Nonlinear responses to food availability shape effects of habitat fragmentation on consumers

• Published in: Ecology (Durham) Vol. 92; no. 1; pp. 98 - 107
• Main Authors: Blackburn, Heather B, Hobbs, N. Thompson, Detling, James K
• Format: Journal Article
• Language: English
• Published: Washington, DC Ecological Society of America 01-01-2011
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Brassica; cabbage looper; connectivity; Conservation biology; consumer-–resource interactions; Demography; Ecology; Ecosystem; Feeding Behavior; Food availability; food distribution; Fundamental and applied biological sciences. Psychology; General aspects; Habitat fragmentation; Habitat loss; Habitats; Invertebrates; Jensen's inequality; Landscape ecology; landscape fragmentation; landscape heterogeneity; Landscapes; Larva; Larvae; Modeling; Models, Biological; Moths - physiology; Natural resources; nonlinearity; patchiness; prediction; Resource availability; resource distribution; Survival analysis; survival rate; Trichoplusia ni; Vegetables; Availability; landscape fragmentation; Landscape; Trichoplusia ni; Insecta; Interaction; resource distribution; patchiness; Feeding; Fragmentation; Heterogeneity; Jensen's inequality; connectivity; Arthropoda; Lepidoptera; Nonlinearity; Habitat; food distribution; Noctuidae; Invertebrata; Food supply; cabbage looper; consumer-resource interactions; landscape heterogeneity
• ISSN: 0012-9658; 1939-9170
• DOI: 10.1890/10-0637.1

Fragmentation of landscapes is a pervasive source of environmental change. Although understanding the effects of fragmentation has occupied ecologists for decades, there remain important gaps in our understanding of the way that fragmentation influences mobile organisms. In particular, there is little tested theory explaining the way that fragmentation shapes interactions between consumers and resources. We propose a simple model that explains why fragmentation may harm consumers even when the total amount of resources on the landscape they use remains unchanged. In particular, we show that nonlinearity in the relationship between resource availability and benefits acquired by consumers from resources can cause a decrease in benefits to consumers when landscapes are subdivided into isolated parts and when the distribution of consumers in fragments is not matched to the distribution of resources. We tested predictions of the model using a laboratory system of cabbage looper (
Trichoplusia ni
) larvae on artificial landscapes. Consistent with the model's predictions, survivorship of larvae decreased when landscapes with heterogeneous resources were fragmented into isolated parts. However, average mass of surviving larvae did not change in response to fragmentation. With basic knowledge of consumer resource use patterns and landscape structure, our model, supported by our experiment, contributes new understanding of the resource-mediated effects of fragmentation on consumers.