Plant-and-Animal Communities (continued)

The Water Communities

Snowfields begin again their summer-long melt. The alpine stream, vocal again, collects its water from a thousand places. Miniature gorges drain the meadow, gurgling with the sparkle and rush of meltwater in the lengthening spring days.

Gathering volume, the stream seems to hurry faster; at the first rock staircase, it begins to sing. I follow the gully downward, drawn like the water. There is excitement in the growing dash and roar, a wind-gust sweeping spray into the air. A rainbow appears, holding steady to the swirling cloud of spray, then doubles and abruptly disappears.

At the first great plunge the water lunges outward over the lip. Like glass at shattering, long shards lance out. But the wind feathers the sharp edges as they fall.

The close thunder of a waterfall beats at your head, and your mind must shout to think. Here is water, a most amazing and most important substance. Perhaps some of this same water was once part of the ancient sea in which was laid down the mud-stone of this ledge; was once drunk by dinosaurs; has coursed the globe countless times; and has flowed in this very stream before. In solid, liquid, or gaseous form, it goes through its own cycle. Together with sunlight, water makes possible and maintains all life on Earth.

Ouzel Music

A glacier might cling to a winter snow a hundred years and turn it to ice, a blue tool to rasp and pluck at rocks, before letting it go. Lingering summer snowfields might delay its passage for a time. But the water always wins at last, becoming, in one decisive instant, liquid again, and beginning its long journey to the sea. Plants and dry air will intercept some of its molecules, sending them back into the atmosphere to bloom as fog and cloud; but as rain, snow, or dew, these are soon commissioned to the land again.

Water is so familiar to us that we seldom think about it. We know that fish swim in the lower lakes, and we are vaguely aware of the bewildering assortment of life-forms abounding in a pond. But life begins in the streams.

Even cups of cold meltwaters, scooped out of a rivulet only a few meters away from its snowbank source, contain some life. Snow algae, which grow on the snowbank surface, often sufficiently dense to give the snow a distinctive red complexion, are released into the meltwater. In summer, small invertebrate life can be discovered in the standing pools of even the highest cirque.

But conditions are not good for the development of complete aquatic food chains in the streams and lakes of higher elevations. Alpine lakes, or tarns, support little visible life. Often flanked by high ridges and peaks, many tarns receive scant direct sunlight during the day. Since these lakes occupy basins that capture tremendous amounts of snowfall, the snowbanks persist in the mountain shadows, and summer makes little progress in warming the water. Iceberg Lake, for example, is seldom free of floating ice, and its temperature never rises above 4° C in summer, even at the surface.

Moving out of the cirque lakes, water is soon churning again, dashing downward many hundreds of meters to the valleys below, in rapids, cascades, and breathless waterfalls. Not surprisingly, few plants and animals are adapted to life in fast-moving water.

Algae can be found covering streambed rocks and stranded, water-polished tree trunks. Securely attached by holdfasts, these small plant forms survive the rigorous stream flow that would destroy the larger vascular plants. Several species exist, from microscopic forms to branched filamentous algae whose long hairlike strands wave in the current.

A surprising number of insects live on the stream bottom, finding a measure of protection from the current in the jumble of rocks. Underwater beetles live under the gravel or among the debris at the stream-edge, or cling to stones and sticks. Scurrying and creeping among the rock-crannies are the larvae of stoneflies, mayflies, and caddisflies. These and the small fish that venture up from lower lakes are the food of the water ouzel, a creature that loves the places where the waters thunder.

The noise of the water is overpowering. A slip into this boiling rage would mean quick death. Looking 10 meters across the dim, mist-slippery, water-scoured canyon, I see a young water ouzel peering out of its unique nest, on the lookout for its parents. Clouds of spray keep the nest of living moss continually wet; but this bird is waterproofed with an oily plumage and keeps its vigil at the nest opening. Peering into the torrent below, then upstream and downstream, it awaits patiently the delivery of the next meal.

