Would East African savanna rodents inhibit woody encroachment? Evidence from stable isotopes and microhistological analysis of feces
Would East African savanna rodents inhibit woody encroachment? Evidence from stable isotopes and microhistological analysis of feces
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DOI：
10.1644/12-mamm-a-146.1
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发表时间：
2013-04-01
影响因子：
1.7
通讯作者：
Bergstrom, Bradley J.
中科院分区：
文献类型：
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作者：
Bergstrom, Bradley J.
众所周知，东非稀树草原上丰富多样的有蹄类动物群对植物的大量消耗，竞争性地抑制了本土草食性到杂食性小型哺乳动物的群体。当这些啮齿类动物从有蹄类动物的竞争中释放出来时，在以金合欢为主的稀树草原上，木本植物的抑制作用在最近才得到证实，但没有直接证据表明涉及哪些物种。为了确定该行会中哪些常见物种最有可能影响树木和杂草的生长，而不是草或昆虫或两者的生长，我提供了来自肯尼亚中部莱基皮亚高原的稀树草原和灌木栖息地的 8 种常见鼠类啮齿动物的粪便碳和氮的原子和同位素比率数据：Acomys percivali、Acomys wilsoni、Aethomys Indiane、Arvicanthis尼罗罗非鱼、Mastomys natalensis、Mus spp. （认为主要是 M. minutoides）、Saccostomus mearnsi 和 Gerbilliscus roughtus。在这个所有草类都是 C-4、所有树木和其他非草类都是 C-3 的地区，植物组织中不同比例的 C-13:C-12(δ C-13) 赋予纯食草动物、纯食草动物和混合食草动物独特的碳同位素特征。杂食程度由 C:N 和 delta C-15 揭示，但后者受膳食蛋白质质量的影响，并且因植物种类和土壤类型而异。结合稳定同位素数据、总 C:N 和粪便的显微组织学分析，可以比单独使用这些数据集更好地解析每个物种的饮食生态位。草要么与啃食（双子叶植物）同等，要么在每个物种的饮食中占主导地位，考虑到啮齿类动物在限制金合欢补充方面的假设作用，这有点出乎意料。所有物种都消耗一些节肢动物。尼罗罗非鱼是唯一的昼夜物种，也是食草性最强的物种，主要是食草动物。 S. mearnsi、A. India 和 M. natalensis 是混食（草食）草食动物。小家鼠属和Acomys spp。是杂食动物，其植物成分主要是草。粗壮棉主要是一种食虫杂食动物，其较小的植物成分是草。在大雨过后的一段时间内，S. mearnsi 和 A. niloticus 的饮食中 C-4 草的比例显着增加，这是先前在大型哺乳动物食草动物的 Delta C-13 饮食研究中记录的模式。对于消耗更多草的啮齿类动物以及通过与有蹄类动物竞争而释放的啮齿类动物，粪便δ C-15 显着较高，这表明这种竞争性释放的部分机制。 S. mearnsi，其次是 A. 印度树和 M. natalensis，最有可能以包括金合欢在内的木本双子叶植物为食。
It is well established that massive consumption of plants by the abundant and diverse assemblage of savanna ungulates in East Africa competitively suppresses the native guild of herbivorous to omnivorous small mammals. An important role of woody plant suppression in the Acacia-dominated savannas for this guild of rodents, when released from ungulate competition, has been demonstrated only recently, but without direct evidence of which species are involved. In an effort to establish which of the common species in this guild are most likely to impact growth of trees and forbs, as opposed to grasses or insects, or both, I present data on atomic and isotopic ratios of fecal carbon and nitrogen from 8 commonly occurring muroid rodents from savanna and bush habitats on the Laikipia Plateau of central Kenya: Acomys percivali, Acomys wilsoni, Aethomys hindei, Arvicanthis niloticus, Mastomys natalensis, Mus spp. (thought to be mostly M. minutoides), Saccostomus mearnsi, and Gerbilliscus robustus. In this region where all grasses are C-4 and all trees and other nongrasses are C-3, different ratios of C-13:C-12(delta C-13) in plant tissues give pure grazers, pure browsers, and mixed-feeding herbivores distinctive carbon isotope signatures. Degree of omnivory is revealed by C:N and, arguably, by delta C-15, but the latter is influenced by dietary protein quality and varies widely by plant species and soil type. Joint consideration of stable-isotope data, total C:N, and microhistological analysis of feces allowed better resolution of dietary niche of each species than any of these data sets could, alone. Grass was either coequal to browse (dicots) or dominated the plant portion of each species' diet, which was somewhat unexpected given rodents' hypothesized role in limiting Acacia recruitment. All species consumed some arthropods. A. niloticus, the only diurnal species, was the most herbivorous, being largely a grazer. S. mearnsi, A. hindei, and M. natalensis were mixed-feeding (grass-browse) herbivores. Mus spp. and Acomys spp. were omnivores whose plant components were largely grass. G. robustus was primarily an insectivore-omnivore whose smaller plant component was grass. Both S. mearnsi and A. niloticus displayed a significant increase in proportion of C-4 grasses in the diet in periods following significant rains, a pattern previously documented from delta C-13 diet studies in large mammalian herbivores. Fecal delta C-15 was significantly higher for rodents that consumed more grass and for rodents released from competition with ungulates, suggesting a partial mechanism for that competitive release. S. mearnsi, followed by A. hindei and M. natalensis, were most likely to feed on woody dicots including Acacia.