Endozoochory of Chrysobalanus icaco (Cocoplum) by Gopherus polyphemus (Gopher Tortoise) facilitates rapid germination and colonization in a suburban nature preserve

Abstract

Some large-seeded plants lack effective seed dispersal agents when they are introduced as ornamental plants to new areas, but can rapidly colonize a landscape if seed dispersal functions are restored. We examined whether Gopherus polyphemus (Gopher Tortoise) facilitated the spread of Chrysobalanus icaco (Cocoplum; Chrysobalanaceae) over a 14-year period in a suburban nature preserve (in Jupiter, FL, USA) by: (i) comparing germination patterns among gut-passed, hand-depulped and whole fruit treatments, and (ii) testing hypotheses about environmental predictors of the spatial distribution of C. icaco, including information about G. polyphemus movement pathways and burrow locations. While we did not find a significant difference in the total proportion of C. icaco seeds that germinated in each treatment, time to event analysis revealed that seeds that were found in faeces germinated significantly earlier than seeds that were hand-depulped or that were planted as whole fruits, supporting a lone scarification effect. Point process modeling revealed that the density of C. icaco bushes was higher near G. polyphemus movement pathways and was lower inside Serenoa repens (Saw Palmetto) patches, supporting a positive effect of tortoise movement patterns on plant distributions. The density of C. icaco increased from west to east, consistent with westward dispersal from the four founder bushes on the east side of the study area. After removal of outliers, we also detected a negative association between C. icaco spatial density and G. polyphemus burrow density that was presumably explained by the fact that seeds defecated deep within burrows were unlikely to germinate and establish without secondary movement. The results suggest that G. polyphemus contributed to the rapid dispersal of C. icaco by scatter dispersal of seeds (via faeces) in areas where tortoises were active and that movement pathways provided suitable conditions for colonization. The spread of C. icaco by G. polyphemus over a relatively short period of time provides a valuable window into the earliest stages of the colonization process and further supports the role of Chelonians as effective seed dispersal agents for large-seeded plants.

The important role of animal social status in vertebrate seed dispersal

“…However, more data on these taxonomic groups is needed to determine whether our framework could be applied in these systems. Although some species of frugivorous reptiles and fish are known to disperse seeds (Anderson et al, 2009, 2011; Corlett, 2017; Costa‐Pereira & Galetti, 2015; Hanish et al, 2020; Piazzon et al, 2012; Platt et al, 2013; Valido & Nogales, 1994), the effects of these taxa on seed‐dispersal patterns are notably understudied (Costa‐Pereira & Galetti, 2015; Genes & Dirzo, 2022). Moreover, reptilian social systems can be highly diverse and complex, yet disproportionately understudied compared with other vertebrate taxa (Doody et al, 2013).…”

Secondary Seed Ingestion in Snakes: Germination Frequency and Rate, Seedling Viability, and Implications for Dispersal in Nature

“…Second, in the primary study only, we tested whether the seeds exposed to gut transit germinated at a greater rate and frequency than those of the controls, viz. the accelerated germination hypothesis (Castilla, 2000;Traveset et al, 2001;Hämäläinen et al, 2017;Hanish et al, 2020;Salazar-Rivera et al, 2020;Yang et al, 2021).…”

The effect of lizards on the dispersal and germination of Capparis spinosa (Capparaceae)

“…The dispersal of many plants depends on transport by seed-dispersing animals [3]. A growing body of research has reported seed dispersal mediated by fish [4], birds [5], primates [6], turtles [7] and lizards [8], which are potential seed dispersers. Lizards can be effective seed dispersers in terms of fruit removal, seed deposition in suitable habitats and seed germination [9].…”