1. Key terms and concepts in the IUCN criteria

2. The purpose of a Red List assessment is to give a relative estimate of the extinction risk for the taxon. What kinds of factors must be considered when evaluating extinction risk? What are some of the causes of extinction?
(Facilitator’s note: The purpose of this slide is to spark a short 5-10 minute discussion on the causes of extinction and the factors to consider when evaluating extinction risk, which leads into the terms and definitions considered in the criteria. Some causes that are likely to come up that directly relate to the terms in the criteria are population decline, restricted range, long lifespan and/or reproductive strategy, population fragmentation, etc.)

3. Critically Endangered A2ace;B1ab(iii)
Rabb’s Fringe-limbed Treefrog Ecnomiohyla rabborum
Photo © Brad Wilson
Range: Known from 3-4 sites in the immediate vicinity of the town El Valle de Antón, between m in central Panama. Suspected to be endemic to this area.
Population: Was never common, but after detection of the chytrid fungus in the region in 2006, has become much harder to find. Previously 1-2 males could be heard calling per night; only one individual has been heard since chytrid was detected.
Threats: Chytrid fungus in the area; some ongoing forest clearing.
Conservation: Attempts at captive breeding have been unsuccessful. Surveys are conducted regularly.
Critically Endangered A2ace;B1ab(iii)
Based on:
Drastic population decline over past 3 generations, inferred from the apparent disappearance of most of the population
Restricted range combined with continuing decline in extent and quality of habitat.
Let’s look at a case study to see how the IUCN Red List criteria consider these extinction risk factors to list species.
(Facilitator’s note: Don’t spend time explaining the criteria or terms such as “inferred” – we don’t want to put people off with too much detail right now. The purpose of this is (1) to show that Red Listing is a fairly straightforward process that can be done with relatively little information, and (2) to casually introduce some of the “lingo” that is used in Red List assessments.)
After going through the example, say:
The Red List criteria include many concepts that relate to measuring extinction risk. Most scientists are familiar with most of these concepts, but some of the terms in the Red List methodology have very specific definitions that differ from the standard scientific definition. It is very important that you learn the IUCN definitions for the terms we’re going to discuss, to ensure you properly apply the criteria to produce a realistic assessment of extinction risk.

4. Population Size Subpopulations Population (mature individuals only)
Population – For the purposes of the Red List criteria, ‘population’ is defined as the total number of individuals of the taxon (including adults, juveniles, senescent individuals, etc.).
Population size – In contrast to the general term ‘population’, the population size is measured as the number of mature individuals only.
Mature Individuals – The number of mature individuals is the number of individuals known, estimated or inferred to be capable of reproduction; juveniles, senescent and repressed individuals are therefore excluded. The purpose of this measurement is to count the number of functional breeders that can contribute to the population. It can be very difficult to define a mature individual for some taxa, such as colonial species (corals, fungi, lichen, etc.). The user guidelines give much more information about how this can be done and when it is appropriate to do so, and also give guidance for dealing with specific issues, such as biased sex ratios.
Subpopulations – Subpopulations are geographically or otherwise distinct groups in the population between which there is little demographic exchange (e.g., 1 successful migrant individual or gamete per year).
Population

5. e.g. ≥ 50% population decline measured over 3 generations
Generation Length
Used to scale time-based measurements to account for different survival and reproduction rates
e.g. ≥ 50% population decline measured over 3 generations
Generation length is a concept used in the Red List methodology to scale time-based measurements (such as population declines) to account for the different rates at which taxa survive and reproduce. It is greater than age at first breeding and less than age of the oldest breeding individual (except in taxa that breed only once). In the Red List Criteria, declines are measured over a given time period, but the time period over which these declines are measured must “make sense” to the taxon being assessed. For a rapidly reproducing, short-lived dragonfly or mouse, for example, 10 years might be a reasonable time period over which to measure a population decline. But for a whale or a redwood tree, 10 years is an insignificant period of time and population declines should be measured over a much longer time period. Because mature individuals of different species have very different average life spans (from hours to millennia), the period over which declines are measured is expressed in generation lengths. In this way ‘generation length’ is used to standardize time-based measures across taxa so that they make sense according to the taxon’s life history.

