Experimental reduction of pollinator visitation modifies plant–plant interactions for pollination

Abstract

The strength of interactions between plants for pollination depends on the abundance of plants and pollinators in the community. The abundance of pollinators may influence plant associations and densities at which individual fitness is maximized. Reduced pollinator visitation may therefore affect the way plant species interact for pollination. We experimentally reduced pollinator visitation to six pollinator‐dependent species (three from an alpine and three from a lowland community in Norway) to study how interactions for pollination were modified by reduced pollinator availability. We related flower visitation, pollen limitation and seed set to density of conspecifics and pollinator‐sharing heterospecifics inside 30 dome‐shaped cages partially covered with fishnet (experimental plots) and in 30 control plots. We expected to find stronger interactions between plants in experimental compared to controls plots. The experiment modified plant–plant interactions for pollination in all the six species; although for two of them neighbourhood interactions did not affect seed set. The pollen limitation and seed set data showed that reduction of pollinator visits most frequently resulted in novel and/or stronger interactions between plants in the experimental plots that did not occur in the controls. Although the responses were species‐specific, there was a tendency for increasing facilitative interactions with conspecific neighbours in experimental plots where pollinator availability was reduced. Heterospecifics only influenced pollination and fecundity in species from the alpine community and in the experimental plots, where they competed with the focal species for pollination. The patterns observed for visitation rates differed from those for fecundity, with more significant interactions between plants in the controls in both communities. This study warns against the exclusive use of visitation data to interpret plant–plant interactions for pollination, and helps to understand how plant aggregations may buffer or intensify the effects of a pollinator loss on plant fitness.

Plant interactions shape pollination networks via nonadditive effects

“…A second limitation relates to the assumption that individual plant species have comparable chemistry when growing together and when growing with other plants (Lazaro et al. ). Foundation and associated species may alter each other's pollinator attractiveness by enhancing floral reward and display (Junker et al.…”

Experimental simulation of pollinator decline causes community‐wide reductions in seedling diversity and abundance

“…In fact, Lázaro et al. () show that a high conspecific density may to some extent buffer the effect of a pollinator decline. The fact that the negative effects of the experiment on seedling abundance were stronger when the most abundant species ( C. jacea ) was removed from the data set, may support the finding that conspecific density buffers negative effects of pollinator decline.…”

“…) and low local conspecific density (Lázaro et al. ) to be most strongly affected by pollinator decline. If responses to pollinator decline vary among species, this should ultimately change the species composition of the plant community.…”

Evaluating the effects of pollinator‐mediated interactions using pollen transfer networks: evidence of widespread facilitation in south Andean plant communities

“…Changes in pollinator availability can thus affect the direction and magnitude of pollinator‐mediated interactions among plants (Lázaro et al . ; Ye et al . ).…”