Biodiversity is a term often used to express the number of different living organisms in an area. To measure biodiversity, biologists group organisms into a number of categories called taxa. Taxa are ranked in the following order;
- species (made up of individuals and populations)
- genera (genus)
- phyla (or divisions)
Species is the basic unit of measurement of biodiversity. All individuals of one species are though to have the same genes. If a species becomes extinct, that collection of genes is lost.
The name of a species has two parts. The first is the genus, the second is the species name eg
Eucalyptus pauciflora or Eucalyptus pauciflora
Global patterns of diversity
Biomes are regions of the earth which have similarities in the diversity, abundance, and characteristics of organisms found there. Terrestrial biomes change according to latitude, ie from the poles towards the equator.
- Polar :
- permanently frozen, little or no free water
- diversity of species is not great
- Boreal or Coniferous forest :
- long cold winters, summers short and warm
- diversity of species fairly low
- Tropical Rainforest :
- areas of high and predictable rainfall
- high species diversity
- Desert and arid shrub lands :
- deserts may be hot or cold, but are usually arid
- usually low species diversity
Two trends are evident
- The closer towards the poles one moves, the lower the productivity
- Moving from wet to dry, there is a decrease in productivity.
- Freshwater :
- the most productive aquatic habitat, about as productive as terrestrial habitats.
- Estuarine :
- where rivers and oceans meet
- quite high productivity
- Coastal areas :
- higher productivity than open ocean, as a result of run-off of nutrients from land.
- Open ocean :
- surface waters often low in nutrients due to nutrients sinking to the bottom
- productivity is not high
In general, it can be seen that global distribution of organisms is largely determined by abiotic factors. Local populations are more likely to be affected by biotic factors.
Population dynamics are affected by;
Using a simple model of a population without immigration or emigration (called a closed population), it is possible to see how population growth changes.
A population with unlimited resources undergoes exponential growth. This situation may occur where there is no intraspecific or interspecific competition.
More usually, populations do experience some resource limitation, so logistic growth occurs. This means that as the density increases, the rate of growth declines.
(Refer Fig 42.8 pg 944 Knox et al)