Community and food web structure of an African savanna. Consequences of alternative land use practices

PhD ceremony: Ms. S.N. de Visser, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen

Title: Community and food web structure of an African savanna. Consequences of alternative land use practices

Promotor(s): prof. H. Olff, prof. P.C. de Ruiter

Faculty: Mathematics and Natural Sciences

Earth’s biodiversity is threatened. As species are linked to each other through many interactions, the loss of one species may lead to consecutive extinctions and loss of ecosystem functioning. In her thesis Sanne de Visser investigate trophic interactions (who-eats-whom) and the influence of human activities on these interactions and diversity in Serengeti National Park, Tanzania.

Serengeti is one of the few relatively untouched ecosystems still containing its large plant feeders and predators. These larger species have been extensively studied, whereas the smaller organisms such as insects and spiders have been neglected.

With observations and diet-analyses using stable isotope technology De Visser has reported of several new trophic interactions of a bird of prey, among insects and spiders and of small mammalian carnivores. Combining these new findings with existing literature on Serengeti’s larger fauna she constructed the first near-complete food web of the Serengeti.

The growing human population and increasing land-use changes outside the park allow for comparisons of human impacts on natural ecosystems. De Visser shows that outside vegetation diversity decreases and arthropods may occur in large abundances, but are less diverse and smaller in size. The park therefore not only protects larger plant feeders and predators but also insects and spiders. Thus, humans impact the food web from the top (predators) as well as the resource level. Most food web studies on species loss underestimate the consequences of human impacts on communities by considering only trophic interactions. The findings of De Vissr emphasize the importance to study complete communities and all species interactions together.