Members of the same species need exactly the same things, which sets up the sharpest competition in any ecosystem. Yet the same species will often work together too. Both happen, sometimes in the same animals on the same day.
📘 What you need to know
Intra means within, so intraspecific relationships are between members of the same species.
In cooperation, both individuals benefit from the interaction.
In competition, one individual does better and the other does worse.
Individuals of the same species compete hardest because they have identical needs.
Plants compete for light, water, minerals and space. Animals compete for food, mates and territory.
Competition does not need visible fighting — sharing a resource is enough.
Two ways to interact
The same species often does both. Meerkats cooperate to watch for predators, then compete with each other for food and rank.
Cooperation: working together pays
Cooperation looks strange at first. Why help a rival? Because in these cases helping is more profitable than going it alone. A share of a big meal beats all of a meal you never catch.
Species
What they do together
Why it pays
Orcas
Hunt as a group, using coordinated movements to reach prey, then share the catch
They can take prey that no single orca could handle alone
Meerkats
Divide the jobs: some act as lookouts while others forage or mind the young
Everyone eats more safely, because someone is always watching for predators
Ants
Build and defend nests, and gather food for the developing young
A colony can build and hold a home no individual ant could manage
The exam phrasing is “both members of the relationship benefit from the interaction”. Learn that sentence — it is the definition, and it works for cooperation within a species and for mutualism between species.
Competition: identical needs, limited supply
Here is why intraspecific competition is so fierce. Two different species usually want slightly different things — different food, different nesting sites, different depths of soil. Two members of the same species want exactly the same things, in exactly the same place, at exactly the same time.
Plants compete for
Animals compete for
Light — the taller plant shades the shorter one
Food — what one eats, another cannot
Water — roots draw from the same soil
Mates — only some individuals get to breed
Minerals such as nitrate and magnesium
Territory — which brings access to both food and mates
Space to spread roots and leaves
Shelter and nesting sites
Named examples
Red deer stags fight each other for access to females. The dominant male mates with most of the group, so the losers pass on far fewer genes.
Robins defend their territory aggressively against other robins — so aggressively that they will attack a bunch of red feathers.
Oak trees growing close together compete for light, water and minerals, and the shaded one grows more slowly.
The competition you cannot see
This is the part students miss. Competition does not require conflict. If two individuals feed in overlapping areas, every insect eaten by one is an insect the other will never find. Nobody fought. Both did worse.
This quiet kind of competition is the everyday version. Fights are dramatic, but rare; shared resources are constant.
Link it back. Intraspecific competition is the classic density-dependent factor. Double the population in the same habitat and each individual gets half as much, so the effect is far stronger when numbers are high. That is exactly what holds a population near its carrying capacity.
WORKED EXAMPLE
Naming the relationship
For each of the following, state whether the relationship is intraspecific or interspecific, and whether it is cooperation or competition: (a) two male robins fighting over a hedge, (b) a group of ants carrying food back to their nest, (c) oak and beech trees growing side by side.
(a) two robinsintraspecific competitionsame species, competing for territory(b) ants in a colonyintraspecific cooperationsame species, and all of them benefit(c) oak and beechinterspecific competitiondifferent species competing for light and minerals — that is next page’s topic
WORKED EXAMPLE
Explaining a slower-growing tree
Two oak saplings of the same age grow three metres apart. One is noticeably smaller than the other. Explain how intraspecific competition could account for the difference. [3]
Point 1: identical needsboth are the same species, so both need light, water and the same soil mineralsPoint 2: one gains an advantagethe taller tree shades the smaller one and its roots take up water and minerals firstPoint 3: the consequencethe shaded tree photosynthesises less, so it has less energy for growth and grows more slowlynotice the chain: less light → less photosynthesis → less growth
💡 Exam tip
Read the species names in the question first. Same species means intra; different species means inter.
For cooperation, always state that both individuals benefit. One-sided help is not cooperation.
Name the resource being competed for. “They compete” scores nothing; “they compete for light” scores.
Territory questions want you to say territory gives access to food and mates, not just space.
If asked why intraspecific competition is more intense than interspecific, the answer is identical requirements.
Link back to density-dependence whenever a question mentions crowding.
⚠ Common mix-up
Intra and inter are one letter apart and it costs marks every year. Intra = within, inter = between.
Competition is not always a fight. Overlapping use of a resource counts.
Cooperation is not the same as mutualism. Cooperation is within a species; mutualism is between species.
Plants compete too. Do not restrict competition answers to animals.
The dominant animal does not “win the competition” once. Competition is ongoing, not a single event.
Do not confuse a group with a population. A meerkat mob is part of a population, not the whole of it.
Up next: Interspecific Relationships — herbivory, predation, mutualism, parasitism and pathogenicity, plus the three mutualisms the IB names directly.
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