Aggregating fields of annual crops to form larger-scale monocultures can suppress dispersal-limited herbivores
- 147 Downloads
An important part of landscape ecology is determining how the arrangement (aggregation or fragmentation) of patches in space influences the population dynamics of foraging organisms. One hypothesis in agricultural ecology is that fine-grain spatial heterogeneity in cropping (many small agricultural fields) should provide better pest control than coarse-grain heterogeneity (few large agricultural fields); this hypothesis has been proposed as an explanation for the increased pest abundance associated with agricultural intensification. However, empirical studies have found mixed support for this hypothesis, and some, surprisingly, demonstrate a strong decrease in pest abundance with increased crop aggregation. We developed a spatially explicit simulation model of pest movement across an agricultural landscape to uncover basic processes that could reduce pest abundance in landscapes with fewer, larger fields. This model focuses on herbivore movement and does not include predation effects or other biological interactions. We found that field aggregation in the model led to severely reduced pest densities and further discovered that this relationship was due to an increased distance between fields and a decreased “target area” in more aggregated landscapes. The features that create a negative relationship between aggregation and pest densities rely on crop rotation and limited dispersal capabilities of the pests. These findings help to explain seemingly counter-intuitive empirical studies and provide an expectation for when field aggregation may reduce pest populations in agro-ecosystems.
KeywordsAgroecology Simulation model Dispersal Land use Habitat fragmentation Agricultural intensification
We thank Soroush Parsa for guidance on the biology of the potato weevil system and Stephen Ellner, Anurag Agrawal, and their respective labs for comments on the manuscript. Two anonymous reviewers provided comments that greatly improved this manuscript.
This study was supported by a grant from the US Department of Agriculture (RAMP grant ARZT-358320-G-30-505) and a National Science Foundation Graduate Research Fellowship Program (NSF GRFP grant DGE-1144153) to C.B.E.
- Chavez A (1997) Actividad Migratoria y Daño del Gorgojo (Premnotrypes spp.) en dos Comunidades del Departamento de La Paz. [B.S.]. Universidad Tecnica de Oruro, OruroGoogle Scholar
- Poveda K, Gomez MI, Martinez E (2008) Diversification practices: their effect on pest regulation and production. Rev Colomb Entomolgia 34:131–144Google Scholar