4.1.2 Biodiversity

• Biodiversity is a measure of all the species worldwide, the genes they contain and the habitats of which they form a part.
• • Genetic diversity – variations in the genetic code
• Species diversity – how many different species in an area
• • Habitat diversity – how many different habitats in an area
• • A species is a group of organisms with similar anatomy, physiology, biochemistry and genetics as well as behavioural characteristics.
  •  They can interbreed to produce fertile offspring.
• • Different species can sometimes interbreed to produce infertile offspring called hybrids
• Habitats

  • The range of physical, biological and other environmental factors within which a species can survive.
  • Habitat biodiversity is high in the U.K.
  • Sand dunes, woodland, meadows and streams.
• Species richness = the number of species
• Species evenness = the abundance of individuals in each species
• We measure diversity because it allows comparisons to be made:

  • Between different areas
  • In the same area, but at different times
• $D=$$1- [Σ(n/N)^2]$

  n = the number of individuals of a particular species

  N = total number of all individuals of all species
• The importance of genetic biodiversity

  • All members of a species share the same genes. There is very little variation within their DNA.
  • They may, however, have different versions of the same genes.
  • These are called alleles.
  • The differences in the alleles among individuals of a species creates genetic biodiversity within the population. 
  • The more alleles present in the population, the more genetically biodiverse the population.

  Species with greater genetic biodiversity are more likely to adapt to changes in their environment and therefore less likely to go extinct.
• When genetic biodiversity increases, this can be because of:

  • Mutation(s) in the DNA of an organism, creating a new allele.
  • Interbreeding between different populations (same species). When an individual migrates from one population and breeds with a member of another population, alleles are transferred. This is called gene flow.
• When genetic biodiversity decreases

  1. Selective breeding (artificial selection)

  2. Captive breeding programmes in zoos and conservation centres

  3. Rare breeds

  4. Artificial cloning (asexual reproduction)

  5. Natural selection
• Selective breeding (artificial selection)


  Only a few individuals within a population are selected due to their advantageous characteristics
• Captive breeding programmes in zoos and conservation centres


  Only a small number of captive individuals of a species are available for breeding, often because the wild population is endangered or extinct
• Rare breeds


  An organism that has been selectively bred and then become less popular, causing the genetic diversity to be low
• Artificial cloning (asexual reproduction)


  Using cuttings to clone a farmed plant
• Natural selection


  Species will evolve to contain primarily the alleles that code for the advantageous characteristics, and over time the alleles coding for less advantageous characteristics will be lost from the population
• Genetic biodiversity in isolated populations e.g. zoos, can be assessed by:

  • Looking at the observable features of the individuals.
  • Measuring the proportion of heterozygotes in a population
  • Measuring the percentage of polymorphic gene loci in the genome of a population
• Sampling is estimating the number of individual organisms present in a particular area so that the abundance of a species can be known.
• Sampling can be used to measure a particular characteristic, for example the height of wheat.
• Samples are representative of the whole
• Sampling can be random or non-random.
• Random sampling: Throwing a quadrat and surveying the organisms within its perimeter introduces personal bias. A better method is to first divide the area into a grid of equal-sized squares and use a random number generator.
• Opportunistic

  • The weakest sampling method
  • May not be representative of the whole
  • This method samples organisms that are conveniently available
• Stratified

  • The population is divided into groups called strata and samples are taken from each group.
  • E.g., random sample can be taken each from females and males
• Systematic

  • Different areas within a habitat are sampled separately
  • This is often carried out using a line transect or a belt transect
• Line transect: a line is placed along the ground and samples are taken at specified points
• Belt transect: two parallel lines – continuous samples are taken along the belt using a quadrat.
• Interrupted belt transect: one line with a quadrat used at specified intervals (combination method). Allows for more rapid data collection.
• A sample is never completely representative of the whole habitat. This might be because of:

  • Sampling bias
  • The selection process could be biased (accidental or deliberate)
  • To remove sampling bias, random sampling must be used
  • Avoiding bias ensures that the data obtained are valid
  • Chance
  • The organisms selected may not be a true representation of the whole population.
  • E.g., five organisms measured may be the longest in their population
  • To improve reliability, the sample size must be as large as possible.
• Species density indicates how many individuals of that species there are per unit area.
• Species frequency is the probability that the species will be found within any quadrat in the sample area
• Sampling animals

  • All organisms must be handled carefully and for as short a time as possible.
  • A pooter is used to catch small insects. The insects are drawn into a holding chamber as the person sucks on a mouthpiece.
  • Sweep nets can be used to catch insects in long grass.
  • Pitfall traps are used to catch small, crawling invertebrates. A hole is dug, deep enough to prevent them crawling out and covered with a roof-structure so the trap does not fill with rain.
• Mark, release, recapture technique

  • This technique can be used to estimate the population size of small animals. It is difficult to accurately determine population size.
  • A sample is captured
  • The individuals are marked in some way
  • The animals are released and the traps are left for another period of time
  • A second sample is captured and population size is calculated
• Ethics of mark release recapture method

  • Marking must use a non-toxic substance
  • Method must not increase chance of predation
  • Method must not reduce chance of reproduction
• Assumptions in mark release recapture method

  • No births or deaths whilst method carried out
  • No migration into or out of population (population size constant)
• A frame quadrat is a square frame divided into a grid with equal sections.
• A point quadrat consists of a frame containing a horizontal bar. At set intervals along the bar, long pins can be pushed through to reach the ground.