IB Environmental systems and societies 3.1A Biodiversity Notes

Biodiversity: The Variety of Life at Three Levels

1. Biodiversity is the total variety of living organisms, and it sustains ecosystem stability, resilience, and productivity.
2. It is measured at three interconnected levels:
   1. Habitat diversity: the range of habitats or ecosystems in an area.
   2. Species diversity: the number and relative abundance of species in a region.
   3. Genetic diversity: the variety of genes within a species.

Habitat Diversity: More Habitats Mean More Niches

1. Habitat diversity is the range of different habitats or niches within an ecosystem or biome.
2. Each habitat supports distinct communities adapted to its conditions.
3. So areas with high habitat diversity usually hold high overall biodiversity.

Species Diversity: Richness and Evenness Together

1. Species diversity has two parts: species richness and species evenness.
   1. Species richness is the number of different species present.
   2. Species evenness is how evenly individuals are distributed among those species.
2. Species-rich ecosystems tend to be more stable, because complex food webs can absorb disturbance.

Genetic Diversity: The Raw Material for Adaptation

1. Genetic diversity is the variety of genes and alleles within a species.
2. Populations with high genetic diversity are more able to adapt to disease, climate change, and other stresses.
3. Low genetic diversity raises extinction risk, because the population has less capacity to evolve.

How the Three Levels Reinforce One Another

1. High habitat diversity creates more niches, which raises species diversity.
2. High species diversity broadens the overall gene pool, which supports genetic diversity.
3. High genetic diversity lets populations adapt and persist, which maintains ecosystem stability.

Biodiversity Builds Ecosystem Resilience

1. Resilience is an ecosystem's capacity to withstand disturbance and recover while keeping its essential functions.
2. Each level strengthens resilience in a different way:
   1. Habitat diversity means that if one habitat is degraded, others still provide refuge and resources.
   2. Species diversity adds redundancy, so if one species is lost others can fill its role, unless it is a keystone species.
   3. Genetic diversity lets populations adapt to gradual or sudden change.

Evolution Generates Biodiversity Over Time

1. Today's biodiversity is the product of billions of years of evolution, the gradual change in the genetic makeup of populations.
2. Natural selection acting on genetic variation is the main process that produces new adaptations and, eventually, new species.

The mechanism of natural selection and how new species form are covered in 3.1B.