Home

Research

Publications

Lab members

Outreach

The Diademed Sifaka

Study Site: Tsinjoarivo

Tsinjoarivo's Biodiversity

Collaborators

Links

Current Research:

My current research examines the effects of forest fragmentation on the heatlh and viability of primate populations. The sifaka populations (Propithecus diadema) in forest fragments at Tsinjoarivo are surviving and reproducing, suggesting that nutritional stress is not sufficient to cause starvation or disrupt reproduction. However, lower body mass in fragments suggests nutritional stress, and mortality is higher in fragments, especially at the immature stage. I hypothesize that the altered diet and ecology are presenting indirect threats to population viability. This research consists of three main projects.

First, I am examining the nutritional consequences of dietary shifts which occur in sifakas in forest fragments. This involves the collection and chemical analysis of samples representing the most common sifaka foods, as well as detailed collection of feeding and intake rate data. This work has characterized the sifakas' diet in terms of energy intake, protein, fiber, sugars, fat and minerals, and thus quantified the nutritional consequences of seasonality, costs of dietary shifts observed in fragments. Future analyses will look at inter-individual variation as well as comparisons with sympatric lemurs. This research is progressing in collaboration with Dr Jessica Rothman, Dr David Raubenheimer and Dr Colin Chapman.

Leaves and fruit of Tongobivy
Leaves and fruit of a sifaka food
parasite egg
Parasite egg found in sifaka feces

Second, I am examining the patterns of disease prevalence and parasitism (in collaboration with Jean-Luc Raharison, whose doctoral work focuses on this issue). This research will investigate the possibility that sifakas' susceptibility to nutritional or other habitat-related stress may increase in fragments, due to: (1) increased proximity to human settlement (i.e. forest edge) and increased potential for cross-species transmission, and (2) reduced body condition and compromised natural defenses.

Third, I am examining more direct indicators of physiologic health, derived from capture of lemur study groups over time (in collaboration with Jean-Luc Raharison, Dr Karen Samonds, Dr Laurie Godfrey and Dr Randy Junge). These data include morphometric data, dental wear, and physiologic data from blood samples. This research will provide the most direct measures of health, which can be linked to dietary intake, and used to assess the utility of indirect predictors such as behavior and parasite load.

Past Research:


1. 2001-2005: PhD Research, conducted while at Stony Brook University.


An adult male in group CONT2

In 2001, I supervised a regional census to examine the distribution of the nine lemur species at Tsinjoarivo in a network of 37 forest fragments varying in size, shape and isolation. This research showed that the primate species differ widely in their tolerance of fragmentation.  Two species (Eulemur fulvus and E. rubriventer) were almost entirely absent from fragments.  The sifaka (Propithecus diadema) is present in medium and large fragments, with a minimum tolerable fragment size of about 25 hectares.  Other species can survive in smaller and more degraded fragments.

During the behavioral study of Propithecus diadema in 2002-2003, I accumulated over 6,000 hours of behavioral data split among four social groups, of which two lived in continuous forest with minimal human disturbance and two lived in highly-disturbed and isolated forest fragments.

I found that the key to survival in fragments was a mistletoe – a small hemiparasitic plant found rooting in the canopies of host trees (for more information, visit the Parasitic Plant Connection website). Continuous forest groups use one mistletoe species (Bakerella clavata) as a keystone resource, meaning they rely heavily on it to get through the dry season, when the fruits they prefer to eat are unavailable. For fragment groups, choices are limited because the preferred fruit trees are absent (likely through a combination of natural mortality and human extraction). As a result, fragment groups have elevated the same mistletoe from keystone to “staple” resource, meaning it is the most important food item in almost all months of the year.  This dietary shift has several consequences, including a drastic decrease in group cohesion (due to the small patch size of individual mistletoes, most individuals feed alone). The fitness consequences of the shift are hard to measure but several indirect lines of evidence suggest nutritional stress in the fragment populations (including a reduced body mass, especially for males – males are subordinate to females in this species, as in most lemurs).


A mistletoe in flower

For fragment groups, choices are limited because the preferred fruit trees are absent (likely through a combination of natural mortality and human extraction). As a result, fragment groups have elevated the same mistletoe from keystone to “staple” resource, meaning it is the most important food item in almost all months of the year. This dietary shift has several consequences, including a drastic decrease in group cohesion (due to the small patch size of individual mistletoes, most individuals feed alone). The fitness consequences of the shift are hard to measure but several indirect lines of evidence suggest nutritional stress in the fragment populations (including a reduced body mass, especially for males – males are subordinate to females in this species, as in most lemurs).

During 2004, Jean-Luc Raharison and I collaborated on broader distribution surveys to better define the distribution of the Tsinjoarivo sifaka and contact more villages.  In 2005, we started a reforestation initiative designed to reclaim fallow land and re-connect isolated forest fragments in the Mahatsinjo region. During this time, field teams led largely by Jean-Luc have continued to monitor the demography and behavior of the main sifaka study groups.

The research team at Tsinjoarivo (myself, Jean-Luc Raharison, and the local research assistants) formed an organization in 2003, the Tsinjoarivo Forest Fragments Project (TFFP).


The TFFP team in 2005

2. 1999-2000: Biological Surveys in Madagascar


Gilbert and Edmond collecting data (2003)

In 1999, I co-led three survey expeditions in the remote rainforest corridor extending north from Ranomafana National Park.  We discovered depressed population density in forests far from the park boundaries and increased prevalence of lemur hunting.

In 2000, I led two survey expeditions. The first was a primate and bird census of Kalambatritra Special Reserve, an extremely remote rainforest isolate located in south-central Madagascar.  This work resulted in the first characterization of the lemur community, and an expansion of the range of the endangered Madagascar Red Owl (Tyto soumagnei). The second survey was a primate inventory of Tsinjoarivo, where Ken Glander had just discovered the sifaka variant unique to that region. We contacted seven sifaka groups and clarified their distribution in intact forest and forest fragments.