Madagascar’s lemurs are the most endangered group of mammals in the world, with 94% of species threatened with extinction. Forest loss is one the greatest threat to these arboreal primates, but hunting, habitat degradation, and climate change also threaten their survival. Lemurs are a diverse group of more than 100 species; and their ecological traits shape how species respond to anthropogenic pressure. Incorporating knowledge of species’ ecological niches and evolutionary histories can contextualize threats and improve conservation assessments. In this dissertation, I investigate what constitutes suitable habitat for lemurs in light of the threats present, their sensitivity to forest fragmentation, their dispersal ability, and their ecological uniqueness.
I obtained data about lemur distributions in two ways. First, I conducted field surveys of the Critically Endangered blue-eyed black lemur (Eulemur flavifrons), which only occurs in the ecotone between eastern rainforest and western dry forest in the Sahamalaza region. I also surveyed the range of sister species, the black lemur (E. macaco), which inhabits nearby eastern rainforest in the Manogarivo region. I focused on areas that have not been surveyed recently and on the poorly studied boundary between the species to collect observations from the breadth of these species’ ecological ranges. I also documented threats, including incursions into protected areas, and collected fecal samples to test whether whole genomes could be obtained noninvasively for analyses of local adaptation in these species.
Second, I searched online databases and published literature for GPS localities for all species of lemur. I used these records, along with the ones collected in the field, to construct ecological niche models for nearly all species of lemur using Maxent. For the blue-eyed black lemur and the black lemur, I estimated the remaining area they can occupy based on these models and the threat survey data. Next, I examined the role of not just forest loss, but forest degradation, in determining where lemur species occur. I used high-resolution forest cover maps to determine lemurs’ tolerance for characteristics of degraded forest, including distance to the edge and mean patch size. I then limited species niche model to only intact, forested habitat. Lastly, using the sportive lemurs (genus Lepilemur) as an example, I evaluate how the inability to disperse across large rivers has influenced ecological niche diversity. I also examine what limited dispersal ability will mean for these species as climate change causes their ranges to shift.
Field surveys in the Sahamalaza and Manongarivo regions revealed extensive threats to blue-eyed black lemurs, from traps to cattle incursions and fire. I found no evidence of sympatry, but did locate an undocumented population of E. flavifrons north of the Andranomalaza River. Madagascar National Parks (MNP) managed protected areas appear to have less human incursion than NGO-managed protected areas. Further investigation of the ecological distinctiveness of these species is possible via non-invasive methods: I sequenced whole genomes at 2.3x coverage from eight of the fecal samples collected during this study. While SNPs indicating a loss of function did not reveal any patterns, sequencing additional samples could make studies of local adaptation and population genetic diversity possible.
At the regional scale, forest conversion is a grave threat to lemurs. When forest loss and degradation are considered in habitat models, lemur species have lost 51% of their habitat in the last 30 years. Proximity to a forest edge rendered more forested areas too degraded for lemurs than did mean patch size. This result is likely the influence of human contact nearer the forest edge. I recommend urgent support for reserves like Beanka, Tsimembo Forest, Ranobe PK 32, and Amoron’i Onilahy, which have highly suitable, intact forest for many lemur species. Spaces like these will be important for conserving the remarkable diversity within the sportive lemur clade. Though their distribution is largely explained by riverine barriers, I show a role for ecological niche divergence and local adaptation in accelerating allopatric speciation. These same rivers will limit their ability to track climatically suitable areas as climate change progresses: sportive lemurs as a group will lose nearly a quarter of their accessible habitat to climate change by the 2070s.
While my results are focused on the particulars of lemur conservation in Madagascar, the methods I have presented here are broadly applicable to other threatened species. Piggybacking fecal sample collection onto rapid field surveys is straightforward. The possibility of obtaining whole genomes from non-invasive samples presents a new way to answer questions about local adaptation without risking injury to other arboreal study subjects, like Neotropical monkeys, or for elusive species like big cats. For threatened species, their climatic niche only dictates part of their distribution. The habitat quantification pipeline presented here takes advantage of thirty-five years of research in Madagascar to estimate species’ tolerance for forest fragmentation. While these records are impressive for primates, they are dwarfed by those available for passerines, through scientific literature and online repositories like eBird. By integrating field surveys, ecological niche modeling, and non-invasive genomics, we can begin to understand the complex threats facing species like lemurs and the options for ensuring their survival.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/d8-g3hy-h580 |
| Date | January 2020 |
| Creators | Tinsman, Jen Casey |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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