The latitudinal diversity gradient (LDG) is one of the most extensive and important biodiversity patterns on the Earth. Various studies have established that species diversity increases with higher taxa numbers from the polar to the tropics. Studies of multicellular biotas have supported the LDG patterns from land (e.g., plants, animals, forests, wetlands, grasslands, fungi, and so forth) to oceans (e.g., marine organisms from freshwater invertebrates, continental shelve, open ocean, even to the deep sea invertebrates). So far, there are several hypotheses proposed to explore the diversity patterns and mechanisms of LDG, however, there has been no consensus on the underlying causes of LDG over the past few decades. Thus, we reviewed the progress of LDG studies in recent years. Although several explanations for the LDG have been proposed, these hypotheses are only based on species richness, evolution and the ecosystems. In this review, we summarize the effects of evolution and ecology on the LDG patterns to synthesize the formation mechanisms of the general biodiversity distribution patterns. These intertwined factors from ecology and evolution in the LDG are generally due to the wider distribution of tropical areas, which hinders efforts to distinguish their relative contributions. However, the mechanisms of LDG always engaged controversies, especially in such a context that the human activity and climate change has affected the biodiversity. With the development of molecular biology, more genetic/genomic data are available to facilitate the estimation of global biodiversity patterns with regard to climate, latitude, and other factors. Given that human activity and climate change have inevitably impacted on biodiversity loss, biodiversity conservation should focus on the change in LDG pattern. Using large-scale genetic/genomic data to disentangle the diversity mechanisms and patterns of LDG, will provide insights into biodiversity conservation and management measures. Future perspectives of LDG with integrative genetic/genomic, species, evolution, and ecosystem diversity patterns, as well as the mechanisms that apply to biodiversity conservation, are discussed. It is imperative to explore integrated approaches for recognizing the causes of LDG in the context of rapid loss of diversity in a changing world. 纬度多样性梯度（LDG）是地球上最广泛和重要的生物多样性模式之一。各种研究已确定，从极地到热带，物种多样性随着高阶分类群数量的增加而增加。对多细胞生物群落的研究支持了从陆地（例如，植物、动物、森林、湿地、草原、真菌等）到海洋（例如，淡水无脊椎动物、大陆架、开阔海洋，甚至深海无脊椎动物）的 LDG 模式。到目前为止，已经提出了几种假说来探讨 LDG 的多样性模式和机制，然而，在过去几十年中，关于 LDG 的潜在原因尚未达成共识。因此，我们回顾了近年来 LDG 研究的进展。尽管已经提出了几种对 LDG 的解释，这些假说仅基于物种丰富度、进化和生态系统。在本综述中，我们总结了进化和生态对 LDG 模式的影响，以综合一般生物多样性分布模式的形成机制。 这些生态学和进化论中交织的因素在 LDG 中通常是由于热带地区的更广泛分布，这阻碍了区分它们相对贡献的努力。然而，LDG 的机制始终引发争议，特别是在这样一个人类活动和气候变化影响生物多样性的背景下。随着分子生物学的发展，更多的遗传/基因组数据可用于促进对全球生物多样性模式的估计，涉及气候、纬度和其他因素。鉴于人类活动和气候变化不可避免地影响了生物多样性丧失，生物多样性保护应关注 LDG 模式的变化。利用大规模遗传/基因组数据来解开 LDG 的多样性机制和模式，将为生物多样性保护和管理措施提供见解。讨论了 LDG 的未来前景，包括综合遗传/基因组、物种、进化和生态系统多样性模式，以及适用于生物多样性保护的机制。 在快速丧失多样性的变化世界中，探索识别 LDG 原因的综合方法是至关重要的。
In 1807, Alexander von Humboldt (1769-1859; Figure 1A) proposed the embryonic framework of latitudinal diversity gradient (LDG) and wrote that “The nearer we approach the tropics, the greater the increase in the variety of structure, grace of form, and mixture of colors, as also in perpetual youth and vigor of organic life” [1,2] (Notes: von Humboldt published the first edition of a series of essays that entitled ‘Ansichten der Natur’ in Berlin, 1807. The essays initiated while he was in South and Central America that was translated variously as ‘Aspects of Nature’ or ‘Views of Nature’. One of the four essays was composed the first edition, ‘Ideas for a physiognomy of plants’ that contains the following paragraph was translated by Otté and Bohn in 1850). Subsequently, the LDG has been recognized and studied by many biologists, ecologists, and geographers for over 200 years [3-12]. The pattern of LDG is responsible for the broadest and most notable of biodiversity patterns globally (Figure 1B). It has been well documented on the land, in the open ocean, and even discernible in deep sea, which distribution patterns have been characterized for plants, animals, fungi, and marine organisms [13,14]. However, distribution patterns of organisms are not balanced around the globe so that many naturalists and scientists have tried to understand the cause of LDG for centuries [15]. Notably, the LDG is mostly consistent, regardless the geographic context, taxonomic affiliation, or time scale of the biota [16,17]. Previous studies have attested and cataloged many hypotheses to explain the underlying mechanisms that increase species diversity and taxon numbers from high latitudes to the tropics [18]. However, the mechanisms of LDG are not very clear, even with little consensus. It is necessary to review the LDG in the context of a changing world wherein human activity and climate warming are affecting the patterns of biodiversity in evolution and ecology. 在 1807 年，亚历山大·冯·洪堡（1769-1859；图 1A）提出了纬度多样性梯度（LDG）的初步框架，并写道：“我们越接近热带，结构的多样性、形态的优雅和颜色的混合，以及有机生命的永恒青春和活力就越大”[1,2]（注：冯·洪堡于 1807 年在柏林出版了一系列名为《自然的观点》的论文的第一版。这些论文是在他在南美和中美洲期间开始的，翻译为《自然的方面》或《自然的视角》。其中一篇论文是第一版的组成部分，《植物的面相构思》，包含以下段落，由 Otté和 Bohn 于 1850 年翻译）。随后，LDG 被许多生物学家、生态学家和地理学家认识并研究了超过 200 年[3-12]。LDG 的模式是全球生物多样性模式中最广泛和最显著的模式（图 1B）。 在陆地、开放海洋甚至深海中，植物、动物、真菌和海洋生物的分布模式已被充分记录[13,14]。然而，生物的分布模式在全球范围内并不均衡，因此许多自然主义者和科学家数百年来一直试图理解 LDG 的原因[15]。值得注意的是，LDG 在地理背景、分类关系或生物群落的时间尺度上大多是一致的[16,17]。先前的研究已经证明并列出了许多假说，以解释从高纬度到热带地区物种多样性和分类单元数量增加的潜在机制[18]。然而，LDG 的机制并不十分清楚，甚至几乎没有共识。在人类活动和气候变暖影响生物多样性演化和生态模式的变化世界中，有必要重新审视 LDG。
The investigation of the LDG has drawn on in ecological and evolutionary studies, i.e., some species survive whereas others die out in the process [15]. Almost six decades ago, Eric Pianka (Figure 1C) proposed the first comprehensive review on LDG and the six major hypotheses that compiled a wide range of ideas to explain and address possible causes for patterns in diversity [6,10,15][6,10,15]. Subsequently, LDG explanations have been focused on evolutionary mechanisms [5], such as differences in the time and area available for diversification in tropical and temperate biomes, latitudinal differences in the rates of diversification, speciation and/or extinction in combination with tropical energy, and niche conservatism [10,15]. However, evolutionary biology and ecology must be combined to 对 LDG 的研究已在生态和进化研究中得到了应用，即一些物种在过程中存活，而另一些物种则灭绝[15]。近六十年前，Eric Pianka（图 1C）提出了关于 LDG 的第一篇综合性综述，以及六个主要假说，汇集了广泛的观点来解释和解决多样性模式的可能原因 [6,10,15][6,10,15] 。随后，LDG 的解释主要集中在进化机制上[5]，例如热带和温带生物群落中可用于多样化的时间和区域的差异、纬度差异对多样化、物种形成和/或灭绝速率的影响，以及热带能量和生态位保守主义的结合[10,15]。然而，进化生物学和生态学必须结合起来。
explain why larger numbers of taxa are distributed in certain areas of the planet [15]. There is still no consensus on the drivers of LDG that elevate tropical diversity [20]. 解释为什么更大数量的分类群分布在地球的某些区域[15]。关于提升热带多样性的 LDG 驱动因素仍然没有共识[20]。
Alternative LDG hypotheses can be tested with the help of a rich body of biodiversity database, including data concerning phylogeny and biogeography [21]. However, the primary cause of LDG at a global scale is unexplained; and a new synthesis has emerged to determine the geographic ranges of species and their concentration of species within regions, based on evolutionary, biogeographical, and contemporary (i.e., climate and environmental variables) factors [15]. Understanding the underlying mechanisms of LDG is a major goal in conservation biology, biogeography, and ecology [22]. Multiple dimensions of LDG have been described, from intraspecific genetic variation to species richness and phylogenetic diversity, all of which are vital for assessing the underlying processes that shape the distribution of life on Earth and for providing maximum support for global biodiversity conservation [23]. Fascination with the pattern of higher biodiversity in tropical regions has stimulated increasing interest in community ecology [17]. Similarly, the erosion of biodiversity from the local/regional level to the global scale has catalyzed many studies in conservation biology [24]. Thus, the study of the LDG provided a unique opportunity to comprehensively understand latitude-associated patterns in ecology, biogeographical origin, and maintenance of species diversity [25]. 替代的 LDG 假说可以借助丰富的生物多样性数据库进行测试，包括有关系统发育和生物地理的信息[21]。然而，全球范围内 LDG 的主要原因尚未得到解释；一种新的综合方法已经出现，旨在根据进化、生物地理和当代（即气候和环境变量）因素来确定物种的地理范围及其在区域内的物种集中度[15]。理解 LDG 的潜在机制是保护生物学、生物地理学和生态学的主要目标[22]。LDG 的多个维度已被描述，从种内遗传变异到物种丰富度和系统发育多样性，这些都是评估塑造地球生命分布的潜在过程的重要因素，并为全球生物多样性保护提供最大支持[23]。对热带地区更高生物多样性模式的着迷激发了对群落生态学的日益关注[17]。同样，从地方/区域层面到全球范围的生物多样性侵蚀也催生了许多保护生物学的研究[24]。 因此，LDG 的研究提供了一个独特的机会，以全面理解与纬度相关的生态模式、生物地理起源和物种多样性的维持[25]。
