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Ecology is the scientific study of the natural environment and of the relationships of organisms to one another and to their surroundings.



An ecological system may be an organism, a population, a community, an ecosystem, or the entire biosphere. These ecological systems represent levels of organization of ecological structure and functioning and form a hierarchy of progressively more complex entities.



Ecologists use several different approaches to study nature, focusing on the interactions of organisms with their environment; the resulting transformations of energy and chemical elements in ecosystems and the biosphere; the dynamics of populations, including evolutionary change; and the interactions of populations within ecological communities.



Different kinds of organisms play different roles in the functioning of ecosystems. Plants, algae, and some bacteria transform the energy of sunlight into stored chemical energy. Animals and protozoans consume these biological forms of energy. Fungi play an important role in decomposing biological materials and replenishing nutrients in the ecosystem. Bacteria are biochemical specialists, able to accomplish such transformations as the assimilation of nitrogen and the use of hydrogen sulfide as an energy source.



Different kinds of organisms may form mutually beneficial partnerships, as in the case of the algae and fungi that constitute lichens. Many organisms live parasitically on or within other organisms, feeding on their hosts' nutrients or tissues and often causing disease.



An individual's habitat is the place where it lives. The habitat concept emphasizes the structure and conditions of the environment. An individual's niche includes the range of conditions that it can tolerate and the ways of life that it can pursue- that is, its functional role in the natural system.



Ecological processes and structures have characteristic temporal and spatial scales. In general, the scales of patterns and processes in time and in space are correlated; large systems tend to change more slowly than small systems.



Ecological systems are governed by a small number of basic ecological principles. Ecological systems function within the physical and chemical constraints governing energy transformations. Furthermore, all ecological systems exchange materials and energy with their surroundings. When inputs and outputs are balanced, the system is said to be in a dynamic steady state.



All living systems must expend energy to maintain their integrity. Organisms must expend energy to replace the energy and materials they lose through natural processes.



All ecological systems are subject to evolutionary change, which results from the differential survival and reproduction within populations of individuals that exhibit different genetically determined traits. As a result of natural selection, organisms exhibit adaptations of structure and function that suit them to the conditions of their environment.



Ecologists employ a variety of techniques to study natural systems. The most important of these are observation development of hypotheses to explain observations, and testing of those hypotheses. Experiments are an important tool for testing hypotheses. When natural systems do not lend themselves readily to experimentation, ecologist may work with microcosms or mathematical models.



Humans play a dominant role in the functioning of the biosphere, and human activities have created an environmental crisis of global proportions. Solving our acute environmental problems will require an understanding of the principles of ecology and their application within the framework of political, economic, and social action.



Why do ecologist consider both organisms and ecosystems to be ecological systems?

They can thick of an ecosystem, like an organism, as having internal processes and exchanges with the external surroundings.


What are the unique processes and structures that are examined when taking the organism, population, community, and ecosystem approaches to studying ecology?

-way in which an individual's form, physiology, and behavior help it survive in its environment.
-understand why each type of organism is limited to some environments and not others, and why related organisms living in different environments have different characteristic appearances
-adaptations of organisms.

-concerned with variation in the number of individuals, the sex ratio, the relative sizes of age classes, and the genetic makeup of a population through time.

-concerned with understanding the diversity and relative abundances of different kinds of organisms living together in the same place.
- focuses on interactions between populations, which both promote and limit the coexistence of species( include feeding relationships)

- describes organisms and their activities in terms of common "currencies" principally amounts of energy and various chemical elements essential for life
-movement of energy and materials and how these movements are influenced by climate and other physical factors


How do the sources of energy acquired by plants, animals, and fungi differ?

Plants use sunlight to produce organic matter (photosynthesis), animals eat plants, other organisms,or their remains, fungi are decomposers.


Compare and contrast an organism's habitat and an organism's niche.

habitat- of an organism is the place, or physical setting, in which it lives. Habitats are distinguished by conspicuous structural features, often including the predominant form of plant life or animal life

niche- represents the range of conditions it can tolerate and the way of life it pursues (its role in the ecological system)


What is the relationship between the frequency of change in environmental conditions and spatial extent of the change?



Describe how ecological systems are governed by general physical and biological principles.



In the Northern Hemisphere, many species of birds fly south during the autumn months. Propose a proximate and an ultimate cause for this behavior.



When experimental manipulations are conducted to test a hypothesis, what is the purpose of including a control?



In what ways do experimental manipulations differ from natural experiments and microcosm experiments?



How can our knowledge of ecological systems help humans to manage these systems?