Influence Of Connectivity Of Ponds On The Distribution Of Amphibians In The Lower Reaches Of The Yellow River Plain Agro-landscape

Landscape connectivity is an indicator for measuring species movement between patches,and a key factor determining the migration of species.With the development of agricultural intensification,the pond habitat was lost gradually,pond connectivity decreased gradually in the plain agricultural landscape,which has an adverse effect on the survival and reproduction of Amphibians.Based on the remote sensing images of Fengqiu County,a typical agricultural area in the middle and lower reaches of the Yellow River,was selected as the sampling point and the study area.All the water in the study area was identified,and the water livable for amphibian was selected as the habitat pond,and then the spatial distribution characteristics of ponds were analyzed.The connectivity of habitat ponds was evaluated based on the calculating in 250m,500m,1000m,2000m diffusion threshold,which made a contribution to determinating the important pond patches and analyzing the spatial distribution characteristics of important patches.The following two aspects were analyzed at each threshold,?1?The indicators were calculated including Number of components?NC?,the probability connectivity index?PC?,the centrality index?BC?,the important value of patch(dPC_intra,dPC_flux,dPC_con)based on the sample pond buffer zone;?2?The centrality index?BC?,the important value of patch(d PC_con,dPC_intra,dPC_flux)were calculated to analyze pond connectivity of study area..The connectivity was measured from two scales:individual and population scales.The correlation between the index of the sample pond connectivity and the relative abundance?average density?of the amphibian in the spot sampling site was analyzed to explore the effect of pond connectivity on amphibian distribution.Finally,we used Graphab software to developed the wetland network map,and added 100m,250m,500m,1000m search grid to determine the new pond.Subsequently,the new ponds were added based on the grid center with optimal connectivity so as to observe the degree of restoration of the connectivity by the new pond.The results were shown below:?1?The landscape connectivity index?IIC,PC?gradually increased with the increase of the threshold,but the value was still very low;group scores?NC?decreased with the increase of the threshold,and there were 222 components of the 2000m threshold,indicating tat the study area pond habitat fragmentation was serious.Under all diffusion thresholds,the"extremely important"habitat patch was 1,and 2 for"stepping stone".All the habitat patches above"important"and"stepping stone"patches with"extremely important"were concentrated in the composition of Chen qiao wetland.Some ponds were not only the important habitats,but also acted as"stepping stone"for migration in wetland of Chen qiao,the connectivity protection center in study area.?2?On the level of the sample pond buffer,the mean density of Bufogargarizans was significantly correlated with the dPC_con value of 2000m diffusion threshold;the Pelophylax nigromaculata,dPC_flux was correlated with the 250m,500m threshold,and Pelophylax plancyi presented a significant correlation with BC at 250m,500m and 1000m.The responses of different amphibian species to different landscape connectivity indices were also different.The relative density of frogs was significantly correlated with the low diffusion threshold?250m and 500m?,while the relationship was significant with Bufo at 2000m threshold,which was closely related to the dispersal ability of amphibians;B.gargarizans and F.multistriata were more likely to be found in the stepping stones,and P.nigromaculata and P.plancyi were distributed in the pond with many links.On the whole level of the study area,there was a significant correlation between dPC_con and B.Gargarizans in 2000m,other amphibians showed no significant.?3?Adding pond in connectivity network by using Graphab software in 250m,500m,1000m,2000m diffusion threshold to increase the level of pond connectivity.The search grid of 100m was higher than the other scales for the connectivity.The smaller the grid was,more accurate for adding ponds location.The greater the diffusion threshold was,the higher the probability of connectivity index?PC?in the study area after the addition of pond.The improvement of PC in the threshold from 250m to 2000m was 0.65%,0.95%,1.23%,and 4.7%,respectively,which can be seen that the effect of adding the pond on the high diffusivity ability of the amphibian is better.