The overlooked benefits of synzoochory: rodents rescue seeds from aborted fruits

Jose M Fedriani,Gemma Calvo,Daniel Ayllón,Pedro J Garrote,Miguel Delibes

doi:10.1002/ecs2.3298

Abstract

AbstractLarge‐scale abortion of immature fruits is a pervasive phenomenon across seed plants due to maternal physiological decisions associated with matching resources with fruit crop size. Aborted fruits are usually disqualified from studies of both fruit production and seed dispersal. However, a considerable number of developing seeds occur within immature aborted fruits. We evaluated the untested hypotheses that seeds within aborted fruits are viable and that incomplete predation of seeds within aborted fruits by hoarding rodents provides, in addition to seed movement, increased germination and seedling emergence. To this end, we studied the system composed by the Iberian pear Pyrus bourgaeana and several rodent species in Mediterranean Spain. About a third of aborted fruits found beneath tree canopies (n = 2430) were partially eaten by rodents. Using a seed sowing experiment, we revealed that a considerable fraction of seeds from P. bourgaeana aborted fruits are viable, germinating, and emerging seedlings. Paradoxically, however, these seeds are de facto unviable since they are confined within the extremely hard pericarp of aborted fruits, which prevents any seedling emergence and thus any contribution to tree recruitment. We show that only when rodents partially gnaw the pericarp walls of aborted fruits, seeds that escaped from predation have the prospect of emerging and thus potentially contributing to tree regeneration. Thus, in this and probably in many other similar synzoochore systems, rodents act as rescuers of seeds confined within aborted fruits, conferring the plants a largely overlooked benefit that could shape the reproductive strategy of many plant species.

Highlights

Despite the fact that ecological interactions are often described as either antagonistic or mutualistic, most of them correspond to a mixture of conflicting and overlapping interests, with the capacity of being positive or negative for the participants (Bronstein 2001, Van Baalen and Jansen 2001, Fedriani and Delibes 2011, Kiers et al.2011)
We evaluate the untested hypotheses that seeds within aborted fruits are viable and that partial consumption of aborted fruits by hoarding rodents provides, in addition to seed movement, increased germination and seedling emergence
We rigorously sampled four trees that had underneath 607.5 Æ 148.1 aborted fruits, with about a third of them (31.6% Æ 5.4; n = 2430) being partially eaten by rodents

Summary

Introduction

Despite the fact that ecological interactions are often described as either antagonistic or mutualistic, most of them correspond to a mixture of conflicting and overlapping interests, with the capacity of being positive or negative for the participants (Bronstein 2001, Van Baalen and Jansen 2001, Fedriani and Delibes 2011, Kiers et al.2011). Some seed-eating animals transport seeds in the mouth or inside their cheeks followed by the hoarding of at least a fraction of those seeds (synzoochory; see Gomez et al 2019 review). In these synzoochorous systems, seeds that are not consumed immediately may benefit from being stored some distance away from the mother plant and forgotten, enhancing seed survival and the population persistence as well as the chances of colonization of vacant habitats (Vander Wall 1990, Iluz 2011). In synzochore systems the animal partner plays a dual role, acting both as seed disperser and seed predator

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