Moving from the Dilution Effect to Dilution Landscapes: Effects of Natural Vegetation Cover and Fragmentation on Host-parasite Eco-evolutionary Dynamics

Ana Paula Lula Costa , Klementyna Gawecka, Paulo Sérgio D'Andrea, Gisele Winck, Cecilia Siliansky de Andreazzi

The conversion and fragmentation of natural landscapes are key drivers of biodiversity loss and the erosion of ecosystem services, including disease regulation. Although habitat degradation is linked to higher zoonotic disease risk, the mechanisms by which landscape structure shapes host-parasite eco-evolutionary dynamics remain poorly understood. Here, we combine a spatially explicit metacommunity and coevolutionary model with empirical host-parasite interactions data to examine how landscape cover and configuration shape ecological and coevolutionary outcomes. We find that (1) landscapes with a higher amount of natural cover and lower fragmentation level dilute the distribution of parasites throughout the host community and lead to more homogenous coevolutionary trajectories; (2) highly degraded, fragmented landscapes constrains host-parasite dispersal, promoting smaller, more heterogeneous interaction networks with divergent coevolutionary dynamics, which rise the risk of new parasite variants emerging; and (3) loss of habitat reduces host diversity, impacting parasite host range. These results extend the dilution effect hypothesis by incorporating the structure of the interaction networks and the coevolutionary dynamics. Our findings suggest an increased risk of zoonotic transmission and strength of parasite-host interactions in a degraded landscape. Hence, conservation actions should focus on maintaining functional connectivity to mitigate the effect of landscape conversion on host-parasite dynamics and promote the disease regulation service of natural ecosystems.