Asymmetric effect of deforestation on the functional roles of interacting plants and hummingbirds

Abstract

Abstract Among global change drivers, deforestation not only erodes biodiversity but also the functions that species play in an ecosystem. The maintenance of many ecosystem functions, such as pollination, depends on the functional roles fulfilled by interacting plants and animals. Given that plants and animals respond differently to deforestation, a perspective that considers the functional roles of both interacting partners is needed but rarely considered. The contribution of species to an ecosystem function, i.e. the functional role, can be measured from the traits of its interacting partners. The functional role of a pollinator is based on the traits of the plants it visits and, conversely, the functional role of a plant species can be measured from the traits of its pollinators. Using 24,554 interactions between 33 hummingbird and 289 plant species, and their functional traits, collected across 14 sites and two years of sampling, we quantified species individual functional roles, the diversity of functional roles as the combination of all species functional roles, and the functional redundancy as the overlap in functional roles. We then evaluated the influence of habitat and elevation on the diversity and redundancy of functional roles. Deforestation disproportionally reduced the diversity and redundancy of functional roles of plants compared to their hummingbird pollinators, implying loss of plant functional roles with deforestation. Although deforestation had no effect on the diversity of functional roles of hummingbirds, the composition of their functional roles changed between habitats. By evaluating both trophic levels we found that deforestation more strongly influences the contribution of plants to ecosystem function. Given that ecosystem functions depend on the functional roles fulfilled by species in the two trophic groups, the reduced diversity of functional roles fulfilled by plants will likely affect the delivery of pollination function. Our evaluation of the functional roles of all species engaged in trophic interactions helped us to unravel an asymmetric effect of deforestation on plants and hummingbirds. Our approach to evaluate species’ functional roles in trophic networks can be extended to other ecosystem functions, in order to gain a holistic understanding on how ecosystem functions are affected by drivers of global change.