Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2013
Publication Date: 6/20/2014
Citation: Banks, J.E., Stark, J.D., Vargas, R.I., Ackleh, A.S. 2014. Deconstructing the surrogate species concept:a life history approach to the protection of ecosystem services.. Ecological Applications. 24(4):770-778. Interpretive Summary: One of the standard methods of protecting endangered species as well as those species providing ecosystem services is to subject a related species to toxic insult and then extrapolate the effects to another species or assemblage of species. This surrogate species approach is often used in a variety of settings to inform policies aimed at protecting sensitive species. Because of the simplistic "one size fits all" approach to assessing toxicity responses in arthropods, the application of the surrogate species approach to assemblages of arthropod species critical in providing ecosystem services is an arena that merits further study. Here we employ a stage-structured Leslie matrix model parameterized with lab-derived life history data to compare scenarios in which both survivorship and fecundity are manipulated for a suite of economically important parasitoid wasps commonly used as biological control agents in agricultural settings. There was a clear difference among the four different parasitoid species in extinction threshold levels for both survivorship and fecundity reductions. We have shown here that incorporating life history data into sumple mathematical models can illuminate important differences in how seemingly similar species may respond to pesticide disturbance. Overall, our results highlight the need for a more deliberate approach, incorporating life history parameters into such assessments to test the assumption that we may extrapolate responses among even closely related species. In particular, quantifying differences in sensitivities among life history parameters among surrogates and species targeted for protection may lead the way to more accurate and reliable surrogate choices.
Technical Abstract: The use of the surrogate species concept is widespread in environmental risk assessment and in particular the protection of species that provide ecosystem services, yet there are no standard protocols in place for the choice of surrogates. Surrogates are often chosen on the basis of convenience or vague resemblances in physiology or life history. As a result, predictive ability of how species of concern will fare when subjected to disturbances such as environmental contaminants/toxicants is often based on woefully misleading comparisons of static toxicity tests. We present here an alternative approach that features a simple mathematical model parameterized with life history data applied to an assemblage of species that provide an important ecosystem service: a suite of parasitoid wasps that provide biological control of agricultural pests. Our results indicate that these parasitoid wasp species have different population responses to toxic insult-that is, we cannot predict how all four species will react to pesticide exposure simply by extrapolating from the response of any one of the species. Futhermore, sensitivity analysis of survivorship and reproduction life history parameters highlights the mechanistic underpinnings of different population responses, with the life stage that is most sensitive to pesticide disturbance varying among species. Taken together, our results suggest that the ability to predict the fate of a suite of species using the response of just one species(the surrogate species concept) is widely variable and potentially misleading.