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Current Extinction Rates Versus Mass Extinction Events 1 Current Extinction Rates Versus Mass Extinction Events Jack Boynton University of Rhode Island Current Extinction Rates Versus Mass Extinction Events 2 Abstract News articles have emerged claiming that Earth is entering its sixth mass extinction event, sometimes called the Holocene or Anthropocene extinction event. An extinction event is when many observable organisms go extinct over a relatively short period of time, causing between 50% and 90% of species to go extinct (Dictionary 2015, Whitty 2007). This mass extinction event seems to be rapidly occurring and articles seem to correlate on the underlying cause: humans. Humans are causing extinction rates to skyrocket through our practices like hunting and traveling (which spreads disease and introduces species) and the consequences of them including climate change, habitat fragmentation, and pollution. This extinction period will reduce species diversity exponentially and promote homogeneity in populations (Vince 2012). This is partially due to many species being few in number (compared with their prior status) and divided between communities due to fragmentation (Whitty 2007). Even formerly resilient species, such as amphibians, are rapidly declining due to a human introduced fungus that they have no defenses against. Some feel that that our actions will soon lead to our own demise (Younker 2015). Some people still debate that this mass extinction event is even a real concern, pitting it up to ecoactivists replacing climate change with loss of diversity so they can keep people paranoid. This is defended with paleontological articles about former mass extinction events determining that climate change is a continuous factor in Earth’s history and mass extinctions have never been caused by climate change alone. Usually a huge natural disaster happens, such as asteroid collisions. They say the extinctions we are causing will certainly change evolutionary history, but they are incomparable to gigantic natural disasters (Hoffman 2010). Current Extinction Rates Versus Mass Extinction Events 3 In order to determine the real status of extinction scientists have turned to studying population dynamics, species abundance, and ecosystem functioning to determine how pressing this matter actually is. Typically ecologists seem to focus their studies on flora, probably due to their role as the primary producers for ecosystems and their sessile nature. A study done in 2001 in Victoria, Australia surveyed thirty locations along a 225 kilometer gradient to understand comparative extinction rates between rural and urban areas. The locations ranged from suburbs to agricultural districts and were labeled as urban, peri-urban, or rural. This area was ideal for studying the effects of urbanization because the once dominant grasslands have been fragmented and reduced to less the 0.5% of their original area. The grasslands were characterized by the grass Themeda triandra, which forms tussock spaces where other small herbaceous species took residence. A list of previously identified flora was compiled from reports dating from 1979 to 1991. Variables were included in the calculations for false identifications and failure to observe. Species that were difficult to identify were excluded and all areas were surveyed twice to make sure absence wasn’t due to different flowering seasons. The research teams were surveying for 166 species in 1104 populations and any species not found was considered extinct. Traits of the different plants were also examined because of their role in survival. Traits examined were, “lifeform, dispersal mechanism, presence or absence of vegetative reproduction, seed mass, presence or absence of persistent soil seed bank, and prevalence of the species.” In this method, they can exam what traits will help a plant survive in urban and rural landscapes as well. By 2001, 289 populations of 126 species were absent and thus declared locally extinct. In urban areas 37% of indigenous species found in that landscape went extinct, comparatively to periurban(27%) and rural(20%). Species of all but one lifeform and all dispersal methods had a higher rate of extinction in urban areas. Some traits of the plants resilient enough to occupy Current Extinction Rates Versus Mass Extinction Events 4 urban areas were vegetative reproduction, and high prevalence. They predict that part of the extinction pattern is grass productivity increasing from lack of fires and nitrogen inputs from run-off, causing less water and nutrients for struggling organisms. This will give way to less diversity in ecosystems over time and promote homogeneity. The study predicts that human disturbance will only increase and with it, rates of plant extinction (Williams 2005). Some scientists disagreed with the prediction rates of others claiming their calculations were off. They said that when they subtract the proportion of the population survival and the detection probability from 1 they should have only been subtracting it from the population survival and then multiplying by the detection probability. They also took issue with some researchers (mostly in older studies) only revisiting once. This would create inflated extinction rates and give higher readings for vulnerability. They also said detection probability’s role in the factors associated with survival, such as habitat, can falsely link those factors because they are affected by the incorrect calculation. To compare using their own calculations they did their own study with 80-100 year old records from north-east Switzerland, targeting 11 species over 367 sites. The study took place in the Swiss Alps among a variety of diverse ecosystems. They made 6 of the species easy to find based on leaf color, size, form, prevalence and other such visibility factors, while the other five were supposedly harder to find. Visits occurred during the flowering season of the individual plants. There wound up being around a 13% difference between the calculations used the original way and the amended calculation used in this study. This study has however been criticized for its small species count and improper use of their “Jackknife” calculator (Kéry 2006). In a study from 2003 that uses an entirely different extinction calculation, the number of extinct past species plus the number of presently recorded species then multiplied by the extinct Current