Definitions of terms for more information on some key concepts relevant to the IUCN Red List of Ecosystems Categories and Criteria:
- Area of assessment - Defines the implementation bounds of the assessment.
- Area of occupancy - Area of occupancy (AOO) is a standardized measure of the area that is occupied by an ecosystem type.
- Characteristic native biota - Biological features that define the identity of an ecosystem type and distinguish it from other ecosystem types and/or drive ecosystem dynamics and function, e.g. ecological processes, ecosystem engineers, trophic or structural dominants, functionally unique elements, species interactions.
- Collapse - Collapse has occurred when all occurrences of an ecosystem have moved outside the natural range of spatial and temporal variability in composition, structure and function. Some or many of the pre-collapse elements of the system may remain within a collapsed ecosystem, but their relative abundances may differ, and they may be organized and interact in different ways with a new set of operating rules. Ecosystem collapse may be viewed as the analogue of functional extinction in species, which precedes or at least coincides with complete elimination of all characteristic biota.
- Collapsed (CO) - An ecosystem is Collapsed when it is virtually certain that its defining biotic or abiotic features are lost from all occurrences, and the characteristic native biota are no longer sustained. Collapse may occur when most of the diagnostic components of the characteristic native biota are lost from the system, or when functional components (biota that perform key roles in ecosystem organization) are greatly reduced in abundance and lose the ability to recruit.
- Continuing decline - A gradual or episodic decline in distribution or ecological process that is likely to continue into the future, and is non-trivial in magnitude and its effect on the sustainability of characteristic native biota.
- Critically Endangered (CR) - An ecosystem is Critically Endangered when the best available evidence indicates that it meets any of the criteria A to E for Critically Endangered. It is therefore considered to be at an extremely high risk of collapse.
- Data Deficient (DD) - An ecosystem is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of collapse based on decline in distribution, disruption of ecological function or degradation of the physical environment. Data Deficient is not a category of threat, and does not imply any level of collapse risk. Listing of ecosystems in this category indicates that their situation has been reviewed, but that more information is required to determine their risk status.
- Disruption of biotic interactions - AA change in interactions among different groups of biota, or between the biota and the physical environment that reduces the capacity of the ecosystem to sustain its characteristic native biota (i.e. biotic degradation cf. environmental degradation). Interactions may be between biota within an ecosystem, with biota of another ecosystem or between biota and environmental factors. Assessment of disruption to biotic interactions under criterion D involves the following steps: i) selection of a suitable biotic variable or variables, with justification of its relationship(s) to salient processes of ecosystem dynamics (e.g. with reference to a process model specific to the ecosystem under evaluation); ii) estimate the value of the variable across the distribution of the ecosystem at the end of the assessment period (present day for D1 & D3, 50 years in future for D2); iii) estimate how much the biotic variable changed since the beginning of the assessment period (50 years ago for D1, present day for D2, 1750 for D3). Generally, patches of the ecosystem that may have been destroyed (e.g. by land conversion) should be excluded from this estimate; iv) calculate the absolute % change in the biotic variable over the assessment period (this may require temporal interpolation or extrapolation and justification of associated assumptions); v) range-standardize the estimated of absolute % change using a collapse threshold estimated specifically for the ecosystem to obtain an estimate of relative severity of degradation; vi) estimate the extent (as % of the ecosystem distribution) over which the change has occurred; and vii) compare the estimates of relative severity and extent to the assessment thresholds under criterion D.
- Distribution - The spatial occurrence of an ecosystem. For criterion A, changes in distribution should be estimated with the best available mapping of an appropriate surrogate for the ecosystem (e.g. remote sensing of terrestrial vegetation, marine reefs, etc.). For criterion B, distribution size must be estimated using the standard metrics.
- Driver - The ultimate factors, usually social, economic, political, institutional, or cultural that enables or otherwise add to the occurrence or persistence of proximate direct threats. There is typically a chain of drivers behind any given direct threat.
- Ecosystem - Complexes of organisms and their associated physical environment, within an area (after Tansley 1935). They have four essential elements: a biotic complex; an abiotic environment or complex; the interactions within and between them; and a physical space in which these operate (Pickett & Cadenasso 2002).
- Ecosystem collapse - Collapse is a transformation of identity, a loss of defining features, and a replacement by a different ecosystem type.
- Ecosystem type - The unit of assessment.
- Endangered (EN) - An ecosystem is Endangered when the best available evidence indicates that it meets any of the criteria A to E for Endangered. It is therefore considered to be at a very high risk of collapse.
