In fragmented landscapes, plant population persistence can hinge upon long distance seed dispersal between habitat patches. With increasing fragmentation and climate change, the need for long distance seed dispersal will also likely increase. Habitat corridors, which connect otherwise isolated patches, have been shown to promote seed dispersal by birds, but this “corridor effect” may vary seasonally. Seasonality often determines plant reproductive timing and the movement patterns of seed dispersing birds. This study compares the utility of corridors for promoting seed dispersal by birds in summer and winter.
This study was conducted in an experimentally fragmented forest at the Savannah River Site (SRS) in South Carolina. The site consists of eight experimental landscapes; each has five 1.4-hectare habitat patches, with four peripheral patches equidistant from a central patch. One peripheral patch in each landscape is connected to the central patch by a corridor. During summer and winter of 2009 and 2010, we planted a single species of fruiting plant, Solanum americanum, in the central patch of each landscape (approximately 40 plants per landscape and equal numbers of fruits each season). We also installed seed traps on top of bird perch poles in each experimental habitat patch.
The proportion of seeds dispersed by birds down corridors was much greater during winter than during summer (likelihood ratio test, <0.01). Many seed dispersing birds at SRS forage in large mixed flocks during winter, while most seed dispersing birds in summer are territorial breeders. Thus bird foraging and movement in summer may be driven more by breeding requirements than by landscape features like corridors. For plants in fragmented landscapes, the utility of habitat corridors for long distance seed dispersal may be significantly determined by plant reproductive timing and seasonal variation in bird behavior.