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