Survival leads to unexpected ties in nature

Voles are a type of short-tailed mouse that, when it's snowy out, inhabit the subnivian zone, which is the network of small caverns that is generated within a snowpack.

In this subnivian zone, temperatures remain within a degree or two of freezing, warm enough for the voles to wander around and chew on the bark of young trees right up to the snow line. Snug and warm with full tummies, voles become reproductive superstars. A well-fed vole can bear up to 17 litters a year -- about 85 babies a year, give or take.

But nature often has another role for the vole, and that is to convert tree bark and other vegetation to protein in the body of a vole. It then becomes a staple in the diet of many predators like the fox, the weasel and the coyote.

Life out there in the cold hills is a battle for food. And the ability of one species to make a go of it, to succeed at adapting to a harsh winter environment, usually means at least several other species can survive as well. Because in nature, things are connected, often in ways you don't see.

Uncommon bonds

The very small and mostly invisible often are linked to the big and wondrous if you know where to look.

Voles are linked to foxes as well as tree bark. Tree bark is linked to soil content and the ability of nitrogen to fix to trees roots. This fixing is courtesy of a certain kind of bacteria. Without this bacteria, tree roots wouldn't be able to fix, or take, nitrogen from the soil. And bark would mostly be a thing dogs do.

To link these strategies then, we have: bacteria learning to live in the soil and forming a relationship with tree roots to take nitrogen out of the air; tree roots bringing that nitrogen to the body of the tree to help make tree bark; voles nibbling at that tree bark in the winter -- under cover of snow -- to live and multiply; and foxes and weasels nibbling on voles.

Those are four connections in which the dumbest of the lot -- bacteria -- is connected to a pretty crafty creature, the fox.

Connection is probably the weakest word we could use. Nitrogen-fixing bacteria are intimately linked to a fox's survival. Without these particular kind of bacteria, the ability of a vole to eat tree bark -- and thus survive the winter -- would be in doubt.

A pinch of soil between your fingers can contain as many as a million different kinds of bacteria, not just the nitrogen-fixing kind. Many of these kinds of bacteria play a role in other types of animal and plant life.

Think about that next time you're digging in your garden or playing in the dirt.

Phil Helfrich is an area agent with the Missouri Department of Conservation. Some information is from "Winter World -- The Ingenuity of Animal Survival" by Bernd Heinrich.