Data from: Complex relationships between competing guilds along large-scale environmental gradients

Despite much research over the past 30 years, there is still little general understanding of how the outcomes of interactions vary along environmental gradients, particularly at large geographic scales. A simple expectation is that decreasing environmental quality should reduce densities of competitors and hence the effects of competition should weaken in poorer environments. A counterintuitive consequence is that associations between densities of competitors might change from negative to positive as environments decrease in quality. Here we test these predictions in a set of vascular plant communities where perennial species share space and resources with less competitive annuals. We surveyed nine gray dune communities annually for 5 years along a cross-European latitudinal gradient of habitat quality. We find that densities of annual and perennial species are negatively correlated at the high-quality end of the gradient, while at the low-quality end, guild densities are uncorrelated or positively correlated, consistent with a weakening of competition linked to increasing environmental limitations. Our results suggest that even simple interactions can give rise to nonobvious changes in species associations along environmental gradients. They highlight that understanding the outcome of species interactions may require explicit characterization of their changing intensity with environmental quality and that the factors limiting species’ codistribution can vary along environmental gradients.尽管过去30年间已有大量相关研究，但学界对生物交互的结果如何沿环境梯度变化仍缺乏普遍认知，在大地理尺度上尤为如此。一个简单的预期是，环境质量下降会降低竞争者的种群密度，因此较差环境中的竞争效应应当减弱。一个反直觉的推论是，随着环境质量下降，竞争者种群密度之间的关联可能从负相关转为正相关。本研究针对一类维管植物群落（vascular plant communities）检验了上述预测：其中多年生物种与竞争力较弱的一年生物种共享空间与资源。我们沿横跨欧洲的生境质量纬度梯度，对9个灰砂丘（gray dune）群落开展了为期5年的年度调查。研究结果显示，在梯度的高质量端，一年生与多年生植物的种群密度呈负相关；而在低质量端，两类功能群的种群密度无关联或呈正相关，这与环境限制加剧导致竞争效应减弱的假说一致。本研究结果表明，即便简单的物种交互，也可能沿环境梯度引发物种关联的非直观变化。研究同时强调，要理解物种交互的结果，需明确刻画其强度随环境质量的动态变化；而限制物种共同分布的因素，也可能沿环境梯度发生改变。