Specialization and interaction strength in a tropical plant–frugivore network differ among forest strata

Authors

  • Matthias Schleuning,

    1. Department of Ecology, Institute of Zoology, University of Mainz, Becherweg 13, 55128 Mainz, Germany
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    •  Present address: Biodiversity and Climate Research Centre (BiK-F), Senckenberganlage 25, 60325 Frankfurt (Main), Germany. E-mail: mschleuning@senckenberg.de

  • Nico Blüthgen,

    1. Department of Animal Ecology and Tropical Biology, Biozentrum, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
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  • Martina Flörchinger,

    1. Department of Ecology, Institute of Zoology, University of Mainz, Becherweg 13, 55128 Mainz, Germany
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  • Julius Braun,

    1. Department of Animal Ecology and Evolutionary Biology, Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany
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    •  Present address: Department of Evolutionary Biology of Invertebrates, Zoological Institute, University of Tübingen, Auf der Morgenstelle 28E, 72076 Tübingen, Germany.

  • H. Martin Schaefer,

    1. Department of Animal Ecology and Evolutionary Biology, Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany
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  • Katrin Böhning-Gaese

    1. Department of Ecology, Institute of Zoology, University of Mainz, Becherweg 13, 55128 Mainz, Germany
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    •  Present address: Biodiversity and Climate Research Centre (BiK-F), Senckenberganlage 25, 60325 Frankfurt (Main), Germany, and Johann Wolfgang Goethe-Universität, Department of Biological Sciences, Siesmayerstr. 70, 60323 Frankfurt (Main), Germany.


Abstract

The degree of interdependence and potential for shared coevolutionary history of frugivorous animals and fleshy-fruited plants are contentious topics. Recently, network analyses revealed that mutualistic relationships between fleshy-fruited plants and frugivores are mostly built upon generalized associations. However, little is known about the determinants of network structure, especially from tropical forests where plants' dependence on animal seed dispersal is particularly high. Here, we present an in-depth analysis of specialization and interaction strength in a plant–frugivore network from a Kenyan rain forest. We recorded fruit removal from 33 plant species in different forest strata (canopy, midstory, understory) and habitats (primary and secondary forest) with a standardized sampling design (3447 interactions in 924 observation hours). We classified the 88 frugivore species into guilds according to dietary specialization (14 obligate, 28 partial, 46 opportunistic frugivores) and forest dependence (50 forest species, 38 visitors). Overall, complementary specialization was similar to that in other plant–frugivore networks. However, the plant–frugivore interactions in the canopy stratum were less specialized than in the mid- and understory, whereas primary and secondary forest did not differ. Plant specialization on frugivores decreased with plant height, and obligate and partial frugivores were less specialized than opportunistic frugivores. The overall impact of a frugivore increased with the number of visits and the specialization on specific plants. Moreover, interaction strength of frugivores differed among forest strata. Obligate frugivores foraged in the canopy where fruit resources were abundant, whereas partial and opportunistic frugivores were more common on mid- and understory plants, respectively. We conclude that the vertical stratification of the frugivore community into obligate and opportunistic feeding guilds structures this plant–frugivore network. The canopy stratum comprises stronger links and generalized associations, whereas the lower strata are composed of weaker links and more specialized interactions. Our results suggest that seed-dispersal relationships of plants in lower forest strata are more prone to disruption than those of canopy trees.

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