Given the potential value of biodiversity conservation efforts, it is critical to examine the mechanisms that create the patterns in biodiversity that produce the LDG. In this review, we aim to identify and discuss the hypotheses for LDG mechanisms, i.e., whether the distribution patterns of different species are consistent with LDG, and explain the factors that cause the number of species to change with latitude. We also discuss the effects and formation of LDG in various periods during which species have been restricted to different latitudes. Additionally, the role of LDG in evolution and ecology will be discussed in relation to global warming and human activity that are affecting the biodiversity. Finally, we concentrate on the relevance of the LDG to biodiversity conservation in the hope that a deeper understanding and reasonable scientific approach (e.g., the big data of genetic/genomic sources) to it can be obtained by studying the LDG. 考虑到生物多样性保护努力的潜在价值，研究产生生物多样性模式的机制以解释物种多样性梯度（LDG）是至关重要的。在本综述中，我们旨在识别和讨论 LDG 机制的假设，即不同物种的分布模式是否与 LDG 一致，并解释导致物种数量随纬度变化的因素。我们还讨论了在不同物种被限制在不同纬度的各个时期 LDG 的影响和形成。此外，LDG 在进化和生态中的作用将与影响生物多样性的全球变暖和人类活动相关联进行讨论。最后，我们集中讨论 LDG 与生物多样性保护的相关性，希望通过研究 LDG 能够获得更深入的理解和合理的科学方法（例如，基因/基因组来源的大数据）。
2. Status of LDG from Previous Studies 2. 先前研究中 LDG 的状态
Pianka’s comprehensive review on LDG aided the organization of the myriad hypotheses regarding it in 1966 [6]. Since then, many major journals have published numerous studies about the LDG, such as the flagship journals, Global Ecology and Biogeography, and Journal of Biogeography, have been the main sources on LDG articles in the past few decades; other mainstream journals including Ecography, Ecology, Ecological Letters, American Naturalist, and Proceedings of the Royal Society B: Biological Sciences, have also published many papers on LDG (Figure 2). In addition, the number of articles on LDG about land-based flora/fauna, marine organisms, and micro-organisms has increased since 1995, although the trend from 2019 and 2020 has slowed (Figure 3). Overall, the body of LDG-related literatures has grown substantially in recent decades. Pianka 对 LDG 的全面回顾帮助组织了 1966 年关于它的众多假说[6]。自那时以来，许多主要期刊发表了关于 LDG 的众多研究，例如《全球生态与生物地理学》和《生物地理学杂志》这两本旗舰期刊在过去几十年中一直是 LDG 文章的主要来源；其他主流期刊包括《生态学》、《生态学快报》、《美国自然主义者》和《皇家学会 B 辑：生物科学论文集》也发表了许多关于 LDG 的论文（图 2）。此外，自 1995 年以来，关于陆地植物/动物、海洋生物和微生物的 LDG 文章数量有所增加，尽管 2019 年和 2020 年的趋势有所放缓（图 3）。总体而言，近年来与 LDG 相关的文献数量显著增长。
All taxa, regardless of the land or the ocean, are conformed to the association between latitude gradients and taxonomic richness, e.g., terrestrial arthropods and terrestrial plants, mangrove trees, birds, mollusks, mammals, corals, freshwater arthropods, marine protists, marine arthropods, and reptiles. The existing distribution patterns of LDG of land-based flora, fauna, micro-organisms, and marine organisms are useful benchmarks to explore the distribution mechanisms so that they are stated briefly as follows. 所有分类群，无论是陆地还是海洋，都符合纬度梯度与分类丰富度之间的关系，例如，陆生节肢动物和陆生植物、红树林树木、鸟类、软体动物、哺乳动物、珊瑚、淡水节肢动物、海洋原生生物、海洋节肢动物和爬行动物。现有的陆地植物、动物、微生物和海洋生物的 LDG 分布模式是探索分布机制的有用基准，简要陈述如下。
Figure 2. Number of documents per journal relating to the LDG research using the keywords “latitudinal diversity gradient” from Web of Science (Data accessed on 22 February 2022); only journals with more than 20 published papers are shown. The size of a block is proportional to the number of relevant papers in the given journal. 图 2. 使用关键词“纬度多样性梯度”从 Web of Science 获取的与 LDG 研究相关的每个期刊的文献数量（数据访问于 2022 年 2 月 22 日）；仅显示发表论文超过 20 篇的期刊。块的大小与该期刊中相关论文的数量成正比。
Figure 3. Search results using Web of Science (Data accessed on 22 February 2022) from 1966 to 2021, with the numbers of the published papers in each year; results include all documents and trends obtained using the keywords, “latitudinal diversity gradient” and “Land-based flora” (including plant, forest, flora, vegetation, algae, bryophyte, pteridophyte, spermatophyte, or lichen); “Land-based fauna” (including animal, zoology, fauna, vertebrate, invertebrate, bird, fish, mammal, amphibians, reptiles, or insect); “Microorganism” (including microbes, microorganism, bacteria, or germ); “Marine organism” (including marine, ocean, or sea), respectively. 图 3. 使用 Web of Science 的搜索结果（数据访问日期：2022 年 2 月 22 日），涵盖 1966 年至 2021 年间每年发表论文的数量；结果包括使用关键词“纬度多样性梯度”和“陆地植物”（包括植物、森林、植物群落、植被、藻类、苔藓、蕨类植物、种子植物或地衣），“陆地动物”（包括动物、动物学、动物群、脊椎动物、无脊椎动物、鸟类、鱼类、哺乳动物、两栖动物、爬行动物或昆虫），“微生物”（包括微生物、细菌或病菌），“海洋生物”（包括海洋、海洋或海）所获得的所有文献和趋势。
2.1. Land-Based Flora 2.1. 陆地植物群
The LDG is most strongly visible in phytogeographical composition. A previous study has observed a similar distribution pattern of all seed plants in China, considering all geographical and climatic variables [26]. Huang et al. revealed that the endemic seed plants show a clear distribution of LDG from north to south, indicating that large-scale phytogeography of endemic flora that is strongly related to latitude, e.g., tropical genera account for approximately 75%75 \% of flora species at the southernmost tip (i.e., Hainan), which decreases to nearly 0 at latitude 45-50^(@)N45-50^{\circ} \mathrm{N} [25]. In Australia, the differences in plant reproductive strategies between communities at high and low latitudes indicate the importance of climate diversity patterns [27]. A global species density map for liverworts showed a significant pattern of LDG in species richness [28]. And latitudinal gradients of the richness of shrub and liana showed the same trends, i.e., the latitudes occupied by shrubs ranged nearly from 18-50^(@)N18-50^{\circ} \mathrm{N}, a greater range than that occupied by shrubs (18-45^(@)N)\left(18-45^{\circ} \mathrm{N}\right) and lianas (18-40^(@)N)\left(18-40^{\circ} \mathrm{N}\right) of latitude in species range size [29]. However, not all plants conform to the obvious LDG, i.e., the latitudinal trend in species richness is weakly negative in some liverworts and woody plants [22]. Notably, climate change is already altering the biogeographical patterns of flora, and the substantially diminish the extent and richness of Europe’s high-latitude mountain flora has demonstrated that climate change is predicted to the lost at high latitudes [30]. Therefore, biogeographic histories of flora affected their vulnerability to the climate change, especially the climate warming; and the vulnerability of the endemic plants, implying high significance for conservation decisions in the shifts of LDG. LDG 在植物地理组成中最为明显。之前的研究观察到中国所有种子植物的分布模式相似，考虑了所有地理和气候变量[26]。黄等人揭示了地方性种子植物从北到南显示出明显的 LDG 分布，表明地方性植物群的大规模植物地理与纬度密切相关，例如，热带属在最南端（即海南）占据的植物种类约为 75%75 \% ，而在纬度 45-50^(@)N45-50^{\circ} \mathrm{N} 时几乎降至 0[25]。在澳大利亚，高纬度和低纬度社区之间植物繁殖策略的差异表明气候多样性模式的重要性[27]。一张全球肝苔类植物物种密度图显示了物种丰富度的 LDG 显著模式[28]。灌木和藤本植物的丰富度的纬度梯度显示出相同的趋势，即灌木所占的纬度范围几乎从 18-50^(@)N18-50^{\circ} \mathrm{N} ，比灌木 (18-45^(@)N)\left(18-45^{\circ} \mathrm{N}\right) 和藤本植物 (18-40^(@)N)\left(18-40^{\circ} \mathrm{N}\right) 的纬度范围更大[29]。然而，并非所有植物都符合明显的 LDG，即在某些肝苔和木本植物中，物种丰富度的纬度趋势呈弱负相关[22]。值得注意的是，气候变化已经在改变植物的生物地理模式，欧洲高纬度山地植物的范围和丰富度显著减少，表明气候变化预计将在高纬度地区造成物种丧失[30]。因此，植物的生物地理历史影响了它们对气候变化，特别是气候变暖的脆弱性；而地方性植物的脆弱性则对 LDG 变化中的保护决策具有重要意义。
2.2. Land-Based Fauna 2.2. 陆地动物
