Model selection and parameterization of the concentration‐response functions for population‐level effects

Population-level effects of the mysid, Americamysis bahia, exposed to varying thiobencarb concentrations were estimated using stage-structured matrix models. A deterministic density-independent matrix model estimated the decrease in population growth rate (lambda) with increasing thiobencarb concentration. An elasticity analysis determined that survival of middle stages provided the largest contribution to lambda. Decomposing the effects of lambda in terms of changes in the matrix components determined that reduced reproduction had a large influence on population dynamics at lower thiobencarb concentrations, whereas reduced survivorship had the largest impact on populations at higher concentrations. A simulation model of a concentration-decay system was developed to demonstrate the importance of integrating chemical half-life and management practices in determining population viability. In this model, mysids were originally exposed to a high thiobencarb concentration (300 microg/L) that decayed an order of magnitude in the number of mysid generations corresponding to thiobencarb half-life values under three different exposure regimes. Environmental stochasticity was added to the model to estimate the cumulative extinction probability of mysids exposed to fluctuating concentrations of thiobencarb in random environments. The cumulative extinction probability increased with thiobencarb half-life, stochasticity, and concentration present at the time of a new exposure. The model demonstrated the expansion of population projection models in determining the ecological impact of a population exposed to pesticides.

Section: Discussionsupporting

confidence: 73%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Projected population‐level effects of thiobencarb exposure on the mysid, Americamysis bahia, and extinction probability in a concentration‐decay exposure system

Raimondo

McKenney

2005

“…Unfortunately, these models have only been tested on a few substances and species because of the large number of parameters values that has to be determined. Alternatively, empirical relationships have been derived [12]. Here, extrapolation is restricted by the lack of a mechanistic basis.…”

Section: Introductionmentioning

confidence: 99%

Meta‐analysis of intrinsic rates of increase and carrying capacity of populations affected by toxic and other stressors

Hendriks

Maas-Diepeveen

Heugens

et al. 2005

Most of the thousands of substances and species that are of concern for environmental management will not be investigated empirically at ecologically relevant levels because of financial, practical, and ethical constraints. To allow risk assessment for these less well‐known categories, we have developed a mechanistic model with classical equations from toxicology and ecology. The parameters are linked to well‐known properties, such as the octanol‐water partition ratio Kow, acute lethal (body) concentrations, and organism size. This allows estimation of intrinsic rates of increase r and carrying capacity K over a wide range of substances and species. The model was calibrated with parameter values (μ ± 95% confidence interval) obtained in reviews and validated by a meta‐analysis with largely independent data from 200 laboratory experiments. For single substances, the 5 to 95% interval of the observations on intrinsic rates of increase overlapped with the range predicted by the model. Model and experiments independently indicated that population growth ceased below 1% of the acute median lethal concentration in about 5% of the cases. Exceptional values and possible explanations were identified. The reduction of the carrying capacity K was nearly proportional to the inhibition of the population growth r. Population‐level effects of mixtures as estimated by concentration addition were confirmed by observations in the experiments. The impact of a toxicant and another stressor could generally be described by response multiplication, with the exception of cases with extreme stress. Data sets on population laboratory experiments are biased to metals and crustaceans. This field will benefit from empirical studies on chemicals, conditions, and species, identified as risky by the model. Other implications of the model for environmental management and research are discussed.

“…Then, the DDE concentration ( C e ) — r curve was fitted by the power function as in Equation 5. C e is the natural logarithm of the concentration (ng/g wet wt of eggs) and its increment variance r , r 0 is the intrinsic rate of increase without DDE exposure in a realistic environment, α is the concentration when r = 0, and β is the curvature of responses, indicating the nonlinearity formula [29]. The difference between r 0 and r was defined as the lost intrinsic rate of increase (Δ Z ) as in Equation 6 [11].…”

Section: Methodsmentioning

confidence: 99%

A method of assessing ecological risk to night heron, Nycticorax nycticorax, population persistence from dichlorodiphenyltrichloroethane exposure

Yao

2006

This paper first introduces a probabilistic method for quantitatively evaluating the effects of chemical pollutants in the environment on a wildlife population, which was applied to assess the ecological risk to night heron (Nycticorax nycticorax) population persistence from dichlorodiphenyltrichloroethane (DDE) exposure in Tai Lake, China. Intrinsic rate of population increase (r) calculated with a population age-structured matrix model was used to measure the adverse effect on population. To perform a probabilistic analysis of risk, lost intrinsic rate of population increase (deltaZ) because of DDE exposure was applied to express the exact extent of risk. The result showed that the risk (i.e., the expectancy of deltaZ of the night heron population exposed to DDE in Tai Lake) was 0.0259, indicating a decrease in gross population size of 2.56% every year compared with that of the previous year without DDE exposure.