| Climate is a major environmental factor that limits the distribution of species.How global climate change would affect the geographical distribution of biodiversity is a crucial issue in ecology and conservation biology.Ecological niche modeling(ENM)is one of the major approaches to unravel this problem.Based on the geographical coordinates of the species occurrence records and climatic variables in different periods,ENM predict potential suitable habitat for species under historical,current and future climatic conditions.However,the extent to which biological interactions limit the geographical distribution of species are rarely studied.Orchidaceae is one of the most species-rich families among angiosperms.Orchids display extraordinary floral diversity,and known as a flagship group in biodiversity conservation.Orchids usually have narrow niche breadth,relying on specific symbiotic fungi for obtaining nutrients,and depending on pollinators for sexual reproduction.Orchids-pollinators interactions has played a key role in the diversification of orchids.However,imperical studies showed that the sexual reproduction in orchids are generally pollinator limited.Thus,orchids are an ideal plant group to study how abiotic and biotic factors could limit the geographical distribution of plants.The pollination mechanism of orchids can be divided into rewarding and non-rewarding pollination systems according to whether the orchid offers rewards to the pollinators or not.Spur is a specialized tubular structure of flower,which generally stores nectar for attracting pollinators.The flowers of many species within Orchidoideae and Epidendroideae have a spur,but not all species with a nectar-secreting spur.Habenaria and Calanthe are the two large genera of orchids with a spur in China.The flowers of Habenaria species are usually greenish-whitish with a long nectar-secreting spur,while the flowers of Calanthe species are usually bright-colored with an empty spur.These two genera are ideal taxa for studying how rewarding and non-rewarding orchids would response to future climate change.In this thesis,we modeled the suitable habitat of eight species of Habenaria and ten species of Calanthe in China under the near current period(1970-2000)and the future period(2081-2100)under moderate and pessimistic climate change scenarios,and we compared the responses of Habenaria and Calanthe species to climate change.We also simulated the suitable habitat of H.dentata,C.discolor and their pollinators at the global scale,and discussed the restriction of pollinators on the potential distribution of H.dentata and C.discolor under future climate change.The main findings of this thesis are as follows:1.Response of the suitable habitat of Habenaria species to future climate change.By 2100,most Habenaria species will expand their suitable habitat.Under the moderate emission scenario,the suitable habitat of six species will expand,and the other two species will shrink.Under the pessimistic emission scenario,the suitable habitat of five species will expand,and the other three species will shrink.Surpringly,we found that the potential range changes of Habenaria species under the future climate change scenarios were not significantly correlated with their near current ranges.It suggests that the sensitivity of Habenaria species to climate change does not correlated with their niche breadths.The distribution of Habenaria species will generally shift to higher latitudes and higher elevations in the future,and only H.rhodocheila will shift to lower elevations.The geographical distribution of most Habenaria species are mainly determined by temperature-related variables,and their overall shifts to higher latitudes and higher elevations may be a response to temperature changes.In contrast,the geographical distribution of H.rhodocheila is mainly determined by precipitation-related variables,and its shift to lower elevations may be a response to future precipitation changes.2.Response of the suitable habitat of Calanthe species to future climate change.By 2100,all ten Calanthe species will shrink their suitable habitats under the moderate and pessimistic emission scenarios.Except for C.sylvatica,other nine Calanthe species are predicted to lose significantly larger suitable areas under the pessimistic emission scenario than that under the moderate emission scenario.In addition,we found that the potential range changes of Calanthe species under the future climate change scenarios were negatively correlated with their near current ranges.It suggests that Calanthe species with wide niche breadths are more sensitive to climate change.The distribution of all ten Calanthe species will shift to higher elevations in the future,and generally shift westwards to the high-elevation regions.The geographical distribution of most Calanthe species are determined by both precipitation and temperature,and their overall shifts to west and higher elevations may be a response to changes in temperature and precipitation.3.The restriction effect of pollinators on the distribution of suitable habitat of H.dentata.The two pollinators of H.dentata,Papilio helenus and Panacra mydon mydon are expect to expand their distribution under both moderate(ssp245)and pessimistic(ssp585)climate change scenarios,while the other pollinator Papilio memnon will expand under ssp245 climatic scenario and shrink under ssp585 climatic scenario.The suitable habitat of H.dentata will shrink by 27.33%-48.38%under future climate change scenarios.With the consideration of the availability of pollinators,the suitable habitat of H.dentata will be further reduced by15.32%-17.42%.Therefore,the range contraction of H.dentata under future climatic conditions will be affected by both climatic factors and pollinators.4.The restriction of pollinators on the distribution of suitable habitat of C.discolor.Under the future climate change scenarios,the distribution range of the two pollinators of C.discolor,Eucera nipponensis and Osmia cornifrons will shrink,while the other pollinator Apis cerana will expand.The suitable habitat of C.discolor will shrink by 35.05%-57.58% under future climate change scenarios.With the consideration of the availability of pollinators,the suitable habitat of C.discolor will almost no change,will only shrink by 0.37%-0.59%.This might be attributed to the broad distribution range of A.cerana,which almost covers the entire distribution range of C.discolor.Furthermore,the suitable habitat of A.cerana will expand greatly in the future.Therefore,the range contraction of C.discolor under future climatic conditions will be mainly affected by climatic factors,and will not be further limited by its pollinators.In conclusion,Calanthe species are much more vulnerable to climate change than that of Habenaria species.One of the underlying reasons might be due to their differences in pollination systems.The nectar rewarding Habenaria species are mainly pollinated by moths,which have relatively high pollination efficiency,thus the fruit set of Habenaria species are usually relatively high.By contrast,the nonrewarding Calanthe species are mainly pollinated by diurnal bees,and their fruit set are relatively low.The distribution of suitable habitat for H.dentata is both limited by climatic factors and the distribution of pollinators.However,the distribution of the suitable habitat for C.discolor is only limited by climatic factors.Pollinators are not a limiting factor for the distribution of C.discolor,because its pollinators are widely distributed.Our study highlights the necessary of incorporating pollinator availability in modeling the potential distribution of orchids. |
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