Trophic strategies of two sympatric endemic pigeons in insular ecosystems: a framework for understanding spatiotemporal frugivory interactions

Abstract

Pigeons are considered to play key ecological roles in frugivory and seed dispersal. They have colonised numerous oceanic islands and diversified into several species in sympatry. How these species coexist in similar niches is poorly understood although dietary separation is among the mechanisms suggested to avoid trophic overlap. We investigated the trophic ecology of the two endemic Columba species co-occurring in the laurel forest and thermosclerophyllous relicts of two of the Canary Islands. This study includes diet description in spatiotemporal terms, its relationship with fruit availability and seed treatment in 10 study areas established on La Palma and La Gomera. We used non-invasive DNA analysis to identify the faeces of the two congeneric species and microhistological methods to examine their diets. The degree of trophic overlap was evaluated by niche similarity and breadth indices. Molecular faecal sampling determined the spatiotemporal distribution of both pigeons to identify their areas of coexistence. These frugivorous pigeons' diets did not differ concerning the main plant species, but they diverged quantitatively in the proportions and parts of plants consumed. Lauraceae fruits were their staple foods although Rhamnaceae and some Fabaceae and Solanaceae were also important. Both pigeons showed selective preferences for some fruits. Significant spatiotemporal variations in their diets were observed along with a general tendency to increase fruit intake at its ripening times. Our results suggest that different trophic strategies facilitate the coexistence of these frugivorous columbids. These pigeons act as seed dispersers and/or predators depending on seed features (size and hardness), and this may have valuable implications for their conservation.