Q7(e):

Define the following terms and give one example for each: (e) Interspecific competition

Step 1: Core Definition & Ecological Context

Interspecific competition is defined as a negative biological interaction between individuals of two or more distinct species that occupy the same trophic level and vie for the same essential, but limited, ecological resources (such as food, water, spatial territory, or light).

Unlike intraspecific competition (which occurs between members of the same species), interspecific competition is a major driver of ecological niche differentiation and evolutionary divergence. The interaction is generally characterized as a $ (- / - ) $ relationship, meaning that both competing species suffer a reduction in fitness, growth rate, or population density as a result of the interaction.

Step 2: Mechanisms of Competition & Theoretical Justification

Interspecific competition operates primarily through two mechanisms:

• Exploitation Competition: Species compete indirectly by depleting a shared resource.
• Interference Competition: Species compete directly. [Theoretical Note: In interference competition, the feeding or foraging efficiency of one species is significantly reduced by the interfering or aggressive presence of the other species, even if the resources are abundant].

Academically, this population dynamic is quantified using the Lotka-Volterra Competition Model. The population growth rate of Species 1 in the presence of competing Species 2 is given by:

$ \frac{dN_1}{dt} = r_1 N_1 \left( \frac{K_1 - N_1 - \alpha N_2}{K_1} \right) $

Where $N$ represents population size, $r$ is the intrinsic rate of increase, $K$ is the carrying capacity, and $\alpha$ is the competition coefficient denoting the per capita effect of Species 2 on Species 1. When competition is severe, it leads to Gause’s Competitive Exclusion Principle, which states that two closely related species competing for the exact same resources cannot coexist indefinitely; the competitively inferior species will eventually be eliminated.

Step 3: Classical Ecological Examples

There are multiple well-documented instances of interspecific competition in field biology.

• Example 1 (Interference / Exclusion): The Abingdon tortoise in the Galapagos Islands became extinct within a decade after goats were introduced to the island. This occurred because the goats possessed a vastly superior browsing efficiency, aggressively outcompeting the native tortoises for the same plant resources.
• Example 2 (Exploitation): In several shallow South American lakes, visiting flamingos and resident fish species exhibit interspecific competition. Despite being vastly different taxonomically, both species compete for the same shared food source: zooplankton in the lake water.

Step 4: Graphical Representation of Competitive Exclusion

The following diagram visualizes Gause's Competitive Exclusion Principle resulting from severe interspecific competition. When placed in the same habitat, the superior competitor reaches its carrying capacity ($K$), while the inferior competitor's population declines to zero.

Final Solution:
Interspecific competition is defined as the biological interaction where individuals of different species compete for the same limited ecological resources (such as food or space), negatively impacting the fitness of both. A classic example is the competition between introduced goats and native Abingdon tortoises on the Galapagos Islands, where the superior browsing efficiency of the goats led to the tortoises' local extinction.