4.1 Insulation in terrestrial endotherms For organisms of similar size and shape in a similar thermal gradient, the rate of heat loss from convection is up to 90 times as fast in water as in air, so in temperate climates, aquatic endotherms need much more efficient insulation than terrestrial species. Since seawater freezes at −1.9° C, but the temperature of the air around the Poles can fall below −50° C, the insulation requirements of aquatic and terrestrial polar animals are not very different. Nonetheless, there are impor
3.3.1 Dormancy in black and brown bears The dormant state of bears differs from true hibernation in that the body temperature does not fall below 31–35° C and a major disturbance (such as an intruding biologist) can arouse them to full activity in a few minutes. Dormant bears do not eat, drink, urinate or defaecate, the heart rate drops from 50–60 beats min−1 to 8–12 beats min−1, and oxygen consumption is only 32% of that of actively foraging bears. Nonetheless, the rate of protein turnover, as mea
3.3 Bears Brown or grizzly bears (Ursus arctos), and black bears (U. americanus) feed throughout the summer on grass, fruit, nuts, fish, small mammalian prey and carrion. In autumn, all brown and black bears fatten rapidly before entering caves or hollow trees where they become dormant for weeks or months. The terms ‘hibernation’ and ‘torpor’ are sometimes used to describe this state in bears. To avoid confusion with true hibernation, this phenomenon is here called ‘dormancyâ
3.1 Introduction It is clear from Sections 1 and 2 that seasonal or irregular periods of fasting are an integral part of living at high latitudes, especially for large animals. When people (and many tropical and temperate-zone mammals) lose weight, either because they are eating less or because they are suffering from a digestive or metabolic disorder, protein is broken down in substantial quantities long before the lipid stores are exhausted. Even frequent and vigorous exercise cannot prevent the breakdown o
2.4 Variable fecundity The food supply for most polar species depends on several unpredictable factors so successful breeding is far from certain, even if births are tightly synchronized with the seasons. Maintaining pregnancy and feeding the offspring after birth (or hatching in birds) are energetically expensive. The death of the offspring before its maturity represents an irredeemable loss of ‘reproductive investment’ for the parents, particularly the mother, although the earlier in parental nurturing that t
2.2 Migration for breeding Birds do not hibernate, but like reindeer, many species undergo daily or seasonal changes in energy expenditure and appetite, and many of the endocrine changes that are an integral part of true hibernation in other groups. The fact that the preliminary stages of hibernation are widespread among vertebrates may help to explain why true hibernation has evolved several times in distantly related taxa. Instead of hibernating, some species of birds migrate to and from breeding areas, where they ar
2.1 Nutrient budgeting All plants and animals respond to environmental changes such as the light–dark cycle and temperature, but the impact of the environment on essential physiological processes such as eating, fattening and breeding is more evident and often more finely controlled in polar species than in those that are native to warmer and more equable habitats. Large effects are nearly always easier to quantify and to investigate experimentally, so arctic species offer an excellent opportunity to study the su
1.2 The polar environment At high latitudes, the Sun's rays always strike the Earth at a large angle from the vertical so they travel through a thicker layer of atmosphere and are attenuated by the time they reach the ground. Because the Earth's axis of rotation is inclined to its path around the Sun, there are large seasonal changes in daylength and the Sun is continuously below the horizon for a period in winter and continuously above the horizon for an equivalent period in summer. The annual changes in daylength an
1.1 Preamble This unit is about animals' structural and physiological adaptations to living permanently in cold climates; hibernation, a special response to transient or seasonal cold, is described in the openlearn unitAnimals at the extremes: hibernation and torpor (S324_2). Living in a polar climate involves adaptations of many physiological systems: appetite, diet, energy storage and reproductive habits as well as thermoregulation. In many cases, such changes involve ‘ordinary’ physio
Learning outcomes By the end of this unit you should be able to: define and use, or recognize definitions and applications of each of the bold terms; outline the special features of the polar regions as a habitat and list some contrasts between the Arctic and the Antarctic; describe some effects of daylength on feeding, fat deposition and reproduction in arctic animals; explain why the environmental controls of appetite, activity level and fecun
Introduction This unit is the third in a series of three on Animals at the extreme. In order to get the most from it you should have previously studiedAnimals at the extreme: the desert environment (S324_1)andAnimals at the extreme: hibernation and torpor
This unit is from our archive and is an adapted extract from Animal physiology (S324) which is no longer taught by The Open University. If you want to study formally with us, you may wish to explore other courses we offer in <
Acknowledgements The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: Figure 2 Nortier, P. and Soustelle, M. (1987) 'Alumina carriers for automotive pollution control', in Cruecq, A. and Frennet, A. (eds) Catalysis and Automotive Pollution Control, Elsevier Science Publishers; Fi
Figures
4.5.6 Catalyst deterioration: summary An ability to withstand mild deactivation is built into the design of the catalytic converter. However, severe deactivation could prevent the system from meeting emissions legislation. The major causes of deactivation are thermal damage and poisoning. High temperatures may cause sintering of the metals and/or the support; this can be prevented to some extent by the addition of ceria as a structural promoter. Damaging interaction
4.5.4 Phosphorus Phosphorus is recognised as a potential poison for automotive catalysts. The phosphorus level in fuel is generally very low (2×10−5 g l−1), but it is present in higher concentrations in engine oils (1.2 g l−1). Phosphorus derived from the engine oil is believed to react with the alumina support, and also to reduce the activity of the noble metal component. This deactivation is particularly important for Pd, with which phosphorus may form an all
Vitamin D Study in Finland: Implications for the Rest of the World
A new study on vitamin D levels and Parkinson's disease risk points to the need for further research on whether vitamin D supplements can protect against the movement disorder, according to an editorial in the July 2010 issue of Archives of Neurology. Dr. Marian Evatt, author of the editorial, discusses the details of the studied, carried out in Finland, and its implications on Parkinson's and general Vitamin D research.
Background
The study, also reported in Archives of Neurology, is the firs
Vitamin D Study in Finland: Implications for the Rest of the World
A new study on vitamin D levels and Parkinson's disease risk points to the need for further research on whether vitamin D supplements can protect against the movement disorder, according to an editorial in the July 2010 issue of Archives of Neurology. Dr. Marian Evatt, author of the editorial, discusses the details of the studied, carried out in Finland, and its implications on Parkinson's and general Vitamin D research.
Background
The study, also reported in Archives of Neurology, is the firs
