Weather can affect food quality

The ways in which weather controls the changes in abundance of other animals can, however, be even more subtle and indirect than any of the foregoing examples. In the case of many herbivorous insects it does so by changing the quality, rather than the quantity, of the insects' food. Right at the beginning of this book I related how I had been fortunate enough to see the effect of the massive outbreaks of spruce budworm on balsam fir, their preferred food plant, in eastern Canada. And as I later...

Successful reproductive strategies

Not all carnivores are so profligate and 'wasteful' of their young, however. Some have, like the kangaroos, evolved the capacity to vary the number and timing of the production of young according to the prospect of success in an uncertainly variable environment. A particularly good example is seen with the European stoat. Stoats are small but ferocious predators which evolved in the northern hemisphere where their principal prey are voles, animals notorious for the wild fluctuations in their...

Social dominance hierarchies

We have seen something of the way in which territorial behaviour operates to sequester the limited amount of good protein food in the environment to only a few females and their growing progeny. And how this meant that all others, including previous young, must be expelled from the territory. Well, the same function is fulfilled by increasingly complex social structures where such expulsion does not happen, or is delayed, or does so only now and then. Here, animals of two or more generations...

With a little help from microbes

Animals cannot produce the enzyme cellulase, so they are unable to digest the cellulose which, as we have seen, makes up the bulk of the tissues of plants. Nor, consequently, can they readily gain access to the nutritious contents of cellulose-walled cells of plants. So it is not surprising to find that many herbivores have evolved a variety of associations with micro-organisms like bacteria, fungi and protozoans, which are able to digest cellulose. Such associations markedly increase the...

Herbivores are fussy eaters

If you take the trouble to look closely at just what a herbivore is eating - be it a sheep grazing in improved pasture or a caterpillar eating gum leaves - you will find that it is a very fussy feeder. It will be highly selective not just about what sort of plant it will eat, but at what stage of its growth it will eat it and what parts of the plant it will eat. There are many, many herbivores, large and small, vertebrates and invertebrates, which browse or graze leaves. None of them, however,...

Meateating vegetarians and cannibals

The tammar wallabies which live on Kangaroo Island in South Australia, were considered to be strict herbivores. However, I have a colleague who spent many hours quietly following them and recording what they ate. To his surprise - and the disbelief of many - he discovered that they are not the obligate vegetarians everyone assumed them to be. On the contrary they are frequently carnivorous. They commonly eat mice and nestling birds, small lizards and insects whenever they encounter and can...