Shared dispersal syndromes and frugivore behaviour influence the seed rain patterns of exotic ornithochorous plants

Background/Question/Methods

Seed dispersal determines potential range expansion of exotic plant species in their novel range. Mutualisms that establish between birds and exotic fleshy-fruited plants should determine the extent to which such exotic plant species expand their distributions. Seed dispersal by birds is often directional and biased toward food sources. The spatial distributions of fleshy-fruited plants in the landscape may thus influence the patterns of seed dispersal of exotic fleshy-fruited plants introduced to a novel habitat. We compared heterospecific bird-dispersed seed rain beneath the canopies of fleshy-fruited and dry-fruited native trees in forested habitats with and without abundant fleshy fruits and in open fields in southeastern Michigan. We hypothesized that the spatial distributions of native fleshy-fruited plants guide the seed-rain patterns of exotic fleshy-fruited plants in the landscape.

Results/Conclusions

Our results indicated that seed rain of exotic fleshy-fruited species was significantly higher beneath the canopies of fleshy-fruited plants than of dry-fruited plants, with over 90% of the seed rain dispersed beneath the canopies of fleshy-fruited plants. In addition, the local neighborhood of fleshy-fruited plant species was strongly represented in the seed rain beneath native fleshy-fruited plants. We suggested two general effects involved in the process of range expansion of exotic ornithochorous species that operate at different spatial scales: landscape effects, whereby native flesh-fruited plants guide the seed-rain patterns of exotic fleshy-fruited plants, and local effects, whereby exotics form invasion hubs through locally contagious dispersal. We suggest that contagious dispersal may be important for the success of the exotic fleshy-fruited species that have invaded our study region.