Avian Seed Dispersal on Virginia Barrier Islands: Potential Influence on Vegetation Community Structure and Patch Dynamics

Abstract

Quantification of seed arrival as an ecological flux may improve understanding of patch dynamics and variations in community structure across the landscape. Microsites favorable for germination are continually being created and destroyed in coastal ecosystems, so seed dispersal to multiple patches is essential for survival and growth. In order to elucidate the role that patches play in seed dispersal on barrier islands, our study was conducted on three Virginia, USA barrier islands: Metompkin, Hog, and Smith, which represent a range of size, topographic complexity and species richness. Artificial perches with an attached fecal seed trap were installed along transects on the islands. Each island had at least one transect positioned at both a woody and a graminoid site. Seed dispersal varied seasonally with most dispersal events (one dispersal event equals one seed collected) occurring during the spring (n = 248) versus the summer (n = 4). Seed dispersal events were greatest on Hog Island (n = 421) and least on Metompkin Island (n = 5). Morella spp. (Morella cerifera and Morella pensylvanica) accounted for 62% of the total seeds collected. Three species that appeared during spring seed counts, Callicarpa americana, Rubus sp. and Sassafras albidum, were not observed within a 10 m proximity of any of the transects. Spatial variation in island position, vegetation structure and island topography were important for seed dispersal. The greatest abundance and diversity of seeds were collected on Hog Island, centrally located relative to the other islands. These results indicate that while the role patches play in influencing seed dispersal is related to island position and location on a given island, we may need to define patches in greater detail to accurately predict which locations will receive the most bird-dispersed seeds.