rom the viewpoints of (1)the environment and the demands it places on the organ- isms in it or(2)organisms and how they adapt to their environmental conditions. An ecosystem consists of an assembly of mutually interacting organisms and their environment in which materials are interchanged in a largely cyclical manner. An ecosystem has physical, chemical, and biological components along with energy sources and pathways of energy and materials interchange. The environment in which a particular organism lives is called its habitat. The role of an organism in a habitat is called its niche For the study of ecology it is often convenient to divide the environment into four broad categories The terrestrial environment is based on land and consists of biomes, such as grasslands, savannas, deserts, or one of several kinds of forests. The freshwater environment can be further subdivided between standing-water habitats (lakes, reservoirs) and running-water habitats(streams, rivers). The oceanic marine environment is characterized by saltwater and may be divided broadly into the shallow waters of the continental shelf composing the neritic zone and the deeper waters of the ocean that constitute the oceanic region. An environment in which two or more kinds of organisms exist together to their mutual benefit is termed a symbiotic environment a particularly important factor in describing ecosystems is that of populations consisting of numbers of a specific species occupying a specific habitat. Populations may be stable, or they may grow exponentially as a population explosion. A population explosion that is unchecked results in resource depletion, waste ccumulation, and predation culminating in an abrupt decline called a population crash. Behavior in areas such as hierarchies, territoriality, social stress, and feeding patterns plays a strong role in determining the fates of populations Two major subdivisions of modern ecology are ecosystem ecology, which views ecosystems as large units, and population ecology, which attempts to explain ece stem behavior from the properties of individual units. In practice, the two approaches are usually merged. Descriptive ecology describes the types and nature of organisms and their environment, emphasizing structures of ecosystems and communities, and dispersions and structures of populations. Functional ecology explains how things work in an ecosystem, including how populations respond to nvironmental alteration and how matter and energy move through ecosystems An understanding of ecology is essential in the management of modern industri- lized societies in ways that are compatible with environmental preservation and enhancement. Applied ecology deals with predicting the impacts of technology and development and making recommendations such that these activities will have minimum adverse impact, or even positive impact, on ecosystems 1. 5. ENERGY AND CYCLES OF ENERGY Biogeochemical cycles and virtually all other processes on Earth are driven by energy from the sun. The sun acts as a so-called blackbody radiator with an effective surface temperature of 5780 K (absolute temperature in which each unit is the same as a Celsius degree, but with zero taken at absolute zero).5 It transmits energy to Earth as electromagnetic radiation(see below) with a maximum energy flux at about 500 nanometers, which is in the visible region of the spectrum. A 1 meter C 2000 CRC Press llcfrom the viewpoints of (1) the environment and the demands it places on the organ￾isms in it or (2) organisms and how they adapt to their environmental conditions. An ecosystem consists of an assembly of mutually interacting organisms and their environment in which materials are interchanged in a largely cyclical manner. An ecosystem has physical, chemical, and biological components along with energy sources and pathways of energy and materials interchange. The environment in which a particular organism lives is called its habitat. The role of an organism in a habitat is called its niche. For the study of ecology it is often convenient to divide the environment into four broad categories. The terrestrial environment is based on land and consists of biomes, such as grasslands, savannas, deserts, or one of several kinds of forests. The freshwater environment can be further subdivided between standing-water habitats (lakes, reservoirs) and running-water habitats (streams, rivers). The oceanic marine environment is characterized by saltwater and may be divided broadly into the shallow waters of the continental shelf composing the neritic zone and the deeper waters of the ocean that constitute the oceanic region. An environment in which two or more kinds of organisms exist together to their mutual benefit is termed a symbiotic environment. A particularly important factor in describing ecosystems is that of populations consisting of numbers of a specific species occupying a specific habitat. Populations may be stable, or they may grow exponentially as a population explosion. A population explosion that is unchecked results in resource depletion, waste accumulation, and predation culminating in an abrupt decline called a population crash. Behavior in areas such as hierarchies, territoriality, social stress, and feeding patterns plays a strong role in determining the fates of populations. Two major subdivisions of modern ecology are ecosystem ecology, which views ecosystems as large units, and population ecology, which attempts to explain eco￾system behavior from the properties of individual units. In practice, the two approaches are usually merged. Descriptive ecology describes the types and nature of organisms and their environment, emphasizing structures of ecosystems and communities, and dispersions and structures of populations. Functional ecology explains how things work in an ecosystem, including how populations respond to environmental alteration and how matter and energy move through ecosystems. An understanding of ecology is essential in the management of modern industri￾alized societies in ways that are compatible with environmental preservation and enhancement. Applied ecology deals with predicting the impacts of technology and development and making recommendations such that these activities will have minimum adverse impact, or even positive impact, on ecosystems. 1.5. ENERGY AND CYCLES OF ENERGY Biogeochemical cycles and virtually all other processes on Earth are driven by energy from the sun. The sun acts as a so-called blackbody radiator with an effective surface temperature of 5780 K (absolute temperature in which each unit is the same as a Celsius degree, but with zero taken at absolute zero).5 It transmits energy to Earth as electromagnetic radiation (see below) with a maximum energy flux at about 500 nanometers, which is in the visible region of the spectrum. A 1-square-meter © 2000 CRC Press LLC