Department of Botany, Palacký University, Olomouc, Czech Republic.
PLoS One. 2013 Jul 26;8(7):e69800. doi: 10.1371/journal.pone.0069800. Print 2013.
Current plant--herbivore interaction models and experiments with mammalian herbivores grazing plant monocultures show the superiority of a maximizing forage quality strategy (MFQ) over a maximizing intake strategy (MI). However, there is a lack of evidence whether grazers comply with the model predictions under field conditions.
METHODOLOGY/FINDINGS: We assessed diet selection of sheep (Ovis aries) using plant functional traits in productive mesic vs. low-productivity dry species-rich grasslands dominated by resource-exploitative vs. resource-conservative species respectively. Each grassland type was studied in two replicates for two years. We investigated the first grazing cycle in a set of 288 plots with a diameter of 30 cm, i.e. the size of sheep feeding station. In mesic grasslands, high plot defoliation was associated with community weighted means of leaf traits referring to high forage quality, i.e. low leaf dry matter content (LDMC) and high specific leaf area (SLA), with a high proportion of legumes and the most with high community weighted mean of forage indicator value. In contrast in dry grasslands, high community weighted mean of canopy height, an estimate of forage quantity, was the best predictor of plot defoliation. Similar differences in selection on forage quality vs. quantity were detected within plots. Sheep selected plants with higher forage indicator values than the plot specific community weighted mean of forage indicator value in mesic grasslands whereas taller plants were selected in dry grasslands. However, at this scale sheep avoided legumes and plants with higher SLA, preferred plants with higher LDMC while grazing plants with higher forage indicator values in mesic grasslands.
Our findings indicate that MFQ appears superior over MI only in habitats with a predominance of resource-exploitative species. Furthermore, plant functional traits (LDMC, SLA, nitrogen fixer) seem to be helpful correlates of forage quality only at the community level.
目前的植物-食草动物相互作用模型和实验表明，在食草动物以单一种群的植物为食时，最大化饲料质量策略（MFQ）优于最大化摄入量策略（MI）。然而，在野外条件下，食草动物是否符合模型预测还缺乏证据。
方法/发现：我们利用植物功能性状评估了绵羊（Ovis aries）在生产力高的湿润地区与低生产力的干燥物种丰富的草地中的饮食选择，这两种草地分别以资源开发性物种和资源保守性物种为主。每种草地类型在两年内进行了两次重复研究。我们在 288 个直径为 30 厘米的样方中调查了第一个放牧周期，即绵羊采食站的大小。在湿润草地中，高样方刈割与叶片性状的群落加权均值有关，表明饲料质量高，即叶片干物质含量（LDMC）低和比叶面积（SLA）高，豆科植物比例高，群落加权均值的饲料指标值高。相比之下，在干燥草地中，高的群落加权均值的冠层高度，即饲料量的估计，是样方刈割的最佳预测因子。在样方内也检测到了对饲料质量与数量的选择存在差异。在湿润草地中，绵羊选择的植物的饲料指标值高于样方特定的群落加权均值的饲料指标值，而在干燥草地中，选择的植物更高。然而，在这个尺度上，绵羊在湿润草地中避免选择豆科植物和具有较高 SLA 的植物，更喜欢具有较高 LDMC 的植物，而在干燥草地中，它们会选择具有较高饲料指标值的植物。
我们的研究结果表明，只有在以资源开发性物种为主的栖息地中，MFQ 似乎优于 MI。此外，植物功能性状（LDMC、SLA、固氮生物）似乎仅在群落水平上有助于预测饲料质量。
