What is Biogeography. Major Emphases

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1 What is Biogeography Attempts to document and understand spatial patterns of biological diversity Distribution of organisms Patterns of geographic variation Variation in biodiversity across geographic gradients Essence: how does diversity vary over the earth s surface Major Emphases Historical Biogeography: reconstruction of origin, dispersal, and extinction of taxa Taxonomic relationships Vicariance vs. dispersal in present/past distributions Ecological Biogeography: accounts for present distributions in terms of interactions between physical and biotic environment What biotic and abiotic factors regulate species distribution? 1

2 Biogeography as synthetic discipline Ecological Data Population biology Systematics Evolutionary biology Earth Sciences The science of Biogeography Largely descriptive Comparative Observational Dependent on data collected over long time periods Best work brings together multiple disciplines 2

3 Emergence of Biogeography Became well-known and recognized as such in 1970 s Emergence of conceptual aspects and testing biogeographic theory at this point Technology has aided work in biogeography History of Biogeography Early history dominated by taxonomy and ecology Tied to European exploration Comparison of Biotas across regions Several persistent themes over time Classifying geographic regions based on biota Reconstructing historical development of lineages (evolutionary history) Explaining differences in numbers and types of species in different geographic areas Explaining differences in geographic variation in populations of closely-related species (morphology, behavior, demography) 3

4 European Exploration-18 th Century Naturalists or geologists driven by calling to serve God Linnaeus ( ) Methodically described and cataloged the natural world Binomial nomenclature Paradisical Mountain from which all life spread after great flood European Exploration-18 th Century Georges-Louis Leclerc, Comte de Buffon ( ) Life originated in northwestern Europe when climatic conditions were more equable Cooling resulted in spreading southward into new and old worlds Key Point: Earth and climate dynamic Buffon s Law: environmentally similar but isolated regions have distinct assemblages of mammals and birds One of first principles of biogeography Other naturalists of late 18 th century confirmed Buffon s law over wider range Described many previously unrecognized species 4

5 Add plants to the mix Karl Ludwig Willdenow & Alexander von Humboldt: Founders of phytogeography Suggested many sites of origination of organisms (mountain refuges) Generalized Buffon s law to include plants Association between plant assemblages and local climate 19 th Century Exploration Increasing numbers of studies on distinctness of biogeographic regions Why do regions with similar climates share so few species? Exceptions to Buffon s law? Causal explanations still lacking Estimate of age of earth Understanding dynamic nature of continents Mechanisms involved in spread and diversification of species 5

6 Geology and Paleontology Lyell and Brongniart: Earth s climate highly mutable Fossil evidence that temperate regions once had tropical organisms Species not mutable Extinction occurred, but diversity constant on grand scale Extinction followed by creation Uniformitarianism: physical and biological processes constant over time 19 th Century British Naturalists Darwin: The Voyage of the Beagle Fossil seashells in Andes Variability in Galapagos Islands Theory of Natural Selection 6

7 How can we explain distribution Dispersal Proposed by Darwin s theory Land Bridges Lyell, Hooker, and others Long distance dispersal was insufficient to explain distribution of many species, especially with Southern floras (southern continents sharing similarities) Hooker: founder of vicariance biogeography Zoogeography Sclater (1857): defines biogeographic regions based on distribution of birds Alfred Russel Wallace: father of zoogeography Worked primarily in Southeast Asia and islands Expanded on ideas of many other researchers Wallace s Line: sharp faunal gap between islands of Bali and Lombok in East Indies 7

8 C. H. Merriam-Life Zones (1894) Elevational changes in vegetation are equivalent to latitudinal vegetation changes 20 th Century Biogeography Paleontology: changes in fauna on each continent Phylogenetics and evolutionary relationships (monographic work on different groups) Ecogeographic work on individual species Dobzhansky: Drosophila Clausen, Keck and Hiesey: Plants 8

9 Recent Biogeographic Developments Acceptance of Plate Tectonics Explained similarities of many species assemblages New Phylogenetic Methods Better understanding of relationships of species over time Ecological Biogeography Effects of competition, predation, mutualism Mechanisms that limit distributions Understanding species distributions: vicariance and dispersal Interspecific interactions/abiotic factors Computer-based technology/gis 9