Seed dispersal processes are influenced by different drivers of global change in a variety of ecosystems worldwide. Habitat loss and fragmentation, defaunation due to hunting, and species invasions appear as the most important causes of seed disperser declines, which in turn have a cascading effect on the plants that depend upon them. Seed dispersal disruption is increasingly being documented, although the ecological and evolutionary consequences for plant reproduction are still largely unknown. In the increasingly abundant novel communities, introduced vertebrate seed dispersers might replace to some extent the function of lost interactions, but more information is still needed to assess how often such such mutualistic interactions are rescued. Here we present several case studies to illustrate both demographic and evolutionary consequences of disrupted seed dispersal mutualisms in the Mediterranean region, specifically in Mediterranean islands.
Results/Conclusions
Daphne rodriguezii and Cneorum tricoccon have experienced an important contraction in their distributional range, and even local extirpations, after losing their main seed disperser (lizards) in some of the Balearic Islands. Whereas the former keeps a healthy population in the only islet where lizards survive, the latter is currently experiencing an expansion in altitude in the largest island of this archipelago due to the introduction of pine martens that legitimately disperse the plant. This carnivore replaces the native disperser to some extent, but only in forested habitats, not in shrubland coastal areas. Gene flow mediated by pine martens seems restricted to populations close to forest, and these alien species show also to exert a strong positive selection on seed size by preferentially consuming larger fruits. Lastly, Chamaerops humilis, a species restricted to the Western Mediterranean area, probably an anachronic species dispersed by mammals already extinct in the region, is currently dispersed by badgers and foxes in the mainland but by alien goats in the Mediterranean islands. Using a comprehensive literature review, we found that similar 'rescue' of seed disperser mutualisms by either alien or suboptimal native species are pervasive in the Mediterranean inland, concerning a wide array of plant species.