Thursday, August 9, 2007

PS 56-17: Bird predation decreases arthropod abundance and biomass in three coffee farms in the Blue Mountains, Jamaica

Natalie J. Levy, University of California Berkeley and Matthew D. Johnson, Humboldt State University.

Shaded coffee farms can supply habitat for native biodiversity, especially forest birds attracted to over-story shade trees.  However, current economic forces encourage modern cultivation techniques with few to no over-story trees and little conservation value.  Ecosystem services provided by insect-eating birds could provide incentives for farmers to retain traditional, environmentally friendly cultivation techniques. This project focused on the impact of birds on arthropods in Jamaica’s Blue Mountains, where the intensification of coffee agriculture threatens native biodiversity. To study this trophic interaction, in summer 2006, we sampled arthropods in 19 paired bird exclosures and controls on three coffee farms located in the Blue Mountains, at an elevation of ~1525 meters.  We hypothesized that there would be a higher abundance and biomass of arthropods inside the bird exclosures, and that the difference between the exclosures and controls arthropod abundance would be positively correlated with the amount of shade cover. Results showed that the abundance and biomass of arthropods and arthropod herbivory were significantly higher in the exclosures than in controls. And that the difference between the exclosures’ and the controls’ arthropod abundance was not significantly correlated with percent shade cover. These results indicate that birds are providing the farmers an ecological service by reducing arthropod abundance and biomass. However this effect of bird predation on arthropods was not related to the amount of shade cover across the range studied.

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