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.

Department of Zoology University of Cambridge Cambridge UK

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

University of Papua New Guinea Port Moresby Papua New Guinea

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Tylianakis JM, Didham RK, Bascompte J, Wardle DA. 2008. Global change and species interactions in terrestrial ecosystems. Ecol. Lett. 11, 1351–1363. (10.1111/j.1461-0248.2008.01250.x) PubMed DOI

Stachowicz JJ. 2001. Mutualism, facilitation, and the structure of ecological communities. Bioscience 51, 235–246. (10.1641/0006-3568(2001)051%5B0235:MFATSO%5D2.0.CO;2) DOI

Gilman SE, Urban MC, Tewksbury J, Gilchrist GW, Holt RD. 2010. A framework for community interactions under climate change. Trends Ecol. Evol. 25, 325–331. (10.1016/j.tree.2010.03.002) PubMed DOI

Laughlin DC, Messier J. 2015. Fitness of multidimensional phenotypes in dynamic adaptive landscapes. Trends Ecol. Evol. 30, 487–496. (10.1016/j.tree.2015.06.003) PubMed DOI

Toby Kiers E, Palmer TM, Ives AR, Bruno JF, Bronstein JL. 2010. Mutualisms in a changing world: an evolutionary perspective. Ecol. Lett. 13, 1459–1474. (10.1111/j.1461-0248.2010.01538.x) PubMed DOI

Schleuning M, et al. 2012. Specialization of mutualistic interaction networks decreases toward tropical latitudes. Curr. Biol. 22, 1925–1931. (10.1016/j.cub.2012.08.015) PubMed DOI

Benadi G, Hovestadt T, Poethke HJ, Blüthgen N. 2014. Specialization and phenological synchrony of plant-pollinator interactions along an altitudinal gradient. J. Anim. Ecol. 83, 639–650. (10.1111/1365-2656.12158) PubMed DOI

Hoiss B, Krauss J, Steffan-Dewenter I. 2015. Interactive effects of elevation, species richness and extreme climatic events on plant-pollinator networks. Glob. Change Biol. 21, 4086–4097. (10.1111/gcb.12968) PubMed DOI

Rico-Gray V, Oliveira PS. 2007. The ecology and evolution of ant-plant interactions. Chicago, IL: The University of Chicago Press; (10.1017/CBO9781107415324.004) DOI

Chamberlain SA, Holland JN. 2008. Density-mediated, context-dependent consumer-resource interactions between ants and extrafloral nectar plants. Ecology 89, 1364–1374. (10.1890/07-1139.1) PubMed DOI

Sagers CL, Ginger SM, Evans RD. 2000. Carbon and nitrogen isotopes trace nutrient exchange in an ant-plant mutualism. Oecologia 123, 582–586. (10.1007/PL00008863) PubMed DOI

Beattie A. 1989. Myrmecotrophy: plants fed by ants. Trends Ecol. Evol. 4, 172–176. (10.1016/0169-5347(89)90122-5) PubMed DOI

Pemberton RW. 1998. The occurrence and abundance of plants with extrafloral nectaries, the basis for antiherbivore defensive mutualisms, along a latitudinal gradient in east Asia. J. Biogeogr. 25, 661–668. (10.1046/j.1365-2699.1998.2540661.x) DOI

Chomicki G, Renner SS. 2015. Phylogenetics and molecular clocks reveal the repeated evolution of ant-plants after the late Miocene in Africa and the early Miocene in Australasia and the Neotropics. New Phytol. 207, 411–424. (10.1111/nph.13271) PubMed DOI

Feldhaar H, Fiala B, Hashim RB, Maschwitz U. 2003. Patterns of the Crematogaster-Macaranga association: the ant partner makes the difference. Insect. Soc. 50, 9–19. (10.1007/s000400300002) DOI

Dáttilo W, Dyer L. 2014. Canopy openness enhances diversity of ant–plant interactions in the Brazilian Amazon rain forest. Biotropica 46, 712–719. (10.1111/btp.12157) DOI

Kersch MF, Fonseca CR. 2005. Abiotic factors and the conditional outcome of an ant-plant mutualism. Ecology 86, 2117–2126. (10.1890/04-1916) DOI

