7 O`simlik hayvonat resurslari va uni muhofaza qilish. Reja

Yo’qolgan turlar
Hech bir inson dinozavrlarning yo’q bo’lib ketish sababini aniq dallillar bilan aytibberolmaydi. Bir narsa aniqqi, inson faoliyati va tabiatga ta’siri dinozavrlardan keyin paydo bo’ldi. Bugun boshqacha hayot. Yo’qolib borish arafasidagi turlar soni oshmoqda. 1980 yildan 2000 yilgacha AQSH da 40 ga yaqin o’simlik va hayvon turlari yo’q bo’lib ketdi. Sababi, insoniyatning yer yuzini katta maydonlarini egallashi va o’zlashtirish, ehtiyojlarini qondirishi hisobiga turlar soni kamayibketmoqda.^1
1Peter Rillero, Dinah Zike Ecology, 2005. (126-127; 129- bet)
The Variety of Life
Imagine walking through a forest ecosystem like the oneshown in Figure 1. Trees, shrubs, and small plants are everywhere.You see and hear squirrels, birds, and insects. You mightnotice a snake or mushrooms. Hundreds of species live in thisforest.Now, imagine walking through a wheat field.You see onlya few species—wheat plants, insects, and weeds. The forest containsmore species than the wheat field does. The forest has ahigher biological diversity, or biodiversity. Biodiversity refers tothe variety of life in an ecosystem.
Measuring Biodiversity The common measure of biodiversityis the number of species that live in an area. For example, acoral reef can be home to thousands of species including corals,fish, algae, sponges, crabs, and worms. A coral reef has greaterbiodiversity than the shallow waters that surround it. Beforedeep-sea exploration, scientists thought that few organismscould live in dark, deep-sea waters. Although the number oforganisms living there is likely to be less than the number oforganisms on a coral reef, we know that the species biodiversityof deep-sea waters is as great as that of a coral reef.
Differences in Biodiversity Biodiversity tends to increaseas you move toward the equator because temperatures tend tobe warmer. For example, Costa Rica is a Central American countryabout the size ofWestVirginia.Yet it is home to as many birdspecies as there are in the United States and Canada combined.Figure 2 compares mammal biodiversity in three NorthAmerican countries. Ecosystems with the highest biodiversity usually have warm, moist climates. In fact, tropical regions containtwo-thirds of all of Earth’s land species.What kind of climate usually has a highbiodiversity?