The LDG pattern of animals is significant in a broad sweep of taxa, e.g., in the tropics, the squamate lineages originating in situ reflect it, and the patterns are driven primarily by the dispersal and diversification rates [14,31][14,31]. Ant species richness also peaks in the tropics, which is consistent with that of many other taxa [32]. Extant birds are globally distributed, although the ubiquity of birds and their penchant for dispersal, and avian diversity studies have shown that both species numbers and the presence of higher taxonomic groups are skewed towards the tropical environments [33]. Approximately 92%92 \% of all mammalian diversity peaks in the tropical regions, with the exception of Lagomorpha, which shows maximum diversity in the northern and temperate regions [34]. LDG patterns are strikingly consistent with the diversification rates, wherein the peaks for species richness are always associated with low extinction rates and/or high speciation rates [34]. 动物的 LDG 模式在广泛的分类群中具有重要意义，例如，在热带地区，原位起源的鳞状动物谱系反映了这一点，而这些模式主要受到扩散和多样化速率的驱动 [14,31][14,31] 。蚂蚁物种丰富度在热带地区也达到峰值，这与许多其他分类群的情况是一致的[32]。现存鸟类在全球范围内分布，尽管鸟类的普遍性及其扩散倾向，以及鸟类多样性研究表明，物种数量和高分类群的存在都偏向于热带环境[33]。大约 92%92 \% 的所有哺乳动物多样性在热带地区达到峰值，除了兔形目，其在北方和温带地区显示出最大多样性[34]。LDG 模式与多样化速率惊人地一致，其中物种丰富度的峰值总是与低灭绝率和/或高物种形成率相关联[34]。
2.3. Microorganisms 2.3. 微生物
The pattern of diversity in microorganisms with a small body size, fast population growth, high abundance, and high dispersal rates, which characteristics are contrary to that of macroorganisms. However, microorganisms unexpectedly showed the LDG pattern existed in bacteria as well as in marine protists (i.e., planktonic foraminifera) on a global scale [16,35,36][16,35,36]. Similarly, the beta diversity and phylogenetic diversity of Streptomyces strains showed an LDG pattern [37]. The LDG patterns were speculated to be involved in the geographic distribution of the host organisms. Surprisingly, both host richness and parasite abundance increased across 20^(@)20^{\circ} of latitude despite assumptions about diversity in parasites suggesting that their parasites exhibited no pattern or reverse latitudinal gradients to their hosts [38]. The reason for the reverse latitudinal gradients or lack of pattern in LDG in microorganisms is that the greater areas of wetlands at higher latitudes provide many habitats for larval amphibians to enhance host density, contributing positively to parasite richness [39]. In different organism groups (e.g., meiofauna, zooplankton and unicellular taxa), there is a significant difference in the LDG pattern between species richness and latitude [35]. 微生物的多样性模式具有小体型、快速种群增长、高丰度和高扩散率，这些特征与宏观生物相反。然而，微生物意外地显示出在全球范围内，细菌和海洋原生生物（即浮游有孔虫）中存在 LDG 模式 [16,35,36][16,35,36] 。同样，链霉菌株的β多样性和系统发育多样性也显示出 LDG 模式[37]。LDG 模式被推测与宿主生物的地理分布有关。令人惊讶的是，尽管关于寄生虫多样性的假设表明它们的寄生虫没有模式或与宿主相反的纬度梯度，但宿主丰富度和寄生虫丰度在 20^(@)20^{\circ} 的纬度上都增加了[38]。微生物中反向纬度梯度或缺乏 LDG 模式的原因是，高纬度地区更大的湿地面积为幼蛙提供了许多栖息地，从而增强了宿主密度，积极促进了寄生虫的丰富度[39]。在不同的生物群体中（例如在 meiofauna、zooplankton 和单细胞分类群之间，物种丰富度与纬度之间的 LDG 模式存在显著差异 [35]。
2.4. Marine Organisms 2.4. 海洋生物
The existence of LDG patterns in the sea is surprisingly controversial, especially when land organisms show pervasive LDG with maximum species richness in the tropical regions [40]. However, the LDG patterns for known marine organisms are well-studied in many taxa. Although the extant data from the deep seas are insufficient to analyze the LDG for sparsely distributed deep-sea organisms, some marine epifauna resident on the surface of the substratum in the ocean show a typical LDG [40]. The diversity of nematodes shows a positive LDG in the deep sea in the Atlantic, with a decline from 0^(@)0^{\circ} to 40^(@)S40^{\circ} \mathrm{S} [41]. The eastern Pacific bivalvia show a strong LDG within increasing numbers of species from the tropics to the southern tropical boundary in the northern Hemisphere; species numbers outside of the tropics show a stepwise decline toward the poles from 5^(@)S5^{\circ} \mathrm{S} to 8-9^(@)N8-9^{\circ} \mathrm{N} [40]. Interestingly, the fossil records of marine bivalves from the three successive slices in the late Cenozoic showed that species with tropical origins tended to expand from the tropics to higher latitudes [13]. These results support LDG in the marine shelf benthos, which is congruent with the diversity trends of gastropods along both northeastern Pacific shelves and the northwestern Atlantic [13,42]. For the coastal plants, e.g., mangrove, the mixing-isolation-mixing cycles can potentially generate species at an exponential rate, thus combining speciation and biodiversity in a unified framework by permitting intermittent gene flow during speciation [43]. But, the LDG pattern is still unclear for this. 海洋中 LDG 模式的存在令人惊讶地具有争议，尤其是当陆地生物在热带地区表现出普遍的 LDG 和最大物种丰富度时[40]。然而，已知海洋生物的 LDG 模式在许多分类群中得到了充分研究。尽管来自深海的现有数据不足以分析稀疏分布的深海生物的 LDG，但一些栖息在海洋底层表面的海洋附生生物显示出典型的 LDG[40]。在大西洋的深海中，线虫的多样性表现出正向的 LDG，从 0^(@)0^{\circ} 下降到 40^(@)S40^{\circ} \mathrm{S} [41]。东太平洋的双壳类动物在从热带到北半球南热带边界的物种数量增加中表现出强烈的 LDG；热带以外的物种数量则呈现出向极地的逐步下降，从 5^(@)S5^{\circ} \mathrm{S} 到 8-9^(@)N8-9^{\circ} \mathrm{N} [40]。有趣的是，晚新生代三个连续切片的海洋双壳类化石记录显示，具有热带起源的物种倾向于从热带扩展到更高纬度[13]。 这些结果支持海洋大陆架底栖生物的 LDG，这与东北太平洋大陆架和西北大西洋的腹足类动物多样性趋势一致[13,42]。对于沿海植物，例如红树林，混合-隔离-混合循环可能以指数速率产生物种，从而通过在物种形成期间允许间歇性基因流动，将物种形成和生物多样性结合在一个统一的框架中[43]。但是，对于这一点，LDG 模式仍然不清楚。
2.5. LDG and Biodiversity Conservation 2.5. LDG 与生物多样性保护
Biodiversity enhances many natural resources that are essential for human well-being, yet human activity has resulted in rapid biodiversity loss [44]. The sixth mass extinction in Earth’s history has been driven by human activity [45,46] and global warming [44,47,48]. Accelerated biodiversity loss is a hallmark of the Anthropocene, in which large declines in population size, habitat loss, fragmentation, biological invasions, pollution, and climate change have been widely observed requiring effective and efficient conservation managements [45,48-51]. LDG, as a wide-scale diversity pattern on Earth, has inevitably been affected by the changing environment. The spatial model indicates that forests and jungles are exposed to anthropogenic threats (e.g., changes in fire regimes and deforestation) in Amazonia, Central America, the Eastern Arc Mountains, the Northern Andes, the Brazilian Atlantic, southeastern Asia, and Sub-Saharan Africa [23,52]. The pattern of LDG will inevitably be influenced in this dynamic environment; hence, the changing trends of biodiversity loss to human activity and climate change in the Anthropocene require more attention. 生物多样性增强了许多对人类福祉至关重要的自然资源，但人类活动导致了生物多样性的快速丧失[44]。地球历史上的第六次大灭绝是由人类活动[45,46]和全球变暖[44,47,48]驱动的。加速的生物多样性丧失是人类世的一个标志，在这一时期，人口规模的大幅下降、栖息地丧失、碎片化、生物入侵、污染和气候变化被广泛观察到，这需要有效和高效的保护管理[45,48-51]。作为地球上广泛的多样性模式，LDG 不可避免地受到环境变化的影响。空间模型表明，亚马逊、中美洲、东弧山脉、北安第斯山脉、巴西大西洋、东南亚和撒哈拉以南非洲的森林和丛林面临人类活动的威胁（例如，火灾制度的变化和森林砍伐）[23,52]。在这个动态环境中，LDG 的模式必然会受到影响；因此，人类活动和气候变化导致的生物多样性丧失的变化趋势需要更多关注。
However, our understanding of the full impact of humanity on biodiversity, as well as of the links between the processes occurring in natural ecosystems, is incomplete [51]. As an important indicator of biodiversity patterns, the LDG patterns will be affected by climate warming and human activity over the global biodiversity framework. Over the past few decades, scientific studies have played important roles in verifying and identifying explicit goals for plant conservation, which are used in assessments of extinction risk, the prediction of range changes under climate change, and adaptation measures [30,53-56]. Therefore, we suggest that the cohesive nature of species richness and ecosystem diversity, particularly the trends of LDG in the changing world, will provide important insights into prioritizing conservation efforts. 然而，我们对人类对生物多样性的全面影响以及自然生态系统中发生的过程之间的联系的理解仍不完整[51]。作为生物多样性模式的重要指标，LDG 模式将受到气候变暖和人类活动的影响，影响全球生物多样性框架。在过去的几十年中，科学研究在验证和确定植物保护的明确目标方面发挥了重要作用，这些目标用于评估灭绝风险、预测气候变化下的分布变化以及适应措施[30,53-56]。因此，我们建议，物种丰富度和生态系统多样性的内在联系，特别是在变化世界中 LDG 的趋势，将为优先考虑保护工作提供重要见解。
