Grazing alters insect visitation networks and plant mating systems
Article first published online: 6 DEC 2013
© 2013 The Authors Functional Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Special Issue: Climate change and species range shifts
Volume 28, Issue 1, pages 178–189, February 2014
How to Cite
Vanbergen, A. J., Woodcock, B. A., Gray, A., Grant, F., Telford, A., Lambdon, P., Chapman, D. S., Pywell, R. F., Heard, M. S., Cavers, S. (2014), Grazing alters insect visitation networks and plant mating systems. Functional Ecology, 28: 178–189. doi: 10.1111/1365-2435.12191
- Issue published online: 23 JAN 2014
- Article first published online: 6 DEC 2013
- Accepted manuscript online: 30 SEP 2013 09:17AM EST
- Manuscript Accepted: 16 SEP 2013
- Manuscript Received: 10 APR 2013
- British Ecological Society. Grant Number: SEPG 1563/1968
- NERC CEH Environmental Change Integrating Fund. Grant Number: NEC03463
- bipartite networks;
- Cirsium palustre ;
- landscape structure;
- reproductive ecology;
- weighted model averaging
- Many flowering plant species have a facultative or obligate dependence on insect pollination for reproductive success. Anthropogenic disturbance may alter these species interactions, but the extent to which structural changes to plant-pollinator networks affect plant species mating systems is not well understood.
- We used long-term livestock grazing of a birch wood ecosystem to test whether disturbance of this semi-natural habitat altered floral resources, the structure of plant–insect visitation networks and the mating system of a focal plant species, Cirsium palustre.
- Grazed habitat had a higher species richness of floral resources for pollinators. Visitation networks in grazed habitats were larger, more diverse, with an increase in the number of pollinators per plant species. Controlling for sampling effects, however, showed networks in grazed habitats were less nested and revealed a positive correlation between network connectance and floral species richness.
- Network connectance was negatively related to C. palustre outcrossing rate within grazed and ungrazed sites. However, on average, the effects of grazing, including greater mean connectance, produced higher overall outcrossing rates and more pollen donors compared with ungrazed habitat. The number of different pollen donors, spatial genetic structure and mating among close relatives were all correlated with greater extent of suitable C. palustre habitat in the landscape, consistent with the effects of increasing plant population size but limited seed dispersal.
- Pre-adaptation of C. palustre to disturbance coupled with a preponderance of highly dispersive flies attracted to the greater food resources in grazed habitat is a likely mechanism underpinning this increased pollen transport.
- Habitat modification by long-term mammalian grazing fundamentally shifted visitation network structure and the state of a plant mating system, indicating how ecosystem disturbance can cascade across levels of biological organization through altered interspecific interactions. Cirsium palustre retains flexibility to bias reproduction towards selfing where pollen donor diversity is limited; such reproductive flexibility may be an important mechanism structuring plant populations in human-modified landscapes.