Back
Home
1.1 outline the impact on the evolution of plants and animals of:
outline the impact on the evolution of plants and animals of:
- changes in physical conditions in the environment
- changes in chemical conditions in the environment
- competition for resources
Changes in physical conditions in the environment
- These include natural conditions, such as temperature and the availability of water.
- The Australia landmass has become drier over time and this has lead to changes in the species of kangaroos that are present today. Approximately 25 million years ago, Australia was considerably wetter than today with large areas of rainforest. During this time, kangaroos were small and omnivorous, with unspecialised teeth, eating a variety of foods from the forest floor. Food was nutritious and abundant; there was no need for specialised grinding teeth.
- As Australia became more arid and grass became the dominant vegetation in some areas, environmental selective pressure resulted in larger kangaroos favouring teeth suitable for grass. These teeth, high-crested molars, efficiently grind low-nutrition grass into a more easily digestible paste. Slicing pre-molars have been reduced.
Changes in chemical conditions in the environment
- Chemicals that can affect the evolution of species include salts and elements, such as iron. For example, many parts of Australia have soils that have a high salinity. There are a range of salt tolerant plants that have evolved to inhabit those areas. The animals that feed from these plants have also evolved to inhabit those areas.
- The sheep blowfly, Lucilia cuprina, is a major problem to the Australian sheep industry. It stresses, weakens and can be lethal to sheep when larvae, laid by females, burrows into wounds and wet wool. Chemicals, such as dieldrin and organophosphates, have been used extensively to control the blowfly. However, genetic resistance has occurred within the fly population that has made these chemicals ineffective. Withholding a particular insecticide for a time allowed the resistance of this particular blowfly population to drop. Continued use of the insecticide has resulted in the mutation of a modifier gene that increases and maintains the resistance. Thus, the insecticides can never be effective again, regardless of the number of blowfly generations that pass.
Competition for resources
- This occurs within a species and between species. If a new species is introduced into an area then the competition may lead to different species using different resources.
- Resources can include food, space or mates. If populations that live in the same area could specialise on slightly different resources or breed at different times, they would avoid direct competition.
- Some species of fruit fly have evolved into different species with each confined to a different type of fruit tree. This is possible if there are different flowering and fruiting times on each tree type suited for different breeding cycles in the fruit flies. Eventually, two distinct species can result.