"Resource partitioning" is searched about 9,100 times a month in the United States, mostly by AP Biology students (it sits in Unit 8, Ecology) and by Grade 10 to 12 biology students who have met the competitive exclusion principle and want the examples that make it concrete. This page gives the definition, the principle it answers, the three types with the classic examples (MacArthur's warblers in full, anoles, finches, barnacles, savanna grazers, hawks and owls), the fundamental-against-realised niche, character displacement, how to tell it from related ideas, and a printable sheet with practice.
Download the resource partitioning sheet with practice (PDF) (A4, the definitions, the types table and the examples on page 1, niches, character displacement and the practice set with answers on page 2, free).
The problem it solves: competitive exclusion
A niche is a species' role and position in its ecosystem: what it eats, where and when it feeds, what eats it, the conditions it tolerates. Two species with identical niches compete for every resource, and in 1934 the Russian ecologist Georgy Gause showed what happens: grown separately, two species of Paramecium each thrived; grown together in one tube of bacteria, P. aurelia always outgrew P. caudatum, which died out within weeks. The competitive exclusion principle (Gause's law): complete competitors cannot coexist. Two species competing for exactly the same limiting resource in the same way cannot both persist; the slightly more efficient one wins.
Yet forests are full of insect-eating birds and savannas full of grazers. They coexist because they are not complete competitors: they have partitioned the resources.
The definition
Resource partitioning is the division of a limited resource among competing species so that each uses a different portion (a different place, time, size or type), reducing competition enough for all of them to coexist. The species' niches overlap but do not coincide. It is observed in the present (who uses what) and explained by the past (natural selection favouring the individuals of each species that competed least).
The three types, with examples
| Type | The resource is divided by | Examples |
|---|---|---|
| Spatial | place: height, depth, microhabitat | MacArthur's warblers at different heights in a spruce; anole lizards on different perches; plant roots at different soil depths; barnacles at different tidal heights; fish at different depths in a lake |
| Temporal | time: day and night, season, time of flowering | hawks hunt rodents by day, owls at night; bats and swifts take insects at different hours; spring and summer wildflowers share pollinators by blooming in turn; dung beetles active at different times |
| Dietary (trophic) and morphological | the size or kind of food, often with different body parts | Darwin's finches with different beak sizes eating different seeds; savanna grazers eating grass at different heights (zebra the tall coarse tops, wildebeest the middle, gazelle the short new growth); herons and egrets with different leg and bill lengths taking different prey; two ant species taking different seed sizes |
MacArthur's warblers (1958)
The classic. Five species of wood warbler, all small insect-eaters, breed in the same spruce and fir forests of the northeastern United States. Robert MacArthur recorded where in the tree each one fed and found each had a zone:
| Warbler | Feeding zone in the tree |
|---|---|
| Cape May warbler | the top, outer tips of the branches |
| Blackburnian warbler | upper middle, mostly outer branches |
| Black-throated green warbler | the middle, both inner and outer |
| Bay-breasted warbler | the lower middle, toward the trunk |
| Yellow-rumped (myrtle) warbler | the lowest branches and the ground |
They also differed in how they moved (hovering at the tips, creeping along branches) and when they nested. The study became the textbook demonstration that species which seem to share one niche in fact divide it, and it won MacArthur his reputation.
Caribbean anole lizards
On each of the Greater Antilles, Anolis lizards have evolved into the same set of ecomorphs: trunk-ground anoles with long legs for jumping between low perches, trunk-crown anoles with large toe pads high in the canopy, twig anoles with short legs on thin branches, grass-bush anoles with long tails. Each island has its own species in each role, evolved independently, which is both resource partitioning (by perch height and diameter) and convergent evolution; Jonathan Losos's work made it the modern classic.
Darwin's finches and character displacement
On the Galápagos, the medium ground finch (Geospiza fortis) and the small ground finch (G. fuliginosa) eat seeds. Where either species lives alone (Daphne Major has only fortis; Los Hermanos only fuliginosa) the beaks are intermediate in size. Where both live together (Santa Cruz, Floreana) fortis beaks are bigger and fuliginosa beaks smaller than those solitary populations, so each takes different seeds. That divergence in sympatry is character displacement, the evolutionary footprint of resource partitioning, documented by David Lack and later measured by Peter and Rosemary Grant.
