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Fitness

An indication of an individual's ability to be successful at surviving and reproducing; it provides a measure of the tendency of some organisms to produce more surviving offspring than others.

Absolute fitness

the ratio of the number of individuals of a particular genotype AFTER selection, to those BEFORE selection.

Relative fitness

The ratio of the number of surviving offspring per individual of a particular genotype to the number of surviving offspring per individual of the most successful genotype.

Co-evolution

The process by which 2 or more species evolve in response to selection pressures imposed by each other.

Symbiosis

Co-evolved intimate relationships between members of 2 different species.

Mutualism

A form of symbiosis whereby both organisms in the relationship are interdependent on each other for resources/other services. Both organisms gain (+/+)

Commensalism

A symbiotic relationship where only one organism benefits from the interaction (+/0)

Parasitism

A symbiotic relationship where the parasite benefits in terms of energy/nutrients and the host is harmed (+/-)

Pairs of species involved in symbiosis

Herbivores and plants; pollinators and plants; predators and prey; parasites and host

Red Queen Hypothesis

States that, in a co-evolutionary relationship, change in the traits of one species can act as a selection pressure on the other species. Both must adapt to avoid extinction.