3. Formation Mechanisms of the LDG 3. LDG 的形成机制
3.1. LDG Hypotheses 3.1. LDG 假设
For the formation mechanism of LDG, there are six main hypotheses in a comprehensive review of LDG have been proposed previously, and these mainly focus on ecology and evolution [6,10]. The hypotheses from 1966 to 2021 for the latitudinal diversity gradient and the other sources are listed in Table 1. With the increase in the knowledge about LDG, more hypotheses have been proposed, but the late-comers are mainly deduced from the six hypotheses. In this review, we simply elaborate the relationships between the six main 关于 LDG 的形成机制，之前在对 LDG 的综合评审中提出了六个主要假说，这些假说主要集中在生态和进化方面[6,10]。1966 年至 2021 年间关于纬度多样性梯度的假说及其他来源列于表 1。随着对 LDG 知识的增加，提出了更多的假说，但后来的假说主要是从这六个假说中推导而来的。在本次评审中，我们简单阐述了这六个主要假说之间的关系。
hypotheses and the others; and mainly focus on the widely embraced hypotheses. Thus, in this review the six broadly accepted hypotheses are revisited. 假设及其他；主要关注广泛接受的假设。因此，在本综述中重新审视了六个广泛接受的假设。
Table 1. Hypotheses from 1966 to 2021 for the latitudinal diversity gradient, P1-P6 from Pianka (1966), F1-F5 from Fine (2015), and O1-O7 from the other sources. 表 1. 1966 年至 2021 年纬度多样性梯度的假设，P1-P6 来自 Pianka（1966），F1-F5 来自 Fine（2015），O1-O7 来自其他来源。
Hypothesis 假设
Primary Focus 主要关注
References 参考文献
P1. The time theory P1. 时间理论
Ecology and evolution 生态学与进化论
[6][6]
P2. The theory of spatial heterogeneity P2. 空间异质性理论
Ecology 生态学
[6][6]
P3. The competition hypothesis P3. 竞争假说
Ecology 生态学
[6][6]
P4. The predation hypothesis P4. 捕食假说
Ecology 生态学
[6][6]
P5. The theory of climatic stability P5. 气候稳定性理论
Ecology and evolution 生态学与进化论
[6][6]
P6. The productivity hypothesis P6. 生产力假说
Ecology 生态学
[6][6]
F1. Time-integrated area, energy, and tropical niche F1. 时间积分面积、能量和热带生态位
Evolution 进化
[15][15]
conservatism 保守主义
Evolution 进化
[15][15]
F2. Climate stability F2. 气候稳定性
Evolution 进化
[15][15]
F3. Temperature and evolutionary speed F3. 温度与进化速度
Evolution 进化
[15][15]
F4. Biotic interactions and speciation rate F4. 生物相互作用与物种形成速率
Ecology 生态学
[15][15]
F5. Biotic interactions and finer niches F5. 生物相互作用和更细的生态位
Hypothesis Primary Focus References
P1. The time theory Ecology and evolution [6]
P2. The theory of spatial heterogeneity Ecology [6]
P3. The competition hypothesis Ecology [6]
P4. The predation hypothesis Ecology [6]
P5. The theory of climatic stability Ecology and evolution [6]
P6. The productivity hypothesis Ecology [6]
F1. Time-integrated area, energy, and tropical niche Evolution [15]
conservatism Evolution [15]
F2. Climate stability Evolution [15]
F3. Temperature and evolutionary speed Evolution [15]
F4. Biotic interactions and speciation rate Ecology [15]
F5. Biotic interactions and finer niches Ecology [32]
O1.The ecological regulation hypothesis Evolution [57]
O2.The "diversification rate hypothesis Ecology and evolution [58]
O3.The out of the tropics hypothesis Ecology and evolution [59]
O4.The out-of-the-extratropics hypothesis Evolution [32]
O5.The evolutionary time hypothesis Evolution [60]
O6.The time-for-speciation hypothesis Ecology [61]| Hypothesis | Primary Focus | References |
| :--- | :--- | :--- |
| P1. The time theory | Ecology and evolution | $[6]$ |
| P2. The theory of spatial heterogeneity | Ecology | $[6]$ |
| P3. The competition hypothesis | Ecology | $[6]$ |
| P4. The predation hypothesis | Ecology | $[6]$ |
| P5. The theory of climatic stability | Ecology and evolution | $[6]$ |
| P6. The productivity hypothesis | Ecology | $[6]$ |
| F1. Time-integrated area, energy, and tropical niche | Evolution | $[15]$ |
| conservatism | Evolution | $[15]$ |
| F2. Climate stability | Evolution | $[15]$ |
| F3. Temperature and evolutionary speed | Evolution | $[15]$ |
| F4. Biotic interactions and speciation rate | Ecology | $[15]$ |
| F5. Biotic interactions and finer niches | Ecology | $[32]$ |
| O1.The ecological regulation hypothesis | Evolution | $[57]$ |
| O2.The "diversification rate hypothesis | Ecology and evolution | $[58]$ |
| O3.The out of the tropics hypothesis | Ecology and evolution | $[59]$ |
| O4.The out-of-the-extratropics hypothesis | Evolution | $[32]$ |
| O5.The evolutionary time hypothesis | Evolution | $[60]$ |
| O6.The time-for-speciation hypothesis | Ecology | $[61]$ |
As known, the other hypotheses originate from the six main hypotheses and make differing predictions about the spatial distribution of organisms. For example, the out of the tropics (OTT) hypothesis describes how the combination of evolutionary dynamics and dispersal may have shaped the LDG of marine species [58]. Later, some groups may have also been shaped by dispersal towards the tropics, as in the out of the extratropics (OET) hypothesis [59]. Similarly, the evolutionary time hypothesis (ETH) suggests that tropical areas have been occupied for longer than temperate region, and thus have had more time to accumulate species [32]. Alternatively, under the diversification-rate hypothesis (DRH), higher richness in some clades is explained by faster rates of net diversification, and high species richness is associated with clades that have accumulated many species in a relatively short period of time [57]. The ecological regulation hypothesis (ERH) posits that there are equilibrated the ecological limits to species numbers, which vary systematically with latitude, perhaps due to the direct influence of climate and/or available energy [32]. The tropical conservatism hypothesis (TCH) suggests that the tropics have been occupied for longer, dispersal out of the tropics is rare, and the greater past area of the tropics yielded more present-day tropical clades [61]. From the above-mentioned examples of hypotheses, each of them is related with one or two of the six main hypotheses. Thus, the review briefly elaborates on the possible causes and/or hypothesis of LDG as follows. 众所周知，其他假说源于六个主要假说，并对生物的空间分布做出不同的预测。例如，热带外假说（OTT）描述了进化动态和扩散的结合如何塑造海洋物种的物种多样性梯度（LDG）[58]。后来，一些群体可能也受到向热带扩散的影响，如热带外假说（OET）所述[59]。类似地，进化时间假说（ETH）建议热带地区的占据时间比温带地区更长，因此有更多时间积累物种[32]。或者，根据多样化速率假说（DRH），某些类群的高丰富度可以通过更快的净多样化速率来解释，高物种丰富度与在相对较短时间内积累了许多物种的类群相关[57]。生态调节假说（ERH）认为，物种数量的生态限制是平衡的，这些限制随着纬度系统性变化，可能是由于气候和/或可用能量的直接影响[32]。 热带保守主义假说（TCH）认为，热带地区的占据时间更长，热带地区的扩散很少，过去热带地区的面积更大导致了现在更多的热带类群[61]。从上述假说的例子来看，每个假说都与六个主要假说中的一个或两个相关。因此，综述简要阐述了 LDG 的可能原因和/或假说，如下所示。
The time hypothesis is perhaps the most widely accepted and the oldest of the six hypotheses. It can be dated back to the time of Alfred Russel Wallace, who proposed that evolutionary (speciation) and ecological (immigration) factors drove the increase in species richness of communities over time [6]. In tropical regions where have been occupied for longer periods, yielding more present-day tropical clades, and dispersal out of the tropics is rare [62]. The evolutionary time hypothesis suggests that the tropics provide more time for lineages to accumulate species [21]. This can be explained by geological events, i.e., the tropical regions remained relatively undisturbed, whereas the diversity in northern latitudes was reduced due to multiple glaciations, which led to the formation of the current LDG patterns [10]. 时间假说可能是六个假说中最被广泛接受和最古老的一个。它可以追溯到阿尔弗雷德·拉塞尔·华莱士的时代，他提出进化（物种形成）和生态（移民）因素推动了物种丰富度随时间的增加[6]。在热带地区，由于占据的时间较长，导致了更多现今热带类群的形成，而热带以外的扩散则很少见[62]。进化时间假说表明，热带地区为谱系积累物种提供了更多时间[21]。这可以通过地质事件来解释，即热带地区相对未受到干扰，而北纬地区的多样性由于多次冰川作用而减少，这导致了当前 LDG 模式的形成[10]。
The environmental heterogeneity hypothesis suggests that habitat heterogeneity promotes species richness [63], and the probability of species coexistence augments different niches [64]. Heterogeneity is beneficial in case of adverse environmental conditions. For the environmental heterogeneity, it has been shown that communities with increasing species capability and speciation withstood isolation or adaptation to diverse environmental conditions [65,66]. In addition, lower species ecological tolerance in the tropics may result in denser speciation and spatial heterogeneity at lower latitudes [54]. 环境异质性假说表明，栖息地异质性促进物种丰富度[63]，而物种共存的概率增强了不同的生态位[64]。在不利环境条件下，异质性是有益的。关于环境异质性，研究表明，具有更高物种能力和物种形成的群落能够抵御孤立或适应多样的环境条件[65,66]。此外，热带地区较低的物种生态耐受性可能导致在低纬度地区更密集的物种形成和空间异质性[54]。
