Understanding plant rarity through space and time

Abstract

Determining what makes a species rare has been a fundamental question in ecology and conservation. A few species are highly abundant in most species assemblages, but many more species are rare. This pattern represents one of the most consistently observed phenomena in ecology. However, researchers in ecology and conservation are yet to come to a clear understanding of what makes a plant species rare and identify the processes that drive plant rarity. In this thesis, I aim to address this knowledge gap through three field-based, empirical research projects, a literature review, and the development of a conceptual framework that explores the drivers and mechanisms that influence plant rarity across time and space . Chapter 1 explored how fire regime variables, fire response traits, and plant rarity are associated across three different vegetation communities in Booderee National Park. I additionally sought to determine if different rarity categorisations influenced the associations between fire regimes and plant rarity. Chapter 2 examined the influence of soil properties and fire regimes in dry sclerophyll forest communities of Booderee National Park. In Chapter 3, I examined how different spatial associations among sets of species, an indicator for biotic interactions between species, influenced the occurrence patterns of rare plant species across three vegetation communities in Booderee National Park. Chapter 4 consists of three key components. First, I conducted a global systematic review of the biological and ecological factors associated with plant rarity. Next, I examined associations between plant rarity and plant growth traits, reproductive features, biotic and abiotic conditions, genetic characteristics, and vegetation communities. My empirical chapters and systematic review led to the development of a conceptual framework that presents the multiple drivers and mechanisms that influence plant rarity. I then demonstrate a new visual tool to examine and visualise changes in the relative rarity of multiple species in an ecosystem in three-dimensional space. This tool can be applied across any study area of interest to improve monitoring and conservation efforts of both rare and common species. My overarching conclusion is that there are many facets to plant rarity, and plant rarity cannot be simply attributed to a particular set of life history and ecological traits. In other words, while plant rarity is common, there are many different ways for a plant species to be rare, highlighting that rarity is a condition more so than a fixed characteristic of a species. More broadly, my research has shown that conservation strategies for rare species need to examine changes in species abundance across time and space and in relation to the combined influences of environmental change, and other abiotic factors and biotic factors. Ultimately, this research will lead to better informed conservation strategies by improving our ability to identify species decline, whether rare or common. Show more