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22 The Abiotic Environment 1. Introduction The development and reproduction of insects are greatly influenced by a variety of abiotic factors. These factors may exert their effects on insects either directly or indirectly (through their effects on other organisms) and in the short- or long-term. | IV Ecology 22 The Abiotic Environment 1. Introduction The development and reproduction of insects are greatly influenced by a variety of abiotic factors. These factors may exert their effects on insects either directly or indirectly through their effects on other organisms and in the short- or long-term. Light for example may exert an immediate effect on the orientation of an insect as it searches for food and may induce changes in an insect s physiology in anticipation of adverse conditions some months in the future. Another abiotic factor to which insects are now routinely subjected deliberately or otherwise are pesticides. Apart from the obvious effect of lethal doses of such chemicals pesticides may have more subtle indirect effects on the distribution and abundance of species for example alteration of predator-prey ratios and in sublethal doses changes in fecundity or rates of development. Under natural conditions organisms are subject to a combination of environmental factors both biotic and abiotic and it is this combination that ultimately determines the distribution and abundance of a species. Frequently the effect of one factor modifies the normal response of an organism to another factor. For example light by inducing diapause Section 3.2.3 may make an insect unresponsive to unaffected by temperature fluctuations. As a result an insect is not harmed by abnormally low temperatures but nor does it become active in temporary periods of warmer weather that may occur in the middle of winter. 2. Temperature 2.1. Effect on Development Rate The body temperature of insects as poikilothermic animals normally follows closely the temperature of the surroundings. Within limits therefore metabolic rate is proportional to ambient temperature. Consequently the rate of development is inversely proportional to temperature Figure 22.1 . Outside these temperature limits the rate of development no longer bears an inversely linear relationship to temperature because of the .
