Glossary

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I

Immigration
Entry of organisms to a population from elsewhere.
Immune response
A response mounted by an animal in which specific antibodies (vertebrates only) and/or cytotoxic cells are produced against invading microorganisms, parasites, transplanted tissue, and many other substances which are recognized as foreign by the body.
Inbreeding depression
A loss of vigor amongst offspring occurring when closely related individuals mate, resulting from the expression of numbers of deleterious genes in a homozygous state and from a generally low level of heterozygosity.
Incidence function
The relationship between island size and the proportion of islands of that size occupied by the species in question.
Incubation period
The period during which the embryo in an egg develops before hatching. Also, in epidemiology, the period between infection and the appearance of symptoms of disease.
Individualistic concept
Concept of the community as an association of species that occur together simply because of similarities in requirements and not as a result of a long coevolutionary history.
Inflorescence
The organ bearing an aggregation of flowers in a flowering plant.
Inhibition (successional)
The tendency of early successional species to resist the invasion of later species.
Inoculation
The introduction of a disease organism or vaccine, usually through a deliberately made wound.
Intensity of abundance
The number of individuals per habitable site in a community (cf. Prevalence (of abundance)).
Intensity of infection
The number of parasites per host in a population (cf. Prevalence of infection).
Interference coefficient
see Coefficient of interference and also Mutual interference.
Interference competition
Competition between two organisms in which one physically excludes the other from a portion of habitat and hence from the resources that could be exploited there.
Interglacial period
Period between glaciations, during which species begin to recolonize locations occupied previously.
Interspecific competition
Competition between individuals of different species.
Intraspecific competition
Competition between individuals of the same species.
Intrinsic rate of natural increase (r)
The per capita rate of increase of a population which has reached a stable age structure without competitive or other restraints.
Inverse cube law
A law which states that the intensity of an effect at a point B due to a source at A varies inversely as the cube of their distance apart.
Inverse square law
A law which states that the intensity of an effect at a point B due to a source at A varies inversely as the square of their distance apart.
Island biogeography
The study of distribution of species and community composition on islands.
Isocline
A line linking points, each of which gives rise to the same rate of population increase for the species being considered. The points may represent combinations of species densities or combinations of resource levels.
Isotherm
A line on a map that joins places having the same mean temperature.
Isotonic
Having the same osmotic pressure.
Isotopes
Atoms of the same element having the same chemical properties but differing in mass and in the physical properties that depend on their mass.
Iteroparity
Where organisms produce offspring in a series of separate events during and after each of which the organisms maintain themselves in a condition that favours survival to reproduce again subsequently (though the 'separate events' may merge into continuous reproduction).

 
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