Bioenergetic modelling of heat loss in endotherms
Başlık:
Bioenergetic modelling of heat loss in endotherms
Yazar:
Mould, Joanne, author.
ISBN:
9780438057104
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (256 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Advisors: Graeme Ruxton.
Özet:
This thesis examines theoretical and empirical factors involved in heat loss in endothermic animals. I investigate the factors imposing limitations on minimum size in birds and aquatic mammals in chapters 1 to 3. In chapter 1 analysis of the heat loss models of Ahlborn and Blake (1999 & 2001) highlighted assumptions made regarding the processes of heat loss that affected the overall predictions of minimum size. Similarly, in chapter 2 the model of Turner (1987a &1988) was found to have flaws regarding assumptions of core size and skin temperature. By reviewing these models I argue that by neglecting the external processes of heat loss the predictions of these models were considerably weakened. The minimum sizes predicted in chapter 1 were significantly larger than those observed in nature, even when the major assumptions were identified and alternative models developed to relax them. Sensitivity analysis showed that the thermal properties of birds were highly influential in determining a minimum size, particularly the thermal conductivity of the feather layer and the temperature gradient across the bird's body. Assumptions regarding the scaling relationship describing the diameter to length ratio of aquatic mammals were particularly flawed and the chapter concluded that the inclusion of the external processes of heat loss in addition to correction of the aforementioned assumptions was necessary to improve the accuracy of any heat loss model. Chapter 2 explicitly examined the composite resistances to heat loss in birds and aquatic mammals including external resistance to heat loss. This chapter highlighted the way in which different components of heat loss were significant for animals of different sizes; heat loss in small animals, for example, was highly dependent on external factors, whereas in large animals the physiological control of heat loss was of more importance. In chapter 3 I developed a model that corrected for all these factors. This model predicted minimum sizes larger than those observed in nature and such sizes were associated with a disproportionately large volume of insulation. I suggest that this discrepancy is due to the main assumption of the model: that these animals thermoregulate passively and do not actively regulate their body temperatures through behavioural or physiological means. By neglecting these processes, I possibly created an over reliance on insulation as the only adjustable parameter when animal size was very small. Accordingly, in chapter 4 I investigated the role of the cardiovascular system for animals of different sizes. Turner (1987a) claimed only animals of intermediate size could successfully utilise blood flow in their thermoregulation. Using the model developed in chapters 1 to 3 I investigated this claim and the model predicted that blood flow rates would have no effect on heat loss rates. This is incorrect and I suggest that the scaling relationship used by Turner (1987a) to describe blood flow was inappropriate. In chapters 5 and 6 I examined the role of behavioural thermoregulation in grey seal pups and adults during the 2003 breeding season on the Isle of May, Scotland. Experimental work examining the incidence of a suite of behaviours thought to be linked to the maintenance of thermal balance in mammals were recorded in seals in relation to weather conditions experienced at the study sites. In chapter 5 I discuss behavioural thermoregulation in grey seal pups: I conclude that the incidence of behavioural thermoregulation seemed to be affected mainly by the developmental stage of the pup than by weather conditions, although both solar radiation and wind speed appeared to exert some effect. In chapter 6, I investigated behavioural thermoregulation in adult grey seal females and found strong evidence weather conditions were linked to behaviour, although the weather parameters exerting an influence appeared to be site dependent. Chapter 7 modelled heat lost from a hauled out resting grey seal. This chapter found that there was little evidence to suggest that seals would suffer from thermal imbalance when exposed to typical winter conditions in the UK although low wind speeds could potentially lead to hyperthermia or overheating. Chapter 8 studied haul out site choice and orientation in grey seals on the Isle of Cumbrae, Scotland. The results found that seals adopted orientations suggestive of maximising heat loss with perpendicular orientation to the wind and parallel orientation to the solar azimuth angle. Coupled with preferential haul out on the windward side of the islands the study indicated that seals choose haul out sites and orientations that maximise the opportunity for heat loss. Further study could determine the importance of orientation for breeding females that are limited energetically for the duration of the breeding season.
Notlar:
School code: 0547
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684569.1) | 684569-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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