Small, Furry, and Integral to the Shrub Steppe By, Kristina Ernest
When we think about mammals of the shrub steppe, those that most often come to mind are deer, coyote, elk, and the elusive badger. We are less likely to conjure up the small mammals who are often not seen unless we’re paying close attention. Yet, some of the most important ecological roles in the shrub steppe are played by small mammals.
Gardeners
Consider, for example, the important job of spreading plant seeds so that new plants may germinate and grow to replace those that have died. Wind carries some seeds, but many are dispersed by small mammals like harvest mice, chipmunks, and ground squirrels. Also, pocket mice, named for their fur-lined cheek pouches into which they stuff seeds, then run those seeds into their burrows to cache for later consumption. Not all the seeds are eaten, though, and those left behind are far from the parent plant in a soil that has been enriched with nitrogen from the urine and feces of the pocket mice. If you look closely at the base of herbaceous plants (like balsamroot) and shrubs, you might see small holes slanting into the ground, which may well lead to the homes of pocket mice. Because they are nocturnal, seeing the mice themselves is unlikely unless you are wandering in the shrub steppe at night. Rest assured, though, that these little gardeners are hard at work with their furry friends planting the next generation of seeds.
Insect Patrol
Another important job in the shrub steppe is to keep insect populations in check. On the ground, shrews and moles are voracious consumers of insects and other invertebrates. Shrews are tiny mammals with long pointed noses that your cat may have brought in. But shrews are important and fascinating creatures with super high metabolic rates; to survive, they must eat at least every couple of hours, 24/7! They stay busy, running through the leaf litter, grass, and bare soil, gobbling up insects as they go. Moles, relatives of shrews, are unwanted guests in many lawns, but they are often misunderstood. They eat invertebrates, not plants, and the mounds of soil they leave behind as they burrow and forage underground are tell-tale signs of their presence. So, in addition to eating grubs and other invertebrates, they perform the important tasks of aerating the soil and mixing in nutrients.
Then, there is the aerial insect patrol-- bats! Washington has 15 species of bats, with at least half occurring in the shrub steppe region. As they swoop through the air, they are scooping up loads of insects. Some bats even pluck insects off foliage or from the ground. Bats are so important to insect control that rice farmers in California rely on them to reduce insect pests of their valuable crops. Unfortunately, bats across much of the United States are being decimated by a fungal infection in what is known as white-nose syndrome. If you visit a cave with bats, you can help prevent the spread of fungal spores that cause white-nose syndrome by carefully washing your clothing and shoes. One Washington bat species, the spotted bat, occurs in the coulee area east of the Columbia River. This is the only local bat whose echolocation calls are low enough in frequency that people can hear them clicking away (most bat echolocation calls are at frequencies above our ability to hear). Helen McCabe Park is a great place to watch bats foraging. Sit quietly near the edge of the pond just before dusk in spring, summer, or early fall, and soon you may be mesmerized by the bats swooping over the pond to gather their evening meal of insects.
Food Providers
Predators, including badgers, coyotes, hawks, owls, and snakes, must eat, and small mammals, like mice, pocket gophers, shrews, voles, chipmunks, ground squirrels, and marmots provide a much-needed food source. Many small mammals are herbivores, feeding on a variety of plant parts, including roots, leaves, stems, flowers, fruits, and seeds. If you garden, you may have noticed this in frustration over the damage they can cause to your hard labor. But in the shrub steppe, they feed on wild plants. Sagebrush voles and montane voles, for example, eat the leaves of a variety of plant species, including grasses and balsamroot. Next time you’re in the shrub steppe, look for their tunnels in the grass or burrows at the base of balsamroot. These small mammals play an important role in the food web, transferring food energy from plants and invertebrates to the larger predatory species.
Ecosystem Engineers
Healthy ecosystems function to maintain and promote biological diversity, and ecosystem health is due in large part to the work of in-house eco-engineers. Many shrub steppe areas contain conspicuous mounds of soil that look a lot like mole mounds but are actually the result of pocket gopher activity. Pocket gophers are tube-shaped rodents with big gnawing teeth and fur-lined cheek pouches. They are strict herbivores, eating only plant roots, stems, and leaves. They burrow through the soil, sometimes chewing on the roots, other times popping up on the surface to grab stems or leaves that they stuff into their cheek pouches to carry down into their burrows. Their extensive burrowing churns the soil, diversifying soil nutrients, decreasing compaction, increasing water retention, and enhancing topography across the landscape, ultimately promoting plant diversity. Gopher burrow systems can also slow soil erosion on steep slows. Thus, pocket gophers are a great example of a shrub steppe ecosystem engineer!
Another magnificent ecosystem engineer living in the shrub steppe is larger than your typical “small mammal” and spends most of its life near streams. These creatures alter the flow of water, and in the process, create a diversity of aquatic habitats that support a higher diversity of plants, insects, and fish. The ponds that they create help retain water, releasing it more slowly into the surrounding riparian area and contributing to flood control. Once nearly wiped out across much of North America, these furry animals are now seeing a come-back, with people translocating them into degraded stream areas to do their ecosystem engineering work for free. Who are these important characters? Beavers, of course!
Evasive and underappreciated, small mammals of the shrub steppe are often overlooked, despite their oversized impact on this amazing ecosystem. Join us for Get Intimate with the Shrub Steppe where we will celebrate the importance of these little ones and maybe even witness some of their important work.
