Re-evaluation of the relationship between rodent populations and acorn masting: a review from the aspect of nutrients and defensive chemicals in acorns
2006
Shimada, Takuya | Saitoh, Takashi
The responses of rodent populations to acorn masting were examined by reviewing 17 studies from the aspect of acorn nutrients and defensive chemicals. Oak species were grouped into three types based on their acorn nutritional characteristics by cluster analysis: Type 1 acorns (two North American red oaks, subgenus Erythrobalanus) were high in tannins and high in fat and proteins (and consequently rich in metabolizable energy); Type 2 acorns (two Japanese evergreen oaks, Cyclobalanopsis; three Japanese deciduous oaks, Lepidobalanus; one North American white oak, Lepidobalanus) were high in tannins but low in fat and proteins; and Type 3 acorns (one Cyclobalanopsis species; seven Lepidobalanus species) were low in tannins and had intermediate levels of fat and proteins. These three acorn groups were nutritionally, and thereby ecologically, not equivalent. Rodents, in general, responded differently to acorn masting depending on their feeding habits and the nutritional characteristics of acorns. Granivorous rodents showed positive responses to masting of Type 1 and 3 acorns, whereas rodents with feeding habits intermediate between granivory and herbivory showed positive responses to masting of Type 3 acorns. In addition, for herbivorous rodents, the responses to masting of any types of acorns have not been reported. The present findings emphasize that the relationship between rodents and acorn masting should not easily be generalized, because there are large variations in characteristics of both acorns and rodents. The viewpoint presented in this review could offer more convincing interpretations to the contradictory observations, found in the studies reviewed, on the response of rodent populations to acorn masting.
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