Population density effects on longevity

Abstract

Population density, or the number of adults in an environment relative to the limiting resources, may have important long and short term consequences for the longevity of organisms. In this paper we summarize the way in which crowding may have an immediate impact on longevity, either through the phenomenon known as dietary restriction or through alterations in the quality of the environment brought on by the presence of large numbers of individuals. We also consider the possible long term consequences of population density on longevity by the process of natural selection. There has been much theoretical speculation about the possible impact of population density on the evolution of longevity but little experimental evidence has been gathered to test these ideas. We discuss some of the theory and empirical evidence that exists and show that population density is an important factor in determining both the immediate chances of survival and the course of natural selection.

Lifespan and oxidative stress show a non-linear response to atmospheric oxygen inDrosophila

“…Flies were given 3.5days to mate and oviposit. This procedure is well-suited to account for the low fecundity of this particular strain (Kaliss and Graubard, 1936) and the resultant population densities are in the range of those that are known not to have an effect on fitness components such as longevity and body size (Graves and Mueller, 1993;Miller and Thomas, 1958 and Loeschcke, 2001). Newly eclosed (<12-h-old) male offspring were then transferred to 25mm5ϫ95mm food-containing glass vials (Genesee Scientific, San Diego, CA, USA) for the longevity assay, which was conducted in duplicate.…”

“…Since high larval density can reduce longevity (Graves and Mueller, 1993), this could account for some of the effects of juvenile P O2 on adult longevity. For example, such an effect could explain the enhanced longevity of flies reared in 10kPa P O2 compared with other treatment B. Rascón and J. F. groups when adults were kept in a P O2 of 10 or 100kPa (Fig.2).…”

Density and age-specific mortality

“…This has been interpreted by Carey et al (1992) to reflect a slowing of the aging process, but might also be explained by declining adult density. Here it is argued that the density explanation, as presented by Graves and Mueller (1993), is unpersuasive for several reasons: extrapolations from Drosophila to Medflies are unjustified; the range of densities they studied is 2-120 times higher than that used in other studies; they ignore data on Medflies held in isolation, which rule out density effects; their own data suggest that initial cohort density has no effect on mortality rates at older ages, which is the relevant part of the life cycle; their experiment is too small to provide accurate estimates of mortality; new Medfly experiments executed at multiple densities show decelerating and then declining mortality rates at advanced ages for all densities. When Drosophila survivorship experiments axe done on a sufficiently large scale they also show a deceleration of mortality at older ages that is not attributable to density effects.…”

“…The deceleration of mortality rates is most likely a real facet of aging, and will have to be taken into consideration in any synthesis of the genetics and evolution of aging. Graves and Mueller (1993) have examined the effects of adult population density on longevity in Drosophila melanogaster, reviewing the existing experimental and theoretical literature and presenting some of their own data. One of the claims they make is that adult density explains observations in the Medfly Ceratitis capitata, in which mortality rates have been reported to decelerate at older ages (Carey et al, 1992).…”

Comparison of UF synthesis by alkaline‐acid and strongly acid processes

“…Graves et al 5 have found that the addition of triethanolamine in the first methylolation reaction improves not only the resistance to hydrolysis, but also the rate of cure and decrease the formaldehyde rate of release.…”