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Environmental Management AS CIE

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Exam code:8291

Abiotic Factors

  • The non-living, physical factors that influence ecosystems and the communities of organisms living within them are known as abiotic factors

  • These include factors such as:

    • Temperature

    • Humidity

    • Water

    • Oxygen

    • Salinity

    • Light

    • pH

  • Changes in these abiotic factors can affect the survival and reproduction of organisms, and the overall functioning of ecosystems

Examples of Abiotic Factors

Abiotic Factor

How Factor Affects Communities

Temperature

Affects the rate of photosynthesis in plants. Also affects the rate of metabolism, growth, and reproduction of organisms. Certain species have adapted to specific temperature ranges and cannot survive outside of those ranges.

Humidity

Humidity levels influence the water content in the air, affecting the water balance of organisms and their ability to regulate body temperature. Humidity levels also influence rates of transpiration in plants.

Moisture and precipitation levels (water availability)

Determines the amount of water available to organisms, impacting their survival, growth, reproduction and distribution. Some species are adapted to areas with high precipitation, while others are adapted to arid environments.

Oxygen levels

Oxygen is crucial for aerobic respiration in many organisms. Oxygen concentration in the air or water can limit the distribution of species and influence their metabolic processes. Some aquatic animals, such as fish, can only survive in water with high oxygen concentrations.

Salinity

Salinity levels in water impact the health and survival of aquatic organisms. Some species are adapted to freshwater conditions, while others thrive in saltwater environments. Soil salinity levels affect the health and survival of plants.

Light intensity

Light is needed by plants for photosynthesis. More light leads to an increase in the rate of photosynthesis and an increase in plant growth rates.

pH

Different species of plants and animals are adapted to different pH levels in soils and water bodies.

Wind intensity

Wind speed affects the transpiration rate in plants. Transpiration influences the rate of photosynthesis as it ensures water and mineral ions are transported to the leaves.

Carbon dioxide levels for plants

CO2 is required for photosynthesis in plants. CO2 concentration affects the rate of photosynthesis.

Biotic Factors

  • The living, biological factors that influence ecosystems and the communities of organisms within them are known as biotic factors

    • In other words, biotic factors are the interactions between the organisms within a community

  • These interactions include:

    • Competition

    • Grazing (herbivory)

    • Predation

  • These biotic interactions mean that each species in an ecosystem has an influence on the population dynamics and carrying capacity of the other species

Competition

  • Competition can be divided into intra-specific competition (competition between members of the same species) and inter-specific competition (competition between members of different species)

    • Intra-specific competition can lower the carrying capacity of a population due to a decrease in food availability caused by high population density

    • Inter-specific competition occurs between species with similar niches, causing a decrease in the carrying capacity of one or both species

Intra-specific Competition

  • Intra-specific competition occurs when individuals from the same species compete for the same resources (“intra” means within)

  • For example:

    • When resources are plentiful, the population of grey squirrels (Sciurus carolinensis) increases

    • As the population increases, however, there are more individuals competing for these resources (e.g. food and shelter)

    • At some point, the resources become limiting and the population can no longer grow in size – the carrying capacity has been reached

Diagram showing two grey squirrels (same species) competing for a limited resource (intra-specific competition)
Intra-specific competition between two grey squirrels (same species) for a limited resource

Inter-specific Competition

  • Competition between different species for the same resources is described as inter-specific competition (“inter” means between)

  • A well-known example of this occurs between the grey squirrel (Sciurus carolinensis) and the red squirrel (Sciurus vulgaris)

  • The introduction of the grey squirrel into the southern UK caused the native red squirrel to be outcompeted for food and shelter

  • The grey squirrel also carries a disease, parapoxvirus, that is harmless to itself but can be fatal to the red squirrel

  • Conservation efforts in northern England and Scotland have slowed the spread of the grey squirrel by:

    • Protecting the red squirrels’ habitats and food

    • Giving the red squirrel legal protection

    • Reintroducing the pine marten, a natural predator of the grey squirrel

Diagram showing a grey squirrel and a red squirrel (different species) competing for a limited resource (inter-specific competition)
Inter-specific competition between a grey squirrel and a red squirrel (different species) for a limited resource

Grazing

  • This is when an organism (either a herbivore or omnivore) feeds on a plant

  • The carrying capacity of herbivorous species is affected by the quantity of plants they feed on

  • An area with more plant resources will have a higher carrying capacity for herbivore species

    • This can also have negative feedback effects – the carrying capacity of the herbivore species may decrease if herbivory rates are too high and the plant population decreases too much due to overgrazing

Predation

  • This is when one animal eats another

    • This lowers the carrying capacity of the prey species

    • This can have negative feedback effects, lowering the carrying capacity of the predator species due to a decrease in prey numbers

  • Consumers that kill and eat other animals are known as predators, and those eaten are known as prey

  • In a stable community, the numbers of predators and prey rise and fall in cycles, limiting the population sizes of both predators and prey

  • The graph below demonstrates some of the key patterns of predator-prey cycles:

    • Initially, the number of predators increases as there is more prey available

    • The number of prey then decreases as there are now more predators

    • Then the number of predators decreases as there is now less prey available

    • As a result, the number of prey increases as there are now fewer predators

    • This cycle repeats continuously

A diagram showing a predator-prey cycle between the Canadian lynx and the snowshoe hare
An example of a graph used to model a predator-prey cycle between the Canadian lynx and the snowshoe hare

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