Abstract
Frugivory is a widespread mutualistic interaction in which frugivores obtain nutritional resources while favoring plant recruitment through their seed dispersal services. Nonetheless, how these complex interactions are organized in diverse communities, such as tropical forests, is not fully understood. In this study we evaluated the existence of plant-frugivore sub-assemblages and their phylogenetic organization in an undisturbed western Amazonian forest in Colombia. We also explored for potential keystone plants, based on network analyses and an estimate of the amount of fruit going from plants to frugivores. We carried out diurnal observations on 73 canopy plant species during a period of two years. During focal tree sampling, we recorded frugivore identity, the duration of each individual visit, and feeding rates. We did not find support for the existence of sub assemblages, such as specialized vs. generalized dispersal systems. Visitation rates on the vast majority of canopy species were associated with the relative abundance of frugivores, in which ateline monkeys (i.e. Lagothrix and Ateles) played the most important roles. All fruiting plants were visited by a variety of frugivores and the phylogenetic assemblage was random in more than 67% of the cases. In cases of aggregation, the plant species were consumed by only primates or only birds, and filters were associated with fruit protection and likely chemical content. Plants suggested as keystone species based on the amount of pulp going from plants to frugivores differ from those suggested based on network approaches. Our results suggest that in tropical forests most tree-frugivore interactions are generalized, and abundance should be taken into account when assessing the most important plants for frugivores.
Highlights
Interactions leading to the escape of seeds from parental plants and the colonization of adequate sites for recruitment play a relevant role in dynamics of many ecosystems [1, 2, 3].PLOS ONE | DOI:10.1371/journal.pone.0140751 October 22, 2015Frugivory in Western Amazonia
For all plant species consumed by primates, we maintained total primate-feeding time from our observations, but modified the proportion assigned to each monkey by using the relative consumption found in intensive studies of primate behavior [52], because they were based on larger datasets
We found no support for the expectations of specialized and generalized dispersal systems since none of seven predictions based on our hypothesis were supported (Table 3)
Summary
Interactions leading to the escape of seeds from parental plants and the colonization of adequate sites for recruitment play a relevant role in dynamics of many ecosystems [1, 2, 3]. The first hypothesis on the evolution of plant-frugivore interactions envisioned a strong role of selective forces imposed by animal agents, in such a way that many fruit traits (i.e. color, accessibility, size, defenses and nutritional contents) evolved to attract particular dispersal agents [21] These ideas were the basis for the formulation of the evolution of specialized vs generalized dispersal systems [22,23,24]. Most plant-animal mutualisms tend to be organized in a nested fashion [38], where specialists interact with subsets of the species with which generalists interact According to these studies, the degree of specialization in mutualistic networks should behave as a continuum and not in a bimodal way, as suggested by generalized vs specialized dispersal systems. We use an estimate of the pulp biomass going to the level of primary consumers (as a proxy of energy use [49]), including information of the strength of the interaction and the abundance of the plant population
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