6. Age of parents of the current cohort (years)
Generation Length
Several definitions (all acceptable):
Average age of parents of the current cohort (i.e., newborn individuals in the population)
Number of parents
Age of parents of the current cohort (years)
There are several definitions for and therefore ways to estimate generation length – the most appropriate one will depend on the specific life history characteristics of the taxon being assessed (more guidance is given in the User Guidelines). The most basic definition of generation length is “the average age of parents of the current newborn individuals in the population”. If we plot the number of parents against the age of the parents of the current cohort, the generation length will be the mean value between the age at first breeding and the age at last breeding. This is the definition most commonly used for species in which mortality increases and fecundity decreases over time.
Age at first breeding
Generation Length
Age at last breeding

7. Several definitions (all acceptable):
Generation Length
Several definitions (all acceptable):
Average age of parents of the current cohort (i.e., newborn individuals in the population)
Mean age at which a cohort of newborns produce offspring
Number of breeders in the cohort
Another definition of generation length is “the mean age at which a cohort of newborns produce offspring”.
Age at first breeding
Generation Length
Age at last breeding
Age of individuals of the current cohort (years)

8. Several definitions (all acceptable):
Generation Length
Several definitions (all acceptable):
Average age of parents of the current cohort (i.e., newborn individuals in the population)
Mean age at which a cohort of newborns produce offspring
Age at which 50% total reproductive output is achieved
Number of offspring
Yet another definition is the age at which 50% of the total reproductive output is achieved.
50%
50%
Age (years)
Age at first breeding
Generation Length
Age at last breeding

9. Several definitions (all acceptable):
Generation Length
Several definitions (all acceptable):
Average age of parents of the current cohort (i.e., newborn individuals in the population)
Mean age at which a cohort of newborns produce offspring
Age at which 50% total reproductive output is achieved
Mean age of parents in a population at the stable age distribution
Time required for the population to increase by the replacement rate
Two more possible definitions of generation length include:
The mean age of the parents in a population at the stable age distribution
The time required for the population to increase by the replacement rate
The important thing to remember is that we estimate generation length to scale time-based measurements in the Criteria to account for the fact that different species survive and reproduce at different rates. Generation length therefore reflects the turnover rate of breeding individuals in a population. When generation length varies under threat, such as in some fish species that breed earlier when they are heavily exploited in order to boost their populations size, the more natural generation length should always be used.
Remember that the most appropriate definition for the taxon that you are assessing will depend on its specific life history characteristics. Formally, the definition of generation length requires age- and sex-specific information on survival and fecundity, and is best calculated from a life table. The User Guidelines outline other acceptable methods for calculating generation length, and IUCN also provides a spreadsheet where this can be calculated automatically.
Scales time-based measurements to account for different survival/reproduction rates.
Reflects turnover rate of breeders.
Always use natural generation length.
See the User Guidelines for methods of calculating generation length

10. Reduction Continuing Decline
Time
Population Size
Reduction is a decline in population size of at least the % stated in criterion A over the specified time period.
Reduction – A reduction is simply a decline in the population size. In the Red List Criteria, a population reduction of at least a specific percentage is measured over a specific time period, but essentially a reduction is just a population decline. The User Guidelines give more details about how to estimate a reduction from population data.
Continuing Decline – A continuing decline is a recent, current or projected future decline which is liable to continue unless remedial measures are taken. The decline may be smooth, irregular or sporadic, but the key point is that it is expected to continue unless something is done to stop or reverse the decline.
Continuing Decline
Continuing Decline is a recent, current or projected future decline which is liable to continue unless remedial measures are taken.

