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by Michael Lau, mwnlau@kfbg.org
Many frogs are collected for food or for trade.
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The Convention on Biological Diversity adopted an
ambitious target to significantly reduce the current rate of
biodiversity loss by 2010. However, there is no simple yet
reliable way to measure rate of biodiversity loss throughout
the world because Earth's biota is extremely diverse
and complex. Despite many years of dedicated work by
taxonomists on different groups, we still cannot give an
accurate estimate of how many species there are in the
world. Advances in technology, like the use of molecular
data, provide powerful tools but they also show that our
understanding of biodiversity and evolution remains very
limited. Similarly, the status of most species, as reflected by
population size, distribution and trends, is not known and
would require tremendous effort and time to find out.
The IUCN Red List Categories and Criteria provide an
explicit, objective system for classifying species according to
their extinction risk, which can be applied consistently by
different people over different animal and plant groups. By
conducting conservation assessments at intervals, changes in
the average threat status of species can be used to monitor
trends in extinction risk and biodiversity loss. So far, birds
have been completely assessed four times and amphibians
once. By 2010 these two groups will have been re-assessed
once more while mammals, reptiles, freshwater fish, sharks,
rays and chimeras, freshwater molluscs and many plant
groups will have been completely assessed once. The Red
List Index (RLI) has been developed based on the Red
List1,2 to illustrate the rate of change in overall threat status
in a particular group, and is being used to track progress
towards the 2010 Target.
Rhacophorus yinggelingensis
- a recently discovered tree frog from Yinggeling Nature Reserve, Hainan
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Ideally RLI would be applied to all taxonomic groups
in order to gain an insight into the global trends of
biodiversity but this is not possible for less well-studied
and/or diverse groups such as fungi and insects. A sampled
RLI (SRLI) has been developed in which a random or
representative sample of species from major taxonomic
groups is selected and these will be assessed at regular
intervals.3 This sampled approach will allow a greater
range of species to be incorporated in the measurement
of changing biodiversity so that it is more representative geographically, taxonomically and by threat level.
Amphibians are a diverse group with over 5,700 species
occurring in many different habitats across all continents
except Antarctica. They form important links in food webs
and in the movement of organic matter from the aquatic to
the terrestrial environment, when tadpoles metamorphose
into young adults. Amphibians are good indicators of
environmental health because of their biphasic life cycle,
permeable skin and unshelled eggs, each of which makes
them especially susceptible to environmental change. They
are often the first group of animals to decline noticeably
when the environment is degraded.
Figure 1. Red List Index for
birds in different biogeographic realms, under the revised formulation;2 an RLI value of
1.0 equates to all species being categorised as Least Concern (not threatened). Tropical Asian
birds show the steepest declines in status. Reprinted from Butchart et al. 2007 with kind
permission of the first author.
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The IUCN Global Amphibian Assessment was completed in 2004. Every known amphibian species (5,743 species altogether) in the world was evaluated using the IUCN Red List criteria.4 The findings were worrying. At least nine species had gone extinct since 1980, 32% were threatened with extinction and 43% of all species had suffered population decline,5 showing that amphibians are in more trouble than other vertebrate groups. A preliminary RLI was carried out for the amphibians and the index value had decreased by 13.7% during the period from 1980 to 2004, equivalent to approximately 30% of the species in each category, from Near Threatened to Critically Endangered, being up-listed by one category.3
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