Vander Wall Stephen B, Longland William S, Pyare Sanjay, Veech Joseph A
Ecology, Evolution, and Conservation Biology Program, Biology Department, University of Nevada, Reno, NV 89557, USA e-mail:
Oecologia. 1997 Dec;113(1):21-28. doi: 10.1007/s004420050349.
Rodents of the family Heteromyidae are proficient gatherers and hoarders of seeds. A major component of their adaptive specialization for harvesting and transporting seeds is their spacious, fur-lined cheek pouches. Precise measurements of cheek pouch capacities are essential if ecologists are to understand the foraging ecology, possible constraints on locomotion patterns, and competitive relationships of heteromyid rodents. To measure the size of these cheek pouches and the rate at which animals load seeds into their pouches during seed harvest, we attracted 56 individuals representing ten species of heteromyid rodents to bait stations in the field and allowed them to fill their cheek pouches with seeds several times while we observed and timed the events with the aid of night-vision equipment. The largest load taken by each individual was used as an estimate of its cheek pouch capacity. At the end of observations, each subject was captured and its mass and other data gathered. The allometric relationship between cheek pouch capacity and body mass for ten species of heteromyids was significant [pouch capacity (ml) = 0.148 body mass (g), r =0.91, P<0.0001]. The regression coefficient is ≈1.0, which indicates that the volume of the cheek pouches scales in direct proportion to body size. When the data were subdivided into quadrupeds (Perognathus and Chaetodipus) and bipeds (Dipodomys) (n=5 for each), the relationships between pouch capacity and body mass were significant, but the two regressions were not significantly different from each other. When all loads (full and partial) were considered, subjects filled their cheek pouches an average of 93 ± 10% of pouch capacity (n=185). Cheek pouch capacities from published studies of artificially filled pouches of heteromyids in the laboratory averaged about 40% below the field measurements obtained here. The allometric relationship between mean loading rate and body mass was also significant [seeds/s=1.067 bodymass (g), r =0.85,P=0.0011), but when quadrupeds and bipeds were considered separately, the relationships were not significant. Seed densities and bulk densities were used to calculate packing coefficients for seed species, which, when used in conjunction with the allometric relationship between cheek pouch capacity and body size, can be used to estimate the maximum load carried by a heteromyid. Except for the very largest kangaroo rat species, a full pouch load of Indian ricegrass seeds represents less than the daily energy requirements of an active heteromyid.
更格卢鼠科的啮齿动物是熟练的种子采集者和贮藏者。它们在适应收获和运输种子方面的一个主要特点是其宽敞且有毛衬里的颊囊。如果生态学家想要了解更格卢鼠科啮齿动物的觅食生态、对运动模式可能的限制以及竞争关系，精确测量颊囊容量至关重要。为了测量这些颊囊的大小以及动物在收获种子时将种子装入颊囊的速率，我们在野外吸引了代表更格卢鼠科十个物种的56只个体到诱饵站，并让它们多次用种子装满颊囊，同时我们借助夜视设备观察并记录这些过程的时间。每个个体所携带的最大负载量被用作其颊囊容量的估计值。在观察结束时，捕获每个实验对象并收集其体重和其他数据。十种更格卢鼠科动物的颊囊容量与体重之间的异速生长关系显著[颊囊容量（毫升）= 0.148×体重（克），r = 0.91，P < 0.0001]。回归系数约为1.0，这表明颊囊的体积与体型成正比。当数据细分为四足动物（粗尾更格卢鼠属和鬃尾更格卢鼠属）和两足动物（更格卢鼠属）（每种n = 5）时，颊囊容量与体重之间的关系显著，但这两个回归彼此之间没有显著差异。当考虑所有负载（满负载和部分负载）时，实验对象将颊囊填充到平均为颊囊容量的93±10%（n = 185）。已发表的关于实验室中人工填充更格卢鼠科动物颊囊的研究中，颊囊容量平均比我们在此处获得的野外测量值低约40%。平均装载速率与体重之间的异速生长关系也显著[种子数/秒 = 1.067×体重（克），r = 0.85，P = 0.0011]，但当分别考虑四足动物和两足动物时，这种关系不显著。种子密度和容重被用于计算种子物种的填充系数，当与颊囊容量和体型之间的异速生长关系结合使用时，可用于估计更格卢鼠科动物携带的最大负载量。除了最大的更格卢鼠物种外，一满颊囊印度三芒草种子所代表的能量少于一只活跃的更格卢鼠科动物的每日能量需求。
