o_19ko2dt161ng2j4e1tgnoqv1s45a.pdf

C. LUSTY, W.A.N.AMARAL, W. D.HAWTHORNE, L.T. HONG & S. OLDFIELD (2007)
example, this knowledge is confidently or partly known for perhaps 100 or so tropical trees in
total, which have been the focus of detailed studies—for lesser known species defining
subpopulations remains highly assumptive, based less on measurement and more on the
assessors willingness to make a judgement based on general ecological knowledge of the
taxonomic group and the presumed extent and distribution of subpopulations. Similarly putting
an estimate on the age of ‘mature individuals’, as a basis for estimates of population size, or
the ‘average age of parents’, the unit for estimating the timeframe within which population
reductions are measured, are challenging for the vast majority of tropical plant species,
especially as these values may not be constant throughout the range of a species.
There are some criteria that are more lenient than others at allowing the use of inference or
proxy data. There are defined terms of assessment based on an increasing degree of assumption:
• Observed is based on firm data.
• Estimated is based on data with an allowance of statistical estimation or assumptions
about observed variables (e.g. indices of abundance) and the measure variable (number
of mature individuals). Estimations are also projected into the future.
• Inferred is a calculation based on indirect evidence but at least within the same units of
measurement (e.g. population declines based on rate of habitat loss). Inferences may also
be made when imposing trends from certain subpopulations to infer the status of lesser
known subpopulations and the global population as a whole.
• Suspected is a type of inference that is based on indirect evidence concerned with another
unit of measurement (e.g. population declines based on changes in habitat quality).
A first step to approaching the Red Listing process might be to realize the potential of the
available dataset and work with the criteria that are suited to the levels of assumption that are
required. For criteria C1 and for D (categories of ‘Endangered’ and ‘Critically Endangered’)
population size must be estimated, whereas criterion A allows the use of proxy data to infer
population reductions.
RULES OF THUMB AND USING PROXY DATA
Rules of thumb can help to tighten the definitions for defined groups of species or geographical
areas so that assessments can be made using a common understanding. Rules of thumb are
“rules of general guidance that are based on experience or practice rather than theory”. They
represent a pragmatic approach to dealing with limited information or circumstances. In the
case of the Red List categories they potentially help to improve replicability, consistency and
Ways of dealing with lack of data:
• estimations, projections, inferences, and suspected trends, including:
– the use of proxy data
– extrapolation from known subpopulations to less well-known subpopulations
– ecological inference from close relatives to less well-known species
• using criteria which are more accepting of qualitative data e.g. A & B
• describing range values and giving best estimates
• establishing rules of thumb
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