  The recent realization that entire communities fuse and separate (community
coalescence) has led to a reappraisal of the forces determining species
diversity and dynamics, especially in microbial communities where coalescence
is likely widespread. To understand if connectedness by coalescence results in
different outcomes from connectedness by individual dispersal, we investigated
chance processes leading to loss of species diversity using a model of a
neutral two-species metacommunity. Two scenarios were investigated: pairwise
coalescence where the communities coalesce in pairs, intermix and then
separate; and diffuse coalescence where several communities mix as a pool and
are re-distributed to their original patches. When standardized for the same
net movement, both types of coalescence led to a longer time to single species
dominance than dispersal. Coalescence therefore may be an important process
contributing to the surprisingly high microbial species diversity in nature.
