High species turnover and unique plant–pollinator interactions make a hyperdiverse mountain

1. We studied α- and β-diversity of pollinators, flowering plants, and
plant–pollinator interactions along the altitudinal gradient of Mt.
Olympus, a legendary mountain and biodiversity hotspot in Central Greece.
2.  We explored ten study sites located on the north-eastern
slope of the mountain, from 327 to 2,596 m a.s.l. Insect surveys were
conducted once a month using hand netting (years 2013, 2014, and 2016),
and they were combined with recordings of flowering plant diversity
(species richness and flower cover). We then calculated α- and β-diversity
of pollinators, plants in flower, and plant–pollinator interactions, and
explored their demographic response along the altitudinal gradient. 3.
 Alpha‐diversity of pollinators, plants, and plant–pollinator
interactions were altitude-dependent; α‐diversity of all pollinators,
bees, non-bumblebee bees, bee flies, and butterflies showed linear
declines with altitude, whereas those of hoverflies and bumblebees showed
unimodal patterns. Beta-diversity and its turnover component of all
pollinators, hoverflies, bees, bumblebees, non-bumblebee bees,
butterflies, and plants showed linear increases, whereas those of bee
flies and of plant–pollinator interactions varied independently from the
pairwise altitudinal difference. 4.  The high dissimilarity and
uniqueness of pollination networks, which is probably a result of the high
biodiversity and endemism of Mt. Olympus, is driven by species turnover
and the formation of new interactions between new species. Contrasting to
the monotonic decline of the remaining groups, the unimodal patterns of
hoverfly and bumblebee α‐diversity are probably the effect of a higher
tolerance of these groups to high-altitude environmental conditions. Our
findings highlight that the high turnover of species and of pollination
interactions along the altitudinal gradient is the mainstay of
hyperdiverse mountains, a fact that conveys important historical,
ecological, and conservational implications.