Seed dispersal effectiveness in a plant-lizard interaction and its consequences for plant regeneration after disperser loss

Mutualistic disruptions, such as those promoted by the loss of seed dispersers, can have negative effects on the plant regeneration of those species that strongly depend upon them. In order to adequately assess how plant communities are affected by such disruptions, we need to know the importance of the dispersal phase, both in its quantitative and qualitative components. We examined this in the narrow interaction between the shrub Daphne rodriguezii and its (only) disperser, the lizard Podarcis lilfordi. We quantified fruit removal and the effect of fruit/seed-size selection, seed treatment in the disperser's guts and seed deposition patterns on seedling emergence and survival. In the only locality in which lizards persist, they removed most fruits and showed preference for larger ones in one of the two study years. Seed treatment in lizard's guts had no effect on germination, although it tended to reduce the effect of seed size on germination (differences between large vs. small seeds in seed germination were higher for non-ingested seeds). Probability of seedling emergence, but not survival, was higher in the locality with lizards. Dispersed seeds under heterospecific shrubs showed higher seedling survival than those under conspecifics in all localities, especially the year with higher rainfall. Our findings support that the movement of seeds to nurse shrubs by lizards is the most important component of the seed dispersal process in the only remaining locality where both species coexist.