Habitat complexity mediates spatiotemporal niche partitioning among native and invasive seed predators

Red imported fire ants dominate certain food webs in North America due to their omnivorous and aggressive feeding behavior. Structural habitat complexity can mediate effects of invasive predators on native insects, by either facilitating or tempering antagonistic interactions, with potential consequences at lower trophic levels. Along a gradient of habitat complexity, we evaluated how refuge affects the activity and foraging behavior of fire ants and native invertebrate seed predators using video surveillance, and then determined their consumption of pigweed seeds in seed removal assays. Fire ants dominated seed predation in our system, and structural complexity increased both their activity and seed removal, while reducing that of native seed predators. In structurally simple habitats with high sun exposure, fire ant activity was restricted to the evening when tem-peratures were milder, while native seed predators foraged during the heat of the day, possibly to avoid antagonistic interactions with fire ants. In relatively shaded, structurally complex habitat, the active foraging period for fire ants expanded earlier into the heat of the day, and almost totally overlapped with that of native seed predators. Our data suggest that structural refuge may facilitate antagonism and site/resource domination by fire ants.

Automated summary

Red imported fire ants dominate certain food webs in North America due to their omnivorous and aggressive feeding behavior. Structural complexity of the habitat can mediate the effects of fire ants on native insects, increasing their activity and seed removal while reducing that of native seed predators.