Plant-Pollinator Networks in the Tropics: A Review

Most tropical plants rely on animals for pollination, thus engaging in complex interaction networks. Here, we present a global overview of pollination networks and point out research gaps and emerging differences between tropical and non-tropical areas. Our review highlights an uneven global distribution of studies biased towards non-tropical areas. Moreover, within the tropics, there is a bias towards the Neotropical region where partial networks represent 70.1% of the published studies. Additionally, most networks sampled so far (95.6%) were assembled by inferring interactions by surveying plants (a phytocentric approach). These biases may limit accurate global comparisons of the structure and dynamics of tropical and non-tropical pollination networks. Noteworthy differences of tropical networks (in comparison to the non-tropical ones) include higher species richness which, in turn, promotes lower connectance but higher modularity due to both the higher diversity as well as the integration of more vertebrate pollinators. These interaction patterns are influenced by several ecological, evolutionary, and historical processes, and also sampling artifacts. We propose a neutral–niche continuum model for interactions in pollination systems. This is, arguably, supported by evidence that a high diversity of functional traits promotes greater importance of niche-based processes (i.e., forbidden links caused by morphological mismatching and phenological non-overlap) in determining which interactions occur, rather than random chance of encounter based on abundances (neutrality). We conclude by discussing the possible existence and direction of a latitudinal gradient of specialization in pollination networks.