Connell's barnacles: fundamental and realised niche
On Scottish shores two barnacles compete for rock. Chthamalus can survive the whole intertidal zone (its fundamental niche, the full range it could occupy), but Balanus grows faster and crowds it off the lower rocks, so Chthamalus is found only in the upper zone (its realised niche, where it actually lives). Balanus cannot tolerate the drying of the upper zone, so it keeps the lower. Joseph Connell showed this in 1961 by removing Balanus: Chthamalus then spread downward. The realised niche is the fundamental niche minus what competitors take, and resource partitioning is the set of realised niches that results.
Related ideas, kept apart
| Idea | What it is | How it differs |
|---|---|---|
| Niche differentiation (niche partitioning) | species evolving to occupy different niches | the general process; resource partitioning is the specific division of a shared resource |
| Competitive exclusion | one species eliminating another that shares its niche | what happens when partitioning fails |
| Character displacement | the evolutionary divergence of traits where competitors coexist | the cause, over generations, of morphological partitioning |
| Mutualism | both species benefit from an interaction | partitioning species do not help each other; they avoid each other |
| Commensalism and parasitism | one benefits, the other unaffected or harmed | not about competition |
Why it matters
Resource partitioning explains biodiversity: how a tropical forest holds hundreds of tree species or a reef hundreds of fish species when the competitive exclusion principle says that sharing a niche is fatal. It predicts that invasive species do most damage when they overlap a native species' niche completely (the grey squirrel against the red in Britain), and it guides conservation (protecting the whole vertical structure of a forest, not just its area, keeps all five warblers). In agriculture, intercropping species with different root depths and nutrient needs is resource partitioning put to work.
Where it sits in each curriculum
| Curriculum | When | What is expected |
|---|---|---|
| US | AP Biology Unit 8, Ecology (community ecology: competition, niche, resource partitioning, competitive exclusion), high-school biology (HS-LS2-2, HS-LS2-6), college ecology | the definition, MacArthur's warblers, competitive exclusion, character displacement |
| IB Biology | Topic C4 (populations and communities: niches, competitive exclusion, fundamental and realised niche) | Connell's barnacles, the niche definitions |
| England | A-level Biology (populations in ecosystems: niche, interspecific competition, competitive exclusion) | niche and competition; examples from the specification |
| Australia | Year 12 Biology (ecosystems, species interactions) | competition and niche |
| India (CBSE) | Class 12 (Organisms and Populations: niche, interspecific competition, Gause's principle, resource partitioning with MacArthur's warblers named) | the NCERT chapter uses exactly these examples |
Practice (answers in the PDF)
- Define resource partitioning and state the principle it allows species to escape.
- Classify each as spatial, temporal or dietary partitioning: owls and hawks; three finch species with different beak depths; two barnacle species at different shore heights; two bat species foraging at dusk and after midnight.
- In MacArthur's study, why does the Cape May warbler not compete strongly with the Yellow-rumped warbler, although both eat insects in the same tree?
- Explain the difference between a fundamental and a realised niche using Connell's barnacles.
- On an island with only G. fortis, beaks are intermediate; on an island with both G. fortis and G. fuliginosa, fortis beaks are larger. Name this pattern and explain it.
- Two species of Paramecium grown together in one tube: one dies out. Grown in a tube with two bacterial food types, both survive. Explain both results.
Download the sheet and the practice set (PDF)
Where to get help
A 1-on-1 online biology class with a tutor who teaches AP Biology, IB and A-level biology, CBSE Class 12 and the Australian Year 11 and 12 every week: ecology taught through the classic studies, so the vocabulary (niche, exclusion, partitioning, displacement) attaches to warblers, barnacles and finches rather than to definitions. The biology page lists the courses; the free 30-minute first class is a real lesson on this week's topic. Related pages: types of ecosystems, adaptations and artificial selection.
Questions parents ask
1What is resource partitioning?
2What is an example of resource partitioning?
3What is the competitive exclusion principle?
4What are the types of resource partitioning?
5What is character displacement?
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