Improving mesocosm data analysis through individual-based modelling of control population dynamics: a case study with mosquitofish (Gambusia holbrooki)

Abstract

Experimental ecosystems such as mesocosms have been developed to improve the ecological relevance of ecotoxicity test. However, in mesocosm studies, the number of replicates is limited by practical and financial constraints. In addition, high levels of biological organization are characterized by a high variability of descriptive variables. This variability and the poor number of replicates have been recognized as a major drawback for detecting significant effects of chemicals in mesocosm studies. In this context, a tool able to predict precisely control mesocosms outputs, to which endpoints in mesocosms exposed to chemicals could be compared should constitute a substantial improvement. We evaluated here a solution which consists in stochastic modelling of the control fish populations to assess the probabilistic distributions of population endpoints. An individual-based approach was selected, because it generates realistic fish length distributions and accounts for both individual and environmental sources of variability. This strategy was applied to mosquitofish (Gambusia holbrooki) populations monitored in lentic mesocosms. We chose the number of founders as a so-called "stressor" because subsequent consequences at the population level could be expected. Using this strategy, we were able to detect more significant and biologically relevant perturbations than using classical methods. We conclude that designing an individual-based model is very promising for improving mesocosm data analysis.This methodology is currently being applied to ecotoxicological issues.

An Individual-Based Model of Zebrafish Population Dynamics Accounting for Energy Dynamics

“…In particular, the relative high frequency of the larger individuals (from 29 to 33 mm) in one population observed in [ 17 ] contradicted usual fish population length distributions. Indeed, usually, older (larger) individuals are less frequent than younger fish [ 13 ].…”

“…Individual-based models (IBMs) are suitable population models to increase the relevance of ecotoxicity tests since they incorporate available mechanistic knowledge on the links between responses at the individual level and responses at the population level [ 12 ]. Predictions for stressed populations could be achieved provided that dose response relationships are known for the key parameters [ 13 – 15 ]. Moreover, toxicokinetic/toxicodynamic (TK/TD) models, able to link exposure concentration and effects at target organ/system level, can be easily integrated into IBMs and then, the processes and the corresponding effects that lead to toxicity within an organism can be dynamically simulated [ 16 ].…”

How to Improve Toxicity Assessment? From Single-Species Tests to Mesocosms and Field Studies

“…More recently, Beaudouin et al (2012) have developed a tool able to precisely predict control mesocosm outputs, to which endpoints in mesocosms exposed to chemicals could be compared. Monitoring mosquitofish (Gambusia holbrooki) populations in lentic mesocosms, they applied a stochastic modeling of the control fish populations to assess the probabilistic distributions of population endpoints.…”

Modelling historical mesocosm data: Application of a fish bioenergetics model in semi‐natural conditions

“…To fill this gap, mesocosm experiments provide a sound basis to reconstruct environmental scenarios and study the biological responses of organisms in semi-natural conditions. Thus, these experiments provide a hazard analysis with an improved ecological realism compared to laboratory experiments (Beaudouin, Ginot, & Monod, 2012;Beaudouin, Monod, & Ginot, 2008). For example, these experiments have been used in ecotoxicology to assess direct and indirect effects of toxicants on populations and also investigate responses at different levels of biological organisation under natural variations of ecological factors (Boyle & Fairchild, 1997;Caquet et al, 2000).…”

“…For example, these experiments have been used in ecotoxicology to assess direct and indirect effects of toxicants on populations and also investigate responses at different levels of biological organisation under natural variations of ecological factors (Boyle & Fairchild, 1997;Caquet et al, 2000). Thus, these experiments provide a hazard analysis with an improved ecological realism compared to laboratory experiments (Beaudouin, Ginot, & Monod, 2012;Beaudouin, Monod, & Ginot, 2008).…”