Interspecific competition in tree squirrels: do introduced grey squirrels (<Emphasis Type="Italic">Sciurus carolinensis</Emphasis>) deplete tree seeds hoarded by red squirrels (<Emphasis Type="Italic">S. vulgaris</Emphasis>)? |
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Authors: | Luc A Wauters Guido Tosi John Gurnell |
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Institution: | (1) Department of Structural and Functional Biology, University of Insubria Varese, Via Dunant, 21100 Varese, Italy,;(2) School of Biological Sciences, Queen Mary and Westfield College, University of London, Mile End Road, London E1 4NS, UK,;(3) Present address: Istituto Oikos, Viale Borri 148, 21100 Varese (VA), Italy, e-mail: l.wauters@libero.it, Fax: +39-0332-817749, |
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Abstract: | Red squirrels (Sciurus vulgaris) and introduced eastern grey squirrels (S. carolinensis) scatterhoard seeds of broadleaf trees. Scatterhoarded seeds are an essential resource in spring and their consumption increases
red-squirrel fitness. We examined whether grey squirrels partly deplete the high-energy food resources cached by red squirrels,
reducing their consumption, in two ways: (1) at the population level, comparing energy intake of feeding on cached seeds between
a study site with red and grey squirrels and one with only red squirrels present; and (2) at the individual level, in the
study site where species co-exist, relating hoard recovery of red squirrels to the amount of core-area overlap with grey squirrels.
There were no significant site differences in the mean daily energy intake of red squirrels feeding on seeds recovered from
caches. However, in the red-grey site, during spring, red squirrels that had a high percentage of their home-range core area
overlapped by grey squirrels had a lower daily energy intake than low-overlap red squirrels. Body mass of red squirrels in
spring was negatively correlated with the percentage of interspecific core-area overlap, but not with core-area overlap with
other red squirrels. Our data suggest that interspecific competition for scatterhoarded seeds, with grey squirrels pilfering
red squirrels' food caches, caused a reduced energy intake in red squirrels with a high degree of interspecific core-area
overlap, and reduced body mass in spring. Therefore, cache pilfering is likely to reduce reproductive output in red squirrels,
and thus play a role in the replacement of red by grey squirrels.
Electronic Publication |
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Keywords: | Interspecific competition Squirrels Hoarding behaviour Cache pilfering Food-energy intake |
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