Biological contact between North and South America causing massive extinction?
464728
Well, the GABI (Great American Biotic Interchange) went both ways, and several families of mammals from North America came to South America, and viceversa. However, only few native South Americans remain today in North America (NA), whereas many originally Holarctic families are thriving in South America (SA) at present. \n\nThe above answerer has outlined the three major "strata" defined by GG Simpson for the mammals of SA. The "original" South American mammals before the GABI included marsupials (shared with Australia, but forming a distinct cohort with different families) but also the exclusively South American xenarthrans (although there is a possible fossil anteater from Europe), and the Caviomorph rodents (closely related to the hystricognathous African rodents). In addition, there were some carnivores that had made it from NA. \n\nAfter the Panama land bridge appeared, the GABI was intense. North and South American faunas mixed and they appear to have coexisted for a long time. \nThe subsequent Pleistocene extinctions involved groups of both origins, but the South American natives were more intensely affected. Among the hypotheses to explain this,  interspecific competition has been mentioned, but also climatic changes. \nFirst of all, direct competition is _very_ difficult to prove, and more so with respect to fossil remains from strata that may not be exactly coeval. A more recent and preferred explanation involves a little paleoclimatology. \n** During the glaciations (and other stressful periods), South American conditions were more benign, because the continent is closer to the Equator, whereas environments in NA were much harsher, facilitating the extinction of the South American immigrants, along with many native North American giant forms. \n**In addition, the Central American corridor, which had been at first a savanna-like environment that permitted passage, later in the Pleistocene became more like a tropical forest. Then many cursorial (running) animals that inhabited open areas were unable to "cross the bridge". The giant ground sloths and glyptodonts were trapped in NA, and when climate and vegetation kept changing toward colder and drier conditions, became extinct.\n\nAnimals left from this: \nAmong the original South American natives, only the xenarthrans (sloths, armadillos, and anteaters) and marsupials (opossums)[early inhabitants], and the caviomorph rodents (originally derived from their African relatives) [second stratum colonizers] are alive today. The immensely diverse native ungulates went extinct, along with the representatives of the megafauna (giant sloths, glyptodonts, etc). At least one species of armadillo (Dasypus novemcinctus) is expanding its range in NA today, and the opossums (I remember Didelphis virginiana, not sure if there are others) are well established there. Caviomorph rodents also occur in NA (porcupines, genus Erethizon), but are mostly confined to Central America. \nThese are the South American contributions to North American fauna. In contrast, about 50% of the South American mammal genera have North American origin.\n\nWith respect to birds, at least the Passeriformes Suboscines are South American in origin, but I have no idea _when_ they colonized NA. They include the Tyrannidae (tyrant flycatchers). Other birds with Neotropical origin are the hummingbirds (Trochiliformes or Apodiformes).\n\n---------------------\nUpdate:\nMmm... I’m not sure what you call “non-speed strategies”. Predators? Running forms such as ungulates? There were many native ungulates in South America and they went extinct; also many marsupial predators such as the marsupial sabertooth “cat”  that also disappeared. Many caviomorph rodents are cursorial (capybaras, agoutis, etc).\nI would relate it more to size. Size _is_ a constraint because large animals have different energetic balance and need large amounts of food and room. And those went extinct in both co
624569
South of North America.
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The big unknown in your question is what the weather would be like.\n\nKeep in mind that the amount of rainfall could still be the same on a worldwide basis.  Almost all of the water evaporated from the ocean falls as rain within about 100 miles of the coast.  \n\nYou know that in South America, rain forests are located far inland, even in the center of the contient.  So, it doesn't take evaporation from the ocean to sustain an extremely wet climate.\n\nPresumably, the ocean basins would be covered by forests.  They put a tremendous amount of water into the air through transpiration.  What would the climate be like at such a low elevation?  This would dramatically change the albedo of the earth; much more sunlight would be absorbed!  Overall, the world would be much hotter.\n\nYou would still have large freswater lakes on the continents, and presumably at some places in the ocean basins.\n\nHeck, I have a PhD in geology and I can't answer this question.  What would the climate be like?  Would the lower albedo cause a runaway greenhouse effect, or would the higher average temperature evaporate more water making more clouds to completely offset the increased albedo?\n\nTell your professor there isn't enough information about what the climate would be like.
247868
Not only biologists but everybody must feel concerned about the vanishing species on earth.This is  because nobody lives in isolation.We are all ( The plants,animals and man) related and dependent upon each other.)\n With every extinction an important link in the life on the earth is broken and gone. It has a cascading effect.\n In Australia, with the disappearance of Dodo ( A bird since extinct) the trees that were dependent on Dodo for germination of their seeds also disappeared. It was established that the seeds must pass through the digestive system of the bird before germination as the hard cover used to get digested by the bird.Scores of insects and bees bring about pollination in plants.Disappearance of these bees due to indiscriminate use of the pesticides will undoubtedly affects those plants.\nLife on this planet is like an intricate web, damage to any of its part will destroy the web and even man will not be spared.
875008
Here is a brief overview of the Pampas and some of the reasons why the area is endangered, in addition to immigration and the expansion of communities/suburbia into these areas:  http://www.blueplanetbiomes.org/pampas.htm\n\nGood luck!
