Chisholm Ryan, Taylor Robert
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08540, USA.
Conserv Biol. 2007 Dec;21(6):1641-5. doi: 10.1111/j.1523-1739.2007.00815.x.
The critical weight range hypothesis for Australian terrestrial mammals states that species in the intermediate size range 35-5500 g are particularly susceptible to extinction. In a 2001 study Cardillo and Bromham found no statistically significant evidence for this hypothesis and suggested that research should instead focus on why small species are resistant to extinction. We used a similar data set of body sizes of Australian mammals grouped by conservation classification, but we used test statistics (mean deviation above and below the median body size) that are more statistically powerful than those of Cardillo and Bromham (quartiles, maxima, and minima of body size distributions). We found strong evidence in favor of the critical weight range hypothesis: the body size distribution of threatened species was more clustered toward the median body size from above and below. This pattern was statistically significant at the continental scale and in the arid zone, but not in the mesic zone. Confusing statistical significance with evidence of no effect, as Cardillo and Bromham did, can have negative implications for conservation biology because it can result in failure to act when action is warranted or provision of incorrect advice that affects policy and planning decisions.
澳大利亚陆生哺乳动物的临界体重范围假说指出，体重在35 - 5500克之间的中等体型物种特别容易灭绝。在2001年的一项研究中，卡迪洛和布罗厄姆没有发现支持这一假说的统计学显著证据，并建议研究应转而关注小型物种为何对灭绝具有抵抗力。我们使用了一个类似的按保护分类分组的澳大利亚哺乳动物体型数据集，但我们使用的检验统计量（中位数体型上下的平均偏差）比卡迪洛和布罗厄姆使用的（体型分布的四分位数、最大值和最小值）在统计学上更具效力。我们发现了有力证据支持临界体重范围假说：受威胁物种的体型分布从上下两端更集中于中位数体型。这种模式在大陆尺度和干旱地区具有统计学显著性，但在湿润地区则不然。像卡迪洛和布罗厄姆那样将统计学显著性与无效应证据相混淆，可能会对保护生物学产生负面影响，因为这可能导致在有必要采取行动时未能采取行动，或者提供影响政策和规划决策的错误建议。
