Patterns Of Seed Rain Research Articles

WINDBREAKS ENHANCE SEED DISPERSAL INTO AGRICULTURAL LANDSCAPES IN MONTEVERDE, COSTA RICA

Planting windbreaks on degraded tropical lands may accelerate natural successional processes by attracting seed-dispersing animals and increasing the seed rain of forest plants. I examined the effects of planted windbreaks on seed deposition patterns in dairy farms in Monteverde, Costa Rica, by comparing annual seed rain patterns in windbreaks and adjacent pastures. I also examined the effects of windbreak connectivity and remnant trees on seed rain patterns. Traps placed in 19 windbreaks and in seven pastures collected more than 3 million seeds (of 199 species) during the year-long study. Windbreaks received significantly greater densities and species richness of seeds of tree and shrub species than pastures. Bird-dispersed seeds occurred in greater densities and species numbers in windbreaks than in pastures; in contrast, the seed rain of bat-dispersed seeds did not differ between windbreak and pasture habitats. Windbreak connectivity had no detectable effect on seed dispersal patterns, whereas the presence of remnant trees increased the number of tree species but not the density of tree seeds. This study suggests that windbreaks can dramatically increase the deposition of tree and shrub seeds within the agricultural landscape, and that the location of windbreaks within the landscape may be important in determining seed deposition patterns.

Seed Dispersal by Monkeys and the Fate of Dispersed Seeds in a Peruvian Rain Forest1

ABSTRACTPrimary seed dispersal by two species of monkeys and the effects of rodents and dung beetles on the fate of dispersed seeds are described for a rain forest in southeastern Perú. During the six‐month study period (June–November 1992) spider monkeys (Ateles paniscus) dispersed the seeds of 71 plant species, whereas howler monkeys (Alouatta seniculus) dispersed seeds of 14 species. Spider and howler monkeys also differed greatly in their ranging behavior and defecation patterns, and as a consequence, produced different seed rain patterns. Monkey defecations were visited by 27 species of dung beetles (Scarabaeidae). Dung beetles buried 41 percent of the seeds in the dung, but the number of seeds buried varied greatly, according to seed size. Removal rates of unburied seeds by rodents varied between 63–97 percent after 30 d for 8 plant species. The presence of fecal material increased the percentage of seeds removed by seed predators, but this effect became insignificant with time. Although seed predators found some seeds buried in dung balls (mimicking burial by dung beetles), depth of burial significantly affected the fate of these seeds. Less than 35 percent of Brosimum lactescens seeds buried inside dung balls at a depth of 1 cm remained undiscovered by rodents, whereas at least 75 percent of the seeds escaped rodent detection at a depth of 3 cm and 96 percent escaped at 5 cm. Both dung beetles and rodents greatly affected the fate of seeds dispersed by monkeys. It is thus important to consider postdispersal factors affecting the fate of seeds when assessing the effectiveness of frugivores as seed dispersers.

The role of seed rain in determining the assembly of a cliff community

Abstract. Cliff‐face communities of the Niagara Escarpment in Ontario, Canada, are dominated by long‐lived Thuja occidentalis and a consistent assemblage of other plants. Our objective was to determine whether seed rain plays a role in determining why these species are dominant. Seed rain was collected from the cliff face and from the surrounding plateau‐and talus communities at two sites over a 2‐yr period in order to compare these three adjacent, but different communities. Multivariate Discriminant Analysis first separated the two sites: primarily due to the importance of Betula papyrifera at one site. The three community types were also separated, although there was still substantial overlap. There was a predictable array of species associated with each community although the seed rain on the cliff faces differed slightly. When characterized by univariate ANOVAs, seed rain in the cliff faces and plateaus had a lower species richness and lower total seed density than the talus sites. Seeds of two of the 11 species analysed individually showed an influence of habitat type on their number. Seed morphology did not influence patterns of seed rain. Finally, there was no correlation between the seed rain and above‐ground vegetation in any of the communities. We conclude that the seed rain patterns that exist do not act to filter the plants that form the mature vegetation of cliffs.