Biodiversity (HL IB Biology)

Biodiversity

• Biodiversity can be thought of as the variety of life that exists in a specified area
  • This can refer to global biodiversity, or to the biodiversity of a smaller region
• Biodiversity is very important for the resilience of ecosystems; the more biodiverse an ecosystem is, the more stable and resistant to change it will be
• Biodiversity can be studied at three different levels:
  • Ecosystem
  • Species
  • Genetic

Ecosystem diversity

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

Species diversity

• Species diversity can be measured in two ways:
  • Species richness is the number of species within an ecosystem
  • Species evenness is the number of individuals of each species within an ecosystem
• For an ecosystem to have high species diversity it must have high species richness and high species evenness
  • An ecosystem would not be species diverse if it had 1000 species, but only had a few individuals of 500 of those species; this would be high richness but low evenness
  • An ecosystem would not be diverse if it had 10 species and had thousands of individuals of each species; this would be high species evenness but low species richness
• 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

Genetic diversity

• The genetic diversity is the number of different alleles of genes that are present
  • This can be in an entire species or in a local population
• Factors that contribute to genetic diversity include:
  • The proportion of genes that have more than one allele
  • The number of different alleles that each gene has
• There can be genetic differences or diversity between populations of the same species
  • This may be because the two populations live in different areas and so are subject to slightly different selection pressures that affect the allele frequencies in their populations
• There can be genetic differences between individuals within a population
  
  • Genetic diversity in a species is important as it can help the population adapt to, and survive, changes in the environment

Types of biodiversity diagram

There are different levels of biodiversity, such as ecosystem (habitat) diversity, species diversity, and genetic diversity

Biodiversity change over time

• Current estimates for global species diversity vary, but recent estimates suggest that there could be around 8.7 million species on Earth
  • Around 1.2 million species have currently been recorded and classified, meaning that if estimates are correct, there are still many more species to be discovered
• The number of species on Earth has not always been the same; the fossil record shows that:
  • Many species that have existed in the past are no longer present
    • This is due to extinction
  • There are many more species alive today than have been alive in the past
    • The process of speciation leads to an increase in the number of species
• When speciation occurs at a higher rate than extinction, global biodiversity will increase
• Despite many extinctions occurring over recent years, periods of speciation in the past mean that global biodiversity levels are still higher than ever before

Speciation gives rise to new species over time, increasing global biodiversity

NOS: Classification is an example of pattern recognition but the same observations can be classified in different ways

• The accuracy of the estimated number of species on Earth is dependent on the process of classification
  • If species are classified correctly then estimates will be more accurate
  • If species are incorrectly classified together then estimates will be too small
  • If species are incorrectly separated then estimates will be too large
• Classification can be subjective; it is not always easy to determine the point at which one species has become two, or whether similar organisms are of the same species, or are two different species
• It can be said that taxonomists are either
  • 'Lumpers'
    • Lumpers focus on similarities more than differences, and are more likely to classify species together
  • 'Splitters'
    • Splitters focus on differences, and are more likely to classify species separately