Biodiversity Arises from Evolutionary Processes (DP IB Environmental Systems & Societies (ESS))

Biodiversity Arises from Evolutionary Processes

• Biodiversity arises from evolutionary processes

• Biological variation arises randomly and can either be beneficial to, damaging to, or have no impact on, the survival of the individual

Natural Selection

• In any environment, the individuals that have the best adaptive features are the ones most likely to survive and reproduce

• This results in natural selection:

  • Individuals in a species show a range of variation caused by differences in genes

  • When organisms reproduce, they produce more offspring than the environment is able to support

  • This leads to competition for food and other resources which results in a ‘struggle for survival’

  • Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce

  • Therefore the genes resulting in these characteristics are passed on to their offspring at a higher rate than those with characteristics less suited to survival

  • This means that in the next generation, there will be a greater number of individuals with the better adapted variations in characteristics

• This theory of natural selection was put forward by Charles Darwin and became known as ‘survival of the fittest’

Example of Natural Selection

• Variation in fur colour exists within rabbit populations

• Rabbits have natural predators like foxes which act as a selection pressure

• Rabbits with a white coat do not camouflage as well as rabbits with brown fur, meaning predators are more likely to see white rabbits when hunting

• As a result, rabbits with white fur are less likely to survive than rabbits with brown fur

• The rabbits with brown fur therefore have a selection advantage, so they are more likely to survive to reproductive age and be able to pass on their genes to their offspring

• Over many generations, the frequency of the gene for brown fur will increase and the frequency of the gene for white fur will decrease

Selective pressures acting on a rabbit population for one generation - predation by foxes causes the frequency of rabbits with brown fur to increase and the frequency rabbits with white fur to decrease

• Remember that organisms better suited to their environments are more likely to survive, but survival is not guaranteed

• Organisms that are less suited to an environment are still able to survive and potentially reproduce within it, but their chance of survival and reproduction is lower than the individuals that are better-adapted

• Also, it is important to be aware that an environment, and the selection pressures it exerts on an organism, can change over time

  • When a change occurs then a different characteristic may become more advantageous

• Finally, remember that all organisms (not just animals) experience selection pressures as a result of the environment they are in

Another good example of natural selection is the evolution of the peppered moth