Beyond species richness : integrating ecological interactions and multiple goals in grassland conservation

This thesis explores how incorporating trophic interactions and a wider range of conservation goals can enhance the design and implementation of biodiversity conservation measures in permanent grasslands. Based on data from two long-term biodiversity monitoring regions in Germany [Schwäbische Alb (ALB) and Schorfheide-Chorin (SCH)], the thesis is structured around three main chapters. Together, these chapters examine (1) the reliability of co-occurrence methods for inferring plant–butterfly interactions, (2) the cost-effectiveness of different land-use management practices for achieving multiple conservation goals, and (3) the detection of ecological thresholds for key drivers of change in these goals at species, community, and ecosystem levels. I employed a combination of literature review, field data, statistical inference models, optimisation algorithms, and multivariate analyses to provide a thorough evaluation of grassland biodiversity and move beyond traditional species richness metrics by incorporating interaction networks and other metrics, thus capturing ecological complexity relevant to conservation planning. Chapter I shows that, despite the Relative Interaction Intensity (RII) with pairwise null models approach performing better than the other methods tested, co-occurrence methods fail to reliably predict known plant–butterfly interactions. This highlights the limited usefulness of such methods for mobile species and the importance of directly observing trophic interactions. Chapter II shows that optimising land-use management for multiple conservation goals under cost-effectiveness can achieve substantial ecological benefits (up to 80% of the maximum) using as little as 30% of the budget. Although trade-offs were observed, certain goals, including trophic interactions, butterfly richness, and network nestedness, showed more synergies. Optimising for sets of goals consistently outperformed single-goal strategies, though regional variation in optimal management highlights the need for region-specific planning. Chapter III presents ecological thresholds for key biodiversity goals along management and landscape gradients. In ALB, most goals showed sharp declines above one to two cuts per year, and low grazing levels were associated with higher multidiversity and more complex interaction networks. In SCH, network connectance and the number of interactions increased even at low levels of forest cover (2–10%), highlighting the importance of maintaining forest patches near grasslands for supporting biodiversity. Additionally, even low fertiliser inputs were associated with species-poor butterfly communities composed mainly of common species with wider distribution ranges. These results provide key insights for improving region-specific management strategies in conservation programmes and show the importance of using multiple conservation goals, especially those capturing species interactions, when designing effective conservation strategies.