Impacts of fruiting neighborhoods on avian seed dispersal in coastal wetlands along the northern Gulf of Mexico

Background/Question/Methods

Frugivorous birds and fruit-bearing plants have an important mutualistic relationship that can be disrupted by introduction of exotic species to an ecosystem. While foraging, these birds will often consume fruit, move to another plant, and then deposit the seeds of that fruit beneath another plant’s canopy. Many factors affect this relationship including fruit availability, canopy cover on the plant underneath which dispersal occurs and the number and variety of fruit-bearing neighbors to this focal plant. Our main objective was to test for impacts of an individual plant’s fruiting neighborhood, and species of focal plant, on characteristics of propagules dispersed beneath its canopy. We expected that seed rain and fruiting neighborhood for each focal plant would differ, and that seed rain composition would differ from that of the fruiting neighborhood, due to disproportionately greater dispersal of exotic species beyond their neighborhoods. Seed traps were installed beneath native and exotic winter-fruiting bird-dispersed plants at two coastal sites along the northern Gulf of Mexico. The fruiting neighborhood surrounding each focal plant was characterized, and traps were sampled once per month (September 2017 - August 2018).

Results/Conclusions

Native and exotic focal plants had significantly different neighborhood and seed rain compositions. Exotic focal species (Triadica sebifera and Cinnamomum camphora) exhibited more traffic and were generally more active hubs for dispersal of exotics than native species (Myrica cerifera and Persea palustris). We found only one single instance of an exotic species being dispersed beneath a native species. Our work suggests that invasive focal plants play an active role in arrival of new propagules into these coastal systems and may accelerate additional invasions. Further research could determine the extent of facilitative relationships between exotic and native bird-dispersed plants in coastal ecosystems of the northern Gulf Coast.