List of skbio changes that might affect QIIME 2

[qiyunzhu]

Lots of changes are being made since skbio 0.5.9. This issues records changes that might break or alter the behavior of QIIME 2 (q2). The skbio team will work the q2 team to ensure compatibility in future skbio and q2 releases.

• Alpha diversity metric observed_otus is deprecated (Replacing observed OTUs with richness #1902). It doesn't affect q2 now. But if it is removed in the future, q2 will need to make a change.