Data from: Geographic variation of reproductive traits and competition for pollinators in a bird-pollinated plant

Geographic variation in the reproductive traits of animal-pollinated
plants can be shaped by spatially variable selection imposed by
differences in the local pollination environment. We investigated this in
Babiana ringens (Iridaceae), an enigmatic species from the Western Cape
region of South Africa. B. ringens has evolved a specialized perch
facilitating cross-pollination by sunbirds and displays striking
geographic variation in perch size and floral traits. Here, we investigate
whether this variation can be explained by geographic differences in the
pollinator communities. We measured floral and inflorescence traits,
abiotic variables (N, P, C and rainfall) and made observations of sunbirds
in populations spanning the range of B. ringens. In each population, we
recorded sunbird species identity and measured visitation rates,
inter-floral pollen transfer and whether the seed set of flowers was
pollen limited. To evaluate whether competition from co-occurring
sunbird-pollinated species might reduce visitation, we quantified nectar
rewards in B. ringens and of other co-flowering bird-pollinated species in
local communities in which populations occurred. Variation in abiotic
variables was not associated with geographical variation of traits in B.
ringens. Malachite sunbirds were the dominant visitor (97% of visits) and
populations with larger-sized traits exhibited higher visitation rates,
more between-flower pollen transfer and set more seed. No sunbirds were
observed in four populations, all with smaller-sized traits. Sunbird
visitation to B. ringens was not associated with local sunbird activity in
communities, but sunbird visitation was negatively associated with the
amount of B. ringens sugar relative to the availability of alternative
nectar sources. Our study provides evidence that B. ringens populations
with larger floral traits are visited more frequently by sunbirds and we
propose that visitation rates to B. ringens may be influenced, in part, by
competition with other sunbird pollinated species.