HIERARCHY OF ECOLOGY

 

In life’s hierarchy of organization, new properties emerge at each level As Figure 1.2 illustrates, the study of life extends from the global scale of the biosphere to the microscopic scale of molecules. At the upper left we take a distant view of the biosphere, all of the environments on Earth that support life. These include most regions of land, bodies of water, and the lower atmosphere. A closer look at one of these environments brings us to the level of an ecosystem, which consists of all the organisms living in a particular area, as well as the physical components with which the organisms interact, such as air, soil, water, and sunlight. The entire array of organisms in an ecosystem is called a community. The community in this forest ecosystem in Madagascar includes the lemurs and the agave plant they are eating, as well as birds, snakes, and catlike carnivores called civets; a huge diversity of insects; many kinds of trees and other plants; fungi; and enormous numbers of microscopic protists and bacteria. Each unique form of life is called a species. A population includes all the individuals of a particular species living in an area, such as all the ring-tailed lemurs in the forest community. Next in the hierarchy is the organism, an individual living thing. Within a complex organism such as a lemur, life’s hierarchy continues to unfold. An organ system, such as the circulatory system or nervous system, consists of several organs that cooperate in a specific function. For instance, the organs of the nervous system are the brain, the spinal cord, and the nerves. A lemur’s nervous system controls its actions, such as climbing trees. An organ is made up of several different tissues, each made up of a group of similar cells that perform a specific function. A cell is the fundamental unit of life. In the nerve cell shown here, you can see several organelles, such as the nucleus. An organelle is a membrane-enclosed structure that performs a specific function in a cell. Finally, we reach the level of molecules in the hierarchy. A molecule is a cluster of small chemical units called atoms held

together by chemical bonds. Our example in Figure 1.2 is a computer graphic of a section of DNA (deoxyribonucleic acid)—the molecule of inheritance.