Editing Autecology (section)

=== Population sizes and replacement level reproduction ===
Autecological theory predicts that populations will reproduce at around replacement level unless a period of environmental change causing unusually high or low survival causes the population to grow or shrink before restabilising at replacement level again.<ref>Robin  J-P,  Denis  V.  1999.  Squid  stock  fluctuations  and  water  temperature:  temporal analysis of English Channel Loliginidae. Journal of Applied Ecology 36: 101-110.</ref> Population numbers may be reduced by introduction of new predation pressure, such as with poor fisheries management or introduction of a biological control agent to control an invasive species, such that net reproductive rate, R0, drops below replacement level.<ref name="Walter2014"/> The species being preyed upon in each case may stabilise at a lower population density where it is more difficult for individuals of the higher trophic level to locate the prey species, but at this point relieving predation tends to make little difference to population size, as individuals continue to reproduce around replacement level as they were at a higher density prior to the introduction of a higher trophic level.<ref>Walter GH (2003) Insect Pest Management and Ecological Research Cambridge University Press, Cambridge, UK.</ref>