Ecophysiological studies of body composition, body size and reproduction in polar bears

For the polar bear (Ursus maritimus), a terrestrial carnivore on the highest trophic level in the Arctic marine ecosystem, periods of nutritional restriction or fasting are a characteristic feature of an annual cycle. The overall objective of my thesis was to examine some of the effects of such a &#...

Full description

Bibliographic Details
Main Author: Atkinson, Stephen Noel
Other Authors: Ramsay, Malcolm
Format: Thesis
Language:English
Published: University of Saskatchewan 1996
Subjects:
Online Access:http://hdl.handle.net/10388/etd-10202004-235652
id ftusaskatchewan:oai:harvest.usask.ca:10388/etd-10202004-235652
record_format openpolar
spelling ftusaskatchewan:oai:harvest.usask.ca:10388/etd-10202004-235652 2023-05-15T15:19:55+02:00 Ecophysiological studies of body composition, body size and reproduction in polar bears Atkinson, Stephen Noel Ramsay, Malcolm January 1996 http://hdl.handle.net/10388/etd-10202004-235652 en_US eng University of Saskatchewan http://hdl.handle.net/10388/etd-10202004-235652 TC-SSU-10202004235652 wildlife biology ursus maritimus polar bears fasting growth body composition lactation reproductive performance text Thesis 1996 ftusaskatchewan 2022-01-17T11:53:33Z For the polar bear (Ursus maritimus), a terrestrial carnivore on the highest trophic level in the Arctic marine ecosystem, periods of nutritional restriction or fasting are a characteristic feature of an annual cycle. The overall objective of my thesis was to examine some of the effects of such a 'feast-or-fast' feeding pattern on the body composition, body size and reproductive performance of this Holarctic ursid. As a reproductive strategy, pregnant polar bears occupy maternity dens for up to 6 months between late summer and spring. While in dens, maternal nutrient stores meet all maintenance energy requirements and sustain the nutritional demands of gestation and early lactation. I quantified the nutritional costs of this prolonged 'reproductive fast' in polar bears and examined the effects of variation in maternal body condition on reproductive performance. While fasting, body mass decreased by 43% and of the change in body energy content 93% was attributable to loss of fat. Bears that were fatter priorto denning produced heavier cubs, which would be more likely to survive. Much of the variation in body condition prior to denning was accounted for by age, older females being in better condition. Using an index of milk quality that was closely related to daily milk energy yield, I investigated the independent effects of maternal body condition and age on lactation. Irrespective of condition, older bears tended to produce higher quality milk. While lactation in polar bears is clearly sensitive to body condition, these results also provide strong support for an age-specific increase in reproductive effort among females. Body size is typically a strong determinant of male reproductive success in polygynous mammals such as polar bears. Consequently, theory predicts that mothers in good condition should invest more in male than female offspring in-order to produce large adult males. An underlying assumption of this theory, however, is that early differences in body size among male offspring, such as those apparent by the end of maternal care, will affect their relative adult body size. I tested the validity of this assumption in polar bears and found that, in comparison to females, variation in body size among 2-year-old males was a weak determinant of adult size. I suggest that, in comparison to females, a longer period of growth after maternal care may predispose the adult size of males to a greater degree of environmentally mediated variation. This lack of persistence in relative body size would limit the ability of mothers to affect the adult size of their male offspring, and thus reduce the effectiveness of sex-biased maternal investment as a reproductive strategy in polar bears. One of the principle physiological adaptations enabling animals to go without food for prolonged periods seems to be a heightened ability to minimize the net catabolism of body protein. I quantified changes in the body composition of free-ranging polar bears during the ice-free season. In contrast to previous studies on fasting bears, catabolism of protein appeared to meet a significant proportion of maintenance energy demands in some individuals. (Abstract shortened by UMI.) Thesis Arctic polar bear Ursus maritimus University of Saskatchewan: eCommons@USASK Arctic
institution Open Polar
collection University of Saskatchewan: eCommons@USASK
op_collection_id ftusaskatchewan
language English
topic wildlife biology
ursus maritimus
