Department of Biology, Tufts University, 200 College Avenue, Medford, Massachusetts, 02155, USA.
Xerces Society, 628 Northeast Broadway Suite 200, Portland, Oregon, 97232, USA.
Ecol Appl. 2019 Oct;29(7):e01975. doi: 10.1002/eap.1975. Epub 2019 Aug 8.
Understanding the factors associated with declines of at-risk species is an important first step in setting management and recovery targets. This step can be challenging when multiple aspects of climate and land use are changing simultaneously, and any or all could be contributing to population declines. We analyzed population trends of monarch butterflies in western North America in relation to likely environmental drivers. Unlike the larger eastern monarch population, past analyses of western monarchs have only evaluated the importance of climate (i.e., not land use) factors as drivers of abundance. We used partial least squares regression (PLSR) to evaluate the potential importance of changes in land use and climate variables. Trends in western monarch abundance were more strongly associated with land use variables than climate variables. Conclusions about importance of climate and land use variables were robust to changes in PLSR model structure. However, individual variables were too collinear to unambiguously separate their effects. We compared these conclusions to the more widely used technique of multiple regression, followed by multi-model inference (MRMI). Naïve interpretation of MRMI results could be misleading, if collinearity were not taken into account. MRMI was also highly sensitive to variation in model construction. Our results suggest a two-pronged approach to monarch conservation, specifically, starting efforts now to restore habitat, while also using experiments to more clearly delineate separate effects of climate and land use factors. They also demonstrate the utility of PLSR, a technique that is growing in use but is still relatively under-appreciated in conservation biology.
了解与濒危物种减少相关的因素是制定管理和恢复目标的重要第一步。当气候和土地利用的多个方面同时发生变化，并且任何一个或所有因素都可能导致种群减少时，这一步可能具有挑战性。我们分析了北美的西部帝王蝶种群趋势与可能的环境驱动因素之间的关系。与较大的东部帝王蝶种群不同，过去对西部帝王蝶的分析仅评估了气候（即非土地利用）因素作为丰度驱动因素的重要性。我们使用偏最小二乘回归（PLSR）来评估土地利用和气候变量变化的潜在重要性。西部帝王蝶丰度的趋势与土地利用变量的相关性强于气候变量。关于气候和土地利用变量重要性的结论对 PLSR 模型结构的变化具有稳健性。然而，个别变量之间的相关性太强，无法明确区分它们的影响。我们将这些结论与更为广泛使用的多元回归技术（随后是多模型推断（MRMI））进行了比较。如果不考虑共线性，对 MRMI 结果的盲目解释可能会产生误导。MRMI 对模型构建的变化也非常敏感。我们的研究结果表明，帝王蝶保护需要采取双管齐下的方法，具体来说，现在就开始努力恢复栖息地，同时使用实验更清楚地区分气候和土地利用因素的单独影响。它们还展示了 PLSR 的实用性，这种技术在保护生物学中越来越受欢迎，但仍未得到充分重视。
