Lai Yunyun, Feng Jianmeng
School of Life Science and Agronomy, Dali University, Dali, Yunnan, China.
PeerJ. 2019 Feb 8;7:e6116. doi: 10.7717/peerj.6116. eCollection 2019.
Geographical patterns of species diversity are one of the key topics in biogeography and ecology. The effects of biogeographical affinities on the elevational patterns of species diversity have attracted much attention recently, but the factors driving elevational patterns of the percentages of plants with tropical and temperate biogeographical affinities have not been adequately explored.
We first used univariate least squares regressions to evaluate the effects of each predictor on the elevational patterns of the percentages of plant genera with tropical and temperate affinities in Nepal. Then, the lowest corrected Akaike information criterion value was used to find the best-fit models for all possible combinations of the aforementioned predictors. We also conducted partial regression analysis to investigate the relative influences of each predictor in the best-fit model of the percentages of plant genera with tropical and temperate affinities.
With the increase of elevation, the percentage of plant genera with tropical affinity significantly decreased, while that of plant genera with temperate affinity increased. The strongest predictor of the percentages of plant genera with tropical affinity in the examined area was the minimum temperature of the coldest month. For the elevational patterns of the percentages of plant genera with temperate affinity, the strongest predictor was the maximum temperature of the warmest month. Compared with mid-domain effects (MDE), climatic factors explained much more of the elevational variation of the percentages of plant genera with tropical and temperate affinities.
The elevational patterns of the percentages of plant genera with tropical affinities and the factors driving them supported the revision of the freezing-tolerance hypothesis. That is, freezing may filter out plant genera with tropical affinity, resulting in the decrease of their percentages, with winter coldness playing a predominant role. Winter coldness may not only exert filtering effects on plant genera with tropical affinity, but may also regulate the interactions between plant genera with tropical and temperate affinities. The elevational patterns of tropical and temperate plant diversities, and those of their percentages, might be controlled by different factors or mechanisms. Freezing-tolerance and the interactions between plant genera with tropical and temperate affinities regulated by climatic factors played stronger roles than MDE in shaping the elevational patterns of the percentages of plant genera with tropical and temperate affinities in Nepal.
物种多样性的地理格局是生物地理学和生态学的关键主题之一。生物地理亲缘关系对物种多样性海拔格局的影响近来备受关注，但驱动具有热带和温带生物地理亲缘关系的植物百分比海拔格局的因素尚未得到充分探究。
我们首先使用单变量最小二乘法回归来评估每个预测变量对尼泊尔具有热带和温带亲缘关系的植物属百分比海拔格局的影响。然后，使用最低校正赤池信息准则值来找到上述预测变量所有可能组合的最佳拟合模型。我们还进行了偏回归分析，以研究每个预测变量在具有热带和温带亲缘关系的植物属百分比最佳拟合模型中的相对影响。
随着海拔升高，具有热带亲缘关系的植物属百分比显著下降，而具有温带亲缘关系的植物属百分比增加。在所研究区域，具有热带亲缘关系的植物属百分比的最强预测变量是最冷月的最低温度。对于具有温带亲缘关系的植物属百分比的海拔格局，最强预测变量是最热月的最高温度。与中间区域效应（MDE）相比，气候因素能解释更多具有热带和温带亲缘关系的植物属百分比的海拔变化。
具有热带亲缘关系的植物属百分比的海拔格局及其驱动因素支持了耐寒性假说的修正。也就是说，结冰可能会筛选出具有热带亲缘关系的植物属，导致其百分比下降，其中冬季寒冷起主要作用。冬季寒冷不仅可能对具有热带亲缘关系的植物属产生筛选作用，还可能调节具有热带和温带亲缘关系的植物属之间的相互作用。热带和温带植物多样性的海拔格局及其百分比格局可能受不同因素或机制控制。在塑造尼泊尔具有热带和温带亲缘关系的植物属百分比海拔格局方面，耐寒性以及由气候因素调节的具有热带和温带亲缘关系的植物属之间的相互作用比中间区域效应发挥了更强的作用。
