Shifting prey selection generates contrasting herbivore dynamics within a large-mammal predator-prey web
by
Owen-Smith N, Mills MG.
Centre for African Ecology, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Wits 2050, South Africa. Norman.Owen-Smith@wits.ac.za
Ecology. 2008 Apr;89(4):1120-33.
ABSTRACT
Shifting prey selection has been identified as a mechanism potentially regulating predator-prey interactions, but it may also lead to different outcomes, especially in more complex systems with multiple prey species available. We assessed changing prey selection by lions, the major predator for 12 large herbivore species in South Africa's Kruger National Park. The database was provided by records of found carcasses ascribed to kills by lions assembled over 70 years, coupled with counts of changing prey abundance extending over 30 years. Wildebeest and zebra constituted the most favored prey species during the early portion of the study period, while selection for buffalo rose in the south of the park after a severe drought increased their vulnerability. Rainfall had a negative influence on the proportional representation of buffalo in lion kills, but wildebeest and zebra appeared less susceptible to being killed under conditions of low rainfall. Selection by lions for alternative prey species, including giraffe, kudu, waterbuck, and warthog, was influenced by the changing relative abundance and vulnerability of the three principal prey species. Simultaneous declines in the abundance of rarer antelope species were associated with a sharp increase in selection for these species at a time when all three principal prey species were less available. Hence shifting prey selection by lions affected the dynamics of herbivore populations in different ways: promoting contrasting responses by principal prey species to rainfall variation, while apparently being the main cause of sharp declines by alternative prey species under certain conditions. Accordingly, adaptive responses by predators, to both the changing relative abundance of the principal prey species, and other conditions affecting the relative vulnerability of various species, should be taken into account to understand the interactive dynamics of multispecies predator-prey webs.
‘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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