The IUCN Red List of Threatened Species™
Red List Criteria: Criterion A
Criterion A
Time
Population Size
Past, present or future population reduction
Criterion A
To use criterion A, we first need to know:What is the generation length? Or is it likely that a three generation time period is less than 10 years?
Time
Population Size
3 generations or 10 years (whichever is the longer)
Criterion A
Based on any of four criteria:
* Up to a maximum of 100 years into the future
Timing of Reduction Reduction Conditions
Past Future Causes Understood
Causes Stopped
Effects are reversible
A1
A2
A3 *
A4 *
Criterion A
Example: a whale
• Generation length ~ 31 years
• Population decline 70-90% over past 3 generations. Populations appear to be recovering.
• Population declines caused by commercial whaling:o Cause and effects of decline is fully understoodo Commercial whaling has stoppedo Pop decline appears to be reversible
• Percentage decline based on:o Whale sightings and observationso Stock monitoring surveys and reportso Whaling statistics and records
• Given uncertainty in the decline and current stability and population recovery, is listed as EN.
EN A1abd
CR/EN A1
CR/EN A1dCR/EN A1bCR/EN A1a
Example: a tree
• Generation length unknown; ~ 50 years in similar species
• Endemic to dry forest, which have been intensively cut for agriculture over last century. Today only highly fragmented forest patches remain, and suffer:
o Intense predation from deer and cattleo Uncontrolled fires
• Estimated 95% habitat loss over past 150 years: given population densities & distribution, suspected population decline of at least 50%.
• Habitat loss ongoing. Regeneration close to zero due to intensive grazing; seeds also consumed by butterfly larvae – suspected population decline of up to 80% over next 100 years.
• Population decline rate based on:o Massive habitat losso Introduced predators
EN A2
CR/EN A3
A2+3cA2+3e
EN A2+3ce
Criterion A
Near Threatened (NT) example:
Should be close to meeting the VU thresholds or possibly meet some of the subcriteria
• Population has declined by 20-25% in the last three generations• Causes of the decline are not understood and appear to be ongoing
(i.e. the population is still declining)NT, nearly meeting VU A2
• Population has declined by 40% in the last three generations• Causes of decline are understood, the causes have stopped, and the
decline is reversible.NT , nearly meeting VU A1
Criterion A
Criterion A4past & future: “shifting time window”
10 years / 3 generations10 years / 3 generations
Present
10 years / 3 generations
Criterion A
Past census data gathered every 2
yrs
Reduction rate over
next 30 yrs
Estimated future populations
Year Population size
Year Population size
1970 10,000 33% 2002 6,160
1972 10,000 38% 2004 5,680
1974 10,000 43% 2006 5,260
1976 10,000 47% 2008 4,900
1978 10,000 51% 2010 4,600
1980 10,000 54% 2012 4,600
1982 9,940 56% 2014 4,180
1984 9,820 57% 2016 4,060
1986 9,640 58% 2018 4,000
1988 9,400 57% 2020 4,000
1990 9,100 56% 2022 4,000
1992 8,740 54% 2024 4,000
1994 8,320 52% 2026 4,000
1996 7,840 49% 2028 4,000
1998 7,300 45% 2030 4,000
2000 6,700 40% 2032 4,000
PresentReliable data
available
If a “moving-window” reduction cannot be calculated over the full time series:
Criterion A4past & future: “shifting time window”
Most confident 10 year / 3 generation time period
Criterion A
3 generations? 10 years?
To use criterion A, an estimate of the generation length is needed
Population reduction may be a one-off event...
... Or it may be ongoing
Points to remember:
Criterion A
Criterion A1 uses higher thresholds than A2, A3 and A4
Points to remember:
Criterion A
A3 = projected FUTURE reduction so cannot be based on direct observation (A3a)
Points to remember:
Criterion A
Consider the pattern of population reduction
Points to remember:
Criterion A
Refer to User Guidelines and ‘CriterionA.xls’ for information and advice