Access

You are not currently logged in.

Access JSTOR through your library or other institution:

login

Log in through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Journal Article

The Effects of Prolonged Fasting of the Body Composition and Reproductive Success of Female Polar Bears (Ursus maritimus)

S. N. Atkinson and M. A. Ramsay
Functional Ecology
Vol. 9, No. 4 (Aug., 1995), pp. 559-567
DOI: 10.2307/2390145
Stable URL: http://www.jstor.org/stable/2390145
Page Count: 9
  • Read Online (Free)
  • Download ($18.00)
  • Subscribe ($19.50)
  • Add to My Lists
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Effects of Prolonged Fasting of the Body Composition and Reproductive Success of Female Polar Bears (Ursus maritimus)
Preview not available

Abstract

1. In total, pregnant Polar Bears that enter maternity dens in late summer/autumn may fast for up to 8 months in addition to meeting the nutritional demands of gestation and lactation. We quantified the nutritional costs of this prolonged `reproductive fast' and examined the effect of variation in maternal body condition on reproductive success. 2. Prior to entering dens, pregnant females were obese, containing as much as 1 kg of fat/kg of lean body mass (LBM). Among bears, LBM increased with body fat mass. This accumulation of LBM may be necessary in order to transport the large fat stores required for fasting, and may also provide a pool of protein essential for reproduction. 3. While fasting, bears lost 43% of body mass. Of the total energy expended on maintenance and reproduction, 93% was drawn from fat stores. This dependency upon fat conforms to the pattern of nutrient metabolism seen among other species adapted to prolonged fasting. Maternal metabolic rate was less than the predicted resting metabolic rate which illustrates the effectiveness of denning as an energy-conserving strategy. 4. Body fat was critically important for reproductive success. In particular, offspring body weight was very strongly related to the size of maternal fat stores before denning. Fatter bears produced heavier cubs which would be more likely to survive. 5. Among bears, pre-denning body condition was positively associated with age. Within the observed range (4-21 years), age-specific reproductive success should thus be highest among older bears. Such an effect could arise if: (1) the body condition of individual bears tends to improve with age and experience or (2) animals of poorer quality and condition die at a younger age.

Page Thumbnails

  • Thumbnail: Page 
559
    559
  • Thumbnail: Page 
560
    560
  • Thumbnail: Page 
561
    561
  • Thumbnail: Page 
562
    562
  • Thumbnail: Page 
563
    563
  • Thumbnail: Page 
564
    564
  • Thumbnail: Page 
565
    565
  • Thumbnail: Page 
566
    566
  • Thumbnail: Page 
567
    567