Fruit-eating habits of birds in a fragmented landscape: Implications for seed dispersal

Few data exist on seed dispersal by frugivorous birds in fragmented landsca pes, originating from tropical dry forests, in contrast to more abundant da ta from tropical rain forests. In this study, we assessed the effect of fru givorous birds in a fragmented landscape of Veracruz, Mexico, now occupied by remnant fragments of tropical semi-deciduous forest and dry deciduous fo rest, grassland, and shrubby patches on sand dunes. We determined four char acteristics related to seed dispersal by birds: the interacting species of plants and birds, the characteristics of these species, spatio-temporal var iation in the dispersal system, and the outcome of the process. During one year, we recorded 54 frugivorous bird species and 33 ornithochorous plant s pecies, which engaged in 176 different bird-plant species interactions. Sim ilarity (Sorensen index) of frugivorous bird communities using different ve getation types was high (>70%), suggesting that many bird species used all of the vegetation types. In contrast, the similarity of ornithochorous plan t communities among vegetation types commonly was low (<37%), suggesting th at most plant species were restricted to particular sites in this landscape . At the landscape level, as well as for tropical deciduous forest, we dete cted a significant positive relationship (Spearman's correlation of rank co efficient >0.65, P < 0.05) among richness per month of frugivorous birds an d plant species bearing fleshy fruits. Seeds of many plant species previous ly detected in studies of seed rain at the site were eaten by birds during this study. Most seeds of zoochorous species, which are deposited in the dr y and decidous tropical forests patches, are produced within these vegetati on types (i.e., they are autochthonous species), whereas bird-dispersed see ds arriving in grassland and shrubby patches are produced outside (i.e., al lochthonous) and are mostly dy species. Birds are important seed dispersers among vegetation types in this landscape but they have different effects i n each one. The four characteristics studied, as well as the landscape appr oach of this research, allowed us to detect spatial and temporal patterns t hat otherwise would have remained undetected.