Getting Humans Off Monkeys' Backs: Using Primate Acclimation as a Guide for Habitat Management Efforts.

Wild primates face grave conservation challenges, with habitat loss and climate change projected to cause mass extinctions in the coming decades. As large-bodied Neotropical primates, mantled howling monkeys (Alouatta palliata) are predicted to fare poorly under climate change, yet are also known for their resilience in a variety of environments, including highly disturbed habitats. We utilized ecophysiology research on this species to determine the morphological, physiological, and behavioral mechanisms howlers employ to overcome ecological challenges. Our data show that howlers at La Pacifica, Costa Rica are capable of modifying body size. Howlers displayed reduced mass in warmer, drier habitats, seasonal weight changes, frequent within-lifetime weight fluctuations, and gradual increases in body mass over the past four decades. These within-lifetime changes indicate a capacity to modify morphology in a way that can impact animals' energetics and thermodynamics. Howlers are also able to consume foods with a wide variety of food material properties by altering oral processing during feeding. While this capability suggests some capacity to cope with the phenological shifts expected from climate change and increased habitat fragmentation, data on rates of dental microwear warn that these acclimations may also cost dental longevity. Lastly, we found that howlers are able to acclimate to changing thermal pressures. On shorter-term daily scales, howlers use behavioral mechanisms to thermoregulate, including timing activities to avoid heat stress and utilizing cool microhabitats. At the seasonal scale, animals employ hormonal pathways to influence heat production. These lines of evidence cumulatively indicate that howlers possess morphological, physiological, and behavioral mechanisms to acclimate to environmental challenges. As such, howlers' plasticity may facilitate their resilience to climate change and habitat loss. While habitat loss in the tropics is unlikely to abate, our results point to a potential benefit of active management and selective cultivation to yield large, interconnected forest fragments with targeted phenology that provides both a complex physical structure and a diversity of food sources. These steps could assist howlers in using their natural acclimation potential to survive future conservation threats.