Behavioral variation, parasite transmission, and demography of isolated populations of Grauer's gorilla (Gorilla beringei graueri)

Great apes have long lives, grow slowly, and reproduce late in life. This evolved life-history pattern now threatens many extant populations. Novel anthropogenic threats occur in tandem with ecological and demographic variation, which can have lasting impacts on population growth rates. Grauer’s gorillas (Gorilla beringei graueri) are among the most critically endangered subspecies among the extant great apes but have been relatively understudied. These group-living primates are found in eastern Democratic Republic of the Congo, a region experiencing rapid forest loss resulting in small, isolated gorilla habitats. In this dissertation, I explored three aspects of gorilla biology. In Chapter 1, I studied the effects of seasonal changes in food availability on within-group social interactions. I found that Grauer’s gorillas exhibit group-level changes in how spread out they are when they are foraging compared to when they are resting. However, in line with previous socioecological predictions, gorillas appear to be highly tolerant of group members while foraging, despite seasonal changes in the types of foods they consume. In Chapter 2, I conducted an exploratory analysis of the population-level transmission of nematodes found in Grauer’s gorillas. I used molecular methods commonly employed by parasitologists to identify the diversity of gastrointestinal nematodes found in multiple social groups living in the same habitat. I found that two of the most common taxa exhibited limited population structure, suggesting that gene flow for these nematodes among social groups may be quite high. I also discuss other explanations for this pattern, including parasite life history and development, abiotic factors, host movement, as well as alternative hosts in the habitat. Finally, in Chapter 3, I examined the effects of demographic stochasticity on the growth rate of a small, at-risk gorilla population (with only 2 adult females) in Mount Tshiaberimu, Virunga National Park. I used population viability analysis models to determine how random fluctuations in the number of births and deaths influenced growth rates. I identified the minimum number of female gorillas needed to reinforce the population to limit the effects of demographic stochasticity on the likelihood of extinction. The results of these studies offer insight into the natural history and ecology of Grauer’s gorillas. This work can help us understand how small, threatened populations are adapting to a rapidly changing landscape, which can improve conservation outcomes for this charismatic primate