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IB DP Biology — Form and Function | SL | B4.2 Ecological Niches
📋 What You Will Learn
- Identify the components of an ecological niche, including abiotic and biotic factors that define a species' role
- Explain the difference between fundamental and realised niches, and why they differ in nature
- Analyse how resource partitioning allows competing species to coexist in the same habitat
- Apply the competitive exclusion principle to predict outcomes when two species occupy identical niches
- Interpret data from field studies and laboratory experiments to evaluate niche overlap and resource use
🔍 Guiding Question How do the ecological roles of species in a community determine the distribution and abundance of organisms?
🌍 Why This Matters In the Galápagos Islands, fourteen species of finch share the same volcanic archipelago — yet each species feeds on different food sources, nests at different heights, and uses its uniquely shaped beak in a distinct way. No two species are doing exactly the same job. This is not coincidence. It is the result of billions of years of evolution shaping each species into a unique ecological role, and it is the reason why biodiversity can be so extraordinarily high in a single location.
What Is an Ecological Niche?
Every species in an ecosystem is more than just a name on a list. It is a player with a specific role — a set of conditions it can tolerate, resources it uses, and interactions it has with other organisms. Understanding this role is the foundation of community ecology.
Before we can explore how species coexist, we need a precise vocabulary. The concept of the niche is one of the most powerful ideas in ecology, and it is worth understanding exactly what it means — and what it does not mean.
📖 Key Definition — Ecological Niche An ecological niche is the full range of abiotic and biotic conditions under which a species can survive, grow, and reproduce, together with the functional role the species plays in its community. It encompasses not just where a species lives, but what it does — what it eats, what eats it, how it interacts with other species, and what environmental conditions it tolerates.
A useful way to think about this: a habitat is the address, but the niche is the occupation. Two species can share the same address — the same forest, the same reef, the same grassland — but they cannot permanently share the same occupation without one eventually displacing the other. This is the central tension of community ecology.
📖 Key Definition — Habitat A habitat is the physical environment in which a species lives — the specific location with its characteristic abiotic conditions (temperature, pH, light intensity, salinity) and biotic community. A habitat is a subset of the niche: it describes where, not what the organism does there.
Abiotic Components of the Niche
The abiotic dimensions of a niche include every physical and chemical variable that affects the species: temperature range, pH tolerance, light availability, water availability, salinity, and soil composition. Each variable defines an axis along which the species can survive. Together, these axes form a multi-dimensional space — the niche hypervolume — within which the species can persist.
For example, a freshwater fish species might tolerate water temperatures between 10°C and 25°C, pH between 6.5 and 8.0, and dissolved oxygen above 5 mg L⁻¹. Outside these ranges, the species cannot survive. These tolerances are not arbitrary — they reflect the biochemical limits of the species' enzymes, membranes, and metabolic pathways.
Biotic Components of the Niche
The biotic dimensions are equally important. They include what the species eats (its trophic level and food preferences), what preys upon it, which species it competes with, which it parasitises or is parasitised by, and which it depends on for pollination, seed dispersal, or other mutualistic services. A species' biotic niche is its web of ecological relationships.
Consider the African lion. Its abiotic niche includes the temperature and rainfall ranges of savanna ecosystems. Its biotic niche includes its prey species (wildebeest, zebra, buffalo), its competitors (hyenas, leopards, cheetahs), its parasites (ticks, tapeworms),