I think, in Australia there is a quite harder ecological pressure for
the development of the species; in Australia, the species have to develop
systems to survive the dry seasons; so they developped 2 main-categories
for surviving: tubers in tuberous Drosera and gemmae in pygmy Drosera;
further you find other different habitats, where could develop own
'species-complexes', like the 'D. petiolaris-complex' and the tropical
Drosera;
I also discussed that problem a little bit with Jan Schlauer and it
seems, that you can find quite 'old' species of Drosera in Australia;
here you can find the highest degree of differentiation.
As you describe, the habitats in Brasil haven't this ecological pressure;
they grow in habitats, which are quite suitable for Drosera; all the year
with cool, humid conditions; no real seasons; so it seems, that there
isn't any reason (no ecological pressure), to develop so many realy new
species; maybe, the development in Brasil is still younger as in
Australia; it seems, that some species in Brasil are at the way of
differentiation, like D. communis or D. montana (I hope that's right, I
just know it from personal communications ;-) )
If you look at another centre of Drosera, South-Africa, you see the same
phenomen as in Brasil: most of the species are still nearly related to
each other, but you can find a lot of populations of one specie with
different appearence (e.g. at D. cistiflora, D. aliciae or D.
cuneifolia); here you also have nearly all-year-round fine conditions for
the growth of Drosera, but they had to develop sometimes organs, to
survive dry seasons ('tubers' of D. cistiflora ...).
Please allow me again one question, maybe you know both regions by your
own:
Do you know, if the habitats of Drosera, Genlisea ... are quite the same
as at the sandstone-regions (Guyanas) in Venezuela? Do you know, if there
is a high degree of endemism at the sandstone-regions of Brasil?
On Mon, 22 May 1995, Fernando Rivadavia Lopes wrote:
>
>
> I was wondering if there was anyone out there specialized in
> plant ecology and who could maybe help me out. For the past few months,
> I've been discussing a question with Allen Lowrie in Australia, by
> snail-mail. We're comparing how the CPs in Australia, and especially the
> Drosera, are so diverse taxonomically and ecologically so specialized, while
> the ones here in S.America are taxonomically much more uniform and act like
> generalists, occupying a wide range of habitats over large geographical
> areas. We've been trying to come to some type of conclusion as to what
> ecological forces are involved. What factors in Australia are working on
> the local flora (CPs and others) forcing them to diversify so much and
> occupy specific soils, mostly over small geographical ranges, apparently
> having very specific pollinators and (in the case of CPs) attracting
> specific prey too? What gave them the extra push in Australia, which
> made the Drosera evolve so much and occupy new kinds of habitats,
> developing such strange structures as tubers and gemmae? What's missing
> here in South America and in other parts of the woyrld?
>
>
>
> FERNANDO RIVADAVIA
> Sao Paulo, Brazil
>
>
>
>