Disentangling habitat use by frugivorous birds: Constant interactive effects of forest cover and fruit availability

摘要

Frugivorous animals contribute to forest regeneration, but the provision of this ecosystem service is spatially filtered by the environmental factors limiting frugivore habitat use. Understanding how this filter acts in real-world landscapes is crucial for better predicting how habitat degradation impacts on seed dispersal services. Fruits and forest cover are main determinants of habitat use by frugivorous birds. The degree of spatial segregation between these habitat features would be expected to determine a trade-off for frugivores between finding food and being safe. Nevertheless, little is known about how such a trade-off may finally affect frugivore habitat use. We studied frugivorous bird habitat use in a landscape representing a gradient of forest loss and fragmentation in the Cantabrian Range (N Spain). For four years we evaluated the spatial patterns of the abundances of frugivorous birds, fruits, and forest cover. Both fruits and forest cover influenced bird habitat use in each year. However, we also found a consistent across-years interaction between the effects of forest cover and fruits. In each study year fruit tracking by frugivores increased in landscape sectors presenting sparce forest cover and vice versa, but that intense search for food or shelter weakened in those areas with dense forest cover and abundant fruits respectively. The simultaneous consideration of the different environmental factors limiting frugivore habitat use revealed long-term, complex landscape effects, which are expected to cascade into fine-grained variability of the spatial patterns of seed rain.