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Competition and Its Ecological Outcomes (STR)
| Topic | Description | Examples |
|---|---|---|
| Introduction to Competition | Competition is an ecological interaction where individuals vie for the same limited resources like food, space, light, or mates. It occurs within the same species (intraspecific) or between species (interspecific), influencing survival, adaptation, and evolution. | Barnacles, Paramecium species |
| Intraspecific Competition | Occurs among individuals of the same species, often intensifying with density. It regulates population size by limiting growth and reproduction when resources are scarce. | Plants competing for sunlight in dense populations |
| Interspecific Competition | Competition between different species sharing overlapping niches, potentially leading to competitive exclusion. | Paramecium aurelia and Paramecium caudatum (Gause’s Competitive Exclusion Principle) |
| Interference Competition | Involves direct interactions like physical fights or chemical deterrents (allelopathy in plants) to control access to resources. | Allelopathy in plants, aggressive animal behavior |
| Exploitative Competition | Occurs indirectly when individuals deplete resources, reducing availability for others. | Taller plants shading shorter plants for sunlight |
| Competitive Exclusion | States that two species competing for identical resources cannot coexist; one will outcompete the other. | Paramecium experiment, Chthamalus and Balanus barnacles in intertidal zones |
| Resource Partitioning | Species evolve to use resources differently, reducing direct competition and allowing coexistence. | MacArthur’s warblers foraging in different parts of trees |
| Character Displacement | Species competing for similar resources evolve differences to reduce competition, especially in sympatric populations. | Darwin’s finches developing distinct beak sizes |
| Competitive Release | Occurs when a species expands its niche in response to the removal of a competitor, allowing it to exploit previously unavailable resources. | Increase in certain populations after removal of competing species |
| Intrinsic Rate of Natural Increase (r) | A population’s growth potential when resources are abundant. Competition reduces this effective growth rate by limiting survival and reproduction. | Impact observed in high-density populations |
| Darwinian Fitness and Competition | Competition affects Darwinian fitness by pressuring species to adapt, increasing specialization and enhancing fitness under specific environmental conditions. | Species adapting to specific niches in competitive environments |
Competition and Its Ecological Outcomes (LTR)
| Aspect | Description | Examples |
|---|---|---|
| Competition Overview | Competition is an interaction where individuals or species compete for limited resources such as food, space, or mates. It can be intraspecific (within the same species) or interspecific (between species) and influences survival, adaptation, and evolutionary processes. | Barnacles, Paramecium, MacArthur’s warblers |
| Intraspecific Competition | This competition occurs among individuals of the same species and increases with population density. It regulates population size by limiting growth and reproduction as resources become scarce. | In dense plant populations, plants compete for sunlight, water, and nutrients. This can lead to “self-thinning” where only the strongest survive. |
| Interspecific Competition | Occurs between individuals of different species that share overlapping ecological niches. It can lead to competitive exclusion, where one species outcompetes the other, forcing it to migrate or become extinct. | In Gause’s Paramecium experiment, P. aurelia outcompeted P. caudatum, resulting in the extinction of P. caudatum in the shared environment. |
| Interference Competition | Involves direct interactions like physical confrontations or chemical deterrents (allelopathy) to control resource access. | Allelopathy in plants where chemicals are released to inhibit nearby plants; aggressive behavior in animals to defend territory. |
| Exploitative Competition | Occurs indirectly as individuals deplete resources, reducing their availability for others. | Taller plants in a forest capture more sunlight, indirectly limiting the light available for shorter plants below. |
| Impact of Goats on Abingdon Tortoise | The Abingdon tortoise on the Galápagos Islands suffered due to the introduction of goats, primarily because of the goats’ browsing behavior. Goats are efficient browsers, meaning they feed on a wide variety of vegetation, including shrubs, leaves, and woody plants. This behavior significantly impacted the tortoises’ food sources. The tortoises, which are primarily grazers, feed on grasses and low-lying plants. As the goats consumed these plants and damaged the landscape by stripping away vegetation, the tortoises’ food became scarcer. Unlike goats, tortoises can’t browse on woody plants and were unable to compete with the goats for the remaining plant resources. Over time, the decline in food availability, combined with the goats’ rapid population growth, contributed to the extinction of the Abingdon tortoise within a decade. This highlights how a change in one species’ feeding behavior can destabilize an ecosystem, especially when the native species are not equipped to handle the competition. | In this case, the introduction of goats and their browsing behavior led to the depletion of food resources for the Abingdon tortoises, causing their eventual extinction. The tortoises could not compete for food because goats consumed more vegetation, leaving less for the tortoises, who were unable to browse on woody plants. |
| Exploitative Competition | Exploitative competition (also known as resource competition) happens when species compete for the same resources, but the competition is indirect. The goats were consuming more of the available plant material, thus depleting the food supply for the tortoises without directly interacting with them. The tortoises couldn’t access enough food to survive because the goats were more efficient at consuming the available vegetation. | This is an example of exploitative competition, where one species outcompetes another for resources without direct interaction. The goats, by consuming the available plant material, indirectly caused the decline and eventual extinction of the tortoises. |
| Competitive Exclusion | This principle states that two species competing for identical resources cannot coexist; one species will always outcompete the other, leading to migration or extinction. | In the intertidal zone, Chthamalus and Balanus barnacles occupy different areas: Balanus dominates the lower intertidal, excluding Chthamalus, which can only survive in the upper zone. |
| Resource Partitioning | Species evolve to use resources in different ways, reducing direct competition and allowing coexistence in the same habitat. | MacArthur’s warblers forage in different parts of trees, minimizing competition by dividing the tree into vertical zones for food sources. |
| Character Displacement | When species competing for similar resources evolve physical or behavioral differences to minimize competition, particularly when they coexist in the same region. | Darwin’s finches on the Galapagos Islands developed different beak sizes to specialize in different food types, reducing competition among species. |
| Competitive Release | Occurs when a species expands its niche following the removal of a competing species, allowing it to access previously unavailable resources. | When goats were removed from certain islands, other species were able to thrive and utilize previously contested resources, illustrating the concept of competitive release. |
| Intrinsic Rate of Natural Increase (r) | Refers to a population’s growth rate under ideal conditions with no limiting resources. Increased competition reduces the effective growth rate by limiting survival and reproductive success. | In high-density populations, resources are scarce, leading to increased mortality and reduced reproduction, thereby decreasing the effective rate of increase (r). |
| Darwinian Fitness and Competition | Competition affects Darwinian fitness by forcing species to adapt, leading to specialization and enhanced survival in specific environmental conditions. | Species adapt to specific ecological niches, increasing their reproductive success and survival under competitive pressures. |