Phylogeny and Conservation

[Peter Rauch]

[Please reply to Paul Williams and/or the list, not to me. Peter]
---------- Forwarded message ----------
Date: Thu, 29 Jan 1998 17:57:21 +0000
From: Paul Williams <P.Williams at nhm.ac.uk>

  ...snip, snip...

If it were possible to send the message below on to the TAXACOM list to
speed up my response to this discussion of our work, I would be very
grateful.

Many thanks
Paul Williams
____________________________________________________________________________

As some of those responsible for the 'lots of paper' to come out of the
'British Museum' on the subject of phylogeny and conservation, we thought
that perhaps it would be useful to clarify what we actually argue.  More
detail can be found on web pages at
http://www.nhm.ac.uk/science/projects/worldmap.

We have followed Stuart Poss's recommendation of an interdisciplinary
approach, working with philosophers, economists, decision support
specialists, systematists, ecologists, and of course, conservation
biologists.  There seem to be many misconceptions about this work, which we
hope may be made a little clearer below.  Part of this may arise from the
different languages spoken within these disciplines.  Because of the volume
of the responses, please forgive us if we have missed other points.

Much of the tension between conservation biologists and others (insofar as
they are different) concerned with the conservation of biodiversity (in the
sense of the variety of organisms) seems to come from their different
attitudes to value and priority.  Conservation biologists often value
threatened species, and equate this value with priority.  For biodiversity
(variety) people, value is derived from the assessment of degrees of
variety within assemblages (i.e. the value is transferred to areas, not
individual species), and we contrast this with priority, which comes from
the urgency with which action is needed to conserve particularly threatened
parts of this variety in particular areas.  The two may result in different
rankings among sites, though it is agreed that high priority sites require
more urgent action.
e.g. Biological Journal of the Linnean Society, 58: 125-157(see p. 132).

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To pick up on some of John Shuey's points from the first message:

1. Our starting point was the need for quantitative methods in order to
ensure EFFICIENCY for selecting areas to represent biodiversity in the face
of competition for resources.  A quantitative approach would also have the
advantage of ACCOUNTABILITY, so that people giving conservationists their
mandate could see that their values were being used to make appropriate
decisions and that their resources were not being squandered.  Methods are
now developing that can answer the question 'with a budget of X DOLLARS,
which areas could add the greatest representation of biodiversity to an
existing network of protected areas?'  Many aspects of these methods
(especially ecological aspects) still need research and it is currently a
very active area.

2. Area selection for conservation may be seen as being about the
persistence VALUE.  There are many possible values in need of conservation,
and different people hold different values.  One subject to which value is
attached is BIODIVERSITY.  In one step towards this, people have sought one
currency (others may be possible) of biodiversity (variety) value that can
be MAXIMALLY represented in a network of protected areas.  The phylogeny in
conservation debate is about one way of doing this.  An assessment of
threat for urgency/priority is still needed.

3. As some have said, initially the use of phylogeny in conservation is a
theoretical discussion of how to identify a CURRENCY of biodiversity
(variety) value.  However, it could have very practical consequences if
people truly wish to conserve as much biodiversity (variety) value as
possible.

Biodiversity is often defined in terms of the VARIETY of organisms.  One
source of value to people in this variety arises from the OPTION VALUE of
different expressed or expressible genes for future use or evolution.

We have argued that in consequence it is the expressed or EXPRESSIBLE GENES
that are important, not any unexpressed variation.  We cannot usually count
these directly.  Phylogenetic approaches are important in this context only
insofar as they are the best way we know (because of homoplasy) to predict
from a small sample what the distribution of the entire 'population' of
different valued genes is among organisms.
e.g. Biodiversity Letters, 2(1994): 67-78.

In consequence, the phylogenetic approach is not about focussing on the
value of individual species, but is about the total variety value of a set
of organisms within a set of areas.

