9-second gridded continental Australia need for assisted dispersal (50% similarity) for Reptiles 1990:2050 CAN ESM2 RCP 8.5 (CMIP5) (GDM: REP_r3_v2)

Need for assisted dispersal for Reptiles as a function of change in long term (30 year average) climates between the present (1990 centred) and projected future (2050 centred) under the CAN ESM2 model (RCP 8.5) based on Generalised Dissimilarity Modelling (GDM) of compositional turnover. \nThe distance to the nearest grid cell with ecological similarity of at least 0.5 is given.\nThis metric describes the nature of the projected 2050 centred future environmental conditions for each 9s grid square. Using a Generalised Dissimilarity Model of compositional turnover (the effects of changing environment on changing species), each future location is compared with the continent in the present. For each cell, the metric looks out to all other cells in the continent, and records the ecological similarity of the future state of the cell to the most similar cell in the present. A value of 1 indicates that the future environment is similar to a current location in the present, and perfect analogue can found somewhere in Australia. A value of 0 indicates that the most similar environment to be found in the present is ecologically so different that we would expect no species in common, i.e. there are no current analogues for this environment; it is novel. Intermediate values show how ecologically similar the most similar cell is. However, no weight is given to the proximity of the most similar cell. The environment may be similar, but the cells thousands of kilometres apart.\n\nThis metric was developed along with others for use in an assessment of the efficacy of the protected area system for biodiversity under climate change at continental and global scales, presented at the IUCN World Parks Congress 2014. It is described in the AdaptNRM Guide “Implications of Climate Change for Biodiversity: a community-level modelling approach”, available online at: www.adaptnrm.org. \n\nData are provided in two forms:\n1. Zipped ESRI float grids: Binary float grids (*.flt) with associated ESRI header files (*.hdr) and projection files (*.prj). After extracting from the zip archive, these files can be imported into most GIS software packages, and can be used as other binary file formats by substituting the appropriate header file.\n2. ArcGIS layer package (*.lpk): These packages contain can be unpacked by ArcGIS as a raster with associated legend.\n\nAdditionally a short methods summary is provided in the file 9sMethodsSummary.pdf for further information.\n\nLayers in this 9s series use a consistent naming convention:\nBIOLOGICAL GROUP _ FROM BASE_ TO SCENARIO_ ANALYSIS\ne.g. A_90_CAN85_S or R_90_MIR85_L\nwhere BIOLOGICAL GROUP is A: amphibians, M: mammals, R: reptiles and V: vascular plants\n\nLineage: Need for assisted dispersal was calculated calculated using the highly parallel bespoke CSIRO Muru software running on a LINUX high-performance-computing cluster, taking GDM model transformed environmental grids as inputs. The distance to the nearest future cell with an ecological similarity > 0.5 to the present cell was calculated. More detail of the calculations and methods are given in the document “BiodiversityModellingMethodsSummary.pdf” provided with the data download. \nGDM Model: \nGeneralised dissimilarity model of compositional turnover in reptile species for continental Australia at 9 second resolution using ALA data extracted 27 February 2014 (GDM: REP_r3_v2)\nClimate data. Models were built and projected using:\na) 9-second gridded climatology for continental Australia 1976-2005: Summary variables with elevation and radiative adjustment\nb) 9-second gridded climatology for continental Australia 2036-2065 CAN ESM2 RCP 8.5 (CMIP5): Summary variables with elevation and radiative adjustment\n \n

基于物种组成周转的广义相异模型（Generalised Dissimilarity Modelling, GDM），本数据集反映了以1990年为中心的当前时段与以2050年为中心的未来预估时段（在CAN ESM2模式、RCP 8.5情景下）之间的长期（30年平均）气候变化下，爬行动物的辅助扩散需求。
本数据集提供了与生态相似度至少为0.5的最近格网单元之间的距离。

该指标用于描述每个9弧秒格网单元在以2050年为中心的未来预估时段的环境特征。本方法基于物种组成周转的广义相异模型（即环境变化对物种组成变化的影响机制），将每个未来点位与当前时段的澳洲大陆环境进行对比。针对每个格网单元，该指标会遍历大陆内所有其他格网单元，记录该单元未来环境状态与当前最相似格网单元的生态相似度。相似度值为1时，表示未来环境与当前某一澳洲本土点位高度相似，可在澳大利亚境内找到完美的现代类似环境；值为0时，表示当前所能找到的最相似环境在生态上差异极大，可认为二者无共有物种，即该未来环境无现代类似物，属于全新环境；中间值则反映了最相似格网单元的生态相似程度。但该指标未考虑最相似格网单元的空间邻近性：即便环境相似，两个格网单元可能相距数千公里。

该指标与其他指标一同开发，用于在大陆及全球尺度下评估气候变化背景下生物多样性保护地系统的效能，相关成果发表于2014年世界自然保护联盟（International Union for Conservation of Nature, IUCN）世界公园大会。该指标的详细说明载于AdaptNRM指南《气候变化对生物多样性的影响：群落级建模方法》，可通过网址www.adaptnrm.org在线获取。

本数据集以两种形式提供：
1. 压缩包形式的ESRI浮点型格网数据：包含二进制浮点格网文件（*.flt）、配套的ESRI头文件（*.hdr）及投影文件（*.prj）。从压缩包解压后，这些文件可导入绝大多数地理信息系统（GIS）软件；通过替换对应头文件，也可作为其他二进制格式文件使用。
2. ArcGIS图层包（*.lpk）：该类数据包可通过ArcGIS软件解压为带配套图例的栅格数据。

此外，数据集附带9sMethodsSummary.pdf文件，其中提供了方法学概要，以供用户获取更多细节。

本系列9弧秒格网数据采用统一命名规则：
[生物类群]_[基准时段]_[情景模式]_[分析类型]
示例：A_90_CAN85_S 或 R_90_MIR85_L
其中生物类群代码对应如下：A为两栖动物，M为哺乳动物，R为爬行动物，V为维管植物。

数据溯源：本数据集的爬行动物辅助扩散需求指标，通过运行于Linux高性能计算集群的定制化并行CSIRO Muru软件计算得到，输入数据为经广义相异模型（GDM）转换的环境格网数据。计算过程中，针对每个当前格网单元，我们求取了与该单元生态相似度>0.5的最近未来格网单元的距离。计算细节与方法学说明载于数据下载包附带的《BiodiversityModellingMethodsSummary.pdf》文件。

广义相异模型（GDM）：
本模型基于2014年2月27日提取的澳大利亚生物图集（Atlas of Living Australia, ALA）数据，构建了澳大利亚大陆范围内9弧秒分辨率下爬行动物物种组成周转的广义相异模型（模型标识：GDM: REP_r3_v2）。
气候数据：模型构建与预估所用气候数据如下：
a) 1976-2005年澳大利亚大陆9弧秒格网气候数据集：包含经高程与辐射校正的汇总气候变量
b) 2036-2065年澳大利亚大陆9弧秒格网气候数据集（CAN ESM2模式、RCP 8.5情景，CMIP5计划）：包含经高程与辐射校正的汇总气候变量