Hello and welcome back to extinctions past present and future. In the previous lecture we discussed the geological significance of humans, that perhaps justifies a new geological epoch the anthropocene. This new epoch would be partly defined by human influenced extinctions, but also many other markers. To continue that theme we'll now look specifically at how human activities have contributed to recent extinctions through habitat alterations, and especially through colonization during the past 500 years or so. Paleontologists who convinced that habitat alteration was a major factor in most if not all mass extinctions of the pre-human passed. In these scenarios ecosystems changed too quickly for most organisms to adapt to the change. That led to rapid declines in some species populations and ultimately extinction. We can then infer from the geologic record that the causes of habitat alteration include global climate change, either becoming too cold or too warm, or oceans becoming too acidic or to anoxic. As we learned radical environmental changes and species losses would have then contributed to trophic cascades as entire ecosystems collapsed, leaving relatively few survivors. So in a way humans have been repeating the same global experiments of the geologic past through their hasty alterations of ecosystems, especially those on land. For example, one of the human activities I mentioned that caused abrupt ecological change is the widespread use of fire. Fires, whether deliberately or accidentally set by humans, would have instantly decreased usable habitat for many species living in grasslands, forests, and other land ecosystems. Another significant human innovation was agriculture, which has been a part of human life since at least the start of holocene about 10,000 years ago. Agriculture changes ecosystems, and their soils and climate are used exclusively for growing just a few species of plants versus the hundreds or thousands of species that might normally live in these places. This shift in biodiversity sometimes involves clearing land of native vegetation, through fire and deforestation or so called slash and burn agriculture. Such swift change deprives animals of their homes and resources, where they ate, drank, reproduced, and otherwise survive long enough to create new generations. If agriculture was implemented enough times and over enough acreage, species from those places became rare or extinct. Another agriculture related factor is animal husbandry, in which humans domesticated formerly wild species of animals for food clothing and other uses. Animal husbandry may have started as long as 8,000 years ago in Middle Eastern, European, and Asian cultures. Most of these species were mammals, and many of those were hoofed mammals, like cattle, pigs, goats, and sheep. And there were common animal companions of humans wherever they went, domestic dogs, domesticated from Eurasian wolves, perhaps more than 20,000 years ago, and domestic cats which are derived from a feline species in Central Asia. Although for the most part we view these two species as beloved companions today in the past each had practical uses. Dogs, for example, help humans hunt other animals through a deadly combination of canine olfactory skills and human tracking, weapons, and strategy. Cats were, and still are very good at killing animals that humans considered pests, like small rodents. Speaking of rodents, mice and rats also proliferated with humans, particularly in places where people grew and stored large amounts of food. And wherever people travel domesticated animals, and unintentionally encourage species went with them. The increased abundance of these human enabled species, displaced native species, competed for their resources, spread diseases, or killed them directly. Mining was another factor altering habitats, humans excavated and processed earth resources, flint for stone tools, iron ore deposits, copper, silver for metalworking, and quarrying of building stones, like limestone. Some types of mining started in the late pleistocene, but they increased dramatically with agriculture. Both pit mines and underground mines change landscapes, alter the flow of surface and ground water, and polluted water supplies, which adversely affected native aquatic and land dwelling species. Another major factor influencing extinctions in the past 500 years or so, was colonization. Why 500 years? Because colonization spread to another hemisphere around 1492. That's when Columbus sailed the ocean blue, or whatever color the Atlantic might have been that year. Spanish occupation and subjugation of native peoples in the Western Hemisphere started soon afterwards. Quickly following the Spanish, were the French, British, Dutch, and Portuguese in the Americas. All with sailing ships and well armed military forces spreading around the world. Within just a few centuries indigenous human populations in the Americas Africa, Australia, Asia, and Pacific Islands were decimated by a combination of warfare, slavery, and disease. The significant loss of human life was accompanied by extinctions of endemic species, which couldn't adapt to the rapid or the cumulative impacts of deforestation, new forms of agriculture, introduction of exotic species, and Mining. And overhunting added to these factors and became far easier than in the pleistocene, because of the introduction of guns. Overhunting was not just done for food and sport, but also to eliminate the competition of native predators. This is a main reason why today in Atlanta Georgia, I can't take a walk and see bobcats, cougars, red wolves, or black bears. Though all of these predators survived the N pleistocene megafauna extinction, and they were abundant in the Southeastern US just 500 years ago. But now their populations are much smaller and restricted, due to this over hunting and habitat alteration. These predators are also examples of extirpation when species become locally extinct in their original geographic ranges. Given such depressingly grim facts, you may need a little pick me up. Ooh, how about some nice delicious ice cream. Only the ice creams made with cream from a domestic dairy cow, which likely grazes on land where large numbers of bison used to roam. I know crispy salty french fries will make us feel better. Mmm, tastes like freedom except those are made from potatoes, a crop appropriated from the Incans by Spanish colonizers and named after another country that colonized Haiti and much of Africa. Well watching a video of frolicking kittens will surely cheer us up, unless you know that domestic cats are responsible for killing millions of birds and other small animals per year. Okay, well how about the fact that at least a few people are making efforts to slow down the permanent loss of species, and that their ingenuity, dedication, and passion make a difference and help save species from extinction. Yes, that will do nicely. So in our next lecture, we'll discuss the rise of conservation biology, and how this new science helped us to recognize mistakes of the past, and how to work toward a better future. See you there.
