Nowicki Piotr, Bonelli Simona, Barbero Francesca, Balletto Emilio
Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, Kraków, Poland.
Oecologia. 2009 Aug;161(2):227-39. doi: 10.1007/s00442-009-1373-2. Epub 2009 May 30.
The relative contribution of density-dependent regulation and environmental stochasticity to the temporal dynamics of animal populations is one of the central issues of ecology. In insects, the primary role of the latter factor, typically represented by weather patterns, is widely accepted. We have evaluated the impact of density dependence as well as density-independent factors, including weather and mowing regime, on annual fluctuations of butterfly populations. As model species, we used Maculinea alcon and M. teleius living in sympatry and, consequently, we also analysed the effect of their potential competition. Density dependence alone explained 62 and 42% of the variation in the year-to-year trends of M. alcon and M. teleius, respectively. The cumulative Akaike weight of models with density dependence, which can be interpreted as the probability that this factor should be contained in the most appropriate population dynamics model, exceeded 0.97 for both species. In contrast, the impacts of inter-specific competition, mowing regime and weather were much weaker, with their cumulative weights being in the range of 0.08-0.21; in addition, each of these factors explained only 2-5% of additional variation in Maculinea population trends. Our results provide strong evidence for density-dependent regulation in Maculinea, while the influence of environmental stochasticity is rather minor. In the light of several recent studies on other butterflies that detected significant density-dependent effects, it would appear that density-dependent regulation may be more widespread in this group than previously thought, while the role of environmental stochasticity has probably been overestimated. We suggest that this misconception is the result of deficiencies in the design of most butterfly population studies in the past, including (1) a strong focus on adults and a neglect of the larval stage in which density-dependent effects are most likely to occur; (2) an almost exclusive reliance on transect count results that may confound the impact of environmental stochasticity on butterfly numbers with its impact on adult longevity.
密度依赖调节和环境随机性对动物种群时间动态的相对贡献是生态学的核心问题之一。在昆虫中，后一个因素（通常以天气模式为代表）的主要作用已被广泛接受。我们评估了密度依赖以及非密度依赖因素（包括天气和割草制度）对蝴蝶种群年度波动的影响。作为模式物种，我们使用了同域分布的阿尔康黄斑蝶和泰莱黄斑蝶，因此，我们还分析了它们潜在竞争的影响。仅密度依赖就分别解释了阿尔康黄斑蝶和泰莱黄斑蝶逐年趋势变化的62%和42%。对于这两个物种，包含密度依赖的模型的累积赤池权重超过了0.97，这可以解释为该因素应包含在最合适的种群动态模型中的概率。相比之下，种间竞争、割草制度和天气的影响要弱得多，它们的累积权重在0.08 - 0.21范围内；此外，这些因素各自仅解释了黄斑蝶种群趋势中另外2 - 5%的变化。我们的结果为黄斑蝶的密度依赖调节提供了有力证据，而环境随机性的影响相当小。鉴于最近对其他蝴蝶的几项研究发现了显著的密度依赖效应，似乎密度依赖调节在这一类群中可能比以前认为的更为普遍，而环境随机性的作用可能被高估了。我们认为这种误解是过去大多数蝴蝶种群研究设计缺陷的结果，包括：（1）强烈关注成虫而忽视了最可能发生密度依赖效应的幼虫阶段；（2）几乎完全依赖样带计数结果，这可能会将环境随机性对蝴蝶数量的影响与其对成虫寿命的影响混淆。
