Feeding is never one-sided. A herbivore gets better at eating plants, so plants get better at not being eaten. A predator gets faster, so prey gets harder to spot. This page is a tour of both sides of those arms races — plus the quiet version of the same fight going on between plants competing for light.
📘 What you need to know
Adaptations are characteristics that aid an organism’s survival in its environment.
Herbivores have adapted mouthparts, teeth, digestive systems and gut bacteria for eating plants.
Plants fight back with mechanical deterrents and toxic secondary compounds.
Predator and prey adaptations come in three kinds: chemical, physical and behavioural.
Predator adaptations help with catching prey; prey adaptations help with avoiding predation.
Plants compete for light using adaptations of form: trees, lianas, epiphytes, stranglers and shade-tolerant plants.
Adaptations for herbivory
Herbivores are heterotrophs that feed on plants. Plant tissue is tough, low in nutrients and often chemically defended, so eating it needs specialist equipment.
In insects
Aphids have specialised mouthparts called stylets, which pierce plant tissue to reach the sugary sap inside the phloem.
Insects such as caterpillars, grasshoppers and beetles have mouthparts called mandibles, which cut through leaves.
Because they feed in completely different ways, an aphid and a caterpillar are not in direct competition even on the same plant.
In mammals
Grazing animals such as sheep and horses have flat teeth for grinding plant matter.
Ruminant mammals such as cattle and deer have stomachs with several compartments, from which they can regurgitate and re-chew their food, breaking it into smaller pieces to aid digestion.
Ruminants also carry specialised communities of bacteria in their digestive tracts that break down cellulose. This matters because the bacteria have the enzymes needed and the herbivore does not.
Dealing with plant poisons
Some deer produce proteins in their saliva that bind to tannins, neutralising them.
Proboscis monkeys have gut bacteria that can neutralise certain toxins found in leaves.
Many mammals use cautious sampling — taking only a small amount when they first meet a new plant, so any toxic chemicals are never consumed in dangerous quantities.
How plants fight back
Herbivory damages plants: it reduces the leaf surface area available for photosynthesis and harms their ability to transport substances. Plants cannot move away, so they deter herbivores instead.
Mechanical deterrents
Cacti have sharp spines to deter herbivores from eating their succulent stems.
Nettles have tiny hairs containing toxins that irritate the skin.
Thick bark stops insects such as aphids piercing the stem.
Many tiny hairs on leaves make it harder for insects to bite into or pierce the tissue.
Toxic secondary compounds
Compound
Plant
Effect
Digitalis
Foxglove
Affects the heartbeat of humans and other animals
Atropine
Deadly nightshade
Causes muscle paralysis by blocking the binding of neurotransmitters
Tannins
Many plants
Deter herbivores by their bitter taste, and reduce the efficiency of digestive processes
Alkaloids, e.g. caffeine and nicotine
Many plants
Deter insect herbivory, with toxic effects on growth and on nerve impulse transmission
Notice the pattern in that table: most of these toxins attack the nervous system or digestion. A plant that cannot run has to make eating it either unpleasant or dangerous.
Predators and prey
Predators hunt and eat other animals, or consume the tissues of recently dead ones. Prey are the animals hunted and consumed. Their adaptations point in opposite directions: predator adaptations assist in catching prey, prey adaptations assist in avoiding predation.
Both sides use the same three categories:
Chemical — compounds that assist in catching prey or avoiding predation.
Physical — features such as specially adapted sense organs or body structures.
Behavioural — things the animal does rather than has.
Predator adaptations
Type
Examples
Chemical
Venoms: adders and rattlesnakes produce haemotoxic venoms that damage the circulatory system, e.g. by interfering with blood clotting; mambas and cobras produce neurotoxic venoms that interfere with the passage of nerve impulses; scorpions use neurotoxic venom to subdue larger prey; spider venoms contain various toxins. Chemical mimicry: bolas spiders release the pheromones female moths use to attract mates, so male moths come to them. Chemical crypsis, or scent camouflage: lets ambush predators such as the pirate perch lie in wait undetected.
Physical
Sense organs: birds of prey have excellent vision for spotting small movements at a distance; eyes at the front of the skull give good distance perception; snakes use the Jacobson’s organ in the roof of the mouth to detect chemicals released by prey; bats find prey by echolocation. Body structures: cheetahs have long limbs and flexible spines for speed; swordfish have a streamlined body shape; mantis shrimps have modified front limbs that strike extremely fast; carnivorous mammals have large canine teeth for catching and holding prey.
Behavioural
Ambush: puff adders can stay motionless for weeks waiting for prey; mantis shrimps hide in cracks between rocks; crocodiles approach underwater then burst out. Pack hunting: orcas, wolves and lions cooperate to raise their chance of success. Pursuit: a burst of speed, as in cheetahs, or persistence hunting over long distances, as in wolves and painted dogs.
Prey adaptations
Type
Examples
Chemical
Poison dart frogs produce skin toxins that can kill predators; skunks produce chemicals that smell unpleasant; tiger moths contain chemicals that make them taste unpleasant to bats. Scent camouflage is used here too — harlequin filefish take on the scent of the corals they feed on, so predators cannot detect them.
Physical
Eyes on the sides of the skull give a wide field of vision. Camouflage lets some insects look like a leaf or a stick. Mimicry can make prey resemble a predator — owl butterflies have wing patterns like owl eyes. Aposematism is bright warning colouring that advertises a chemical defence, as in poison dart frogs. Other mimics copy a defended species without making toxins themselves, e.g. king snakes copy the stripes of venomous coral snakes. Mechanical defences include tough exoskeletons, shells and spines.
