Species do not become extinct as a sudden.There are classified as vulnerable, endangered and critically endangereddepending on their rate of decline, habitat size and population size. Oncepopulation gets small, it becomes easier for it to be affected by changes. Insmall populations, inbreeding occurs and random genetic drift has more effectthan large populations.
As a result of these, genetic diversity is lost and thepopulation becomes vulnerable to environmental effects. In harsh conditions,population become even smaller and may go extinction. This phenomenon is calledan extinction vortex 1.
- Thesis Statement
- Structure and Outline
- Voice and Grammar
Up to date, lots of species have goneextinct and lots of are on the red list of International Union for theConversion of Nature 2. Heath hens vanished from East Coast during the mid1800s, the Tasmanian tiger which declared as extinct in 1986, Baji dolphinwhich is native to China and cheetah which occupy 9% of their previousterritory now are some of the examples. Some of these losses have resulted fromnatural selection; however, the much higher percentage has resulted fromanthropogenic effects. Declining population paradigm whichexamines what drives a population to smallness points four main reasons to lossof species diversity: habitat destruction/fragmentation, overkill, chains ofextinction and introduced species 3. In this paper, species loss resultedfrom deforestation which is a subcategory of habitat destruction/fragmentationwill be investigated.Island can be considered is the area whichis isolated from its surroundings.
Species diversity on an island is directlycorrelated with the size of the island. This theory is called as biogeographicisland theory. It makes a correlation between area-species diversity and itassumes that the number of species becoming extinct can be predicted from theshrinking habitat 4. Besides habitat size, the formula-driven also considersspecies-specific index and growth rate of the population. Therefore, it can besaid that consequences of habitat loss or fragmentation can be different fordifferent species. More adapted ones which have a broadened niche may toleratewhereas the ones with narrower niche may become extinct 5. In addition, thereare well-established relationships among species; therefore, effects ofdeforestation on species loss may not be restricted to only species losingtheir habitats but also species feeding on the ones becoming extinct or speciesrequire symbiosis relationship with the ones becoming extinct are alsoaffected.
For example, plants require pollinators to reproduce; therefore whentheir pollinators are affected by deforestation their survival will mostprobably decrease.. Therefore it can be said that deforestation results inchain effects on survival of species.
Drivers of species loss caused by deforestation:According to Food and AgricultureOrganization, approximately 7.3 million hectares are cleared from forestsyearly. World’s forests are being cleared mainly because of antrophogenicactivities. For instance, increased temperature due to increased emission ofgreenhouse gases such as CO2 and N2O leads to wildfires.
Deforestation leads to loss of ecologicalniche which is defined as conditions required for a particular species to grow,reproduce and survive. Because there are many different species living inforests, their survivorship declines due to deforestation. In a study, the effectsof different sources on species extinction weremcompared and it was found outthat habitat loss is far ahead for both global and Canadian species and mostaffected ones from habitat loss are terrestrial organisms 11.Even though terrestrial ones are the mostaffected part, it can be seen from Figure 1 that marine species also getaffected by deforestation. In another study, responses of fish species residein the western Brazilian Amazon to deforestation was tested 12.
This regionis suitable for research of species lost because it has gone through twodeforestation: one was in 1991 to 1995 and 19 % of it was cleared and the otherone was from 2001 to 2004 and 23% of it was cleared. They examined one streamfrom a highly deforested region and one stream from a less deforested region,and they found that species diversity was higher in less deforested streamwhereas stream taken from the highly deforested region was homogeneous whichconsisted only adaptable ones 12. Regarding of this study, it can be saidthat deforestation impacts species in different amounts but it results in speciesdiversity loss definitely.