Extinction Rates Versus Mass Extinction Events 5 past species, 446 species were searched for in the Swiss lowlands in Küsnacht. Küsnacht used to have many variable ecosystems caused by the glacial formation of the landscape. This created many different landforms, soil types, and niches to cause the multitude of habitats. Due to recent urbanization these ecosystems have plummeted in the percentages of land they still occupy, especially vineyards with only two individual vineyards left. Currently eutrophication of the soil and habitat management seem to be persistent causes of extinction. The factors taken into account for each species were “habitat affiliation, life-form, resource requirements, and extinction risks.” Habitat affiliation was broken up into forests, meadows, wetlands, rocks, and disturbed sites. Some factors showed positive or negative reactions to certain habitats, for instance medium soil moisture requirements worked best for plants in meadows and disturbed sites. Of the environmental factors, soil requirements were most heavily tied in with extinction rates. A high demand for light was also a large contributor. Extinction rates also varied greatly in different habitats. Rocky and forest sites had the lowest rates at 9% and 13% respectively. Meadows had 20%, disturbed sites 23%, and at the top of the extinction rates were wetlands at 28%. Of all lifeforms, aquatic species went extinct at the fastest rate of 61%. Overall 127 species went locally extinct leaving the extinction total between 17% and 28% with a higher probability towards the prior (Stehlik 2007). One study also viewed the species and functional group dispersion in order to see how the extinction of functional groups occurred in relation to species. Four hypothetical communities were utilized to compare results. All species were compared by species richness, functional group richness, and functional group evenness. Community 1 was used as the standard where community 2 differed in species richness, community 3 in functional group evenness, and community 4 in functional group richness. Species richness was a major attribute for Current Extinction Rates Versus Mass Extinction Events 6 communities, creating better functional redundancy and allowing functional groups to maintain their order with 80% of species within going extinct. This was higher than community 2 which had less species rich environments and lost a functional group 16% of species before community 1. In addition to a healthy diversity, functional richness improves chances of survival be 24% and evenly distributed species were preferred. Overall, 75% of species could typically go extinct before the functional group itself did. This is a positive message because ecosystems are much more highly impacted by functional group extinction than species extinctions (Fonseca 2001). So in conclusion, especially since these studies are only comparing local extinctions, we are not quite near the standards necessary for a mass extinction event. Even in local regions with relatively high urbanization species extinctions still don’t typically exceed the necessary 50% marker. However, we are able to see that urbanization is increasing species extinction at an alarming rate (Williams 2005). Even with possible biases factored in, extinction rates are still much higher than average (Kéry 2006). Extinction rates can vary depending on ecosystem type, but are rising independent of the ecosystem and diversity is falling correspondingly (Stehlik 2007). Finally, functional group extinctions will not start occurring until a good portion of the species within have gone extinct (Fonseca 2001). So even though we are not currently in a mass extinction event, it seems like our effect on the planet is certainly gearing us up to experience one a lot sooner than we might think. The only question left is what do we do about it? It has been suggested by some to stop trying to revert ecosystems and upkeep them as they are now, even going as far as to suggest manipulating them to our desire and then preserving them. Some have hopes that measures will be taken, or that science will find a way to counteract extinction rates with cloning (Vince 2012). Nobody truly knows, but as species diversity continues to fall our ability to save them will only fall with it (Fonseca 2001). Current Extinction Rates Versus Mass Extinction Events 7 References Dictionary.com Unabridged. (July 18, 2015), Dictionary.com website. Retrieved from http://dictionary.reference.com/browse/mass+extinction Fonseca, C. R. and Ganade, G. (2001), Species functional redundancy, random extinctions and the stability of ecosystems. Journal of Ecology, 89: 118–125. Retrieved from http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2745.2001.00528.x/full Hoffman, L., Doug. (September 12, 2010). The Developing Diversity Scam. The Resilient Earth. Retrieved from http://theresilientearth.com/?q=content/developing-diversity-scam Kéry, M., Spillmann, J. H., Truong, C. and Holderegger, R. (2006), How biased are estimates of extinction probability in revisitation studies?. Journal of Ecology, 94: 980–986. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2006.01151.x/full Stehlik, I., Caspersen, J. P., Wirth, L. and Holderegger, R. (2007), Floral free fall in the Swiss lowlands: environmental determinants of local plant extinction in a peri-urban landscape. Journal of Ecology, 95: 734–744. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2007.01246.x/full Vince, Gaia. (November 1, 2012), A looming mass extinction caused by humans. BBC News. Retrieved from http://www.bbc.com/future/story/20121101-a-looming-mass-extinction Whitty, Julia. (April 30, 2007) Animal Extinction - the greatest threat to mankind. The Independent. Retrieved from http://www.independent.co.uk/environment/animalextinction--the-greatest-threat-to-mankind-397939.html Current Extinction Rates Versus Mass Extinction Events 8 Williams, N. S. G., Morgan, J. W., McDonnell, M. J. and McCarthy, M. A. (2005), Plant traits and local extinctions in natural grasslands along an urban–rural gradient. Journal of Ecology, 93: 1203–1213. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2005.01039.x/full Younker, Nick. (June 21, 2015) Holocene Extinction: Scientists Say the World Has Entered Into its 6th Mass-Extinction Event. Latin Post. Retrieved from http://www.latinpost.com/articles/61058/20150621/scientists-claim-the-world-hasentered-into-its-6th-mass-extinction-event.htm