SEARCH

SEARCH BY CITATION

Keywords:

  • Assessment endpoint;
  • Population-scale assessment;
  • Regional-scale assessments;
  • Ecological risk assessment

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. POPULATION LEVEL REPLACED BY POPULATION SCALE
  5. CRITERIA FOR ENDPOINTS
  6. POPULATIONS AS ASSESSMENT ENDPOINTS
  7. POPULATIONS AS ASSESSMENT ENDPOINTS AND SUGGESTIONS FOR SELECTION
  8. TRANSITION TO PART 2
  9. Acknowledgements
  10. References

The selection of appropriate assessment endpoints is a basic element of an ecological risk assessment, especially at regional or watershed scales. Because ecological services often are tied to specific species, the risk to populations is a critical endpoint and feature of ecological risk assessments. The first item is a discussion of the replacement of population-level risk assessment with the construct of a population-scale assessment endpoint. Next, the criteria that are currently used for assessment endpoints are reviewed and evaluated for utility in an ecological risk assessment. Following this examination, assessment endpoints from a number of regional-scale ecological risk assessments are compared. The outcome of this evaluation is that population-scale assessment endpoints are important expressions of the valued components of ecological structures. Finally, a few recommendations for the selection of assessment endpoints at a population scale are listed.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. POPULATION LEVEL REPLACED BY POPULATION SCALE
  5. CRITERIA FOR ENDPOINTS
  6. POPULATIONS AS ASSESSMENT ENDPOINTS
  7. POPULATIONS AS ASSESSMENT ENDPOINTS AND SUGGESTIONS FOR SELECTION
  8. TRANSITION TO PART 2
  9. Acknowledgements
  10. References

Assessment endpoints are the fundamental aspect of an ecological risk assessment since they are the actualized expressions of the valued aspect of the ecological structure that is being managed. Conceptual models are designed to express the causative pathways from the stressor to the assessment endpoint. Because of the pivotal role of assessment endpoints, a critical question is how to determine assessment endpoints that accurately reflect the valued ecological services. The definition and use of population-related endpoints has been the subject of an intense discussion (Landis 2002; Munns et al. 2002; Suter et al. 2005; Tannenbaum 2005). The goal of this commentary is to continue the dialogue and evaluate the selection of assessment endpoints in the context of a regional-scale ecological risk assessment. At a regional scale the assumption is that there are multiple stressors affecting multiple endpoints in a spatially explicit manner.

Perhaps some of the reluctance to evaluate population-scale risk assessments has been caused by the perceived difficulty of the analysis. Stark et al. (2004) and Spromberg and Meador (2005) have demonstrated that such analyses are clearly possible and that the characteristics of populations can have important influences upon the persistence of ecological resources.

This paper is the 1st of a series of 2 commentaries geared to risk assessments at regional scales. In this paper, the objective is to describe the utility of populations as assessment endpoints in reflecting stakeholders' values, especially in a regional or landscape context. The 2nd commentary will discuss the attributes of populations that can be used effectively in the analysis of risk.

There are several parts to the current paper. First is a discussion of the idea of population-level risk assessment and proposal to replace this with the construct of a population-scale assessment endpoint. Second is an evaluation of the criteria that are currently used for assessment endpoints and the utility of these approaches. Assessment endpoints from a number of regional-scale ecological risk assessments are compared. The outcome of this evaluation is that population-scale assessment endpoints are useful expressions of the valued components of ecological structures. Next is a survey of the population-scale assessment endpoints that have been used at the regional scale. At the end of this paper are guidelines for population-scale assessment endpoints and an introduction to the second part of this series on what to measure.

