Behavioural responses to acorn germination by tree squirrels in an old forest where white oaks have long been extirpated

Abstract

Many plants and animals have evolved physical and/or chemical defences to protect them from a wide range of predators, and in turn these predators have also developed effective offensive strategies in morphology, physiology and behaviour to counterbalance the evasive strategies of their prey. However, little is known about how morphology, physiology and behaviour in either predator or prey respond to local extinction of their interacting partners. Interactions between scatter-hoarding squirrels and oaks provide a valuable model system to explore such questions. In an ancient forest in southwest China, where nondormant white oaks have long been extirpated, we investigated how free-ranging Asian red-cheeked squirrels, Dremomys rufigenis, manipulated acorn germination, even when they had no experiences of white oak acorns in their habitat. We also tested the food perishability hypothesis, which suggests that rapid germination of seeds can lead to loss of energy and nutrients during storage. Our results were mostly consistent with the food perishability hypothesis: like several other squirrel species in both Asia and North America, (1) the focal squirrels were able to distinguish subtle differences between dormant and nondormant acorns, with more nondormant acorns having their embryos removed and dormant acorns being hoarded more; and (2) embryo-removed acorns had significantly lower germination success. Our study suggests that embryo removal behaviour by scatter-hoarding squirrels may be an adaptive trait allowing squirrels to use nondormant acorns as a long-term food supply and such adaptive behaviour can remain unchanged even when white oaks are extinct in their habitats.