Podolsky Robert H, Price Mary V
Department of Biology, University of California, 92521, Riverside, CA, USA.
Oecologia. 1990 May;83(1):83-90. doi: 10.1007/BF00324638.
Granivorous desert rodents of the family Heteromyidae forage nonrandomly among "microhabitats" that vary in substrate, seed densities, and seed species composition. To explore the hypothesis that microhabitat use is sensitive to seed patch profitability, we quantified effects of seed size (1.96 vs. 5.21 mg/seed) and density (0.4-10.6 seeds/cm) on Dipodomys deserti harvest rates, which is a measure of profitability when expressed as mg of seed taken per min. By manipulating seed density, we created large-seed and small-seed patches of known relative profitability and exposed D. deserti individuals to pairwise choices in the laboratory and field. We used three treatment classes: 1) large-seed patches that were more profitable than small-seed patches (equal seed densities); 2) large-seed and small-seed patches that were equally profitable (small-seed densities somewhat higher): and 3) large-seed patches that were less profitable than small-seed patches (small-seed densities much higher). Harvest rate increased nearly linearly with seed density, and profitability of large-seed patches was greater than small-seed patches of the same density. Cumulative harvest from a patch increased linearly with residence time up to a plateau; this "gain curve" indicates that animals move systematically within patches and hence avoid resampling already depleted areas. In the laboratory, animals visited small-seed patches first more often and visited them more frequently when they were more profitable than large-seed patches. When large-seed patches were of greater or equal profitability, large-seed patches were preferred by both measures. The expressed preference for large-seed patches, when animals were presented with equally profitable patches, suggests an underlying preference for large seeds. In the field, animals depleted all patches to a constant low profitability, in accord with qualitative predictions of optimal patch use models. These results suggest that patch preferences by D. deserti are affected by the economics of seed harvest.
异鼠科食谷沙漠啮齿动物在底物、种子密度和种子物种组成各异的“微生境”中进行非随机觅食。为探究微生境利用对种子斑块收益性敏感这一假说，我们量化了种子大小（1.96对5.21毫克/粒）和密度（0.4 - 10.6粒/平方厘米）对沙漠更格卢鼠收获率的影响，收获率是以每分钟获取种子的毫克数表示的收益性指标。通过操控种子密度，我们创建了已知相对收益性的大种子和小种子斑块，并在实验室和野外让沙漠更格卢鼠个体进行两两选择。我们使用了三类处理方式：1）大种子斑块比小种子斑块收益更高（种子密度相同）；2）大种子和小种子斑块收益相同（小种子密度略高）；3）大种子斑块比小种子斑块收益更低（小种子密度高得多）。收获率几乎随种子密度呈线性增加，相同密度下大种子斑块的收益性大于小种子斑块。斑块的累积收获量随停留时间线性增加直至平稳期；这条“收益曲线”表明动物在斑块内有系统地移动，从而避免重新采样已耗尽区域。在实验室中，动物更常先访问小种子斑块，当小种子斑块比大种子斑块收益更高时会更频繁地访问。当大种子斑块收益更高或相等时，两种衡量方式都显示更偏好大种子斑块。当向动物呈现收益相同的斑块时，对大种子斑块的明显偏好表明对大种子存在潜在偏好。在野外，动物将所有斑块消耗至恒定的低收益水平，这与最优斑块利用模型的定性预测一致。这些结果表明，沙漠更格卢鼠对斑块的偏好受种子收获经济学的影响。
