狼群經(jīng)常被描繪成一種合作狩獵的模式,，然而并非所有的灰狼（Canis lupus）都會(huì)一起合作捕獲它們的獵物,。
根據(jù)日前發(fā)表在《行為生態(tài)學(xué)》雜志上的一項(xiàng)研究結(jié)果，一些狼竟然也吃白食,。
研究人員通過(guò)對(duì)生活在美國(guó)黃石國(guó)家公園中的狼群進(jìn)行研究后發(fā)現(xiàn),，隨著狼的數(shù)量的增加，狼群捕獵的成功率并沒(méi)有像預(yù)期那樣增加,；與此相反的是,，一旦它們的數(shù)量超過(guò)4只，其捕獵成功率便會(huì)呈現(xiàn)出平穩(wěn)狀態(tài),。
這似乎是因?yàn)榇笮屠侨褐型鶗?huì)有那么幾個(gè)吃白食的家伙——它們通常都是那些不用養(yǎng)育后代,，因此也就不用冒著生命危險(xiǎn)供養(yǎng)幼崽的狼。
黃石灰狼恢復(fù)項(xiàng)目的生物學(xué)家Daniel Stahler指出,，這些不勞而獲的狼貌似也會(huì)參與捕獵的合作,，但直到殺死獵物之前，它們實(shí)際上只作出了非常小的貢獻(xiàn),。
這樣一來(lái),，它們也能夠像一個(gè)大家庭的成員那樣一道參加周末的晚宴——這些家伙大多數(shù)只知道吃，但絕不會(huì)把家里的培根也帶過(guò)來(lái),。（生物谷 Bioon.com）
doi:10.1093/beheco/arr159
PMC:
PMID:
Nonlinear effects of group size on the success of wolves hunting elk
Daniel R. MacNultya, Douglas W. Smithb, L. David Mechc, John A. Vucetichd and Craig Packera
Despite the popular view that social predators live in groups because group hunting facilitates prey capture, the apparent tendency for hunting success to peak at small group sizes suggests that the formation of large groups is unrelated to prey capture. Few empirical studies, however, have tested for nonlinear relationships between hunting success and group size, and none have demonstrated why success trails off after peaking. Here, we use a unique dataset of observations of individually known wolves (Canis lupus) hunting elk (Cervus elaphus) in Yellowstone National Park to show that the relationship between success and group size is indeed nonlinear and that individuals withholding effort (free riding) is why success does not increase across large group sizes. Beyond 4 wolves, hunting success leveled off, and individual performance (a measure of effort) decreased for reasons unrelated to interference from inept hunters, individual age, or size. But performance did drop faster among wolves with an incentive to hold back, i.e., nonbreeders with no dependent offspring, those performing dangerous predatory tasks, i.e., grabbing and restraining prey, and those in groups of proficient hunters. These results suggest that decreasing performance was free riding and that was why success leveled off in groups with >4 wolves that had superficially appeared to be cooperating. This is the first direct evidence that nonlinear trends in group hunting success reflect a switch from cooperation to free riding. It also highlights how hunting success per se is unlikely to promote formation and maintenance of large groups.
