@article{MartinJagerNisbetetal.2014,
  author    = {Martin, Benjamin and Jager, Tjalling and Nisbet, Roger M. and Preuss, Thomas G. and Grimm, Volker},
  title     = {Limitations of extrapolating toxic effects on reproduction to the population level},
  series = {Ecological applications : a publication of the Ecological Society of America},
  volume    = {24},
  journal   = {Ecological applications : a publication of the Ecological Society of America},
  number    = {8},
  publisher = {Wiley},
  address   = {Washington},
  issn      = {1051-0761},
  doi       = {10.1890/14-0656.1},
  pages     = {1972 -- 1983},
  year      = {2014},
  abstract  = {For the ecological risk assessment of toxic chemicals, standardized tests on individuals are often used as proxies for population-level effects. Here, we address the utility of one commonly used metric, reproductive output, as a proxy for population-level effects. Because reproduction integrates the outcome of many interacting processes (e.g., feeding, growth, allocation of energy to reproduction), the observed toxic effects in a reproduction test could be due to stress on one of many processes. Although this makes reproduction a robust endpoint for detecting stress, it may mask important population-level consequences if the different physiological processes stress affects are associated with different feedback mechanisms at the population level. We therefore evaluated how an observed reduction in reproduction found in a standard reproduction test translates to effects at the population level if it is caused by hypothetical toxicants affecting different physiological processes (physiological modes of action; PMoA). For this we used two consumer-resource models: the Yodzis-Innes (YI) model, which is mathematically tractable, but requires strong assumptions of energetic equivalence among individuals as they progress through ontogeny, and an individual-based implementation of dynamic energy budget theory (DEB-IBM), which relaxes these assumptions at the expense of tractability. We identified two important feedback mechanisms controlling the link between individual- and population-level stress in the YI model. These mechanisms turned out to also be important for interpreting some of the individual-based model results; for two PMoAs, they determined the population response to stress in both models. In contrast, others stress types involved more complex feedbacks, because they asymmetrically stressed the production efficiency of reproduction and somatic growth. The feedbacks associated with different PMoAs drastically altered the link between individual- and population-level effects. For example, hypothetical stressors with different PMoAs that had equal effects on reproduction had effects ranging from a negligible decline in biomass to population extinction. Thus, reproduction tests alone are of little use for extrapolating toxicity to the population level, but we showed that the ecological relevance of standard tests could easily be improved if growth is measured along with reproduction.},
  language  = {en}
}
@article{MartinJagerNisbetetal.2013,
  author    = {Martin, Benjamin T. and Jager, Tjalling and Nisbet, Roger M. and Preuss, Thomas G. and Grimm, Volker},
  title     = {Predicting population dynamics from the properties of individuals - a cross-level test of dynamic energy budget theory},
  series = {The American naturalist : a bi-monthly journal devoted to the advancement and correlation of the biological sciences},
  volume    = {181},
  journal   = {The American naturalist : a bi-monthly journal devoted to the advancement and correlation of the biological sciences},
  number    = {4},
  publisher = {Univ. of Chicago Press},
  address   = {Chicago},
  issn      = {0003-0147},
  doi       = {10.1086/669904},
  pages     = {506 -- 519},
  year      = {2013},
  abstract  = {Individual-based models (IBMs) are increasingly used to link the dynamics of individuals to higher levels of biological organization. Still, many IBMs are data hungry, species specific, and time-consuming to develop and analyze. Many of these issues would be resolved by using general theories of individual dynamics as the basis for IBMs. While such theories have frequently been examined at the individual level, few cross-level tests exist that also try to predict population dynamics. Here we performed a cross-level test of dynamic energy budget (DEB) theory by parameterizing an individual-based model using individual-level data of the water flea, Daphnia magna, and comparing the emerging population dynamics to independent data from population experiments. We found that DEB theory successfully predicted population growth rates and peak densities but failed to capture the decline phase. Further assumptions on food-dependent mortality of juveniles were needed to capture the population dynamics after the initial population peak. The resulting model then predicted, without further calibration, characteristic switches between small-and large-amplitude cycles, which have been observed for Daphnia. We conclude that cross-level tests help detect gaps in current individual-level theories and ultimately will lead to theory development and the establishment of a generic basis for individual-based models and ecology.},
  language  = {en}
}
@article{MartinJagerNisbetetal.2013,
  author    = {Martin, Benjamin T. and Jager, Tjalling and Nisbet, Roger M. and Preuss, Thomas G. and Hammers-Wirtz, Monika and Grimm, Volker},
  title     = {Extrapolating ecotoxicological effects from individuals to populations - a generic approach based on Dynamic Energy Budget theory and individual-based modeling},
  series = {Ecotoxicology},
  volume    = {22},
  journal   = {Ecotoxicology},
  number    = {3},
  publisher = {Springer},
  address   = {Dordrecht},
  issn      = {0963-9292},
  doi       = {10.1007/s10646-013-1049-x},
  pages     = {574 -- 583},
  year      = {2013},
  abstract  = {Individual-based models (IBMs) predict how dynamics at higher levels of biological organization emerge from individual-level processes. This makes them a particularly useful tool for ecotoxicology, where the effects of toxicants are measured at the individual level but protection goals are often aimed at the population level or higher. However, one drawback of IBMs is that they require significant effort and data to design for each species. A solution would be to develop IBMs for chemical risk assessment that are based on generic individual-level models and theory. Here we show how one generic theory, Dynamic Energy Budget (DEB) theory, can be used to extrapolate the effect of toxicants measured at the individual level to effects on population dynamics. DEB is based on first principles in bioenergetics and uses a common model structure to model all species. Parameterization for a certain species is done at the individual level and allows to predict population-level effects of toxicants for a wide range of environmental conditions and toxicant concentrations. We present the general approach, which in principle can be used for all animal species, and give an example using Daphnia magna exposed to 3,4-dichloroaniline. We conclude that our generic approach holds great potential for standardized ecological risk assessment based on ecological models. Currently, available data from standard tests can directly be used for parameterization under certain circumstances, but with limited extra effort standard tests at the individual would deliver data that could considerably improve the applicability and precision of extrapolation to the population level. Specifically, the measurement of a toxicant's effect on growth in addition to reproduction, and presenting data over time as opposed to reporting a single EC50 or dose response curve at one time point.},
  language  = {en}
}