The competition hypothesis was proposed based on natural selection in the temperate zone, which was controlled by abiotic more than biotic factors with stronger biotic interactions and increased speciation rates for positive feedback; niches are narrower, competition is stronger, and co-evolutionary rates across the geographic mosaic have reduced the extinction rates [6,10,15][6,10,15]. Therefore, competition in the tropical regions is lower, as intense predation in the tropical environments results in reduced populations. 竞争假说是基于温带地区的自然选择提出的，该地区的控制因素更多是非生物因素而非生物因素，生物相互作用更强，物种形成速率增加以实现正反馈；生态位更狭窄，竞争更强，地理马赛克中的共同进化速率降低了灭绝率 [6,10,15][6,10,15] 。因此，热带地区的竞争较低，因为热带环境中的强烈捕食导致种群减少。
As an alternative to the competition hypothesis, the predation hypothesis suggests that competition in the tropics is lower due to higher predation in tropical environments, which causes a reduction in population size [6,10]. From the polar to tropical regions, more diversification was observed in the community composition and structure that are the greater probability that a larger proportion of predators can be maintained. Predators can then effectively control the number of prey and producer populations, such that there are more predators, parasites, and prey in the tropics than in other regions [67]. In tropical forests, trees attract their consumers, so that the consumption of seeds and seedlings by animals/herbivores reduces the number/survival rate of seeds/seedlings, and consequently the density of the population. In this way, herbivores increase the space available for the invasion of seeds and seedlings of other plant species, concomitantly increasing the diversity of tree species in the tropical forests [68]. 作为竞争假说的替代，捕食假说认为热带地区的竞争较低是由于热带环境中捕食率较高，这导致了种群规模的减少[6,10]。从极地到热带地区，观察到社区组成和结构的多样性增加，这意味着更大比例的捕食者能够被维持。捕食者能够有效控制猎物和生产者种群的数量，因此热带地区的捕食者、寄生虫和猎物的数量比其他地区更多[67]。在热带森林中，树木吸引它们的消费者，因此动物/食草动物对种子和幼苗的消费减少了种子/幼苗的数量/存活率，从而导致种群密度的降低。通过这种方式，食草动物增加了其他植物种类的种子和幼苗入侵的可用空间，同时增加了热带森林中树种的多样性[68]。
The climatic stability hypothesis predicts that the tropical regions have a higher species richness, greater specialization, and narrower niches due to their stable climate [6,9,10]. The stable climate in tropical regions increases species richness; for example, climate oscillations have affected species diversity globally especially during the Late Quaternary period [69]. However, in the tropical regions with relatively stable climate trends that are likely to have prevented large demographic fluctuations, thus promoting the maintenance of species richness and intraspecific genetic diversity [69,70]. By contrast, rapid climate change in temperate and cold and/or arid regions has led to more profound effects on precipitation and temperature trends, which has directly or indirectly affected species demographics over time [69,71-73]. LDG patterns of increasing latitudinal ranges in animal and plant species richness from low to high are related to the tolerance to seasonal temperature variability [11,74] and Ice Age temperature fluctuations [75]. 气候稳定性假说预测热带地区由于其稳定的气候具有更高的物种丰富度、更大的专业化和更窄的生态位[6,9,10]。热带地区的稳定气候增加了物种丰富度；例如，气候波动在全球范围内影响了物种多样性，尤其是在晚更新世时期[69]。然而，在气候趋势相对稳定的热带地区，这可能防止了大规模的人口波动，从而促进了物种丰富度和种内遗传多样性的维持[69,70]。相比之下，温带和寒冷及/或干旱地区的快速气候变化对降水和温度趋势产生了更深远的影响，这直接或间接地影响了物种的人口动态[69,71-73]。动物和植物物种丰富度从低纬度到高纬度的增加的 LDG 模式与对季节性温度变异的耐受性[11,74]和冰河时代温度波动[75]有关。
The productivity hypothesis suggests that species richness increases because of the greater productivity in tropical regions, allowing tighter species packing and narrower niches with a greater overlap of niches [6,10]. Energy input may enhance mutation and physiological rates, which then increase speciation by decreasing generation times [76]; thus population sizes should also correlate positively with productivity [77]. The net primary productivity and constraint on species richness due to limited resources may lead to geographical variation in species diversity [7,78]. Plant richness is primarily limited by water availability and solar energy at the base of the global food web [77,78]. For example, higher amounts of energy lead to faster evolutionary rates and more species richness in flowering plants [54]. In turn, predator richness is limited by the secondary production of herbivores in the food chain, whereas herbivore richness is limited by the net primary production of plants [78]. A positive relationship between richness and productivity could be responsible for the LDG pattern; however, the productivity hypothesis has not been accepted as an important cause of the LDG [17]. 生产力假说表明，物种丰富度的增加是由于热带地区更高的生产力，这使得物种的紧密聚集和更窄的生态位以及生态位的更大重叠成为可能[6,10]。能量输入可能增强突变和生理速率，从而通过缩短世代时间来增加物种形成[76]；因此，种群规模也应与生产力呈正相关[77]。由于资源有限，净初级生产力和对物种丰富度的限制可能导致物种多样性的地理变异[7,78]。植物丰富度主要受到水分可用性和全球食物网基础上的太阳能的限制[77,78]。例如，更高的能量量导致开花植物的进化速率更快和物种丰富度更高[54]。反过来，捕食者的丰富度受到食物链中草食动物的二次生产的限制，而草食动物的丰富度则受到植物的净初级生产的限制[78]。 丰富度与生产力之间的正相关关系可能是 LDG 模式的原因；然而，生产力假说并未被接受为 LDG 的重要原因[17]。
3.2. Climate Change, Temperature, and Precipitation 3.2. 气候变化、温度与降水
There is an equilibrium ecological limit to species numbers that varies systematically with latitude in LDG patterns due to the direct influence of available energy and/or climate [79,80][79,80]. The LDG mechanisms are difficult to determine due to the strong correlations between related ecological parameters, including climate, latitude, and temperature [37]. The species richness often varies with elevation and latitude or between geographic regions and temperature, precipitation, or other factors [7]. That is, the effects of species distribution on different species reflect different climatic tolerance among them. Thus, the explanations of the climatic variability hypothesis for variation along the latitudinal gradient favor the evolution of broader climatic tolerance of species at high latitudes [29,30]. 物种数量存在一个平衡生态极限，该极限在 LDG 模式中随着纬度的变化而系统性变化，这直接受到可用能量和/或气候的影响 [79,80][79,80] 。由于相关生态参数之间的强相关性，包括气候、纬度和温度[37]，LDG 机制难以确定。物种丰富度通常随着海拔和纬度的变化，或在地理区域、温度、降水或其他因素之间变化[7]。也就是说，物种分布对不同物种的影响反映了它们之间不同的气候耐受性。因此，气候变异假说对沿纬度梯度变化的解释支持高纬度物种更广泛气候耐受性的演化[29,30]。
During the geological ages, i.e., between the Tertiary and early Eocene period increased, global atmospheric temperatures increased and taxa evolved in tropical regions (low latitudes), and dispersed to higher latitudes, showing latitudinal patterns through tropical areas to higher latitudes [26]. And the current day species richness is also affected by climate oscillations on species demographic during the Late Quaternary [69,81]. Trends have been observed in the changes in the relative frequencies of tropical and temperate genera along the temperature, precipitation, and radiation gradients along the LDG [25]. For most plants, climate cooling (i.e., freezing tolerance) created an evolutionary barrier or survival limit, which determined the distribution range of many flowering plant taxa. For example, cold-intolerant plants of the boreotropical and evergreen flora were forced southward by climate cooling in the northern hemisphere [82]. Thus, this evolutionary process for cold adaptation is reasonable, and the tropical genera in flora descend along latitudes from low to high [26]; even some genera colonized from warm to cold [83]. An understanding of the environmental aspects that influence the traits underpinning adaptive resilience to changing climates could help in assessing the vulnerability of populations to climate change [84,85]. 在地质时代，即在第三纪和早期始新世期间，全球大气温度上升，热带地区（低纬度）的分类群进化，并向更高纬度扩散，显示出从热带地区到更高纬度的纬度模式[26]。而现今物种丰富度也受到晚更新世期间气候波动对物种人口的影响[69,81]。在沿着温度、降水和辐射梯度的 LDG 上，观察到了热带和温带属相对频率变化的趋势[25]。对于大多数植物而言，气候变冷（即耐寒性）造成了进化障碍或生存极限，这决定了许多开花植物分类群的分布范围。例如，北热带和常绿植物的耐寒植物因北半球气候变冷而被迫向南迁移[82]。因此，这种冷适应的进化过程是合理的，植物中的热带属沿纬度从低到高下降[26]；甚至一些属从温暖地区扩散到寒冷地区[83]。 理解影响适应性韧性特征的环境因素，有助于评估人群对气候变化的脆弱性 [84,85]。
