Conservation of fruit-frugivore networks in human dominated landscapes in the Neotropics may rely upon specialized interactions

Jennifer C. Knight, Biological Sciences, Eastern Kentucky University, Richmond, KY and Valerie E. Peters, Department of Biological Sciences, Eastern Kentucky University, Richmond, KY

Background/Question/Methods
Ecosystem deterioration due to anthropogenic influences has bolstered the study of mutualistic interactions due to their strong influence on ecosystem function. Seed-dispersal mutualisms ensure the local persistence and gene flow of plants in any community but are especially critical in tropical regions. Neotropical ecosystems host numerous species of birds and a large proportion of the bird community consumes fruits either obligatorily or opportunistically. Available bird habitat in these systems has diminished due to deforestation and loss of habitat. Given the importance of the ecosystem services provided by birds, determining methods to protect their remaining habitats is important. Agroforestry systems provide opportunities for biodiversity conservation through their multi-strata structure which can resemble natural forest conditions. We aimed to identify priority plant species that provide resources for birds in diverse, biodiversity-friendly agroforests. Our study was conducted in six coffee farms in the San Luis Valley, Puntarenas, Costa Rica. Visual sightings of birds foraging on fruit were recorded along a 100m transect in all six farms and were repeated three times per month, each month, excluding January and September, during the year 2008. We constructed a weighted bipartite network and used quantitative modularity analysis to determine the topological roles of all observed plant species.
Results/Conclusions
The full network comprised 18 trees, 61 birds, with a total of 1302 interactions. Within the network, Acnistus arborensens, Cecropia obtusifolia, and Ficus pertusa supported the highest species richness of birds observed foraging fruit. Network-level indices for connectance, weighted nestedness, and robustness are (0.19), (0.35), (0.70), respectively. The network consisted of 7 modules and was found to be significantly modular (Qobs=0.38, ZQ=25.95). Core roles in a network that would serve as top candidates for conservation or restoration initiatives are network hub or connector species, those linking species and enhancing stability. All plant species in our network were identified as peripherals. Peripherals are specialists that have limited links in the network and interact mostly with species within their own module. The modularity analysis of the network indicates that subsets of more specialist interactions dominated the network. The network demonstrates low connectance and nestedness, but high modularity with a high robustness index indicating it can withstand loss of species, altogether questioning whether the high degree of specialization displayed may be stabilizing the network, a concept which challenges traditional network theory.