Birds as predators in tropical agroforestry systems
Birds as predators in tropical agroforestry systems
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Date
2008-04
Authors
Van Bael, Sunshine
Philpott, Stacy
Greenberg, Russell
Bichier, Peter
Barber, Nicholas
Mooney, Kailen
Gruner, Daniel
Advisor
Citation
Ecology, 89(4), 2008, pp. 928-934.
DRUM DOI
Abstract
Insectivorous birds reduce arthropod abundances and their damage to plants in
some, but not all, studies where predation by birds has been assessed. The variation in bird
effects may be due to characteristics such as plant productivity or quality, habitat complexity,
and/or species diversity of predator and prey assemblages. Since agroforestry systems vary in
such characteristics, these systems provide a good starting point for understanding when and
where we can expect predation by birds to be important. We analyze data from bird exclosure
studies in forests and agroforestry systems to ask whether birds consistently reduce their
arthropod prey base and whether bird predation differs between forests and agroforestry
systems. Further, we focus on agroforestry systems to ask whether the magnitude of bird
predation (1) differs between canopy trees and understory plants, (2) differs when migratory
birds are present or absent, and (3) correlates with bird abundance and diversity. We found
that, across all studies, birds reduce all arthropods, herbivores, carnivores, and plant damage.
We observed no difference in the magnitude of bird effects between agroforestry systems and
forests despite simplified habitat structure and plant diversity in agroforests. Within
agroforestry systems, bird reduction of arthropods was greater in the canopy than the crop
layer. Top-down effects of bird predation were especially strong during censuses when
migratory birds were present in agroforestry systems. Importantly, the diversity of the
predator assemblage correlated with the magnitude of predator effects; where the diversity of
birds, especially migratory birds, was greater, birds reduced arthropod densities to a greater
extent. We outline potential mechanisms for relationships between bird predator, insect prey,
and habitat characteristics, and we suggest future studies using tropical agroforests as a model
system to further test these areas of ecological theory.