Ecological contributions of small waterbodies to animal biodiversity in a Mediterranean semiarid region

Resum

In the last decades, the biodiversity associated to freshwater ecosystems has experienced a more marked decline than the biota inhabiting terrestrial or marine environments. Among the different types of freshwater ecosystems, small waterbodies are of particular interest due to their great contribution to the total water surface on the earth. However, the potential of small waterbodies for supporting biodiversity has not been recognized until some years ago. Today, there is a broad scientific consensus on the important role of small waterbodies to maintain freshwater biodiversity at local and regional scale. Nevertheless, several aspects related to their importance for terrestrial wildlife remain unexplored, as well as their potential for replacing natural ponds in our future human-dominated landscapes. The main objective of this PhD thesis is to assess the potential of small waterbodies to be used by animal communities (especially terrestrial birds) in semiarid regions. For that purpose, 39 small waterbodies distributed along the Province of Murcia (SE Spain) were surveyed, belonging to three traditional typologies: drinking troughs, cattle ponds and traditional artificial pools. Bird surveys were conducted through direct observation within a portable hide and encompassing three visits within the same breeding period (April-July). Surveys began at sunrise, lasted three hours and all birds observed within a 10-m buffer around each waterbody were recorded. Mist-netting and conventional video cameras were also used as alternative survey methods to direct observation, in order to compare the effectiveness of different techniques to detect bird species at small waterbodies. Moreover, traditional lineal transects (1 km) were conducted around each waterbody in order to get a representative picture of the terrestrial breeding bird community inhabiting the surrounding landscape. Additionally, breeding amphibians and freshwater macroinvertebrates were also inventoried for each waterbody through dip netting. As a complement to these data on aquatic communities, similar information already available for small waterbodies from France and Switzerland was also used. Direct observation and the combined method of direct observation plus video cameras yielded greater estimates than mist-netting for detecting bird species associated to small waterbodies. Thus, both observational methods provided more representative data than mist netting on the bird use of small waterbodies. A total of 80 bird species were recorded making use of the studied small waterbodies. Drinking troughs supported the higher estimated terrestrial bird richness, followed by cattle ponds and traditional artificial pools. A positive relation was observed between bird richness and environmental heterogeneity. Cattle ponds were particularly important for threatened and conservation concern species. The three types of traditional small waterbodies were used, on average, by the 71% of the terrestrial bird species inhabiting the surrounding landscape, thus highlighting the great importance of these small habitats for terrestrial wildlife at local scale. In relation to aquatic communities, different types of artificial waterbodies made a complementary contribution to the regional richness of amphibians, water beetles and aquatic snails. On average, artificial waterbodies supported the 50% of the regional richness of the three animal groups, thus highlighting artificial waterbodies make a moderate contribution to the freshwater biodiversity at regional scale. However, a greater richness of aquatic taxa was found for natural ponds located in the same region than the studied artificial waterbodies. Therefore, artificial waterbodies could not compensate the loss of natural ponds in future human-dominated landscapes.