Effects Of Burying On Nutrient Of Plant Seeds And Hoarding Behavior Of Small Rodents

Seed dispersal,movement of seeds away from mother trees to a safe site,is one of the key stages of plant regeneration.Rodents often scatter hoard seeds into safe sites and some of these seeds will escape from predation and then germinate and become to seedlings in the future.Thus,as prominent seed dispersers,rodents play a significant role in seed dispersal and seedling recruitment in plants,and subsequently affect plant regeneration and community structure.In the plant-rodent seed dispersal system,it was once thought that seed dispersal is largely determined by rodents' incidental activities of depositing seeds into safe sites,rather than controlled by mother trees.However,recent studies argue that plants can produce seeds with traits that cause rodents to behave in a way that benefits the plants.They do this by increasing the probability that seeds will be buried and decreasing the likelihood that the buried seeds will be removed.In the system of plant-rodent mutualism,plants do not expect the buried seeds to be retrieved and consumed by rodents,so that the dispersed seeds can archive a higher fitness of dispersal.If nutrients of seeds attenuate with burying time,the buried seeds would be less available and attractive to rodents.Probability of survival of buried seeds would undoubtedly increase,benefiting to plants regeneration.Thus I presented the Nutrients Attenuation Hypothesis that nutrients of seeds will attenuate quickly when they are buried in soil,and thus reduce availability and attractiveness of seeds to animals.As a result,rodents may give up retrieving and consuming these seeds,and finally improve probability of seed survival,benefiting to seed dispersal and regeneration of plants.According to this hypothesis,I predicted that:(1)relative content of nutrients(e.g.,protein,fat)of buried seeds will decrease,and those of crude fibre and tannin will increase with the increasing of burying time;(2)seed discovery rate by rodents will decrease with the increasing of burying time;(3)seed removal rate will decrease with the increasing of burying time in the field.The subjects of wild apricot(Armeniaca sibirica)and Liaodong oak(Quercus wutaishanica)are widely distributed in northern China.Their seeds are dispersed by rodents only.Armeniaca sibirica seeds have hard endocarp,high fat and protein and highly physical defense of hard endocarps,whereas Q.wutaishanica acorns have thin and fragile endocarps,high starch,and highly chemical defense of tannin.Here in,I tested the Nutrients Attenuation Hypothesis in A.sibirica seeds and Q.wutaishanica acorns in Donglingshan area,western Beijing city.I was sought to know that(1)what nutrients are there in A.sibirica seeds and Q.wutaishanica acorns?(2)whether the relative content of nutrients of A.sibirica seeds and Q.wutaishanica acorns change with burying time?(3)whether nutrient change of A.sibirica seeds and Q.wutaishanica acorns affects seed hoarding behaviors of rodents?(4)what are the differences in nutrient change with burying time between A.sibirica seeds and Q.wutaishanica acorns?Crude protein,crude fat,crude fibre and tannin were detected in A.sibirica seeds.When seeds were buried in the soil,proportions of crude fat,crude fibre and tannin decreased with the increasing of burying time,while that of crude protein had little changes.In the field,proportions of seed discovery and seed removal rate by rodents of buried seeds were significantly lower than those of refrigerated seeds till to 60 days of burying.Under enclosure conditions,Korean field mice(Apodemus peninsulae)preferred to consume less buried seeds than refrigerated seeds.Crude starch,crude fat,crude fibre,crude protein and tannin were detected in Q.wutaishanica acorns.When acorns were buried in the soil,proportions of tannin decreased with the increasing of burying time,while those of crude starch,crude fat,crude fibre and crude protein had little changes.Under enclosure conditions,A.peninsulae had no preference for buried acorns and refrigerated acorns in consumption and hoarding.In the field,buried acorns had no significant differences in consumption,discovery from those of refrigerated acorns.Nutrients of A.sibirica seeds may attenuate with burying,while those of Q.wutaishanica acorns did not change greatly,implying different plant seeds may have different strategies of nutritional fluctuation to regulate animals.Nutrients of seeds attenuate with burying time may reduce seed availability to rodents,and possibly improve post-caching survival of seeds and plant regeneration.These results partially support the Nutrient Attenuation Hypothesis.