Plant and animal community composition changes at higher elevations on mountains. Plant and animal species richness generally declines with elevation, but the shape of the relationship differs between taxa. There are several proposed mechanisms, including the productivity hypotheses; that declines in available plant biomass confers fewer resources to consumers, thus supporting fewer species. We investigated resource availability as we ascended three aspects of Helvellyn mountain, UK, measuring several plant nutritive metrics, plant species richness and biomass. We observed a linear decline in plant species richness as we ascended the mountain but there was a unimodal relationship between plant biomass and elevation. Generally, the highest biomass values at mid-elevations were associated with the lowest nutritive values, except mineral contents which declined with elevation. Intra-specific and inter-specific increases in nutritive values nearer the top and bottom of the mountain indicated that physiological, phenological and compositional mechanisms may have played a role. The shape of the relationship between resource availability and elevation was different depending on the metric. Many consumers actively select or avoid plants based on their nutritive values and the abundances of consumer taxa vary in their relationships with elevation. Consideration of multiple nutritive metrics and of the nutritional requirements of the consumer may provide a greater understanding of changes to plant and animal communities at higher elevations. We propose a novel hypothesis for explaining elevational diversity gradients, which warrants further study; the ‘nutritional complexity hypothesis’, where consumer species coexist due to greater variation in the nutritional chemistry of plants.

山上海拔较高的动植物群落组成发生变化。植物和动物物种的丰富度通常随着海拔的升高而下降，但是关系的形状在不同的分类单元之间是不同的。提出了几种机制，包括生产率假说。可用植物生物量的减少会给消费者带来更少的资源，从而支持更少的物种。我们调查了英国Helvellyn山的三个方面的资源可用性，测量了几种植物营养指标，植物物种丰富度和生物量。当我们登上山峰时，我们观察到植物物种丰富度呈线性下降，但植物生物量与海拔之间存在单峰关系。通常，海拔升高时最高的生物量值与最低的营养值相关，除了矿物质含量随海拔升高而下降。靠近山顶和谷底的营养价值在种内和种间增加表明，生理，物候和组成机制可能起作用。资源可用性和海拔高度之间关系的形状因指标而异。许多消费者根据其营养价值积极选择或避免使用植物，并且消费者分类单元的丰富程度与海拔的关系也有所不同。考虑多种营养指标和消费者的营养需求可能会更好地了解较高海拔地区动植物群落的变化。我们提出了一个新颖的假设来解释海拔多样性梯度，值得进一步研究。