You are unlikely to observe considerable or even devastating damage by invertebrate herbivores in alpine vegetation. Why is that so? Several factors restrict the impact of invertebrate herbivores in high mountains:

• In general, the number and impact of herbivorous invertebrates decrease with altitude.
• Their activity is often limited due to the physical conditions of the alpine environment, especially the low temperatures.
• Most invertebrates are relatively immobile due to wing antropy etc.

Still, there is large year-to-year variability in invertebrate populations and temporary and locally restricted outbreaks of some species may occur. In this situation even invertebrate herbivores can have a severe effect on vegetation.

In contrast to most lowland habitats, there are relatively few specialist herbivores in the alpine zone. This may reduce herbivore pressure for particular plant species. Nevertheless, nearly all herbivores have clear preferences in the plant species they feed upon.

1 - Miramella alpina

Grasshoppers

Grasshoppers need favourable conditions, especially insolation, to become active. They are extremely efficient in obtaining sufficient resources during the often very short periods of favourable weather in the alpine environment: some New Zealand alpine grasshoppers are able to eat to satiation in about 15 min. The passage of food through the gut takes at least 5 h and thereby sets of the minimum period between two feeds.

Grasshoppers often cut whole leaves which they then feed upon by nibbling from the edges. This means that although their food intake may be low they still cause considerable damage to the plants. Although most grasshoppers generally feed on a variety of plant species, they prefer some species over others (e.g. they prefer plants with high nitrogen content or succulent leaves over plants with tough leaves). Grasshoppers concentrate their feeding at more suitable sites. They are often particularly abundant at grassland-scree ecotones, e.g. at the upper altitudinal limit of grasslands, where they take advantage of increased solar radiation.

In conclusion, the leaf cutting habit of grasshoppers and their preferences for particular sites and plants suggest that these herbivores have the potential to influence at least some alpine plant communities.

2 - Melasoma collaris

Melasoma collaris

Another example of a herbivore with a localised impact on vegetation is Melasoma collaris, a chrysomelid beetle which feeds on Salix species in Fennoscandian alpine environments. Unlike most other alpine insects, the species has a one-year life cycle. Imagines hibernate and become active as soon as the snow melts. Eggs are laid after a short feeding period, and development from newly laid eggs to hatching of imagines takes about two months.

Melasoma collaris occurs in patches of vegetation where species of Salix are dominant in snowbed vegetation where the snow melts relatively early (normally before July). Thus, around the periphery of a snowbed the impact of this beetle may be severe with up to 100% of the leaves of Salix being damaged. In contrast, there may be no damage to plants in the inner part of a snow bed, where the vegetation period is too short for the insect to complete its life cycle.

3 - Arianta arbustorum alpicola

Molluscs

Although some molluscs do occur in the alpine environment, the number of individuals decreases strongly with altitude. There is no information about the ecological impact of these animals in alpine environments. Due to their low abundance, their impact is probably much less than in lowland environments, where they often have a heavy impact especially on seedlings.

29 August 2011
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