Ant Functional Diversity in Temperate Zone Forests: A Comparison with Neotropical Ants

Predicted impacts of climatic change on ant functional diversity and distributions in eastern North American forests Aims--Climatic change is expected to rearrange species assemblages and ultimately affect organism-mediated ecosystem processes. We focus on identifying patterns and relationships between common ant species (representing 99% of total ant records) richness and functional diversity; modelling how these patterns may change at local and regional scales in future climatic conditions; and interpreting how these changes might influence ant-mediated ecosystem processes. Location--Forested ecosystems of eastern North America. Methods--We used a previously published dataset to evaluate functional diversity at 67 sites in the eastern U.S. and quantified 14 taxonomic, morphometric and natural history traits for 70 common ant species in the region. We used functional diversity metrics, functional groups and species distribution modelling methods to address our aims. We used stacked species distribution models and stacked functional group models to predict species assemblages and functional richness at the 67 sites and at a regional scale for current and future climatic conditions. Results--Species richness and functional diversity are positively correlated throughout the region. Under future climate scenarios, species richness and functional group richness were predicted to decrease in southern ecoregions and increase in northern ecoregions. This may be due to increased thermal stress for species in the southern extent of their ranges and increased habitat suitability in the northern ecoregions. Decomposers, arthropod community regulators and seed dispersers are forecast to be the most threatened ant functional groups. Main Conclusions--Climate change will likely lead to major changes in ant species richness and functional group richness in the forests of the north-eastern United States, and this may substantially alter ant-mediated ecosystem processes and services. Morphological structure of ant assemblages in tropical and temperate forests Morphological variation in co-occurring species often is used to infer species assembly rules and other processes structuring ecological assemblages. We compared the morphological structure of ant assemblages in two biogeographic regions along two extensive latitudinal gradients to examine common patterns and unique characteristics of trait distribution. We sampled ant assemblages along extensive latitudinal gradients in Tropical Atlantic Forest in eastern Brazil and temperate forests in the eastern United States. We quantified 14 morphological traits related to the ecology and life history of each of 599 ant species and defined the morphological space occupied by different ant assemblages. Null models were used to test whether tropical and temperate ant assemblages differed from random expectation in morphological structure. Correlations between traits and climate were used to infer associations between habitat characteristics and morphological space occupied by ant assemblages. Tropical ant assemblages had higher morphological diversity and variation in the space of occupied morphospace, whereas temperate assemblages had higher variance in size. Although tropical ant assemblages had smaller morphological distances among species, species packing (i.e., mean nearest-neighbor distance) did not differ between regions. Null model analysis revealed scant evidence of habitat filtering or niche differentiation within assemblages. Different traits had different means, variances, skewness, and kurtosis values along each environmental gradient. Mean trait values within assemblages were associated mainly with region and correlated with temperature but trait variances had more complex responses to climate, including interactions between temperature and precipitation in the models. The higher functional diversity in tropical ant assemblages occurs by expansion of the morphospace rather than through an increase in species packing. Different traits vary independently along environmental gradients. Analysis of individual traits together with categorization of the moments of trait distributions (statistical central tendencies) provide new directions for quantifying morphological diversity in ant assemblages.

《气候变化对北美东部森林蚂蚁功能多样性与分布的预测影响》
研究目标：气候变化预计将重塑物种类群，并最终影响由生物介导的生态系统过程。本研究旨在明确占总蚂蚁记录99%的常见蚂蚁物种的物种丰富度（species richness）与功能多样性（functional diversity）之间的模式与关联；构建模型以预测未来气候情景下，这些模式在局域和区域尺度上的变化；并阐释这些变化可能如何影响由蚂蚁介导的生态系统过程。
研究区域：北美东部森林生态系统。
研究方法：本研究使用已发表的数据集，评估美国东部67个样点的功能多样性，并量化该区域70种常见蚂蚁的14项分类学、形态测量（morphometric）及自然历史（natural history）性状。我们采用功能多样性指标、功能群（functional group）及物种分布建模（species distribution modelling）方法来实现研究目标。分别使用堆叠物种分布模型（stacked species distribution models）与堆叠功能群模型，对当前及未来气候情景下67个样点及区域尺度的物种类群与功能丰富度进行预测。
研究结果：整个区域内物种丰富度与功能多样性呈正相关。在未来气候情景下，南部生态区的物种丰富度与功能群丰富度预计将下降，而北部生态区则会上升。这可能是由于物种分布南界区域的热胁迫加剧，以及北部生态区的生境适宜性提升所致。分解者、节肢动物群落调控者与种子传播者这三类蚂蚁功能群预计将受到最严重的威胁。
主要结论：气候变化或将导致美国东北部森林的蚂蚁物种丰富度与功能群丰富度发生显著变化，这可能大幅改变由蚂蚁介导的生态系统过程与服务功能。

《热带与温带森林蚂蚁类群的形态结构》
研究背景：共存物种的形态变异常被用于推断构建生态类群的物种组装规则与其他过程。本研究沿两条广泛的纬度梯度，对比两个生物地理区域内蚂蚁类群的形态结构，以探究性状分布的共有模式与独特特征。我们在巴西东部的热带大西洋森林与美国东部的温带森林中，沿大范围纬度梯度采样蚂蚁类群。我们量化了599种蚂蚁的14项与生态学及生活史相关的形态性状，并界定了不同蚂蚁类群所占据的形态空间（morphospace）。使用零模型（null model）检验热带与温带蚂蚁类群的形态结构是否偏离随机预期。通过性状与气候的相关性，推断生境特征与蚂蚁类群占据的形态空间之间的关联。
研究结果：热带蚂蚁类群的形态多样性与占据的形态空间变异度更高，而温带类群的体型方差更大。尽管热带蚂蚁类群的物种间形态距离更小，但物种集群（species packing，即平均最近邻距离）在两个区域间并无差异。零模型分析显示，几乎没有证据表明类群内部存在生境过滤（habitat filtering）或生态位分化（niche differentiation）。不同性状沿各环境梯度的均值、方差、偏度（skewness）与峰度（kurtosis）均存在差异。类群内的性状均值主要与区域相关，且与温度呈相关性，但性状方差对气候的响应更为复杂，包括模型中温度与降水的交互作用。热带蚂蚁类群更高的功能多样性源于形态空间的扩张，而非物种集群的增加。不同性状沿环境梯度独立变化。对单个性状的分析，结合性状分布矩（统计集中趋势）的分类，为量化蚂蚁类群的形态多样性提供了新的研究方向。