Dryland state transitions alter trophic interactions in a predator-prey system

Authors: WAGNON, CASEY - University Of Illinois; Bestelmeyer, Brandon; SCHOOLEY, ROBERT - Benedictine University Of Illinois

Submitted to: Journal of Animal Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Environmental change is expected the effects that native animals have on vegetation in drylands. Here, we examined how environmental change caused by shrub encroachment affects trophic interactions in a dryland. The predator-prey system included an apex canid predator (coyote; Canis latrans), an intermediate canid predator (kit fox; Vulpes macrotis), and two herbivorous lagomorph prey (black-tailed jackrabbit, Lepus californicus; and desert cottontail, Sylvilagus audubonii) in the Chihuahuan Desert of New Mexico, USA. We evaluated alternative hypotheses for how shrub encroachment could affect trophic interactions including 1) modifying bottom-up processes by reducing herbaceous forage; 2) modifying top-down processes by changing canid abundances or the landscape of fear experienced by lagomorph prey; and 3) altering intraguild interactions between the dominant coyote and the intermediate kit fox. Lagomorph prey responded strongly to bottom-up pulses during years of high summer precipitation, but only on sites with moderate to high shrub cover. This outcome is inconsistent with the hypothesis that bottom-up effects should be strongest in grasslands because of greater herbaceous food resources. Instead, this interaction likely reflects changes in the landscape of fear because perceived predation risk in lagomorphs is reduced in shrub-dominated habitats. Shrub encroachment did not directly affect predation pressure on lagomorphs by changing population abundances of canids. However, both canid species responded positively to jackrabbit abundance indicating additional bottom-up effects. Finally, we detected interactions between the predators in which coyote abundances constrained spatial abundances of kit foxes, but these intraguild interactions also depended on shrub encroachment. Our findings demonstrate how environmental change affect trophic interactions by altering perceived predation risk in prey.

Technical Abstract: Environmental change is expected to alter trophic interactions and food-web dynamics with consequences for ecosystem structure, function, and stability. However, the mechanisms by which environmental change influences top-down and bottom-up processes are poorly documented. Here, we examined how environmental change caused by shrub encroachment affects trophic interactions in a dryland. The predator-prey system included an apex canid predator (coyote; Canis latrans), an intermediate canid predator (kit fox; Vulpes macrotis), and two herbivorous lagomorph prey (black-tailed jackrabbit, Lepus californicus; and desert cottontail, Sylvilagus audubonii) in the Chihuahuan Desert of New Mexico, USA. We evaluated alternative hypotheses for how shrub encroachment could affect trophic interactions including 1) modifying bottom-up processes by reducing herbaceous forage; 2) modifying top-down processes by changing canid abundances or the landscape of fear experienced by lagomorph prey; and 3) altering intraguild interactions between the dominant coyote and the intermediate kit fox. We used seven years of camera-trap data collected across grassland-to-shrubland gradients under variable precipitation to test our a priori hypotheses within a structural equation modeling framework. Lagomorph prey responded strongly to bottom-up pulses during years of high summer precipitation, but only on sites with moderate to high shrub cover. This outcome is inconsistent with the hypothesis that bottom-up effects should be strongest in grasslands because of greater herbaceous food resources. Instead, this interaction likely reflects changes in the landscape of fear because perceived predation risk in lagomorphs is reduced in shrub-dominated habitats. Shrub encroachment did not directly affect predation pressure on lagomorphs by changing population abundances of canids. However, both canid species responded positively to jackrabbit abundance indicating additional bottom-up effects. Finally, we detected interactions between the predators in which coyote abundances constrained spatial abundances of kit foxes, but these intraguild interactions also depended on shrub encroachment. Our findings demonstrate how environmental change may affect trophic interactions beyond traditional top-down and bottom-up processes by altering perceived predation risk in prey. These results have implications for understanding spatial patterns of herbivory and the feedbacks reinforcing of shrubland states in drylands globally.