[EMAIL PROTECTED] wrote: >[Spanish] for trout, the word is 'trucha'.
... except in sierra in Peru, where it can also signify a very large green frog, boiled. But back to habitats. First principle biology would suggest that one niche should support one species. This has led to what is called the "paradox of the plankton", whereby observation of the ocean - for example, where the habitat in any cubic metre of seawater is pretty uniform - nevertheless yields twenty or more plankton species, each competing for the same apparent niche. It turns out that this diversity exists because the habitat niches are created by the dynamics of the population - relative increases and decreases - and that what looks uniform in fact is not, when seen in this way. Let me park that and come back to it in a moment. Biodiversity increases from pole to equator in a fairly linear manner. There is no meaningful explanation on offer as to why tropical forests are as biodiverse as they are - the current best guess is that mutation just happens faster when a cell is hot. This said, the forest is a patchwork of tree and sub-story species which churns, slowly, in the manner of the ocean just discussed. What one finds is, therefore, patches of very similar niches in which marginally different dynamics give rise to different and locally-stable species mixes. However, if the niches are extremely similar, so will be the biological solutions to them: Bulbophyllums in Asia do pretty much what can be expected of Pleurothallids in the Americas. Consequently, one gets local patches of - let us say, Erias and Bulbophyllums - and a kilometre away, the Erias are still there but the Bulbophyllums have been replaced by Ceratostylis or Dendrochilum. And so on: very much the same kind of mat being created on the upper branches, with a gradual substitution of one of its constituents by another as one plods along. This situation changes completely, however, when the "ocean" of the forest is broken by something analogous to a sea shore: literal rocks, ground disturbance, low fertility soil. Suddenly, a host of niches appear that are very different from each other: shaded shrubs, open rock faces, grassland... and into these emerge an equally large number of orchids, themselves highly differentiated in size, form and floral type. One sees this in the Himalayas and the Andes, and in islands such as Borneo and Sumatra. Coastal Borneo has a repetitious orchid flora; the Crocker range has more, Mount Kinabalu and extraordinary wealth of species. Papua New Guinea shows much the same pattern. Peter O'Byrne's excellent book aside, the coastal area is not so rich, the midlands much more exciting, but with the bulk of the highland biomass in some places being made up of (not very visually exciting) orchid species. Orchid diversity does not exactly follow that of plant species in general, therefore, as it tends to peak in the equatorial regions, but at an altitude of 1000-2500m and in places where fertility is otherwise low. I suspect that this occurs because (epiphytic) orchids are slow growing opportunists, something of a contradiction in terms. That is, they rely on their extraordinary ability to survive extremes of drought and nutrient scarcity in order to prosper where others cannot, or upon their efforts by hitching a ride into the sky, to the light and away from herbivores. For this to work, their hosts have to be slow growing, or their habitat-rocks have to be immune to smothering rivals. Poor or rocky soil and relatively cool conditions all deliver this, whilst fast churning tropical lowland forest does not do so. One notes that oil palms (with a 25 year life) support few orchids, but that coconut palms (nearer 50 years) do; and that rubber plantations - which let in much more light than oil palms, but which have similar life spans - have intermediate levels of colonization. (e.g. Acriopsis, Thecostele, Cymbidium sp.. Dendrobiums.) This has got far too long. My apologies: my point is that we really do not understand orchid ecology at all well, and if that is the case, then we cannot really understand their cultivation either. Certainly, we no longer follow the C19th habit of darkened, blindingly hot stove houses - supposedly imitating the jungle from which all orchids were said to have come - but we have yet to emulate the realities which one finds on the ground: cycles of extreme drought, very bright light, extremely active insect and other life in the rhizosphere. And do we need to do so? Looking at my dark green, fleshy and probably over-lush (and chronically non-flowering) orchids in cultivation, I do wonder if I am not stressing them enough! ______________________________ Oliver Sparrow +44 (0)20 7736 9716 www.chforum.org _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
