Fundamental vs Realized Niche: Difference and Comparison

The fundamental niche refers to the theoretical ecological space a species could occupy based on its physiological tolerance and resource requirements. In contrast, the realized niche is the actual ecological space a species occupies in nature, which may be constrained by interactions with other species, competition, and environmental factors, narrower than the fundamental niche due to these limitations.

Key Takeaways

1. The fundamental niche refers to the entire set of environmental conditions that a species can potentially occupy.
2. The realized niche, on the other hand, is the actual set of environmental conditions where a species exists due to biotic interactions.
3. The realized niche is smaller than the fundamental niche and can be influenced by competition, predation, and other biotic factors.

Fundamental vs. Realized Niche

A fundamental niche is the environmental conditions where a species can live without competition. They can live and reproduce in this niche. Realized niche describes creatures that survive by adapting to their environment and battling it out with other species.

The term fundamental niche is defined as the fullest condition through which an animal population species can reproduce and survive.

It is a set of conditions mainly used by pop species after being interacted with by other species (competition and predation), which have been considered. One example of a fundamental niche is the sparrow in the forest.

The term realized niche is considered smaller or limited than the fundamental niche. For example, once an invasive species is introduced into the ecosystem, it will always compete with an existing species to get space, food, and other resources.

So, the realized niche of an existing species can change and may vary from the fundamental niche.

Comparison Table

Feature	Fundamental Niche	Realized Niche
Definition	All the environmental conditions in which a species could survive, reproduce, and thrive without competition from other species or pressure from predators.	The actual environmental conditions where a species does live and reproduce, taking into account competition from other species and pressure from predators.
Also known as	Pre-competitive niche	Post-competitive niche
Competition	Absent	Present
Predation	Absent	Present
Resource Availability	Unlimited	Limited by abiotic factors (like temperature) and competition with other species.
Size	Larger or equal to the realized niche	Subset of the fundamental niche
Example	A squirrel species might fundamentally survive in any forest with sufficient nut trees, regardless of other animals present.	In reality, the squirrel might be relegated to the upper branches of trees due to competition from other animals for resources on the ground.

What is Fundamental Niche?

The fundamental niche of a species represents the entire range of environmental conditions under which it can survive and reproduce in the absence of interactions with other species. It’s essentially the ecological “blueprint” of a species, outlining the theoretical conditions where it could thrive based solely on its physiological capabilities and resource requirements.

Understanding the Concept

1. Physiological Tolerance: The fundamental niche encompasses the full spectrum of environmental factors, including temperature, humidity, pH levels, and nutrient availability, within which a species can maintain its metabolic functions and reproductive processes. For instance, a plant species might have a fundamental niche spanning a wide range of temperatures and soil types suitable for its growth.
2. Resource Requirements: This niche defines the resources a species needs to survive and reproduce, such as food sources, nesting sites, or specific habitat structures. For example, a bird species might have a fundamental niche that includes various types of insects, seeds, and nesting materials.

Constraints and Limitations

1. Abiotic Factors: Despite its theoretical breadth, the fundamental niche may be limited by abiotic factors like climatic extremes, soil composition, or water availability. For instance, although a plant species may have the physiological capacity to tolerate a wide range of temperatures, its fundamental niche may be restricted by factors like frost intolerance in colder climates.
2. Biotic Interactions: Interactions with other species, such as competition, predation, or mutualism, can further constrain the fundamental niche. For example, a plant species may be outcompeted for sunlight or nutrients by other plant species, narrowing its realized niche compared to its fundamental potential.

What is Realized Niche?

The realized niche of a species delineates the actual ecological space it occupies in nature, which may be narrower than its fundamental niche due to interactions with other species, competitive pressures, and environmental constraints. Unlike the theoretical breadth of the fundamental niche, the realized niche reflects the practical limitations and adaptations that shape a species’ distribution and behavior within an ecosystem.

Unveiling the Reality

1. Interaction Dynamics: The realized niche arises from the complex interplay between a species and its biotic and abiotic environment. It reflects the outcomes of species interactions, such as competition, predation, symbiosis, and mutualism, which can modify a species’ habitat use and resource exploitation strategies. For instance, a predator species may limit the distribution of its prey, causing the prey’s realized niche to shrink in areas where predation risk is high.
2. Environmental Constraints: Environmental factors, including climate variability, habitat fragmentation, and resource availability, also play a pivotal role in shaping the realized niche. These constraints may restrict a species’ distribution to specific geographical regions or habitats within its fundamental niche. For example, a plant species may be confined to certain soil types or elevations due to its physiological requirements and tolerance limits.

Deviations from the Fundamental Niche

1. Competitive Exclusion: Interspecific competition can lead to the exclusion of one species from portions of its fundamental niche, resulting in a realized niche that differs from its theoretical potential. This phenomenon, known as competitive exclusion, occurs when one species outcompetes another for essential resources, thereby restricting the latter’s distribution and niche breadth.
2. Adaptation and Specialization: Species may also undergo evolutionary adaptations or niche specialization to exploit specific ecological niches more effectively. These adaptations can enable a species to occupy niches that differ from its fundamental potential, allowing it to coexist with competitors or thrive in challenging environmental conditions. For instance, certain bird species may develop specialized foraging techniques to exploit unique food sources within their habitats.

Main Differences Between Fundamental Niche and Realized Niche

• Definition:
  • Fundamental Niche: Represents the theoretical ecological space a species could occupy based on its physiological tolerance and resource requirements.
  • Realized Niche: Represents the actual ecological space a species occupies in nature, constrained by interactions with other species, competition, and environmental factors.
• Scope:
  • Fundamental Niche: Encompasses the entire range of environmental conditions where a species could potentially survive and reproduce.
  • Realized Niche: Reflects the subset of the fundamental niche that a species effectively utilizes in its natural habitat, narrower due to biotic and abiotic constraints.
• Factors influencing Niches:
  • Fundamental Niche: Primarily influenced by the species’ physiological capabilities and resource needs.
  • Realized Niche: Influenced by interspecific interactions, competitive pressures, predation, symbiosis, and environmental constraints.
• Adaptations and Limitations:
  • Fundamental Niche: Represents the species’ ecological potential, broader and not limited by factors such as competition or predation.
  • Realized Niche: Reflects the species’ adaptations to biotic and abiotic pressures, as well as constraints imposed by interspecific interactions and environmental conditions.
• Ecological Significance:
  • Fundamental Niche: Provides insights into a species’ ecological requirements and potential distribution, serving as a foundation for studying species interactions and ecosystem functioning.
  • Realized Niche: Offers insights into the practical realities of species distributions, competitive dynamics, and adaptation strategies within ecosystems, aiding conservation and management efforts.

References

1. Realized versus fundamental niche functions in a model of chaparral response to climatic change
2. Realized and potential climate niches: a comparison of four Rhododendron tree species