Data from: Novel nectar robbing negatively affects reproduction in Digitalis purpurea

With many plant-pollinator interactions undergoing change as species’
distributions shift, we require a better understanding of how the addition
of new interacting partners can affect plant reproduction. One such group
of floral visitors, nectar robbers, can deplete plants of nectar rewards
without contributing to pollination. The addition of nectar robbing to the
floral visitor assemblage could therefore have costs to the plant´s
reproductive output. We focus on a recent plant colonist, Digitalis
purpurea, a plant that in its native range is rarely robbed, but
experiences intense nectar robbing in areas it has been introduced to.
Here, we test the costs to reproduction following experimental nectar
robbing. To identify any changes in the behaviour of the principal
pollinators in response to nectar robbing, we measured visitation rates,
visit duration, proportion of flowers visited and rate of rejection of
inflorescences. To find the effects of robbing on fitness, we used proxies
for female and male components of reproductive output, by measuring the
seeds produced per fruit and the pollen export respectively. Nectar
robbing significantly reduced the rate of visitation and lengths of visits
by bumblebees. Additionally, bumblebees visited a lower proportion of
flowers on an inflorescence that had robbed flowers. We found that flowers
in the robbed treatment produced significantly fewer seeds per fruit on
average but did not export fewer pollen grains. Our finding that robbing
leads to reduced seed production could be due to fewer and shorter visits
to flowers leading to less effective pollination. We discuss the potential
consequences of new pollinator environments, such as exposure to nectar
robbing, for plant reproduction.