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      Linkage Rules for Plant–Pollinator Networks: Trait Complementarity or Exploitation Barriers?

      1 , * , 2
      PLoS Biology
      Public Library of Science

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          Recent attempts to examine the biological processes responsible for the general characteristics of mutualistic networks focus on two types of explanations: nonmatching biological attributes of species that prevent the occurrence of certain interactions (“forbidden links”), arising from trait complementarity in mutualist networks (as compared to barriers to exploitation in antagonistic ones), and random interactions among individuals that are proportional to their abundances in the observed community (“neutrality hypothesis”). We explored the consequences that simple linkage rules based on the first two hypotheses (complementarity of traits versus barriers to exploitation) had on the topology of plant–pollination networks. Independent of the linkage rules used, the inclusion of a small set of traits (two to four) sufficed to account for the complex topological patterns observed in real-world networks. Optimal performance was achieved by a “mixed model” that combined rules that link plants and pollinators whose trait ranges overlap (“complementarity models”) and rules that link pollinators to flowers whose traits are below a pollinator-specific barrier value (“barrier models”). Deterrence of floral parasites (barrier model) is therefore at least as important as increasing pollination efficiency (complementarity model) in the evolutionary shaping of plant–pollinator networks.

          Author Summary

          Whether they are antagonistic—as between predator and prey—or beneficial—as between pollinator and flower, interactions among all the key species in an ecosystem follow regular patterns. Connectivity (the proportion of possible interactions that are actually realised), for instance, decreases with network size. The “forbidden links” hypothesis proposes that connectivity decreases because interactions are prevented by a mismatch of biological attributes between certain species. Mismatches could arise from the evolution of complementary traits in mutualistic relationships (such as insects preferring to pollinate only flowers of a certain colour) or of traits that prevent exploitation in antagonistic ones (such as a plant growing a long corolla so that insects without a long proboscis cannot reach the nectar reward). We explored the consequences of simple linkage rules based on these two variants on the topology of plant–pollination networks. When compared to data for 37 real plant–pollinator networks, we show that a “mixed” model that combines simple rules from both “complementarity” and “barrier” models best explains the pattern of interactions. This implies, for example, that deterring floral parasites is at least as important as increasing pollination efficiency in the evolution of plant–pollinator networks. Our work emphasises the value of explaining the underlying ecological and evolutionary mechanisms generating such patterns.


          The topology of plant-pollinator networks can be explained by relatively simple rules incorporating both "complementarity" and "barrier" traits, thus providing insights into the possible evolutionary and ecological processes driving the pattern.

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          Most cited references67

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          Flowering Plants

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            Patterns of Mutualistic Interactions in Pollination and Seed Dispersal: Connectance, Dependence Asymmetries, and Coevolution

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              The latitudinal gradient in niche breadth: concepts and evidence.

              We examine Robert MacArthur's hypothesis that niche breadth is positively associated with latitude (the latitude-niche breadth hypothesis). This idea has been influential and long standing, yet no studies have evaluated its generality or the validity of its assumptions. We review the theoretical arguments suggesting a positive relationship between niche breadth and latitude. We also use available evidence to evaluate the assumptions and predictions of MacArthur's latitude-niche breadth hypothesis. We find that neither the assumptions nor the predictions of the hypothesis are supported by data. We propose an alternative hypothesis linking latitude with niche breadth. Unlike previous ideas, our conceptual framework does not require equilibrial assumptions and is based on recently uncovered patterns of species interactions.

                Author and article information

                Role: Academic Editor
                PLoS Biol
                PLoS Biology
                Public Library of Science (San Francisco, USA )
                February 2007
                23 January 2007
                : 5
                : 2
                : e31
                [1 ] Mediterranean Institute for Advanced Studies, University of the Balearic Islands/Spanish Council for Scientific Research, Esporles, Mallorca, Spain
                [2 ] Estación Experimental de Zonas Áridas, Spanish Council for Scientific Research, Almería, Spain
                University of London, United Kingdom
                Author notes
                * To whom correspondence should be addressed. E-mail: luis.santamaria@ 123456uib.es
                06-PLBI-RA-0707R3 plbi-05-02-10
                Copyright: © 2007 Santamaría and Rodríguez-Gironés. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                : 3 May 2006
                : 1 December 2006
                Page count
                Pages: 9
                Research Article
                Evolutionary Biology
                Custom metadata
                Santamaría L, Rodríguez-Gironés MA (2007) Linkage rules for plant–pollinator networks: Trait complementarity or exploitation barriers? PLoS Biol 5(2): e31. doi: 10.1371/journal.pbio.0050031

                Life sciences
                Life sciences


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