Further notes on Rain pools

 Here I make some points which I had missed, or failed to emphasise previously (see [1] and Blog 28/12/2010). First, in terms of species composition and by contrast with those on soil [2], rain pools on rock are characterised by high density mono-cultures of  the larvae of indigenous insect species, typically those of  chironomid species.Small habitat patches like these rain pools, seem too small to provide barriers to gene flow upon which speciation commonly depends. The presence of a single species in each pool could therefore have been be predicted. The same is true of the fish populations of some very small lakes in Cameroon which, by contrast to the massive adaptive radiation seen among the cichlid flocks of the larger African lakes, are each inhabited by a single fish species [3], pp 200, 201. Such monocultures are the hallmark of the extreme habitats and are termed extremophiles [4]. Extremophiles provide the focus for exobiology – the search for life elsewhere in the universe. Perhaps, in a sense, parasites could be included here. The reason for this suggeston is that parasites are typically likewise confined to a single host where adaptive evolution has enabled them to circumvent formidable host defences. When occupation of a host is achieved there is no interspecific competition for the rich host resources leading to high density monocultures, ecologically equivalent to the high invertebrate densities of rain pool faunas.

Second, in terms of duration, rain pools on rock can useful to compare cecidomyian gall midges inhabiting mushrooms. Like rain pools mushroom provide a transient habitat because they are consumed by the inhabitants. The strange adaptive consequences are described by Gould [5], p93. I do not detail them here but it is worth reading Gould's account for its heuristic value. 

1.         McLachlan, A.J. and R. Ladle, Life in the puddle: behavioural and life-cycle adaptations in the Diptera of tropical rain pools. Biological Reviews 2001. 76: p. 377-388.

2.         Williams, D.D., The Biology of Temporary Waters. 2006, Oxford: Oxford University Press.

3.         Coyne, J. A. (2009). Why Evolution is true. Oxford University Press, UK.
4.         Nee, S., Introducing the extremophiles. Vol. 448. 2007, London: Nature.
5.         Gould, S, J. (1980). Organic Wisdom. Or Why Should a Fly Eat its Mother From Inside. In: Ever Since Darwin. Reflections in Natural History. Penguine Books.