| Plant species distribution patterns of island and its influence mechanism has been the priority areas and research hotspot in ecology and biogeography. Human activities have become the main cause of plant habitat loss and fragmentation, and how is the "island effect" of habitat fragmentation affect the distribution pattern of plant species? How is the "Island effect" influence on the distribution patterns of different groups of plants in real islands and "habitat islands"? How the Ocean islands and "habitat islands" response to "area of effect" in the different groups of plants? Whether there exist some special rules? These issues need to be further research. The theory of island biogeography is simple, easy to understand, and it seems reasonable, and its application is very wide, which had become the theoretical basis for biodiversity protection, but at the same time, many researchers also found that it exists some limitations. Many ecologists began to doubt the accuracy of the range and availability of island biogeography theory, and the role and significance of the theory to guide practice has also been some criticism, it should be supplemented and expanded in more study.In this study, we first explored the status and dynamic changes of vascular plant species in Hainan Island, then we chose the extremely small populations and endemic plants of Hainan island, and the plants of some small island of South China Sea as the key research object. Through comparing the relationship between different groups of plants and "area effects" on oceanic islands and "habitat islands", to improve and perfect the island biogeography, which can be really applied to the management of nature reserves and to provide theoretical basis for the protection of biological diversity. The following results have been obtained in this study:(1) We carried out a comprehensive study of plant species diversity in Hainan using field survey methods and literature review methods. There were6,036vascular plants recorded in Hainan province (6016species distributed in Hainan Island, the other20species distributed in Paracel Islands and the Spratly Islands). In these species, the Latin names of1,226species had been revised,1,180species were synonymously processed. In Hainan Island,4,622species were native wild plants,491species were endemic plants,512species were rare and endangered plants,170species had been naturalized (including63invasive species) as well as1,244species were introduced for cultivation.(2) We explore the effects of island area, distance between island and mainland, elevation, annual mean temperature and annual precipitation on the distribution pattern of different group of plants in the South China Sea. Our results showed that:①The most important factor on the different group of plants richness was elevation. It was different from the theory of island biogeography that the species richness was considered to be affected by island area, the distance between island and mainland. Elevation not only had a larger contribution for all groups plant, but also had the best explanatory power on the liana plants (R2=0.798);②The independent effects of environmental heterogeneity included area and elevation had the best explanatory power for all plant richness, which was46.8%, while the independent effect of the distance on the island and the mainland herbaceous plant richness was10.7%;③Due to the habitat heterogeneity of continental island and volcano island were complicated, this study only considers the area and elevation as habitat heterogeneity were still not enough, and a better measure of habitat heterogeneity (e.g., soil, forest coverage rate, micro topography) in future, is still need to explore the long-term target.(3) The extremely small populations of wild plants underwent human disturbances and threats, and they were often found in fragmental habitats. The leading factors changing the appearance frequency of extremely small populations differed among plant species, and the direct factors making them susceptible to extinction were human disturbances. The peak richness of extremely small populations always occurred at the medium level across environmental gradients, and their species richness always decreased with increasing human disturbances. However, the appearance frequencies of three orchid species increased with the increasing human disturbances. Our study thus indicate that knowledge on how the external factors, such as the ecological environment, land use type, roads, human activity, etc., affect the distribution of the extremely small populations should be taken for the better protecting them in the future.Mild anthropogenic interference have a certain role in promoting for distribution pattern of endemic plants, it has a positive significant regression with endemic species richness (R2=0.662), and it also had a larger contribution in stepwise regression model; The topography factor had a larger explanatory power on the proportion of endemic plants richness (R2=0.853), and the maximum contribution was altitude; but the comprehensive model including topography, vegetation and climate factors had the strongest explanation on endemic species abundance distribution pattern (R2=0.939), which was higher than that of each independent factor (R2<0.886). In addition, the main factors affecting the composition of endemic plant species were terrain roughness, altitude, mild forest area proportion.(4) In general, different groups of plant species richness of ocean islands and the "habitat islands" were positively correlated with area, in line with the "area effect"; In addition, when the area in the range of0.1-0.3km2of ocean islands or in the range of 15-18km2of "habitat islands", the number of species increased rapidly, then the increase rate of species began slowing down when the area were larger. When the proportion of different growth form of plants in balance, the area of oceanic islands and "habitat islands" was in the range of1.8-2.1km2,40-43km2, respectively. Then with the increase of area, the proportion of trees species increases rapidly, while the proportion of shrub, herb, and vine began decline.The different plant growth forms have a balanced proportion at the area of1.8-2.1km2in Ocean islands. As the same,"habitat islands" have a balanced proportion at the area of40-43km2. And then the proportion of trees increase with the increasing area of the ocean islands or nature reserve. The ratio of the minimum area and species number is0.0333-0.0358(km2/species) in "habitat islands", slightly higher than the oceanic islands0.0236-0.0276(km2/species). These not only indicating the environment of "habitat islands" was more complex than the ocean island, therefore need a bigger area to maintain the stability of ecosystem, but also showed that the different groups of plants of oceanic islands and the "habitat islands" had a consistent in response to "area effect".Finally, based on the ratio of minimum area and species number of0.0236-0.0276(km2/species number) in oceanic islands, we verify the minimum area to13natural protection zone in Hainan Island. Among them, four nature protection area (Tongguling National Nature Reserve, Ganshiling Provincial Nature Reserve, Nanwang Provincial Nature Reserve, Huoling City Nature Reserve.) did not meet the minimum area. But the surrounding environment of different countries or different parts maybe completely different, the degree of the theoretical application value also need further validation and in-depth research. |
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