POPULATION LEVEL REPLACED BY POPULATION SCALE

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. POPULATION LEVEL REPLACED BY POPULATION SCALE
  5. CRITERIA FOR ENDPOINTS
  6. POPULATIONS AS ASSESSMENT ENDPOINTS
  7. POPULATIONS AS ASSESSMENT ENDPOINTS AND SUGGESTIONS FOR SELECTION
  8. TRANSITION TO PART 2
  9. Acknowledgements
  10. References

So what is wrong with the term “population-level” ecological risk assessment or using “population-level” assessment endpoints? Words imply models of reality, and in this case the reference is to an incomplete model of the interaction of populations with ecological systems. The traditional model of hierarchy in ecological systems is the organism-population-community-ecosystem organized from lower to higher levels. This metaphor has been extensively used, but there are serious scientific issues with its overarching organizational principal. O'Neill (2001) reviewed many of these problems and recognized the central roles of spatial scale, heterogeneity, and natural selection in determining patterns in ecological systems. The hierarchical patch dynamics paradigm (HPDP) as developed by Wu and colleagues (Wu and Loucks 1995; Wu and David 2002) addressed these issues by incorporating spatial and temporal heterogeneity and the dynamics of populations and processes. The classic idea of population level in a systems context does not adequately incorporate the concepts of heterogeneity and dynamics. Populations do incorporate individuals with organismal characteristics, but interact with differences over space and time with a variety of communities and ecological systems. The spatial scale with which a population of migratory birds interacts can be much larger than the wetlands ecological system that may serve as a breeding ground. Invertebrates such as mussels have life stages that bridge many types of ecological interactions as the larvae are pelagic and the adult forms become sessile. There are temporal dynamics as well. Populations have very different timelines regarding migration, reproduction, and growth and each timeline should be assessed when examining a population as an endpoint.

Population “scale” is more descriptive and incorporates spatial and temporal heterogeneity as described in the HPDP. The risk assessment by definition must incorporate the spatial and temporal heterogeneity of the population and the dynamics relative to the stressor. Also, there are no assumptions of inherent stability. A recognition of the landscape patterns of a population will also mandate an understanding of source and sink relationships, migratory pathways, and the potential of the population to interact with many ecological systems.

There is another issue with the reference to “level of organization” in the context of the times in which this article is being written. Levels of organization begs the question, “Who is the organizer?” Organizations are usually created for a purpose, implied or otherwise. Given the widespread movement in the United States for the teaching of intelligent design as an alternative to evolution by natural selection, it is important to be extremely specific in our word choice. It is clear that patterns and interactions exist in ecological systems. Complex systems are recognizable because the interactions and the dynamics of the components produce recognizable patterns at a variety of different scales. However, design derived from a purposeful intelligence other than humankind is not one of the properties attributable to ecological structures.

CRITERIA FOR ENDPOINTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. POPULATION LEVEL REPLACED BY POPULATION SCALE
  5. CRITERIA FOR ENDPOINTS
  6. POPULATIONS AS ASSESSMENT ENDPOINTS
  7. POPULATIONS AS ASSESSMENT ENDPOINTS AND SUGGESTIONS FOR SELECTION
  8. TRANSITION TO PART 2
  9. Acknowledgements
  10. References

Several criteria have been set for the selection of assessment endpoints. This presentation will compare the US Environmental Protection Agency (USEPA) guidance as set in the Framework for Ecological Risk Assessment (USEPA 1992), the Guidelines for Ecological Risk Assessment (USEPA 1998), and Generic Ecological Assessment Endpoints (USEPA 2003) with the criteria proposed by Suter and Barnthouse (1993).

The selection criteria proposed by USEPA in 1992 and 1998 are similar (Table 1). The criteria in both sets place ecological relevance as the primary criteria. Susceptibility to the stressor, number 3 in the original 1993 formulation, was elevated to number 2 in the 1998 guidance document. In neither formulation is policy or management goals the primary criterion. “Policy Goals and Societal Values” is ranked 2nd in the 1992 framework and number 3 in the 1998 guidance. The criteria set forth in 2003 for generic assessment endpoints (USEPA) are somewhat different. “Generally useful” in the USEPA decision-making process is 1st on the list: In some ways this may be derived from policy and precedent. “Being practical and well defined” is next. Other sets of criteria exist.

The criteria as set forth by Suter and Barnthouse (Table 2) have been more useful in setting assessment endpoints. Compared to the USEPA documents, the relevance to societal goals is the primary criterion in Suter and Barnthouse (1993). Biological relevance is second and is followed by factors critical in defining the assessment endpoint. This is a fundamentally different approach to the risk assessment process as it gives the societal and management goals primacy.

If ecological systems are going to be managed to suit human-derived values, then this has to be the focus of the assessment process. Ecological risk assessments are performed because ecological services are valued and these values are often expressed in laws and regulations. Stakeholders involved in the risk assessment process are participating because of an individual or a societal value. Ecological or biological relevance has to be evaluated by how each meets the goal of matching the values of the society managing the ecological structure.

