Dear list-members

A week or so ago I enquired about whether measuring gene flow was a practical
possiblity for determining dispersability of dead wood dependent invertebrates,
fungi, bryophytes etc in the context of forest management in Tasmania, or
whether ecological methods were more appropriate. I received over fifty
responses, and felt it would be worth summarising the main points here. We're
now hoping to develop pilot projects to follow up on some of these leads.

With many thanks to all those who responded.

Simon Grove

.........................................................

From the range of responses, there are research groups and individuals working
on aspects of this subject at various places around the world, with key projects
in Australia and Fennoscandia - some of which are potential future
collaborators. There was some indication in the responses and in the literature
referred to, that dispersability was more likely to be a limiting factor (in
managed forests at least) for some invertebrate groups, and rather less so for
fungi and bryophytes, where substrate availability per se may be more important.
Having said that, most studies are confined to the commoner species which lend
themselves best to statistical analysis; it is reasonable to suppose that rarity
itself may sometimes be a symptom of poor dispersability.

There is a general feeling from respondents that a combination of genetic with
ecological (observational and experimental) approaches is most likely to give
the clearest assessment of dispersability. Genetic methods can give wonderful
results (especially, it seems, for fauna studies), but are best interpreted in
conjunction with data from ecological methods - though the latter become very
difficult in complex natural forest settings. Most genetic methods (other than
microsatellites) tend to reflect past dispersal over many generations, whereas
ecological methods can tell you what's happening currently. But some genetic
methods can tell you whether dispersal has been followed up by breeding, which
is difficult to ascertain using ecological methods. Using multiple gene markers
is better than single ones ("genotype flow" rather than gene flow).

Not all species are suitable for study - many may be too rare, too
small/cryptic, or too poorly known (taxonomically, genetically or ecologically).
But it remains important to minimise bias by working on an ecologically
appropriate cross-section of biota.

A. Genetic methods

1. Allozymes - relatively quick and dirty; can be adequate for some taxa but a
bit hit-and-miss (has worked well for an Australian wood-living cockroach and
for some Australian aquatic invertebrates and frogs); requires fresh material
2. Microsatellites - increasingly popular due to greater precision and wider
availability of suitable techniques (PCR etc), but takes time and money,
especially if there are no suitable DNA primers available for the taxa under
study; works with spirit-preserved material; good at picking up short-term and
small-scale dispersal patterns; proven to work well with some Australian CWD
invertebrates
3. Mitochondrial DNA - better for longer-term processes and larger distances;
works with spirit-preserved material

B. Non-genetic methods

1. Mark-recapture methods (fluorescent/phosphorescent dyes, radioactive
isotopes, laser-marking) - suitable for invertebrate studies (but difficult in
natural forests)
2. Spore/diaspore traps for fungi and bryophyte studies - deposition from spore
"rain" onto agar plates or inoculated wood discs; for fungi, prime traps with
homokaryotic mycelia and then check cultures for heterokaryon arising through
colonisation of another strain (again, difficult in natural forests with
multiple sources)
3. Bait-logs for studies of invertebrates, fungi and bryophytes - infer
dispersability by seeing what arrives at logs placed at varying distances from
likely source populations, and in what order (also not easy in natural forests
with multiple sources); correlate succession with functional traits of biota
4. Transplant bryophytes/lichens to unoccupied (isolated) habitats and see if
they prosper - if so, then dispersal may have been limiting
5. Survey/sample distribution of key biota within forests with differing
distributions of CWD, at a range of scales and distances, to look at degree of
population aggregation and to gain insights into (meta)population structures
which reflect dispersal strategies and dispersability


Dr Simon J Grove, Biology and Conservation Branch,
Division of Forest Research and Development
Forestry Tasmania, GPO Box 207, Hobart, Tasmania 7001, Australia.
Tel. 61 3 6233 8141. Fax 61 3 6233 8292.
Email: simon.grove@....
Web address: http://forestrytas.com.au/