The Origin, Expansion, and Demise of Plant Species

The Origin, Expansion, and Demise of Plant Species

The Origin, Expansion, and Demise of Plant Species

The Origin, Expansion, and Demise of Plant Species

Synopsis

Each plant species has its own unique passage that is affected by its gene pool, dispersal ability, interactions with competitors and pests, and the habitats and climactic conditions to which it is exposed. This book will explore plant species as dynamic entities within this passage, following the four stages of plant species life that normally occur. Those four stages can be identified as birth, expansion, differentiation and loss of cohesion, and decline/extinction. Each chapter focuses on part of the speciation process and examines it closely in the light of exploring the species passage from birth to death.

Excerpt

This book is an exploration of species as dynamic entities. Specifically, it is an exploration of the species' passage from birth to death. Each species has its own unique passage that is affected by its gene pool, dispersal ability, interactions with competitors and pests, and the habitats and climatic conditions to which it is exposed.

We may identify stages in the lives of species. The first is the birth or origin of species. Each species has a beginning in a geographically defined context. The second stage is expansion. All successful species spread from their focus of origin. The third stage is differentiation and loss of cohesion. Most species undergo some form of geographical differentiation, even if the most divergent entities are not formally recognized. In the process, the ability of populations to exchange genes is reduced. The fourth stage is decline and extinction. All species eventually come to an end following the contraction and fragmentation of a once larger range. This book is arranged so that it follows these stages.

Chapter 1 provides a broad rationale for the aforementioned approach and includes a discussion of species concepts. Chapter 2 focuses on the ecological transition, which is an essential part of the speciation process. A highlight of the chapter is the evolutionary lability of reproductive and vegetative characters. Patterns of radiation also are discussed. Chapter 3 is concerned with the genetic transition that accompanies speciation. The prime issues are the genetic basis for species differences in ecological and reproductive attributes, the genetic and chromosomal bases for postpollination reproductive barriers, and the rate of genetic transitions. Chapter 4 concerns the geographical scale of speciation. The primary issue is whether speciation is a local or regional phenomenon. I argue for the former. Chapter 5 deals with the geographical expansion of neospecies. In addition to describing neospecies per se, migrations of introduced species and postglacial migrations are discussed as these entities are . . .

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