Burner Ryan C, Stephan Jörg G, Drag Lukas, Potterf Mária, Birkemoe Tone, Siitonen Juha, Müller Jörg, Ovaskainen Otso, Sverdrup-Thygeson Anne, Snäll Tord
U.S. Geological Survey Upper Midwest Environmental Sciences Center La Crosse Wisconsin USA.
Faculty of Environmental Sciences and Natural Resource Management Norwegian University of Life Sciences Ås Norway.
Ecol Evol. 2023 Oct 19;13(10):e10588. doi: 10.1002/ece3.10588. eCollection 2023 Oct.
Functional trait approaches are common in ecology, but a lack of clear hypotheses on how traits relate to environmental gradients (i.e., trait-niche relationships) often makes uncovering mechanisms difficult. Furthermore, measures of community functional structure differ in their implications, yet inferences are seldom compared among metrics. Community-weighted mean trait values (CWMs), a common measure, are largely driven by the most common species and thus do not reflect community-wide trait-niche relationships per se. Alternatively, trait-niche relationships can be estimated across a larger group of species using hierarchical joint species distribution models (JSDMs), quantified by a parameter Γ. We investigated how inferences about trait-niche relationships are affected by the choice of metric. Using deadwood-dependent (saproxylic) beetles in fragmented Finnish forests, we followed a protocol for investigating trait-niche relationships by (1) identifying environmental filters (climate, forest age, and deadwood volume), (2) relating these to an ecological function (dispersal ability), and (3) identifying traits related to this function (wing morphology). We tested 18 hypothesized dispersal relationships using both CWM and Γ estimates across these environmental gradients. CWMs were more likely than Γ to show support for trait-niche relationships. Up to 13% of species' realized niches were explained by dispersal traits, but the directions of effects were consistent with fewer than 11%-39% of our 18 trait-niche hypotheses (depending on the metric used). This highlights the difficulty in connecting morphological traits and ecological functions in insects, despite the clear conceptual link between landscape connectivity and flight-related traits. Caution is thus warranted in hypothesis development, particularly where apparent trait-function links are less clear. Inferences differ when CWMs versus Γ estimates are used, necessitating the choice of a metric that reflects study questions. CWMs help explain the effects of environmental gradients on community trait composition, whereas the effects of traits on species' niches are better estimated using hierarchical JSDMs.
功能性状方法在生态学中很常见，但缺乏关于性状如何与环境梯度相关的明确假设（即性状-生态位关系）往往使得揭示机制变得困难。此外，群落功能结构的测量方法在其含义上有所不同，但很少对不同指标的推断进行比较。群落加权平均性状值（CWMs）是一种常见的测量方法，很大程度上由最常见的物种驱动，因此本身并不能反映整个群落范围内的性状-生态位关系。或者，可以使用分层联合物种分布模型（JSDMs）在更大的物种群体中估计性状-生态位关系，通过参数Γ进行量化。我们研究了关于性状-生态位关系的推断如何受到测量指标选择的影响。在芬兰破碎化森林中，我们以依赖枯木（腐木性）的甲虫为研究对象，遵循了一个研究性状-生态位关系的方案，即（1）确定环境过滤因素（气候、森林年龄和枯木体积），（2）将这些因素与一种生态功能（扩散能力）联系起来，以及（3）确定与该功能相关的性状（翅形态）。我们使用CWMs和Γ估计值在这些环境梯度上测试了18个假设的扩散关系。CWMs比Γ更有可能显示出对性状-生态位关系的支持。高达13%的物种实现生态位可由扩散性状解释，但效应方向与我们18个性状-生态位假设中不到11%-39%的假设一致（取决于所使用的指标）。这凸显了在昆虫中将形态性状与生态功能联系起来的困难，尽管景观连通性与飞行相关性状之间存在明确的概念联系。因此，在假设开发中需要谨慎，特别是在明显的性状-功能联系不太清晰的情况下。当使用CWMs与Γ估计值时，推断会有所不同，这就需要选择一个能反映研究问题的指标。CWMs有助于解释环境梯度对群落性状组成的影响，而使用分层JSDMs能更好地估计性状对物种生态位的影响。
