Life-history strategies as a tool to identify conservation constraints: A case-study on ants in chalk grasslands

Species’ life-history traits underlie species–environment relationships. Therefore, analysis of species traits, combined into life-history strategies, can be used to identify key factors shaping the local species composition. This is demonstrated in a case-study on ants in chalk grasslands. We developed four life-history strategies based on traits related to reproduction, development, dispersal and synchronization that are documented in the literature. These theoretical strategies reflect different responses to certain environmental conditions. They can be characterized as generalists (G), poor dispersers (D), species whose distribution is limited to sites with high food availability (F) and species that are restricted to sites with high soil temperatures during nest founding (T). Next, we tested whether the occurrence of these strategies differed between six Dutch chalk grasslands and four reference sites situated in Germany and Belgium. We found significant differences in species numbers between sites for strategies D and T but not for strategies F and G. The differences could be explained by differences in connectivity and microhabitat conditions; species richness of strategy D decreased exponentially with increasing distance to the next nearest chalk grassland, while summer soil temperature strongly affected species richness of strategy T. From these relationships we could successfully identify the most relevant bottlenecks for the occurrence of both of these strategies in Dutch chalk grasslands. Management recommendations resulting from this analysis include adapting the management timing in Dutch chalk grasslands and focussing on counteracting habitat isolation. With this case-study we demonstrate that the life-history strategy approach is a valuable alternative to approaches that try to identify key factors by analysing the variation in environmental parameters. The main advantage of the presented alternative is the focus on mechanistically understanding species responses, allowing a comparison of processes rather than occurrences of single species.