The Study Of Bird Elevational Range Size In The Lebu Valley,Eastern Himalayas

Species range size,the reflect of niche,is the directly cause of species richness pattern,and it also associates with the species abundance.Most previous studies about species range size mainly focused on testing Rapoport's rule.At present,there are still many controversies in the research on the species range size,such as the verification method of the species range size pattern and the related factors.Beginning in the 1990s,due to the advantages of vertical elevation gradients in testing ecological theories(in a small spatial scale,it contains a large number of ecological changes,and it is convenient to collect data),scholars have also begun to conduct research on elevational range size.However,research in this area is relatively lacking.In order to improve the theory and hypothesis of elevational range size,we conducted four bird surveys in Lebu Valley(2350-4949 m above sea level),which located in Cuona County,Shannan City,Tibet.A total of 123 species of breeding birds were recorded.Based on this data,we conducted the following two sub-studies:1.Research on the relationship between the species elevational range size,related environmental factors,and species richness.We used the Stevens method,the midpoint method and the specimen method to test the species elevational range size pattern.At the same time,the influence of relevant environmental factors(annual temperature range,primary productivity,habitat heterogeneity and mid-domain effect)on the species elevational range size pattern was tested to test the relevant hypotheses corresponding to the above environmental factors(climate variability hypothesis,ambient energy hypothesis,habitat heterogeneity hypothesis and middomain effect hypothesis).In addition,we also tested the influence of species elevational range size on the species richness pattern(rescue effect).the result showed:(1)The different methods to describe the species elevational range size pattern will affect its specific pattern.For example,the Stevens method measuring the species elevational range size pattern caused a low-plateau pattern.The mid-point method and the specimen method caused a mid-peak pattern.(2)Due to the difference in the species elevational range size pattern,the main influencing factors were also different:the low-plateau pattern was mainly affected by the annual temperature range and the mid-domain effect;the mid-peak pattern was mainly affected by the mid-domain effect.Our results supported the mid-domain hypothesis,while the climate variability hypothesis,ambient energy hypothesis and habitat heterogeneity hypothesis were weakly to explain the species elevational range size pattern in Lebu Valley.(3)The species elevational range size in Lebu Valley affected the species richness humpshape pattern,which supported the non-directional rescue effect,that is,species from low and high elevation increases the species richness at mid-elevation at the same time,and both the difference in inflow intensity will affect the hump-shaped pattern to be biased towards low elevation.2.Research on the relationship between species range size and abundanceIn this part,we recorded the species elevational abundance pattern in Lebu Valley,verified the relationship between the abundance of overall breeding birds and the species elevational range size,and compared the abundance-elevational range size relationship,abundance and elevational range center of endemic species and non-endemic species.the result showed:(1)The species elevational abundance pattern in Lebu Valley was a hump-shaped pattern.(2)The endemism of regional birds influenced the abundance-range size relationship.It showed that the abundance-range size relationship of overall species and non-endemic species were positively correlated,and the positive correlation of non-endemic species was more significant.However,the abundance-range size relationship of endemic species was not correlated.(3)The differences of regional species composition(the abundance and elevational range center of endemic species were higher than those of non-endemic species)caused by geographic isolation were one of the important reasons for the variations of abundanceelevational range size relationship.