Nitellopsis obtusa (also known as Starry Stonewort) is a Eurasian charophyte first introduced into the Laurentian Great Lakes in the 1970s. Over the last decade, there have been increasing reports of N. obtusa invasion of inland lakes in the Great Lakes basin. To improve our understanding of N. obtusa’s habitat preferences, we sampled 60 lakes across a geological transition zone in Ontario, Canada. Targeting this geological transition zone allowed us to study an array of lakes representing broad nutrient and water-hardness gradients within the same geographic and climatic region. Calcium is an important macronutrient for N. obtusa, thus it was anticipated that the presence of N. obtusa would respond strongly to calcium availability. Nitellopsis obtusa was documented at 37 sites in 19 of the 60 lakes surveyed. Lakes with N. obtusa had significantly higher cation (calcium, potassium, sodium, and magnesium) concentrations than lakes without N. obtusa (general linear mixed model with binomial error, p < 0.05). An ecological niche model based on a boosted regression tree (BRT) identified habitat features most associated with N. obtusa occurrence. Interestingly, the BRT model demonstrated that depth and the cations potassium, magnesium, and sodium were better predictors of N. obtusa presence than calcium. Although N. obtusa was found within a constrained range of calcium (15 – 57.9 mg L⁻¹ Ca), it appears that other environmental parameters have a stronger influence on N. obtusa distribution in Ontario lakes.

百日草（Nitellopsis obtusa，又名星光石藻（Starry Stonewort））是一种欧亚风化藻类植物，于1970年代首次引入劳伦山脉五大湖中。在过去的十年中，越来越多关于钝角猪笼草入侵大湖盆地内陆湖泊的报道。为了增进对钝角猪笼草栖息地偏好的了解，我们在加拿大安大略省的一个地质过渡带采样了60个湖泊。针对这个地质过渡带，我们可以研究一系列湖泊，这些湖泊代表着同一地理和气候区域内广泛的养分和水硬度梯度。钙是钝角猪笼草的重要常量营养素，因此可以预见，钝角猪笼草的存在将对钙的有效性产生强烈的反应。在被调查的60个湖中的19个湖中，有37个站点记录了钝角猪笼草。具有钝角猪笼草的湖泊的阳离子（钙，钾，钠和镁）浓度显着高于没有钝角猪笼草的湖泊（具有二项式误差的一般线性混合模型，p <0.05）。基于增强回归树（BRT）的生态位模型确定了与钝ob猪笼草的发生最相关的栖息地特征。有趣的是，BRT模型证明深度和阳离子钾，镁和钠比ob钙更好地预测了钝ob猪笼草的存在。尽管钝角猪笼草在钙的限定范围内（15 – 57.9 mg L ^-1 Ca）被发现，看来其他环境参数对安大略湖中钝角猪笼草的分布有更强的影响。