What is Biodiversity? (SL IB Environmental Systems & Societies (ESS))

Why is biodiversity important?

• Biodiversity can be thought of as a study of all the variation that exists within and between all forms of life
• Biodiversity looks at the range and variety of genes, species and habitats within a particular region
• It can be assessed at three different levels:
  • The number and range of different ecosystems and habitats
  • The number of species and their relative abundance
  • The genetic variation within each species

• Biodiversity is very important for the resilience of ecosystems, in that it allows them to resist changes in the environment

Habitat diversity

• This is the range of different habitats within a particular ecosystem or biome
• If there is a large number of different habitats within an area, then that area has high biodiversity
  • A good example of this is a coral reef. They are very complex with lots of microhabitats and niches to be exploited
• If there is only one or two different habitats then an area has low biodiversity
  • Large sandy deserts typically have very low biodiversity as the conditions are basically the same throughout the whole area

Photo by Francesco Ungaro on Unsplash 

A coral reef is an example of a habitat with high biodiversity

Species diversity

• An ecosystem such as a tropical rainforest that has a very high number of different species would be described as species-rich
• Species richness is the number of species within an ecosystem
• Species diversity looks at the number of different species in an ecosystem, and also the evenness of abundance across the different species present
• The greater the number of species in an ecosystem, and the more evenly distributed the number of organisms are among each species, then the greater the species diversity
• For example, an ecosystem can have a large number of different species but for some species, there may only be 3 or 4 individuals. As a result, this ecosystem does not necessarily have high species diversity
• Ecosystems with high species diversity are usually more stable than those with lower species diversity as they are more resilient to environmental changes
• For example in the pine forests of Florida, the ecosystem is dominated by one or two tree species. If a pathogen comes along that targets one of the two dominant species of trees, then the whole population could be wiped out and the ecosystem it is a part of could collapse

Photo by Worm Funeral on Unsplash 

The lack of species diversity in the pine forests of Florida makes them vulnerable to collapse when pathogens enter the ecosystem

Genetic diversity

• Genetic diversity is the diversity of genes found within different individuals of a species
• Although individuals of the same species will have the same total set of genes, these genes can take a variety of different forms
• This makes it possible for genetic diversity to occur between populations of the same species
  • For example, some humans can digest milk even as adults. (this ability is called lactase persistence), while others cannot
  • It depends on a gene called LCT, which has different versions in different populations
  • In European populations, there is a gene variant called C/T-13910 that is linked to lactase persistence - if someone has the CC version of the gene, they are more likely to be able to digest milk as adults, but if they have the TT version, they may have difficulty digesting milk
  • In East Asian populations, like Chinese and Japanese, there is a different gene variant called G/C-13915 - people with the GG version of this gene are more likely to have lactase persistence, while those with the CC version may struggle with digesting milk
  • So, these differences in a single gene can affect whether individuals can digest lactose or not
  • This shows how genetic variations can contribute to the observed differences in lactase persistence among different human populations.

• Genetic diversity within a single population also occurs
  • This diversity is important as it can help the population adapt to, and survive, changes in the environment
  • The changes could be in biotic factors such as new predators, pathogens and competition with other species
  • Or the changes could be through abiotic factors like temperature, humidity and rainfall

 Biodiversity is a broad concept encompassing the total diversity of living systems, which includes the diversity of species, habitat diversity and genetic diversity