Showing papers by "Michael A. Steele published in 2001"
TL;DR: It is concluded that the primary advantage to the preference for caching red oak acorns is that they are less perishable, due to their dormancy, and the effects of this preference on the dispersal of red and white oak acorn and the subsequent effects of differential dispersal on the ecology and evolution of oaks.
Abstract: SYNOPSIS. We have shown that eastern gray squirrels and other animals consistently prefer to store intact acorns from the red oak group rather than those from the white oak group. We hypothesized that the ultimate advantage to this behavior comes from the dormancy of red oak acorns. Acorns of the white oak group germinate early in the autumn; thus, we hypothesize that avoiding germination is the primary selective advantage to the preference for caching red oak acorns. Here, we test two alternative hypotheses to explain the benefits of this caching preference: 1) storing red oak acorns allows the high tannin concentrations in red oak acorns to decline (making them more palatable), and 2) storing red oak acorns minimizes losses to insects, presuming they are less infested with insects. We also test the effect of germination schedule on squirrel caching preferences directly, by presenting them with dormant red oak acorns, and red oak acorns about to germinate. We find no evidence that tannin concentrations in red oak acorns decline, although tannin levels did decline in our white oak acorns. We found high losses to insect infestations in one white oak species, but a second white oak species lost very little mass to insects. Finally, we found that germination schedule directly affects squirrel caching preferences: red oak acorns that are near germination are treated like white oak acorns. We conclude that the primary advantage to the preference for caching red oak acorns is that they are less perishable, due to their dormancy. We discuss the effects of this preference on the dispersal of red and white oak acorns, and the subsequent effects of differential dispersal on the ecology and evolution of oaks.
130 citations
TL;DR: The results support the previous hypothesis that the behavior of embryo excision is geographically widespread and has important implications for cache-management strategies of some diurnal tree squirrels and their effect on dispersal of oaks.
Abstract: We conducted 2 field experiments to assess relative importance of acorn-embryo excision in the caching decisions of small mammals. In the 1st, we selectively provisioned small mammals with metal-tagged acorns of red oak (Quercus rubra) and white oak (Q. alba) at 40 point locations in 8 sites in an oak forest in northeastern Pennsylvania. We then followed the fate of cached seeds by relocating acorns with metal detectors soon after they were cached and again in spring after seeds began to germinate. At least 1 species of small mammal excised embryos of .70% of the cached acorns of white oak and ,4% of those of red oak. Animals also were observed to revisit caches in spring and excise embryos of germinating acorns. More excised acorns of white oak were found intact in spring than those of red oak, indicating that the behavior is important for long-term storage of these seeds. In a 2nd experiment, we presented free-ranging Mexican gray squirrels (Sciurus aureogaster) with pairs of acorns of 5 native white oak and 5 native red oak species and recorded caching events and whether or not cached seeds had their embryos removed. Squirrels cached significantly more acorns of white oak species, frequently excised embryos of these seeds, and only excised embryos of red oaks when they were germinating. These results support our previous hypothesis that the behavior of embryo excision is geographically widespread and has important implications for cache-management strategies of some diurnal tree squirrels and their effect on dispersal of oaks.
94 citations
TL;DR: It is argued that a chemical cue in the shell of acorns is important in the detection of seed dormancy and the decision to cache acorns, and that such a cue might ultimately contribute to the differential dispersal of red and white oaks by rodents.
Abstract: Previously we have shown how a range of physical and chemical characteristics of acorns influences the behavioral decisions of food-hoarding rodents which in turn affects the dispersal, establishment and spatial arrangement of oaks. One such behavior involves the selective caching of acorns of red oaks (subgenus: Erythrobalanus) over those of white oaks (Quercus) because of reduced perishability that results from delayed germination of acorns in the red oak group. In this study, we sought to identify the specific proximate cues (visual and olfactory) that eastern gray squirrels (Sciurus carolinensis) use when making these decisions. In two series of field experiments, we presented individual, free-ranging animals with pairs of experimentally altered acorns (that differed with respect to a single chemical or visual characteristic) and recorded their feeding and caching responses. Squirrels cached artificial acorns with pericarps (shells) of red oak acorns and ate those with shells of white oak reg...
65 citations