Precipitation Drives Frugivory in a Subtropical Generalist Herbivore,
the Gopher Tortoise, and Alters its Functional Role as a Seed Disperser
Abstract
Consumers employ a variety of foraging strategies, and oftentimes the
foraging strategy employed is related to resource availability. As
consumers acquire resources, they may interact with their resource base
in mutualistic or antagonistic ways – falling along a
mutualism-antagonism continuum – with implications for ecological
processes such as seed dispersal. However, patterns of resource use vary
temporally, and textbook herbivores may switch foraging tactics to
become more frugivorous in periods of greater fleshy fruit availability.
In this study, we investigated how fleshy fruit consumption of a
generalist herbivore – the gopher tortoise (Gopherus polyphemus) –
shifts intra-annually following seasonal precipitation and subsequently
examined how this shift toward increased frugivory influences the suite
of plant syndromes dispersed. We noted a clear intra-annual shift toward
a more frugivorous diet which coincided with seasonal precipitation and
subsequently observed a marked shift in the plant syndromes dispersed
with increasing frugivory. We found that as this generalist herbivore
became more frugivorous, it dispersed a greater variety of plant
syndromes at low levels of frugivory. However, when the gopher tortoise
exhibited high levels of frugivory, the seed load was dominated by those
exhibiting the Endozoochory syndrome. This study illustrates a
functional shift in a seed dispersing herbivore toward that of a
classical frugivore, suggesting that temporal variation in foraging
strategy and the temporal scale in which foraging habits and seed
dispersal interactions are quantified have implications for the suite of
plant syndromes species disperse. Furthermore, tradeoffs may exist that
provide plants with the Endozoochory syndrome with a competitive
advantage over seeds with contrasting traits, such as the Foliage is the
Fruit syndrome which is expected to experience greater dispersal by
classical herbivores.