Large vertebrates as the missing components of seed-dispersal networks

• Large frugivores may be key as seed dispersers.
• The loss of large frugivores can deeply affect seed-dispersal networks.
• Large vertebrates are often absent from descriptions of seed-dispersal networks.
• Possible causes are defaunation, taxonomic bias and secretive behavior.
• We suggest an approach to assess the importance of large frugivores.

Large-bodied frugivores may play a key role in the networks of plants and their seed dispersers. These species, however, are often threatened by human impacts that lead to defaunation. In this paper, we discuss the potential implications of the loss of large frugivores for seed-dispersal networks. First, we review the role of large vertebrates as seed dispersers in different tropical ecosystems to show that these species are likely to be important components of seed-dispersal networks. Second, we showed that, despite their importance, large vertebrates are absent from most of the seed-dispersal networks described in the available literature. We identified three main reasons for this absence: (1) large vertebrates have already died out in the studied areas; (2) studies focus on particular taxonomic groups that consist mostly of small birds; and (3) it is inherently difficult to describe the interactions of naturally rare and secretive species such as large vertebrates. We argue that a proper evaluation of the importance of large frugivores within seed-dispersal networks would benefit from considering aspects other than the frequency of interactions. We suggest weighting pairwise interactions by their ecological consequences to quantify the contribution of large frugivores to outcomes of seed dispersal, such as landscape connectivity.