1. Biodiversity & Distribution of Life

What you need to know...

    • Biotic, abiotic and human influences are all factors that affect biodiversity in an ecosystem.

    • Grazing and predation are biotic factors; pH and temperature are abiotic factors.

    • Biomes are the various regions of our planet as distinguished by their similar climate, fauna and flora.

      • Global distribution of biomes can be influenced by temperature and rainfall.

    • An ecosystem consists of all the organisms living in a particular area and the non-living components with which the organisms interact.

    • A niche is the role that an organism plays within a community.

      • It includes the use it makes of the resources in its ecosystem and its interactions with other organisms in the community including competition, parasitism, predation, light, temperature and nutrient availability.

Source: SQA


In this unit we're learning about life on earth. We start off in this topic by learning about the distribution of the different species on the planet, and what affects this distribution. Although you may feel that you understand many of the concepts discussed in this topic already, you must make sure that you are able to explain these concepts in the detail required for the National 5 course. As you can see from the list above, you are required to know a lot of terminology for this topic and you need to be able to use it confidently.


Perhaps the best place to start in this topic is with Biomes. Biomes are regions of our planet which have a particular climate. Biomes with similar climates will also therefore have similar animal species (fauna) and plant species (flora). Some of these biomes are shown in the image below.

Global Biomes by SEDACMaps

As you can probably tell, the distribution of biomes on the planet is influenced by two main factors: temperature and rainfall. For example, in the image above tropical biomes are characterised by high temperature and high rainfall, whereas deserts also have high temperature but low rainfall. The flora and fauna which are found in these biomes are therefore quite different, but the species found in all desert biomes are similar in their adaptions which allows them to survive the extremes of temperature and rainfall.

You can explore the species of the world's biomes in this excellent online exhibit.


Biomes consist of ecosystems. An ecosystem is defined as both the organisms living in a particular area and the non-living components they interact with. All the organisms in a particular ecosystem are known as a community and these organisms interact with each other and their environment. There are many different ecosystems on the planet and BBC Bitesize is a good place to explore some of them.

The variety of different species in the community of an ecosystem is known as biodiversity. Some ecosystems consist of a large variety of species, such as tropical forests, whereas others consist of much less variety, such as deserts.

Image by barloventomagico

The biodiversity in ecosystems is affected by the following three factors:

Biotic: Biotic factors are the interactions between the living things in an ecosystem. This can include grazing and predation. Animals which graze on the plant species in an ecosystem can influence which species of plants can survive. Similarly, animal species which predate on other animal species can influence which species are present in a particular ecosystem.

Abiotic: Abiotic factors are the non-living factors in an ecosystem such as temperature, pH or moisture levels. Extremes of an abiotic factor can reduce the biodiversity of the ecosystem. For example, ecosystems with a very low temperature tend to have low biodiversity.

Human Influences: Human activity increasingly affects the biodiversity in ecosystems also. This can range from pollution to habitat destruction.

Image showing deforestation from WikiMedia Commons


The final term we'll introduce in this topic is niche. Niche is a word which means lots of different things outside of biology, so if you're searching for more information on niche it's best to search for 'ecological niche'. The following video is a great introduction to niches.

The niche of a species is the unique role it plays in a community. In order to determine the niche of an organism you need to study both the abiotic and biotic conditions it is associated with. Each species in a particular habitat will make use of the available resources in a different way and have different interactions with the species present in the community. Obviously, factors such as light, temperature and nutrient availability will be important in determining the niche of a species, but biological interactions such as predation, competition and parasitism are important also.

Competition: Organisms of a community will compete for the available resources, both within species and between different species. Competition between species will affect the niche of both species.

Predation: Predation is when one organism consumes another in order to obtain energy and nutrients. The presence or absence of predators and prey will influence the distribution of species in a habitat.

Parasitism: Parasitism is an interaction between species which provides energy to one, to the detriment of the other. The species which is negatively affected is known as the host, and is normally not killed by the parasite. The presence or absence of the host species will significantly impact upon the survival of the parasite, especially as many parasites have a highly specialised niche and can only survive on or in a particular host species.

We'll return to predation and competition in more detail in the next topic. In the meantime, what would be an example of a niche? A good example from a Scottish perspective is the red squirrel. Once prevalent throughout the UK, their distribution is now primarily restricted to Scotland, the North of England and the West of Ireland as shown in the following maps from the Red Squirrel Survival Trust.

Image used with permission from the Red Squirrel Survival Trust

As you can see from the maps above, grey squirrels are now the dominant species throughout much of England and Wales where they outcompete the native red squirrels. But why are red squirrels able to survive where they do? It's all to do with their niche as explained in the video below.

Red Squirrel Niche

This video on YouTube includes a very detailed explanation of ecological niche using plant species in Australia as examples.