Harmony and Conflict in the Living World - Alexander F. Skutch [45]
Among the exploiters of plants are seed-eating birds and rodents. Although some members of the large parrot family are nectar drinkers and pollinators, the majority are seed predators, using thick, doubly hinged bills to extract nutritious embryos from seed coats that are often hard. With strong, crushing bills, grosbeaks and other finches remove embryos from hard-shelled seeds. Little goldfinches and many seed-eaters that swarm in tropical grasslands prefer smaller seeds that they can swallow whole. Cross-bills with overlapping mandibles pluck seeds from the scaly cones of pines and other coniferous trees. Squirrels, agoutis, rats, and other
Page 87
rodents devour many seeds. Seed predatorsboth invertebrate, like many beetles, and vertebrate, like a number of birds and mammalsgreatly reduce the reproductive potential of the plants that supply them with rich sources of energy. However, certain jays and nutcrackers among birds, agoutis and squirrels among rodents, compensate the sources of their seeds by burying a few or many for future use. The forehanded animal may die or forget some of its hidden seeds, which upon germinating, perhaps at a distance from the parent tree or shrub, propagate the species.
Among grazers, browsers, and seedeaters are many highly gregarious mammals and birds, which through much of the year live in peace with others of their own and of different species. In general, they neither fear one another nor are feared by animals of different habits. Mutual aid in avoiding or repelling predators is frequent among them, as told in chapter 4. Conflicts arise among the males of these vegetarians mainly in the mating season, when they contend for females, often fiercely. Unless their populations become excessive, they do no great harm to the plants that support them: grasses are well able to withstand grazing; seeds of many plants are produced in such abundance that the existence of their species is not jeopardized by the consumption of many of their embryos; vigorous trees and shrubs can replace lost foliage.
More harmful to vegetation appear to be the largely terrestrial mammals and birds that dig up and devour the subterranean storage organs, rich in starch and other nutrients, of many herbaceous and suffrutescent plantstheir tubers, corms, bulbs, and thickened roots. On the whole less gregarious than grazers, browsers, and seed predators, they tend to forage alone or in small groups, which is fortunate for the plants they eat. While humans were in the hunting and gathering stage, the storage organs that they extracted from the soil with digging sticks must have contributed substantially to their diets, but the extent of this injury to vegetation is now difficult to assess. Exceedingly harmful to plants are huge animals like elephants, which, where numerous, may destroy light woodlands by pushing over small trees to supply the immense quantity of provender that each individual needs every day.
Page 88
The greatest, most destructive exploiter of vegetation, as of much else, is humankind. I refer not to agriculture, which is essentially a mode of cooperation between people and cultivated plants (although its side effects upon the native flora are often disastrous), but to the widespread destruction of trees to provide grazing for beef cattle, or to supply timber, pulpwood, charcoal, and other products. After destroying most broad-leaved forests in the North Temperate Zone of the Old World and the New, exploiters of trees and the lands on which they grow have been attacking tropical rain forests with such unrestrained greed that if this plundering cannot be halted, the forests will disappear in the next century. So great is this destruction that whole species of animals and plants are becoming extinct or have already vanished. The trees that people plant, as some slight compensation