[MUSIC] Hotspots of biodiversity are regions containing high concentrations of endemic species, that are also facing threats of rapid species loss. More than 35 biodiversity hotspots have been identified around the world. Half of them are located in mountain regions. Although these hotspots represent just over 2% of the Earth's land area, they're also home to about half of the world's endemic species identifying hotspots of diversity has become an important tool to help managers prioritize and focus their conservation efforts. Protecting hotspots of biodiversity and the abundance of endemic species they support, offers one of the best opportunities to curb high rates of extinction. The Andes region of South America is one of these hotspots of species, diversity, and these natural alpine habitats are also among the most threatened areas of the world. Explanations for this concentration of endemic species include past climate shifts and tectonic events, modern ecological interactions, and limited dispersal. Historically, the upland areas were isolated from the lowlands by the Andean uplifts, which began 25 to 30 million years ago. This eventually created a complex mosaic of high mountains and deep valleys. This ancient uplift and resulting isolation were important drivers for speciation. Resulting in high concentrations of endemic birds, mammals, amphibians and plants. Well, mountains are often hot spots of biodiversity compared with other regions of the world. There's also considerable variation in the patterns of species diversity within mountain ranges. Where would you expect to find the highest biodiversity? There are several hypotheses that could explain these patterns of biodiversity. For now, let's consider two of them, the geographical area hypothesis and the productivity hypothesis. According to the geographical area hypothesis, larger areas can support more species. Therefore, decreasing species diversity at higher latitudes and elevations may just be a consequence of inherently small areas of habitat availability. The productivity hypothesis proposes that the amount of primary productivity, which forms the resource base of food webs, determines the number of species that can be supported in an area. Therefore, higher primary productivity associated with higher temperatures in the tropics and lower elevations contributes to higher biodiversity. In fact, there are many factors that influence the distribution of species in mountain environments, at various geographical scales. Habitat fragmentation, as a result of past environmental changes such as glaciation, can be particularly influential in determining patterns of mountain biodiversity. Professor Terry Callaghan from Tomsk State University in Russia and Sheffield University in the UK, has spent decades studying these patterns. I spoke to Terry during a visit to the Altai Mountains in Siberia. >> Mountains are extremely important in determining the distribution of many species on planet Earth. They all effect distribution in many ways. At the small scale, you find distributions of plants according to their altitude. The species that cannot tolerate shade, but can tolerate low temperatures, tend to be at the top of the mountains. Those that are best adapted to cold conditions are found on the side of the mountain away from the sun. So the northern hemisphere is on the north side of the mountains. At the larger geographical scale mountains that are connected that run north south are important, allowing corridors of distribution of plants from the south to the north following the ice movements after the last ice age and previous ice ages. In the moment after the little ice age and the early cold periods we have something called nunataks and these nunataks are the tops of mountains that are sticking out of our ice sheets. The most famous one is in southwest Greenland 100 kilometers from any ice free area. And there, there are plants growing. As we see climate warming those individual nunataks separated from neighboring nunataks are going to become connected as ridges, and then the species will move along. At the moment those isolated species are endemics very often because they've been separated isolated from other gene pools for a long time. Of course, when they meet again, then we'll have a new evolutionary trend and you'll mix the species as the genes flow again. And the moment as the mountains are isolated, it depends where you are. In the cold regions they're isolated because of maybe ice between them. And in other latitudes it may be just distance and forest and even tropical forests between them. Those mountains in those situations are reservoirs, they're refugia, reservoirs of all species, endemic species and species that cannot tolerate or move across the barrier below the mountains. >> You’ve probably heard about accelerating loses of biodiversity and may even be familiar with various conservation efforts to preserve biodiversity. >> But why does biodiversity matter and in particular, why is species diversity important in mountains? One argument for protecting biodiversity is simply the beauty of nature itself. People derive great enjoyment from experiencing the diversity of life in mountains. The variety of unique and charismatic species in mountains attracts tourists and therefore can be economically important as well. Beyond its aesthetic value, maintaining biodiversity is critical to the functioning of mountain ecosystems. Biodiversity acts as insurance, buffering ecosystems against losses of individual species in the face of environmental change. Different species have different tolerances for environmental change. So higher species diversity generally increases the probability that mountain ecosystems can cope with an extreme environmental event. Such as winter rainfall or icing, increased fire frequency, or drought. The diversity of vegetation in mountains is also critical for slope stability. The steep terrain of mountains increases the susceptibility of soils to erosion. Soil erosion in mountain landscapes increases the risk of avalanches and landslides that can increase sedimentation in streams degrading the quality of water supplies. While bare soils are highly prone to erosion, the roots of vegetation anchor soils to enhance their stability. The diversity-stability hypothesis is based on the observation that species vary in their morphology and physiology, and that in highly diverse systems, there will be some species that can compensate for the loss of others after disturbance. Thus, species rich systems are more likely to be considered stable, or less variable and subject to change. Sites that contain only a few rare species with one dominant species are less able to withstand environmental disturbances. All of these values associated with mountain biodiversity can be thought of as ecosystem services, a concept we introduced in an earlier lesson. The term ecosystem services was defined in the 2005 Millennium Ecosystem Assessment as a way of quantifying the benefits people obtain from both natural and managed ecosystems. Mountain ecosystems provide a vast array of goods and services to humanity, both for people living in the mountains and for people living far away from mountains. So there are great many reasons to care about mountain biodiversity. In previous lessons, we've discussed several physical characteristics of high mountain ecosystems, that living organisms must contend with. Remember that there's a reduction in partial pressures of oxygen, carbon dioxide, and water vapor at higher elevations. As a consequence of reduced water vapor, the capacity of the air to absorb and retain heat diminishes, leading to lower temperatures. Additionally, the thinner atmosphere at higher elevations. Results in greater solar radiation and an increased fraction of ultraviolet radiation. Slope aspect and steepness, poor soil development, water drainage, wind, and the seasonally variable patterns of precipitation also create challenging conditions for species to cope with. Mountains are home to truly unique ecological communities, and although mountain environments may seem to be hostile and difficult places to live, most mountain dwelling organisms have evolved a wide variety of biological adaptations or traits that enhance their ability to survive and reproduce in these high places. Let's look at some of this in more detail.