Sachs JL, Simms EL. 2006. Pathways to mutualism breakdown. Trends Ecol. Evol. 21, 585–592. (10.1016/j.tree.2006.06.018) PubMed DOI

Koptur S. 1985. Alternative defenses against herbivores in Inga (Fabaceae: Mimosoideae) over an elevational gradient. Ecology 66, 1639–1650. (10.2307/1938026) DOI

Trimble ST, Sagers CL. 2004. Differential host use in two highly specialized ant-plant associations: evidence from stable isotopes. Oecologia 138, 74–82. (10.1007/s00442-003-1406-l) PubMed DOI

Rodríguez-Castañeda G, Forkner RE, Tepe EJ, Gentry GL, Dyer LA. 2011. Weighing defensive and nutritive roles of ant mutualists across a tropical altitudinal gradient. Biotropica 43, 343–350. (10.1111/j.1744-7429.2010.00700.x) DOI

Sam K, Koane B, Novotny V. 2015. Herbivore damage increases avian and ant predation of caterpillars on trees along a complete elevational forest gradient in Papua New Guinea. Ecography (Cop.). 38, 293–300. (10.1111/ecog.00979) DOI

Blüthgen N, Menzel F, Hovestadt T, Fiala B, Blüthgen N. 2007. Specialization, constraints, and conflicting interests in mutualistic networks. Curr. Biol. 17, 341–346. (10.1016/j.cub.2006.12.039) PubMed DOI

Olesen JM, Bascompte J, Dupont YL, Jordano P. 2007. The modularity of pollination networks. Proc. Natl Acad. Sci. USA 104, 19 891–19 896. (10.1073/pnas.0706375104) PubMed DOI PMC

Dáttilo W, Guimarães PR, Izzo TJ. 2013. Spatial structure of ant-plant mutualistic networks. Oikos 122, 1643–1648. (10.1111/j.1600-0706.2013.00562.x) DOI

Brühl CA, Gunsalam G, Linsenmair KE. 1998. Stratification of ants (Hymenoptera, Formicidae) in a primary rain forest in Sabah, Borneo. J. Trop. Ecol. 14, 285–297. (10.1017/S0266467498000224) DOI

Longino JT, Branstetter MG, Colwell RK, Smith M.. 2014. How ants drop out: ant abundance on tropical mountains. PLoS ONE 9, e104030 (10.1371/journal.pone.0104030) PubMed DOI PMC

Colwell RK, et al. 2016. Midpoint attractors and species richness: modelling the interaction between environmental drivers and geometric constraints. Ecol. Lett. 19, 1009–1022. (10.1111/ele.12640) PubMed DOI

R Core Team 2014. R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing.

Dormann CF, Strauss R. 2014. A method for detecting modules in quantitative bipartite networks. Methods Ecol. Evol. 5, 90–98. (10.1111/2041-210X.12139) DOI

Blüthgen N, Menzel F, Blüthgen N. 2006. Measuring specialization in species interaction networks. BMC Ecol. 6, 9 (10.1186/1472-6785-6-9) PubMed DOI PMC

Dormann CF, Frund J, Bluthgen N, Gruber B. 2009. Indices, graphs and null models: analyzing bipartite ecological networks. Open Ecol. J. 2, 7–24. (10.2174/1874213000902010007) DOI

Hoeffding W. 1948. A non-parametric test of independence. Ann. Math. Stat. 19, 546–557. (10.1214/aoms/1177730150) DOI

Blüthgen N. 2010. Why network analysis is often disconnected from community ecology: a critique and an ecologist's guide. Basic Appl. Ecol. 11, 185–195. (10.1016/j.baae.2010.01.001) DOI

de Wilde WJJO. 1998. The myrmecophilous species of Myristica (Myristicaceae) from New Guinea. Blumea 43, 165–182.

