From: andrewt@watson.ibm.com (Andrew Taylor)
Subject: rainforests and diversity
Date: Mon, 16 Nov 1992 05:08:14 GMT
Disclaimer: This posting represents the poster's views, not necessarily those of IBM
Organization: IBM T.J. Watson Research Center

In article <STEINLY.92Nov13121933@topaz.ucsc.edu> steinly@topaz.ucsc.edu (Steinn Sigurdsson) writes:
>Not necessarily true, there was a recent paper in Nature I believe
>that argued that rainforest diversity was overestimated and that
>grasslands were actually more diverse.

This seems unlikely. Certainly, in terms of raw species diversity rainforests
are much richer. I would think they would be also richer in most other
interesting measures of diversity. Particular groups, such as reptiles,
may well be more diverse in grasslands. Do you have a ref. for the paper?

>Most ecosystems vary considerably on evolutionary time
>scales and the species within experience a range of conditions
>to adapt to, further, the set of species which is critically
>dependent on a particular feature of an ecosystem is small (although
>they do make very nice examples for PBS specials), most adaptation
>is incidentally appropriate to a range of conditions and species
>can often occupy different niches as conditions change, sometimes
>sub-optimally in some limited sense, sometimes they thrive, indeed may
>do better than in the niche they evolved in.

Your assertion is too vague and sweeping to evaluate but if you are trying
to suggest that most *species* occupy niches with only a few critical
variables and that hence we are under-estimating their ability to
adapt to anthropogenic change, I think you are wrong.

It is difficult to make statements about the set of all species.
We neither know (to an order of a magnitude) how many species there are 
nor what proportions various groups are of these species. However, the work
of Terry Erwin and others suggest there are a great number of tropical
arthropod species each occurring only on a single species of tree.
Erwin suggests there could be 30 million such arthropods, others
believe 5-10 million may be more accurate.

Whatever there number, these arthropods certainly constitute a significant
fraction, if not the majority, of the world's species and clearly they are
critically dependent on at least one eco-system feature, their tree.

Arthropods specific to a tree species will only constitute a small
fraction of the arthropod species that occur in that tree species but it is
in this small fraction that the diversity lies.

I think this will apply to other groups of species and other eco-systems.
Most species in a particular location may occupy niches constrained in only
a few variables but it will tend to be the few species (in that location)
occupying heavily-constrained niches which are important to global diversity.

The adaptability of tropical forest species is somewhat moot as the usual
anthropogenic change is complete destruction of the forest.  The burning
question is how long can diversity persist in the islands of forest that
remain (and the prognosis seems dim).  In a few areas even this is a moot
point as no forest at all remains.

Andrew Taylor
Newsgroups: sci.environment