At the regional scale, Landis and Weigers (2005) summarized the criteria very simply as

  • 1.
    What do you care about and where?
  • 2.
    Make a map.

“What do you care about and where” refers specifically to the ecological services that are provided by the ecological system. Stakeholders and legislative mandates are likely to set different values upon different parts of the ecological structure. “Make a map” is an important criterion as well. In a spatially distinct system, a coordinate for the location is also required to describe the assessment endpoint. Different parts of the system may be managed for warm-water fish, another for cold-water fish, and another for an urban park. Codorus Creek, Pennsylvania, USA (Obery and Landis 2002, 2005) is an example of a watershed with spatially distinct criteria. “Making a map” will also describe the spatial relationships of these assessment endpoints. This feature will be important in establishing causal relationships during the conceptual model phase.

In contrast to the approach of Landis and Wiegers (2005), Suter et al. (2005) present the formula

Assessment endpoint = attribute + entity.

This formula is a suggestion for writing the specifications for an assessment endpoint, and is not equivalent to a mathematical or chemical equation. At a regional or landscape scale the location of the entity (what you care about) should be specified, as should be habitat preference for the life stages of the constituents of the population, and the acceptable dynamics. Genetic composition and diversity of a population are also important in many conservation scenarios. In other words, the specification list for an assessment endpoint has a number of dimensions, and this reality must be kept in mind.

Although common to USEPA (1992, 1998) and Suter and Barnthouse (1993), “susceptibility to hazardous agents” is not a valuable criterion. At the initiation of the risk assessment process at regional scales, it is not clear what the susceptibility of the various ecological services will be to the numerous stressors that exist. Undetected indirect effects, novel modes of action, and the importance of spatial relationships are unknowns for the factors that contribute to many ecological services. Demonstrating that an assessment endpoint is not susceptible is tantamount to attempting to prove a negative statement, a typically untenable approach.

Now that the criteria for selecting assessment endpoints have been discussed, it is time to examine the types of assessment endpoints that are selected. The discussion is directed at watershed-, regional-, and landscape-scale assessments.

Table Table 1.. US Environmental Protection Agency (USEPA) criteria for selection of assessment endpoints
Criteria for assessment endpoints identified in Framework for Ecological Risk Assessment (USEPA 1992)
  • 1.
    Ecological relevance: Ecologically relevant endpoints reflect important characteristics of the system and are functionally related to other endpoints.
  • 2.
    Policy goals and societal values: Good communication between the risk assessor and risk manager is important to ensure that ecologically relevant assessment endpoints reflect policy goals and societal values.
  • 3.
    Susceptibility to the stressor: Ideally, an assessment endpoint would be likely to be both affected by exposure to a stressor and sensitive to the specific type of effects caused by the stressor.
Criteria for assessment endpoints identified in Guidelines for Ecological Risk Assessment (USEPA 1998, p. 30)
“Three principal criteria are used to select ecological values that may be appropriate for assessment endpoints: 1) ecological relevance, 2) susceptibility to known or potential stressors, and 3) relevance to management goals.”
Criteria identified in Generic Ecological Assessment Endpoints (GEAEs) for Ecological Risk Assessment (USEPA 2003, p. 5)
  • 1.
    Generally useful in USEPA's decision-making process
  • 2.
    Practical
  • 3.
    Well defined

POPULATIONS AS ASSESSMENT ENDPOINTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. POPULATION LEVEL REPLACED BY POPULATION SCALE
  5. CRITERIA FOR ENDPOINTS
  6. POPULATIONS AS ASSESSMENT ENDPOINTS
  7. POPULATIONS AS ASSESSMENT ENDPOINTS AND SUGGESTIONS FOR SELECTION
  8. TRANSITION TO PART 2
  9. Acknowledgements
  10. References

A comparison was made of the regional-scale ecological risk assessments that have used the relative risk model as its baseline approach. This approach explicitly incorporated spatial relationships and the interactions between sources, stressors, habitats, and effects with multiple stressors (Landis and Wiegers 1997, 2005). The sites were generally comprised of watersheds (catchments) of various sizes with a large number of potential sources of stressors. None of the sites examined have been in the context of a contaminated site clean-up; in each there were multiple sources of a variety of stressors. Although the sites included Australia, North America, and South America, the dominant value structures were derived from European culture, combined in some instances with that of the indigenous people. The study sites are described in Table 3, along with lists of population-scale and other assessment endpoints. In each of the sites listed there may be an observer effect, although extensive efforts were made to obtain a fair sampling of stakeholder values. More extensive descriptions of the sites and risk assessments can be found in Landis (2005).

