Pikas Pick Phenol-Heavy Plants to Preserve
A blog? What do you mean I have a blog? Oh…this blog. Right. Sorry folks (and by “folks”, I mean the five people a week my traffic counter says still visit this dry and forsaken land), apparently consistency is not my strong point! But since I’m currently unemployed I really have no excuses to not get back in the swing of science blogging. So to celebrate my return to the internets, I’m going to start with a little post on one of my favorite local mammals: the pika!
Most of you probably know this, but despite how adorably mousy our fluffy pika friends look, they are actually not rodents. They are lagomorphs (bunny relatives), and they live in alpine habitats – mainly over about 8,200 feet in our area. There are 30 known species of pika, but only two in North America, and the American Pika (Ochotona princeps) is the one most people are familiar with (Ochotona collaris lives in Alaska and Canada), so that’s the one I’ll be talking about.
Pikas are really quite amazing because they live in extremely inhospitable areas – cold climate, high elevations, and steep, rocky talus slopes. In many parts of their range the growing season is only about two months long, and as herbivores who rely mainly on grasses and forbs (herbaceous broad-leaved plants) they pretty much have to gather and store ten months worth of food in those two months, as well as continuing to feed themselves and put on weight for the winter at the same time. The activity of gathering food to store for later is called “haying” (insert image of pika in overalls and holding a pitchfork here).
If you see a pika on a hike, chances are it has a mouthful of grasses or leaves that it’s taking to cache in various locations beneath the rocks. One study found that pikas make around 14,000 trips to gather food over an 8-10 week season! Storing food for the long cold season is vital for them because, unlike so many other small mammals that live in similar conditions, pikas don’t hibernate. They are active all year long, even if most of that time is spent being active under the snow, in their talus slope burrows. While they do manage to collect some food during that time, in the form of lichen and evergreen plants, the main source of sustenance comes from their food caches.
But, as you might imagine, storing food for 10 months or more can be a problem, particularly when what you’re storing is leafy plant material. Plants decompose, they get moldy and develop bacteria, they lose nutritive value. How can a pika possibly ensure it has food stored that will keep all year?
Well, the genius of the pika is that it turns the plants’ own defenses against them. Plants don’t like having their leafy parts eaten, because it reduces their ability to photosynthesize, so they have evolved countless ways of discouraging predation by herbivores, and the herbivores have co-evolved countless ways overcoming those defenses. One of the main ways plants make themselves undesirable or inedible is to produce toxic compounds, the most common of which are tannins and other phenols, which make them unpleasant to eat and difficult or impossible to digest. Some animals have evolved a resistance to these compounds, such as enzymes or gut bacteria that help break them down, but the pika does something else entirely.
In the summer months, the pika will gorge itself on plants that are low in phenolic compounds, as they are readily digestible. But it will select a range of plants to store for later that are higher in phenols. The pika won’t eat these plants immediately, it caches them for the winter. The reason for this is that phenolic compounds don’t just discourage predation, they also act as a preservative. Plants higher in phenols don’t decompose as quickly as the more immediately-desirable kinds. What’s more, as they age, the toxins break down as well, rendering them edible and what’s more, more nutritious than plants stored for the same time that were low in phenols to begin with.
Turns out pikas can tell the difference between plants with high and low phenol levels; even when they are presented with a choice of plants which are the same species but individually have differing phenol levels, pikas selected the lower level plants for immediate consumption. This is a fantastic strategy for a creature like the pika. They eat the most nutritious and digestible food first, then move on to the other plants as they become more consumable over time, while at the same time ensuring they have supply of food throughout the whole winter and that it will remain nutritious and safe to eat (due to anti-bacterial and anti-fungal action of the phenols). The pika has completely co-opted the plant strategy for it’s own benefit.
Sadly, these little guys may be among the species most effected by climate change, as warming temperatures reduce their habitat and force them to move to higher elevations to combat the heat. However, in the past year there has been new evidence of pikas living at lower elevations than it was previously thought that they could tolerate, so perhaps the pika is even more adaptable than we think. Given their clever food storage habits, it wouldn’t surprise me.