Temperature, latitude and reproductive effort

Abstract

The traditional IBP formulation of the energy budget is unsuitable for many marine organisms, partly because it sets production and respiration as alternative sinks when in reallty they are linked but also because it fails to recognise the heterogeneous nature of respiratory demand.The vanous components of total respiration reflect separate demands for ATP which are hkely to differ in their response to temperature and season.Such subdivision of total respiration emphasizes the difference between reproductive effort (RE, that fraction of the total energy flux diverted to reproduction) and reproductive output (RO, weight-specific gonad production) as measures of reproductive energehcs.Model calculahons demonstrate that the variation of basal metabolic rate with temperature (and hence latitude) influences both RE and RO, but in differing ways.If annual RE is assumed to be roughly constant in tropical, temperate and polar populations, then for organisms of similar size and ecology annual R0 will decrease with increasing latitude.Conversely if R 0 remains constant then annual RE will increase at high latitudes.Similar arguments predict an increase in net growth efficiency at low temperatures.When Lifetime RE is considered in relation to the slower growth rates and increased age of first breeding frequent at high latitudes, then data for the caridean shrimp Pandalus borealis suggest the possibility that there is a balance between basal metabolism and growth rate, resulting in a relatively constant lifetime RE across the latitudinal range.Clearly rather than there being a simple competition between growth and reproduction, energy is divided between several competing sinks which include the costs of maintenance and activity.