3.4.6 Biodiversity within a community

Okay so first it's probably a good idea for us to learn some terms:

• species diversity is the number of different species and the number of individuals of each species within any one community
• genetic diversity is the variety of genes possessed by the individuals that make up a population of a species
• ecosystem diversity refers to the range of different habitats from a small local habitat to the whole of the Earth

A good measurement of species diversity (the number of different species and the number of individuals of each species within any one community) is species richness. Species richness is a measure of the number of different species in a community. One way of measuring species diversity is to use the equation:

d = (N(N-1))/(Σn(n-1))

NOTE:
d = index of diversity
N = total number of organisms of all species
n = total number of organisms of each species

An index of diversity describes the relationship between the number of species in a community and the number of individuals in each species.


Efforts to provide enough food for the human population at a low cost has led to a reduction in biodiversity. This is because basically as natural ecosystems develop they become complex communities with a high index of diversity. However, agricultural ecosystems are controlled by humans and farmers often select species for particular qualities to make the farms more productive. Any particular area can only support a certain biomass. If most of the area is taken up by the desirable species there is smaller area for the other species and the other species must out-compete one another for the small area. Furthermore, pesticides exclude species that compete for light/mineral ions/water/food required by the farmed species.

We need to know about the balance between conservation and farming. Certain practices that have (directly) reduced species diversity include:

• removing hedgerows
• creating monocultures
• draining marshland/filling in ponds
• over-grazing of land

Practices that have indirectly reduced species diversity include:

• the use of pesticides/inorganic fertilisers
• escape of effluent from silage stores/slurry tanks into water courses
• absence of crop rotation

A number of management techniques can be applied to increase species diversity without largely raising food costs/lowering yields. These include:

• maintaining hedgerows
• planting hedges as boundaries instead of fences
• maintaining ponds
• planting native trees
• using organic fertilisers
• reducing the use of pesticides
• using crop rotation that includes a nitrogen-fixing crop
• creating natural meadows