4. In practice, such detailed information is rarely available.
Nonetheless, this currency provides one approach with an explicit and
consistent basis for looking at other ways of comparing the value of
different assemblages.  Where SURROGACY or indicator relationships can be
shown, such as the predictiveness for this value of numbers of species,
numbers of higher taxa, numbers of habitat types or whatever, then these
more practical approaches can be used with the added justification that
they represent variety or option value.  We have been interested in whether
a whole range of approaches based on taxa, assemblages, and environmental
variables might be viewed as a scale of surrogacy for this kind of
underlying biodiversity value.  This might bring together at least some of
the pattern value (and hopefully by selecting areas with assemblages of
species, indirectly some of the process aspects) across the levels of
genetic, species and ecosystem diversity.  Much more work needs to be done
on the conditions required for these surrogates to be useful.
e.g. World Conservation, 1: 12-14.
e.g. pages 54-76 in: Biodiversity: a biology of numbers and difference. K.
J. Gaston (ed. 1996). Blackwell Science, Oxford.
e.g. Trends in Ecology and Evolution, 12: 66-67, 12: 444-445.

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To pick up on some of Daniel Barker's points:

1. Working from this idea of option value for future use or evolution, we
recommended the use of only expressed or expressible genes as a currency.
This is important because these may show a very different pattern of change
through time among lineages to unexpressed and selectively neutral changes,
thereby strongly affecting the branch lengths for these changes on the
trees.  Thus the phylogenetic approach requires (i) a phylogenetic
topology, (ii) an evolutionary model for the distribution of value across
that topology, and (ii) a measure of that predicted value for a particular
subset (assemblage) of species.
e.g. Biodiversity Letters, 2(1994): 67-78.

2. We believe that phylogeny is likely to be a better predictor than
phenotype classification of the overall differences of value among
organisms because of HOMOPLASY.  The need for using phylogenetic pattern is
to enable data from small samples of genes or characters to be used to
predict the overall distribution of all valued genes or characters (most of
them unsampled) across the phylogeny, and so to compare richness in this
relative value among different assemblages of organisms.
e.g. Trends in Ecology and Evolution, 12: 444-445.

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To pick up on some of Stuart Poss's points:

1. In practice, we need predictors or surrogates for a fundamental currency
of value that cannot usually be measured directly.  The expressible genes
argument can add an additional justification to using other more practical
approaches.  Without measures of value, we cannot judge efficiency and so
whether or not other approaches are 'better'.
e.g. World Conservation, 1: 12-14.

2. Using phylogenetic measures is not about targeting 'favourite' species,
it is about comparing the relative combined value of different assemblages
of species (usually in particular areas) as directly as possible.

3. The approach we have pursued is aimed at capturing areas with the
greatest differences and variety of organisms first, then 'filling in'
areas later with more similar organisms as opportunities arise.

4. The utilitarian interpretation of option value is based on maximising
representation of variety precisely because of the uncertainty as to which
parts will be most useful and valuable in the future.  Because of this
uncertainty, all parts have to be valued equally, and the the best
conservation strategy is then to protect as many parts as possible.
e.g. pages 54-76 in: Biodiversity: a biology of numbers and difference. K.
J. Gaston (ed. 1996). Blackwell Science, Oxford.

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To pick up on some of John Shuey's points from the second message:

1. The phylogenetic approach is not about targeting single species, but
about the relative value of assemblages.  In principle, it might be
extended to justify using community types as surrogates, whereupon we are
probably in agreement.

2. The phylogenetic approach is not about single or unique species, but
about the relative variety value of an assemblage of organisms within a set
of areas.
e.g. pages 54-76 in: Biodiversity: a biology of numbers and difference. K.
J. Gaston (ed. 1996). Blackwell Science, Oxford.

3. Using Complementarity to represent species automatically focusses on
narrow endemics because they are necessary to ensure complete or efficient
representation of the variety.  This is actually used explicitly as a
heuristic device by many area selection algorithms.

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Paul Williams, Miguel Araujo, Dick Vane-Wright, Chris Humphries


**********************************************************
NEW - measuring biodiversity value & conservation priority
http://www.nhm.ac.uk/science/projects/worldmap
**********************************************************
Biogeography & Conservation Laboratory
Department of Entomology
The Natural History Museum
Cromwell Road, London SW7 5BD, UK