Mkhize Ntuthuko R, Heitkӧnig Ignas M A, Scogings Peter F, Hattas Dawood, Dziba Luthando E, Prins Herbert H T, de Boer Willem F
Resource Ecology Group, Wageningen University, Wageningen, the Netherlands.
Agricultural Research Council, Animal Production Institute, Hilton, South Africa.
PLoS One. 2018 Jan 2;13(1):e0189626. doi: 10.1371/journal.pone.0189626. eCollection 2018.
Although condensed tannins (CTs) are known to reduce forage intake by mammalian herbivores in controlled experiments, few studies have tested these effects in the field. Thus the role of CTs on foraging ecology of free-ranging herbivores is inadequately understood. To investigate the effects of CTs under natural savanna conditions, we pre-dosed groups of goats with polyethylene glycol (PEG, a CT-neutralising chemical), CT powder or water before observing their foraging behaviour. While accounting for the effects of season and time of the day, we tested the hypothesis that herbivores forage in ways that reduce the intake rate (g DM per minute) of CTs. We expected pre-dosing goats with CTs to reduce CT intake rates by (1) consuming diets low in CTs, (2) reducing bite rates, (3) increasing the number of foraging bouts, or (4) reducing the length of foraging bouts. Lastly, (5) expected CT to have no influence the number of dietary forage species. In both wet and dry seasons, pre-dosing goats with CTs resulted in lower CT consumption rates compared to PEG goats which seemed relieved from the stress associated with CT consumption. During dry season, the number of dietary forage species was similar across treatments, although goats that were dosed with PEG significantly increased this number in the wet season. Dosing goats with PEG increased the number and length of browsing bouts compared to goats from the other treatments. Pre-loading goats with PEG also tended to increase bite rates on browse forages, which contributed to increased consumption rates of CTs. Based on the behavioural adjustments made by goats in this study and within the constraints imposed by chemical complexity in savanna systems, we concluded that herbivores under natural conditions foraged in ways that minimised CTs consumption. More research should further elucidate the mechanism through which CTs regulated feeding behaviour.
尽管在对照实验中已知缩合单宁（CTs）会降低哺乳动物食草动物的采食量，但很少有研究在野外测试这些影响。因此，CTs对自由放养食草动物觅食生态的作用尚未得到充分了解。为了研究自然稀树草原条件下CTs的影响，我们在观察山羊的觅食行为之前，给山羊群预先投喂聚乙二醇（PEG，一种CT中和化学物质）、CT粉末或水。在考虑季节和一天中时间的影响时，我们检验了以下假设：食草动物以降低CTs摄入率（每分钟克干物质）的方式觅食。我们预期给山羊预先投喂CTs会通过以下方式降低CTs摄入率：（1）食用CTs含量低的食物，（2）降低啃咬率，（3）增加觅食回合数，或（4）缩短觅食回合长度。最后，（5）预期CTs对食物草料种类数量没有影响。在雨季和旱季，与PEG处理的山羊相比，预先投喂CTs的山羊CTs消耗率更低，PEG处理的山羊似乎从与CTs消耗相关的压力中得到缓解。在旱季，各处理间食物草料种类数量相似，尽管在雨季中，投喂PEG的山羊显著增加了这一数量。与其他处理的山羊相比，给山羊投喂PEG增加了啃食回合的数量和长度。给山羊预先投喂PEG还倾向于增加对啃食草料的啃咬率，这导致CTs消耗率增加。基于本研究中山羊做出的行为调整以及稀树草原系统化学复杂性所带来的限制，我们得出结论：自然条件下的食草动物以尽量减少CTs消耗的方式觅食。更多研究应进一步阐明CTs调节摄食行为的机制。
