Invertebrate assemblages of pools in arid-land streams have high functional redundancy and are resistant to severe drying
Invertebrate assemblages of pools in arid-land streams have high functional redundancy and are resistant to severe drying
复制标题
DOI：
10.1111/fwb.12280
复制
发表时间：
2014-03-01
影响因子：
2.7
通讯作者：
Lytle, David A.
中科院分区：
文献类型：
--
作者：
Boersma, Kate S.;Bogan, Michael T.;Lytle, David A.
季节性干旱是干旱区水文学可预测的组成部分，许多干旱区水生类群已经适应了它们的极端环境。然而，气候变化正在改变这种可预测的水文，产生更长、更严重的干旱，并为常驻生物创造新的干扰机制。从流动溪流到破碎池再到干河床的水文转变往往伴随着分类和功能多样性的急剧减少，称为生物多样性丧失的阈值。随着碎片池逐渐干涸和非生物条件加剧，分类群如何在这些阈值之间做出反应，人们所知甚少。虽然日益极端的环境可能会减少分类和性状的丰富度，但适应可预测的季节性破碎化的物种可能会抵抗水位下降，直到所有地表水消失。我们利用水生生态系统测试了旱地流无脊椎动物丰富度与水池干燥之间关系的两个相互竞争的假设：(i)干旱脆弱性假设（丰富度随着干燥逐渐减少）和（ii）抗旱性假设（丰富度保持不变，直到完全干燥发生）。我们用来自美国亚利桑那州旱地溪流的水生无脊椎动物接种了重复的中生态系统，并应用了三种干燥处理，代表了在夏季干旱季节（水深：10、7和1cm）在当地溪流中常见的连续干燥压力。覆盖中生态系统是为了限制扩散和定植过程，并将抗性（物种的原位生存）与复原力（干扰后的群落恢复）分离开来。45天后，我们对所有中生态系统的无脊椎动物进行破坏性取样，并计算了各种分类和功能性状指标。不同干燥处理间的分类丰富度和组成没有差异，为抗旱假说提供了有力支持。与中度和对照处理相比，重度干燥处理与较低的无脊椎动物丰度和较高的密度相关。这一发现表明，在干旱期间，可用生境减少所产生的密度依赖过程可能比该系统中的非生物胁迫更重要地决定了群落组成。我们观察到在三种处理中，营养性状（体型和功能摄食组）和抗性性状（呼吸方式和滞育）几乎完全重叠。这种高度的功能冗余可以为生态系统功能的变化提供缓冲，即使在严重干旱引起的栖息地收缩和破碎化的情况下也是如此。
Seasonal droughts are predictable components of arid-land stream hydrology, and many arid-land aquatic taxa have adapted to their extreme environment. However, climate change is altering this predictable hydrology, producing longer and more severe droughts and creating novel disturbance regimes for resident organisms. The hydrologic transitions from flowing stream to fragmented pools to dry stream bed are frequently associated with steep decreases in taxonomic and functional diversity, referred to as thresholds of biodiversity loss. Less is known about how taxa respond between these thresholds, as fragmented pools gradually dry and abiotic conditions intensify. While an increasingly extreme environment may be expected to reduce taxonomic and trait richness, species adapted to predictable seasonal fragmentation may be resistant to declining water levels until all surface water is lost. We used aquatic mesocosms to test two competing hypotheses of the relationship between richness and pool drying for arid-land stream invertebrates: (i) the drought vulnerability hypothesis (richness gradually decreases with drying) and (ii) the drought resistance hypothesis (richness remains constant until complete drying occurs). We inoculated replicate mesocosms with aquatic invertebrates from arid-land streams in Arizona, U.S.A., and applied three drying treatments representing a continuum of drying stress commonly observed in local streams during the summer dry season (water depths: 10, 7 and 1cm). Mesocosms were covered to restrict dispersal and colonisation processes and to isolate resistance (in situ survival of species) from resilience (community recovery following disturbance). After 45days, we destructively sampled all invertebrates in the mesocosms and calculated various taxonomic and functional trait metrics. Taxonomic richness and composition did not differ between drying treatments, providing strong support for the drought resistance hypothesis. Severe drying was associated with lower invertebrate abundances and higher densities than the moderate and control treatments. This finding suggests that density-dependent processes generated by decreased available habitat may be more important determinants of community composition during droughts than abiotic stress in this system. We observed a near-complete overlap of trophic traits (body size and functional feeding group) and resistance traits (respiration mode and diapause) among the three treatments. This high functional redundancy may provide a buffer against changes to ecosystem functioning, even in cases of severe-drying-induced habitat contraction and fragmentation.