Long-term ecosystem dynamics in the Serengeti: lessons for conservation
by
Sinclair AR, Mduma SA, Hopcraft JG, Fryxell JM, Hilborn R, Thirgood S.
Serengeti Biodiversity Program, SWRC, Arusha, Tanzania. sinclair@zoology.ubc.ca
Conserv Biol. 2007 Jun;21(3):580-90.
ABSTRACT
Data from long-term ecological studies further understanding of ecosystem dynamics and can guide evidence-based management. In a quasi-natural experiment we examined long-term monitoring data on different components of the Serengeti-Mara Ecosystem to trace the effects of disturbances and thus to elucidate cause-and-effect connections between them. The long-term data illustrated the role of food limitation in population regulation in mammals, particularly in migratory wildebeest and nonmigratory buffalo. Predation limited populations of smaller resident ungulates and small carnivores. Abiotic events, such as droughts and floods, created disturbances that affected survivorship of ungulates and birds. Such disturbances showed feedbacks between biotic and abiotic realms. Interactions between elephants and their food allowed savanna and grassland communities to co-occur. With increased woodland vegetation, predators' capture of prey increased. Anthropogenic disturbances had direct (hunting) and indirect (transfer of disease to wildlife) effects. Slow and rapid changes and multiple ecosystem states became apparent only over several decades and involved events at different spatial scales. Conservation efforts should accommodate both infrequent and unpredictable events and long-term trends. Management should plan on the time scale of those events and should not aim to maintain the status quo. Systems can be self-regulating through food availability and predator-prey interactions; thus, culling may not be required. Ecosystems can occur in multiple states; thus, there may be no a priori need to maintain one natural state. Finally, conservation efforts outside protected areas must distinguish between natural change and direct human-induced change. Protected areas can act as ecological baselines in which human-induced change is kept to a minimum.
‘I’ll find an answer that’s good enough for them,’ he said to himself, as he slipped the letter into his post-box.{246} THE FERRY-BOAT. THE FERRY-BOAT. "Why, I thought it was on a hill, or something of the sort; I had no reason to think so, of course, but I had formed that picture of it." The Clockwork man shook his head. "We have houses, but they are not full of things like yours are, and we don't live in them. They are simply places where we go when we take ourselves to pieces or overhaul ourselves. They are—" his mouth opened very wide, "the nearest approach to fixed objects that we have, and we regard them as jumping-off places for successive excursions into various dimensions. Streets are of course unnecessary, since the only object of a street is to lead from one place to another, and we do that sort of thing in other ways. Again, our houses are[Pg 146] not placed together in the absurd fashion of yours. They are anywhere and everywhere, and nowhere and nowhen. For instance, I live in the day before yesterday and my friend in the day after to-morrow." This principle is somewhat obscure, and the nature of percussive forces not generally considered—a matter which may be illustrated by considering the action of a simple hand-hammer. Few [103] people, in witnessing the use of a hammer, or in using one themselves, ever think of it as an engine giving out tons of force, concentrating and applying power by functions which, if performed by other mechanism, would involve trains of gearing, levers, or screws; and that such mechanism, if employed instead of a hammer, must lack that important function of applying force in any direction as the will and hands may direct. A simple hand-hammer is in the abstract one of the most intricate of mechanical agents—that is, its action is more difficult to analyse than that of many complex machines involving trains of mechanism; yet our familiarity with hammers causes this fact to be overlooked, and the hammer has even been denied a place among those mechanical contrivances to which there has been applied the name of "mechanical powers." ‘When anyone prefers beauty to virtue, what is this but the real and utter dishonour of the soul? For such a preference implies that the body is more honourable than the soul; and this is false, for there is nothing of earthly birth which is more honourable than the heavenly, and he who thinks otherwise of the soul has no idea how greatly he undervalues this wonderful possession.’47 Monday, 3rd hour That is the truth. We left the caravan far behind. In the gorge with its rosy-pink soil the silence was exquisite, the air had the freshness of a mountain height, and quite inexplicably amid these barren rocks, where there was not a sign of vegetation, there was a scent of honey and almonds. Life went on very much the same at the post when there was only the infantry left in possession. As there was nothing to do at any time, there was nothing the less for that. On the principle that loneliness is greatest in a crowd, Stanton was more isolated now[Pg 183] than Grant had been in the days when there had been no railroad west of Kansas. The railroad was through the southwest now, but it was a hundred miles away. It was unsafe to ride outside the reservation, there was no one for hops, the only excitement was the daily addition to the list of slaughtered settlers. Felipa spent most of her time with the Ellton baby. Miss McLane had been married to Landor's second lieutenant for a year and a half, and they were very happy. But Felipa in the knowledge of the strength of her own love, which gained new might each time that she wrestled with it and threw it back upon the solid ground of duty, found their affection decidedly insipid. Like the majority of marital attachments, it had no especial dignity. It was neither the steadfast friendship she felt for her husband, nor the absolute devotion she would have given Cairness. Si strode over to the group, snatched the bat from Harry's hand, spanked him with it, and started for the others of the group. HoME日本1级:A片
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