S ome principles of ecology

Ecologists are often employed to solve serious environ- mental problems. Early in this century, for example, southern Ohio was ravaged by a terrible flood. The inhabitants of the area, determined to prevent a repetition of the disaster, constructed large earthen dams across the valleys north of Dayton to contain future floodwaters. Since the slopes of these dams consisted of gravel with an admixture of clay, they washed away easily. It was necessary to stabilize the steep slopes quickly with plant cover. Knowing which plants would grow best in such places, an ecologist recommended the scattering of alfalfa and clover seed, followed by brome grass and Japanese honeysuckle. His recommendations were followed, and dam slopes were soon covered with a fine cohesive turf. Many of the hills on neighboring farms lacked such cover and were quickly eroded. In the Dust Bowl region of Texas, sandy soil in dry areas blew into great dunes after the land was plowed for wheat. Bulldozing these dunes was thought too expensive. However, an ecologist recommended that certain plants be raised near the shifting dunes. The plants in front of the dunes caught and held the soil, while those behind them kept the rear from blowing deeper. In a short time, wind had leveled off the high dune tops and vegetation had anchored the soil.

Applications of ecology

E cology and Wildlife Conservation Measures for the preservation of ducks and other migratory wild fowl are examples of ecological work with animals. When these birds grew scarce, state and federal agencies sought ways to protect them and help them reproduce. At first, laws were recommended that forbade shooting the birds in the spring when they were flying north to nest. Every female killed in the spring could mean one less brood returning in the fall. Further studies showed that many of the birds' breeding places were being destroyed when the land was drained for other uses. Some of these sites were not well-suited for the sustained growth of crops; others, where marshes and potholes once released stored water slowly, now contributed to downstream floods. Draining thus had a doubly harmful effect. Ecologists captured the endangered birds and put aluminum bands on their legs to trace their breeding places and movements. In this way it was discovered that the problem was international. As a result, the United States began to work in close cooperation with Canada and Mexico for the protection of migratory birds. Ecologists also investigated the food habits of birds. They recognized that if proper food was unavailable, the birds would disappear even if hunting was regulated. Experts examined the stomach contents of thousands of birds from many different areas. This work led to the finding that bird food consists mainly of plant materials that thrive under natural conditions. To ensure the availability of these materials, man had to cease altering many natural communities and to stop polluting them with his wastes. By the 1970s ecologists had accumulated considerable evidence demonstrating that the widely used pesticide DDT and its metabolites, principally DDE, altered the calcium metabolism of certain birds. The birds laid eggs with such thin shells that they were crushed during incubation. This discovery was one of many that led to the imposition of legal restraints on the use of some agricultural pesticides. Ecologists know that the well-being of a biotic community may require the preservation of a key member-species. For example, the alligator performs a valuable service in the Florida Everglades by digging “'gator holes.” These are ponds created by female alligators when they dig up grass and mud for their nests. During extremely dry spells, these holes often retain enough water to meet the needs of bobcats, raccoons and fish until the arrival of rainy weather. Many birds use the holes for watering. Willow seeds take root along the edges, and fallen willow leaves later add substance to the soil. Thus, many forms of life are sustained by 'gator holes. But poachers have been hunting the alligators almost to extinction for their valuable hides. As a result, the number of 'gator holes can be expected to dwindle, and various forms of Everglades wildlife may be deprived of these refuges. Such ecological findings strengthen the case for the protection of alligators. (See also Conservation, “Wildlife Conservation.”) Another ecological threat to the Everglades arose in the late 1960s, when plans were made to build a jet airport near the northern end of the national park. The airport would have wiped out part of a large swamp that furnishes the Everglades with much of its surface water. Ecologists and conservationists opposed the project, arguing that it would hamper the flow of surface water through the park and thus endanger the biota of the unique Everglades ecosystem. Their arguments aroused public concern, and in 1970 plans for the airport were dropped.