It concerns plant, microbial and/or animal communities. This hypothesis arises from trophic, symbiotic and signalling relationships having evolved to ensure the stability of terrestrial and marine ecosystems. I think that if we are able to discern discontinuities along transects when and where the environment is continuously changing, then this would prove the existence of ecological attractors. Species, when dispersing in a heterogeneous environment, are attracted to places where they can benefit from positive interactions with other species with which they share complementary functional traits. This results in dynamically stable communities. When the environment changes (for instance in the course of global warming) there is a redistribution, species having to find new places. Some can do it, some others cannot, or can do it at a slower rate, depending on their dispersal rate. Best data would be transects (whether marine or terrestrial) with a fine resolution (in order to test for the apparence of biotic discontinuities along a continuously changing abiotic environment) and, if possible (for testing the second part of the hypothesis), repeatedly sampled in time.
One can study this problem using interpolation of data or using approximation by least squares.The methods are much.
Yes, you are right about the methods, but who could provide me with raw data, which I cannot collect by myself, being retired?
Dear Jean-François, we have a lot of data from permanent soil monitoring sites in Germany that can be arranged along environmental gradients such as soil pH, soil moisture, C/N-ratio, heavy metal content etc., mirrored by structural changes in the soil community. There are clear discontinuities, e.g. the disappearance of endogeic and anecic earthworms at critical values of soil pH. Such tipping points are accompanied by structural and functional changes of the soil community and influence decomposition processes, humus form and topsoil formation.
Article Critical values of soil acidification for annelid species an...
Dear Ulfert,
Yes I know that you have found such discontinuities in the composition of annelid communities (be sure that all your publications are well-known to me). You are one of the few soil animal scientists to have search (and given) evidence that discontinuities exist in the composition of communities and do not results from a priori classificatory systems. However, more remains to be done in this respect, in particular along spatially delimited environmental gradients, i.e; transects. Imagine (as I have the feeling it be true, based on my own field experience) that you pass abruptly from a given community composition to another while environmental conditions change monotonously. This would be a nice demonstration of the existence of ecological attractors at community level, no? There is a dearth of literature (mostly theoretical) on the matter, but nothing definitely demonstrative, to my opinion.
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