ARS | Publication request: Spillover of functionally important organisms between managed and natural habitats

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 19, 2011
Publication Date: January 1, 2012
Repository URL: http://handle.nal.usda.gov/10113/53947
Citation: Blitzer, E.J., Dorman, C.F., Holzschuh, A., Klein, A., Rand, T.A., Tscharntke, T. 2012. Spillover of functionally important organisms between managed and natural habitats. Agriculture, Ecosystems and Environment. 146: 34-43.

Interpretive Summary: Agricultural expansion and intensification has led to a mosaic landscape which juxtaposes human-managed and natural areas. In such human-dominated and heterogeneous landscapes the movement or “spillover” of organisms across habitat types may be an important ecological process structuring ecological communities. While there is much evidence for spillover from natural habitats to managed areas, little attention has been given to flow in the opposite direction. Here we synthesized studies from five functionally important trophic groups, pollinators, seed dispersers, pathogens, herbivores, and predators, and found evidence for spillover from managed to natural systems in all five groups. We argue that this effect has been underestimated in the past. The largest number of studies documenting spillover from managed to natural systems report pathogen and vertebrate predator spillover, with a smaller number reporting spillover of pollinators and herbivores. We conclude that in the ecology and conservation literature the valuation of mutual influences between managed systems and natural habitat is largely biased towards positive effects of natural areas (e.g. as sources of important biological control agents or pollinators), and negative effects of managed areas (e.g., human subsidized predators causing increased rates of nest predation in adjacent natural areas). In contrast, in agronomy, the negative effects of natural habitats (e.g. insect pest and pathogen spillover from natural habitats into agricultural systems) have been well documented. As habitat modification progresses, resulting in increasingly fragmented landscapes, the likelihood and size of any spillover effects will only increase. Timely empirical studies are needed in each focal group as well as across disciplines to fully understand the cumulative effects of this phenomenon on natural communities.

Technical Abstract: Land use intensification has led to a mosaic landscape which juxtaposes human-managed and natural areas. In such human-dominated and heterogeneous landscapes spillover across habitat types, especially in systems which differ in resource availability, may be an important ecological process structuring communities. While there is much evidence for spillover from natural habitats to managed areas, little attention has been given to flow in the opposite direction. Here we synthesize studies from five functionally important trophic groups, pollinators, seed dispersers, pathogens, herbivores, and predators, and found evidence for spillover from managed to natural systems in all five groups. We argue that this effect has been underestimated in the past. The largest number of studies documenting spillover from managed to natural systems report pathogen and vertebrate predator spillover, with a smaller number reporting spillover of pollinators and herbivores. We conclude that in the ecology and conservation literature the valuation of mutual influences between managed systems and natural habitat is largely biased towards positive effects of natural areas, and negative effects of managed areas, whereas in agronomy, pest spillover from natural habitats has been well documented. As habitat modification progresses, resulting in increasingly fragmented landscapes, the likelihood and size of any spillover effect will only increase. Timely empirical studies are needed in each focal group as well as across disciplines to fully understand the effects of this phenomenon on natural communities.