Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Direct and Indirect Effects of Avian Predation on Grasshopper Communities in Northern Mixed-Grass Prairie

Author
item Branson, David

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 2, 2005
Publication Date: October 1, 2005
Citation: Branson, D.H. 2005. Direct and indirect effects of avian predation on grasshopper communities in northern mixed-grass prairie. Environmental Entomology. 34(5):1114-1121.

Interpretive Summary: The ecological interactions between grasshoppers, predators and resources that can limit the population growth of grasshoppers are poorly understood. A number of field experiments have generally shown decreased grasshoppers densities in the presence of avian predation, indicating that top-down control by avian predators can regulate grasshopper populations in some systems. Avian predator limited sites tend to have low population densities with few large bodied grasshoppers. However, the effects of avian predators on grasshopper populations can differ between years and between sites in the same habitat. I conducted experiments examining grasshopper populations in avian exclosures and control plots for three years at two locations in eastern Montana, USA. Grasshopper population densities, species richness and diversity at the two sites were not consistently significantly affected by avian predation, indicative of weaker top-down effects. The effects of predation varied among years and between the two sites. Avian predators modified body size composition of grasshopper populations through size selective predation on medium bodied grasshoppers. Even in years when avian predators did not limit grasshopper populations, size selective predation by birds appeared to indirectly mediate competitive interactions among grasshoppers. Species richness and diversity of grasshopper assemblages were not significantly affected by avian predation in this study. Bottom up factors and abiotic conditions may play a more important role in determining grasshopper population densities at these sites.

Technical Abstract: The ecological interactions between grasshoppers, predators, climate conditions and plants that can limit the population growth of grasshoppers are poorly understood. A number of field experiments have generally shown decreased grasshoppers densities in the presence of avian predation, indicating that top-down control by avian predators can regulate grasshopper populations in some systems. Avian predator limited sites tend to have low population densities with few large body size grasshoppers. However, the effects of avian predators on grasshopper populations can differ between years and between sites in the same habitat. I conducted experiments examining grasshopper populations in avian exclosures and control plots at two locations in eastern Montana, USA. Avian predation did not have consistently strong top-down effects on grasshopper densities, species richness or species diversity at the two sites. The effects of predation varied among years and between the two sites. Bird predation led to a reduced percentage of medium body size grasshoppers in control plots exposed to birds in most years. Therefore, birds modified species composition through size selective predation even in years when they did not reduce overall grasshopper densities. Bottom up factors and abiotic conditions may play an important role in the population dynamics of grasshoppers at these sites.

Last Modified: 8/27/2014