Previous work has shown that among 428 species of bees occurring in Germany, decline or extinction over the past 40 years have been correlated with late-season emergence and restricted habitats, while other factors, such as pollen specialization, body size, nesting sites, and sociality, played no role in models that included a phylogeny of these bees. Doing best are spring-flying, city-dwelling species. Building on these results, we here investigate changes in bee diversity from the 1990s to 2018 at three protected sites within the city perimeter of Munich, focusing on the correlates of flight season (spring or summer), flight duration (in months), and number of habitats (one or two vs. three to six). Local species pools were assessed against the total species pool from 1795 onwards. Twenty years ago, 150 species were present at one or more of the sites, while in 2017/2018, this was true of 188 species, with the increase at two sites being of similar proportion. In two of the three areas, broad habitat use was positively correlated with persistence. Flight season or duration had no statistical effect. These results underscore the function of urban protected sites in bee conservation and imply that summer food shortages, which negatively affect bees in agricultural areas, play no role in urbanized regions so that late-season flight is not an extinction handicap.

中文翻译：

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1990 年代至 2018 年间大型城市保护区蜜蜂种类的减少和增加

以前的工作表明，在德国发生的 428 种蜜蜂中，过去 40 年的减少或灭绝与晚季出现和栖息地受限有关，而其他因素，如花粉专化、体型大小、筑巢地点和社会性，在包含这些蜜蜂系统发育的模型中没有任何作用。表现最好的是春天飞翔的城市栖息物种。基于这些结果，我们在此调查了 1990 年代至 2018 年慕尼黑城市周边三个受保护地点的蜜蜂多样性变化，重点关注飞行季节（春季或夏季）、飞行持续时间（以月为单位）和数量的相关性栖息地（一两个与三到六个）。从 1795 年起，根据总物种库评估本地物种库。二十年前，150 个物种出现在一个或多个地点，而在 2017/2018 年，有 188 个物种，两个地点的增加比例相似。在这三个地区中的两个地区，广泛的栖息地利用与持久性呈正相关。飞行季节或持续时间没有统计影响。这些结果强调了城市保护区在蜜蜂保护中的作用，并暗示夏季食物短缺对农业地区的蜜蜂产生负面影响，在城市化地区没有任何作用，因此晚季飞行不是灭绝的障碍。