Metapopulation Dynamics: Indirect Effects and Multiple Distinct Outcomes in Ecological Risk Assessment

Abstract

A toxicant-dosed metapopulation model was used to explore the range of possible dynamics of populations in contaminated field sites. A single species metapopulation model was developed that is discrete, deterministic, and incorporates doseresponse curves and biotic growth rates to describe the effects of contamination on a metapopulation. The distribution of the chemical contamination is assumed limited to one patch and contagious within that patch. Both persistent and degradable toxicants were modeled. Five principal conclusions resulted from our simulation studies. (1) Mortality in one subpopulation has ecologically significant effects on nondosed subpopulations. This hypothesis we term ''action at a distance'' because no direct contact with a toxicant has occurred except in the dosed patch. (2) Because uncontaminated sites connected to the contaminated site by migration of the biota are affected, these uncontaminated sites cannot be reference sites. (3) The arrangement of the patches is critical to the dynamics of the system and the overall impact of a toxicant. (4) Due to the contagious distribution of the toxicant and the stochastic function describing exposure effect, multiple discrete outcomes often are possible from the same initial conditions. These outcomes can range from extinction to the reaching of the carrying capacity for a patch. (5) If sufficient cleanup is not possible, it may be necessary to isolate the contaminated patch, allowing the formerly connected patches to regain more typical population dynamics.

Darstellung maskierter Nutzungseffekte auf naturraumspezifische Artengemeinschaften grasiger Feldraine mithilfe von Restvarianzmustern

“…Darüber hinaus bietet es die Möglichkeit zur Validierung von Bewertungssystemen für die Auswirkung von Pflanzenschutzmitteln auf terrestrische Arthropoden und Pflanzen (Toschki 2008;Plachter et al 2002). Die standortsbezogenen, artspezifischen Empfindlichkeitswerte erlauben zudem eine regionalisierte Betrachtung ökotoxikologischer Effekte und die Integration in räumlich explizite Effektbewertungsmodelle (Linkov et al 2002;Spromberg et al 1998).…”

Conceptual Site Models as a Tool in Evaluating Ecological Health: The Case of the Department of Energy'S Amchitka Island Nuclear Test Site

“…Risk assessment examines the potential risk to target organisms or systems from chemical, physical, or other CONCEPTUAL SITE MODELS FOR EVALUATING ECOLOGICAL HEALTH 1225 environmental hazards (Burger & Gochfeld, 1997). Often, risk assessments require a range of risk characterizations and population models that incorporate dose-response curves, biotic growth curves, and contaminants information (Lemly, 1996;Spromberg et al, 1998), as well as uncertainty analysis (Duke & Taggart, 2000). Several government agencies have elaborate policies and guidelines for ecological risk assessment to address their regulatory needs (Bilyard et al, 1993).…”

Uncertainty in the Extrapolation from Individual Effects to Impacts upon Landscapes

“…Using a template from Wu and Vankat (1991) and Wu et al (1993), we have developed a computer model of a generic animal metapopulation that has contaminated patches (Spromberg et al 1998;Landis and McLaughlin 2000;McLaughlin and Landis 2000). The singlespecies model is discrete, deterministic, and uses a stochastic function to simulate exposure of the organism to the xenobiotic.…”

“…The findings of these initial modeling efforts have led Spromberg et al (1998) to hypothesize "Action at a Distance." The basic premise is that information about a stressor event can be transmitted to other patches by the migration of organisms and resources and the resultant patterns can be expressed at a variety of biochemical, organismal, and ecological layers.…”