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高原鼢鼠挖掘取食活动的能量代价及其最佳挖掘取食行为

1. 中国科学院西北高原生物研究所，西宁
• 出版日期:2006-07-27 发布日期:2007-07-20

ENERGY COST OF FORAGING AND OPTIMAL F0RAGING IN THE FOSSORIAL RODENT (MYOSPALAX BAILEYI)

SU Jianping

• Online:2006-07-27 Published:2007-07-20

Abstract: This paper deala with the optimal foraging and burrowing of the plateau zokor(Myospalax baileyi)，a typical species of fossor ial rodent distributed on Qinghai-Tibet Plateau，based on the following two hypotheses.
H1: If burrowing is optimal，burrowing efficiency would be maximum which means that burrowing a certain length expends a minimal energy．
H2：If foraging is optimal foraging benefit to the cost would be maximum．
According to the zokor's foraging burrow structure and observed behavioural characteristics associated with foraging by burrowing，a model slightly distinguishing from equation 2 of Vleck (1981)was established for describing the energy cost of foraging by burrowing．
Ec =Ks·C·(S+L)+(KP·C+Kt／A)·(s ／2+2s·L+L )+5D·g·C·S (a)
where E c=energy cost of excavating a segment of foraging burrow，S =segment length (distance between two adjacent laterals or mounds)，L=lateral length，D =burrow depth，C= b2p，in which p is soil density in terms of soil mass par unit volume and b the radium of burrow，g=gravitational acceleration， Ks=energy coat of shearing l g of soil loose，Kp energy cost of pushing 1 g soil a centimeter， Kt=energycost of travelling one centimeter，A =length of a small piece of burrow，when which established the loose soil must be pushed out．
Having a complete segment established，the energy benefit of a zokor from soil can be described by the following equation:
Efg = ·b 2·S·D e·Ra (b)
where Efg=assimilable energy gained from soil of a segment， De=energy in food available for zokor per unit volume of soil， R．=assimilating rate of food by zokor ．
From the two hypotheses，(E c／s)would be minimum (H1)and(Efg／Ec )maximum(H2)．Thus．it could be deduced that segment must meet the following definition： Sopt=[2L2 +2K s·C·L／(K p·C 十Kt A) re)]1/2 Which made H 1 and H2 stand．
On the basis of data of burrowing metabolic rate, burrowing rate(burrowing length to the burrowing time), lateral length，burrow radium from 12 individuals，and of soil density，we calculated the mean values: C=61.473g／cm，Ks = 1.118J／g， Kp C十Kt／A=2.94 E-1J／cm2，and Sopt=127.4cm which did not differ from the observed segment length of 126.3±47.85cm (t=O.312，P> O.50). This result was baaed on sampies from Kohresia humilis meadow，and showed zokors behave optimally in foraging by burrowing，i．e．foraging and burrowing effieieneies were maximum.
The results above suggested that optimalization of oraging and burrowing be synchronous．This was not difficult to understand because both the efficiencies of foraging and burrowing were influenced by segment length in the same means. When segmeut lengthened，the soil in the burrow would be pushed averagely a longer distance and burrow ing rate declined. which resulted in decreases in both burrowing length and foraging benefit within a certain peroid．As segment shortened，more laterals had to be established and the same result as increasing segment length appeared. The trade-off
between the two situations above made zokors select a optimal segment neither too short nor too long．
It was worthy to note that zokors performed two obvious different patterns in for aging by burrowing. In spring and autumn，foraging occured ata deeper layer of soil， typical burrows and mounds appeared , But in summer，foraging was almost near
the ground surface，no burrows and mounds needed to shape excepting cracks on ground surface．Although the optimal foraging by burrowing model was deduced from the first case．it was still fit to the second situation for summer in which L= 0 ，thus Sopt = 0 according to equa tion (c)．One could view this case as each point of the surface cracks was "a small mound".