5. The geography of biological diversity

How are we to comprehend all of nature’s diversity from the cellular level up through all taxonomic, biological, and ecological levels of organization? “The geography of biological diversity” focuses on the measures and meaning of biological diversity, and the general patterns across the principal geographic dimensions (e.g. latitude, area and isolation) which allow us to visualize it. Hotspots of diversity are concentrated in tropical regions, especially in large, topographically complex and isolated systems. Our exploration of these hotspots, and the patterns governing how rich and which types of species inhabit them, may provide key insights for attempts to conserve biological diversity long into the future.

4. Retracing evolution across space and time

Evolution occurs not only over time, but across space as well. “Retracing evolution across space and time” explores the sub-discipline of historical biogeography, giving an overview of approaches used to reconstruct the geographic and evolutionary origins of the lineages of natural life forms. Contemporary approaches to mapping these lineages confirm Buffon’s Law—that environmentally similar but isolated regions have different plant and animal life. These maps aim to delineate the regions of life and describe their biotic composition.

1. Biological diversity and the geography of nature

Throughout history, insights into understanding the diversity of life forms have come from placing natural phenomena within an explicit geographic context. “Biological diversity and the geography of nature” maps the discoveries of early explorers in the field, from the Age of Enlightenment to the present day. Where do distinct species occur? How and why do they vary from place to place? Buffon’s Law identified three fundamental processes of biological diversity: evolution, dispersal (or immigration), and extinction. Biological processes are complex—not only because they arise from a variety of factors and processes including evolution, but because the species themselves interact to influence each of the fundamental processes.

3. The geography of diversification

“The geography of diversification” returns to a central theme of biogeography—that place matters, and that each region, down to an island or lake, can be an evolutionary arena, producing its own distinct plant and animal life. Case studies from the Hawaiian Islands, Madagascar, and the Rift Valley Lakes of East Africa illustrate the phenomenon of adaptive radiation, the process by which organisms diversify from an ancestral species into a multitude of new forms. This diversification is driven by the combined effects of biogeographic processes, geographic dimensions such as area and isolation, and ecological interactions among the species. Why are the adaptive radiations of some lineages so much greater than others?

7. The geographic and ecological advance of humanity

“The geographic and ecological advance of humanity” argues that the global expansion of the human species was influenced by the same factors that shaped the expansions of other life forms. Our indigenous populations were also strongly influenced by the forces of natural selection, driving human micro-evolution across the geographic template, such as larger size in higher latitudes and darker skin in tropical regions. Unfortunately, the expansion of our species has simultaneously homogenized biological communities across the globe—driving unique, locally endemic species to extinction and introducing a redundant set of species into even the most isolated regions of the planet. It is therefore imperative that we now apply the lessons on the geography of life to conserve the Earth’s remaining species.

6. Macroecology and the geography of micro-evolution

“Macroecology and the geography of micro-evolution” shifts the focus from macroevolutionary patterns in species richness to micro-evolutionary patterns of biogeographic variation within species. These patterns are driven by natural selection and adaptation, which in turn are driven by variation in environmental characteristics among regions and across the geographic template. How do physiological, behavioral, and ecological traits of species vary across their regional populations? Exotic, insular life forms, shaped by their island homelands void of mammalian competitors and predators, often suffered extinctions after colonization by humans and their many commensal species.

2. Dynamic maps of a dynamic planet

“Dynamic maps of a dynamic planet” introduces the geographic template—highly regular spatial patterns of variation in environmental conditions across the planet. Despite the regular nature of this geographic template at any given time, Earth is a dynamic planet that has undergone geological upheavals over the last three and a half billion years of life. Beyond the dynamics created across land and sea by plate tectonics, species assemblages have had to adapt to rapid upheavals, such as the Pleistocene Epoch or “Ice Ages.” Why, after surviving the previous twenty or so interglacial periods, should gargantuan megafaunal mammals and birds suffer extinction during the most recent periods?