OCCUPANCY AND CO-OCCURRENCE OF FOREST WILDLIFE IN SOUTHERN ILLINOIS

Author

Justin John Remmers, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2023

Degree Name

Doctor of Philosophy

Department

Agricultural Sciences

First Advisor

Nielsen, Clayton

Abstract

Understanding how anthropogenic and natural habitat characteristics, in conjunction with interspecific interactions, influence a species’ occupancy is critical to developing effective management strategies and of scientific interest. Occupancy modeling has arisen as a cost-effective modeling approach to investigate a wide array of species across varying systems. Despite how prevalent occupancy modeling has become in the literature, few studies investigate community occupancy across large geographic regions to understand how varying environmental characteristics and interspecific interactions affect community assemblage. I used camera trap data collected from 357 camera clusters comprising 3-4 camera locations (n = 1,188 camera locations) across a 16,058 km2 region of southern Illinois, USA, during January-April 2008-2010. I used a variety of novel occupancy models, meta-analysis techniques, partial redundancy analyses, partial Mantel tests, and kernel density analyses to quantify the influence of environmental characteristics and interspecific interactions on biodiversity and occupancy of individual species and communities. There were 87,303 photographic captures of 14 forest wildlife species or taxonomic groups across 29,988 camera days. Camera cluster detection and occupancy probabilities ranged from 0.300 ± 0.001 (bobcat) to 0.898 ± 0.001 (raccoon) and 0.068 ± 0.000 (southern flying squirrel) to 0.987 ± 0.001 (white-tailed deer), respectively. Camera location detection and occupancy probabilities ranged from 0.14 ± 0.050 (eastern cottontail, wild turkey) to 0.34 ± 0.050 (fox squirrel) and 0.15 ± 0.030 (eastern cottontail) and 0.70 ± 0.100 (coyote), respectively. Models incorporating Simpson’s diversity index of patch types, distance to major road, and agriculture clumpiness index were most supported in explaining alpha diversity. Forest proximity and percentage forest cover explained minor variations in beta diversity, and I found weak, positive correlations between beta diversity and percentage forest cover and forest proximity index. Fox squirrels had higher occupancy at sites with more open forest structure and greater anthropogenic influence, while eastern gray squirrels had higher occupancy at sites with denser forests and less anthropogenic influence. I found a moderate level of activity overlap between the 2 squirrel species (Δ = 0.59, CI = 0.55, 0.62); however, no evidence of temporal partitioning was observed. Forest structure and grassland cover were influential on predator and prey occupancy at larger scales, while forest structure and anthropogenic influences were more influential on predator and prey occupancy at smaller scales. I did not find support for the influence of predators on prey occupancy. Mammalian biodiversity was strongly influenced by generalist species and highest with (1) moderate levels of habitat heterogeneity, (2) low to moderate levels of anthropogenic influence, and (3) nearby forest cover, as anthropogenic influences and agriculture can provide novel food resources and additional habitat that generalist species could exploit while tolerating any accompanying landscape fragmentation or disturbance. Between 2 sympatric squirrel species, habitat characteristics and spatial scale were more influential in partitioning than peak activity times. Predator and prey occupancies were more affected by habitat characteristics than interspecific interactions at both larger and smaller scales. My dissertation illustrates the usefulness of novel modeling approaches in investigating multiple questions from the same dataset and shows the importance of habitat in dictating the occupancy of forest wildlife across a large geographic region.