Rodent Responses to Land Modification for Agriculture: Implications for Trophic Dynamics In the Northern Great Plains

Abstract

My thesis examines rodent species responses to agricultural land modification and their implications for trophic dynamics on the northern Great Plains. I first validated owl pellet analysis as a landscape-level sampling method for small mammal studies by comparing mammal diversity and composition between owl pellets and trapping from 27 studies of 15 owl species. Then using a dataset of >10,000 owl pellet samples collected from landscapes varying in agricultural intensity, I estimated rodent species responses to habitat loss and fragmentation, predicting species would respond relative to their affinity for unmodified grassland habitat. I found species responded irrespective of grassland specialization, indicating habitat specialization is not a universal proxy for sensitivity to land modification. I investigated the implications of these responses to sympatric great horned owl and burrowing owl diets, predicting great horned owls may competitively exclude endangered burrowing owls when diet composition was similar between the two species. I found both owl diets were dominated by small mammal prey in similar species composition, suggesting competitive exclusion of burrowing owls where their home ranges overlap with great horned owls. I also investigated whether woody encroachment facilitated increased great horned owl densities in mixed-grass prairie. Using 51 building surveys, I estimated the effect of forest cover on the presence of great horned owls in buildings. My results were inconclusive; I observed a potentially biologically relevant but statistically insignificant decline in building use with increasing percent forest cover, indicating my study lacked statistical power or influential conditions (e.g., internal conditions, forest edge, prey availability near buildings) responsible for owls roosting in buildings. This is the first landscape-level perspective of rodent responses to land modification and their implications for two sympatric raptor species. On the northern Great Plains, rodent population responses to land modification may change the spatial composition of rodent communities, facilitating interactions between great horned owls and burrowing owls that may further limit burrowing owl population persistence on the northern Great Plains. Globally, these results inform a broader debate regarding which conservation strategy, land sparing or land sharing, will be most effective at meeting global biodiversity targets while increasing food production to feed a growing human population.