Introduction Mammals come in a bewildering variety of shapes and sizes and yet all of the 4700 or so species have some characteristics in common. Indeed, it's the existence of these common features that justifies the inclusion of all such diverse types within the single taxonomic group (or class) called the Mammalia. This is the first in a series of units about studying mammals. To get the most from these units, you will need access to a copy of The Life of Mammals (2002) by David Attenboroug
9 Wildebeest migration The skill of thinking in a scientific way is as much a part of being a scientist as is knowing facts – perhaps more so. In this series of units, you'll not only come across facts about particular techniques, such as radio transmitters and bat detectors, but also the tactics that scientists use to inves 8.3 Shortage of minerals You may be familiar with salt licks that are provided for domesticated cattle. In the wild, grass is also often low in minerals (e.g. it has almost no sodium and very little calcium), so grazers may have to go to extraordinary lengths to supplement their diet with additional minerals obtained from the most unlikely places. LoM gives some examples, but the most impressive activity takes place in the caves of Mount Elgon in Kenya [pp. 113–114]. You'll probably recall this spectacular footage 7 Plant defences Watch the ‘Plant Predators’ programme from 05.03–12.07 and make notes in answer to the following questions. (a) In what ways do plants shown in this sequence protect themselves against their predators? (b) H 6 Grazers and browsers A good deal of the discussion so far has been related to animals that eat leaves in the form of grass and other herbaceous plants, the grazers, but this is not the only type of plant food. Also available as food are the leaves of trees and bushes. These form the diet of the browsers. 5.2 Pseudo-ruminants Animals in the third suborder of the Artiodactlya, the pigs, peccaries and (according to most authorities) the hippopotamuses (suborder Suina), use a slight variant on the ruminant method, and are often referred to as pseudo-ruminants. You might like to add this information to your version of Table 2. These animals do have st 5.1 Ruminants The earliest ruminant was probably an ancestor of the present-day chevrotain. The chevrotain skeleton appears to have remained virtually unchanged for the past 30 million years and, although there are now only four species confined to the jungles of Africa and Southeast Asia, they once had a worldwide distribution. So, chevrotains are placed in the suborder Ruminantia within the order Artiodactyla, to which other deer, antelopes, cattle, sheep and goats also belong. A second suborder, the Tyl 3 Herbivore teeth Tables are a useful way of recording key information. The headings for Tables 1 and 2 have been prepared for you, and you can copy and complete the tables in your notebook. If you need to find any of this information again later, then it is very useful to have it summarised in a table. I 2 The herbivore lifestyle – living on leaves Leaves are a much less nutritious food than most kinds of animal material, so large herbivores have to eat large quantities of plants and they have special ways to digest their food. As author David Attenborough (DA) says, ‘Leaves are extremely poor food’ [p. 89]. To find out why living on a diet of leaves is particularly difficult, we need to know something about how leaves work. Learning outcomes By the end of this unit you should be able to: describe the particular problems in digesting plant material; give examples of the ways in which teeth are modified for a herbivorous diet; explain the importance of digestive enzymes; explain the importance of microbes in digesting plant material; compare the main features of the digestive systems of ruminants and hindgut fermenters; describe some of the way Introduction The plant predators, or herbivores, are a varied group, but they share certain characteristics. Many of them are large; among the smallest is the chevrotain (or mouse-deer) at about two kilograms weight, and the elephant is the largest, with a typical bull male weighing around six tonnes. In this unit we'll be looking in more detail at some of the problems and consequences of adopting a plant-eating way of life. Leaves are a much less nutritious food than most kinds of animal material, so lar Acknowledgements The content acknowledged below is Proprietary (see terms and conditions). This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: The content acknowledged be 6 Reflection If you are working through all the units in this series, you'll be aware that this unit has taken a somewhat different tack from earlier ones. I've used rodents to explore some fundamental biological principles that have a relevance far beyond this particular order. It is especially appropriate to talk about issues such as biological success in connection with rodents, given their very wide geographical distribution and the very large number of rodent species and individuals. You'll recall (f 5.3 The effect of environment on reproductive behaviour Review your reading of Section 4.2 on the family life of marmots (or re 5.2 Differences between the sexes In biology, ‘sex’ refers to a particular form of reproduction, sexual reproduction, that is distinct from asexual reproduction. As you know, sexual reproduction involves the production of eggs by females and sperm by males; eggs (or ova) and sperm are known as gametes. It is a universal feature of mammalian biology that in sexual reproduction there are two types of gametes and that progeny are produced by the fusion of two unlike gametes to form a single cell called the zygote. The zygote 5.1 Monogamy and polygamy You've seen plenty of evidence that reproduction in rodents – more precisely what I've called their reproductive strategies – are versatile and varied. You'll appreciate that ‘versatile and varied’ describes the range of sexual habits seen in the rodents as a group, not the behaviour within a single species. As DA says, some are monogamous, which means that individuals mate exclusively with one partner, over at least a single breeding cycle or season. The marmots are an example of a g 4.1 A measure of success If what I have highlighted so far were the whole story, the only adaptive features shown would be those that equipped the rodent for times of famine, which is patently not the case. It is obviously a very important factor in the production of new species because the most productive of rodents (rats and mice) account for about 1300 of the 2000 or so rodent species, following the figures given in the TV programme. In LoM you have seen many interesting characteristics to which adaptive functions 3.6 The numbers game … or the struggle for existence In the majority of The Life of Mammals TV sequences there is relatively little evidence of any struggle for existence, apart from the occasional predator/prey interaction. Even then you are offered the comforting reassurance that ‘four out of five chases end with the prey escaping’. So you could be forgiven for thinking that most mammals survive to a ripe old age, or at least until, like the topi, they have fulfilled their reproductive potential. Not so! Four out of five chases may 3.5 Natural selection Darwin summarised his theory of natural selection in the introduction to The Origin of Species as follows: As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life 3.4 Competition In plants it is particularly obvious that many more potential offspring (seeds) are produced than can survive. To a very large extent it is a matter of chance as to which are the survivors. Some are eaten, others overlooked or stored away and forgotten. Those that survive to germinate might be on unsuitable soil, too dry or too wet, so that they shrivel or rot. The successful seedling could be in poor soil, deficient in minerals, or there may be many other plants that are already established
Activity 5
Activity 5