11. Reduction Continuing Decline
Timing:
One-off event
Ongoing
Decline is expected to continue unless something is done to stop it.
Applies to:
Population size
Extent of occurrence
Area of occupancy
Area, extent and/or quality of habitat
# locations
# subpopulations
There are two main differences between a reduction and a continuing decline in the Red List Criteria.
The primary difference between the two is that a reduction can be a one-off event or it can be ongoing, while a continuing decline must be ongoing. So, a volcano could erupt and cause a population to decline by 25%, but we might expect that population to then recover from the event. This would be a population reduction of 25%, but it would not be considered a continuing decline because the population will not continue to decline.
Second, a reduction only applies to the population size, while a continuing decline can be measured over many different variables, from population size to number of subpopulations to quality of habitat.
Note that a continuing decline is not possible without a reduction, but a reduction is possible without a continuing decline. In other words, a continuing decline always involves a population reduction, but a reduction does not have to be continuing - it can be a one-time event.

12. Extreme Fluctuations
Population size or distribution area varies widely, rapidly and frequently (typically tenfold increase or decrease)
Population Size
Extreme fluctuation – Extreme fluctuations occur where population size or distribution area varies widely, rapidly and frequently, typically with a variation greater than one order of magnitude (i.e., a tenfold increase or decrease).
Many populations fluctuate somewhat and in a lot of species the visible number of mature individuals changes by season or by year, but for the Red List Criteria, extreme fluctuations must represent real changes in the total population size or distribution area. In this example, the number of adult butterflies actually changes significantly from one year to the next. This might be caused by a change in the availability of the host plant, changes in water or climatic conditions, or for any other reason – the important point is that the actual population size fluctuates from year to year, and the variation in population size is greater than one order of magnitude.
The fluctuation doesn’t have to occur in the population size. The distribution area of a species may also fluctuate significantly (for example, in response to flood dynamics for freshwater species).
Real changes in total population size (e.g., dormant eggs/seeds damaged or lost) therefore extreme fluctuation

13. Extreme Fluctuations
Population Size
In this example a species of killifish relies on temporary ponds. Each year during the rainy season, the ponds fill up, stimulating development of eggs into adult fish. Many mature individuals are then visible and reproducing, but as the ponds dry out and the dry season approaches, the adults die off and only the eggs are left behind. The actual population hasn’t changed in size; the apparent loss of the population in the dry season is simply a change between life forms. The species still exists as a population of dormant eggs, but assuming the next wet season arrives as normal, the population size will again return to normal.
This is a natural seasonal fluctuation, not a real change in population size, and therefore is not an extreme fluctuation.
Say, however, that one year there is a drought and the rain is delayed. Many of the eggs die off. When the rain finally does come, the emerging adult population is more than 10 times smaller than it was in previous years. If this happens with some frequency (that is, it’s not just a one-off event) it would be an extreme fluctuation.
There are more details in the User Guidelines about how to measure extreme fluctuations.
(Note to Facilitators: Another example, for plants: Fires may stimulate mass recruitment from large persistent seed banks when there were few mature individuals before the event. Mature plants may die out during the interval between fires, leaving a store of immature individuals (seeds) until they are stimulated to germinate by the next fire. Such cases do not fall within the definition of extreme fluctuations unless the dormant life stages are exhaustible by a single event or cannot persist without mature individuals. However, plant taxa that were killed by fire and had an exhaustible canopy-stored seed bank (serotinous obligate seeders), for example, would be prone to extreme fluctuations because the decline in the number of mature individuals represents a decline in the total number.)
Natural seasonal fluctuations – flux of individuals between different life stages. Not real changes in total population size, therefore not extreme fluctuation