The most common classes of assessment endpoints were

  • 1.
    Water quality and supply (human health, agriculture, and ecological systems);
  • 2.
    Harvest or use of ecological resources for subsistence, recreation, or commercial purposes;
  • 3.
    Protection of threatened or endangered species (parks, reserves, and other spaces); and
  • 4.
    Protection of property and property values (flood control, erosion).
Table Table 2.. Criteria for selection of assessment endpoints proposed by Suter and Barnthouse (1993)
1. Societal relevance
2. Biological relevance
3. Unambiguous operational definition
4. Accessibility to prediction and measurement

Water quality is important because of the impacts to human health, agriculture, and to ecological systems. The stakeholders recognized this assessment endpoint as the key element in an aquatic system and the unification of the ecological services that the environment provided. In the study sites, the water has been used as a drinking source or for agriculture (irrigation).

Items 2 and 3 are often the key biological services provided by watersheds. Subsistence use by native peoples or by the poor can be a vital ecological service. Tribes and First Nations in North America also have special rights to harvest fish, shellfish, and other resources to be used for food, in rituals, and for commercial purposes. Recreational opportunities is a critical economic service provided by the ecological system. In Codorus Creek, Pennsylvania, USA, both a cold-water (trout) and warm-water (bass, sunfish) fishery is maintained. Both are important for maintaining tourism in the region. Similarly, fishing and boating are enterprises provided by sections of the Androscoggin River, Maine, USA, and they form an important economic base for that region. The protection of threatened and endangered species is also mandated in many areas by both federal and state-provincial governments. This protection is a clear population-scale mandate, often with numbers so low that each individual organism is a significant fraction of the population.

Protection of property and property value is a significant ecological service in watersheds. Flood control and protection against erosion is important in both urban and agricultural areas. The Willamette and McKenzie rivers (Oregon, USA) receive large inputs from spring flooding, and Codorus Creek has flooded the city of York. Both of these rivers have been modified to prevent flooding and the erosion of farmland or residential property. The management of these stream or river banks can be in conflict with the habitat necessary to maintain population-scale resources or water quality.

Population-scale assessment endpoints have become more common to other watershed or regional-scale risk assessments conducted by other scientists. The Waquoit Bay, Massachusetts, USA, risk assessment (USEPA 2002) contains 7 population-scale assessment endpoints (Table 4). Each of these either deal with abundance of a species or the sustaining habitat. The first endpoint is to establish a scallop population that can support a recreational fishery. This is not just a specification for a certain population size but also for a specified productivity. Endpoint 1 is redundant with endpoint 4, scallop abundance. Endpoint 2 is also a population-scale specification requiring eelgrass to cover a designated percentage of the estuarine habitat. Endpoint 3 is shorthand for the requirement that a number of finfish species are maintained at certain scales of abundance; again a population-scale specification. The next 3 endpoints are population-scale endpoints for species for which Waquoit Bay is but a small part of the landscape used by each species. Anadromous fish reproduction (endpoint 5) implies that conditions are adequate to maintain the runs or stocks of these species to meet the ecological service goals for each. A similar situation exists for endpoints 6 and 7. Wetland birds and habitat exist throughout New England, but the presence of these species at Waquoit Bay region is seen as an important ecological service. Piping plover is a threatened species and by law is considered an important ecological resource to be protected in this region. Only endpoint 8, “tissue contamination,” is not explicitly at a population scale.

