Community Ecology
Community Ecology
Community - Definition: A group of populations of different species that interact with each other within a defined geographic area.
Community Ecology: The scientific study of these interactions, focusing on how species interactions, predation, competition, and disturbance affect community structure, species diversity, and relative abundance of different populations.
Presenter disclaimer: The speaker is not a professional community ecologist and the material may be basic review for some students.
Interspecific Interactions
Definition: Interactions that occur between individuals of different species.
Classification of interactions based on the effect on each species:
Helpful: () - Denotes a positive impact on a species (e.g., increased survival, reproduction).
Harmful: (-$)- Denotes a negative impact on a species (e.g., decreased survival, reproduction).
Neutral: (0-/-$$)
Definition: Occurs when individuals of different species compete for the same limiting resources, which are in short supply. These resources can include food, water, light, nesting sites, or space.
Description: This is often characterized as a “lose-lose” situation because the presence of competitors reduces the availability of resources for all competing species, thereby negatively impacting the growth, reproduction, and survival of both species involved. Increased competition leads to fewer resources and potentially reduced fitness for all competitors.
Example: Weeds, regarded as fast-growing plants, compete intensely with cultivated garden plants (e.g., tomatoes, beans) for essential resources like water, soil nutrients, and sunlight. This competition can significantly reduce the yield of desirable crops.
Competitive Exclusion
Principle:
The Competitive Exclusion Principle states that two species competing for the exact same limiting resource in the same place at the same time cannot coexist indefinitely. One species will always have a slight reproductive advantage.
One species will inevitably outcompete the other by utilizing the shared resources more efficiently or reproducing at a faster rate, leading to the local elimination (extinction) of the less efficient competitor or forcing it to occupy a different niche.
Experimental evidence:
In the 1930s, Russian ecologist G.F. Gause demonstrated competitive exclusion using two species of the microbe Paramecium:
Paramecium aurelia and Paramecium caudatum.
When grown separately in laboratory cultures with a constant food supply, both species exhibit logistic growth curves and reach their respective carrying capacities, indicating they can thrive under isolated conditions.
However, when grown together in the same culture, Paramecium aurelia consistently outcompetes Paramecium caudatum due to its more efficient resource acquisition and faster population growth. This leads to the eventual decline and extinction of Paramecium caudatum from the shared environment, while Paramecium aurelia flourishes.
Ecological Niches
Definition: An organism’s ecological niche encompasses the totality of a species’ use of both biotic (living components like food sources, predators, competitors) and abiotic (non-living components like temperature, water availability, pH, sunlight) resources and conditions in its environment. It describes the specific set of environmental factors a species requires and tolerates, as well as its role in the ecosystem (e.g., producer, consumer, decomposer).
Everyday definition: Often seen as a form of specialization, detailing a species'