Glossary

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O

Obligate mutualism
A condition in which a mutualistic relationship with other species is essential for a species to survive.
Oligophagous
Consuming a small range of types of food items.
Omnivory
Feeding on prey from more than one trophic level.
Ontogenetic
Occurring during the course of an organism's development.
Opportunistic species
One that is capable of exploiting spasmodically occurring environments.
Optimal diet model
Mathematical formulation of prey selection that would, in theory, provide the best energy returns to the consumer: used as a yardstick to assess actual performance.
Optimum similarity
The level of similarity between competing species, which, if either exceeded or reduced, would lead to a lowering of fitness for individuals in at least one of the species.
Ordination
Mathematical system for categorizing communities on a graph so that those that are most similar in species composition appear closest together.
Osmoregulation
Regulation of the salt concentration in cells and body fluids.
Osmosis
Diffusion of water across a semi-permeable membrane.
Osmotic pressure
The tendency of water to move across a semi-permeable membrane into a solution.
Outbreeding
In which genetically dissimilar organisms mate with each other.
Overcompensating density dependence
Density dependence which is so intense that increases in initial density lead to reductions in final density.
Overexploitation
Exploitation of (removal of individuals or biomass from) a natural population at a rate greater than the population is able to match with its own recruitment, thus tending to drive the population towards extinction.
Overgrowth competition
Competition amongst sessile organisms where the mechanism is the growth of one individual over another, preventing the efficient capture of light, suspended food or some other resource.

 
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