Ecological marginalisation in terrestrial mammals

Abstract

Humans shape species distributions and niches, causing them to shrink, shift or collapse. Despite increases in the area of land protected globally, population declines and species losses continue. A potential contributing factor to continuing declines is the restriction of species into marginal habitats where they experience poor performance. Range contraction restricts species into a limited subset of historic habitats and niche conditions. Marginalisation occurs when contraction constrains species to geographic or ecological extremes. In this thesis, I ask 1) how widespread is ecological and geographic marginalisation in terrestrial mammals and does it influence extinction risk; 2) what are the physiological and performance consequences of maintaining species in marginal habitats, 3) does marginality influence species in both fragmented and unfragmented landscapes and 4) how does marginalisation influence conservation planning. I begin this thesis with a general introduction and a critical evaluation of methods used in this thesis. In Chapter 3, I use a combination of phylogenetic and niche modelling to evaluate the intrinsic and extrinsic factors associated with range collapse and niche shift across 4785 mammal species. This chapter demonstrates ecological marginalisation is a common consequence of range contraction and increases extinction risk. In Chapter 4, I evaluate whether ecological and demographic factors drive glucocorticoid concentrations in Cape mountain zebra (Equus zebra zebra, CMZ). This chapter highlights the importance of using validated assays and links elevated faecal glucocorticoid concentrations to poor population performance. In Chapter 5, I use DNA metabarcoding of diet, microbiome, and nemabiome to investigate the macrophysiological consequences of food limitation across the CMZ species range. This chapter finds dietary composition alters microbiome and nemabiome composition and links low grass diets, and associated physiological consequences, to poor performance. In Chapter 6, I use DNA metabarcoding of diet, microbiome, and nemabiome to investigate seasonal dietary switching and its macrophysiological consequences across an ecological gradient in the Grevy’s zebra (Equus grevyi). This chapter demonstrates animals in a relatively unfragmented landscape can become restricted to marginal habitats. I conclude by discussing the conservation implications of marginalisation and suggest potential solutions. Published materials available in Appendices 1, 2 and 3 expand on these ideas. This thesis argues ecological marginalisation is an unappreciated conservation threat across terrestrial mammals.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Angela Harris (Supervisor) & Susanne Shultz (Supervisor)