Biodiversity & Biogeography PDF

Where Is the World’s Biodiversity? Chapter 2  Patterns of Diversity: Biogeography This chapter examines the early explorations of the earth and the distribution of life we see on the planet Biogeography is the study of how species are distributed across space and through time....

Where Is the World’s Biodiversity? Chapter 2  Patterns of Diversity: Biogeography This chapter examines the early explorations of the earth and the distribution of life we see on the planet Biogeography is the study of how species are distributed across space and through time. Analyses of these patterns of biological diversity can be divided into two scientific disciplines: 1. Historical biogeography 2. Ecological biogeography 10/4/2023 Add a footer 2  Pangea with modern borders. The breakup of the Pangaea supercontinent. (Image: © U.S. Geological Survey)  Historical biogeography It examines past geological events in Earth’s history and uses these to explain patterns in the spatial and temporal distribution of organisms (usually species or higher taxonomic ranks). For example, an explanation of the distribution of closely related groups of organisms in Africa and South America is based on the understanding that these two landmasses were once connected as part of a single landmass (known as Gondwana). 10/4/2023 Add a footer 4  The ancestors of those related species, which are now found in Africa and South America, are assumed to have had a cosmopolitan distribution stretching across both continents when they were connected. Following the separation of the continents by the process of plate tectonics, the isolated populations are assumed to have undergone allopatric speciation. Allopatric speciation is speciation achieved between populations that are completely geographically separate. This separation resulted in the closely related groups of species on the now separate continents. Allopatric Speciation 10/4/2023 Add a footer 5 These large regions have a broadly similar biological evolutionary history Figure 2.2 Map of the World’s Major Biogeographic Realms (Horning/ Laverty c CBC-AMNH. Used by permission) 10/4/2023 Add a footer 6 10/4/2023 Prepared By: 7 10/4/2023 Add a footer 8  Ecological Biogeography The field of ecological biogeography focuses on current populations and interactions of species on shorter time scales. It first examines the dispersal of organisms (usually individuals or populations) and the mechanisms that influence this dispersal Then uses this information to explain the spatial distribution patterns of these organisms. It is considers the number of species an area supports, or its species richness. It was the theory of island biogeography that changed biogeography from a primarily historical focus. 10/4/2023 Add a footer 9  The term, island biogeography, was first coined in the 1960s by Robert MacArthur and E.O. Wilson. According to the theory the number of species on an island can be predicted based on the distance from the mainland and the size of the island. It was once thought that continents provided the source for species found on islands, and the process was one-way, with continents feeding islands with species. Thus, the further an island was from a continent the fewer species it had. 10/4/2023 Add a footer 10  A 2005 study by ornithologists Christopher Filardi and Robert Moyle turned this traditional vision of species distribution and evolution on its head. Their study examined the genetic ancestry of a group of South Pacific island birds, the Monarch flycatchers, which revealed that some species in fact recolonized Australia and New Guinea. Thus, islands can lead to speciation and these species can later repopulate continents. 10/4/2023 Add a footer 11 Why Are There More Species in the Tropics? There are more species in warm tropical ecosystems than cold temperate ecosystems found at high latitudes. In fact, not only there are more species in the tropics, but there are also more groups at higher taxonomic levels (i.e., genera, families). This distribution applies for many different groups from mammals to insects. Various hypotheses have been raised to explain these patterns of species richness. 10/4/2023 Add a footer 12  One of the theories, the “climate-speciation hypothesis,” links warmer temperatures to higher rates of speciation. Directly link where warmer temperatures lead to increased mutation rates, and thus increased molecular evolution and more species. Indirectly connects a warmer climate to increased growth rates and thus shorter generation times, at which natural selection operates, and thus leads to increased speciation rates. Alternatively shorter generation times could also lead to faster molecular evolution and again increased speciation rates. 10/4/2023 Add a footer 13  Mountainous environments can be subdivided vertically into altitudinal belts, each with a different ecosystem. Climatic conditions at higher elevations usually have lower temperatures and humidity, conditions under which fewer species can survive. species richness decrease as we move up 10/4/2023 Prepared By: 14  In oceans and freshwater ecosystems, the pattern reverses itself; with increasing depth below the surface, species richness declines. However, in the oceans there may be a rise in species richness close to the seabed, which is associated with an increase in ecosystem heterogeneity 10/4/2023 Prepared By: 15 WHERE TO CONSERVE? Understanding species and ecosystem distributions aid conservation scientist in selecting regions to conserve. For example, conservation are often interested in areas that have a high proportion of endemic species. Endemic species are species whose distributions are naturally restricted to a limited area. Areas that support a large number of endemic species are obvious choices for conservation, since those species are found nowhere else and if they disappear, these species are lost forever. 