Quantifying Sexual Partitioning in Diet and Habitat Use in Wild Mandrills in a Dynamic Rainforest Savannah Landscape (Ref IAP-17-126)

As natural habitats are confronted with substantial environmental change, we urgently need more information on the resilience of at-risk populations in the face of disturbance. Historically, our efforts to predict responses to environmental stress has been hampered because of challenges in studying both how wild animals exploit space and what they eat. For example, although habitat and dietary choices differ substantially across species, inferring how these factors affect resilience to change is quite difficult because different taxa vary in many characters in addition to habitat and diet. Intraspecific sexual differences in functional traits also have dramatic effects on how individuals acquire and use environmental resources. Species with strong dimorphism are therefore ideal for studying how functional traits affect resilience to disturbance. The extreme sexual dimorphism of Mandrills (Mandrillus sphinx) presents an opportunity to study plasticity in diet and habitat use within the same species, a sharp contrast that isolates spatial and dietary differences from other variables including differences due to phylogenetic background.

Mandrills are the most sexually dimorphic primates: males possess remarkable ornaments that are important for sexual signalling, weigh three times as much as females and take much longer to reach sexual maturity. Both ornamental traits and size have strong links with resource availability, and may at least partly explain observations of sexual differences in space use within Lopé National Park in Gabon. Whatever the proximate cause of differences in space use, females exploit a wider range of habitats, and travel within very large groups, while mature males range less and spend much of the year outside of the group.

Work at Lopé has shown that forest structure and composition changes over relatively small temporal and spatial scales, and that fruit resources have recently declined and become less predictable; such changes mirror global forecasts of increasing uncertainty surrounding environmental change. Consequently, the sexual difference in mandrill space use (and its implications for how males and females exploit ephemeral and widely spaced food resources) may be a useful model for the prospects of at-risk populations. In addition, this work will shed light on condition-dependent sexual selection in heterogeneous environments.

Methodology
This PhD studentship contributes to a broader, integrative, effort to study the natural history and resilience of Mandrills in the face of environmental change. It has three main aims:
1. To quantify sexual difference in habitat use, and relate this space use to the nutritional resources contained therein. Here we will exploit the existence of a number of radiocollared animals in the Lopé NP mandrill horde. The candidate will combine historical measures of animal movement with continued tracking of animals of both sexes using radio telemetry.
2. To quantify temporal variation in food resource availability, and relate this variation to diet and space use as well as sexual trait expression. Here we will take advantage of modern analytic tools and continued monitoring of the fruiting phenology of food producing trees in Lopé NP. The candidate will map resource availability alongside habitat use, monitor changes in sexual trait expression over time using camera trap networks, and collect dung and tissue samples to assess the effects of local environmental resources on both diet and habitat use for both sexes. We will analyse these samples using isotope ecology at the state-of-the-art Life Sciences Mass Spectrometry Facility at SUERC in East Kilbride.
3. To calibrate SIA estimates of diet use through careful measures of a captive mandrills. The candidate will measure tissue turnover rates (e.g., by examining growth rates of different hairs on different individuals), and use diet manipulations to calculate the diet-tissue discrimination factor for the different isotope ratios.

For more information and background reading, see: https://goo.gl/y4BHXd