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ECOLOGY, PHYSIOLOGY AND BEHAVIOUR OF EQUIDS: DEVELOPING MARKERS FOR INDIVIDUAL STATUS AND POPULATION HEALTH

Lea, Jessica

[Thesis]. Manchester, UK: The University of Manchester; 2017.

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Abstract

Understanding the causes of poor population performance is vital for effective species conservation. This thesis aimed to develop physiological and behavioural markers for individual status and population health in two equid species, using faecal hormone monitoring and social network analysis. First, individual physiology and population structure were evaluated in Welsh mountain ponies (Equus caballus) in response to an annual management practice involving the temporary translocation of the whole population and the removal of several stallions. An increase in mare faecal corticosterone metabolite concentrations was observed between days 5-10 post-release, however a high degree of variability was observed between individuals. Further investigation is required to validate faecal glucocorticoid measurements in response to an acute stressor. Social network structure was disrupted after the removal of key individuals, signified by an increase in network connectivity and a decrease in the strength of individual ties. Stallion faecal androgen metabolite concentrations were elevated after a time lag of five days and remained elevated until the end of the sampling period, possibly as a result of intensified male competition. These results indicate that targeted removals may have negative consequences for the stability of the social structure of the Welsh mountain pony population. Next, the ecology and physiology of the Cape mountain zebra (Equus zebra zebra) was investigated to identify the factors leading to poor population growth. Habitat quality, quantified by the abundance of palatable grass and nutrient content within reserves, was positively correlated with three measures of population performance: population growth rate, zebra density, and the number of foals per mare (or female fecundity). Faecal glucocorticoid and androgen metabolite concentrations were assessed across seven populations; faecal glucocorticoids were elevated aseasonally in populations in low quality habitat, and faecal androgens were significantly higher in populations with heavily male-biased adult sex ratios. Populations in low quality habitat may be chronically stressed as a result of poor nutrition, and excess stallions may cause increased male competition. Both hormones were negatively correlated with population performance. These results indicate two separate causes of poor population growth: low habitat quality and sex ratio skew. The Cape mountain zebra is an example of a partial refugee species, where some populations perform poorly due to their preservation in suboptimal habitat. Physiological markers of individual status were successfully identified, and can be used to indicate population health, to evaluate on-going conservation management strategies, and potentially to inform species response models to future perturbations.