Winter in water: differential responses and the maintenance of biodiversity

The ecological consequences of winter in freshwater systems are an
understudied but rapidly emerging research area. Here, we argue that
winter periods of reduced temperature and light (and potentially oxygen
and resources) could play an underappreciated role in mediating the
coexistence of species. This may be especially true for temperate and
subarctic lakes, where seasonal changes in the thermal environment might
fundamentally structure species interactions. With climate change already
shortening ice-covered periods on temperate and polar lakes, consideration
of how winter conditions shape biotic interactions is urgently needed.
Using freshwater fishes in northern temperate lakes as a case study, we
demonstrate how physiological trait differences (e.g., thermal preference,
light sensitivity) drive differential behavioral responses to winter among
competing species. Specifically, some species have a higher capacity for
winter activity than others. Existing and new theory is presented to argue
that such differential responses to winter can promote species
coexistence. Importantly, if winter is a driver of niche differences that
weaken competition between relative to within species, then shrinking
winter periods could threaten coexistence by tipping the scales in favor
of certain sets of species over others.