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Proc Biol Sci. 2017 Mar 15;284(1850). pii: 20162564. doi: 10.1098/rspb.2016.2564.

Network reorganization and breakdown of an ant-plant protection mutualism with elevation.

Plowman NS1,2,3, Hood AS3,4, Moses J5,3,6, Redmond C5,2,3, Novotny V5,2,3, Klimes P2,3, Fayle TM5,2,3.

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Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic
Institute of Entomology, Biology Centre of Czech Academy of Sciences, Ceske Budejovice, Czech Republic.
New Guinea Binatang Research Center, Madang, Papua New Guinea.
Department of Zoology, University of Cambridge, Cambridge, UK.
Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic.
University of Papua New Guinea, Port Moresby, Papua New Guinea.


Both the abiotic environment and the composition of animal and plant communities change with elevation. For mutualistic species, these changes are expected to result in altered partner availability, and shifts in context-dependent benefits for partners. To test these predictions, we assessed the network structure of terrestrial ant-plant mutualists and how the benefits to plants of ant inhabitation changed with elevation in tropical forest in Papua New Guinea. At higher elevations, ant-plants were rarer, species richness of both ants and plants decreased, and the average ant or plant species interacted with fewer partners. However, networks became increasingly connected and less specialized, more than could be accounted for by reductions in ant-plant abundance. On the most common ant-plant, ants recruited less and spent less time attacking a surrogate herbivore at higher elevations, and herbivory damage increased. These changes were driven by turnover of ant species rather than by within-species shifts in protective behaviour. We speculate that reduced partner availability at higher elevations results in less specialized networks, while lower temperatures mean that even for ant-inhabited plants, benefits are reduced. Under increased abiotic stress, mutualistic networks can break down, owing to a combination of lower population sizes, and a reduction in context-dependent mutualistic benefits.


altitudinal gradients; biotic defence; global change; herbivory; myrmecophyte; network specialization

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