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，但学界对生物交互作用的结果如何沿环境梯度变化仍缺乏普遍认知，在大地理尺度下这一问题尤为突出。一个直观的预期是：环境质量下降会降低竞争物种的种群密度，因此在环境较差的生境中，种间竞争的作用强度会随之减弱。但由此会产生一个反直觉的推论：随着环境质量下降，竞争物种的种群密度关联可能会从负相关转为正相关。本研究以一类维管植物群落（vascular plant communities）为研究对象，其中多年生植物与竞争力较弱的一年生植物共享空间与资源，并据此检验上述预测。我们沿横跨欧洲的生境质量纬度梯度，对9个灰沙丘群落（gray dune communities）开展了为期5年的年度调查。研究结果显示：在环境梯度的高质量端，一年生与多年生植物的种群密度呈负相关；而在低质量端，二者的功能群密度则无相关或呈正相关，这与环境限制增强导致竞争作用减弱的理论预期相符。本研究表明，即便简单的物种交互作用，也可能沿环境梯度引发物种关联模式的非直观变化。同时研究也提示，要阐明物种交互作用的结果，需明确其作用强度随环境质量的动态变化；而限制物种共分布的驱动因子，同样会沿环境梯度发生改变。