14. Severely Fragmented
Most individuals (>50%) found in small, isolated subpopulations between which there is very little dispersal. These subpopulations may be too small to be viable.
Taxa with highly mobile adult stages or producing large numbers of small, mobile diaspores can disperse more easily and are not so vulnerable to isolation through fragmented habitats.
Severely fragmented – Populations are considered ‘severely fragmented’ when most of the individuals (>50%) are found in small, isolated subpopulations between which there is very little dispersal. These subpopulations may be too small to be viable, and so may go extinct with little probability that they will be rescued or re-colonized by dispersing individuals.
CLICK: It’s not enough just to have small, isolated subpopulations to consider a taxon severely fragmented. Taxa with highly mobile adults or that produce large numbers of easily dispersed diaspores can more easily rescue or re-colonize sites where populations are declining, and are therefore less vulnerable to extinction.
CLICK: Here you can see that even though the subpopulations are small and fragmented, when some subpopulations go extinct they are re-colonized by the other subpopulations. These would not be considered severely fragmented.
CLICK: However, taxa that don’t produce very many diaspores or only produce larges ones that don’t disperse easily are more isolated and there is less movement between them.
CLICK: In this example, there is no movement or dispersal between the subpopulations, so that when one subpopulation goes extinct, the others can’t re-colonize the area. The risk of extinction for this taxon is higher than for the previous taxon.
Taxa producing small numbers of diaspores (or none at all), or only large ones are less able to disperse over wide areas and are more easily isolated.

15. Extent of Occurrence Area of Occupancy
Extent of Occurrence: area within the shortest continuous imaginary boundary drawn around all known, inferred, or projected sites presently occupied by the taxon.
…EOO ≠ the species’ range.
Extent of occurrence and area of occupancy are two different ways to measure characteristics of a taxon’s distribution. Note that neither of them measure the ‘range’ per se; rather, they both measure characteristics of a taxon’s range that influence its extinction risk.
Extent of occurrence (or EOO) is the area contained within the shortest continuous imaginary boundary drawn around all the known, inferred or projected sites where the taxon is currently found, or is believed to be present. This is often called the ‘minimum convex polygon’. Extent of occurrence measures the spatial spread of the areas currently occupied by the taxon, and hence the spatial spread of extinction risk. The intent behind this parameter is to measure the degree to which risks from threatening factors are spread spatially across the taxon’s geographical distribution. It is not intended to be an estimate of the amount of occupied or potential habitat, or a general measure of the taxon’s range.
There is currently some debate within IUCN as to whether EOO may exclude large areas of unsuitable habitat (e.g. the spaces between the green circles in the diagram); some people argue, for example, that it wouldn’t make sense to include the Atlantic Ocean in the EOO measurement for a species found only on the east coast of the USA and the western coast of France. However, if you exclude these large areas of unsuitable habitat, you are getting close to the definition of area of occupancy, so others argue that such areas should be included in the measurement.
Area of occupancy is the area within a taxon’s extent of occurrence that is actually occupied by a taxon. The measure reflects the fact that a taxon will not usually occur throughout the area of its extent of occurrence, which may contain unsuitable or unoccupied habitats. IUCN recommends it be measured by laying a 2x2 km grid over a map of the species distribution or point localities and counting the number of occupied cells; the User Guidelines go into much more detail about how to measure area of occupancy, and how to scale up or scale down AOO estimates if other grid cell areas have been used.
Area of Occupancy: area within the extent of occurrence which is actually occupied by the taxon (measured by overlaying a 2x2 km grid and counting number of occupied cells).

16. EOO
This is how EOO and AOO measurements might look on a range map. Here we have three separate subpopulations. Extent of occurrence is measured by drawing a minimum convex polygon around all of the known populations. Area of occupancy is represented by the blue polygons, and (CLICK) would be measured using a 2x2 km grid.
AOO

17. Extent of Occurrence
Comparison of taxa with same AOO but different EOO – a single threatening event is more likely to impact the taxon with the smaller EOO:
Threatening event
Let’s look at EOO and AOO in more detail. Remember that extent of occurrence measures the spatial spread of extinction risk across the taxon’s range. The larger the area over which a taxon is distributed, the less likely it is that any one threatening event will affect the entire population.
The diagram illustrates the effect of having a larger EOO, but same AOO and same threatening event:
Both species occupy the same amount of habitat and have the same AOO, but the species on the left has a much more restricted range, and thus a smaller EOO.
If we consider a threatening event – say the average spread of pollution, or the average size of a logging tract – and apply that threatening event to both species…
AOO = 10x4 = 40 km2
EOO = 44 km²
AOO = 10x4 = 40 km2
EOO = 105 km²

