Population density effects on longevity revisited

Abstract

A note in response to 'Density and age-specific mortality' by J.W. Curtsinger Joseph L. Graves, jr.a & Laurence D. Mueller 2 1Department of Life Sciences, Box 37100, Arizona State University West, Phoenix, AZ 85069-7100, USA 2Department of Ecology and Evolutionary Biology, University of California, Irvine, Irvine, CA 92717, USA Received 19 April 1994 Accepted 10 August 1994 J.W. Curtsinger, in his short communication in this volume entitled 'Density and Age-Specific Mortality', states that our suggestion that population density might has been a confounding variable affecting the demon- stration of declining late-age mortality rates observed in the Medfly experiments in Carey et al. (1992) is specious. His claim results from four lines of argu- ment: first that Medflies are not Drosophila, second that our experiments investigating density effects in D. melanogaster were small in size, third that we used extremely high densities to show significant effects, and finally that the density effects we showed only could have had significant impacts on early mortality rates. He continues in this piece to ask if the declining late-life mortality rates observed when utilizing large initial populations are real, and if so, what do they tell us about the fundamental processes underlying senes- cence. la argue for the plausibility of this phenomenon in Medflies. This of course argues for the construction of experimental techniques which would not confound density and aging as in Carey et al. (1992). It is curious that after asserting the difference between Drosophi- la and Medflies, Curtsinger then goes on to cite his own research with Drosophila, which to him suggests that density should not be an important confounding factor in Carey's Medfly experiments. At this point, we suggest that Curtsinger take his own advice. In the end no amount of post-hoc arguing will rescue a badly designed experiment. The only way to really address the question of density effects in Medflies is to carry out experiments with that species to show how these might be manifested in that species. It can be noted that Curtsinger cites a new experiment in his com- ment (Vanpel, Carey and Liedo, submitted) designed to examine the density question. Medflies are not