| Decalobanthus boisianus is a native noxious species in Hainan Island but outbroke in recent years.The area of this species in Hainan Island is more than 2000 ha and therefore brought serious damage to forest ecosystems.We collected 77 individuals of D.boisianus from eight forests with diffent disturbance density to assess patterns of genetic diversity and structure using inter-simple sequence repeat(ISSR)markers;then assessed the community stability,interspecific associations and niche characteristics in 48 typical communities invaded by this species;finally we assessed the potential distributed area of D.boisianus in Hainan Island to realize the early warning and prevention of its expansion based on 370 distribution points of the species and 69 bioclimatic variables including precipitation,temperature,DEM and vegetation coverage under two climate patterns.Results are shown as follow:1)A total of 220 loci were scored with 13 primers,198 loci of them were polymorphic.The genetic diversity of D.boisianus(PPL=90.00%,I=0.33±0.22,H=0.21±0.17)are higher than other noxious species,indicated the high level in gentic diversity of this species.The genetic diversity of this species varies significantly with human disturbance intensity,with the high,medium and low genetic diversity observing in low intensity group(population in WZS),moderate intensity group(populatoin in YGL,BWL,JFL,DLS)and high intensity group(populatoin in LMS,BSL and GSL),respectively.Over 70%of the total genetic variation was present within populations.while less than 30%of variation was found among populations.The high average genetic similarity(0.93)and results of Mental test(r=0.39.P=0.10)indicated the close relationships among eight populations in Hainan Island.2)Species in the community were positively associated,Machilus suaveolens,Litsea variub ilis and Schefflera octophylla showed closer associations with D.boisianu,indicated that these species had similar resource requirements.Decalobanthus boisianus had the highest niche width.The niches among the companion species were seldom overlapped while those between D.boisianus and companion species like Machilus suaveolens,Litsea variabilis and Aporusa dioica were highly overlapped.The communities were unstable maybe due to the interspecific competition,environmental pressure and disturbance activities.We therefore suggest to strengthen the protection of the forest and reduce the external disturbance as far as possible,so as to reduce the invasion probability of that species.3)Results from "Jackknife" indicated that DEM,mean temperature of wettest quarter and monthly total precipitation in May are 3 most important bioclimatic variables that correlated positively to the growth and distribution of D.boisianus.MaxEnt model showed that D.boisianus is concentrated in some counties and cities in the central and southwestern parts of the island in the present and may further spread to its surrounding areas.Percentages of the species in the high-risk,medium-high-risk,medium-risk and low-risk potential distributed areas in Hainan island were 6.82%.11.32%.16.31%and 65.55%under current climate pattern(AUC=0.937)and will be 16.01%.11.92%,16.16%and 55.92%under the climate pattern in 2050(RCP 2.6)when the average temperature will be increased with 1?(AUC=0.889).By then.D.boisianus will entirely cover cities and counties in central in the island included Baisha County.Qiongzhong County,Wuzhishan City,Baoting County and Lingshui County,and with a large extent to the western regions in the same time.Therefore,these areas should be the focus of preventing and controling of D.boisianus. |
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