18. Extent of Occurrence
Comparison of taxa with same AOO but different EOO – a single threatening event is more likely to impact the taxon with the smaller EOO:
…we can see that the threatening event affects a larger proportion of the left-hand population than it does for the right-hand example. The overall effect is that the left-hand example suffers more from the same event than the right-hand example does. The extinction risk for a taxon with a smaller EOO is thus higher, because any one threatening event will affect more of the population.
AOO = 7x4 = 28 km2
EOO = 28 km²
AOO = 8x4 = 32 km2
EOO = 82 km²

19. Extent of Occurrence Migratory species: EOO summer summer summer
When measuring EOO, in the case of migratory species, EOO should be based on the minimum of the breeding or non-breeding (wintering) areas, but not both, because such species are dependent on both areas, and the bulk of the population is found in only one of these areas at any time.
For freshwater species, EOO is based on the total area of the occupied river catchments, rather than the area inside a minimum convex polygon. If the taxon is only found in a few streams, you can use the area of the sub-basin rather than the entire catchment.
EOO
winter

20. Area of Occupancy
Linear habitats: AOO measurement must be consistent with threshold values – in most cases, use 2x2 km grid for AOO estimates.
AOO can be measured as the smallest area essential at any stage to the survival
When measuring area of occupancy, there is sometimes a concern that grids do not have much ecological meaning for species that live in linear habitat, like along the coastline or in rivers or streams. Some people believe the AOO should be measured by multiplying the length of the river times the width, because the species is only found within the water and the grid includes areas of land. However, it is important that the AOO measurement be consistent with the threshold values given in the criteria. If AOO measurements were based on estimates of length x breadth of habitat, there may be very few taxa that exceed the VU threshold, so a 2x2 grid should be used even for linear habitats.
In some cases, (e.g., irreplaceable colonial nesting sites, crucial feeding sites for migratory taxa) the area of occupancy is the smallest area essential at any stage to the survival of existing populations of a taxon, such as the area of colonial nesting grounds. Much more advice on measuring AOO is provided in the User Guidelines.

21. Location
Location is a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon.
Location – Pay close attention to the definition of location, as it is one of the most misunderstood and misapplied terms in the Red List criteria. The term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. A location is therefore defined entirely by the most significant current or plausible potential threat - IT DOES NOT MEAN THE NUMBER OF SITES OR LOCALITIES THE SPECIES IS RECORDED FROM.
The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat. If there are no serious threats acting on the population (and no plausible threats expected to affect the population in the foreseeable future), no consideration should be given to how many locations there are. Without a threatening event, the number of locations cannot be measured.
For example, where the most serious plausible threat is habitat loss, a location is an area where a single development project can eliminate or severely reduce the population. Where the most serious plausible threat is volcanic eruption, hurricane, tsunami, frequent flood or fire, locations may be defined by the previous or predicted extent of lava flows, storm paths, inundation, fire paths, etc. Where the most serious plausible threat is collection or harvest, then locations may be defined based on the size of jurisdictions (within which similar regulations apply) or on the level of access (e.g., ease with which collectors may reach different areas), as well as on the factors that determine how the levels of exploitation change (e.g., if collection intensity in two separate areas changes in response to the same market trends in demand, these may be counted as a single location).

22. Location 2 locations Invasive species
Let’s look at a few examples. Here we have an aquatic species, distributed in a river system and in a nearby lake. (CLICK) The most serious threat to the species is invasive species, which are introduced to the river and quickly spread throughout the entire river. (CLICK) How many locations do you think there should be?
In this case, introducing invasive species just once into the river affected all of the individuals in the river, so we would consider that one location (CLICK). The lake would be a second location (CLICK), as we would have to introduce invasive species separately into the lake to affect those individuals, but once we did so, all individuals in the lake would be affected.