Table Table 3.. Summary of study sites and a listing of population-scale and other endpoints for each area. Modified from Landis and Wiegers (2005)
Site location and sizeSite descriptionPopulation-scale endpointsOther endpoints
Port Valdez, Alaska, USA, 94.5 mi2 (151.2 km2)Deep-water fjord that serves as the shipping point for the Alaskan pipeline; also has a refinery, fishing fleet, and the city of ValdezDecrease in hatchery salmon returns, population fisheries, declines in wild populations of anadromous fish, decreased bird populations, decreased food for wildlife populationsWater quality, sediment quality
Willamette-McKenzie Watersheds, Oregon, USA, 1351 miles2 (2179 km2)Rapid flowing rivers with sources from the Cascades and Coastal Ranges of Oregon, area extended from Eugene to CorvallisSalmonids—spring Chinook, rainbow and cutthroat trout, summer steelhead warm water fisheries. Many of the populations have specific numbers associated with specific locations within the watershedWater quality, flood control, irrigation
Mountain River, Tasmania, Australia 190 km2Catchment with varied uses but with a relatively low human densityMaintenance or increase of native stream bank vegetation and reduction of weed density to less that 10% of ground coverWater quality, maintenance of adequate stream flow, maintenance of primary industries, landscape aesthetics, and maintenance of a good residential environment
Parque Estadual Turistico do Alto Ribeira, Brazil 1000 km2Atlantic rainforest on the east coastSelf-sustaining epigean (surface) and hypogean (cave) aquatic fauna
Codorus Creek, Pennsylvania, USA, 719 km2 (278 mi2)Small creek with a pulp and paper mill, channelization, agriculture, and urban areaSelf-sustaining native and non-native fish populations, adequate food supply for aquatic speciesWater quality, water supply, recreationa land and water resources, stormwater control and treatment
Squalicum Creek, Washington, USA, 62 km2Small creek flowing from agricultural areas to an increasing human disturbance and that empties into Bellingham BayBiotic endpoints; viable nonmigratory coldwater fish populations, life cycle opportunities for salmonids, viable native terrestrial wildlife species populations, adequate wetland habitat to support wetland species populationsAbiotic endpoints; flood control, adequate land, and ecological attributes for recreational uses
Cherry Point, Washington, USA, 715 km2Deep-water port on the Washington Coast in Georgia Straits. Site included the historic spawning range of the Cherry Point Pacific herring run. Proposed aquatic reserve area by the Washington Department of Natural ResourcesCherry Point Pacific herring run for retrospective assessment; prospective assessment includes Coho salmon, juvenile English sole and surf smelt embryos, juvenile Dungeness crab, adult littleneck clam, and Great Blue heronEelgrass beds are a habitat for many other species, so these represent both a population and a physical, chemical, and community structure that serves as habitat for other marine species
Leaf River, Mississippi, USA, 5766 km2 (3575 mi2)Large river in the coastal plain of Mississippi with a pulp and paper millFish, macroinvertebrates (both populations and community structureWater quality, water quantity, recreational uses, wastewater treatment, channel modifications
Table Table 4.. Waquoit Bay, Massachusetts, USA, assessment endpoints (USEPA 2002)
1. Reestablish a self-sustaining scallop population in the bay that can support a viable sport fishery
2. Estuarine percent eelgrass cover
3. Finfish diversity and abundance
4. Scallop abundance
5. Anadromous fish reproduction
6. Wetland bird habitat distribution and abundance
7. Piping plover habitat distribution and abundance

POPULATIONS AS ASSESSMENT ENDPOINTS AND SUGGESTIONS FOR SELECTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. POPULATION LEVEL REPLACED BY POPULATION SCALE
  5. CRITERIA FOR ENDPOINTS
  6. POPULATIONS AS ASSESSMENT ENDPOINTS
  7. POPULATIONS AS ASSESSMENT ENDPOINTS AND SUGGESTIONS FOR SELECTION
  8. TRANSITION TO PART 2
  9. Acknowledgements
  10. References

The examples above demonstrate that population-scale assessment endpoints are common in a variety of risk assessments in a wide variety of environments. Populations are critical as ecological services valued by a variety of stakeholders. This brief survey demonstrates that population-scale endpoints have been and should be incorporated into ecological risk assessments, especially in regional, watershed, or landscape-type assessments.

The selection of population-scale assessment endpoints has 2 parts. First is the selection of the population to be considered in the risk assessment. The 2nd is choosing properties of the population to be measured and assessed in the risk assessment. The conclusion of this commentary deals with suggestions to be used when selecting the population.

