INRAE, Unité EABX - Écosystèmes Aquatiques et Changements Globaux, HYNES (Irstea-EDF R&D), 50 avenue de Verdun, 33612 Cestas Cedex, France.
INRAE, Unité EABX - Écosystèmes Aquatiques et Changements Globaux, HYNES (Irstea-EDF R&D), 50 avenue de Verdun, 33612 Cestas Cedex, France.
Sci Total Environ. 2020 Dec 15;748:141260. doi: 10.1016/j.scitotenv.2020.141260. Epub 2020 Aug 2.
Most key life-events of organisms are synchronized by complex interactions of several environmental cues to ensure optimal survival and growth of individuals and their offspring. However, global change is known to affect multiple components of ecosystems and cues at the same time. Therefore, detecting joint trends in covariate time series is a crucial challenge in global change ecology that has rarely been addressed so far. In this context, we designed an innovative combination of kernel density estimations and Mann-Kendall trend tests to detect joint temporal trends in a pair of environmental variables. This methodological framework was tested on >30 years (1976-2019) of water temperature and discharge data for 6 large French rivers (the Garonne, Dordogne, Rhône, Rhine, Loire and Vienne rivers). The implications of such trends in both temperature and discharge for diadromous species key life-cycle processes were then explored by checking if significant bivariate environmental changes occurred during seasons of upstream and downstream migration, and reproductive activities. Results were contrasted between rivers and seasons: many rivers displayed an increase in the number of days with high water temperature and low river discharge, but local discharge regulation measures could have mitigated the trend in discharge. Our findings showed that species migrating or spawning in spring were likely to be strongly impacted by the new environmental conditions in the Garonne, Loire and Rhône rivers, given the marked changes in water temperature and discharge associations detected by our new method. Conditions experienced by fall-running and spawning species have been strongly affected in all the rivers studied. This innovative methodology was implemented in a new R package, ChocR, for application to other environments and ecosystems.
大多数生物体的关键生命事件都是通过几种环境线索的复杂相互作用来同步的，以确保个体及其后代的最佳生存和生长。然而，众所周知，全球变化同时影响着生态系统的多个组成部分和线索。因此，检测协变量时间序列的共同趋势是全球变化生态学中的一个关键挑战，迄今为止很少有人解决这个问题。在这种情况下，我们设计了一种核密度估计和曼恩-肯德尔趋势检验的创新组合，以检测一对环境变量的共同时间趋势。该方法框架在法国 6 条大河（加龙河、多尔多涅河、罗纳河、莱茵河、卢瓦尔河和维埃纳河）的 30 多年（1976-2019 年）的水温与流量数据上进行了测试。然后，通过检查洄游物种关键生命周期过程的上溯和下溯迁徙以及生殖活动期间是否发生显著的双变量环境变化，探讨了温度和流量变化对这些物种的影响。结果根据河流和季节进行了对比：许多河流显示出高温和低流量天数增加的趋势，但局部流量调节措施可能减轻了流量的趋势。我们的研究结果表明，鉴于我们的新方法检测到水温和流量关联的显著变化，在加龙河、卢瓦尔河和罗纳河洄游或产卵的物种很可能受到新环境条件的强烈影响。所有研究河流中的秋季洄游和产卵物种所经历的条件受到了强烈影响。这种创新的方法被实现为一个新的 R 包 ChocR，用于应用于其他环境和生态系统。