- Environmental degradation - A change in the abiotic features of an ecosystem that reduce its capacity to sustain its characteristic native biota. Assessment of environmental degradation under criterion C involves the following steps: i) selection of a suitable environmental variable or variables, with justification of its relationship(s) to salient processes of ecosystem dynamics (e.g. with reference to a process model specific to the ecosystem under evaluation); ii) estimate the value of the variable across the distribution of the ecosystem at the end of the assessment period (present day for C1 & C3, 50 years in future for C2); iii) estimate how much the degradation variable changed since the beginning of the assessment period (50 years ago for C1, present day for C2, 1750 for C3). Generally, patches of the ecosystem that may have been destroyed (e.g. by land conversion) should be excluded from this estimate; iv) calculate the absolute % change in the degradation variable over the assessment period (this may require temporal interpolation or extrapolation and justification of associated assumptions); v) range-standardize the estimated of absolute % change using a collapse threshold estimated specifically for the ecosystem to obtain an estimate of relative severity of degradation; and vi) estimate the extent (as % of the ecosystem distribution) over which the degradation has occurred.
- Estimated - Information that is based on calculations that may include statistical assumptions about sampling, or biological assumptions about the relationship between an observed variable and the variable of interest (e.g. relationship between an index of abundance and the number of mature individuals; IUCN Standards and Petitions Subcommittee, 2014). These assumptions should be stated and justified in the assessment documentation. Estimation may also involve interpolation in time to calculate the variable of interest for a particular time step (e.g. a 50-year reduction in distribution based on observations of distribution 40 and 60 years ago).
- Extent of occurrence - Extent of occurrence (EOO) is a standardized measure of the area within which all occurrences of an ecosystem type exist.
- Geographic distribution - The geographic distribution of an ecosystem type represents all spatial occurrences of an ecosystem type.
- Grain size - The size of the spatial unit (e.g. grid cell, polygon segment) used to measure a distribution.
- Inferred - Information that is based on indirect evidence and on variables that are indirectly related to the variable of interest, but in the same general type of units (IUCN Standards and Petitions Subcommittee, 2014). Inferred values rely on more assumptions than estimated values. For example, inferring disruption of biotic interactions from catch statistics not only requires statistical assumptions (e.g. random sampling) and biological assumptions (about the relationship of the harvested section of the population to the total population), but also assumptions about trends in effort, efficiency, and the spatial and temporal distribution of harvest in relation to the population. Inference may also involve extrapolating an observed or estimated quantity from known ecosystem occurrences to calculate the same quantity for other occurrences. Whether there are enough data to make such an inference will depend on how large the known occurrences are as a proportion of the whole distribution, and the applicability of threats and trends observed in the known occurrences to the rest of the ecosystem.
- Least Concern (LC) - An ecosystem is Least Concern when it has been evaluated against the criteria and does not qualify for Critically Endangered, Endangered, Vulnerable or Near Threatened. Widely distributed and relatively undegraded ecosystems are included in this category.
- Location - A geographically or ecologically distinct area in which a single threatening process can rapidly affect all occurrences of an ecosystem type.
- Near Threatened (NT) - An ecosystem is Near Threatened when it has been evaluated against the criteria but does not qualify for Critically Endangered, Endangered or Vulnerable now, but is close to qualifying for or is likely to qualify for a threatened category in the near future.
- Not Evaluated (NE) - An ecosystem is Not Evaluated when it is has not yet been evaluated against the criteria.
- Observed - Information that is directly based on well-documented records of all known occurrences of the ecosystem (IUCN Standards and Petitions Subcommittee, 2014).
- Projected - Same as estimated, but the variable of interest is extrapolated in time towards the future (IUCN Standards and Petitions Subcommittee, 2014). Projected variables require a discussion of the method of extrapolation (e.g. justification of the statistical assumptions or the ecosystem model used) as well as the extrapolation of current or potential threats into the future, including their rates of change.
- Relative severity - The estimated magnitude of past or future environmental degradation or disruption to biotic processes, expressed as a percentage relative to a change large enough to cause ecosystem collapse.
- Spatial extent - The total area of the geographic distribution of an ecosystem type estimated with a specified metric.
- Stress - Stresses are the effects on ecosystem features that are impaired directly by threats (e.g. reduced abundance of keystone species, fragmentation of habitat). A stress is not a threat in and of itself, but rather a degraded condition or symptom of the target that results from a direct threat. The RLE risk protocol aims to quantify these symptoms to assess declines towards collapsed states.
- Temporal resolution - The units of time over which trends are measured.
- Thematic scale - A measure of the similarity of features within and among ecosystem types. May be represented by the levels of a hierarchical classification.
- Threat - Direct threats are the proximate activities or processes that have impacted, are impacting, or may impact the status of the ecosystem being assessed (e.g., unsustainable fishing or logging). Threats can be past (historical), ongoing, and/or likely to occur in the future. Natural phenomena are also regarded as direct threats in some situations.
- Time frame - The total period over which ecosystem change is assessed.
- Vulnerable (VU) - An ecosystem is Vulnerable when the best available evidence indicates that it meets any of the criteria A to E for Vulnerable. It is therefore considered to be at a high risk of collapse.