With the approach of one of the adults, three other heads crowd the opening, begging yellow mouths agape. Flying low, the ouzel parent zeros through the heavy spray, alighting on a slippery boulder below the nest ledge. Preparing to fly up to the nest with its load of insect larvae, the ouzel spots me across the water. At its sharp jigic, jigic alarm, the bills of the young snap instantly shut. Nervously the bird regards my close presence, dipping its entire body rapidly up and down, as if keeping time with the surging torrent.

Discovering no danger, the dusky blue-grey bird bobs more slowly. The other adult, returning from an upstream forage, alights on the same rock, occasioning a new outcry from the fledglings. Each in turn, the parent birds fly up to feed their young, beating their wings to maintain their position at the perchless nest. Not pausing to regard me further, they split the stream between them again, one flying upstream and one down, to continue the hunt. Blinking and shaking the collected mist from its bill, the single young sentry renews its watch.

In Shallow Waters

Life abounds in the shallow lakes and ponds. Calm, protected Johns Lake offers a fine example of how a complex aquatic plant-and-animal community can exist in balance in a confined space. The water teems with the microscopic algae, protozoans, and rotifers that sustain the barely visible zooplankton. Dancing, flitting, hopping, and swaying through the water, these zooplankton in turn support the larger plankton-eating animals.

Dragonflies and damselflies shoot past, crackling their wings, and perch in the bog grass. Looking into the shallow water, you will see a wealth of small animal life. A spotted frog swims into view, floating to the surface beside a lily pad so that its eyes protrude above the water.

The ribbonlike form of a leech swims across the bottom toward deeper water. Looking closer, you see that the water swarms with bizarre shapes—water boatmen propelling themselves with oarlike appendages, a gliding mayfly nymph, then a predacious diving beetle surfacing, grasping a bubble of air beneath its shiny brown wing plates and disappearing downward again—the bubble's edge shining silver—into the brown bottom debris. Suddenly a whirligig beetle sets the surface to spinning, wrinkling the view below.

Everywhere in the water there is animal life, forms that are attached, free-swimming, crawling on the bottom, and clinging to or swimming on the surface film. The gray, slimy encrustation on a sunken log looks like a covering of lichen but is really a freshwater sponge, a colonial animal that feeds by filtering minute plankton from the water. Another attached creature is the barely visible hydra; this twig-shaped predator, related to marine jellyfish, captures water fleas and other small animals in its several poisonous tentacles.

Water beetles, backswimmers, water boatmen, and many other creatures move about more or less freely in the water, propelling themselves along with jerky movements. Suspended between surface and bottom are the zooplankton, the tiny water fleas, cyclops, daphnia, and others, which feed by filtering minute algae. On the bottom and below live scavenging worms. Water striders skate on the surface film.

Along the shore, frogs, salamanders, garter snakes, and water shrews are hunting. Dabbling and diving ducks patrol about, tipping or submerging for the bottom plants. Moose tracks circle the muddy shore. Because it produces vegetation abundantly, John's Lake sustains a great diversity of animal life.

Beaver Ponds

Fully 10 percent of all the present meadow area in the Rocky Mountains is estimated to have been created by heaver, the only animal besides man that engineers extensive changes in the environment to suit its own needs.

When beavers dam a stream, they set in motion another form of succession. If the resulting backwater floods a forest area, the trees are soon killed, creating a broad opening in the forest canopy. Water-associated plants and shrubs quickly invade the pond and shoreline, creating favorable habitat for waterfowl, moose, blackbirds, amphibians, wading birds, warblers, marsh hawks, and a score of other animals.

After many years the water becomes shallow, filling in with silt and plant debris. When the beavers abandon the site, the dam may rupture for lack of maintenance and the pond will rapidly drain. Or it may continue to hold, delaying for several more years its slow conversion to meadow. Stimulated by the nutrient-rich mud, the water grasses, sedges, and shrubs finally choke the water with their accumulating debris, transforming the area into a bog.

Gradually the ground firms as more humus is created and more silt is trapped. The area becomes meadow, supporting grasses, sedges, and other flowering plants. Trees begin to reinvade the drier ground, and eventually the meadow reverts to forest. Centuries may be required to see this cycle through, from forest to pond, to bog, to meadow, to forest again. At each stage many of the animal inhabitants change: the song of the western robin and the chatter of a red squirrel in the original, pre-beaver forest give way to the croak of a heron; the heron is replaced by the insect-and-berry-eating cedar waxwing; the waxwing is followed by the tree-dwelling western robin and red squirrel.

