Department of Earth and Biological Sciences, Loma Linda University, Loma Linda, CA 92350, USA.
Animalia Herpetofauna, P.O. Box 63077, Pipe Creek, TX 78063, USA.
Toxins (Basel). 2024 Mar 18;16(3):157. doi: 10.3390/toxins16030157.
Island tameness results largely from a lack of natural predators. Because some insular rattlesnake populations lack functional rattles, presumably the consequence of relaxed selection from reduced predation, we hypothesized that the Santa Catalina Island, California, USA, population of the southern Pacific rattlesnake (, which possesses a functional rattle), would exhibit a decrement in defensive behavior relative to their mainland counterparts. Contrary to our prediction, rattlesnakes from the island not only lacked tameness compared to mainland snakes, but instead exhibited measurably greater levels of defensiveness. Island snakes attempted to bite 4.7 times more frequently as we endeavored to secure them by hand, and required 2.1-fold more time to be pinned and captured. When induced to bite a beaker after being grasped, the island snakes also delivered 2.1-fold greater quantities of venom when controlling for body size. The additional venom resulted from 2.1-fold larger pulses of venom ejected from the fangs. We found no effects of duration in captivity (2-36 months), which suggests an absence of long-term habituation of antipredator behaviors. Breeding bird surveys and Christmas bird counts indicated reduced population densities of avian predators on Catalina compared to the mainland. However, historical estimates confirmed that populations of foxes and introduced mammalian predators (cats and pigs) and antagonists (herbivorous ungulates) substantially exceeded those on the mainland in recent centuries, and therefore best explain the paradoxically exaggerated defensive behaviors exhibited by Catalina's rattlesnakes. These findings augment our understanding of anthropogenic effects on the behaviors of island animals and underscore how these effects can negatively affect human safety.
岛屿温顺主要是由于缺乏自然捕食者。由于一些岛屿响尾蛇种群缺乏功能响环，据推测这是捕食减少导致选择放松的结果，我们假设美国加利福尼亚州圣卡塔利娜岛的南部太平洋响尾蛇（拥有功能响环）种群的防御行为相对于它们的大陆同类会有所减少。与我们的预测相反，与大陆蛇相比，来自该岛的响尾蛇不仅没有温顺，反而表现出明显更强的防御性。当我们试图用手抓住它们时，岛上的蛇试图咬人的次数增加了 4.7 倍，而被钉住并捕获所需的时间增加了 2.1 倍。当被抓住后被诱导咬一个烧杯时，与控制体型相比，岛上的蛇也会释放出 2.1 倍更多的毒液。额外的毒液来自于从毒牙中喷出的 2.1 倍更大的毒液脉冲。我们发现圈养时间（2-36 个月）没有影响，这表明对捕食者的防御行为没有长期习惯化。繁殖鸟类调查和圣诞节鸟类计数表明，与大陆相比，鸟类捕食者在卡塔利娜的种群密度降低。然而，历史估计证实，在最近几个世纪，狐狸和引入的哺乳动物捕食者（猫和猪）以及拮抗剂（食草有蹄类动物）的数量大大超过了大陆上的数量，因此最好地解释了卡塔利娜响尾蛇表现出的反常夸张的防御行为。这些发现增加了我们对人类活动对岛屿动物行为的影响的理解，并强调了这些影响如何对人类安全产生负面影响。
