Analysis of the Efect of a Consoecitic Competitor Oil the Caching of Oil Tea Seeds by Edward's Rats
CHENG Jinrui,ZHANG Zhibin, XIAO Zhishu
2005, 25(2):
143-149.
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Previous research work has shown that some birds cache fewer food items in the presence of a conspecific competitor, but some rats cache more. None of these studies paid attention to the dispemd distances of buried food and the microhabitats where the food was buried.
In order to examine the efect ofthe presence of a conspecific competitor on dispersal distances of buried food and microhabitats where food was buried, an experiment was conducted from November to Decenlber 2002. The experiment was performed in two
enclosures that were built with bricks in secondary forest in Dujiangyan, District,Sichuan Province,China. The climate is subtropica1. The wall ofthe enclosures extended 1.3 m above and 0.5 m below ground to prevent subjects from escaping during the
experiment. A piece of 8 cm mesh net covered each enclosure to isolate predators from the outside.
The subjects used in the experiment were Edward's rats(Leopoldamys edwardsi). The food provided for Edward's rats to eat and bury were oil tea seeds(Camellia oleifera). Each subject was given 50 seeds and 1 night to eat and bury the seeds. The
next morning,the number of seeds eaten,buried and dispersed were recorded，as well as the dispersal distances of the buried seeds and their mierohabitats. The results showed that in the presence of a conspecific competitor,Edward's rats cached more oil
tea seeds, and the mean cache size increased. The dispersal distances of buried seeds was much larger in the presence of a conspecific competitor. Furthermore, in the presence of a conspecific competitor,Edward's rats cached a larger proportion of buried seeds under grass or under shrubs,and a smaller proportion in open ground.
We discuss the diference in caching behavior in the presence of a conspecific competitor between birds and rodents. The presence of a conspecific competitor promoted Edward's rats to bury more food,supporting the hypothesis that rats would bury more food in the presence of a competitor. When there were competitors,each rat would share fewer food items. In order to gain an advantage over the others,a subject would cache more food items for later use only by itself．Birds receive information from outside mainly by vision. Since the competitor would notice the cacher caching the food items,which would lead to loss of the buried food items,birds would cache fewer food items to avoid wasting their energy investment. Rodents receive information from
outside mainly by olfaction，while vision performs less of a function,especially in secondary forest at night. When facing a coinpetitor, rodents worried less about the loss of buried food iterns than birds, so they cached more food iterns. Edward's rats cached oil tea seeds more widely in the presence of a compecific competitor,which brings an advantage to oil tea. Seeds were buried much farther away from where they were released (or where they dropped on the ground),causing the population of this plant to develop faster and more widely.
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