23. Location 4 locations Pollution
Here’s another example. This time, pollution is the most serious threat. When pollution enters the river upstream, it affects the entire river downstream, but doesn’t travel up the tributaries. How many locations should we have in this example?
Generally speaking, we would have 4 locations, as it would take 4 separate pollution events to affect all of the individuals of the species we are evaluating: one in the main river body, one in each tributary, and one in the lake. This is somewhat subjective, as you could have more than one location in the main river body or in the tributaries if pollution were introduced at some point below where some of our individuals are located. In a real assessment, you would have to consider where the most likely areas for pollution to enter the river would be located and count the number of locations accordingly.

24. Location
If most serious threat does not affect entire distribution: can use other threats to count locations in areas not affected by most serious threat.
Fishing
Pollution
Pollution
Dam
Where the most serious plausible threat does not affect all of the taxon’s distribution, other threats can be used to define and count locations in those areas not affected by the most serious plausible threat. When parts of the distribution are not affected by any threat (as long as less than half of the distribution is unaffected), locations in those areas could be defined based on (a) the number of subpopulations in those areas, (b) on the smallest size of locations in the currently affected areas, or (c) the most likely threat that may affect the currently-unaffected areas in the future. In any case, the basis of the number of locations should be documented.
In this example our species is distributed throughout a river basin and pollution is the most serious threat affecting the largest proportion of the population. But, there are different threats affecting other parts of the basin. How many locations would you count here? (There should be 5 locations.)
Remember, if there are no plausible threats, the number of locations cannot be counted and the subcriteria that refer to the number of locations cannot be used.
5 locations
If there are no plausible threats, do not consider locations at all.

25. Quantitative Analysis
Quantitative Analysis is any form of analysis which estimates the extinction probability of a taxon based on known life history, habitat requirements, threats and any specified management options (e.g., Population Viability Analysis (PVA)).
Quantitative analysis – A quantitative analysis any form of analysis which estimates the extinction probability of a taxon based on known life history, habitat requirements, threats and any specified management options. Population viability analysis (PVA) is one such technique. Such detailed data isn’t available for most species, but if you can run a quantitative analyses, the assumptions, the data used and the uncertainty in the data or quantitative model must be documented. Quantitative analyses are used for assessing taxa under Criterion E.

26. Key terms and concepts Severely Fragmented:
Increased extinction risks due to the fact that most individuals are found in small and relatively isolated subpopulations, and dispersal is limited between these subpopulations. These small subpopulations may go extinct, with a reduced probability of recolonization.
Extent of Occurrence (EOO):
Area contained within the shortest continuous imaginary boundary (minimum convex polygon) which can be drawn to encompass all known, inferred, or projected sites presently occupied by the taxon.
Area of Occupancy (AOO):
Area within the extent of occurrence (EOO) which is actually occupied by the taxon (usually measured by overlaying a grid and counting number of occupied cells).
Note to Facilitators: Bring this slide up when reviewing the examples from each team, so the definition is visible to all (it also helps you make sure you ask for results from each team).
Location:
Geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon (not a locality or site).

27. Number of mature individuals only
Key terms and concepts
Reduction:
A specific (%) decline in the number of mature individuals; the decline can be caused by a one-time event
Generation Length:
Average age of parents of the current cohort, reflecting the turnover rate of breeding individuals in the population
Mature Individuals:
The number of individuals known, estimated or inferred to be capable of reproduction
Extreme Fluctuations:
Population size or distribution area varies widely, rapidly and frequently, typically with a variation greater than one order of magnitude (i.e. a tenfold increase or decrease)
Population Size:
Number of mature individuals only
Note to Facilitators: Bring this slide up when reviewing the examples from each team, so the definition is visible to all (it also helps you make sure you ask for results from each team).
Subpopulations:
Geographically or otherwise distinct groups in the population between which there is little demographic or genetic exchange
Continuing Decline:
A recent, current or projected future decline which is liable to continue unless remedial measures are taken