Animals at the extremes: The desert environment
Animals at the extremes: The desert environment

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Animals at the extremes: The desert environment

2.2 How animals interact with the environment is affected by their body size

Willmer et al. (2000) classify desert animals in terms of the range of body sizes and the rate of evaporation (Figure 8).

Figure 8
Willmer, P., Stone, G. and Johnston, I. (2000) Environmental Physiology of Animals. Blackwell Science Limited ©
Willmer, P., Stone, G. and Johnston, I. (2000) Environmental Physiology of Animals. Blackwell Science Limited
Figure 8 Classification of desert animals based on body size and rate of evaporation

The logic of this classification can be appreciated by the following exercise. If you represent a small animal by a cube, and then make a larger scale model of it twice natural size, the linear dimensions of the larger animal would all be twice as large (Figure 9).

Figure 9
Figure 9 The linear dimensions, surface areas and volumes of three different-sized cubes are compared here to show how surface area: volume ratio decreases as the linear dimensions increase

However, the surface area of the model would not be increased by a factor of 2, nor would the volume, as can be seen by comparing Figure 9a and b. If the linear dimensions double; the surface area increases by a factor of 4 (22) and the volume by a factor of 8 (23). So the ratio of surface area to volume is lower in a large animal than a smaller one. Since heat is transferred at the surface, a small animal has greater potential for rapidly gaining and losing heat than a larger one because of its relatively large surface area. A smaller animal also has greater relative potential for evaporative water loss through its greater area of skin.

However, animals are not cube-shaped, and as you will learn in Section 2.5, certain desert species have features that can increase their surface area relative to their volume.

S324_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371