Lower breeding success in the invaded range: no evidence for the enemy release hypothesis in South American Barn Swallows

It is widely assumed that colonizing species thrive because they lack natural enemies in their new range, increasing their survival and reproductive success. Barn Swallows (Hirundo rustica) started to breed in South America around 1980 and since have increased dramatically their population size and geographic range, in stark contrast with the decline of the source population in North America. The reasons behind the growth of the South American population are unknown. However, because this species had never bred in this area in recorded times, the lack of natural predators, parasites or pathogens could lead to higher breeding success, as predicted by the enemy release hypothesis. Here we test whether breeding success is higher in the newly colonized range than in the native range to test the enemy release hypothesis. We studied the breeding biology of South American Barn Swallows quantifying seven breeding parameters: clutch size, overall breeding success, offspring mortality by predatio...

学界普遍认为，拓殖物种能够成功繁盛，是因为它们在新分布区内缺乏自然天敌，进而提升了自身的存活与繁殖成功率。家燕（Hirundo rustica）约于1980年开始在南美洲繁殖，此后其种群规模与地理分布范围均出现大幅扩张，这与其北美源种群的衰退形成了鲜明对比。目前南美家燕种群快速增长的原因尚不明确。鉴于该物种在有记录的历史中从未在南美洲繁殖，根据天敌释放假说（Enemy Release Hypothesis），其缺乏自然捕食者、寄生虫或病原体的情况，或许能带来更高的繁殖成功率。本研究旨在检验新拓殖分布区的繁殖成功率是否高于原生分布区，以此验证天敌释放假说。我们对南美家燕的繁殖生物学展开研究，量化了7项繁殖参数：窝卵数、总繁殖成功率、捕食导致的后代死亡率……