Pollinator availability and pollinator spectra

Alpine plants and their pollinators

Pollinators prefer sunny days

The visiting rate of pollinators to flowers at high altitudes is strongly influenced by quickly changing weather conditions. Under a completely overcast sky, flower visits may be nil, while on a sunny day pollinators are abundant. For instance, on a bright day above 2200 m, Müller (1881), the first naturalist to study pollinators in alpine habitats, counted 93 insect species as flower visitors on 60 different plant species.

Measured visiting rates of pollinators to flowers are substantially lower at high altitudes. Nevertheless, pollination efficiency may be similar to that in the lowland, because alpine flowers may compensate for fewer visits with a longer flowering time.

Shifts in pollinator spectra with altitude

In contrast to the number of insect species, the pollinator spectrum definitely does change with elevation because of different energy requirements of pollinator groups:

• In the Alps beetles and bees become less abundant, while butterflies, bumblebees and particularly flies become more important at higher elevations.
• A shift from bee to butterfly pollination seems to be a common tendency in subnival flora. In the Himalayas and in the tropics bee pollinated species disappear completely above 4000 m and butterflies and flies become the most important pollinators.
• Bumblebees are of particular importance for the pollination of alpine plants because they carry a lot more pollen, exhibit particularly high visitation rates, fly over large distances and at temperatures as low as 4 °C.
• Above the treeline flies are, together with butterflies, the second most important group of pollinators preferring whitish, unspecialised flowers in habitats unfavourable for other pollinator groups.