Ecosystems & Niches (SQA National 5 Biology): Revision Note

Ecosystems

• An ecosystem consists of:

the community of organisms living in a habitat and the non-living components with which they interact

• Ecosystems can be very large or very small, e.g.:

  • Caledonian forest is a remnant native woodland ecosystem in the Scottish Highlands, dominated by Scots pine and home to species such as red squirrel, capercaillie and pine marten

  • a garden pond is a small, freshwater ecosystem with aquatic plants, invertebrates, amphibians and visiting birds

Communities

• In ecology, a community is:

all of the populations of different species living in an area

• The organisms within a community are interdependent, meaning that a change in one population will affect other populations

• The interactions between populations in an ecosystem can be seen clearly in food webs, e.g. for the food web below, a decrease in the rabbit population might lead to:

  • an increase in grass growth, due to decreased feeding

  • a decrease in the fox population, due to reduced food availability

  • an increase in caterpillars and earthworms, due to increased growth of grass

  • a decrease in the frog and mouse populations, as foxes would need to compensate for the reduction in rabbit prey

Non-living components of an ecosystem

• In an ecosystem, communities also interact with non-living, or abiotic, components in the environment; examples of these factors are:

  • temperature

  • water availability

  • light intensity

  • soil pH and mineral content

  • oxygen / carbon dioxide concentration

Niche

• A niche can be defined as:

the role that an organism plays within a community

• The role of a species includes considerations such as:

  • the resources it requires, e.g. light, nutrients and oxygen

  • its interactions with other organisms, e.g. what it eats, which predators depend on it for food and which species it competes with

  • the conditions it can tolerate, e.g. environmental temperatures and soil moisture

• An example of a niche description could be as follows:

  • Species: red squirrel (Sciurus vulgaris)

  • Resources:

    • seeds from conifers, as well as fungi, buds, berries and nuts

    • mature conifers with suitable branches for next building

    • twigs, moss and bark for nest construction

  • Interactions:

    • disperses seeds for several tree species

    • competes with invasive grey squirrels

    • prey for pine martens, raptors and foxes

  • Conditions required:

    • cool, temperate conditions with sufficient rainfall to support conifer woods

    • enough light for conifer growth

Rhododendrites, via Wikimedia Commons (opens in a new tab)