461824
Extinct species, if not extinct by human activity (shooting them, cutting their forests down, etc.), have extinct for a reason - they did not fit well to the enviournment.\nRecreation of such species may destabilize the delicate balance of nature.\nMoreover, any human interferance with nature, whether trying to do good or bad, can only harm it.\n\nThere are two (1.5) reasons. I think you can start with these, and probably the rest will come to mind after writing this. If not, I believe that other people will have further ideas.\n\nGood luck!
1033738
Because animals in that area existed in abundance, and there were no natural predators other than man, of which they had a natural fear. Men did not need to overhunt the megafauna in Africa as they did in North America. Moreover, since men had arrived only recently in America, megafauna on the American continent had no fear of them and were much easier to hunt as a result.\n\nAnother theory says that the megafauna of America were driven to extinction by climate change. Apparently the climate change during the Late Pleistocene that may have driven North American animals to extinction was not as severe in Africa.\n\nA newer theory states that disease that spread through America but not Africa was to blame, but the offending microbes, if they indeed existed, have yet to be isolated or identified.
408132
The experimental fragmentation of landscapes of a natural ecosystem resulted in declines in the abundance and distribution of most species in the multispecies animal community inhabiting the landscapes and the extinction of many species. These declines caused the deterioration of the positive interspecific relation between local population abundance and distributional extent in this community. However, when patches were connected by habitat corridors, an immigration "rescue effect" arrested declines in both abundance and distribution and maintained the observed positive relation between them. These results demonstrate the importance of metapopulation dynamics and landscape connectivity for the persistence of populations in fragmented landscapes.
169500
The Columbian Exchange (also sometimes known as The Grand Exchange) has been one of the significant events in the history of world ecology, agriculture, and culture. The term is used to describe the enormous widespread exchange of agricultural goods, livestock, slave labor, communicable diseases, and ideas between the Eastern and Western Hemispheres that occurred after 1492. That year, Christopher Columbus' first voyage launched an era of large-scale contact between the Old and the New World that resulted in this ecological revolution: hence the name "Columbian" Exchange.
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The massive ice sheets in the Arctic are melting at alarming rates. This is causing the oceans to rise. Rising ocean levels, an estimated six feet over the next 100 years or sooner, will cause massive devastation and economic catastrophe to population centers worldwide.\n\nMalaria. Dengue Fever. Encephalitis. These names are not usually heard in emergency rooms and doctors’s offices in US. But if we don’t act to curb global warming, they will be. As temperatures rise, disease-carrying mosquitoes and rodents spread, infecting people in their wake. Doctors at the Harvard Medical School have linked recent U.S. outbreaks of dengue (‘breakbone’s) fever, malaria, hantavirus and other diseases directly to climate change.\n\nSuper powerful hurricanes, fueled by warmer ocean temperatures are the “smoking gun” of global warming. Since 1970, the number of category 4 and 5 events has jumped sharply. Hurricane Katrina, in September 2005 almost became a category 6 event. Human activities are adding an alarming amount of pollution to the earth’s atmosphere causing catastrophic shifts in weather patterns. These shifts are causing severe heat, floods and worse.
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Extinction. \n  \n\nExtinction is a hot topic, of central interest to conservation, environmentalism and also to academic ecology. Ecologists are increasingly realizing that extinction has shaped the communities and ecosystems we see today, and that it operates on a range of timescales and spatial scales. \n\nExtinction doesn't just involve the complete loss of species, vanishing from the Earth. Extinction of local populations is often of key importance in shaping communities, even though other populations of the same species may exist in the same general area. \n  \n\nLocal extinction of populations. \n\nIn any area of forest, or patch of swamp, or coral reef, populations of animals and plants will be coming and going. If you were to compile lists of (say) all the bird species nesting in an fairly small isolated area of forest in Connecticut in one year then come back 20 years later, although most of the species in the list would be the same, the chances are that some of them would be absent (but quite likely replaced by other species). The ones that have come and gone would likely be the ones that had relatively few nesting pairs there anyway. \n\nWhy would they have gone extinct? Well, most often it would simply be that the population had a run of bad luck. Maybe there were 3 pairs nesting, and just by chance there for several years in a row there were late frosts that killed all the insects so the parents had nothing to feed their young, so the nestlings all died. Small populations are at the mercy of such 'bad luck', known as stochasticity. Even an initially abundant population (of say 150 nesting pairs) might still suffer a series of bad luck events (an exceptionally cold winter knocking back the population, followed by the late spring frosts) that can take it down from abundance to nothing at all in a few generations. \n\nAnother problem in a small population might be inbreeding. In species that normally have quite large populations and lots of exchange of genes, a range of harmful recessive genes can be present in the population without often showing themselves. Only when the population shrinks due to bad luck is there a significant chance of close relatives mating (e.g. if there are only 2 nesting pairs in the forest each year, the young are bound to end up mating with close relatives). When close relatives mate, they each have a good chance of carrying some recessive lethal genes in common; the result may be high mortality among the offspring. Experiments with repeated brother-sister crossings in domesticated animals (for several generations in a row) show that within 3 or 4 generations the young almost never survive to maturity because they have so many things wrong with them. This inbreeding effect is thought likely to hammer many isolated populations as their numbers get low, adding to the bad luck, although there are no well-documented cases of it occurring in wild populations. An apparent example of inbreeding effects appears to be the cheetah (see below), which has very low genetic variability apparently due to its numbers crashing to only 4 or 5 individuals at some unknown time in the last 10,000 years, then expanding rapidly again. Cheetahs have low fertility rates (e.g. very low viable sperm counts), and their cubs have high death rates that seem to be the result of its recent history of inbreeding. In this case, the population remained viable and recovered despite the inbreeding effects, but one can imagine that the problems might equally well kill off less lucky populations/species that reach very low numbers. \n\nObservations suggesting the importance of inbreeding in causing near-extinction:\n\n1) Gray Wolves of Isle Royale, Canada. The population was established by 1 breeding pair of wolves around 1949. By 1980 the population had grown to approximately 50 individuals, but by 1990 it had dropped to 14. Few pups were sighted by investigators who also noted that females were not breeding. Furth
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i think it might of been the start of the extinction and possibly other factors as well.   through out time animals adapt so it is possible that the meteor hit along with the rapid climate change caused this all the happen or appear to happen at once.   how do we know that the extinction was not already in progress before the meteor hit.   i don't think we will ever know.   Science is fact and a little bit of art when they come up with these ideas.
