Data from: The Urban Heat Island and its spatial scale dependent impact on survival and development in butterflies of different thermal sensitivity

Climate alteration is one of the most cited ecological consequences of urbanization. However, the magnitude of this impact is likely to vary with spatial scale. We investigated how this alteration affects the biological fitness of insects, which are especially sensitive to ambient conditions and well-suited organisms to study urbanization-related changes in phenotypic traits. We monitored temperature and relative air humidity in wooded sites characterized by different levels of urbanization in the surroundings. Using a split-brood design experiment, we investigated the effect of urbanization at the local (i.e., 200 × 200 m) and landscape (i.e., 3 × 3 km) scale on two key traits of biological fitness in two closely related butterfly species that differ in thermal sensitivity. In line with the Urban Heat Island concept, urbanization led to a 1°C increase in daytime temperature and an 8% decrease in daytime relative humidity at the local scale. The thermophilous species Lasiommata megera responded at the local scale: larval survival increased twofold in urban compared to rural sites. Urbanized sites tended to produce bigger adults, although this was the case for males only. In the woodland species Pararge aegeria, which has recently expanded its ecological niche, we did not observe such a response, neither at the local, nor at the landscape scale. These results demonstrate interspecific differences in urbanization-related phenotypic plasticity and larval survival. We discuss larval pre-adaptations in species of different ecological profiles to urban conditions. Our results also highlight the significance of considering fine-grained spatial scales in urban ecology.

气候变化是城市化最常被提及的生态后果之一。然而，该影响的强度大概率随空间尺度而异。我们探究了此类气候变化如何影响昆虫的生物适合度——昆虫对环境条件尤为敏感，且是研究城市化相关表型性状变化的理想模式生物。我们对周边城市化水平各异的林地样地的气温与相对空气湿度进行了监测。我们采用分群设计（split-brood design）实验，探究了局地（即200×200米）与景观（即3×3千米）尺度下的城市化，对两种热敏感性存在差异的近缘蝴蝶物种的两项关键生物适合度性状的影响。依据城市热岛（Urban Heat Island）概念，局地尺度下的城市化使日间气温升高1℃，日间相对空气湿度降低8%。嗜热物种捷眼蝶（Lasiommata megera）在局地尺度下表现出响应：相较于乡村样地，城市样地的幼虫存活率提升了一倍。城市样地所羽化的成虫体型往往更大，不过这一现象仅在雄性个体中存在。对于近期拓展了生态位的林地物种木蝇蝶（Pararge aegeria），我们未观测到此类响应，无论在局地还是景观尺度下均是如此。上述结果揭示了不同物种在城市化相关表型可塑性与幼虫存活率方面的种间差异。我们还讨论了不同生态特征物种的幼虫对城市环境的预适应机制。本研究结果同时凸显了在城市生态学研究中考虑细粒度空间尺度的重要性。