Lakes Cold and Deep

Seeming to skate on its own reflection, a spotted sandpiper comes in low over the quiet water, wingtips almost touching the surface of the lake. It alights at the shore and folds its wings. Amid the rounded rocks, this plain but elegant little shorebird is all but swallowed up. Teetering constantly on long legs, it sets off along the water's edge, pecking here and there, coming closer and closer, never forgetting to stop and curtsy, as if acknowledging, while hurrying offstage, the applause of an audience.

As it draws near, several water striders skate away from the shore. A stonefly, scuttling between two rocks, is deftly speared. So large a morsel makes the bird pause and rough its feathers, then scamper into the water to take a drink. Teetering again, it passes in front of me and continues down the shore, where I soon lose sight of it rounding a rocky point.

I am sitting at the foot of Lake McDonald, watching the darkness gather over the valley, seeing the last light slide upward to the tips of the distant mountains. As daylight dissolves, this long fleet of familiar peaks seems almost to glide toward darkness, slow and silent as sailing ships.

The sheet of motionless water stretches many kilometers away between tree-covered moraines. The water is deep and cold. No emergent plants line the barren shore. It would seem that no life, except for the single gull that rests on the water far away, exists in this nearly thousand-meter-high lake.

Considering the great volume of Glacier's large, deep lakes, the life they support is indeed meager. A large part of the reason lies with the nature of their shores, where almost no plants grow. A combination of factors prevents the development of a lush shoreline growth.

Contoured like bathtubs, these steep-sided lakes exhibit narrow or non-existent shoreline shallows, which are vital for the production of rooted plants. Strong wave action and extensive seasonal fluctuations in the level of these natural reservoirs prevent the development of emergent water plants in locations where they might otherwise be expected.

Since sunlight cannot penetrate to the bottom of these deep lakes, they are deprived of bottom-anchored plants in midlake as well. As a result, herbivorous animal life must depend almost wholly on algal growth. Wave action inhibits the spread of free-floating algae by washing much of it onto the shore. Deep lakes are also low in available oxygen, preventing the development of bottom decomposers, which would rapidly release nutrients as they break down the accumulating debris washed into the lake. Without a steady supply of nutrients, plant growth is retarded.

Since the food chain depends upon green plants, the ability of a lake to support higher animals such as fish depends upon its ability first to produce adequate plant growth. The production of one kilo of trout requires that a lake produce about 1,000 kilos of plants to support 100 kilos of herbivorous invertebrates, which are eaten by 10 kilos of carnivorous insects, on which the trout feed.

Compared to smaller shallow lakes, which teem with visible life, cold, deep, nutrient-poor lakes such as McDonald appear to be watery deserts. Yet because of their great volume—Lake McDonald contains 5 or 6 cubic kilometers of water—these large lakes do sustain significant numbers of fish. Of the 22 kinds of fishes found within the park, most are coldwater species. Trout, whitefish, grayling, suckers, minnows, and carp fill the roles of herbivore, carnivore, and scavenger. Agile, highly mobile, and acutely sensitive, fish represent the most successful total adaptation to the aquatic environment.

Through the stocking of nonnative species, including plantings in formerly fish-free lakes, the natural aquatic communities of many of Glacier's lakes and streams have been permanently modified.

Aquatic food chains are not confined to the water. Ospreys, ducks, mergansers, otter, mink, and many other semi-aquatic or terrestrial birds and mammals utlilize the plants and animals of the water. In fall, a remarkable spectacle occurs along the outlet of Lake McDonald. Attracted to the kokanee salmon concentrations, which run from Flathead Lake to spawn and die in these clear, shallow waters, bald eagles collect to exploit the vulnerable fish. In 1977, 444 eagles were counted in one census. This food resource is also exploited by grizzlies, coyotes, skunks, gulls, loons, and other animals. On occasion, even whitetail deer have been observed swallowing salmon!