- Each species of organism has an ecological niche - a set of environmental conditions in which it can survive and reproduce
- Adaptations within an environment may be behavioural, physiological or morphological
- Hydrophytes are flowering plants adapted for living in water, while xerophytes are plants adapted for living in dry habitats
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- Environmental factors affect the distribution of organisms and include abiotic, climatic and edaphic (soil) factors, and biotic fators.
- Interspecific competition is an important biotic factor. The competitive exclusion principle is that no two species may occupy the same ecological niche
- Zonation occurs where there is an environmental gradient that affects the distribution of organisms
- On a rocky shore, rough periwinkles are adapted to the upper shore and common periwinkles are adapted to the middle shore
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- Within sexually reproducing species, genetic variation is generated by the process of meiosis (crossing over and independent assortment) and cross fertilisation. Mutation occurs in all species and introduces new alleles into the population
- Genetic variation is acted on by the process of selection, which reduces the range of variation exhibited. The genetic forms selected for are regarded as the 'fittest'. They exhibit better adaptations within their environment , so that they survive to reproduce and pass on their 'fitter' alleles.
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- Stabilising selection favours the adaptive norm and selects against extreme variations from the norm. It operates to maintain the constancy of a characteristic in a stable environment
- Directional selection favours one extreme and selects against the other. It brings about a change in the genetic composition of the population, resulting in evolutionary change. It is important in maintaining the adaptability of a species within a changing environment
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