| Dispersal is not only a form of movement of an organism,but also one of its most important life-history traits.It is not only helpful to expand the range of population,adjust age and genetic structure of population,but also avoid inbreeding and intraspecific competition.Its evolutionary mechanism includes inbreeding avoidance hypothesis,competition avoidance hypothesis and changing breeding site hypothesis.In the present study,dispersal direction and distance,relationships between age and breeding dispersal,population density and breeding dispersal,and differences of dispersal for offspring and their opposite-sex parents,were explored using GPS tracking,bird banding and field observation.We aim to document dispersal pattern,verify several hypotheses of dispersal,in order to provide a theoretical basis for the planning of subsequent reintroduction projects and effective protection of the Crested Ibis.The main results are outlined as follows:(?)The direction of natal dispersal was concentrated in the southwest(Rayleigh's Z=6.923>Z0.05=2.948,P<0.05)with mean vector of 229.655°±57.57°.The natal dispersal of females and males also tend to concentrate in the southwest(Rayleigh's Z=4.315>Z0.05=2.885,P<0.05;Rayleigh's Z=3.801>Z0.05=2.910,P<0.05)with mean vector of 224.433°±45.01° and 235.14°±63.34°,respectively.(?)The mean natal dispersal distance of individuals was 18.14±25.97(n=19)km,in which the average distance of females(36.02±35.76km,n=8)was significantly larger than that of males(7.13±5.8km,n=11)(Mann-Whitney Test:Z=-2.10,P=0.04).Thus,the pattern of natal dispersal is female-biased,which is in accordance with Inbreeding Avoidance Hypothesis and Mating System Hypothesis.(?)There is no significant concentrated tendency(Rayleigh's Z=2.598<Z0.05=2.948,P>0.05)in the breeding dispersal direction irrespective of female and male individuals(Rayleigh's Z=1.318<Z0.05=2.972,P>0.05;Rayleigh's Z=1.335<Z0.05=2.972,P>0.05).(?)The breeding dispersal rates of female and male Crested Ibises are 81.3%(n=16)and 66.7%(n=21)respectively,without significant difference between males and females(Fisher's exact test,P=0.46).The breeding dispersal distance of individuals averaged at 0.53±0.84km(n=73),in which the dispersal distance females(0.73±1.05km,n= 5)was significantly greater than that of males(0.32±0.47km,n=3 8)(Mann-Whitney Test:Z=-2.17,P=0.03).Therefore the pattern of breeding dispersal is female-biased which is in accordance with Mating System Hypothesi(?)There was a positive correlation between age and breeding dispersal distance(Spearman,r=0.59,P=0.04,n=73)either for both sexes combined,or for females and males separately(Spearman,r=0.81,P=0.02,n=35;Spearman,r=0.83,P=0.02,n=38),indicating that the dispersal distance increased with age.(?)There was a positive correlation between population density and dispersal distance(Spearman,r=0.81,P=0.01),that is the breeding dispersal distance increased with population density,which might be explained by Competition Avoidance Hypothesis(?)The trend of offspring's natal dispersal direction approximately concetrated on the southwest(Rayleigh's Z=4.179>Z0.05=2.945,P<0.05)with mean vector of 227.837°±64.78°,whereas the breeding dispersal direction of its opposite-sex parents was evenly distributed(Rayleigh's Z=2.572<Z0.05=2.945,P>0.05).This means that offspring will be separated from their opposite-sex parents in spatial distribution.Backcrossing just can be effectively avoided which might be possible to fit Inbreeding Avoidance Hypothesis.(?)There was a significant difference in dispersal distance between offspring and their opposite-sex parents(Paired T-test,P=0.04),meaning that they willdisperse in different directions and distances.Inbreeding can be effectively avoided which could be explained by Inbreeding Avoidance Hypothesis.(?)The above results not only document the distance,pattern and mechanism of dispersal of our focal population,but also provide theoretical basis for the establishment of habitat corridor in the process of population reintroduction. |
PDF Full Text Request