, the size of the potential and realized niche of endozoochorous species were more similar compared with those of hydrochorous and endozoochorous species. This may be because endozoochorous species benefited from a nutrient boost in their germination, which could facilitate having larger niches even when environmental conditions were not entirely favorable, and from directional dispersal between climatically favorable areas through regular birds movements.
Beta diversity patterns can be explained by multiple factors, which may be related to geography, environment, the dispersal ability of the species, among others. In this thesis it is addressed how these three factors affect the turnover component of beta diversity patterns in the Azores. Analyses were performed at three different scales: between islands (large scale), within island (intermediate scale) and within the different habitats of each island (small scale). The habitats evaluuated were natural forests, naturalized vegetation and seminatural pastures. Species turnover increased with decreasing scale, particularly in seminatural pastures. Only animal-dispersed species (endozoochorous and epizoochorous) had an effect on beta diversity. Nevertheless, this effect was minor. In all cases, epizoochorous increased beta diversity, probably due to the randomness associated with this type of dispersal, while endozoochorous contributed to homogenize communities and thus decreased beta diversity. As for other potential factors influencing beta diversity, such as climatic or geographic distance, their effect varied with scale and context. As scale increased, the effect of geographic distance on beta diversity was larger, being significant at all scales. In contrast, climatic distance only had a significant effect on beta diversity at the small and intermediate scales, but the effect was context-dependent at each island and habitat.
Finally, we studied how dispersal syndromes were distributed in the geographic and climatic space of the Azores and the Canary Islands. These two archipelagos have different climates and geological history, which may result in different patterns. As the different evolutionary histories of endemic and non-endemic native plants may lead to different diversity patterns, these two sets of species were studied separately. In both species sets and archipelagos, the distribution of all dispersal syndromes was related to climatic gradients and was not homogeneous in the geographic space. In non-endemic native species, zoochory was the most common syndrome and increased with increasing temperatures and precipitation. Anemochorous and hydrochorous species were more common in dry and warm areas. In the case of endemic species, the pattern was different when compared to non-endemic native species, showing opposite patterns: where non-endemic native species with a certain syndrome were more common, endemic species with that syndrome decreased and viceversa. Autochorous species were the least common in both archipelagos and in both sets of species.These results suggest that the distribution of dispersal syndromes depends not only on characteristics strictly related to the dispersal process but also on the evolutionary origin of the species and the climatic and geographic variations within the islands. Thus, the usefulness of dispersal syndromes as a general proxy for dispersal ability is questionable and results based on them should be interpreted with caution.
Overall, the results of this thesis show that the role of dispersal in small-scale species distribution patterns is not yet fully elucidated. Also, plant dispersal syndromes do not seem to be the best approach to study dispersal-dependent processes, being therefore necessary to use other methods to understand how dispersal conditions the distribution of plant diversity.
