Kenagy G J
Department of Biology, University of California, Los Angeles, California, USA.
Oecologia. 1976 Jun;24(2):105-140. doi: 10.1007/BF00572754.
Populations ofDipodomys microps andD. merriami in eastern California (37°11'N. Lat.) are active on the surface throughout the night and during the whole year. These two species, and the males and females within each species, show no significant differences in times of beginning or end of activity. Beginning and end of nightly activity generally fall within the brighter part of the twilights, even though the total time spent on the surface by individuals is at times only an hour or two, or even less, per night. Near the summer solstice in southern Saskatchewan, Canada (50°45'N. Lat.), when sunset and sunrise were 7 h 43 min apart, the time from onset to end of activity in a population ofD. ordii (the northernmost of all kangaroo rats) was only 6 h; these animals were also only on the surface at intervals during the night.During the course of the year, the light intensity at which the first individualD. microps andD. merriami became active on the surface varied between 200 and 2,000 lux, and the light intensity at which the last individual was active in the morning varied between 50 and 20,000 lux. There was no apparent influence of the moonlight cycle upon the onset and end of activity; in fact the light levels at beginning and end of activity are about 2 to 4 orders of magnitude brighter than that at full moon. The onset of activity is fairly synchronous within the population in that most individuals surface within about a fhalf hour of each other; furthermore, two-thirds of the individuals appearing in the first 32 min of activity had already appeared within the first 12 min. There appears to be a similar, synchronous, but less well marked end of activity in the morning.There were systematic seasonal changes in the time relative to sunset and sunrise respectively, and in the corresponding light intensities, at which the animals began and ended activity. The phase relationship between the onset of activity and sunset (ψ ) showed tow maxima and two minima per year, but the phase relationship between the end of activity and sunrise (ψ ) showed only one maximum and one minimum per year. On the other hand, the annual range of change in the evening phaseψ (28 min) was half the annual range of change in the morning phaeψ (57 min). Such a conspicuous difference in frequency and amplitude ofψ andψ has not previously been reported for any species, nor has it been predicted by models of circadian rhythms and phase relationships. The resemblance of the course of annual change inψ to annual change in length of twilight and the resemblance of annual change inψ to change in length of night are discussed. These differences may underline a circadian system based on two separate, but normally coupled components, which could be separately synchronized by dusk and dawn respectively.The daily running-wheel activity of 10 individually housedD. merriami under natural skylight in Los Angeles (34°05'N. Lat.) began and ended at light intensities two to three orders of magnitude lower than corresponding values for surface activity in the field. The onset and end of activity for the captive population did not show the synchronous peaks typical of the field populations; nor did the nightly activity patterns of individuals show peaks at the beginning and end of the night. The social isolation of the captive kangaroo rats is suggested as a factor contributing to differences between activity parameters in captivity and field.Proximate and ultimate factors shaping the periodicity of activity in kangaroo rats are discussed. It is hypothesized that social interactions involving some form of territoriality may give rise to a population peak in onset of activity in some solitary mammals such as kangaroo rats. A set of criteria is presented for comparing vertebrate species with regard to the periodicity and synchronization of both daily and seasonal functions.
在加利福尼亚州东部（北纬37°11′），微小更格卢鼠和梅氏更格卢鼠种群全年整夜都在地面活动。这两个物种以及每个物种中的雄性和雌性，在活动开始或结束时间上没有显著差异。夜间活动的开始和结束通常在黄昏较明亮的时段内，尽管个体在地面上花费的总时间有时每晚只有一两个小时，甚至更少。在加拿大萨斯喀彻温省南部（北纬50°45′）接近夏至时，日落和日出间隔7小时43分钟，奥氏更格卢鼠（所有更格卢鼠中最靠北的物种）种群的活动从开始到结束时间只有6小时；这些动物在夜间也只是间歇性地出现在地面上。在一年的过程中，第一批微小更格卢鼠和梅氏更格卢鼠开始在地面活动时的光照强度在200至2000勒克斯之间变化，而早晨最后一批个体停止活动时的光照强度在50至20000勒克斯之间变化。月光周期对活动的开始和结束没有明显影响；实际上，活动开始和结束时的光照水平比满月时的光照水平亮约2至4个数量级。活动的开始在种群内相当同步，因为大多数个体在彼此大约半小时内出现在地面上；此外，在活动的前32分钟内出现的个体中有三分之二在最初的12分钟内就已经出现了。早晨似乎也有类似的、同步的但不太明显的活动结束。相对于日落和日出的时间以及相应的光照强度，动物开始和结束活动存在系统性的季节性变化。活动开始与日落之间的相位关系（ψ）每年有两个最大值和两个最小值，但活动结束与日出之间的相位关系（ψ）每年只有一个最大值和一个最小值。另一方面，傍晚相位ψ的年度变化范围（28分钟）是早晨相位ψ年度变化范围（57分钟）的一半。此前尚未有任何物种报道过ψ和ψ在频率和幅度上如此明显的差异，昼夜节律和相位关系模型也未对此进行预测。文中讨论了ψ的年度变化过程与黄昏长度年度变化的相似性以及ψ的年度变化与夜晚长度变化的相似性。这些差异可能突显了一个基于两个独立但通常耦合的组件的昼夜节律系统，这两个组件可能分别由黄昏和黎明同步。在洛杉矶（北纬34°05′）自然天光下单独饲养的10只梅氏更格卢鼠的每日转轮活动开始和结束时的光照强度比野外地面活动的相应值低两到三个数量级。圈养种群的活动开始和结束没有表现出野外种群典型的同步峰值；个体的夜间活动模式在夜晚开始和结束时也没有出现峰值。圈养更格卢鼠的社会隔离被认为是导致圈养和野外活动参数差异的一个因素。文中讨论了塑造更格卢鼠活动周期性的近端和远端因素。据推测，涉及某种形式领地行为的社会互动可能导致一些独居哺乳动物如更格卢鼠的活动开始出现种群峰值。提出了一组标准，用于比较脊椎动物物种在日常和季节性功能的周期性和同步性方面的情况。
