The evolutionary consequences of habitat change in grasses

Abstract

Grass dominated habitats cover more than 40% of Earth’s total land surface. These ecosystems support diverse faunal communities, play a significant role in global nutrient cycling, and provide many other important ecosystem services. However, they are also at significant risk globally, and conserving these them requires a more complete understanding of their unique evolutionary histories.The initial expansion of grassland habitats and subsequent assembly of modern grassland floras were among the most important ecological transitions of the past 66 million years. Despite an extensive body of work exploring the impacts of this transition (e.g., on mammalian faunas) few studies have examined the effects of this ecological shift on grasses themselves. Using a combination of modern and fossil data, I investigated how the transition from closed to open, grass dominated habitats helped drive the evolution of two key grass traits: herbivore defense and seed dispersal strategy. Although a number of changes are apparent in the family (e.g., increased adoption of wind dispersal in more open habitats), the results demonstrate the complexity of responses, showing very little consistency across the family. This reinforces the need to consider both group (e.g., tribe) and context (e.g., North American grasslands) to understand the evolutionary changes experienced by grasses during the establishment and expansion of grassland ecosystems.