Department of Entomology and Nematology, University of California, Davis, California, 95616, USA.
Ecology. 2020 Jan;101(1):e02880. doi: 10.1002/ecy.2880. Epub 2019 Nov 25.
Many organisms experience seasonal windows of opportunity for growth and reproduction. These windows represent intervals in time when organisms experience improved prospects for advancing their life history objectives, constrained by the combined effects of seasonally variable biotic and abiotic conditions acting independently or in combination. Although seasonal windows of opportunity are likely to be widespread in nature, relatively few studies have conducted the repeated observations necessary to identify them or suggest the factors that structure them in time. Here, we present the results of three experimental studies conducted at different field sites in three different years in which we manipulated the phenology of monarch caterpillars (Danaus plexippus) throughout the growing season. The primary aims of these experiments were (1) to identify seasonal windows of opportunity for successful larval development on milkweed (Asclepias spp.), and (2) to suggest which factors are most likely to constrain these windows of opportunity in time. We found strong seasonal windows of opportunity in the developmental success of monarchs, with distinct periods of higher developmental prospects during each study year. We evaluated the role of seasonal variation in abiotic thermal stress, host plant density, host plant defensive traits, and natural enemy risk as potential factors that may limit seasonal windows of opportunity. By comparing the seasonal patterns of larval success and potential explanatory factors across all 3 yr, we find patterns that are consistent with seasonally variable abiotic conditions, host plant availability, host plant traits, and natural enemy risk factors. These results suggest the potential for seasonal variation in the factors that limit monarch larval development and population growth. More generally, this study also highlights the value of temporally explicit experimental studies that can identify and examine seasonal patterns in species interactions.
许多生物都有季节性的生长和繁殖机会窗口。这些窗口代表了生物在时间上经历改善其生命历史目标前景的间隔期，这些机会受到季节变化的生物和非生物条件的综合影响，这些条件独立或组合作用。尽管季节性机会窗口在自然界中可能很普遍，但相对较少的研究进行了必要的重复观测，以识别它们或提出随时间构建它们的因素。在这里，我们介绍了在三个不同年份的三个不同野外地点进行的三项实验研究的结果，在这些研究中，我们在整个生长季节操纵帝王蝶幼虫（Danaus plexippus）的物候。这些实验的主要目的是：（1）确定在乳草（Asclepias spp.）上成功幼虫发育的季节性机会窗口，以及（2）提出最有可能随时间限制这些机会窗口的因素。我们发现帝王蝶幼虫发育成功存在强烈的季节性机会窗口，在每个研究年中都有明显的较高发育前景时期。我们评估了季节变化的非生物热应激、宿主植物密度、宿主植物防御特性和天敌风险作为可能限制季节性机会窗口的潜在因素的作用。通过比较所有 3 年的幼虫成功和潜在解释因素的季节性模式，我们发现与季节变化的非生物条件、宿主植物可用性、宿主植物特性和天敌风险因素一致的模式。这些结果表明，限制帝王蝶幼虫发育和种群增长的因素可能存在季节性变化。更一般地说，这项研究还强调了具有时间明确的实验研究的价值，这种研究可以识别和检查物种相互作用中的季节性模式。
