Competition Knowledge-Based Study

Study notes

1. What is Competition?

   In ecology, competition is an interaction between individuals or species in which the fitness or population growth of one is lowered by the presence of another. This negative-negative interaction ($-$/$-$) arises because organisms rely on common, limited resources such as food, water, light, territory, or nesting sites.

   Levels of Competition

   Ecologists classify competition based on the taxonomic relationship of the interacting organisms:

   • Intraspecific Competition: Occurs between members of the same species. Because individuals of the same species have identical resource requirements, intraspecific competition is often particularly intense and serves as a major density-dependent factor regulating population size.
   • Interspecific Competition: Occurs between individuals of different species whose ecological requirements overlap. It shapes community structure, species diversity, and evolutionary adaptations.

   How Do Organisms Compete?

   Competition operates through distinct behavioural and physiological mechanisms. The two primary forms are:

   • Exploitation Competition (Indirect): Organisms interact indirectly by consuming or depleting a shared, limited resource. When one individual uses the resource, less remains for others, reducing their survival or reproduction. For example, fast-growing plants absorbing soil nitrogen leave fewer nutrients available for nearby plants without direct physical confrontation.
   • Interference Competition (Direct): Individuals interact directly through aggressive behaviour, territorial defense, or chemical inhibition to prevent competitors from accessing resources. A classic botanical example is allelopathy, where certain plants release toxic chemicals into the soil to inhibit the germination or growth of neighboring competitors.

   Gause's Principle

   In the 1930s, Russian ecologist G. F. Gause formulated the Competitive Exclusion Principle based on laboratory experiments with protozoa (Paramecium aurelia and Paramecium caudatum).

   The principle states that:

   Two species competing for the exact same limiting resource cannot coexist indefinitely in a stable environment if other ecological factors remain constant.

   The species with even a slight competitive advantage will outcompete, deplete resources more efficiently, and eventually drive the other species to local extinction or an ecological shift.

   Ecological Niches and Coexistence

   To avoid competitive exclusion, competing species frequently evolve differences in resource use. Understanding this requires distinguishing between two types of ecological niches:

   • Fundamental Niche: The full range of environmental conditions and resources an organism could theoretically occupy or utilize in the absence of competitors and predators.
   • Realized Niche: The actual set of conditions and resources an organism occupies in the presence of biotic interactions such as competition. The realized niche is typically narrower than the fundamental niche.

   Resource Partitioning and Character Displacement

   Over evolutionary time, natural selection favors individuals that utilize distinct resources or microhabitats, a phenomenon known as resource partitioning. For instance, different species of Caribbean anole lizards forage at different heights in the forest canopy.

   When resource partitioning leads to morphological differences between sympatric populations of competing species, it is known as character displacement (such as divergence in beak depths among Darwin's finches living on the same island).