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

每一个物种都在有限的地理区域内生存和繁殖。虽然分布限制是普遍存在的，但人们对阻碍射程扩大的进化限制知之甚少。这项研究将研究加利福尼亚州内华达山脉猴花(Mimulus lewisii和M.Cardinalis)在海拔范围内的范围限制。项目目标是确定在射程限制下减少存活和繁殖的生命阶段、特征和环境因素，并对射程限制模型进行经验测试。由于中心种群和边缘种群之间的匹配会产生不适合边缘环境的后代，因此可能会出现范围边界。为了验证这一模型，将在边缘环境中比较中心边缘和边缘边缘后代的存活和繁殖。或者，性状之间的相关性可能会限制适应的方向，造成范围限制，在这种范围内不会产生一组适合边缘环境的性状。这一模型将通过比较物种在范围限制下的最佳性状值和物种的实际性状值来检验。地理范围界限的起源和维持是达尔文最先讨论的进化之谜，然而150年后的实验数据却是有限的。对自然资源保护者来说，范围限制也是一个重要的话题，因为随着全球气候变化，物种的分布预计将向两极和更高的海拔转移。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偏移的大小。

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.