Niche and adaptationEdexcel International A Level Biology: Revision notes
Section 1
The concept of a niche
The niche of a species is its role in its community: where it lives, what it eats, when it is active, how it behaves, how it interacts with other species (as predator, prey, competitor, parasite or mutualist) and the range of abiotic conditions it tolerates.
The habitat is the place where an organism lives, such as a rock pool or the forest canopy. The niche is wider, because it includes what the organism does there. For example, two bird species may live in the same woodland (same habitat) but one feeds on seeds on the ground by day and the other on insects in the canopy at dusk (different niches).
Two species with very similar niches compete strongly (interspecific competition) for the same resources. Species that coexist generally differ in some part of their niche, such as food, feeding position or time of activity, which reduces competition between them.
A niche is not the same as a habitat. A habitat is where an organism lives. A niche is what it does there and how it interacts with other species.
Section 2
What is an adaptation?
An adaptation is an inherited feature that increases an organism's chance of survival and reproduction in its environment. Adaptations arise because individuals with advantageous alleles survive, reproduce and pass those alleles on (natural selection). A species' adaptations largely determine its niche.
Adaptations are grouped into three types: anatomical (structural), physiological (metabolic or functional) and behavioural. In an exam answer, name the adaptation, state its function and link it to the advantage in that environment.
Use the three-step pattern: the feature, what it does, and why that helps survival in that habitat.
Section 3
Anatomical adaptations
Anatomical adaptations are structural features of the body that can be seen in the form of the organism.
- Fennec fox: large ears have a large surface area to volume ratio, so more heat is lost by radiation, which keeps the fox cool. Arctic fox: small ears and a thick coat reduce heat loss.
- Marram grass (sand dunes): rolled leaves with hairs and sunken stomata trap a humid layer of air, which reduces the water potential gradient and so reduces transpiration.
- Cactus: leaves reduced to spines reduce surface area and so water loss, and the fleshy stem stores water.
- Wading birds: bill length and shape differ, so each species reaches prey at a different depth in mud.
- Fish and aquatic mammals: streamlined body shape reduces drag.
Section 4
Physiological adaptations
Physiological adaptations are processes inside the body, such as metabolism, excretion and the control of body temperature. They cannot always be seen by looking at the organism.
- Kangaroo rat: the kidneys produce very concentrated urine, so little water is lost, and the rat never needs to drink.
- Marine birds: salt glands excrete excess salt from the body.
- Arctic fox: vasoconstriction of skin blood vessels in the legs and paws reduces heat loss by radiation.
- Hibernating mammals: the metabolic rate and body temperature fall during hibernation, which saves energy when food is scarce.
- Venomous snakes and poisonous plants: producing toxins deters predators or immobilises prey.
- Polar fish: antifreeze proteins in the blood stop ice crystals forming.
Do not call a feature physiological just because it involves water or a chemical. It is physiological if the adaptation is a process in the body, such as concentrating urine or excreting salt.
Section 5
Behavioural adaptations
Behavioural adaptations are the ways in which an organism acts that increase its chance of survival or reproduction.
- Nocturnal activity: desert animals feed at night, when it is cooler, so less water is lost.
- Burrowing: a burrow is cooler and more humid than the surface in a desert, and warmer than the surface in the cold.
- Curling up (Arctic fox) reduces the exposed surface area, so less heat is lost.
- Migration and hibernation: avoid harsh seasons or a shortage of food.
- Courtship displays: help individuals to find a mate of the same species.
- Feeding behaviour: probing, pecking or hunting at different times and places lets species avoid competition.
- Basking in the sun by reptiles raises body temperature.
Section 6
Linking niche and adaptation
Adaptations make a species suited to its own niche. Adaptations of any of the three types can reduce the overlap between niches, so several species can share one habitat. For example, three wading birds on a mudflat can coexist because bill length (anatomical), the way they search for food (behavioural) and where they feed differ, so each takes different prey.
If two species had identical niches, they would compete for the same limiting resources and the better adapted species would be likely to survive and reproduce more, while the other declined. Environmental change can alter niches, because a species may no longer be adapted to new conditions.
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Niche and adaptation
- A tropical rainforest contains many species of tree frog. Several species live in the same area of forest, but each feeds at a different height in the trees, at different times of the night and on different kinds of insect.Explain why several species of tree frog can live in the same area of forest without competing strongly.2 marks
- The kangaroo rat lives in a hot desert and never drinks. It produces very concentrated urine, spends the day in a cool, humid burrow and searches for seeds at night. The Namib desert beetle stands on a dune crest in the early morning with its body tilted head-downwards, so that fog condenses on its back and runs down to its mouthparts.Explain how spending the day in a burrow and searching for food at night reduces water loss in the kangaroo rat.2 marks
- The fennec fox lives in the Sahara and has very large ears. The Arctic fox lives in northern Canada, where winter temperatures fall to −40 °C, and has small ears and a thick coat. When resting, the Arctic fox curls up with its tail over its nose, and it constricts the blood vessels in the skin of its legs and paws.Explain how the difference in ear size is an anatomical adaptation in each fox.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).