African Primate Assemblages Exhibit a Latitudinal Gradient in Dispersal Limitation

Terrain Ruggedness and Canopy Height Predict Short-Range Dispersal in the Critically Endangered Black-and-White Ruffed Lemur

Dispersal is a fundamental aspect of primates' lives and influences both population and community structuring, as well as species evolution. Primates disperse within an environmental context, where both local and intervening environmental factors affect all phases of dispersal. To date, research has primarily focused on how the intervening landscape influences primate dispersal, with few assessing the effects of local habitat characteristics. Here, we use a landscape genetics approach to examine between- and within-site environmental drivers of short-range black-and-white ruffed lemur (Varecia variegata) dispersal in the Ranomafana region of southeastern Madagascar. We identified the most influential drivers of short-range ruffed lemur dispersal as being between-site terrain ruggedness and canopy height, more so than any within-site habitat characteristic evaluated. Our results suggest that ruffed lemurs disperse through the least rugged terrain that enables them to remain within their preferred tall-canopied forest habitat. Furthermore, we noted a scale-dependent environmental effect when comparing our results to earlier landscape characteristics identified as driving long-range ruffed lemur dispersal. We found that forest structure drives short-range dispersal events, whereas forest presence facilitates long-range dispersal and multigenerational gene flow. Together, our findings highlight the importance of retaining high-quality forests and forest continuity to facilitate dispersal and maintain functional connectivity in ruffed lemurs.

Differential habitat use by sympatric species of mouse lemurs across a mangrove–dry forest habitat gradient

Understanding the mechanisms by which similar species coexist in sympatry is a major driver of ecological research. Niche partitioning and ecological plasticity can facilitate spatial and habitat use overlap between generalist and specialist species. Mouse lemurs (Microcebus spp.) are a highly speciose group of small primates that are endemic to the forests of Madagascar. In northwestern Madagascar, the relatively widespread M. murinus occurs sympatrically with the microendemic M. ravelobensis. We investigated spatial distributions and densities of these two species across a mangrove–dry forest habitat gradient in Mariarano commune. We used capture-mark-recapture techniques and nocturnal line transect surveys along six transects during June and July 2017. Spatial capture-recapture and distance sampling models were used to estimate lemur densities across habitat types. The congeners displayed differential patterns of spatial distribution and densities. Microcebus murinus was found in similar densities across all habitat types, while M. ravelobensis was found at much higher densities in dry forests compared with mangroves. This suggests that the generalist M. murinus uses a wider array of habitats more evenly than the specialist M. ravelobensis. Our study provides empirical evidence of how cryptic lemur species differ in their habitat use and distribution across an environmental gradient and provides new insights into their ecology in an understudied habitat. Lemurs are one of the most threatened groups of mammals in the world, and understanding how these species are distributed across different forest types is crucial for planning and implementing conservation measures to protect lemur habitat.

Effects of Environmental Stress on Primate Populations

Environmental stress on primate populations can take many forms. Abiotic factors, such as temperature and precipitation, may directly influence the behavior of primates owing to physiological demands of thermoregulation or through indirect influences on vegetation that primates rely on for food. These effects can also scale up to the macro scale, impacting primate distributions and evolution. Primates also encounter stress during interactions within and between species (i.e., biotic interactions). For example, selective pressure from male-perpetrated infanticide can drive the development of female counterstrategies and can impact life-history traits. Predation on primates can modify group size, ranging behavior, and habitat use. Finally, humans have influenced primate populations for millennia. More recently, hunting, habitat disturbance, disease, and climate change have increased in frequency and severity with detrimental impacts on primate populations worldwide. These effects and recent evidence from camera traps emphasize the importance of maintaining protected areas for conserving primate populations.