Geographical variation in the trait-based assembly patterns of multitrophic invertebrate communities

It has been argued that the mechanisms structuring ecological communities
may be more generalizable when based on traits than on species identities.
If so, patterns in the assembly of community-level traits along
environmental gradients should be similar in different places in the
world. Alternatively, geographic change in the species pool and regional
variation in climate might result in site-specific relationships between
community traits and local environments. These competing hypotheses are
particularly untested for animal communities. Here we test the geographic
constancy of trait-based assembly patterns using a widespread
multi-trophic community: aquatic macroinvertebrates within bromeliads. We
used data on 615 invertebrate taxa from 1656 bromeliads in 26 field sites
from Mexico to Argentina. We summarized invertebrate traits with four
orthogonal axes, and used these trait axes to examine trait convergence
and divergence assembly patterns along three environmental gradients:
detrital biomass and water volume in bromeliads, and canopy cover over
bromeliads. We found no overall signal of trait-based assembly patterns
along any of the environmental gradients. However, individual sites did
show trait convergence along detrital and water gradients, and we built
predictive models to explore these site differences. Sites that showed
trait convergence along detrital gradients were all north of the Northern
Andes. This geographic pattern may be related to phylogeographic
differences in bromeliad morphology. Bromeliads with low detritus were
dominated by detritivorous collectors and filter feeders, where those with
high detritus had more sclerotized and predatory invertebrates. Sites that
showed the strongest trait convergence along gradients in bromeliad water
were in regions with seasonal precipitation. In such sites, bromeliads
with low water were dominated by soft-bodied, benthic invertebrates with
simple life cycles. In less seasonal sites, traits associated with
short-term desiccation resistance, such as hard exoskeletons, were more
important. In summary, we show that there are strong geographic effects on
the trait-based assembly patterns of this invertebrate community, driven
by the biogeography of their foundational plant species as well as by
regional climate. We suggest that inclusion of biogeography and climate in
trait-based community ecology could help make it a truly general theory.
(excerpted from Srivastava, DS et al. 2022. Geographical variation in the
trait-based assembly patterns of multitrophic invertebrate communities.
Functional Ecology)

有观点认为，基于功能性状（traits）构建的生态群落（ecological communities）结构机制，或许比基于物种身份的机制更具普适性。若果真如此，那么沿环境梯度（environmental gradients）的群落功能性状集合模式，在全球不同区域应具有一致性。反之，物种种库（species pool）的地理变化与区域气候差异，可能会导致群落性状与局域环境之间出现位点特异性（site-specific）的关联。这类相互对立的假说，在动物群落中尚未得到充分检验。本研究针对一类广泛分布的多营养级群落（multi-trophic community）——凤梨科植物（bromeliads）内的水生大型无脊椎动物（aquatic macroinvertebrates），检验性状集合模式的地理恒定性。我们使用了从墨西哥到阿根廷的26个野外样点（field sites）、1656株凤梨科植物中采集的615个无脊椎动物类群数据。我们通过四个正交轴（orthogonal axes）总结无脊椎动物的功能性状，并利用这些性状轴，沿三个环境梯度（凤梨科植物内的碎屑生物量（detrital biomass）、水量，以及冠层覆盖度（canopy cover））检验性状趋同（trait convergence）与趋异（trait divergence）的群落集合模式。研究结果显示，在所有环境梯度上均未观测到整体的性状集合模式信号。但单个样点确实在碎屑与水量梯度上呈现出性状趋同现象，我们据此构建了预测模型以探究这些位点差异。沿碎屑梯度呈现性状趋同的样点，全部位于北安第斯山脉以北区域。该地理格局或与凤梨科植物形态的系统地理（phylogeographic）差异相关。碎屑含量较低的凤梨科植物生境，以食碎屑者（detritivorous）和滤食者（filter feeders）为优势类群；而碎屑含量较高的生境，则拥有更多硬化躯体（sclerotized）的捕食性无脊椎动物。在沿凤梨科植物水量梯度呈现最强性状趋同的样点，均位于降水具有季节性的区域。在这类区域中，水量较低的凤梨科植物生境，以躯体柔软、生活史简单的底栖无脊椎动物（benthic invertebrates）为优势类群。在非季节性降水区域，与短期抗干燥能力（desiccation resistance）相关的性状（如坚硬的外骨骼）则更为重要。综上，本研究表明，这类无脊椎动物群落的性状集合模式存在显著的地理效应，该效应由其栖息的建群植物的生物地理学（biogeography）特征以及区域气候共同驱动。我们提出，在基于性状的群落生态学研究中纳入生物地理学与气候因素，或有助于推动该领域发展为真正具有普适性的理论。（节选自Srivastava, DS等人2022年发表于《功能生态学（Functional Ecology）》的《多营养级无脊椎动物群落基于性状的集合模式的地理变异》）