Patrones, procesos y conservación de comunidadesaves acuáticas en una red de humedales artificiales

Resum

The study of communities in ecology has lately acquired more importance because it allows more general and precise evaluations of the species organization patterns and their related processes. In this thesis we have studied the distribution patterns of a waterbird community using artificial irrigation ponds, the processes behind the patterns, and the implications for conservation. As the destruction of natural wetlands advances, several studies have already indicated that artificial wetlands can be used by waterbirds as complementary habitat. In this sense, irrigation ponds also seem to be an important new habitat for waterbirds. The system was exploited by several bird species. Seven species used the ponds to breed, and the abundance of some of these species was higher than in the protected wetlands at the area. Other species bred at the wetlands in the area but used the ponds as a complementary foraging area, which may be important for some of the species. The ponds were used year-round, but there were some seasonal differences in the composition of the community. The community was rich, but the general diversity was low. The waterbirds using the ponds behave as a metacommunity where each pond could be assimilated to an individual habitat patch. We found that the distribution of the species was related to the spatial configuration of the ponds, to the habitat characteristics and to the social information provided by heterospecifics. The importance of each variable depended on the focal species, but there were some general patterns. As predicted by the Island Biogeography Theory, both patch size and isolation degrees were important factors determining the configuration of the community. Big low-isolated patches were more prone to be colonized and had lower extinction rates. The habitat structure also influenced the species distribution pattern. The presence of different types of vegetation, ultimately related with the food availability, were one of the most important variables. Nevertheless, the construction design of the ponds (related to the naturalization degree and the shore slope) was in general the variable that had a higher effect on the community. Both structural and environmental features were also behind the nested pattern of the community. The community was nested every year and season, but the causes of the pattern varied in time, mainly seasonally. Therefore, the studies analyzing nestedness should try to include information about more than one snapshot. Facilitation interactions between species were dominant in the community. Both breeding and foraging waterbirds used heterospecifics to evaluate the quality of the habitat and co-occurred more often than expected by random. These results seem to confirm the Heterospecific Attraction Hypothesis, even though these analyses were performed with observational data and causal inference should be confirmed with manipulative experiments. The information about the processes behind the distribution patterns of the community may also be useful for conservation purposes. As the distribution of the species depends on the habitat characteristics, a correct management of the ponds may enhance their value as breeding and foraging habitat for waterbirds. We also evaluated several management projects in the network of natural and artificial wetlands at the study area. We developed a cost-effectiveness evaluation protocol which included information on both the biology of the species and the economic cost of the projects. We tried to find a trade-off between sophistication and practicality. The protocol prioritized the projects in the most important wetlands of the network.