Glossary

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G

Gamete
A reproductive cell (haploid) which unites with another in fertilization to produce a zygote from which a new individual (genet) arises.
Gause's principle
The idea that if two competing species coexist in a stable environment, then they do so as a result of differentiation of their realized niches; but if there is no such differentiation, or if it is precluded by the habitat, then one competing species will eliminate or exclude the other.
Gene
A unit of inherited material - a hereditary factor.
Gene flow
The consequence of cross-fertilization between members of a species across boundaries between populations, or within populations, which results in the spread of genes across and between populations.
Generation length (T)
Not quite the average length of time between the birth of a parent and the birth of its offspring (the 'cohort generation time'): the production by offspring of their own offspring during the life of the original parent makes the average, computed over many generations, less than the cohort generation time.
Genet
The organism developed from a zygote. The term is used especially for modular organisms and members of a clone to define the genetic individual and to contrast with 'ramet' the potentially physiologically independent part that may arise from the iterative process by which modular organisms grow.
Genetic drift
Random changes in gene frequency within a population resulting from sampling effects rather than natural selection, and hence of greatest importance in small populations.
Genetic engineering
Any change in the genetic constitution of an organism brought about by artificial means other than simple artificial selection and which would not usually occur in nature, such as the introduction of a gene from one species to another.
Genotype
All the genetic characteristics that determine the structure and functioning of an organism.
Geometric series
A series of numbers in which each is obtained by multiplying the preceding term by a constant factor, e.g. 1, 3, 9, 27, etc.
'Ghost of competition past'
A term coined by J.H. Connell to stress that interspecific competition, acting as an evolutionary force in the past, has often left its mark on the behaviour, distribution or morphology of species, even when there is no present-day competition between them.
Global stability
The tendency of a community to return to its original state even when subjected to a large perturbation.
Global warming
The predicted warming of the planet resulting from increasing atmospheric concentrations of radiative gases such as carbon dioxide, methane, nitrous oxide and chlorofluorocarbons.
Glycoside
A derivative of glucose (or another sugar) in which one hydrogen atom is replaced by an organic radical. (= Glucosinolate.)
Gonad
Organs of animals which produce gametes.
Gradient analysis
The analysis of species composition along a gradient of environmental conditions.
Granivores
Animals that eat seeds.
Grazer
A consumer which attacks large numbers of large prey during its lifetime, but removes only a part of each prey individual, so that the effect, although often harmful, is rarely lethal in the short term, and never predictably lethal.
Grazer - scrapers
Aquatic animals that graze the organic layer of algae, microorganisms and dead organic matter on stones and other substrates.
Greenhouse effect
Warming of the earth's atmosphere as a result of increases in CO2 and other gases.
Gross primary production (GPP)
The total fixation of energy by photosynthesis in a region.
Group selection
The evolutionary process which is supposed to act through the different numbers of descendants left by groups rather than by individuals.
Guild
A group of species that exploit the same class of environmental resources in a similar way.

 
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