Dissertation Research: Geographic Range Limits of Monkeyflowers (Mimulus): Testing the Roles of Gene flow, Trade-offs and Population Dynamics

每个物种都在一个有限的地理区域内生存和繁殖。虽然分布限制是普遍的，但对阻碍范围扩展的进化约束知之甚少。本研究将考察猴花（Mimulus lewisii和M. cardinalis）在加州内华达山脉海拔范围内的分布范围。项目目标是确定在范围极限下降低生存和繁殖的生命阶段、特征和环境因素，并对范围极限模型进行经验检验。由于中心种群和边缘种群之间的交配产生了不适合边缘环境的后代，因此可能出现范围边界。为了验证这一模型，我们将在边缘环境下比较中心边缘和边缘后代的生存和繁殖情况。另外，性状之间的相关性可能会限制适应的方向，在没有产生适合边缘环境的一组性状的情况下，产生范围限制。该模型将通过比较范围极限处的最优性状值与物种的实际性状值来检验。地理范围限制的起源和维持是达尔文首先讨论的进化谜题，但150年后的实验数据有限。范围限制对自然资源保护主义者来说也是一个重要的话题，因为预测物种的分布将向两极和更高的海拔转移，以应对全球气候变化。然而，如果不了解在范围边界上运行的过程，就很难准确预测这种分布变化的幅度。

Every species survives and reproduces in a limited geographic area. Although distribution limits are universal, little is known about the evolutionary constraints that hinder range expansion. This study will examine range limits of monkey-flowers (Mimulus lewisii and M. cardinalis) across their elevation ranges in California's Sierra Nevada Mountains. Project goals are to identify life stages, traits, and environmental factors that decrease survival and reproduction at range limits and to conduct empirical tests of models of range limits. Range boundaries may arise because matings between central and edge populations create offspring unfit for the edge environment. To test this model, the survival and reproduction of central-edge versus edge-edge offspring will be compared in the edge environment. Alternatively, correlations among traits may constrain the direction of adaptation, creating range limits where a set of traits appropriate for the edge environment is not produced. This model will be tested by comparing optimum trait values at the range limit to species' actual trait values. The origin and maintenance of geographic range limits are evolutionary riddles first discussed by Darwin, yet 150 years later experimental data are limited. Range limits are also a topic of importance to conservationists because species' distributions are forecasted to shift towards the poles and to higher elevations in response to global climate change. However, without knowledge of the processes operating at range boundaries, accurate predictions about the magnitude of such distribution shifts are difficult.