PhD Dissertation, Sarah Sells (2015-2019)

Territoriality is a fundamental and conspicuous behavior of numerous species, including many carnivores. Although relatively uncommon, carnivore sociality is likewise a conspicuous behavior where it occurs. Territorial and social behavior are of theoretical, empirical, and conservation interest because these behaviors can strongly shape demographic processes. Natural selection has likely shaped animals to make decisions that maximize benefits and minimize costs, but the mechanisms driving territory selection and social decisions remain uncertain. The goals of this research were to increase understanding of these mechanisms, and develop reliable methods to predict outcomes of territorial and social behaviors, absent costly monitoring efforts. Gray wolves (Canis lupus) provided a case study for developing and applying mechanistic and predictive models for territory selection and group size. This research comprised four parts:

• Part 1 was to develop a mechanistic model for the economics of territory selection. Through simulations, we developed numerous predictions for what may be observed empirically if animals select territories economically based on the benefits of food resources and costs of competition, travel, and predation risk. A literature search demonstrated that the model’s predictions matched empirical observations for many species.
• Part 2 tested the mechanistic territory model’s predictions on wolves. We analyzed territory sizes of wolf packs in Montana using wolf location data. As predicted, territory size varied inversely with prey abundance, number of nearby competitors, and group size.
• Part 3 entailed further applications and tests of the mechanistic territory model. After parameterization with limited, readily-available data, the model produced spatially-explicit predictions for territory location, size, and overlap for the Montana wolf population. It reliably predicted wolf distribution and the territory sizes and locations for specific packs, without using empirical data for wolves.
• Part 4 was to develop a predictive model for group size. We demonstrated that wolf pack sizes in Montana were positively related to the local abundance of prey and density of packs, and negatively related to terrain ruggedness, local mortalities, and intensity of harvest management. A predictive model for pack sizes reliably estimated the annual wolf pack sizes observed and illuminated possible underlying mechanisms influencing variation in pack sizes over space and time.

Learn more: 

Sells, S. N., and M. S. Mitchell. 2020. The economics of territory selection. Ecological Modelling 438: 109329.

Sells, S. N., M. S. Mitchell, K. M. Podruzny, J. A. Gude, A. C. Keever, D. K. Boyd, T. D. Smucker, A. A. Nelson, T. Parks, N. Lance, M. S. Ross, and R. M. Inman. 2021. Evidence of economical territory selection in a cooperative carnivore. Proceedings of the Royal Society of London B: Biological Sciences 288: 20210108.