polar bears
fasting
growth
body composition
lactation
reproductive performance
spellingShingle wildlife biology
ursus maritimus
polar bears
fasting
growth
body composition
lactation
reproductive performance
Atkinson, Stephen Noel
Ecophysiological studies of body composition, body size and reproduction in polar bears
topic_facet wildlife biology
ursus maritimus
polar bears
fasting
growth
body composition
lactation
reproductive performance
description For the polar bear (Ursus maritimus), a terrestrial carnivore on the highest trophic level in the Arctic marine ecosystem, periods of nutritional restriction or fasting are a characteristic feature of an annual cycle. The overall objective of my thesis was to examine some of the effects of such a 'feast-or-fast' feeding pattern on the body composition, body size and reproductive performance of this Holarctic ursid. As a reproductive strategy, pregnant polar bears occupy maternity dens for up to 6 months between late summer and spring. While in dens, maternal nutrient stores meet all maintenance energy requirements and sustain the nutritional demands of gestation and early lactation. I quantified the nutritional costs of this prolonged 'reproductive fast' in polar bears and examined the effects of variation in maternal body condition on reproductive performance. While fasting, body mass decreased by 43% and of the change in body energy content 93% was attributable to loss of fat. Bears that were fatter priorto denning produced heavier cubs, which would be more likely to survive. Much of the variation in body condition prior to denning was accounted for by age, older females being in better condition. Using an index of milk quality that was closely related to daily milk energy yield, I investigated the independent effects of maternal body condition and age on lactation. Irrespective of condition, older bears tended to produce higher quality milk. While lactation in polar bears is clearly sensitive to body condition, these results also provide strong support for an age-specific increase in reproductive effort among females. Body size is typically a strong determinant of male reproductive success in polygynous mammals such as polar bears. Consequently, theory predicts that mothers in good condition should invest more in male than female offspring in-order to produce large adult males. An underlying assumption of this theory, however, is that early differences in body size among male offspring, such as those apparent by the end of maternal care, will affect their relative adult body size. I tested the validity of this assumption in polar bears and found that, in comparison to females, variation in body size among 2-year-old males was a weak determinant of adult size. I suggest that, in comparison to females, a longer period of growth after maternal care may predispose the adult size of males to a greater degree of environmentally mediated variation. This lack of persistence in relative body size would limit the ability of mothers to affect the adult size of their male offspring, and thus reduce the effectiveness of sex-biased maternal investment as a reproductive strategy in polar bears. One of the principle physiological adaptations enabling animals to go without food for prolonged periods seems to be a heightened ability to minimize the net catabolism of body protein. I quantified changes in the body composition of free-ranging polar bears during the ice-free season. In contrast to previous studies on fasting bears, catabolism of protein appeared to meet a significant proportion of maintenance energy demands in some individuals. (Abstract shortened by UMI.)
author2 Ramsay, Malcolm
format Thesis
author Atkinson, Stephen Noel
author_facet Atkinson, Stephen Noel
author_sort Atkinson, Stephen Noel
title Ecophysiological studies of body composition, body size and reproduction in polar bears
title_short Ecophysiological studies of body composition, body size and reproduction in polar bears
title_full Ecophysiological studies of body composition, body size and reproduction in polar bears
title_fullStr Ecophysiological studies of body composition, body size and reproduction in polar bears
title_full_unstemmed Ecophysiological studies of body composition, body size and reproduction in polar bears
title_sort ecophysiological studies of body composition, body size and reproduction in polar bears
publisher University of Saskatchewan
publishDate 1996
url http://hdl.handle.net/10388/etd-10202004-235652
geographic Arctic
geographic_facet Arctic
genre Arctic
polar bear
Ursus maritimus
genre_facet Arctic
polar bear
Ursus maritimus
op_relation http://hdl.handle.net/10388/etd-10202004-235652
TC-SSU-10202004235652
_version_ 1766350123727585280