The seed dispersal syndrome hypothesis in ungulate-dominated landscapes

Abstract

The Seed Dispersal Syndrome Hypothesis (SDSH) posits that fruit traits predict the main dispersers interacting with plant species. Mammalian dispersers, relying heavily on olfactory cues, are expected to select dull-colored, scented, and larger fruits compared to birds. However, challenges like overabundant seed predators and context-dependency of frugivore-plant interactions complicate SDSH expectations. We studied the Iberian pear, Pyrus bourgaeana, an expected mammal-dispersed tree based on its fruit traits. Extensive camera-trapping data (over 35,000 records) from several tree populations and years revealed visits from seven frugivore groups, with ungulate fruit predators (59-97%) and carnivore seed dispersers (1-20%) most frequent, while birds, lagomorphs, and rodents were infrequent (0-10%). Red deer and wild boar were also the main fruit removers in all sites and years but acted as fruit and seed predators, and thus likely exert conflicting selection pressures to those exerted by seed dispersers. Although, as predicted by the SDSH, most Iberian pear fruits were consumed by large and medium-sized mammals, the traits of Iberian pear fruits likely reflect selection pressures from dispersal vectors in past times. Our results do not challenge the SDHS but do reveal the importance of considering frugivore functional roles for its adequate evaluation.

Figure 1

Frequency of visits and number of visited Pyrus bourgaeana trees by the main four functional groups in the three study sites (Andujar, Matasgordas, Reserva) within southern Spain. The Andujar and Reserva populations were sampled during the fruiting seasons of 2019 and 2022, respectively. The Matasgordas populations was sampled during 2019, 2021 and 2022 fruiting seasons. The percent of handled fruits by the main frugivore functional groups in Andujar are also shown (A).