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Form and function - Ecological niches

Grade 12IBBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Ecological Niche: The functional role and position of a species within its ecosystem, encompassing its habitat, resource use, and interactions with other organisms. It is defined by the tolerances and requirements of the species.

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Fundamental Niche: The entire set of conditions (temperaturetemperature, pHpH, food availability) under which a population, species, or individual can survive and reproduce itself in the absence of interspecific competition and predation.

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Realized Niche: The actual conditions and resources used by a species after interactions with other species (competition and predation) are taken into account. Realized Niche⊆Fundamental Niche\text{Realized Niche} \subseteq \text{Fundamental Niche}.

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Competitive Exclusion Principle (Gause's Law): Two species competing for the exact same limiting resource cannot coexist at constant population values. One will eventually outcompete the other, leading to the latter's local extinction or an evolutionary shift toward a different niche.

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Niche Partitioning: An evolutionary process where natural selection drives competing species into different patterns of resource use or different niches (e.g., different feeding times or different parts of a tree canopy) to minimize competition.

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Form and Function Adaptations: Morphological, physiological, and behavioral traits are shaped by the requirements of the niche. For example, the specialized beak shapes of Galapagos finches represent morphological 'form' adapted to specific dietary 'functions' within their niches.

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Generalists vs. Specialists: Generalists have a broad niche (e.g., raccoons), whereas specialists have a narrow niche and specific requirements (e.g., pandas eating only bamboo).

📐Formulae

dN1dt=r1N1(K1−N1−α12N2K1)\frac{dN_1}{dt} = r_1 N_1 \left( \frac{K_1 - N_1 - \alpha_{12} N_2}{K_1} \right) (Lotka-Volterra Competition Model showing how species 2 affects species 1 population growth)

H′=−∑i=1spiln⁡piH' = - \sum_{i=1}^{s} p_i \ln p_i (Shannon-Wiener Index, used to quantify niche breadth or ecosystem diversity)

Niche Overlap=∑(p1ip2i)∑p1i2∑p2i2\text{Niche Overlap} = \frac{\sum (p_{1i} p_{2i})}{\sqrt{\sum p_{1i}^2 \sum p_{2i}^2}} (Pianka's Niche Overlap Index)

💡Examples

Problem 1:

In a rocky intertidal zone, two species of barnacles, Chthamalus stellatusChthamalus\ stellatus and Semibalanus balanoidesSemibalanus\ balanoides, compete for space. ChthamalusChthamalus can live in both high and low tide zones when SemibalanusSemibalanus is removed. However, when both are present, SemibalanusSemibalanus outcompetes ChthamalusChthamalus in the lower zone. Identify the fundamental and realized niches of ChthamalusChthamalus.

Solution:

Fundamental Niche of Chthamalus=High tide and Low tide zones\text{Fundamental Niche of } Chthamalus = \text{High tide and Low tide zones} Realized Niche of Chthamalus=High tide zone only\text{Realized Niche of } Chthamalus = \text{High tide zone only}

Explanation:

The fundamental niche represents the potential area a species can occupy without competition (high+lowhigh + low). The realized niche is the actual area occupied due to the presence of a superior competitor (SemibalanusSemibalanus).

Problem 2:

Calculate the population growth rate change for Species 1 (N1=50N_1 = 50, r1=0.1r_1 = 0.1, K1=100K_1 = 100) if a competitor Species 2 (N2=20N_2 = 20) is introduced with a competition coefficient α12=0.5\alpha_{12} = 0.5.

Solution:

dN1dt=0.1×50×(100−50−(0.5×20)100)\frac{dN_1}{dt} = 0.1 \times 50 \times \left( \frac{100 - 50 - (0.5 \times 20)}{100} \right) dN1dt=5×(100−50−10100)\frac{dN_1}{dt} = 5 \times \left( \frac{100 - 50 - 10}{100} \right) dN1dt=5×(40100)=2.0\frac{dN_1}{dt} = 5 \times \left( \frac{40}{100} \right) = 2.0

Explanation:

The presence of Species 2 reduces the available carrying capacity for Species 1. Without Species 2, the growth rate would have been 5×(50/100)=2.55 \times (50/100) = 2.5. The competition reduces it to 2.02.0.