quote:CHAPTER 2 THE ECONOMY OF NATURE [T]he study of the regulation of animal numbers forms about half the subject of ecology, although it has hitherto been almost untouched. CHARLES ELTON
... Charles Elton is nowhere near as famous as Darwin or Malthus, but he is known to biologists as the founder of modern ecology, and the central mystery that gripped him was how the numbers of animals are regulated.
While previous naturalists had seen a community as one entity, or as a collection of species, Elton took a novel, functional approach. It was obvious to Elton that in the economy of Arctic islands, the precious commodity was food. So he traced where every creature’s food came from.
But the connections among the inhabitants of the tundra extended far beyond a few animals. The droppings from the seabirds contained nitrogen, which was used by bacteria, which nourished plants, which produced food for insects, both of which were consumed by land birds (ptarmigan, sandpiper), which in turn were food for the arctic fox. In this manner, the food chains in a community were connected into larger networks that Elton dubbed foodcycles, later called food webs. Elton drew a schematic of these chains and webs, the first of its kind, in a paper published with Summerhayes in 1923. (Figure 2.3)
Very readable 17 pages.
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Hairston, Nelson G., Frederick E. Smith, and Lawrence B. Slobodkin. "Community Structure, Population Control, and Competition." The American Naturalist 94, no. 879 (1960): 421-25. JSTOR: Access Check.
... known as the "Why is the world green" paper.
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quote:Reporting their results in the March issue of the British Ecological Society’s Journal of Ecology, a team lead by Professor John Terborgh of Duke University says that the role of predators is the key to keeping the world green, because they keep the numbers of plant-eating herbivores under control. Their results support the so-called “green world hypothesis” first proposed in 1960 by Hairston, Smith and Slobodkin and seem to lay to rest the competing theory that plants protect themselves from being eaten through the physical and chemical defences they have developed.
Terborgh and his team monitored the vegetation at 14 sites of differing size. Nine of the sites were on predator-free islands, while the others were on the mainland or on islands with a complete or nearly complete suite of predators. They found that by 1997, small sapling densities on small islands were only 37% of large land masses and by 2002 this had fallen to just 25%. Most of the vertebrates present in regional the dry forest ecosystem had disappeared from small islands, including fruit eaters and predators of vertebrates, leaving a hyperabundance of generalist herbivores such as iguanas, howler monkeys and leaf-cutter ants.
“Mere numbers do not do justice to the bizarre condition of herbivore-impacted islets. The understory is almost free of foliage, so that a person standing in the interior sees light streaming in from the edge around the entire perimeter. There is almost no leaf litter,and the ground is bright red from the subsoil brought to the surface by leaf-cutter ants. Dead twigs, branches and vine stems from canopy dieback litter the ground, and in places lie in heaps. But in striking contrast with this scenario of destruction, the medium islands presented a relatively normal appearance,” Terborgh says.
As well as proving that the green world hypothesis is correct, Terborgh’s results have important implications for the debate raging in many countries over reintroduction of top predators such as wolves. “The take-home message is clear: the presence of a viable carnivore guild is fundamental to maintaining biodiversity,” he says.