Functional Diversity of Iberian Waterbird Communities From Natural Lakes and Man-Made Reservoirs Shows Divergent Temporal Dynamics

Abstract

Aims

Artificial waterbodies are widely recognized as vital habitats for waterfowl conservation, particularly in the Mediterranean region, where natural lentic ecosystems have suffered extensive loss and degradation. Man-made reservoirs represent the widespread and relatively deep artificial bodies of water and are often assumed to harbour poor waterbird communities in comparison with natural lakes. However, no study to date has compared the diversity of natural lakes with that of dam reservoirs on an extensive spatial and temporal scale.

Location

Spain.

Methods

We used long-term wintering waterbird census data (spanning 20-year on average) to compare the functional diversity and temporal dynamics of waterbird communities (n = 2459) from natural shallow lakes (‘lagunas’ in Spanish) and reservoirs in the Iberian Peninsula.

Results

We found species richness had a strong non-linear trend, increasing from the mid-1980s to the late-1990s, followed by a gentle decrease. Our results indicate that reservoirs presented higher functional richness in comparison with their natural counterpart, which suggests that environmental filtering acts more restrictively in natural lakes, as they constitute habitats with harsher and more unpredictable conditions. When analysing temporal dynamics, we found that reservoirs exhibited a marked temporal increase in functional richness whereas lakes showed little change over time. The rise in functional richness in reservoirs is mainly driven by the increasing dominance of functionally distinctive species—particularly piscivores and large wading birds such as storks—whose traits extend the multidimensional niche volume of the assemblages.

Main Conclusions

Our findings highlight that temporal change in functional diversity is not driven solely by increases in richness or the distinctiveness of colonizing species, but by whether the species gained over time occupy unique filled regions of the functional space. Overall, the present study underlines the important and increasing role of reservoirs as habitat for a diverse group of birds.