Much of our understanding of mutualism is derived from pairwise obligate interactions between specialized participants. These observations may not adequately inform conservation efforts for facultative mutualist species, especially for areas in which invasive species are present and affect the mutualism. We evaluate the effects of ant attendance on larval survival for the endangered Fender’s blue butterfly ( Icaricia icarioides fenderi Macy) in situ and examine the effects of biotic and abiotic factors—specifically ant community composition and microhabitat structure—on this mutualistic interaction in Oregon, USA. Fender’s blue larval survival was as much as three times higher in plots with a high proportion of ant attendance compared to plots in which larvae were rarely tended, and ant recruitment was reduced by dense, invasive European grasses. Thatch from these dense invasives, specifically tall oatgrass ( Arrhenatherum elatius Beauv.) and tall fescue ( Schedonorus arundinaceus Schreb.), are a threat to larval survival. In addition, variation in microhabitat structure determined which ant species occurred in our plots. Larvae were associated with ten ant species but primarily tended by only two: Prenolepis imparis Say and Aphaenogaster occidentalis Emery, and we observed no difference in butterfly larval survival between the two predominant ant species. Conservation efforts for this species would benefit from actions that reduce invasive grasses and facilitate ant tending interactions. Our study demonstrates how invasive grasses and forbs in degraded prairie systems can negatively impact the conservation of an at-risk species by disrupting an important mutualistic interaction.

中文翻译：

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兼性共生增加了濒临灭绝的蚂蚁蝴蝶的生存

我们对互惠主义的大部分理解来自专业参与者之间的成对强制互动。这些观察结果可能不足以为兼性共生物种的保护工作提供信息，特别是对于存在入侵物种并影响共生的地区。我们就地评估了蚂蚁出勤对濒临灭绝的 Fender 蓝蝴蝶 (Icaricia icarioides fenderi Macy) 幼虫存活的影响，并检查了生物和非生物因素——特别是蚂蚁群落组成和微生境结构——对美国俄勒冈州这种互惠互利的影响. 与幼虫很少照料的地块相比，在蚂蚁出勤率高的地块中，Fender 的蓝色幼虫存活率高出三倍之多，而密集的侵入性欧洲草减少了蚂蚁的招募。来自这些密集入侵者的茅草，特别是高燕麦草 (Arrhenatherum elatius Beauv.) 和高羊茅 (Schedonorus arundinaceus Schreb.)，对幼虫的生存构成威胁。此外，微生境结构的变化决定了我们的地块中出现了哪些蚂蚁物种。幼虫与 10 种蚂蚁有关，但主要由两种蚂蚁照料：Prenolepis imparis Say 和 Aphaenogaster occidentalis Emery，我们观察到这两种主要蚂蚁物种之间的蝴蝶幼虫存活率没有差异。该物种的保护工作将受益于减少入侵草和促进蚂蚁抚育互动的行动。我们的研究表明，退化的草原系统中的入侵草和杂草如何通过破坏重要的互惠互动对濒危物种的保护产生负面影响。