Ministry of Environment Conservation Data Centre

Element Occurrence Ranking Factors

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		About CDC Ecology Ranking Methology Element Ranking (pdf 258 KB) Element Occurrence Ranking Element Occurrence Ranks Element Occurrence Ranking Factors Element Occurrence Specifications Spatial Patterns

Element Occurrence Ranking Factors

Introduction
Size
Condition
Landscape Context

Introduction

Because EO ranks are used to represent the relative conservation value of an EO as it currently exists, EO ranks are based solely on factors that reflect the present status, or quality, of that EO. There are three EO rank factors, each reflecting what is currently known (in an ideal situation) about an EO: size, condition, and landscape context. These factors are used as the basis for estimating the viability of an EO, i.e., its EO rank. Thus:

Size + Condition + Landscape Context => Estimated Viability EO Rank

For community Elements, the term “viability” is used loosely, since communities are comprised of many separate species, each with their own viability. Thus, the viability of a community is considered to be the sum of the viability or persistence of the component species and their ecological processes. More directly, EO ranks reflect the degree of negative anthropogenic impact to a community (i.e., the degree to which people have directly or indirectly adversely impacted community composition, structure, and/or function, including alteration of natural disturbance processes). Occurrences with relatively less impacts would generally be ranked “A”, “B”, or “C” (at least “fair” viability), and those with significant degradation would be ranked “D” (“poor” viability).

It is not necessary to have knowledge of each of the three rank factors to develop EO rank specifications (especially for species). For some Elements, information on one factor may be sufficient to rank an occurrence (e.g., a large population size may require, and thus imply, adequate condition and landscape context). For other Elements, information may be scant or incomplete. In such cases, EO ranks will be based on only one or a combination of the rank factors. The three EO rank factors are summarized in the table below.

Factor	Components	Species	Commu-nities
Size	Area of occupancy
	Population abundance
	Population density
	Population fluctuation (average population and minimum population in worst foreseeable year)
Condition	Reproduction and health (evidence of regular, successful eproduction; age distribution for long-lived species; persistence of clones; vigor, evidence of disease affecting reproduction/survival)
	Development/maturity (stability, old-growth)
	Species composition and biological structure (richness, evenness of species distribution, presence of exotics)
	Ecological processes (degree of disturbance by logging, grazing; changes in hydrology or natural fire regime)
	Abiotic physical/chemical factors (stability of substrate, physical structure, water quality) [excluding processes]
Landscape Context	Landscape structure and extent (pattern, connectivity, e.g., measure of fragmentation/ patchiness, measure of genetic connectivity)
	Condition of the surrounding landscape (i.e., development/maturity, species composition and biological structure, ecological processes, abiotic physical/chemical factors)

Size

Size is a quantitative measure of the area and/or abundance of an occurrence. Components of this factor are:

a) area of occupancy;
b) population abundance, (i.e., total count or qualitative estimate) (for species);
c) population density (for species);
d) population fluctuation (for species).

For communities, size is equal to the area of the occurrence. For species, the (population) size of an EO can be determined in several ways. Most commonly, information on both population abundance and the area of occupancy is used to calculate population size; however when appropriate (e.g., for territorial and colonial species), population abundance alone can be used as the EO (population) size. If population density is to be used in determining the population size of a species occurrence (e.g., when sampling a population in order to estimate its size), density must be used in combination with the area of occupancy. In addition, information on population fluctuations can be considered when calculating EO population size, particularly for species known to typically have high fluctuations in population.

EO size varies as a function of both natural and anthropogenic factors. Larger EOs are generally presumed to be more valuable for conservation purposes, all other rank factors being equal. Larger occurrences are typically less influenced by edge effects, and less susceptible to degradation or extirpation by stochastic events.

Condition

Condition is an integrated measure of the quality of biotic and abiotic factors, structures, and processes within the occurrence, and the degree to which they affect the continued existence of the EO. Components of this factor are:

a) reproduction and health (for species);
b) development/maturity (for communities);
c) ecological processes;
d) species composition and biological structure (see next paragraph);
e) abiotic physical/chemical factors.

Although terrestrial communities are usually classified and assessed by analyzing their vegetation composition and structure, the zoological component of a community should be considered in determining EO rank specifications. For example, an “A”-ranked community should be large enough to sustain habitat-specific animal species that are characteristic of that community (e.g., prairie chickens for prairie communities; edge-sensitive, forest interior birds for eastern forested communities). Note, however, that wide-ranging animal species (e.g., bison) may be dependent on landscape or multi-community factors (i.e., above the scale of the individual EO), and the rank specifications need not consider the ability of the community to support such species. Note also that the principle of “best EOs that are reasonably and conceivably achievable” may preclude setting “A”-rank specifications at levels to support all historically component species. For a particular community EO, evidence that the fauna currently present no longer represent the full suite of species to be expected (e.g., due to past aerial spraying of pesticides, due to destruction of the upper soil horizons and litter layer) may be cause to significantly lower the condition rating of that community.

Landscape Context

Landscape context is an integrated measure of the quality of biotic and abiotic factors, structures, and processes surrounding the occurrence, and the degree to which they affect the continued existence of the EO. Components of this factor are:

a) landscape structure and extent, including genetic connectivity;
b) condition of the surrounding landscape (see components of “condition” listed above, excluding reproduction).

In terms of EO rank, genetic connectivity refers to the degree of connectivity between different EOs. Although EOs for non-migratory species are delineated in part by the degree of genetic connectivity between adjacent populations (see Section 4.3, Separating EOs), there is usually some small amount of gene flow between adjacent EOs. If, due to an EO’s isolation, there is virtually no genetic connectivity between a particular EO and any other EOs, the EO rank might be lowered. For example, the EO rank for spotted owl is influenced by the degree of isolation of a population from other populations.

Source: Draft Element Occurrence Data Standard