Environmentally sensitive life-cycle traits have low elasticity: implications for theory and practice.

Abstract

Abstract. The relationships between population growth rate and the life-cycle traits contributing to it are nonlinear and variable. This has made it difficult for ecologists to consistently predict changes in population dynamics from observations on changes in life-cycle traits. We show that traits having a high sensitivity to chemical toxicants tend to have a low elasticity, meaning that changes in them have a relatively low impact on population growth rate, compared to other life-cycle traits. This makes evolutionary sense in that there should be selection against variability in population growth rate. In particular, we found that fecundity was generally more sensitive to chemical stress than was juvenile or adult survival or time to first reproduction, whereas fecundity typically had a lower elasticity than the other life-cycle traits. Similar relationships have been recorded in field populations for a wide range of taxa, but the conclusions were necessarily more tentative because stochastic effects and confounding variables could not be excluded. Better knowledge of these relationships can be used to optimize population management and protection strategies and to increase understanding of the drivers of population dynamics.

Demographic responses to mercury exposure in two closely related Antarctic top predators

“…According to life history theory, environmental stressors should have the strongest effects on life history traits with the lowest sensitivity, e.g., traits with the lowest importance for population growth (, Forbes et al 2010). In long‐lived species, adult survival rate has the highest elasticity and should be the least affected by environmental stressors, whereas breeding success has the lowest elasticity and should be the most sensitive to stressors (, ), including toxic chemicals (Forbes et al 2010).…”

Integrative demographic modeling reveals population level impacts of PCB toxicity to juvenile snapping turtles

“…Because elasticity values calculated from the REF population showed that survival to year 2 juveniles had relatively low elasticity (Fig. 3b, first two columns), changes in this stage (or age) would perhaps not be expected to translate to statistically significant effects on PGR (Pfister, 1998;Forbes et al, 2010). The significant reduction in PGR we observed from our model therefore indicates that the effects observed on juveniles exposed to PCBs were sufficient to manifest as a potential effect on population-level endpoints.…”

Full life-cycle toxicity assessment on triclosan using rotifer Brachionus calyciflorus

“…Meantime, the variability in population growth rate had been thought to have negative consequences for fitness during the process of nature selection (Forbes et al, 2010). Therefore, TCS at the concentration higher than 1 µg/L released into water body should raise concern due to its significant influence on rotifer population growth rate.…”