Ecological niches provide a framework for understanding how species interact with their environment and with each other. By exploring the fundamental and realised niches, the competitive exclusion principle, and the uniqueness of ecological niches, we can gain insights into species' behaviours, interactions, and their implications for biodiversity.

Distinction between Fundamental and Realised Niches

Fundamental Niche

• Definition: The full spectrum of conditions and resources under which a species can potentially survive, reproduce, and thrive.
• Environmental Factors: It encompasses various environmental conditions such as temperature, humidity, pH level, salinity, and more.
• Potential Role: Not just about survival, but also about the potential role or job a species might have in an ecosystem. This could range from being a primary producer to a top predator.
• Limitations: Even though the fundamental niche defines the 'ideal' conditions for a species, not all species can exploit their fundamental niche fully due to competition and other biotic factors.

Realised Niche

• Definition: The portion of the fundamental niche that a species actually occupies in nature due to biotic constraints.
• Biotic Constraints: These constraints can include competition (for food, territory, mates), predation, disease, or symbiotic relationships (like mutualism or parasitism).
• Practical Outlook: In essence, while the fundamental niche provides a theoretical or potential outlook, the realised niche is more practical, reflecting the actual conditions under which the species exists.

Key Distinctions

• The fundamental niche represents the "ideal world" scenario for a species without any competition or other biotic interactions.
• The realised niche, on the other hand, is often a subset of the fundamental niche and represents the "real world" scenario, taking into account various biotic interactions.

Concept of Competitive Exclusion

Definition

• The competitive exclusion principle asserts that two species competing for identical resources cannot coexist indefinitely. One species will inevitably have a slight advantage, which will result in a higher reproductive rate and eventual dominance.
• This principle was derived from observations and experiments by Russian ecologist G.F. Gause.

Stage 1 depicts a smaller (yellow) species of bird that was initially searching the entire tree for insects to eat. In stage 2, the yellow bird faces competition for resources from a larger, invasive (red) species of bird that has been introduced into the ecosystem. Stage 3 illustrates how, over time, the invasive red species outcompetes the yellow species in their struggle for the centre of the tree and the more plentiful resources.

Image courtesy of Dhanscom17

Outcomes of Interspecies Competition

• Resource Partitioning: When two species evolve in response to the evolutionary pressure of interspecific competition, they tend to use resources in different ways. An example can be seen in birds that feed on the same tree but on different parts of the tree or at different times of the day.
• Shift in Realised Niche: A species may alter its behaviour or habits to avoid competition. Such changes can include altering feeding times, changing territories, or even adapting physiologically to new food sources.
• Extinction of the Less Competitive Species: If one species can't adapt quickly enough, it might face local extinction.
• Mutualistic Relationships: In some unique scenarios, what begins as competition might evolve into a mutualistic relationship. Both species adapt behaviours that benefit not just themselves but also their former competitors.

Uniqueness of Ecological Niches

Significance

• Each species evolves in response to both abiotic and biotic factors, resulting in a unique niche. This not only reduces direct competition but also contributes to ecosystem diversity and complexity.
• This uniqueness is often the outcome of millions of years of evolution, shaped by natural selection and environmental challenges.

Implications for Biodiversity

• Niche Diversity Promotes Species Diversity: A diverse array of niches can support a diverse set of species. The rainforests, for example, are a testament to this, where the availability of a multitude of niches supports a vast number of species.
• Biodiversity Resilience: If an ecosystem has a myriad of species with varied niches, it can better withstand changes. In case one species faces decline, others can potentially step in to fill its role.
• Ecosystem Stability: Greater niche diversity usually translates to greater ecosystem stability. Each species plays a role, and together, they contribute to the ecosystem's health and functioning.
• Niche Overlap as a Warning Sign: Overlapping niches can indicate potential problems. If multiple species are contesting for the same resources, it may lead to fierce competition and the risk of local extinctions.

Evolution and Niche Dynamics

Co-evolution

• As species interact over long periods, they can influence each other's evolution. For example, a predator's efficiency might drive the evolution of better defences in its prey and vice versa.
• Co-evolution can lead to tighter niche specifications and further diversify roles in an ecosystem.

Image courtesy of Inspirit Learning

Niche Construction

• Some species actively modify their environment, leading to new niches. Beavers, by building dams, create ponds which become a habitat for several other species.