Intraspecific genetic diversity and high levels of species richness are also correlated with the past inter-annual precipitation variability [23]. For example, frequent variations in precipitation during the Late Quaternary and the resultant fluctuations are proposed to have driven population isolation and adaptive divergence in suitable habitats at lower latitudes [86,87]. Precipitation can be used to explain the patterns of selection of local and regional variations in climate regimes [88]. 种内遗传多样性和高水平的物种丰富度与过去的年际降水变异性也相关联[23]。例如，晚更新世期间降水的频繁变化及其导致的波动被认为推动了低纬度适宜栖息地中的种群隔离和适应性分化[86,87]。降水可以用来解释地方和区域气候模式变异的选择模式[88]。
Model selection and hierarchical partitioning of species richness in liverworts showed that water-related variables are dominant [89]. For precipitation seasonality and availability, the spatial precipitation heterogeneity in mosses is considered an important predictor of species richness, but the temperature variables generally have higher explanatory power than water variables in woody plants [22]. Also, hierarchical partitioning in the species richness of liverworts and mosses indicated that the independent effects of temperature variables are higher than those of water variables and that water variables have more variation in these families than in woody plants [29]. This is consistent with the evolution of terrestrial plants, which involves their ability to adapt to water deficiencies [89]. Additionally, population persistence due to long-term climate stability results in a higher accumulation of species richness in the tropics than at higher latitudes, and climate-driven processes at lower latitudes always result in higher population divergence due to frequent precipitation variability [23]. 肝苔类物种丰富度的模型选择和分层划分显示，水相关变量是主导因素[89]。对于降水季节性和可用性，苔藓中的空间降水异质性被认为是物种丰富度的重要预测因子，但在木本植物中，温度变量通常具有比水变量更高的解释力[22]。此外，肝苔类和苔藓的物种丰富度的分层划分表明，温度变量的独立效应高于水变量，并且在这些类群中，水变量的变异性大于木本植物[29]。这与陆生植物的进化一致，涉及它们适应水分不足的能力[89]。此外，由于长期气候稳定导致的种群持续性，使得热带地区的物种丰富度积累高于高纬度地区，而低纬度的气候驱动过程总是导致由于频繁的降水变异而产生更高的种群分化[23]。
4. Evolutionary Responses for LDG 4. 进化响应对于 LDG
Generally, evolutionary responses are prerequisites for the long-term persistence of biodiversity during ongoing and projected scenarios of the extreme climate events [85,90]. Many LDG results from ecological, historical geology, and demographic events that influence dispersal and diversification can be explained by the evolutionary responses based on the historical contingency proposed [62,91]. Likewise, the diversification rate suggested that extinction and/or speciation rates vary systematically with LDG [32]. Evolutionary responses (i.e., speciation, extinction, diversification, and dispersal rates) are inevitable in 一般来说，进化响应是生物多样性在持续和预测的极端气候事件场景中长期存在的前提[85,90]。许多 LDG 的结果可以通过基于历史偶然性提出的进化响应来解释，这些结果源于影响扩散和多样化的生态、历史地质和人口事件[62,91]。同样，多样化速率表明灭绝和/或物种形成速率与 LDG 系统性变化[32]。进化响应（即物种形成、灭绝、多样化和扩散速率）在
LDG patterns. The evolutionary forces generated by LDG have been debated for many years [5,62]. Here, related evolutionary responses are listed to address the LDG pattern. LDG 模式。由 LDG 产生的进化力量已经争论了许多年[5,62]。在这里，列出了相关的进化响应以解决 LDG 模式。
4.1. Speciation Rate 4.1. 物种形成速率
The key to explaining LDG patterns is to understand the variation in speciation and extinction rates with latitude; however, it is difficult to estimate the diversification rates associated with specific geographic locations [34]. The speciation rates differ due to a range of factors and in different geographic regions [7]. In tropical clades, speciation is relatively high, and extinction appears to be very low, whereas in temperate lineages, speciation and extinction are very high [31,92]; the speciation rate is always linked to the diversification rate. For example, the relative stability in tropical climes led to older, slower-evolving but still species-rich communities, and long-term cooling had a disproportionate effect on the non-tropical diversification rates, leading to dynamic young communities outside of the tropics [93]. Thus, nonequilibrium explanations for LDG have been proposed based on different speciation rates in the tropics [35]. For example, in tropical regions where the ambient conditions are warmer, environmental factors could increase the mutation rates and lead to faster rates of evolution [8,94]. Thus, the speciation rate affects LDG patterns. 解释 LDG 模式的关键在于理解物种形成和灭绝率随纬度的变化；然而，估计与特定地理位置相关的多样化率是困难的[34]。物种形成率因多种因素和不同地理区域而异[7]。在热带类群中，物种形成相对较高，而灭绝率似乎非常低，而在温带谱系中，物种形成和灭绝率都非常高[31,92]；物种形成率始终与多样化率相关。例如，热带气候的相对稳定性导致了较老、进化较慢但仍然物种丰富的群落，而长期的降温对非热带多样化率产生了不成比例的影响，导致热带以外的动态年轻群落[93]。因此，基于热带地区不同的物种形成率，提出了对 LDG 的非平衡解释[35]。例如，在环境条件较温暖的热带地区，环境因素可能会增加突变率，从而导致更快的进化速率[8,94]。因此，物种形成率影响 LDG 模式。
4.2. Extinction Rate 4.2. 灭绝率
The extinction rates have led to geographic patterns of species richness; for example, a geographic region with climatic stability may play a key role in extinction levels [7]. In addition, species with larger distributions are less prone to extinction, and regions experiencing intense climatic fluctuations always experience increased extinction rates [70,95,96]. In the phylogeny, the older crown groups from the phylogenetic tree always accumulate more species as expected, whereas the stem groups have fewer species so that older temperate taxa have an apparently attenuated extinction [31,92]. And in the tropics, the mammals, e.g., amphibians, and squamates, also have lower extinction rates that contributed to more net diversification than speciation [31,34,97][31,34,97]. The dependence of extinction and speciation on diversity is a general process that regulates the shapes of taxonomic diversity curves [5]. Together, the association between a high species richness and low extinction rate suggested that extinction may play a more important role in driving differences in net diversification rates than speciation along latitudinal gradients [7]. 灭绝率导致了物种丰富度的地理模式；例如，气候稳定的地理区域可能在灭绝水平中发挥关键作用[7]。此外，分布范围较大的物种不易灭绝，而经历剧烈气候波动的区域总是会经历更高的灭绝率[70,95,96]。在系统发育中，来自系统发育树的较老冠群总是如预期那样积累更多物种，而茎群的物种较少，因此较老的温带分类群的灭绝率明显减弱[31,92]。在热带地区，哺乳动物，例如两栖动物和鳞状动物，也具有较低的灭绝率，这导致净多样性比物种形成更高 [31,34,97][31,34,97] 。灭绝和物种形成对多样性的依赖是一个调节分类多样性曲线形状的一般过程[5]。总的来说，高物种丰富度与低灭绝率之间的关联表明，灭绝在推动纬度梯度上净多样性率差异方面可能比物种形成更为重要[7]。
4.3. Net Diversification Rate 4.3. 净多样化率
The outcome of both speciation and extinction is the net diversification rate, which is typically higher in tropical clades and represents the difference between speciation and extinction [31]. The rates of diversification are higher in tropical latitudes; a strong, consistent role of net diversification in driving latitudinal species richness gradients has been proposed [7,8,71][7,8,71]. Net diversification rates suggest that higher temperatures or energy fluxes promote more rapid evolution; and a more equitable climate favors habitat specialization, leading to the dispersal and gene flow reduced and/or more intense biological interactions drive the adaptive changes [6,11,54,98]. Notably, the areas with high net diversification rates are more likely to be evolutionary cradles [14]. In the tropics, the squamate lineages suggested the greater species richness due to speciation, but the LDG appears to be driven primarily by the diversification rates [31]. Nevertheless, there are exceptions; e.g., the clades of passerines and swallowtails showed a significant latitudinal effect on the relative diversification rates [99]. 物种形成和灭绝的结果是净多样化率，通常在热带类群中较高，代表物种形成和灭绝之间的差异[31]。多样化率在热带纬度较高；有研究提出净多样化在推动纬度物种丰富度梯度中起着强大而一致的作用 [7,8,71][7,8,71] 。净多样化率表明更高的温度或能量流动促进更快速的进化；而更公平的气候有利于栖息地专业化，导致扩散和基因流动减少，以及/或更强烈的生物相互作用推动适应性变化[6,11,54,98]。值得注意的是，净多样化率较高的地区更可能是进化的摇篮[14]。在热带地区，鳞片类谱系由于物种形成而显示出更高的物种丰富度，但 LDG 似乎主要是由多样化率驱动的[31]。然而，也有例外；例如，雀形目和燕尾蝶的类群在相对多样化率上显示出显著的纬度效应[99]。
4.4. Dispersal Rate 4.4. 分散率
