3-ma’ruza Mavzu: Populyatsiyalar ekologiyasi

Cheklovchi omillar. Cheklovchi omil tirik va notirik organizmlarning ekotizmini o'z ichiga oladi.Cheklovchi omil aloqada bo'luvchi bir necha populyatsiyaga ta'sir eta oladi. Biroz yomg'ir yog'ishi ham o'tloqdagi o'simliklarni o'sishini cheklay oladi. O'simliklar urug'ni sichqonlar yeydi, bu oziqlanish jarayoni cheklovchi omilga aylanishi mumkin.^1
1Peter Rillero, Dinah Zike . Ecology, 2005 (10-16- betlar).


Populations. Suppose you meet an ecologist who studies how a herd of bison moves from place to place and how the female bison in the herd care for their young. This ecologist is studying the members of a population. A population is made up of all organisms of the same species that live in an area at the same time. For example, all the bison in a prairie ecosystem are one population. All the cowbirds in this ecosystem make up a different population. The grasshoppers make up yet another population.
Ecologists often study how populations interact. For example, an ecologist might try to answer questions about several prairie species. How does grazing by bison affect the growth of prairie grass? How does grazing influence the insects that live in the grass and the birds that eat those insects? This ecologist is studying a community. A community is all the populations of all species living in an ecosystem. The prairie community is made of populations of bison, grasshoppers, cowbirds, and all other species in the prairie ecosystem. An arctic community might include populations of fish, seals that eat fish, and polar bears that hunt and eat seals. Figure 3 shows how organisms, populations, communities, and ecosystems are related.
Food and Space Organisms living in the wild do not always have enough food or living space. The Gila woodpecker, shown in Figure 5, lives in the Sonoran Desert of Arizona and Mexico. This woodpecker makes its nest by drilling a hole in a saguaro
(suh GWAR oh) cactus. Woodpeckers must compete with each other for nesting spots. Competition occurs when two or more organisms seek the same resource at the same time.
Population Size. Ecologists often need to measure the size of a population. This information can indicate whether or not a population is healthy and growing. Population counts can help identify populations that could be in danger of disappearing. Some populations are easy to measure. If you were raising crickets, you could measure the size of your cricket population simply by counting all the crickets in the container.What if you wanted to compare the cricket populations in two different containers? You would calculate the number of crickets per square meter (m2) of your container. The number of individuals of one species per a specific area is called population density.