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ABSTRACT Within any particular geographic area certain species of crayfish predominate: reasons for this predominance may be found in the demographic response of crayfish populations to such factors as nutrient addition, predation (including exploitation by man), or interaction with other crayfish species. Polytrophic crayfish utilize both primary and detrital production, both of which are governed by nutrient availability and energy distribution. The result is a sharply pulsed cycle of food availability at high latitudes in contrast to a more continuous cycle at low latitudes. Through modifications in their demographic response, life cycles of crayfish are adjusted to both the environmental conditions and resulting food availability prevalent at various latitudes. Often the end result is a match of young-of-the-year production to food production at each latitude. Most year to year differences in the cohort (year class) production of various species are due to fluctuations in mortality rates rather than to adjustments in growth or fecundity rates. The highest production rates are achieved by species with low mortality rates that coincide with the period of greatest growth (early age/size groups). Major impacts on these production rates are: exploitation, nutrient addition, and/or addition of new crayfish species. Exploitation, particularly in high latitudes. can increase the influence of environmental conditions on cohort mortality rates. Nutrient addition further modifies the cohort survival of certain species, depending on the latitude as well as on the presence of opportunistic competitors which may be better adjusted bioenergetically to exploit the prevailing food production cycle.

Affiliations: 1: Department of Biology, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada


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