Behavioural
Innate preferences for dark, sheltered places, as in woodlice; moving away when a predator is detected, e.g. rabbits bolting at a predator’s wing shape; avoiding places or times of day when predators are around, e.g. desert rodents emerging only at night; grouping together so individuals are hard to pick out, mobbing a predator to drive it off, or giving warning calls; and bluffing, such as opossums playing dead or frill-necked lizards making themselves look bigger.
Look at a cat and a rabbit side by side and you can tell which one hunts before you know anything else about it.
Useful trick. If a question asks for adaptations, deliberately give one chemical, one physical and one behavioural. It shows you know the categories and it stops you writing three versions of the same point.
Plant adaptations for harvesting light
Plants rely on photosynthesis, and their leaves are well adapted for it. But they also have adaptations at the level of the whole organism that maximise light absorption. These are called adaptations of “form”, and in a forest they are what let a plant compete effectively with other plants for light.
Every one of these is a different answer to the same problem: the canopy takes the light first, so how do you get some?
Trees
Trees make up the uppermost layer of plants, the canopy. Some grow above it and are called emergent trees; some form a layer beneath it, the understory.
Maximising height lets the tallest trees gain the most sunlight, because nothing sits between them and the sun.
They can then photosynthesise at a high rate, giving them the molecules to grow quickly and compete effectively.
Lianas
Lianas are woody vines that use the trunks of trees as their supporting structure to gain height, so their leaves reach the canopy and can absorb light.
They germinate on the forest floor, grow towards the base of a trunk, then grow upwards.
Their roots stay in the soil, so they take nutrients and moisture from the ground.
They compete with trees for light, nutrients and moisture.
Epiphytes
Epiphytes grow high up in tree branches, but they do not begin life on the forest floor, and they often take their nutrients from high in the canopy.
Moss gains water and nutrients from rainwater running across the bark it grows on; bromeliads collect rainwater among their leaves; some orchids have aerial roots that absorb moisture straight from the air.
The pay-off: they get the advantage of height without spending energy on upward growth.
Strangler epiphytes
Some epiphytes grow roots downward to the forest floor, so they gain nutrients and water from the soil while still using the height of the tree for light.
This is not the same as a liana: strangler epiphytes begin life in the canopy, not on the floor.
The strangler fig starts in the canopy and grows both upwards and downwards to maximise its access to resources. It can kill its host tree by taking all its resources.
Shade-tolerant shrubs and herbaceous plants
These grow on the forest floor, adapted to absorb the limited range of light wavelengths that get through the canopy and understory.
They may contain different photosynthetic pigments, letting them absorb wavelengths the canopy has not already taken.
They often have especially large leaves, maximising the surface area available for absorbing light.
Their flowers are often brightly coloured or strongly scented, to attract pollinators in low light.
Shrubs are not tall like trees but do have woody stems. Herbaceous plants, or herbs, lack woody stems and rely on soft tissues with turgid cells for support.
Worked examples
WORKED EXAMPLE
Outline one chemical, one physical and one behavioural adaptation of predators. [3]
ChemicalCobras produce neurotoxic venom, which interferes with the passage of nerve impulses and subdues prey.PhysicalCheetahs have long limbs and a flexible spine, allowing very high running speed.BehaviouralLions hunt in packs, cooperating to increase their chance of successeach one needs the feature and what it achieves.
WORKED EXAMPLE
Explain why ruminant mammals depend on bacteria in their digestive systems. [3]
Say what the food is made of
Plant material contains large amounts of cellulose.
Now the problemThe mammal does not produce the enzymes needed to break cellulose down.And the solutionBacteria in the digestive tract have those enzymes, so the cellulose can be digested“the herbivore lacks the enzyme” is the line that earns the middle mark.
WORKED EXAMPLE
Compare how a liana and a strangler fig reach the forest canopy. [3]
Where each one startsA liana germinates on the forest floor and climbs up a tree trunk.A strangler fig begins life as an epiphyte in the canopy and grows roots downwards.What they have in commonBoth use a tree for height and both take water and nutrients from the soilthe starting point is the difference examiners are testing.
💡 Exam tip
Sort adaptations into chemical, physical, behavioural before you write. It stops repetition.
Every adaptation answer should be feature + how it works + benefit.
Name real species. “A snake” is weaker than “a cobra produces neurotoxic venom”.
For plant defences, split mechanical from toxic secondary compounds.
Remember eye position as a quick predator-or-prey identifier. It is a favourite data question.
For the forest plants, the deciding detail is usually where the plant starts its life.
⚠ Common mix-up
Mixing up lianas and strangler epiphytes. Lianas start on the floor; stranglers start in the canopy.
Saying epiphytes are parasites. They take nutrients from rainwater and debris, not from the tree.
Confusing camouflage, mimicry and aposematism. Camouflage hides you; mimicry makes you look like something else; aposematism advertises that you are dangerous.
Getting the venom types the wrong way round. Haemotoxic affects blood and circulation; neurotoxic affects nerves.
Thinking ruminants digest cellulose themselves. Their bacteria do it.
Calling a shrub a small tree. Shrubs have woody stems but are not tall; herbaceous plants have no woody stems at all.
Listing adaptations with no function. A list of features usually scores one mark at most.
Up next: Competition Between Species — what happens when two species want the same niche, and why one of them always loses.
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