Caching rodents disproportionately disperse seed beneath invasive grass

Pacifica Sommers,Peter Chesson

doi:10.1002/ecs2.1596

Abstract

AbstractSeed dispersal by caching rodents is a context‐dependent mutualism in many systems. Plants benefit when seed remaining in shallow caches germinates before being eaten, often gaining protection from beetles and a favorable microsite in the process. Caching in highly unfavorable microsites, conversely, could undermine the dispersal benefit for the plant. Plant invasions could disrupt dispersal benefits of seed caching by attracting rodents to the protection of a dense invasive canopy which inhibits the establishment of native seedlings beneath it. To determine whether rodents disproportionately cache seed under the dense canopy of an invasive grass in southeastern Arizona, we used nontoxic fluorescent powder and ultraviolet light to locate caches of seed offered to rodents in the field. We fitted a general habitat‐use model, which showed that disproportionate use of plant cover by caching rodents (principally Chaetodipus spp.) increased with moonlight. Across all moon phases, when rodents cached under plants, they cached under the invasive grass disproportionately to its relative cover. A greenhouse experiment showed that proximity to the invasive grass reduced the growth and survival of seedlings of a common native tree (Parkinsonia microphylla) whose seeds are dispersed by caching rodents. Biased dispersal of native seed to the base of an invasive grass could magnify the competitive effect of this grass on native plants, further reducing their recruitment and magnifying the effect of the invasion.

Highlights

Plant invasions in many parts of the world are reducing the abundance of native plants and altering important species interactions (Vitousek et al 1997, Shea and Chesson 2002, Levine et al 2003)
Use of vegetation overall did Across all eight surveys, we located 99 caches, 74 of which were under vegetation and 45 of which were under Pennisetum ciliare (Appendix S1)
We found that rodents disproportionately cached seed under the invasive grass Pennisetum ciliare rather than under native plants at our study site, given equal availability

Summary

Introduction

Plant invasions in many parts of the world are reducing the abundance of native plants and altering important species interactions (Vitousek et al 1997, Shea and Chesson 2002, Levine et al 2003). Among the important affected species interactions are seed-dispersal mutualisms (Traveset and Richardson 2014). Dispersal of native seed can be disrupted by invasive plants bearing attractive fruits, as these can satiate frugivores that ignore native fruits, which remain under the parent plant (Heleno et al 2013, Mokotjomela et al 2013). Seed-caching mutualisms, in which animals harvest beyond satiation, should not be disrupted in the same way because satiation does not deter harvest and caching of even less desirable seed. Such mutualisms could be disrupted, if seed were transported disproportionately to sites where it has little chance of germinating or surviving. Invasive plants could cause such a disruption by providing a novel, attractive

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Conclusion