Dispersal always promotes gene flow wherein the colonization of habitats among isolated patches occurs. It has played a key role in species and population persistence in fragmented systems under rapid climatic change [81]. Two main hypotheses on dispersal dominance have been proposed. Firstly, the “out of the tropics” hypothesis suggests that lineages originate and diversify in the tropics and disperse from the tropics to the temperate 扩散总是促进基因流动，其中孤立斑块之间的栖息地被殖民。它在快速气候变化下的碎片化系统中对物种和种群的持续存在发挥了关键作用[81]。关于扩散主导的两种主要假说已被提出。首先，“热带外扩散”假说认为谱系起源于热带并在热带多样化，然后从热带扩散到温带。
regions. Secondly, the “tropical niche conservatism” hypothesis suggests that the lineages originate in the tropics and accumulate in tropical regions, because it is difficult to disperse and adapt in temperate regions [13,34][13,34]. Most of the present-day diversity in marine bivalves in extratropical regions is from taxa shared with the tropics, which has supported dispersal and the persistence of an LDG [40,58][40,58]. The role of dispersal in generating diversity gradients has been determined by studying the frequency of shifts from temperate to tropical biomes and vice versa [9]. More lineages are dispersed from the tropical to temperate regions than from the temperate to tropical regions, and the dominance of tropical to temperate dispersal is statistically significant in all scenarios [9,12,13]. In tropical regions, the newly evolved taxa might have extended northward into the temperate regions [100]. However, the range of extension in warm regions was curbed by frost tolerance; rapid and large-scale range contractions and expansions may have resulted in population extirpation and the subsequent loss of species richness at these latitudes [80,81]. 区域。其次，“热带生态位保守主义”假说表明，谱系起源于热带并在热带地区积累，因为在温带地区扩散和适应是困难的 [13,34][13,34] 。目前在温带地区的海洋双壳类动物的多样性大部分来自与热带共享的分类群，这支持了扩散和 LDG 的持续存在 [40,58][40,58] 。通过研究从温带到热带生物群落及其反向转变的频率，已确定扩散在产生多样性梯度中的作用[9]。从热带到温带的扩散谱系数量多于从温带到热带的谱系数量，热带到温带的扩散在所有情境中都是统计显著的[9,12,13]。在热带地区，新进化的分类群可能向北扩展到温带地区[100]。然而，温暖地区的扩展范围受到耐霜冻能力的限制；快速和大规模的范围收缩和扩展可能导致种群消失以及这些纬度物种丰富度的随之丧失[80,81]。
5. Future Perspectives 5. 未来展望
The most unique feature of the Earth is the existence of life, and the most extraordinary feature of life is its diversity (i.e., genes, species, and ecosystem diversity), which provides numerous essential services to a human-dominated society [48,49]. Considering that LDG is the broadest and most notable biodiversity pattern [15], the conservation efforts should be linked to the mechanisms of ecology and evolution from genetic/genomic diversity, species diversity, and ecosystem diversity in the future projects. 地球最独特的特征是生命的存在，而生命最非凡的特征是其多样性（即基因、多样性和生态系统多样性），这为以人类为主导的社会提供了众多基本服务 [48,49]。考虑到 LDG 是最广泛和最显著的生物多样性模式 [15]，未来的保护工作应与生态和进化的机制相联系，从基因/基因组多样性、物种多样性和生态系统多样性入手。
In recent decades, the studies of LDG have evolved due to the promotion of studies on land-based flora/fauna, microorganisms, and marine organisms (Figure 3). Using the comprehensive review written by Pianka as a milestone [6,10], the myriad of hypotheses for LDG has been organized into a manageable framework for future studies. Many studies on LDG have developed scientific tools for the elucidation of diversity and the related causes. However, most biodiversity patterns of LDG have mainly been explored based on ecosystem and species numbers [10,15]. As known, species is the evolutionary unit, and species diversity is the basic element for evolutionary change. Also, the ecosystem diversity of specific areas preserves many species and the subsequent genetic diversity [48]. According to the Convention on Biological Diversity (CBD, www.cbd.int, accessed on 23 January 2022), genetic diversity is recognized as one of the three basic elements of biodiversity and is the focus of many conservation genetics studies. Thus, we suggest that LDG patterns are useful for investigating the ecological and evolutionary mechanisms from genetic/genomic and phylogenetic diversity to facilitate the estimation of cladespecific diversification rates in relation to latitude, climate, and other factors. Estimating the contribution of these factors from ecology and evolution in promoting the LDG patterns from phylogenetic and/or genetic/genomic data is challenging, but the availability of big data is gradually reality. Also, it is worth noting that the development of Geographic Information System (GIS) mapping and satellite imagery has provided unprecedented resources to study LDG from the perspectives of global patterns of climate, productivity, landform, and species richness [10]. In addition, LDG can be explored with technological achievements from both paleo- and modern studies [18]. 在最近几十年中，由于对陆地植物/动物、微生物和海洋生物研究的推动，LDG 的研究不断发展（图 3）。以 Pianka 撰写的综合评述作为里程碑[6,10]，LDG 的众多假说已被整理成一个可管理的框架，以便于未来的研究。许多关于 LDG 的研究开发了科学工具，以阐明多样性及其相关原因。然而，LDG 的大多数生物多样性模式主要是基于生态系统和物种数量进行探索的[10,15]。众所周知，物种是进化单位，物种多样性是进化变化的基本要素。此外，特定区域的生态系统多样性保留了许多物种及其后续的遗传多样性[48]。根据《生物多样性公约》（CBD，www.cbd.int，访问于 2022 年 1 月 23 日），遗传多样性被认为是生物多样性的三个基本要素之一，并且是许多保护遗传学研究的重点。 因此，我们建议 LDG 模式对于研究生态和进化机制，从遗传/基因组和系统发育多样性出发，以促进对与纬度、气候和其他因素相关的类群特异性多样化速率的估计是有用的。估计这些因素在促进 LDG 模式方面的生态和进化贡献，基于系统发育和/或遗传/基因组数据是具有挑战性的，但大数据的可用性正逐渐成为现实。此外，值得注意的是，地理信息系统（GIS）制图和卫星影像的发展为从气候、生产力、地形和物种丰富度的全球模式的角度研究 LDG 提供了前所未有的资源。此外，LDG 还可以通过古代和现代研究的技术成就进行探索。
With the coming of new era of the Anthropocene, the biodiversity crisis is closely connected to the human activity. Predicting the influence of human-induced climatic change on a short and/or long-term organismal distribution is imperative in contemporary biology [101]. Over the course of a century, humans have markedly altered the planet, causing various effects, including an increase in ocean acidity to landscape fragmentation and climate change [48]. The far-reaching influence of human activity has contributed to a loss of biodiversity, changing land use, habitat loss, plant extinction, predatory fish, defaunation, and a reduction in species abundance [48,102]. Therefore, investigations of the LDG pattern must consider the knock-on effects on biodiverse communities from the concomitant influence of human activity and climate change. According to the shifts or trends of LDG patterns, some protected areas can be identified. Protected areas are 随着人类世新纪的到来，生物多样性危机与人类活动密切相关。预测人类引起的气候变化对短期和/或长期生物分布的影响在当代生物学中是至关重要的[101]。在一个世纪的时间里，人类显著改变了地球，造成了各种影响，包括海洋酸度增加、景观破碎和气候变化[48]。人类活动的深远影响导致了生物多样性的丧失、土地利用变化、栖息地丧失、植物灭绝、捕食性鱼类、动物灭绝以及物种丰度的减少[48,102]。因此，对 LDG 模式的研究必须考虑人类活动和气候变化的共同影响对生物多样性社区的连锁反应。根据 LDG 模式的变化或趋势，可以识别出一些保护区。保护区是
safeguarded from human activity to a certain extent through conservation planning and prioritization in a human-dominated and fast-changing world [48]. Now the solution of human activity to biodiversity is easily found to these issues, i.e., the establishments of related legislations and conservation areas to decrease the impacts from human activity. However, little is known about the effects of climate change on biodiversity, and thus, significant research on this aspect is crucial. Previous research on well-studied large organisms showed that biodiversity may be more sensitive to climate, such that the impact of ongoing Anthropocene climatic change may be much more serious than previously thought [58]. In particular, wide-scale extinctions and population decline across taxonomic groups have been caused by human activity over the past 500 years [103]. However, most studies on LDG have mainly focused on ecological factors, i.e., species and ecosystems. Therefore, the impact of human activity or imprint and climate change (e.g., the warming climate) on the diversity of ecosystems along latitudinal gradient has been generally disregarded. 在一个以人类为主导且快速变化的世界中，通过保护规划和优先排序，在一定程度上保护了人类活动的影响[48]。现在，解决人类活动对生物多样性的影响的方法很容易找到，即建立相关立法和保护区以减少人类活动的影响。然而，关于气候变化对生物多样性的影响知之甚少，因此在这一方面进行重要研究至关重要。以往对研究较多的大型生物的研究表明，生物多样性可能对气候更加敏感，因此正在进行的人类世气候变化的影响可能比之前认为的要严重得多[58]。特别是，在过去 500 年中，人类活动导致了各分类群的广泛灭绝和种群下降[103]。然而，大多数关于 LDG 的研究主要集中在生态因素上，即物种和生态系统。因此，人类活动或印记以及气候变化（例如，气候变暖）对沿纬度梯度生态系统多样性的影响通常被忽视。
