Frugivores vary in their response to neighborhood effects in a novel ecosystem

Abstract

Seed dispersal is critical for maintaining ecosystem structure and over half of plant species worldwide rely on animals for dispersal. Animal-mediated seed dispersal requires tight links between animals and plants. The introduction of invasive species threatens this mutualism by potentially creating competition between native and invasive plants for dispersers and by altering the consumption of native fruits by introduced dispersers. Although the first critical step in seed dispersal is fruit consumption, we have limited knowledge of the characteristics that attract dispersers to a given plant. In particular, characteristics of the neighborhood surrounding a plant may alter frugivory and frugivores may vary in their responses to these characteristics. Identification of key neighborhood characteristics would help to identify the mechanisms which facilitate or limit seed dispersal, aiding in the management of species in novel ecosystems. We deployed camera traps on Oʻahu, Hawaiʻi to quantify how the total fruit abundance, percent invasive fruit, percent conspecific fruit, canopy cover, and ground vegetation density of the neighborhood influence visitation and fruit removal by introduced avian frugivores. Results showed that neighborhood effects had little influence on frugivory overall, but did influence avian foraging groups in disparate ways. In particular, visitation by arboreal foragers increased with canopy cover and the amount of fruit on the focal plant but decreased with higher neighborhood fruit abundance and more conspecific fruit. Ground forager visitation decreased with higher ground vegetation density and increased with more conspecific fruit. These findings suggest the neighborhood can be modified to facilitate arboreal foragers, which are higher quality dispersers on Oʻahu, and to limit ground foragers, which are primarily seed predators. We argue studies should consider differences among dispersers to adequately address the role of the neighborhood on frugivory in environments with multiple disperser species.