Movement and dietary preferences of migratory ungulates as estimated from stable isotope ratios in tail hair

Kabalika, Zabibu (2023) Movement and dietary preferences of migratory ungulates as estimated from stable isotope ratios in tail hair. PhD thesis, University of Glasgow.

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Globally, ungulate populations face considerable threats from human activities, which have resulted in the global decline (and local extinction) of major ungulate species including the African elephant (Loxodonta Africana), the black rhinoceros (Diceros bicornis) and most recently, the African giraffe (Giraffa camelopardalis) . However, the most common animal response is movement, and the most common human mitigation strategy has been expanding coverage of protected areas. Yet, a significant loss of ungulates’ species and biodiversity has been reported across different protected areas, suggesting that expanding protected areas alone might not be the most effective solution. Restoring historical connectivity and migratory corridors might offer a more sustainable and manageable solution. However, to effectively apply conservation and restoration methods, historical information on the extent of animal movement patterns as well as their dietary preferences is of utmost importance. Yet, answering the question of where, how and why animals move has always been methodologically challenging, limiting our understanding of the extent of their movements as well their associated dietary preferences. The use of tracking devices and other traditional methods for studying animal movement has proven expensive and can pose serious concerns for animal welfare. Furthermore, studying movement retrospectively is impossible using the aforementioned techniques. Stable isotope ratio analysis techniques offer an alternative solution for exploring animal movement that is relatively cheap, easy to interpret and more importantly non-invasive to individual animals. Furthermore, the technique offers a possibility of understanding the historical range of animal movements retrospectively using archived materials such as specimens from museums. The primary contribution of this thesis is to demonstrate the applicability of isotopic analysis of tail hair to studies of movement and dietary interactions of migratory ungulates using the Serengeti ecosystem in East Africa as a case study.

The use of tail hair is promising because it represents a less-invasive way of recreating time series information of animal’s movement and feeding history. The Serengeti ecosystem presents a powerful model system to explore the use of isotopic methods applied to the tail hair of migratory ungulates because it harbors more than 27 species of ungulates including the migratory blue wildebeest (Connochaetes taurinus) and plain zebra (Equus quagga). Furthermore, the ecosystem has a diversity of soil types as influenced by the underlying geological parent material, which gives the ecosystem a strong spatial variability in the isotope values. The study presented here seeks to: demonstrate the potential of utilizing a less-invasive technique of stable isotope ratios in tail hairs to investigate animal movement. Then, to examine the feasibility of using isotopic ratios in tail hair for geolocating migratory animals. Furthermore, the study aims to demonstrate how isotopic ratios in tail hair can help to distinguish between resident and migrant life history strategies in a mixed population. And lastly, to employ isotopic ratios in tail hair to gain insight into the periods of dietary convergence and partitioning during the annual cycle of co-migrating species.

Using spatial generalized additive model (GAM), this study establishes an interpolated map for the variation of sulfur stable isotope ratios (δ 34S) in the grass across the Serengeti ecosystem (hereby referred to as the δ 34S isoscape). The isoscape was underpinned by a positive relationship between δ 34S and the local lithology. Using tail hairs sampled from cattle (Bos taurus), the created isoscape is used to test the hypothesis that δ 34S in tail hair reflects the δ 34S values of the diet (in this case, grass), and they can therefore be used for animal geolocation. Through a series of mathematical models and tail hair samples from GPS collared wildebeest, the δ 34S isoscape is used to identify the scenarios in which δ 34S in the tail hair are useful in the analysis of movement of migratory animals. Furthermore, I show using a series of state-space models of animal movement, how the δ 34S isoscape can be used in combination with variation of δ 34S in tail hair to differentiate resident versus migrant life-history forms of wildebeest. Using Stable Isotope Mixing Models (SIMMs), stable isotope ratios of carbon (δ 13C) and nitrogen (δ 15N) in the tail hair of wildebeest and zebra are used to understand seasonal periods of diet convergence and partitioning for the co-migrating animal species.

The results of this study suggest that the Serengeti ecosystem has strong spatial variability in δ 34S across its geological ranges. Furthermore, the results suggest that the δ 34S values in the tail hair strongly reflect the δ 34S values in the grass, suggesting that the variation of δ 34S in the tail hair can be used as a natural bio-logger for differentiating local versus non local movement of animals. The output from the mathematical models suggests that
the values of δ 34S take an average of 78 days from when the forage is ingested to isotope reflection in the tail hair of migratory wildebeest, suggesting that δ 34S might not be as effective for geolocating large mobile animals. On the other hand, the results from state-space models of animal movement suggest that the variation of δ 34S in the tail hair is effective in differentiating resident from migrant life history strategies. This finding led to the creation of a classification key for identifying resident versus migrant life-histories. Results from SIMMs have demonstrated that, using time-series information generated from tail hair samples, we can detect the periods of diet convergence versus diet partitioning between co-migrating animals. For example, the highest dietary niche overlap between wildebeest and zebra has been observed in August and the lowest in May. This finding suggests that we can identify periods of strong competition for pasture and possible mitigations that species take to maintain their co-existence using stable isotope ratios technique.

The results from this thesis highlight the importance and application of isotopic methods to understand movement and dietary preferences of migratory ungulates. The created δ 34S isoscape for the Serengeti acts as a baseline from which other isotopic studies can be conducted. Furthermore, the study has developed a classification key which can be adopted, modified and applied to a diversity of taxa for identifying resident and migrant life-histories. The study has further helped an understanding of niche partitioning and coexistence of species especially in biodiverse regions where multiple species all focus on the same general resource.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QH Natural history > QH345 Biochemistry
Q Science > QL Zoology
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
Supervisor's Name: Hopcraft, Professor Grant, Haydon, Professor Daniel, Newton, Dr. Jason, McGill, Dr. Rona and Morrison, Dr Thomas
Date of Award: 2023
Depositing User: Theses Team
Unique ID: glathesis:2023-83862
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 25 Oct 2023 15:40
Last Modified: 26 Oct 2023 11:08
Thesis DOI: 10.5525/gla.thesis.83862
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