Comment on "Patterns of diversity in marine phytoplankton".

Barton et al. (Reports, 19 March 2010, p. 1509) argued that stable conditions enable neutral coexistence of many phytoplankton species in the tropical oceans, whereas seasonal variation causes low biodiversity in subpolar oceans. However, their model prediction is not robust. A minor deviation from the neutrality assumption favors coexistence in fluctuating rather than stable environments.