Suggestions for selecting population-scale endpoints

(1) Select a population that is important to stakeholders and policy makers. These populations are often listed by resource management agencies with clear specifications as to management goals. The populations include endangered species, important recreational fisheries, and populations that define habitats (i.e., eelgrass habitat). In many instances, the population important to the stakeholders within the study area may be poorly understood and defined; however, such populations can have special cultural value.

The province of British Columbia (British Columbia Ministry of Environment Lands and Parks 1998) has established, in its guidance for contaminated sites, clear descriptions of the types of populations to be included for the different land use types. Example conceptual models provide illustrations of the assessment endpoints specific to the type of land use. Such guidance makes the selection of population-scale endpoints relatively straightforward. Rural areas and parks are land uses having a variety of populations that should be considered; industrial sites only a few.

Furthermore, be particularly attentive to stakeholders that have specific values attached to particular populations. Many indigenous peoples, such as Native Americans or members of First Nations, have special treaty rights that allow the harvesting of resources for both consumption and use in cultural activities. Subsistence farming or harvesting in impoverished areas can be critical to survival. The ecological populations providing those resources should be considered as assessment endpoints.

(2) Location is a critical consideration in selecting endpoints at a regional or similar scale. Populations do not use a landscape in a random manner. Parts of the region may be critical as spawning sites or rookeries for populations harvested elsewhere. Protected populations are particularly vulnerable to changes in landscape. Other geographic areas can be important corridors for migration between habitat patches for waterfowl during migration in the fall and spring. Association with the entire site of interest should not be a requirement for selection as an assessment endpoint.

(3) It is clearly useful if the population biology of the species is understood. In areas where there are a number of impediments to migration, there may essentially be a number of isolated populations of small size. The genetic structure of the population can also be an essential element if conservation is under consideration.

(4) Spatially structure the area of interest to accommodate the populations that represent ecological resources. At a regional scale there will be multiple patterns of exposure and multiple potential effects. Averaging exposure over a heterogeneous study site will underestimate risk.

(5) Do not worry about a reference population in the sense of a laboratory or field control; they cannot exist. Being complex and historical structures, populations are particularly sensitive to initial conditions and historical events. In some circumstances, a number of populations may be exposed to different amounts of stressors so that a gradient design can be used to determine a concentration response. In the case of rare species, it may prove impossible to use even a gradient design. This brings us to the characteristics of the population, or attributes sensu Suter et al. (2005), that should be incorporated into a full specification for the assessment endpoint.

TRANSITION TO PART 2

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. POPULATION LEVEL REPLACED BY POPULATION SCALE
  5. CRITERIA FOR ENDPOINTS
  6. POPULATIONS AS ASSESSMENT ENDPOINTS
  7. POPULATIONS AS ASSESSMENT ENDPOINTS AND SUGGESTIONS FOR SELECTION
  8. TRANSITION TO PART 2
  9. Acknowledgements
  10. References

This commentary covered a number of topics, from a refutation of “level of organization” to suggestions for choosing populations as assessment endpoints. Populations are important in the ecological risk assessment process. Discussing the characteristics of populations (or attributes) that are useful in the construction of the assessment endpoint specification was purposefully not included.

The characteristics of a population that should be incorporated deserve a commentary of its own. Part 2 will cover selection of these characteristics in light of stakeholders' values, ecological reality, causality, and practicality. Detection of risks due to direct and indirect effects will also be considered.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. POPULATION LEVEL REPLACED BY POPULATION SCALE
  5. CRITERIA FOR ENDPOINTS
  6. POPULATIONS AS ASSESSMENT ENDPOINTS
  7. POPULATIONS AS ASSESSMENT ENDPOINTS AND SUGGESTIONS FOR SELECTION
  8. TRANSITION TO PART 2
  9. Acknowledgements
  10. References

I would like to thank anonymous reviewers for comments and suggestions and Linda S. Landis for her careful and patient editing.

Disclaimer—The peer-review process for this article was managed by the Editorial Board without the involvement of Board member W. Landis, who appears as an author in this article.

