On specialists and generalists: niche range strategies across the tree of life

Generalists can survive in many environments whereas specialists have a limited distribution. Although a classical concept in ecology, niche breadth has remained challenging to quantify because it depends on an objective definition of the environment. Here, by defining the environment of a microbe as the community it resides in, we integrated information from over 22 thousand environmental sequencing samples to derive a quantitative social niche breadth score for all microbial taxa. At the level of genera, we explored niche range strategies across the tree of life. We found that generalists include opportunists that stochastically dominate local communities, while specialists are stable but low in abundance. Generalists have a more diverse and open pan genome than specialists, but we found no global correlation between niche breadth and genome size. Instead, we observed two distinct evolutionary strategies, where specialists have relatively small genomes in habitats with low local diversity, but relatively large genomes in habitats with high local diversity. Together, our global analysis shines a new, data-driven light on microbial niche range strategies.