| Liangshui Nature Reserve is one of the remaining primitive Korean pine forests in China. From1998, for the purpose of protection, Nature Reserve permitted contractors manually picked the Korean pine(Pinus Koraiensis) cones. The picking activities objectively reduced the number of Korean pine seeds providing for predation and hoarding of animals in the forest, and artificially changed the mutually beneficial relationship between Korean pine and hoarding animals which formed in long co-evolutionary history. Especially since implementation of "clear-picking" in2008, with the ahead of the picking time schedule and the increase of picking intensity, cone picking further reduced Korean pine seed availability. Regarding to such a long-term accumulative effect of continuous cone-picking, how did the hoarders depending on Korean pine seeds respond to this artificial disturbance? Did the intensive cone-picking activities change the co-evolution network forming in the Korean pine forest? We analyzed the hoarding behavior and population dynamic of two animals with different hoarding patterns:squirrels (Sciurus vulgari) as scatter-hoarders and chipmunks (Eutamias sibiricus) as larder-hoarders to research the response mechanism of animals with different hoarding strategies and their fitness changes.The sample-plot, transect and encounter rate methods were used to investigated the squirrel’s hoarding behavior and population dynamics, and cave excavation and mark-recapture method were used to investigated chipmunk’s hoarding behavior and population dynamics. The results showed that:(1) for scatter-hoarding squirrels, continuous picking activities broke the co-evolution relationship between squirrels and Korean pines, and changed their hoarding behavior and population density obviously. Compared with "Selective picking" period, the average cache size of squirrels was significantly smaller and the proportion of single seed caches increased, for example single seed cache was up to77.52%in2010. The cache density of squirrels changed synchronously with cone production in "selective picking" period, for example the cache density was8150±1625/hm2in2003(mast-year), but that of "clear-picking" period was unrelated to cones production, for example the cache density was3900±75/hm2in2011(mast-year). With the increase of cone-picking intensity, the average cache size and total cache quantity of squirrels were further declined, and the proportion of miss-retrieved caches was up to40.50%in2012. In "selective picking" period, the change of squirrels population presents positively correlated with cone production, but in "clear-picking" period, the encounter rate of squirrel rapidly declined and dropped to1±1times/km in2011.(2) For larder-hoarding chipmunks, the hoarding behaviors and population dynamics have not changed with cone-picking. The shelled and shell-less pine seeds hoarded by chipmunks were610±122 and406±208respectively in2010, and were664±83and398±75respectively in2011.The average population density of chipmunks was8.91+2.76/hm2in the fall of2011,6.14+1.29/hm2in the spring of2012, and9.69±4.17/hm2in the fall of2012.The accumulative effect of artificial picking had different effects on animals with different hoarding strategies. The response of chipmunks is more positive, because the characteristics of larder-hoarding, cave living, hibernation and omnivore can increase their fitness when food is reduced in habitat. On the contrary, the biological characteristics of squirrels is non-hibernation, no cheek pouches, scatter-hoarding, and food preference (high dependency to pine seed), and they have close co-evolution relationship with Korean pines which can not increase their own fitness when food is lacking. Furthermore hoarding behavior of squirrels changed obviously and their population was unable to adapt for the dramatic environmental change in a short period and showed declining trend. The continuous cone-picking activities destroyed the neutral process of co-evolution in Korean pine forest, and made the species in the network unbalanced development. |
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