A SIMPLE-MODEL TO ESTIMATE GROWTH-RATE OF LOTIC INSECT LARVAE AND ITS VALUE FOR ESTIMATING POPULATION AND COMMUNITY PRODUCTION

Data from the literature on growth of lotic insects were used to develop an empirical model predicting the instantaneous growth rate (g, in d-1) as a function of individual dry mass (W, in mg) and water temperature (T, degree-C). Growth rates were found to decrease with increasing size, and to increase with an increase in temperature with an average Q10 of 1.78. The equation Log10g = -2.09 - 0.27 Log10 W + 0.025 T explained 49% of the observed variance in logtransformed growth rates from field studies. The relation between growth rate and body mass and temperature was found to vary among insect orders. On average, Diptera grow 1.5x faster than what is predicted by the general model, whereas Trichoptera grow at only 0.7x the predicted rate. The coefficients for body mass and temperature also varied among orders. On average, body mass affects less the field growth rates of Diptera and Ephemeroptera than rates of Trichoptera. The growth models can be combined with information on the biomass size distribution of populations of single species or communities to estimate secondary production. Estimates so obtained agree closely (r = 0.93, n = 31) with those obtained by using standard methods for populations of single species. For production of communities, computer simulations show that errors in predicted growth rates decrease the precision of estimates but suggest that estimates of production of communities of tens of species calculated from monthly description of biomass size distribution for a year would on average be 70-140% of the true value. Thus, the model may be used to estimate production for species or groups of species with indistinguishable cohorts when estimates of growth rates are not available.