10/4/2023 Add a footer 16  Conservation biologists may also seek to conserve areas that are particularly threatened or that host a large number of species. Sometimes areas of high endemism overlap with areas of high species richness; however, this varies greatly with the taxa and region. Two key approaches for deciding what and how to conserve biodiversity are the ecoregion and the hotspot approach. 10/4/2023 Add a footer 17  Ecoregions Both the World Wide Fund for Nature (WWF) and The Nature Conservancy (TNC) use the ecoregion approach to conservation planning. Scientists at the WWF initially identified a comprehensive list of 825 terrestrial and 450 freshwater ecoregions on the planet. Among these ecoregions, they then selected the top priorities for global conservation called—the “Global 200”—though these actually cover 238 ecoregions. 142 terrestrial 53 freshwater 43 marine ecoregions, they then selected the top priorities for global 10/4/2023 18 conservationAdd a footer 10/4/2023 Prepared By: 19  These ecoregions were selected because they 1. harbor exceptional biodiversity 2. representative of the variety of Earth’s ecosystems. They considered factors such as species endemism, richness, and global rarity Each ecoregion is also assigned a conservation status: critical or endangered, vulnerable, stable or intact. Over half of the Global 200 are endangered. One outcome of this approach was that some ecosystems, such as Mediterranean forests, were found to be more endangered than tropical ones. 10/4/2023 Add a footer 20  Also, in 2007 TNC and WWF launched a parallel program focused solely on the marine realm—the first ever classification of the world’s coastal areas. Marine realm: very large regions of coastal, benthic or pelagic ocean across which biotas are internally coherent at higher taxonomic levels, as a result of a shared and unique evolutionary history. Realms have high levels of endemism, including unique taxa at generic and family levels in some groups. Driving factors behind the development of such unique biotas include water temperature, historical and broad scale isolation, and the proximity of the benthos. The Marine Ecosystems of the World (MEOW) centers on identifying key areas of the coast and shelf, classifying them into 12 realms, 62 provinces, and 232 ecoregions. 10/4/2023 Add a footer 21  Biodiversity Hotspots Norman Myers first identified ten tropical forest hotspots based on plant endemism and threat in 1988, and his method was later adopted by CI(Conservation International) in 1989. The method of selecting a hotspot has been refined since then. Biodiversity hotspots are geographical areas or large regions containing exceptional concentrations of plant endemism and experiencing high rates of habitat loss. 10/4/2023 Add a footer 22  A terrestrial biodiversity hotspot is now defined quantitatively as an area that has at least 0.5 percent, or 1,500 of the world’s 300,000 species of green plants, and that has lost at least 70 % of its primary vegetation. Marine biodiversity hotspots are quantitatively defined based on measurements of relative endemism of multiple taxa (i.e., species of corals, snails, lobsters, and fish) within a region and the relative level of threat to that region. 10/4/2023 Add a footer 23 Coverage of hotspots New biodiversity hotspots are periodically added based on scientific assessments of new regions. For example, the Forests of East Australia was the latest hotspot that had been added after research showed that the area fulfilled all criteria in 2011. However, in February 2016, the North American Coastal Plain was recognized as meeting the criteria and became the Earth's 36th hotspot Changing circumstances such as sustained habitat loss or the discovery of new species may mean that areas previously not considered biodiversity hotspots could qualify in a future reassessment. Biodiversity hotspots from Conservation International (CI)  Today CI recognizes 36 hotspots most of which occur in tropical forests; these hotspots once covered 15.7 % of the planet, but already 86 % of the hotspots have been destroyed and they now cover just 2.3 % of the planet. They contain around 50% of the world’s endemic plant species and 42% of all terrestrial vertebrates. Overall, Hotspots have lost around 86% of their original habitat and additionally are considered to be significantly threatened by extinctions induced by climate change. 10/4/2023 Add a footer 26 10/4/2023 Add a footer 27  To complement its hotspot program, CI has also identified five key remaining Wilderness Areas: Amazonia, Congo Basin, New Guinea, North American deserts, and Southern Africa. In contrast to the hotspots, these areas are largely intact with more than 70 % of their original vegetation; however, they each harbor significant portions of the planet’s biodiversity. 10/4/2023 Add a footer 28  Conservation biologists are also interested in areas that have relatively low biological diversity but also include threatened or rare species (called biodiversity coldspots). Just has hotspots do not imply that the ecosystem is physically “hot” (although most hotspots are coincidentally located in the hot tropics), coldspots similarly are no necessarily “cold.” Although these areas are low in species richness, they can also be important to conserve, as an individual “coldspot” may be the only location where a rare species is found. Extreme physical environments (low or high temperatures or pressures, or unusual chemical composition) inhabited by just one or two specially adapted species are “coldspots” that warrant conservation because they represent unique environments that are biologically and physically interesting. 10/4/2023 Add a footer 29