The health of an ecosystem directly depends on the species richness and species diversity. Ecosystems have evolved to accommodate more number of individuals and species in it, so as to remain stable despite environmental disturbances.
How does an ecosystem achieve this accommodation?
There are two major processes that affect the ability of an ecosystem to host organisms: the environmental factors and the adaptations of organisms to these factors. We’ve already seen how adaptations play a major role in generating diversity in ecosystems and how it eventually leads to evolution. Let’s take a closer look at the environmental factors and the role they play in an ecosystem.
Environmental factors are the sum total of all biotic and abiotic fators of a particular place. Together, they affect organisms and how they live. Their effect on the organism is both structural and functional. This is where the concepts of habitat and niche comes in.
Habitat and Niche
A habitat is crudely the address of an organism, it is the place where it lives. For example, the habitat for whales is oceans. The habitat for tigers is the forest (On a side note, it is fascinating to realize that humans have transcended their traditional habitats of African grasslands to enter, dominate and alter almost every possible habitat on Earth!).
The habitat is largely defined by the abiotic factors of the place; the topography, sunlight, water etc. It is merely a place with conditions that could (but not necessarily) sustain a particular organism. Its area can vary with scale and context; for example forests are the habitat for many, many species but within a forest, micro-organisms live on the forest soil which becomes its specific habitat. It is a structural concept.
A niche, on the other hand, is crudely defined as the profession of an organism. It illustrates the functional role of an organism in an ecosystem with respect to other organisms surrounding it. Niches describe the position of an organism on the food chain and its relationship with other species (whether it is beneficial, adverse or neutral) in that ecosystem. There is no concept of scale, as this is not a spatial parameter. An earthworm could have its habitat described as the soil (small scale) or agricultural land (large scale), but its role in both remains the same, which is to decompose dead material (niche).
These two concepts are important in the generation of diversity and richness in an ecosystem because the process of adaptation and evolution is to achieve a specific habitat and niche.
By specifically adapting to a particular set of environmental abiotic conditions, organisms increase their ability of obtaining a “permanent address” and ensuring a habitat for themselves in the ecosystem.
Similarly, organisms, by way of interaction with other organisms, adapt to a particular process in the ecosystem (in the food chain and nutrient cycling process), gaining the ability of having “a job” and establishing themselves permanently.
How are habitat and niche interrelated?
Have you ever wondered why a desert ecosystem has less number and diversity of species than a forest or ocean ecosystem?
When an ecosystem can support a variety of habitats, it is likely to be able to produce more niches and more opportunities for organisms to fit into.
Deserts have the same habitat over a wide range of area; the environmental factors of high solar insolation, water scarcity and dry winds are present ubiquitously. Forests and oceans, within their large spatial extent have a variety of different environmental factors. This gives life a greater choice of habitats and niches.
It is important to note that habitats can exist without niches. Habitat is the sum total of all conditions for an organism to live in (potential habitat). A habitat is only occupied (realized habitat) when an ecosystem develops and niches are integrated into it. This is called habitat differentiation and is deeply interconnected with the presence of a thriving ecosystem.
It is possible that two organisms can have the same niche (same role) in an ecosystem, provided they live in different habitats. For example, deer and rabbits both play the role of herbivores, but you find deer in the woody areas of a forest while rabbits are found in the open areas.
What would happen if organisms evolved into the same niche enter the same habitat?
They begin to compete. If deer were brought into a open areas, both deer and rabbits would begin to fight for the same resource. Eventually, one would eliminate the other (survival of the fittest). Hence, niches play an important role in keep diversity alive in a species–they ensure organisms have specific roles and they roles do not overlap so as to avoid competition and elimination.
Habitats are the physical parts of an ecosystem and niches are the functional parts. Habitat and niches are both integral for an ecosystem to survive and support high species richness and diversity.
- On the distinction between habitat and niche, and some implications for species differentiation, Looijen, Rick. C, Cognitive Patterns in Science and Common Sense 1995.
- Niche, habitat and ecotope, R.H Whittaker; S.A. Levin; R.B. Boot; The American Naturalist 1973.
- Ecology and Environment, Twelfth Edition, P.D. Sharma.