Trophic Ecology of Seahorse Key, Florida: A Unique Bird-Snake Interaction Network Analysis

Abstract

In 2015 the entire breeding colony of nesting waterbirds on Seahorse Key (Florida, U.S.A.) unexpectedly abandoned the island and have not returned. These birds have a unique trophic relationship with a sympatric cottonmouth snake (Agkistrodon conanti) population, as well as potentially important positions within the entire insular food web. Species-interaction network analysis was used to compare two trophic networks; pre- and post-abandonment. Trophic data were used to create a weighted adjacency matrix for each network and the resulting network metrics were compared using the network analysis software package UCINET and visualized using NetDraw. Results for the pre-abandonment network indicated a large, complex, diffuse network with low centrality and seven sub-networks. Several species of colonial nesting birds were identified as holding important positions within the network for resource transfer from marine and intertidal environments to terrestrial trophic guilds, particularly to the snakes. Post-abandonment analysis showed the network significantly fractured with the terrestrial trophic guild that includes the snakes being smaller, more isolated and potentially less stable.