Investigating factors affecting the future survival of Exmoor ponies: implications for ecological restoration and management of the breeding population

Davy, Deborah Kim (2024) Investigating factors affecting the future survival of Exmoor ponies: implications for ecological restoration and management of the breeding population. PhD thesis, University of Glasgow.

Abstract

The current global climate and biodiversity crises are interlinked. Top-down trophic rewilding, using large herbivores, may make an important contribution to the restoration efforts needed to mitigate the global biodiversity crisis and increase ecosystems capacity to mitigate climate change. Exmoor ponies, a rare breed, are widely used in this role, as ecological engineers, on conservation grazing sites and in rewilding projects.

The overall purpose of this study was to investigate factors affecting the future survival of the Exmoor pony population, including the implications of their role in ecological restoration and rewilding. Since most Exmoor ponies are bred in free-living herds, it is expected that the continual exposure to environmental pressures increases selection of natural survival fitness traits. The specific aims of the study were to: 1) investigate the effects of grazing manipulations, using Exmoor ponies, on biodiversity and flowering plant abundance; 2) assess the impact of parasite load and seasonality on body condition in a herd of free-living Exmoor ponies; and 3) combine pedigree and molecular data to inform conservation breeding management of the Exmoor pony population.

In ecological restoration projects, herbivores are used to manipulate biodiversity, sometimes with the aim of increasing or decreasing the abundance of particular species. There is considerable anecdotal evidence of the positive impact of Exmoors grazing from established projects, but quantification of the results of their impact, and of their impact in comparison to other species of large herbivores would improve information for conservation managers. To investigate the impact of different grazing treatments the study described in Chapter 2, I used exclosures, enclosures, unmanipulated grasslands, and areas grazed exclusively for >30 years by Exmoor ponies or commercial livestock, to test whether the effects of different grazing treatments impacted overall vegetative biodiversity and, specifically, flowering plant abundance. The long-term grazed plots were used as an indicator of the stabilised effects of grazing by different large herbivore species. I found that Exmoor grazing positively impacted biodiversity and increased the abundance of flowering plants in comparison to the other treatments, including grazing by commercial cattle and sheep. A dynamic Bayesian model suggested the changes resulting from Exmoor grazing would be persistent. These results support anecdotal evidence from conservation grazing projects about the positive impact of Exmoors’ grazing and that they can be used as eco-engineers to improve overall biodiversity and flowering plant abundance.

Animals on restoration or rewilding sites rarely receive routine anthelmintic treatment or supplementary feeding in winter, so need to be resistant to the challenges of parasite loads, and of seasonal variation in vegetation quality and abundance, combined with the increased energy demands of winter weather. Seasonal variation in weather and changes in the availability of food resources, and gastro-intestinal parasite load can negatively impact the body condition of free-living horses. In Chapter 3 I assessed whether this low intervention management associated with restoration or rewilding projects could have impacts on body condition which could compromise the welfare of Exmoors in rewilding. Body condition scoring and faecal egg counts were performed in spring and autumn to investigate the impact of seasonality and parasite load on the body condition of free- living Exmoor ponies, not receiving supplementary feeding, or treated with anthelmintics. While winter resource limitation negatively correlated with body condition scores, individuals consistently gained condition in summer. Whilst parasite load was negatively correlated with body condition, parasite loads were generally lower than reported in other studies of free-living horses. Parasite load capacity is shown to be moderately heritable in Sable Island feral horses. If further investigation verified the comparatively lower parasite loads in Exmoors, this trait could be positively selected.

Exmoors are known to have suffered a genetic bottleneck of <50 individuals in the 1940s. Genetic bottlenecks are likely to be followed by increased inbreeding and genetic load. As most Exmoors are bred in free-living herds, pedigree verification by observation is not always reliable. Accurate identification of post-bottleneck founder lines could facilitate targeted breeding to prevent further loss and improve even representation of founders across the population. In Chapter 4 I combined Stud Book records with mtDNA and whole genome sequencing (WGS) to verify matrilines, estimate inbreeding based on runs of homozygosity (ROH) and investigate deleterious allele frequencies in relation to inbreeding. Using DNA extracted from hair samples from animals selected to represent a broad cross-section of the UK founder bloodlines, we aimed to get a representative view of the extant population. mtDNA haplotype networks revealed good overall congruence with recorded matrilines. Stud Book records revealed that representation of the founder lines within the population was uneven. Investigation of ROHs showed Exmoors to have varying, but mostly not significantly different historic and current levels of inbreeding in comparison with 23 other breeds. The proportion of loss of function to synonymous derived alleles declined significantly with increasing 10Mb ROH values, possibly indicating purging of deleterious alleles. These results improve stud book record accuracy, and understanding of inbreeding and relatedness and can therefore inform targeted conservation breeding to safeguard the future population.

Exmoor ponies need a role to ensure their future survival and linking that role to the preservation of their habitat will increase their conservation value and therefore population viability. The future of the Exmoor pony population is likely to be linked with their role as ecological engineers. This role may be crucial to their survival in a world threatened by the crises of biodiversity loss and climate change, as their value in contributing to biodiversity gains and to climate change mitigation is increasingly understood and appreciated. It is likely that a large proportion of the Exmoor population will continue to be born into free-living herds, where they will continue to be subject to natural, environmental selection pressures, increasing the likelihood that they will retain the survival and ecological interaction traits needed for them to thrive when rewilded. Ongoing monitoring of the founder representation, inbreeding and deleterious alleles could inform breeding so that a healthy, viable population can be maintained.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences; Q Science > QH Natural history; Q Science > QL Zoology
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Supervisor's Name: Mable, Professor Barbara and Matthiopoulos, Professor Jason
• Date of Award: 2024
• Depositing User: Theses Team
• Unique ID: glathesis:2024-84480
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 05 Aug 2024 13:21
• Last Modified: 05 Aug 2024 13:21
• Thesis DOI: 10.5525/gla.thesis.84480
• URI: https://theses.gla.ac.uk/id/eprint/84480