Parasites for population growth from Avian malaria-mediated population decline of a widespread iconic bird species

Parasites have the capacity to affect animal populations by modifying host survival, and it is increasingly recognized that infectious disease can negatively impact biodiversity. Populations of the house sparrow (<i>Passer domesticus</i>) have declined in many European towns and cities, but the causes of these declines remain unclear. We investigated associations between parasite infection and house sparrow demography across suburban London where sparrow abundance has declined by 71% since 1995. <i>Plasmodium relictum</i> infection was found at higher prevalences (averaging 74%) in suburban London house sparrows than previously recorded in any wild bird population in Northern Europe. Survival rates of juvenile and adult sparrows and population growth rate were negatively related to <i>Plasmodium relictum</i> infection intensity. Other parasites were much less prevalent and exhibited no relationship with sparrow survival and no negative relationship with population growth. Low rates of co-infection suggested sparrows were not immunocompromised. Our findings indicate that <i>P. relictum</i> infection may be influencing house sparrow population dynamics in suburban areas. The demographic sensitivity of the house sparrow to <i>P. relictum</i> infection in London might reflect a recent increase in exposure to this parasite.

寄生虫可通过改变宿主存活率对动物种群产生影响，而传染病可对生物多样性造成负面影响这一观点，也日益得到学界的广泛认可。家麻雀（*Passer domesticus*）的种群数量在欧洲诸多城镇中持续下滑，但此次种群衰退的具体诱因仍未明确。本研究针对伦敦郊区开展了寄生虫感染与家麻雀种群统计学特征之间的关联分析——该区域自1995年以来，家麻雀的种群丰度已下降71%。本次研究在伦敦郊区家麻雀体内检测到的里氏疟原虫（*Plasmodium relictum*）感染率（平均达74%），高于此前北欧地区所有野生鸟类种群的记录值。家麻雀幼体与成体的存活率以及种群增长率，均与里氏疟原虫的感染强度呈负相关关系。其他寄生虫的感染率则极低，且未发现其与家麻雀存活率存在关联，也未表现出与种群增长率的负相关关系。混合感染率较低的结果表明，家麻雀并未出现免疫功能受损的情况。本研究结果显示，里氏疟原虫感染可能正在影响郊区家麻雀的种群动态。伦敦地区家麻雀对里氏疟原虫感染的种群统计学敏感性，或反映出该地区家麻雀近期接触该寄生虫的概率有所上升。