Ecological Niches and Competitive Exclusion Practice Flashcards

Definition of the Ecological Niche

• An ecological niche represents the specific role and space an organism occupies within its ecosystem.

• It encompasses all interactions between the organism and both biotic (living) and abiotic (non-living) components of the environment.

• The niche describes how and where an organism lives, including:

  • The full range of resources the organism utilizes.

  • The specific methods and timing of resource usage.

  • All biological adaptations that allow the organism to survive and reproduce in that specific environment.

Types of Ecological Niches

• Fundamental Niche: This refers to the full potential range of environmental conditions and resources a species could theoretically occupy and use in the absence of limiting factors like competition or predation.

• Realised Niche: This is the actual portion of the fundamental niche that a species occupies in reality. It is typically narrower than the fundamental niche due to interactions with other species, such as competition and predation, which restrict the organism to a subset of its potential habitat.

The Competitive Exclusion Principle

• The principle states that two distinct species that require the identical resources cannot coexist indefinitely in the same niche.

• Survival of both species is only possible if they possess different environmental requirements or if they partition resources differently.

• Example: Barnacles: Different species of barnacles found on coastal rocks grow in very specific, distinct horizontal zones. They do not mix freely because each species is adapted to a particular level of exposure to water and air, and competition prevents them from inhabiting the same vertical space on the rock surface.

Case Study: Townsville Broad-Tailed Geckos

• Researcher: Anders Zimny conducted studies on these specific geckos.

• Specific Niche Analysis: This case study focuses on the Phyllurus genus in the North Queensland region, specifically looking at species with highly restricted or specific niches.

• Geographic Species Distribution:

  • Phyllurus gulbaru: A species with a highly specific niche and restricted distribution.

  • Phyllurus amnicola: Another species within the same geographic context but occupying different specific ranges.

• Locations Studied:

  • Paluma Range

  • Patterson's Gorge

  • Hervey Ranges

  • Mt Elliot

  • Magnetic Island

• Mapping Data: The distribution is often measured against topographical features, such as the $500\,m$ contour line, and evaluated through climatic and non-climatic suitability factors.

• Suitability Indices: Habitat suitability is often quantified on a scale from $0$ to $1.0$. Specific legend markers used in niche mapping include:

  • $0-0.5$

  • $0.5-0.6$

  • $0.6-0.7$

  • $0.7-0.8$

  • $0.8-0.9$

  • $0.9-1.0$

• Comparison: While Phyllurus gulbaru maintains a specific niche, the Velvet Gecko is noted for occupying a much broader niche across similar regions like Cairns and Townsville.

Case Study: Intertidal Limpet Interactions in California

• Study Objective: To examine the interactions and niche distributions of three species of limpets living on pier pylons in California, USA.

• Species Involved:

  • L. digitalis

  • L. paradigitalis

  • L. scabra

• Methodology:

  • Researchers measured the vertical distribution of each species by recorded their distance from the top of the pylon in centimeters ($cm$).

  • Initial observations were made with all three species present (Graph A).

  • Experimental manipulation involved the removal of L. digitalis to observe the resulting effects on the distribution of L. paradigitalis and L. scabra (Graph B).

Analysis of Limpet Distribution Data

• Initial State (All Species Present):

  • Measurements were tracked over a full year from October (O) through the following October (O).

  • The species occupy different average depths from the top of the pylon, ranging from $0\,cm$ to over $100\,cm$.

• Experimental Phase (Removal of L. digitalis):

  • Effect on L. paradigitalis: Upon the removal of L. digitalis, L. paradigitalis showed a significant shift in its vertical distribution. It moved higher up the pylon, occupying the space previously dominated by L. digitalis.

  • Effect on L. scabra: The distribution of L. scabra remained relatively consistent or showed less dramatic shifts compared to L. paradigitalis.

• Deductions and Conclusions:

  • Competitive Interaction: The shift in L. paradigitalis suggests that its realized niche was being restricted by L. digitalis. This indicates interspecific competition between these two species for the upper pylon space.

  • Fundamental vs. Realised Niche: The move of L. paradigitalis toward the top of the pylon after the removal of a competitor demonstrates that its fundamental niche includes the higher zones, but its realized niche was lower down when L. digitalis was present.

  • Niche Differentiation: The three species utilize different vertical zones of the pylon to reduce direct competition, illustrating the competitive exclusion principle in a real-world environment.