Adaptations, interdependence and competition

Biology · Ecology. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

Test this topic free All Biology topics

The idea

An ecosystem is a community of organisms together with the non-living parts of their environment. Organisms need materials from their surroundings and from other organisms, so they compete. Plants compete for light, space, water and mineral ions. Animals compete for food, mates and territory.

Species also depend on each other for food, shelter, pollination and seed dispersal. This is interdependence: if one species is removed, the whole community can be affected. In a stable community the population sizes stay fairly constant.

Organisms have adaptations, features that help them survive where they live. Communities are affected by non-living (abiotic) and living (biotic) factors.

Rules to remember

Abiotic factors: light intensity, temperature, moisture, soil pH and mineral content, wind intensity and direction, carbon dioxide level (plants), oxygen level (aquatic animals).
Biotic factors: availability of food, new predators, new pathogens, one species outcompeting another.
Structural adaptation = a feature of the body, e.g. thick fur, large ears, spines.
Behavioural adaptation = something the organism does, e.g. migrating, hunting at night.
Functional adaptation = a process inside the body, e.g. making concentrated urine, antifreeze proteins.
Extremophiles live in extreme conditions: high temperature, high pressure or high salt concentration, e.g. bacteria in deep-sea vents.

Common mistake

Students write that plants compete for food. Plants make their own food by photosynthesis; they compete for light, space, water and mineral ions.

Worked example

A cactus has spines instead of broad leaves, a thick stem that stores water, and it opens its stomata only at night. How does each feature help it survive in a hot desert?

Spines have a small surface area, so less water is lost; they also stop animals eating the plant.
The thick stem stores water for long dry periods.
At night it is cooler, so less water evaporates through the open stomata.

Answer: All three features reduce water loss or store water, so the cactus is adapted to a very dry habitat.

Ask about this

Type what you are stuck on. The helper finds the explanation, worked examples and the notes to read, free and instant.

Read the full notes

Ecology — Worksheet

Keep going

← Classification of living organisms Organisation of an ecosystem →Take a Biology test