Interacting roles of diet, cortisol levels, and parasites in determining population density of Belizean howler monkeys in a hurricane damaged forest fragment

Primates in fragments, because of their increased vulnerability to stochasticity, are in double jeopardy with the expected increases in severe weather patterns due to global climate change. It is thus increasingly important to have a better understanding of how severe weather events affect primate populations, especially those in fragments. This study explores the interacting effects of diet, cortisol levels, and parasites on the density of a black howler (Alouatta pigra) population following a major hurricane. In October 2001, Hurricane Iris made landfall in Southern Belize resulting in substantial damage to the 96-km² Monkey River watershed forest fragment and a loss of nearly 80 % of the population by 3 years after the storm. Late in 2004 the population stabilized and began to recover. From 2001 to 2006, demographic, behavioral, and dietary data along with fecal samples were collected from six monkey groups in an 86-ha study site in the Monkey River forest. Changes in population density over the 5-year period were explained primarily by fruit consumption both directly through inadequate fruit intake leading to energy malnutrition and indirectly through physiological stress (measured through fecal cortisol). Cortisol levels had a lesser direct effect on population density and were affected not only by low fruit consumption, but by multispecies parasite infections. This study highlights the importance of taking a multifactorial approach to understanding population density and shows how diet, stress, and parasites can have interacting effects in influencing primate population dynamics.