The soil mosaic hypothesis: a synthesis of multi-trophic diversification via soil heterogeneity

Myriad unexplored mechanisms potentially drive ecological speciation and could help explain global variation in diversity. Here, we develop a novel hypothesis focused on variation in biotic, chemical, and physical properties of soil as a factor contributing to diversification in communities of plants and animals. The Soil Mosaic Hypothesis (SMH) suggests that differences in soil attributes can affect intraspecific variation in phytochemistry, leading to cascading ecological and evolutionary effects on higher trophic levels. To illustrate the potential importance of the SMH, we examine three underlying ideas: (1) plant species and species assemblages shift over time, exposing them to novel soil environments, which can lead to genetic differentiation; (2) differences in soil properties can alter phytochemistry via plasticity and local adaptation; (3) phytochemistry can drive herbivore diversification via divergent natural selection (i.e. ecological speciation). The SMH provides insight into the process of diversification in a variety of landscapes and at a variety of scales and may inform analyses of diversification at local, regional, and global scales.