1. Focal species (i.e. indicators, keystones, umbrellas, and flagships) have been advocated for the management and conservation of natural environments.2. The assumption has been that the presence or abundance of a focal species is a means to understanding the composition and/or state of the more complex community.3. We review the characteristics of focal species, and evaluate their appropriateness and utility judged against conservation objectives.4. It appears that indicator species (of both composition and condition) may be of greatest general utility, and that several types of focal species may exhibit useful indicator properties.

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Zooplankton samples, usually together with morphometric, physical, and chemical data, were collected from 696 lakes in glaciated eastern North America between 1969 and 1978. Geographical distributions of the 44 Crustacea and 4 Diptera species suggest six broad categories: 23 species appear to have no barriers to dispersal throughout the area; 7 have restricted ranges, possibly because of either recent evolution or competitive exclusion; 3 may be gradually invading the area from centres to the south or west; 1 is a euryhaline estuarine form with a limited freshwater distribution; 4, possibly 5, are found almost exclusively in areas of former glacial lakes or spillways and may be classified as "glacial opportunists"; 9 species have distributions which appear to be linked in some unspecified way to calcium–magnesium water hardness.

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Ecological scales, levels and wide-range scaling There is a mushrooming ecological literature on the problem of spatial and temporal scales and its relationship to ecological 'level'; the collections (Powell and Steele, 1995; Peterson and Parker, 1998) contain many recent examples. At first sight, the distinction seems clear enough: scale refers to the spatial extent of an ecological field (such as biomass density, population number density) or to the duration of an ecological process. In contrast, the notion of 'ecological level' refers to a (possibly) corresponding level of 'organization' ('trophic level', 'landscape level', 'canopy level', etc.), and hence to a specific

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ABSTRACT1. If marine environments are to be systematically protected from the adverse effects of human activities, then identification of the types of marine habitats and the communities they contain, and delineation of their boundaries utilizing a consistent classification is required. Human impacts on defined communities can then be assessed, the 'health' of these communities can be monitored, and marine protected areas can be designated as appropriate.2. Schemes to classify habitats at local and regional scales, according to their geophysical properties, may identify different factors as determinants, and/or use them in different sequences in a hierarchical classification. We examined the reasons for these differences in local and regional applications of a global concept, and argue that a common set of factors could be applied in a defined and defensible sequence to produce a common hierarchy of habitat types among geographic regions.3. We show how simple mapping and GIS techniques, based on readily available data, can lead to the identification of representative habitat types over broad geographic regions. We applied a geophysical framework first to the entire Canadian coastline and second to the Scotian Shelf of Atlantic Canada to establish broad scale marine natural regions and 'seascapes', respectively. This ecosystem level approach } which defines representative habitat types } is a fundamental prerequisite for many purposes. It can form the basis for further analyses including: definition of community types from habitat } community relationships; evaluation of the potential roles of focal species in marine conservation; evaluation of candidate marine protected areas; definition of unaffected reference areas against which the effects of human activities can be gauged; guidance for water quality monitoring studies; management of marine resources.