“No moon is an island”...or is it? Investigating the possibility of metacommunity dynamics in the Solar System

Abstract

The core theory of Island Biogeography (Core IBT) has informed ecological thought for over half a century and has inspired several other ecological theories. Although the original IBT was concerned with dispersal of biota from species-rich ‘mainlands’ to islands surrounded by water, its authors pointed out that the principles underlying the theory were applicable to any patch of habitat surrounded by a matrix of inhospitable habitat. The fundamental simplicity and robustness of IBT also suggests that the model can scale upwards or downwards whilst retaining the same basic predictions. While the upscaling of IBT to the postulated interplanetary transfer of biota is not a new concept, discussions for the time being are mainly theoretical and have been useful in identifying key processes and filters. We propose to expand on previous discussions by postulating the application of metacommunity paradigms to possible interplanetary dispersal. In this case, the habitat patches would be planets or their moons, whilst the ‘inhospitable matrix’ would be interplanetary space. The species-rich ‘mainland’ is currently represented by Earth, the only solar system body that has, to our knowledge, abundant and diverse surficial life. The other planets and moons of the solar system are considered as ecological ‘islands’ and are possible targets for colonisers. On a ‘local’ within-patch scale, biogeographical dynamics comprise well-characterised processes of dispersal, colonisation and extinction. In this context, dispersal across terrestrial continents would still be considered a local event at this scale and would presumably be subject to natural selection. On a ‘regional’ (interplanetary) scale, successful dispersal-colonisation across patches now represents an extraordinary event that is almost entirely stochastic, passive, and not necessarily subject to natural selection. The main ecological filter operates during interpatch transfer of propagules. The abiotic conditions characterising ejection from the mainland (emigration), interplanetary transport (dispersal) and deposition in a sink patch (immigration) restrict these processes to a very small subset of potentially-tolerant terrestrial prokaryotes.