The timing of copepod diapause as an evolutionarily stable strategy

Diaptomus sanguineus, a small freshwater copepod, avoids periods of intense fish predation by producing diapausing eggs. We developed a computer simulation of the copepod's life history and used it to compete populations that switched to diapause at different intervals of time before the onset of fish predation (the catastrophe). With no variation about the catastrophe date, the evolutionarily stable strategy (ESS) is one in which the switch to diapause comes exactly one generation before the catastrophe, as Taylor (1980) has shown analytically. With increasing variation about the catastrophe date, the ESS becomes one of switching to diapause at time intervals increasingly greater than one generation. Using field data on copepod mortality rates from 5 yr, we have estimated the mean and variance about the catastrophe date. Using field and laboratory data, we have estimated the copepod generation time and the timing of the switch to diapause. We find, in close agreement with simulation-derived ESSs, that D. sanguineus starts making diapausing eggs 1.3 generations before the major onset of fish-induced mortality

Assessing Risks to Wildlife Populations from Multiple Stressors: Overview of the Problem and Research Needs.

Wildlife populations are experiencing increasing pressure from human-induced changes in the landscape. Stressors including agricultural and urban land use, introduced invasive and exotic species, nutrient enrichment, direct human disturbance, and toxic chemicals directly or indirectly influence the quality and quantity of habitat used by terrestrial and aquatic wildlife. Governmental agencies such as the U.S. Environmental Protection Agency are required to assess risks to wildlife populations, in its broadest definition, that result from exposure to these stressors, yet considerable uncertainty exists with respect to how such assessments should be conducted. This uncertainty is compounded by questions concerning the interactive effects of co-occurring stressors, appropriate spatial scales of analysis, extrapolation of response data among species and from organisms to populations, and imperfect knowledge and use of limited data sets. Further, different risk problems require varying degrees of sophistication, methodological refinement, and data quality. These issues suggest a number of research needs to improve methods for wildlife risk assessments, including continued development of population dynamics models to evaluate the effects of multiple stressors at varying spatial scales, methods for extrapolating across endpoints and species with reasonable confidence, stressor-response relations and methods for combining them in predictive and diagnostic assessments, and accessible data sets describing the ecology of terrestrial and aquatic species. Case study application of models and methods for assessing wildlife risk will help to demonstrate their strengths and limitations for solving particular risk problems

Weighing the evidence of ecological risk from chemical contamination in the estuarine environment adjacent to the Portsmouth Naval Shipyard, Kittery, Maine, USA

In characterizing ecological risks, considerable consensus building and professional judgments are required to develop conclusions about risk. This is because how to evaluate all the factors that determine ecological risk is not well defined and is subject to interpretation. Here we report on the application of a procedure to weigh the evidence of ecological risk and develop conclusions about risk that will incorporate the strengths and weaknesses of the assessment. The procedure was applied to characterize ecological risk of chemical contamination in nearshore areas adjacent to the Portsmouth Naval Shipyard, located at the mouth of the Great Bay Estuary, New Hampshire and Maine, USA. Measures of exposure and effect were used to interpret the magnitude of risk to the assessment endpoints of pelagic species, epibenthic species, the benthic community, eelgrass plants, the salt marsh community, and avian receptors. The evidence of chemical exposure from water, sediment, and tissue and the evidence of biological effects to representative pelagic, epibenthic, benthic, eelgrass, salt marsh, and avian species were weighed to characterize ecological risk. Individual measures were weighted by the quality and reliability of their data and risk was estimated from the preponderance, magnitude, extent, and strength of causal relationships between the data on exposure and effects. Relating evidence of risk to hypothesized pathways of exposure made it possible to estimate the magnitude of risk from sediment and water and express the confidence associated with the findings. Systematically weighing the evidence of risk rendered conclusions about risk in a manner that was clearly defined, objective, consistent, and did not rely solely on professional judgment