845010
The other answer is right as this the human presence is still expanding. \n\nGenerally though aborigines were in Australia 40,000 years ago. People also arrived in the Americas at this time (coinciding with the extinction of the wooly mammoth). \n\nAfrica of course was the origin of the human race and with land links to Europe and Asia these were fairly easily colonised.
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By itself it is not, but there is a large one near the Yucatan Peninsula, thought to be the result of a strike that led to the dinosaur extinction.
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Rainforests must be the only natural thing left that delays human extinction!\n\nAnswerer 1 is also very right! \n\nBut that doesn't mean that his answer is better than mine!
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Man_with_a_Plan has no proof that there is no proof. His statement that no theories are sound or have proof is just his opinion and purely speculatory. There is no proof.\n\nI, on the other hand, like the "Murder on the Orient Express Theory". I think that there was huge changes in ocean circulation due to the continents coming together WELL BEFORE Pangaea formed. The geologic evidence suggests that the extinction happened in different places around the world at different times, which suggests that no single event is responsible. I believe that cooling events like plume volcanism in the Siberian traps coupled with warming events like methane hydrate release and greenhouse effect along with the continental positioning at the time may have worked together to cause extreme changes in ocean circulation at various parts of the world at different times, attributing to the extinction event.\n\nVariations in temperature due to greenhouse warming and on/off sulphide cooling would have had the greatest immediate impact on planktic (ocean surface) and shallow water organisms. I also think that ocean circulation was also greatly affected not only by the temperature variations but also the circumstantial orientation of the continents. Heat transport to the north would have been innefficient and consequently northern regions would have been subject to extreme cooling, even at relatively low latitudes. In the southern regions there would have been a huge temperature gradient between top and bottom waters. If this was enough to stop deep water formation and ocean turnover, benthic (bottom dwelling) species would have been destroyed by the lack of oxygen and intermediate to surface water species would have suffered from a lack of nutrients. Because most of the Earth's life at the time was in the water, I am quite sure that it was likely some change in ocean circulation that dealt the fatal blows to life. Obviously good carbon isotope data from the period would be needed to verify this hypothesis. \n\nLife on land would have suffered greatly by climate changes induced by changes in ocean circulation, as well as the extreme variations in temperature. Tropical species would have been devastated by cooling events caused by the plume volcanism.\n\nThere is lots of proof for everything; there just is no definite information that can, as of yet, say for sure exactly how it all happened. That's a tough thing to do, but I really dislike people who refute the claims of others without presenting any evidence themselves.
464754
Copied from the referenced website:\n\nThe Caucasus Mixed Forests are located at a biogeographical crossroads where flora and fauna of at least three biogeographic provinces converge. Mount Elbrus, Europe’s highest point at 5,642 m a.s.l. Speciation level is high; accordingly, the Caucasus forests have one of the highest levels of endemism in the temperate world. 23 percent of vascular plants and 10 percent of vertebrate are endemic to the region. Landscape and habitat diversity favors high species richness as well-- about 5,000 vascular and 7,000 lower plants (including high mountains), and 700 vertebrate animals are found in this ecoregion (Georgia 1996, Azerbaijan 1998, Armenia 1999). \n\nCharacteristic mammals include the East and West Caucasian tur (Capra cylindricornis and Capra caucasica), chamois (Rupicapra rupicapra), Caucasian red deer (Cervus elaphus maral), wild goat (Capra aegagrus), mouflon (Ovis orientalis gmelini), brown bear (Ursus arctos), and the critically endangered Caucasus leopard (Panthera pardus ciscaucasica). Unsustainable forest use, including poor management and illegal cutting in combination with uncontrolled timber export, represent chief threats for these forest ecosystems.