Variability in Population Abundance and the
Classification of Extinction Risk
HOWARD B. WILSON, BRUCE E. KENDALL, HUGH P. POSSINGHAM
Conservation Biology, Volume 25, Issue 4, pages 747–757, August 2011
In conservation
practice it is standard practice to Classify species
according to their risk of extinction. The reliability of the classification
depends on the accuracy of threat categorizations. When it comes to errors in the process we
have very limited info. It involves getting information from many sources.
Understanding the quality of each source is de rigueur to evaluate the
overall status of the species.
One common criterion used to classify
extinction risk is a decline in abundance. Abundance is a direct measure of
conservation status. So counts of individuals are generally the preferred method
of evaluating whether populations are declining.
Using the thresholds from criterion A of the
International Union for Conservation of Nature (IUCN) Red List (critically
endangered, decline in abundance of >80% over 10 years or 3 generations;
endangered, decline in abundance of 50–80%; vulnerable, decline in abundance of
30–50%; least concern or near threatened, decline in abundance of 0–30%), the
researchers assessed 3 methods used to detect declines solely from estimates of
abundance
1)
Use of just 2 estimates of abundance
2)
Use
of linear regression on a time series of abundance;
3)
Use of state-space models on a time series
of abundance.
The researchers
generated simulation data from empirical estimates of the typical variability
in abundance and assessed the 3 methods for classification errors.
The estimates of the proportion of falsely
detected declines for linear regression and the state-space models were low
(maximum 3–14%), but 33–75% of small declines (30–50% over 15 years) were not
detected. Ignoring uncertainty in estimates of abundance (with just 2 estimates
of abundance) allowed more power to detect small declines (95%), but there was
a high percentage (50%) of false detections. For all 3 methods, the proportion
of declines estimated to be >80% was higher than the true proportion
The researchers conclude that use of
abundance data to detect species at risk of extinction may either fail to
detect initial declines in abundance or have a high error rate.
No comments:
Post a Comment