Dissertations, Theses, and Capstone Projects

Date of Degree

2-2023

Document Type

Dissertation

Degree Name

Ph.D.

Program

Anthropology

Advisor

Andrea Baden

Committee Members

Ryan Raaum

Larissa Swedell

Shawn Lehman

Subject Categories

Biological and Physical Anthropology

Keywords

Madagascar, isolation-by-resistance, circuit theory, gravity models, landscape genetics, conservation

Abstract

Dispersal is a fundamental aspect of primates’ lives, influencing population connectivity through gene flow, driving community structure and assembly, and having important consequences for adaptation and speciation. Primates disperse within an environmental context, with both intervening and local environmental factors affecting the motivation, capacity, timing, and success of dispersal at all phases. Direct evaluations of primate dispersal are challenging given the rarity of dispersal events and the large distances that animals often settle from their departure site, therefore indirect measures– such as the use of population genetic data– are more common.

The field of landscape genetics enables researchers to combine population genetic data with landscape information to explicitly evaluate the influence of both local and intervening environmental variables in driving dispersal. To date, research in primate landscape genetics has primarily focused on the role of the intervening landscape in driving dispersal, while the effects of local habitat characteristics remain untested. Additionally, although the effect of environmental variables is likely scale dependent, no published studies have assessed the differential influence of environmental factors on smaller-scale gene flow resulting from typical dispersal events compared to multigenerational gene flow at larger geographic scales.

Therefore, the primary goal of this dissertation was to use a landscape genetics approach to examine the influence of both between- and within-site environmental variables in driving short-range black-and-white ruffed lemur (Varecia variegata) dispersal in the Ranomafana National Park (RNP) and adjacent Ambositra-Vondrozo Forest Corridor (COFAV) and compare results to published studies assessing the drivers of long-range dispersal. This dissertation had three main objectives: 1) Characterize habitat quality across the RNP-COFAV region using traditional botanical plots and transects to enable an evaluation of the role of local environmental quality in driving ruffed lemur dispersal; 2) Characterize ruffed lemur population genetic structure and diversity across the RNP-COFAV region to evaluate functional connectivity and dispersal characteristics of ruffed lemurs in the region; and 3) Combine data from objectives 1 and 2 to evaluate the short-range environmental drivers of ruffed lemur dispersal and functional connectivity across the RNP-COFAV region, and compare findings to previously identified drivers of long-range dispersal.

This dissertation focused on the region of southeastern Madagascar containing the Ranomafana National Park (RNP), the park’s 3-km buffer zone, and the adjacent Ambositra-Vondrozo Forest Corridor (COFAV). This region is characterized by a broad diversity of historic and contemporary forest modification within both RNP and the COFAV. In Chapter 2, I found significant ecological variability between sites throughout the region, with the pristine and strictly protected site of Mangevo (in southeastern RNP) exhibiting significantly taller canopy, larger DBH, greater basal area, and greater species diversity than almost all other sites investigated. The sites differing the most from Mangevo and having the smallest canopies, DBH, basal areas, and lowest species diversity were also found within RNP, but were previously subject to intensive modification in the late 1980s. Interestingly, I found no significant differences in forest structure and floristic diversity between the strictly protected RNP compared to the park’s buffer zone and the COFAV, both of which are designated for sustainable extractive use.

In Chapter 3, I found that ruffed lemurs in the RNP-COFAV region retain levels of genetic diversity comparable to or greater than those found in prior studies in the area, as well as compared to several other lemur species. Using both Bayesian and multivariate structure analyses I reveal that ruffed lemurs in the RNP-COFAV region constitute a single genetic population, suggesting significant functional connectivity throughout the region. This result is further corroborated by the identification of four first-generation migrants that were sampled within RNP but have an assigned natal location within the COFAV. Furthermore, my results indicate that both male and female ruffed lemurs disperse– corroborating recent work– although I was unable to determine if any biases exist between the sexes in frequency and distance of dispersal.

Finally, in Chapter 4, I found that the most influential drivers of short-range ruffed lemur dispersal were between-site terrain ruggedness and canopy height, more so than any within-site habitat characteristic evaluated. My results suggest ruffed lemurs disperse through the least rugged terrain that enables them to remain within their preferred tall-canopied forest habitat. Furthermore, I noted a scale-dependent effect of the environment when comparing my results to landscape characteristics identified as driving long-range ruffed lemur dispersal, with forest structure driving short-range dispersal and forest presence critical for facilitating long-range dispersal and multigenerational gene flow. Taken together, my findings suggest that it is crucial that we retain high quality forests and forest connectivity to facilitate continued dispersal and maintain functional connectivity in ruffed lemurs.

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