Queen palm fruit selection and foraging techniques of squirrels in the Atlantic Forest

Abstract

Queen palm seeds (Syagrus romanzoffiana) are a vital source of nutrients for Ingram's squirrel (Guerlinguetus ingrami), a common inhabitant of the Atlantic forest biome of Brazil. G. ingrami acts as both a seed predator and disperser of this important palm; however, little is known about how G. ingrami selects or efficiently opens queen palm seeds. The objectives of this study were to: (1) investigate the squirrel's capacity to determine the germinal orifice among the fruit's three pores, which permits more efficient opening of the fruit; (2) assess whether the thickness and size of the fruit endocarp influence the squirrel's palm selection during foraging; and (3) evaluate whether the rodents preferentially select fruits with invertebrate infestations. To answer these questions, we used a series of behavioral experiments measuring patterns of squirrel feeding behavior (fruit opening, fruit selection, and patch selection), controlling for environmental variables. We found that (1) squirrels identify the queen palm germinal pore by its greater relative depth to the other pores; (2) the average size and thickness of fruit does not influence the squirrel's choice of palm for foraging; and (3) squirrels preferentially consume fruits infested by invertebrates. The development of methods for more efficient processing of queen palm fruit highlights the importance of this resource for G. ingrami. In addition, due to its preferential selection of infested fruits, G. ingrami may benefit palms by reducing parasite population loads.

Associated evolution of fruit size, fruit colour and spines in Neotropical palms

“…Seed predation can significantly impact fitness (Gómez, 2004; Orrock, Levey, Danielson, & Damschen, 2006) and plants that invest on producing large seeds also invest in defending them against predation (Bodmer, 1991). The evolutionary relationship between fruit size and presence of spines could be a response to seed predation pressure by vertebrates, especially rodents such as squirrels, which occasionally act as seed dispersers (Muñoz, Schaefer, Böhning‐Gaese, & Schleuning, 2017) but often consume palm seeds (Alves, Mendes, & Ribeiro, 2018; Mendes, Koprowski, & Galetti, 2019). However, even though the effectiveness of spines in preventing seed predation has not been systematically investigated, the spiny trunks of Astrocaryum spp.…”

Intrinsic and extrinsic drivers of intraspecific variation in seed dispersal are diverse and pervasive

“…disproportionately dispersed and cached seeds from Pinus armandii individuals with larger mean seed mass (Wang and Ives 2017), although the greater probability of their seeds being consumed cancelled the benefits of increased dispersal. By contrast, mean seed size of the Queen palm ( Syagrus romanzoffiana ) had no influence on tree selection by squirrels (Alves et al 2018), and Garrulus glandarius preferentially fed on Quercus ilex trees with smaller acorns (Morán-López et al 2015a). Thus, although evidence is limited, there is potential for seed size to contribute to interindividual variation in the quantity and quality of seed dispersal by synzoochorous dispersers.…”

“…Endocarp or seed coat thickness as a deterrent has long been considered an evolutionary response to synzoochory, in particular to managing the dual role of seed dispersal and seed predation, and there is substantial interspecific support for the idea that these dispersers select and handle seeds at least partly based on endocarp or seed coat thickness (see Vander Wall 2010). Intraspecific studies on the effects of seed coat thickness are sparse and inconsistent; mean endocarp thickness of the palm S. romanzoffiana did not influence tree selection by the squirrel Guerlinguetus ingrami (Alves et al 2018), but P. flexilis seeds with thicker seed coats were more likely to be cached by rodents and were dispersed further than seeds with thinner coats (Siepielski and Benkman 2008). Chemical deterrents may also play a role in interindividual dispersal by synzoochorous dispersers.…”

NEOSQUIRREL: a data set of ecological knowledge on Neotropical squirrels

“…Invertebrates do appear to be a common food source; squirrels sometimes prefer to feed upon fruits containing beetle larvae than on fruits without larvae (Alves et al. ). It is very probable that the difficulty in observing when squirrels are consuming fruits containing larvae contributes to the underestimation of invertebrates as a food source for these rodents (Silvius ).…”