Seed predation by rodents results in directed dispersal of viable seed fragments of an endangered desert shrub

Abstract

Abstract. Seed predation and seed dispersal are important ecological processes with antagonistic effects on plant recruitment. In the southern edge of the Atacama Desert in Chile, Myrcianthes coquimbensis is an endangered, large-seeded, vertebrate-dispersed shrub that in the present-day has no known dispersers. Native rodents hoard and eat the seeds of M. coquimbensis but leave viable seed fragments at the hoarding sites; soil interspaces within rock outcrops where seedlings recruit. Here we examined whether rodents act as effective dispersers of M. coquimbensis by discarding viable seed fragments in sites suitable for recruitment. We simulated different levels of endosperm loss to determine if seedlings could develop from seed fragments. We assessed how frequently rodents discarded fragments, and the probability that these fragments produced seedlings. Finally, we compared emergence and seedling survival at the hoarding sites and in two other habitats where seeds arrive to evaluate the suitability of the hoarding sites. Seeds of M. coquimbensis developed seedlings even after 87% of their storage tissue was removed. Rodents left seed fragments in more than 50% of the trials; almost 60% of the discarded fragments produced seedlings. Seedlings did not emerge from open ground habitats, and emergence was higher under M. coquimbensis shrubs than in rock habitats. Survival of two-year-old seedlings was higher in rock habitats than under conspecific adult shrubs. Our results suggest that rodents may play a dual role in the recruitment dynamics of M. coquimbensis, acting simultaneously as seed predators and effective dispersers. Therefore, though seed predators impose costs, their net effect on plant fitness in this system-where dispersers of largeseeded species have been lost-is likely positive.

Implications of lemuriform extinctions for the Malagasy flora

“…Although large-seeded orphans persist today, this persistence is likely due to their long generation times and uncertain and inefficient secondary dispersal agents, such as Rattus rattus or strong winds during cyclones (18,32,33,35). Our study suggests that their long-term survival may be tenuous.…”

“…Dispersal to growing sites removed from parent trees enhances gene flow, reduces competition among related individuals, and promotes escape from specialized herbivores (30,31). Dispersal alternatives for large-seeded orphans include the strong winds of cyclones and secondary dispersal through the movement of fallen seeds by rodents (18,32,33). Although effective in some circumstances (34), secondary dispersal has generally been shown to be inefficient and unreliable (18,32,33), and cyclone-mediated seed dispersal is, at best, an extreme and unreliable dispersal mechanism (35).…”

Connecting Resource Tracking by Frugivores to Temporal Variation in Seed Dispersal Networks

“…To date, directed dispersal has been disproportionately studied for specialized and rare plant species (Wenny, 2001;Loayza et al, 2014). Classic examples of directed dispersal include the dispersal of mistletoes into suitable sites within its host trees and ant-plant mutualisms (Wenny, 2001;Green et al, 2008;Salazar et al, 2013).…”

Dispersal of semi-fleshy fruits to rock crevices by a rock-restricted rodent

“…In other rodent frugivory cases, the fruits may be partially damaged. [11][12][13][14] Globally, rodent frugivory, in which the seed is not ingested and left undamaged, has only been documented in a few studies. 13,15 Exotic rodents have been documented to disperse seeds while only consuming the pericarp.…”