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1 PLATE TECTONICS, BIOGEOGRAPHY AND EVOLUTION Biogeography is the study of the geographical distributions of animals and plants. Ecological biogeography is the analysis of present-day distribution patterns in terms of current environmental conditions (e.g. climate, soil type) and interactions with other species that limit distributions. For example, the holly tree in Europe has a northern limit to its distribution that appears to be determined by temperature (winter frost, summer warmth). Ecologists assume that the plant is in equilibrium with present-day conditions; that is, that it extends as far north as possible. This might be questioned – as we know that climate shifts have been rather dramatic over the last 20,000 years at least, and perhaps there has not been sufficient time for the tree to disperse farther north. As you will see, not all present-day distributions can be understood in terms of current conditions and for that we turn to studies of historical biogeography. Historical biogeography is the analysis of present-day distribution patterns in light of historical factors that may have influenced the distribution of species. Historical factors might include plate movements, mountain building, sea level and climate change, for example. This lecture will be concerned with historical biogeography, and especially the impact of plate tectonics on the evolution of vertebrates. The movement of the earth's plates can result in the separation of continental landmasses, or the joining of previously separate landmasses. A drop or rise in sea level can produce similar effects. Mountain building can produce new barriers to dispersal and separate previously contiguous populations. Mountain building in the ocean over hot spots can result in island formation, providing new land for colonization. All of these geologic activities can have an impact on the evolution of life, in some cases favoring the evolution of new species. To understand how this works, it is necessary to look more closely at the process of speciation. What is a species? According to the leading evolutionary biologist of the 20th century, Ernst Mayr. " Species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups." (Mayr, 1940). The phrase "reproductively isolated" refers to the fact that viable offspring are not produced by matings between the groups. In some cases, it may be that viable offspring could be produced, such as crosses between coyotes and gray wolves, but we still consider them separate species because such matings are rare in nature, despite the fact that coyotes and wolves often coexist. There are behavioral differences between the species that usually prevent hybridization. There is a large literature on species concepts and we will not discuss it further here – the important fact to remember is that species should
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2 be reproductively isolated from one another, either due to physiological or
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This note was uploaded on 03/11/2010 for the course GE CLST 70B taught by Professor Morris,m.r./friscia,a.r./moldwin,m.b./vanvalkenburgh,b during the Winter '10 term at UCLA.

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