References

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. POPULATION LEVEL REPLACED BY POPULATION SCALE
  5. CRITERIA FOR ENDPOINTS
  6. POPULATIONS AS ASSESSMENT ENDPOINTS
  7. POPULATIONS AS ASSESSMENT ENDPOINTS AND SUGGESTIONS FOR SELECTION
  8. TRANSITION TO PART 2
  9. Acknowledgements
  10. References
  • British Columbia Ministry of Environment, Lands and Parks 1998. Protocol for contaminated sites guidance and checklist for tier 1 ecological risk assessment of contaminated sites in British Columbia. Victoria (BC): British Columbia Ministry of Environment, Lands and Parks.
  • Landis WG. 2002. Population is the appropriate unit of interest for a species-specific risk assessment. SETAC Globe 3: 3132.
  • LandisWG, editor., 2005. Regional scale ecological risk assessment using the relative risk model. Boca Raton (FL): CRC. 286 p.
  • Landis WG, Wiegers JK. 1997. Design considerations and a suggested approach for regional and comparative ecological risk assessment. Hum Ecol Risk Assess 3: 287297.
  • Landis WG, Wiegers JK. 2005. Chapter 2: Introduction to the regional risk assessment using the relative risk model. In: LandisWG, editor. Regional scale ecological risk assessment using the relative risk model. Boca Raton (FL): CRC. p 1136.
  • Munns WR Jr, Beyer WN, Landis WG, Menzie C. 2002. What is a population? SETAC Globe 3: 2931.
  • Obery AM, Landis WG. A regional multiple stressor risk assessment of the Codorus Creek watershed applying the relative risk model. Hum Ecol Risk Assess 8: 405428.
  • Obery AM, Thomas JF, Landis WG. 2005. Chapter 6 Codorus Creek Watershed: A regional ecological risk assessment with field confirmation of the risk patterns. In: LandisWG, editor. Regional scale ecological risk assessment using the relative risk model. Boca Raton (FL): CRC. p 119142.
  • O'Neill RV. 2001. Is it time to bury the ecosystem concept? (With full military honors, of course!). Ecology 82: 32753284.
  • Spromberg JA, Meador JP. 2005. Relating results of chronic toxicity responses to population-level effects: Modeling effects on wild Chinook salmon populations. Integr Environ Assess Manage 1: 921.
  • Stark JD, Banks JE, Roger V. 2004. How risky is risk assessment: The role that life history strategies play in susceptibility of species to stress. Proc Natl Acad Sci USA 101: 732736.
  • Suter GW II, 1993. Ecological risk assessment. Chelsea (MI): Lewis. 538 p.
  • Suter GW II, Barnthouse LW. 1993. Assessment concepts. In: SuterGWII, editor. Ecological risk assessment. Boca Raton (FL): Lewis. p 2147.
  • Suter GW, Norton SB, Fairbrother A. 2005. Individuals versus organisms versus populations in the definition of ecological assessment endpoints. Integr Environ Assess Manage 1: 397400.
  • Tannenbaum, LV. 2005. A critical assessment of the ecological risk assessment process: A review of misapplied concepts. Integr Environ Assess Manage 1: 6672.
  • [USEPA] US Environmental Protection Agency. 1992. Framework for ecological risk assessment. Washington DC: Risk Assessment Forum, US Environmental Protection Agency. EPA/630/R-92/001.
  • [USEPA] US Environmental Protection Agency. 1998. USEPA guidelines for ecological risk assessment. May 14, 1998. Fed Reg 63 (93) 2684626924. Washington DC: US Environmental Protection Agency. EPA/630/R-95/002F.
  • [USEPA] US Environmental Protection Agency. 2002. Waquoit Bay watershed ecological risk assessment: The effect of land-derived nitrogen loads on estuarine eutrophication. Washington DC: US Environmental Protection Agency. EPA/600/R-02/079.
  • [USEPA] US Environmental Protection Agency. 2003. Generic ecological assessment endpoints (GEAEs) for ecological risk assessment. Washington DC: US Environmental Protection Agency. EPA/630/P-02/004F.
  • Wu J, David JL. 2002. A spatially explicit hierarchical approach to modeling complex ecological systems: Theory and applications. Ecol Model 153: 726.
  • Wu J, Loucks OL. 1995. From balance of nature to hierarchical patch dynamics: A paradigm shift in ecology. Q Rev Biol 70: 439466.