Gullan PJ, Buckley RC, Ward PS. 1993. Ant-tended scale insects (Hemiptera: Coccidae: Myzolecanium) within lowland rain forest trees in Papua New Guinea. J. Trop. Ecol. 9, 81–91. (10.1017/S0266467400006994) DOI

Edwards DP, Ansell FA, Woodcock P, Fayle TM, Chey VK, Hamer KC. 2010. Can the failure to punish promote cheating in mutualism? Oikos 119, 45–52. (10.1111/j.1600-0706.2009.17591.x) DOI

Maunsell SC, Kitching RL, Burwell CJ, Morris RJ. 2015. Changes in host-parasitoid food web structure with elevation. J. Anim. Ecol. 84, 353–363. (10.1111/1365-2656.12285) PubMed DOI

Morris RJ, Sinclair FH, Burwell CJ. 2015. Food web structure changes with elevation but not rainforest stratum. Ecography (Cop.). 38, 792–802. (10.1111/ecog.01078) DOI

Fonseca CR, Ganade G. 1996. Asymmetries, compartments and null interactions in an Amazonian ant-plant community. J. Anim. Ecol. 65, 339–347. (10.2307/5880) DOI

Rico-Gray V, García-Franco JG, Palacios-Rios M, íz-Castelazo C, Parra-Tabla V, Navarro JA.. 1998. Geographical and seasonal variation in the richness of ant-plant interactions in México. Biotropica 30, 190–200. (10.1111/j.1744-7429.1998.tb00054.x) DOI

Fiala B, Jakob A, Maschwitz U, Linsenmair KE. 1999. Diversity, evolutionary specialization and geographic distribution of a mutualistic ant-plant complex: Macaranga and Crematogaster in South East Asia. Biol. J. Linn. Soc. 66, 305–331. (10.1111/j.1095-8312.1999.tb01893.x) DOI

Moses J. 2014. A tropical elevational gradient in ants (Hymenoptera: Formicidae): diversity patterns, food preferences and scavenging activities on Mt Wilhelm, Papua New Guinea. MSc thesis, University of Papua New Guinea, Port Moresby, Papua New Guinea.

Brühl CA, Mohamed M, Linsenmair KE. 1999. Altitudinal distribution of leaf litter ants along a transect in primary forests on Mount Kinabalu, Sabah, Malaysia. J. Trop. Ecol. 15, 265–277. (10.1017/S0266467499000802) DOI

Kwon TS, Kim SS, Chun JH. 2014. Pattern of ant diversity in Korea: an empirical test of Rapoport's altitudinal rule. J. Asia. Pac. Entomol. 17, 161–167. (10.1016/j.aspen.2013.12.006) DOI

Ramos-Jiliberto R, Domínguez D, Espinoza C, López G, Valdovinos FS, Bustamante RO, Medel R. 2010. Topological change of Andean plant–pollinator networks along an altitudinal gradient. Ecol. Complex. 7, 86–90. (10.1016/j.ecocom.2009.06.001) DOI

Dunne JA, Williams RJ, Martinez ND. 2002. Network structure and biodiversity loss in food webs: robustness increases with connectance. Ecol. Lett. 5, 558–567. (10.1046/j.1461-0248.2002.00354.x) DOI

Rico-Gray V, Díaz-Castelazo C, Ramírez-Hernández A, Guimarães PR, Nathaniel Holland J. 2012. Abiotic factors shape temporal variation in the structure of an ant-plant network. Arthropod. Plant. Interact. 6, 289–295. (10.1007/s11829-011-9170-3) DOI

Davidson DW, Longino JT, Snelling RR. 1988. Pruning of host plant neighbors by ants: an experimental approach. Ecology 69, 801–808. (10.2307/1941029) DOI

Fargione J, Tilman D, Dybzinski R, HilleRisLambers J, Clark C, Harpole WS, Knops JMH, Reich PB, Loreau M. 2007. From selection to complementarity: shifts in the causes of biodiversity-productivity relationships in a long-term biodiversity experiment. Proc. R. Soc. B 274, 871–876. (10.1098/rspb.2006.0351) PubMed DOI PMC

Plowman NS, Hood ASC, Moses J, Redmond C, Novotny V, Klimes P, Fayle TM. 2017. Data from: Network reorganization and breakdown of an ant-plant protection mutualism with elevation. Dryad Digital Repository. (10.5061/dryad.r9q18) PubMed DOI PMC

Phylogenetic structure of moth communities (Geometridae, Lepidoptera) along a complete rainforest elevational gradient in Papua New Guinea

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