Abstract
Plants flowering together may influence each
other’s pollination and fecundity over a range of physical
distances. Their effects on one another can be competitive,
neutral, or facilitative. We manipulated the floral neighborhood
of the high-alpine cushion plant Eritrichium nanum
in the Swiss Alps and measured the effects of coflowering
neighbors on both the number of seeds produced
and the degree of inbreeding and outbreeding in the offspring,
as deduced from nuclear microsatellite markers.
Seed set of E. nanum did not vary significantly with the
presence or absence of two Saxifraga species growing as
near neighbors, but it was higher in E. nanum cushions
growing at low conspecific density than in those growing at
high density. In addition, floral neighborhood had no
detectable effect on the degree of selfing of E. nanum, but
seeds from cushions growing at low conspecific density
were more highly outbred than seeds from cushions at high
density. Thus, there was no evidence of either competition or facilitation between E. nanum and Saxifraga spp. as
mediated by pollinators at the spatial scale of our experimental
manipulation. In contrast, the greater fecundity of
E. nanum cushions at low density was consistent with
reduced intraspecific competition for pollinators and might
also represent a beneficial effect of highly outbred seeds as
brought about by more long-distance pollinator flights
under low-density conditions.
Wirth, L R