Glossary
Commensalism
A symbiotic relationship where one species benefits, and the other species is neither helped nor harmed.
Example:
Cattle egrets often feed near grazing livestock, eating insects stirred up by the animals; the egrets benefit, while the livestock are largely unaffected, demonstrating commensalism.
Community
A group of different populations of various species living and interacting within the same geographical area.
Example:
A forest is a complex community where populations of deer, oak trees, squirrels, and various fungi all coexist and interact.
Interspecies Competition
A type of competition that occurs when two or more different species require the same limited resources, such as food, water, or space.
Example:
When different bird species in a forest forage for the same type of insect, they are engaged in interspecies competition for food resources.
Keystone Species
A species that has a disproportionately large effect on its environment relative to its abundance, often playing a critical role in maintaining the structure of an ecological community.
Example:
Sea otters are considered a keystone species because their predation on sea urchins prevents the urchins from overgrazing kelp forests, thus maintaining the entire kelp ecosystem.
Mutualism
A symbiotic relationship between two species where both organisms benefit from the interaction.
Example:
The relationship between bees and flowering plants is a prime example of mutualism; bees get nectar, and plants get pollinated.
Niche Partitioning
The process by which competing species use the environment differently in a way that helps them to coexist, often by specializing in different resources or habitats.
Example:
Different species of warblers living in the same tree avoid interspecies competition through niche partitioning, by feeding in different parts of the tree or on different types of insects.
Parasitism
A symbiotic relationship where one organism (the parasite) lives on or in another organism (the host) and benefits by deriving nutrients at the host's expense.
Example:
A tapeworm living in the intestines of a mammal is an example of parasitism, as the tapeworm absorbs nutrients from the host, weakening it.
Predator and Prey
An ecological interaction where one organism (the predator) hunts and kills another organism (the prey) for food.
Example:
The relationship between a lion and a zebra is a classic example of predator and prey, where the lion hunts the zebra for sustenance.
Simpson's Diversity Index
A quantitative measure used to calculate the diversity of a community, indicating the probability that two randomly selected individuals will belong to different species.
Example:
After surveying a pond, a biologist used Simpson's Diversity Index to determine that the pond with a more even distribution of algae, fish, and insect species was more diverse than one dominated by a single species.
Species Diversity
The variety of different species in a community, considering both the number of species (richness) and their relative abundance (evenness).
Example:
A rainforest typically exhibits high species diversity, with countless different plant and animal species living in close proximity.
Trophic Cascades
Powerful indirect interactions that can control entire ecosystems, occurring when a predator limits the abundance of its prey, thereby enhancing the survival of the next lower trophic level.
Example:
The reintroduction of wolves to Yellowstone National Park led to trophic cascades, as fewer elk meant more willow and aspen growth, which in turn benefited beaver populations.