Biodiversity and Conservation

The three important components of biodiversity are:

1. Genetic diversity
2. Species diversity
3. Ecological diversity

Ecologists estimate the total number of species in the world by using the species inventory of well-studied groups and then extrapolating from the ratio of species richness in temperate and tropical regions. Since tropical regions are much richer in species and many species are still undiscovered there, scientists compare the temperate-tropical ratio for an exhaustively studied group and apply that ratio to other taxa. This gives a gross estimate of total species diversity. For example, Robert May estimated the global species diversity at about 7 million.

The chapter gives three hypotheses for greater species richness in the tropics:

1. More evolutionary time: Tropics were not disturbed by frequent glaciations, so species had a long time to diversify.
2. More constant climate: Tropical environments are less seasonal and more predictable, which promotes niche specialisation and hence more species.
3. More solar energy: Greater solar energy leads to higher productivity, which indirectly supports greater diversity.

The slope of regression in a species-area relationship is represented by **$Z$** in the equation

$$\log S = \log C + Z \log A$$

It shows how rapidly species richness increases with area.

- For most regions and taxa, **$Z$ is 0.1 to 0.2.
- For very large areas like continents, the slope is much steeper, $Z$ = 0.6 to 1.2.

A steeper slope** means species richness increases much more rapidly with increase in area.

The major causes of species loss in a geographical region are the four causes of the Evil Quartet:

1. Habitat loss and fragmentation
2. Over-exploitation
3. Alien species invasions
4. Co-extinctions