Sketch out a plan (on one side of a sheet of paper) for an essay in answer to this question: Describe the interrelationships between the rabbits and the other species on the South Downs, and so explain how and why the local vegetation changed after the myxomatosis outbreak. The South Downs, which is chalk grassland, extends from Winchester in Hampshire to Eastbourne in East Sussex. On the South Downs there is a rich diversity of plants and animals. A species of the South Downs is the european rabbit, Oryctolagus cuniculus which was introduced into Britain in the Middle Ages.
The first thing to look at is the interrelationships between the rabbits and other species. Rabbits are herbivores, primary consumers. They are highly selective grazers that concentrate on the most nutritious plants and keep the surrounding vegetation short. The elder bushes were unpalatable to the rabbits. Grazing by rabbits can be very beneficial to maintain the diversity of the habitat. The animals that benefited from this are the stone curlew, a species that favours to dwell in short grass.
Another species of bird, the wheater, benefited from the behaviour of rabbits as they use discarded rabbit holes for nesting. An insect that relies on the rabbit population is the minotaur beetle. The dung produced by the rabbits is used by the minotaur beetle larvae for food. Rabbits act as competition for the brown hare, other herbivores and other grazing animals as they all compete for food and territory. The scratching around for food and burrowing of the rabbits exposed areas of bare chalk, which encouraged the establishment of weeds such as nettles, thistles and ragwort.
Trees could not become deep-rooted because the rabbits damaged or killed them by eating the leaves. Trees grow from the tip down. When trees die, they decay and the nutrients are returned to the soil and utilised by other flora. This process is part of the food chain. When the myxoma virus was introduced in the early 1950s (the virus had spread from France), it produced an acute illness that resulted in death. The european rabbits had no immunity to the virus. After infection, skin tumours appeared after the 3rd day and had spread everywhere by the 4th day.
The symptoms were typically swelling of the genitals and the head, especially the eyelids which resulted in blindness. Approximately 13 days after infection, death occurred. The virus was spread by rabbit fleas and mosquitoes. This disease decimated the rabbit population. There is no evidence that the disease was intentionally brought into Britain but there is no doubt that some farmers moved the diseased rabbits around to control the population of rabbits locally. As the rabbit population died the flora and fauna community changed. Saplings managed to become established, as they were not being eaten.
Ragwort, elder bushes and plants that take longer to grow were crowded out and the hawthorn and juniper grew rapidly, as they were not being kept in check by grazing. Foxes, badgers and buzzards suffered, as they were predators of the rabbit. What was once a rich, thriving and vibrant community was evolving into shrubland and if left ignored would develop into woodland. This in turn would lead to the loss of low growing flowering plants and associated animals. In time, the rabbits developed some natural immunity to the myxoma virus, but the population has not fully recovered.
The stone curlew and wheatear no longer breed on the South Downs. There are now 300 or so species of low-growing herbs and flowers to be found on the undisturbed downland and over 20 of the species are orchids. Hawthorn trees are being physically chopped down. Sheep are now grazing there and farmers are discouraged from using pesticides, as the area is environmentally sensitive. Living organisms have developed by changing their structure, behaviour and adaptive mechanisms to enable them a better chance to survive and reproduce (fitness).
These organisms pass on these genes to their young and therefore continue the species (evolution). This is process is known as natural selection. Ecosystems are dynamic and are liable to change within communities over time, ie. change from grassland to woodland (succession). If a species (i. e. rabbits) is removed from an area then things become unstable and the outcome can be devastating. For one species has an affect on others if you follow its own chain from the producers to the consumers. Everything has a knock on effect and to change one part could have an affect on everything else in the long run.