Data from: Impacts of warming revealed by linking resource growth rates with consumer functional responses

Warming global temperatures are driving changes in species distributions, growth and timing, but much uncertainty remains regarding how climate change will alter species interactions. Consumer-Resource interactions in particular can be strongly impacted by changes to the relative performance of interacting species. While consumers generally gain an advantage over their resources with increasing temperatures, nonlinearities can change this relation near temperature extremes. We use an experimental approach to determine how temperature changes between 5 and 30 °C will alter the growth of the algae Scenedesmus obliquus and the functional responses of the small bodied Daphnia ambigua and the larger D. pulicaria. The impact of warming generally followed expectations, making both Daphnia species more effective grazers, with the increase in feeding rates outpacing the increases in algal growth rate. At the extremes of our temperature range, however, warming resulted in a decrease in Daphnia grazing effectiveness. Between 25 and 30°C both species of Daphnia experienced a precipitous drop in feeding rates, while algal growth rates remained high, increasing the likelihood of algal blooms in warming summer temperatures. D. pulicaria performed significantly better at cold temperatures than D. ambigua, but by 20°C there was no significant difference between the two species and at 25°C D. ambigua out-performed D. pulicaria. Warming summer temperatures will favor the smaller D. ambigua, but only over a narrow temperature range and warming beyond 25°C could open D. ambigua to invasion from tropical species. By fitting our results to temperature dependent functions we develop a temperature and density dependent model which produces a metric of grazing effectiveness, quantifying the grazer density necessary to halt algal growth. This approach should prove useful for tracking the transient dynamics of other density dependent consumer-resource interactions, such as agricultural pests and biological control agents.

全球气温变暖正驱动物种分布、生长状况及发生时序发生改变，但气候变化将如何重塑物种间相互作用仍存在诸多不确定性。其中，消费者-资源（Consumer-Resource）相互作用受相互作用物种相对性能变化的影响尤为显著。尽管总体而言，随着温度升高，消费者相较于其资源物种会获得竞争优势，但在极端温度附近，非线性关系会改变这一态势。本研究采用实验方法，探究5至30℃的温度变化对斜生栅藻（Scenedesmus obliquus）的生长，以及小型蚤状溞（Daphnia ambigua）和大型溞（D. pulicaria）的功能响应（functional responses）的影响。升温的整体影响符合预期：两种溞类均成为更高效的牧食者，其摄食速率的提升幅度超过藻类生长速率的增幅。然而在温度区间的极端端点，升温反而会降低溞类的牧食效能。在25至30℃之间，两种溞类的摄食速率均出现骤降，而藻类生长速率仍维持在较高水平，这提升了夏季升温环境中藻华暴发的可能性。在低温环境下，大型溞（D. pulicaria）的表现显著优于小型蚤状溞（D. ambigua）；但到20℃时，二者的性能无显著差异，而在25℃时，小型蚤状溞的表现则超过大型溞。夏季升温将更有利于小型蚤状溞，但仅局限于较窄的温度区间；当温度超过25℃时，小型蚤状溞可能面临热带物种的入侵竞争。通过将实验结果拟合至温度依赖函数，我们构建了一个兼具温度与密度依赖性的模型，该模型可生成牧食效能（grazing effectiveness）指标，量化出阻止藻类生长所需的牧食者种群密度。该方法可用于追踪其他密度依赖性消费者-资源相互作用的瞬态动态，例如农业害虫与生物防治因子（biological control agents）的相互作用。