Biodiversity requirements for self-sustaining space colonies

Human colonization of space or other planets is often justified as a bet-hedging strategy, an effort to avert human extinction in the event of a catastrophe on Earth. To fulfill this bet-hedging role, space colonies would need to be self-sustaining in the sense of providing long-term support for human life in the absence of material or technological inputs from Earth. Existing life support systems and experiments with closed ecological systems have demonstrated the difficulty of attaining such self-sufficiency. Natural ecological systems persist in the long-term by incorporating a high level of biodiversity, providing functional redundancy and adaptability in the face of changing conditions. Humans will invariably bring a diverse assemblage of microbial species with them into space, and macroscopic species can serve a variety of resource-provisioning or ecosystem-regulating roles. I suggest that a high degree of biodiversity will be required to assemble truly self-sustaining ecological systems capable of providing for long-term persistence of human populations. The spread of Earth's biodiversity carries ethical implications which deserve careful consideration.