In addition, the explanations of LDG patterns and/or mechanisms from genetics and genomics are rare. The reasonable utilization and benefit of sharing of genetic resources have been inferred from the CBD to ensure the conservation of biodiversity [104]. Based on whole genomes, a strategy for cataloging adaptive genetic diversity to climate change across a range of ecologically important non-model species has improved population datasets and provided a high-resolution record of variation in structural information and genomes [88]. The models linking genomics with eco-evolution provide unique opportunities for predicting and tracking vulnerability and adaptive responses to climate change, which will benefit the biodiversity issues along the LDG distribution. Thus, LDG taken from large-scale genetic/genomic data (e.g., the DNA data from NCBI) or the genetic variation in specific taxa in wild populations with a vast distribution will reveal the distribution patterns and mechanisms to assist the CBD in meeting targets to halt the acceleration in biodiversity loss. In the face of environmental change, the ever-increasing availability of ecological studies is going on, integrating the big data from evolution across large-scale distributions and taxa, will provide important and novel opportunities to enhance our understanding of the adaptive potential of LDG globally. Hence, ecologists, evolutionists, and related scholars are called upon to rethink the LDG in view of the available genetic resources in the changing world. 此外，关于遗传学和基因组学的 LDG 模式和/或机制的解释很少。从《生物多样性公约》（CBD）推断出合理利用和共享遗传资源的好处，以确保生物多样性的保护[104]。基于全基因组的策略， cataloging 适应气候变化的遗传多样性，涵盖一系列生态重要的非模式物种，改善了种群数据集，并提供了结构信息和基因组变异的高分辨率记录[88]。将基因组学与生态进化联系起来的模型为预测和追踪对气候变化的脆弱性和适应性反应提供了独特的机会，这将有利于 LDG 分布沿线的生物多样性问题。因此，从大规模遗传/基因组数据（例如，来自 NCBI 的 DNA 数据）或在广泛分布的野生种群中特定分类群的遗传变异中提取的 LDG，将揭示分布模式和机制，以帮助 CBD 实现停止生物多样性丧失加速的目标。 面对环境变化，生态研究的日益增加正在进行中，整合来自大规模分布和分类群的进化大数据，将为增强我们对全球 LDG 适应潜力的理解提供重要而新颖的机会。因此，生态学家、进化论者和相关学者被呼吁重新思考在变化世界中可用的遗传资源下的 LDG。
6. Conclusions 6. 结论
Half a century ago, the review from Pianka is believed to be a milestone in understanding LDG patterns, which is and will be the manageable framework for future studies [6,10][6,10]. Subsequently, a time-integrated biogeographic analysis of geographical diversification suggests that both time-integrated and stable climate areas will determine the baseline of marine diversity and terrestrial patterns at the global scale. Patterns of the LDG mainly focused on the ecology and evolution in tropics from the species richness to mechanism. The tropics are geologically older, and have had more time for diversification, which is consistent with the time hypothesis, in which biotic interactions likely augment coexistence and diversification [15]. Thus, the related studies from tropical regions to warm and/or cold regions are the key points we have to take into account, e.g., the different taxa and/or communities along with latitudinal gradients. According to our own experience, Engelhardia is distributed from 10^(@)S10^{\circ} \mathrm{S} to 30^(@)N30^{\circ} \mathrm{N} on a latitudinal distribution in Southeast Asia, where the plants are typical to unique substrates to disentangle the LDG from integrated disciplines [100,105][100,105]. 半个世纪前，Pianka 的评审被认为是理解 LDG 模式的一个里程碑，这将是未来研究的可管理框架 [6,10][6,10] 。随后，对地理多样化的时间综合生物地理分析表明，时间综合和稳定气候区域将决定全球范围内海洋多样性和陆地模式的基线。LDG 的模式主要集中在热带的生态和进化，从物种丰富度到机制。热带地区在地质上较为古老，拥有更多的多样化时间，这与时间假说一致，在该假说中，生物相互作用可能增强共存和多样化[15]。因此，从热带地区到温暖和/或寒冷地区的相关研究是我们必须考虑的关键点，例如，不同的分类群和/或沿纬度梯度的群落。根据我们的经验，Engelhardia 在东南亚的纬度分布从 10^(@)S10^{\circ} \mathrm{S} 到 30^(@)N30^{\circ} \mathrm{N} ，这些植物在独特的基质上典型，以解开来自综合学科的 LDG [100,105][100,105] 。
Here, this review presents a systematic overview of the broad and comprehensive literatures on the state of LDG in a changing world where ecology and evolution have been applied to its distribution patterns. In the future, we suggest that genetic/genomicbased approaches on LDG should be integrated for the understanding of biodiversity conservation. This facet is still underdeveloped, and the numbers of studies that elaborate biodiversity patterns of LDG based on the genetic/genomic data are still scarce, especially regarding the relationship between the variations in genetic/genomic data and the 在这里，本综述提供了关于在生态和进化应用于其分布模式的变化世界中，LDG 状态的广泛和全面文献的系统概述。未来，我们建议将基于遗传/基因组的方法整合到 LDG 的研究中，以理解生物多样性保护。这个方面仍然不够成熟，基于遗传/基因组数据阐述 LDG 生物多样性模式的研究数量仍然稀少，特别是关于遗传/基因组数据变异与生物多样性之间关系的研究。
pre-existing data from ecosystems and speciation (e.g., phylogeny and genetic diversity). Moreover, the use of molecular studies (i.e., genetic/genomic diversity) is important to highlight the potential for the establishment of theories on LDG that do not have sufficient support from genetic/genomic implementation, because the dataset for a considerably large-scale distribution is difficult to obtain, especially the vast regions across oceans. However, genetic/genomic criteria of specific taxa with a vast distribution are useful and possible in some plants with a large latitudinal distribution if the field works is comprehensive. The large-scale taxa collection combined the big data DNA information, will enable the CBD to ensure biodiversity conservation through the sharing and utilization of benefits from genetic/genomic resources. Thus, exploring the LDG from large-scale DNA data to disentangle the diversity mechanisms and patterns to inform biodiversity conservation and management measures may be a valid approach. Comprehensive biodiversity patterns, together with the determination of ecological and evolutionary mechanisms should therefore be used to understand the mechanisms and causes of LDG in a changing environment where biodiversity is rapidly declining and disappearing. 生态系统和物种形成的既有数据（例如，系统发育和遗传多样性）。此外，分子研究（即遗传/基因组多样性）的使用对于强调建立缺乏遗传/基因组支持的 LDG 理论的潜力是重要的，因为大规模分布的数据集难以获得，尤其是跨越海洋的广阔区域。然而，具有广泛分布的特定分类群的遗传/基因组标准在某些具有大纬度分布的植物中是有用且可能的，前提是实地工作是全面的。大规模的分类群收集结合大数据 DNA 信息，将使 CBD 能够通过共享和利用遗传/基因组资源的利益来确保生物多样性保护。因此，从大规模 DNA 数据中探索 LDG，以解开多样性机制和模式，从而为生物多样性保护和管理措施提供信息，可能是一种有效的方法。 因此，综合生物多样性模式以及生态和进化机制的确定应被用来理解在生物多样性迅速下降和消失的变化环境中，LDG 的机制和原因。
Author Contributions: Conceptualization, Y.Z. and H.-H.M.; Funding acquisition, H.-H.M. and Y.-G.S.; Project administration, H.-H.M.; Visualization, Y.Z. and H.-H.M.; Formal Analysis, Y.Z.; Writing-original draft, Y.Z., Y.-G.S., C.-Y.Z., T.-R.W., T.-H.S., P.-H.H., J.L. and H.-H.M.; Writingreview and editing, Y.Z., Y.-G.S., C.-Y.Z., T.-R.W., T.-H.S., P.-H.H., J.L. and H.-H.M. All authors have read and agreed to the published version of the manuscript. 作者贡献：概念化，Y.Z. 和 H.-H.M.；资金获取，H.-H.M. 和 Y.-G.S.；项目管理，H.-H.M.；可视化，Y.Z. 和 H.-H.M.；正式分析，Y.Z.；撰写原稿，Y.Z.，Y.-G.S.，C.-Y.Z.，T.-R.W.，T.-H.S.，P.-H.H.，J.L. 和 H.-H.M.；撰写审阅和编辑，Y.Z.，Y.-G.S.，C.-Y.Z.，T.-R.W.，T.-H.S.，P.-H.H.，J.L. 和 H.-H.M. 所有作者均已阅读并同意发表的手稿版本。
Funding: This research was funded by National Natural Science Foundation of China (No. 42171063); Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences (No. Y4ZK111B01); the Special Fund for Scientific Research of Shanghai Landscaping & City Appearance Administrative Bureau (Nos. G192422 and G212406); Youth Innovation Promotion Association, Chinese Academy of Sciences (No. 2018432); and the CAS “Light of West China” Program. 资助：本研究由中国国家自然科学基金（编号 42171063）；中国科学院东南亚生物多样性研究所（编号 Y4ZK111B01）；上海市园林绿化和市容管理局科学研究专项资金（编号 G192422 和 G212406）；中国科学院青年创新促进会（编号 2018432）；以及中国科学院“西部之光”计划资助。
Institutional Review Board Statement: Not applicable. 机构审查委员会声明：不适用。
Data Availability Statement: Not applicable. 数据可用性声明：不适用。
Acknowledgments: The authors are grateful to Chong-Rui Ai (Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences) and Hui-Jie Qiao (Institute of Zoology, Chinese Academy of Sciences) for their kind assistances and suggestions in the references & literatures investigation for this paper. 致谢：作者感谢艾崇瑞（中国科学院西双版纳热带植物园）和乔慧杰（中国科学院动物研究所）在本论文的参考文献和文献调查中给予的友好帮助和建议。
Conflicts of Interest: The authors declare no conflict of interest. 利益冲突：作者声明没有利益冲突。
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