Revision notes · Ecology
Adaptations, interdependence and competition
Communities4.7.1.1
Definition: A community is made up of all the populations of different species living and interacting in a habitat.
Organisms within a community depend on each other and compete for limited resources to survive.
- •Plants compete with each other for light, space, water, and mineral ions.
- •Animals compete with each other for food, mates, and territory.
- •Interdependence means that each species within a community depends on others for food, shelter, pollination, and seed dispersal.
- •In a stable community, all species and environmental factors are in balance so population sizes remain relatively constant.
- •Quantitative sampling using a quadrat allows scientists to estimate population size and distribution within a community.
⚠️ Common mistake: Confusing a population (members of one species) with a community (all species in a habitat).
🧠 Remember: Community = all species, Population = one species, Ecosystem = community plus abiotic environment.
Abiotic factors4.7.1.2
Definition: Abiotic factors are the non-living chemical and physical parts of the environment that affect living organisms.
Changes in non-living environmental conditions directly affect the size and distribution of populations in a community.
- •Key abiotic factors include light intensity, temperature, moisture levels, and soil pH and mineral content.
- •Carbon dioxide levels limit the rate of photosynthesis in plants, while dissolved oxygen levels affect aquatic animals.
- •Wind intensity and direction influence transpiration rates in plants and animal shelter options.
- •A decrease in light intensity reduces photosynthesis, lowering plant growth and affecting the entire food web.
⚠️ Common mistake: Classifying predators or disease as abiotic factors when they are living (biotic) factors.
🧠 Remember: Abiotic = Apart from living (non-living factors like light, temperature, and water).
Biotic factors4.7.1.3
Definition: Biotic factors are the living components of an ecosystem that affect other organisms.
Living factors in an ecosystem determine species survival and alter community food webs.
- •Key biotic factors include availability of food, arrival of new predators, and introduction of new pathogens.
- •One species outcompeting another can cause population numbers to fall too low for successful breeding.
- •An increase in predators can rapidly decrease the population size of prey species.
- •New diseases can devastate populations that have no natural immunity.
⚠️ Common mistake: Assuming temperature changes are biotic factors because they affect living things.
🧠 Remember: Biotic = Biological (living factors: food, predators, pathogens, competition).
Adaptations4.7.1.4
Definition: An adaptation is a specific feature that an organism has evolved to help it survive in its normal environment.
Organisms possess structural, behavioural, or functional features enabling survival in diverse habitats.
| Type | Examples |
|---|---|
| Structural | Physical shape/structure — e.g. a camel's wide feet, a seal's thick blubber |
| Behavioural | Actions — e.g. bird migration, hunting at night |
| Functional | Internal processes — e.g. producing concentrated urine to conserve water |
- •Extremophiles are organisms, usually microorganisms, adapted to live in extreme conditions like high temperature, pressure, or high salt concentrations.
⚠️ Common mistake: Describing internal physiological processes (functional adaptations) as physical body structures (structural adaptations).
🧠 Remember: Structural = Shape/body, Behavioural = Behaviour/action, Functional = Function inside.
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