From dilution effect to dilution landscapes: effects of natural vegetation cover and fragmentation on host-parasite...

The degradation of natural landscapes is a key driver of biodiversity loss and the erosion of ecosystem services, including disease regulation. Although 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 to examine how landscape configuration shapes ecological and coevolutionary outcomes. We found that: (i) landscapes with more natural cover and lower fragmentation level dilute the distribution of parasites throughout the host community and lead to more homogeneous coevolutionary trajectories; (ii) highly degraded, fragmented landscapes constrain host-parasite dispersal, promoting smaller, more heterogeneous interaction networks with divergent coevolutionary dynamics, which raise the risk of new parasite variants emerging; and (iii) loss of habitat reduces diversity, reducing 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 increased zoonotic transmission risk and stronger parasite-host interactions in degraded landscapes. Hence, conservation actions should focus on maintaining forest core integrity to mitigate the effects of landscape conversion on host-parasite dynamics and to promote the disease-regulation service of natural ecosystems.