• Biome is a large area characterised by: 

  1. vegetation

  2. soil

  3. climate

  4. wildlife. 

• Five major types of biomes are:

  1. aquatic

  2. grassland

  3. forest

  4. desert

  5. tundra

• Some biomes can be further divided into the following categories:

  1. freshwater

  2. marine

  3. savanna

  4. tropical rainforest

  5. temperate rainforest

  6. taiga

Two ways looking at the level of species in ecosystems:

1. Taxonomy

2. Ecology

Definition:

“a species is a group of organisms that can interbreed and produce fertile offspring”

• Individual organism is a member of a species

• Sometimes, two species breed together to produce hybrid offspring. A hybrid may survive to adulthood but cannot produce viable gametes and so is sterile. Examples include:

  • Horse (Equus caballus) + donkey (Equus asinus) à Mule

  • Male tiger (Panthera tigris) + lioness (Panthera leo) à Tigon

  • Female tiger + male lion à Liger

Limitation to the species concept:

• Cannot clarify whether geographically isolated populations belong to the same species

• Cannot classify species in extinct populations

• Cannot account for asexually reproducing organisms

• Cannot clearly define species when barriers to reproduction are incomplete

Taxonomists use various tools to identify and classify organisms. One tool is called dichotomous key.

A dichotomous key is a tool used for the identification of an organism with which you are not familiar

• Dichotomous means ‘divided into two parts’. 

• The dichotomous key is written so that identification is done in steps. 

• At each step, you have a choice of two options, based on different possible characteristics of the organism you are looking at. 

• Sometimes, such keys are presented in written form, sometimes they are drawn as a tree diagram

There are limitations to the use of dichotomous keys. These include:

• Only the physical characteristics of the organism can be used with dichotomous keys, rather than being able to use behaviours. Two species that have very similar physical characteristics may display very different behaviours.

• Some dichotomous keys use technical terms that only an expert would understand.

• There may not be a dichotomous key available for the type of organisms you are trying to identify.

• Some physical characteristics of organisms cannot be easily established in the field. For example, whether an animal has a placenta; whether an animal is endothermic or ectothermic (warm- or cold-blooded). Some organisms show significant changes in their body shape during their lifetime (e.g. frogs have an aquatic tadpole juvenile form that is very different from the adult), which keys must take into account. Many insects, for example, show differences between male and female individuals of the species that can cause difficulties when identifying the species.

DNA profiling in dichotomous keys

• Organisms can also be classified based on their specimens in a herbarium 

• Museums often use DNA profiling techniques to identify differences between specimens. 

  • More accurate way of determining the identity of an organism than using only its physical appearance.