Biodiversity

• Biodiversity


  The variety of living organisms in a particular habitat
• Habitats with higher biodiversity include tropical rainforests, which host an abundance of plant and animal life, compared to desert or arctic habitats
• Ways to define biodiversity


  • Species diversity
  • Habitat diversity
  • Genetic diversity
• Species diversity


  The variety of different species living in an area
• Habitat diversity


  The number of different habitats within an area
• Genetic diversity


  The number of different alleles within a population
• Endemism


  A species is described as 'endemic' if it is found in one location only
• Endemic species are vulnerable to extinction because if a natural disaster or some other threat to their survival wipes out the population, there will be no other individuals remaining
• Conservation programmes are particularly important for endemic species
• Heterozygosity Index

  Genetic diversity is a measure of the number of different alleles within a population. It can be measured using something called the Heterozygosity Index which calculates the extent of genetic diversity by determining the proportion of heterozygotes (genotypes with two different alleles) within a population. The higher the number of heterozygotes, the higher the genetic diversity. The Heterozygosity Index is measured using the equation below:

  
• Index of Diversity

  Species diversity can be measured by calculating the Index of Diversity (D) of a particular habitat. It takes into account both the number of different species and the abundance of each species. The larger the value for the Diversity Index, the more biodiverse the habitat is. It is calculated using the following equation:

  
• N is the total number of organisms of all species living in that habitat and n is the number of organisms of a single species.
• Example of Index of Diversity:

  
• Niche


  The role that an organism plays in the ecosystem and includes its biotic (living) interactions, such as the food it eats and the predators which it needs to hide from, as well as its abiotic (non-living) interactions, such as the gases which it breathes or the sunlight it absorbs
• Within a habitat, different organisms each occupy a particular niche
• If two different species try to occupy the same niche, one will be out-competed by the other until only one species survives
• To increase their chances of survival, organisms will be adapted to the niche that they occupy
• Gorillas' niche


  • Fruits and bamboo shoots which they eat
  • Oxygen they inhale
  • Carbon dioxide they exhale
  • Trees that they use for shelter
• Adaptation


  Features of living organisms which make them suited to their niche and more likely to survive
• Types of adaptation


  • Behavioural
  • Physiological
  • Anatomical
• Behavioural adaptations


  • The way that an organism acts which increase its chances of survival
• Behavioural adaptations


  • Fish swimming in groups called schools for protection
  • Birds migrating south during the winter to find food
• Physiological adaptations


  • Processes which occur within the body of an organism which increase its chances of survival
• Physiological adaptations


  • Sloths having a low metabolism to survive on food with low calories
  • Plants like deadly nightshade producing poison as a defence against being eaten
• Anatomical adaptations


  • Structural features of an organism which increase its chances of survival
• Anatomical adaptations


  • Polar bears being camouflaged against the snow
  • Cacti having spines to prevent being eaten
• Natural selection


  The process by which species evolve
• Evolution


  The change in allele frequency within a population over time
• Evolution


  1. Variation within the population

  2. Gene mutations cause new alleles to appear

  3. Organisms with advantageous alleles more likely to survive and reproduce

  4. Greater proportion of individuals in next generation have advantageous allele

  5. Frequency of advantageous allele increases in population
• Variation within the population is because different individuals have different alleles
• Some gene mutations may be harmful but some may be beneficial
• Organisms with alleles which give them characteristics most suited to their environment


  Are more likely to survive to reproductive age and pass on their genes to their offspring
• Organisms with advantageous alleles


  Are also more likely to survive and reproduce, and pass on the advantageous allele to their offspring
• Over time, the frequency of the advantageous allele increases in the population - this is evolution
• Speciation


  The development of a new species
• Speciation


  1. Two groups of a population become reproductively isolated from each other

  2. Reduced gene flow between the two groups

  3. Natural selection acts separately on the two sub-populations

  4. Frequency of alleles within their gene pools will change differently

  5. Two groups become so different they can no longer breed with each other
• Reproductive isolation


  • Prevents the transfer of genes between two groups
• Causes of reproductive isolation


  • Behavioural changes (e.g. new courtship behaviours)
  • Mechanical changes (e.g. changes to genitalia structure)
  • Temporal changes (e.g. different pollen production times)
• Allopatric speciation


  Speciation involving organisms becoming geographically separated from one another
• Sympatric speciation


  Speciation occurring in the absence of a geographical barrier