Geoscience Reference
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1.3.3. On the level of the population
The decrease in rates of survival, growth and reproduction, as well
as the modification of individual behavior - as far as it is due to
them - leads to a modification in the population's dynamic, which can
go as far as the disappearance of the species in a polluted habitat
[CAS 01]. For a single disruption at an individual level, the effect on
the population is lesser or greater according to the pattern of the
species' life history [SPR 05].
In practice, the pattern of the species' life history is a group of data
that includes: the species' biodemographic parameters in a given
environment (lifespan, number of developmental stages, number of
offspring, fecundity, etc.) and the ratios between these parameters
(ratio between lifespan and age at which an organism first reproduces,
ratio between rates of growth and fecundity, etc.). Each pattern of the
species' life history corresponds to a coadaptation of the species'
biological and ecological characteristics depending on the biotic and
abiotic factors of its habitat. These characteristics can be classified
into two categories. Those that are linked to the developmental cycle
of the organism influence the probability of survival above all. Those
that are linked to reproduction influence fecundity above all.
Thus, the number of developmental stages and the population's
vulnerability in terms of the probability of survival at these stages are
major determinants of a population's resistance to disruptions [SPR
05]. In effect, among certain organisms, there are critical periods or
stages of development during which the organism's probability of
survival is weaker than at other stages [KOE 91]. These stages are
particularly vulnerable to instances of pollution. For example, this is
the case during periods of larval molts among crustaceans [KOI 92] or
the metamorphosis between the larval and juvenile stages of fish (for
example, flat fish, which pass from a pelagic larval life stage to a
benthic stage during their juvenile and adult phases).
The characteristics influencing organisms' reproduction, along
with their lifespan, strongly influence a population's response to
contaminants [CAL 97, IND 99]. In effect, the number of descendants
produced per year in a population depends, according to [SPR 05]:
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