Since animals are generally free to move about, their association with definite habitats is not at first sight so obvious as in the case of plants. Nevertheless, while studying various plant associations, contact with animal life will inevitably occur. Associated, for example, with a coppice or small wood are the various birds which build their nests in its shelter, blackbirds, thrushes, robins, wrens and hedge sparrows, while the vegetation provides food and shelter for innumerable insect larvae, snails and slugs on which the birds. Various small mammals, e.g. field mice, weasels, stoats and even rabbits, may be found burrowing into the relatively dry soil among the tree , while hedgehogs hibernate beneath the piles of dead which accumulate beneath the bushes. Wolf spiders and spinners are also generally abundant, the former hunting among the dead leaves for their prey and the latter spreading their webs among the branches of the bushes.
Animals are linked to the plants which provide their food, and in any one habitat food chains occur. For example, in a birch-oak wood association will be found various insect larva?on the foliage of the trees, e.g. tortrix moth caterpillars ; on these in turn feed the small insectivorous birds, e.g. warblers and tits ; while on these feed the birds, the hawks and the owls. Some insect larva? are found on certain particular food plants, e.g. cinnabar moth caterpillars on the ragwort, and hence occur only where these plants are found.
Two closed associations of animals, I.e. limited habitats sharply marked off and not forming part of more general societies, are found in a fresh-waterand in a rock pool on the seashore. Both of these repay study by the number of interesting types of animals found inhabiting these small ’worlds. ’
The Fauna of a Fresh-water Pond
The following typical examples occur :—
Amoeba species in the mud ; Vorticella and a similar colonial form known as Carchesium, both found clinging to water weeds and the hanging roots of duck-weed; various other free-swimming ciliates such as Paramecium and similar species, e.g. Stylonychia.
Hydra, both green and brown, clinging to theof water weeds.
Minute water ’fleas, ’ e.g. Daphnia and Cyclops, on which Hydra and fish feed. Many aquatic insects and their larvae, e.g. water scorpion, water boatman, water beetles, dragon-fly, gnat, mosquito and caddis fly larva?, water skaters and whirligig beetles.
Pond snails of various forms, e.g. ram ’s horn and ‘winkle ’types. Occasionally fresh-water mussels.
Minnows, sticklebacks and, in large, eels, roach, pike, carp and char.
Newts and their larva? and, in spring and summer, frog tadpoles and adult frogs.
Moorhens and sedge warblers.
Voles with their burrows in the banks.
The Fauna of a Rock Pool
Typical examples are :—
Ceel enter ates
Sea, e.g. the beadlet and colonial forms allied to Hydra, e.g. Sertularia found on the surface of seaweeds such as Fucus.
Seamats, common on surface of Fucus.
Paddle worms, tube worms, comb worms and lug worms.
Crabs, hermit crabs, shrimps and prawns.
Mussels, whelks, periwinkles and limpets.
Starfish and sea urchins.
Small fish such as sucker fish and gobies.