Species Diversity And Distribution Pattern Of Mistletoes Along Gradients In The Shennongjia Of Western Hubei

Mistletoes are evergreen shrubs that parasites on other plants,and its distribution pattern along altitude gradients may be related to specific habitats and host plants.The study presented a case study on diversity and numbers of mistletoes,species of hosts and parasitic height of mistletoes on hosts in subtropic forest community along altitude gradients in western Hubei.Three transects along the elevation gradient(175.0–3106.2 m)were established and 360 quadrats were investigated to examine,(1)species diversity of mistletoes;(2)host selectivity of mistletoes;(3)the distribution patterns of mistletoes along the altitude gradient;(4)spatial distribution pattern in parasitic height.Results showed that,Firstly,there were 3 genera and 7 species in Loranthaceae in the study area in the Shennongjia.Among these speices,Taxillus sutchuenensis was the most abundant,and Viscum liquidambaricolum was the rarest.The lowest elevation of mistletoes distribution was 194 m(Taxillus levinei),and the highest elevation was 2011 m(Taxillus sutchuenensis).The species richness(the number of species and Margalef index),? diversity index(Shannon-Wienner and Simpson index)and ? diversity index(Cody index)of mistletoes firstly increased and then decreased with increasing altitude.The species diversity was of mistletoes highest ranging from the 600 m to 1000 m,and showed a unimodal distribution pattern;Secondly,in study area,there were 40 host species or potential host plants belonging to 14 families and 28 genera,in the study area.Among these host plants,there were 38 tree and small tree species,and only 2 shrub and vine species.Mistletoes showed preference for host plants.Most of them was prone to choose tall deciduous trees(36 species)as their hosts.There were 4 and 5 mistletoes choosing Salicaceae and Fagaceae,respectively.And Taxillus sutchuenensis has 38 hosts,while Viscum coloratum has only one host.The parasitic intensity of the same mistletoes species was different on different host plants.The parasitic intensity of V.liquidambaricolum on the Ebenaceae plants is much greater than that on other host plants,showing the preference of mistletoes for host plants;Thirdly,the parasitic relative height of mistletoes on host plants ranged from 0.76 to 0.92,and there were not significant differences among different parasitic species or host species.The spatial autocorrelation at parasitic height of mistletoes was significant.That is,the parasitic heights of mistletoes on host plants showed spatial aggregation distribution(Moran's I = 0.577).The dimensionality of various influence factors was reduced by PCA(Principle Components Analysis),the first three principal components(height,energy supply of host plant and light)explained 83.53% explanation of variances of the mistletoes' parasitic relative height.And thus,height,energy supply of host plant and light were the main factors affecting parasitic height of mistletoes.Our results suggested that,(1)the “mid-altitude bulge” distribution pattern of mistletoes along elevation gradients may result from the combination of environmental factors and host selectivity;(2)The parasitic height of mistletoes on the host plants showed a spatial aggregation distribution.