Marine Ecology Research Group, School of Biological Sciences, University of Canterbury, Christchurch, New Zealand.
PLoS One. 2011;6(9):e24318. doi: 10.1371/journal.pone.0024318. Epub 2011 Sep 8.
Anthropogenic impacts, including urbanization, deforestation, farming, and livestock grazing have altered riparian margins worldwide. One effect of changes to riparian vegetation is that the ground-level light, temperature, and humidity environment has also been altered. Galaxias maculatus, one of the most widely distributed fishes of the southern hemisphere, lays eggs almost exclusively beneath riparian vegetation in tidally influenced reaches of rivers. We hypothesized that the survival of these eggs is greatly affected by the micro-environment afforded by vegetation, particularly relating to temperature, humidity and UVB radiation. We experimentally reduced riparian vegetation height and altered shading characteristics, tracked egg survival, and used small ground-level temperature, humidity and UVB sensors to relate survival to ground-level effects around egg masses. The ground-level physical environment was markedly different from the surrounding ambient conditions. Tall dense riparian vegetation modified ambient conditions to produce a buffered temperature regime with constant high relative humidity, generally above 90%, and negligible UVB radiation at ground-level. Where vegetation height was reduced, frequent high temperatures, low humidity, and high UVB irradiances reduced egg survival by up to 95%. Temperature effects on egg survival were probably indirect, through reduced humidity, because developing eggs are known to survive in a wide range of temperatures. In this study, it was remarkable how such small variations in relatively small sites could have such a large effect on egg survival. It appears that modifications to riparian vegetation and the associated changes in the physical conditions of egg laying sites are major mechanisms affecting egg survival. The impacts associated with vegetational changes through human-induced disturbances are complex yet potentially devastating. These effects are particularly important because they affect a very small portion of habitat that is required to complete the life history of a species, despite the wide distribution of adults and juveniles across aquatic and marine environments.
人为影响，包括城市化、森林砍伐、农业和牲畜放牧，已经改变了世界各地的河岸带。河岸带植被变化的一个影响是，地面光照、温度和湿度环境也发生了变化。麦加利长尾鳕是南半球分布最广的鱼类之一，它几乎只在受潮汐影响的河流河岸带植被下产卵。我们假设这些卵的存活率受到植被提供的微环境的极大影响，特别是与温度、湿度和 UVB 辐射有关。我们通过实验降低了河岸带植被的高度并改变了遮荫特性，跟踪了卵的存活率，并使用小型地面温度、湿度和 UVB 传感器来将存活率与卵周围的地面环境联系起来。地面物理环境与周围环境条件明显不同。高大茂密的河岸带植被改变了环境条件，产生了一个缓冲的温度格局，具有恒定的高相对湿度，通常在 90%以上，地面水平的 UVB 辐射可以忽略不计。当植被高度降低时，频繁的高温、低湿度和高 UVB 辐照度会使卵的存活率降低多达 95%。对卵存活率的温度影响可能是间接的，通过降低湿度，因为已知发育中的卵可以在很宽的温度范围内存活。在这项研究中，令人惊讶的是，如此小的相对较小的地点的微小变化，会对卵的存活率产生如此大的影响。似乎河岸带植被的改变以及与产卵地点物理条件的相关变化是影响卵存活率的主要机制。与人类引起的干扰相关的植被变化的影响是复杂的，但可能是毁灭性的。这些影响尤其重要，因为它们只影响到完成物种生命周期所需的栖息地的一小部分，尽管成年鱼和幼鱼在水生和海洋环境中分布广泛。
