1.A recent study has provided clues to predator-prey dynamics in the late Pleistocene era. Researchers compared the number of tooth fractures in carnivores that lived 36,000 to 10,000 years ago and that were preserved in the Rancho La Brea tar pits in Los Angeles. The breakage frequencies in the extinct species were strikingly higher than those in the present-day species.
In considering possible explanations for this finding, the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples. They rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits. They ruled out local bias because breakage data obtained from other Pleistocene sites were similar to the La Brea data. The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores—in particular, more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species. Such thorough carcass consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and a high rate of carcass theft due to relatively high predator densities.
近期的一项研究为更新世后期食肉动物的捕食动态提供了线索。就食肉动物牙齿的磨损情况,研究者在现今食肉动物和生活在3600到10000年前的食肉动物(遗存于洛杉矶的拉布雷亚牧场沥青坑中)之间做了对比。这些已灭绝物种的牙齿破损发生率要明显高于现存物种。 在考虑对这一发现各种可能的解释时,研究者排除了统计偏差,因为年老个体没有过多占据化石样本总体。排除了可能因保存不当造成的偏差,因为两个完全没有破损的灭绝物种化石表明磨损不是由坑中的摩擦造成的。排除了地域性偏差,因为从其它更新世发掘地获得的数据与拉布雷亚的数据相近。而后研究者得出了他们认为最合理的解释——是因为灭绝物种和现存物种行为上的差异,尤其是由于已灭绝捕食者对猎物更彻底的啃食,使其牙齿与猎物骨头有更多的接触。研究者由这种彻底的啃食行为推断,不是猎物太少(至少是季节性的),就是捕食者太多,以致猎杀时有激烈的竞争和频繁的猎物盗取。 |