experimental condition	reasoning: ecological theory + application to microbiome
taxon match	organisms can become locally adapted [25]. Local adaptation of a microbial species to a given host may mean it is not adapted to hetero-specific hosts and will perform poorly after transplantation [26]
donor and recipient environment	during community assembly, the local environment acts as a filter, incorporating species from a wider species pool [21]. From the microbiome's perspective, the host's physiology and the external environment are one intertwined environment. Therefore, the external environment can affect microbiome dynamics in two ways: indirectly through impacting the host physiology [27], and directly through the wider microbial species pool that the host and its microbiome has access to
donor and recipient physiology	the local environment acts as a filter in community assembly [21]. For this experimental condition, we define physiology as physiological states that would occur regardless of the external environmental context (e.g. gene knock-out, disease-state). We differentiate intrinsic physiology from mutable host physiological responses to the external environmental context. Although these indirect environmental effects acting through host physiology are relevant [27], they are captured by the ‘environment’ experimental condition. A host's physiology is the de facto environment of inhabitant microbes, and changes or dysregulation in the host may disrupt associations between host and the microbes that persist under homeostatic physiological conditions
transplanted microbiome	the interactions within an invading community, including predation or mutualism, can impact whether colonisation is successful or not [20]. Thus, a full community microbiome transplantation may differ significantly from the transplantation of a single microbe monoculture at artificially high densities
transplant method	species have different dispersal abilities [27] and local environments filter species from the wider species pool [28]. Active transplantations may circumvent differing dispersal abilities of microbial species and may undermine host filtering of the microbial community. Furthermore, active transplant methods can stress the host thereby changing host physiology and disrupting endogenous microbial communities [29]
recipient pre-transplant microbiome	high species diversity in a community is predicted to reduce niche opportunities and to increase invasion resistance [20]. Germ-free or antibiotic perturbed recipients are likely to have lower invasion resistance than recipients with intact microbiomes
housing conditions	dispersal between patches is an integral ecological process which can maintain stable populations or can rescue extirpated populations [21,30]. Recipient host cohabitation allows for further transmissions of the microbiome.