The tundra biome, encompassing both the Arctic and high-elevation Alpine regions, is defined by extreme environmental conditions, including frigid temperatures and permafrost. This permanently frozen ground prevents deep root growth and proper drainage. This harsh environment results in a very short growing season, typically lasting only 50 to 90 days, creating challenges for organisms to secure nutrition. Survival in this treeless environment hinges on specialized feeding and energy storage strategies developed to cope with scarcity.
The Foundation Tundra Plant Life
The base of the food web consists of vegetation adapted to grow low to the ground, often forming a dense, protective carpet. Due to the permafrost, plants are restricted to the shallow “active layer” of soil that thaws briefly in the summer, forcing them to develop tiny, shallow root systems. Primary producers are predominantly slow-growing, low-lying species such as mosses, sedges, and grasses.
Lichens, a symbiotic organism of fungus and algae, are particularly significant and are often referred to as reindeer or caribou moss. They can grow on rocks and exposed surfaces where soil is minimal. Dwarf shrubs, including species of willow and birch, also survive by hugging the ground, which protects them from strong winds and helps them conserve heat. These resilient plants must complete their entire reproductive cycle during the short summer.
Diets of Primary Consumers
A variety of herbivorous animals, or primary consumers, rely directly on this limited vegetation for survival. Large grazers like caribou and musk oxen consume sedges, grasses, and the leaves of dwarf shrubs during the summer months. In winter, they switch their diet to less energy-dense but more accessible food sources, digging through snow to find lichens and mosses.
Smaller mammals, such as lemmings and voles, remain active throughout the winter by living in the subnivean zone, the space between the ground and the snowpack. They forage on the roots and underground stems of grasses and sedges, which are insulated by the snow layer. The low nutritional density of tundra plants requires all herbivores to graze continuously and build thick layers of fat reserves for warmth and energy during the long periods of food scarcity.
Diets of Secondary Consumers
The predators and scavengers of the tundra, known as secondary and tertiary consumers, have diets centered around the populations of primary consumers. Small rodents, particularly lemmings and voles, are keystone prey species whose population cycles heavily influence the success of many predators. Arctic foxes primarily hunt these small mammals, along with arctic hares and birds.
Predatory birds, such as the snowy owl, also depend heavily on lemmings; their breeding success is directly tied to years of high rodent abundance. Larger carnivores, like the Arctic wolf, prey on caribou and musk oxen, often targeting the old, young, or weak individuals. In coastal regions, the top predator is the polar bear, whose specialized diet consists almost entirely of fat-rich marine mammals, predominantly ringed seals.
Seasonal Shifts in Food Availability
The drastic difference between the brief, light-filled summer and the long, dark winter forces nearly all tundra animals to adopt seasonal feeding strategies. Summer brings an explosion of plant growth and an abundance of insects, allowing animals to rapidly gain the fat reserves needed for the coming cold. Migratory birds arrive during this time to feast on insects and breed, departing before the heavy snows.
Animals that remain year-round must change their behavior as winter sets in and fresh food sources disappear. Arctic foxes switch to scavenging carrion left by larger predators or cached food, sometimes following polar bears to feed on seal scraps. Large grazers rely on their ability to locate and excavate lichens beneath the snow, while small burrowing rodents continue to feed under the insulating snowpack. These seasonal changes in diet and foraging technique are fundamental to the survival of the entire tundra food web.