Flowering a week later due to shifted hay cut is dearly bought off by lower reproductive success through pollinator mismatch – The intrigues of pollination biology in agricultural landscapes

Horčičková, E. (1), Janovský, Z. (1), Herben, T. (1,2)

1) Dept. of Botany, Charles University in Prague

2) Institute of Botany, Academy of Sciences of the Czech Republic, Průhonice

Dramatic changes of agricultural practices during the 20th century have led to substantial changes in pollinator diversity and abundances in cultural landscape. At the same time, the importance of pollinators for crops has been recognised as well as the lack in numbers of the “traditional” pollinator groups, such as honeybees and bumblebees, leading to what some call “pollination crisis”. In our work, we attempt to discover, how these changes in pollination availability are being perceived by wild plants surviving in agricultural landscapes.

This led us to conducting pollinator censuses at places with occurrence of wild plants, namely we focused on meadow and verge sites (verges of fields, roads etc.), which often serve as refuges for wild plants in intensively managed landscapes. The censuses revealed that at most places hoverflies (Syrphidae) were more abundant than honeybees, bumblebees and solitary bees. Their dominance was more pronounced at isolated verge sites. They were greatly outnumbered only at some meadow patches with high concentration of plants preferred by honeybees and bumblebees.

We examined how this pollinator distribution affected reproduction biology of two relatively common wild plant species in agricultural landscape, Achillea ptarmica and A. millefolium. We followed their seed production and seed germination at the same sites as we censused pollinators. The data were conducted in three runs covering approximately the beginning, middle and end of the month, in which both species flower (during high summer).

Both species were predominantly pollinated by hoverflies (69%). The path analysis of all important factors influencing the seed production and germination revealed that pollinator abundance was positively related to both reproductive output measures. After accounting for all direct and indirect effects the influence of pollinator abundance was approximately 2,5 times greater than the influence of differences between verge and meadow sites. The timing within the season did not affect in any way the plant reproductive output with except of a very strong influence on pollinators. Plants flowering early in the season experienced almost 4 times higher pollinator densities. Thus time within season was responsible for approximately two thirds of the differences in pollinator abundances with only the remaining third attributable to the differences among sites within the landscape.

In general, we can conclude that there are only slight (though significant and negative) differences of study plant reproductive performance between verge and meadow sites and thus verge sites can be seen as valuable refuges for wild plants for pollination point of view. Our results also emphasize the importance of phenology of flowering for plant reproductive success. Phenology however is not only the inherent plant property, but it is also shaped by landscape management (e.g. variable date of hay cut due to agroenvironemental schemes).These induced shifts in flowering at the scale of one or two weeks (which happen in agricultural landscape almost always either in one or the other direction) can greatly affect the population biology of common wild plant species through causing pollinator mismatch - an aspect of landscape management we usually do not take into account.

Presentováno na kongresu ke 100 letům Výročním setkání Britské ekologické společnosti v Londýně ve dnech 18.-23.8. 2013.

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