Biology, Karl Irvin Baguio [the speed reading book txt] 📗

The linear transfer of food energy from producers to consumers is known as the food chain. Many food chains intertwine in a complex manner to form a food web. Decomposers, the organisms of decay, are found at each level of food chains and food webs. The organisms of decay are usually bacteria and/or fungi.

The food pyramid is a way of expressing the availability of food in an ecosystem at a successive number of trophic levels. The number of producers, always at the base of the pyramid, is high and the number of consumers, at the top of the pyramid, is low. The difference in numbers occurs because only a small percentage of the food energy available at one level can be passed on to the next. The total dry mass of food at each level of the pyramid is called the biomass.

Another phenomenon of an ecosystem is the recycling of elements. Carbon, nitrogen, and phosphorus typify those elements that are recycled. Much of the carbon is recycled in respiration, but more is recycled in decomposition, principally by bacteria and fungi.

Nitrogen, which is vital for the synthesis of proteins and nucleic acids, is released to the atmosphere as waste by bacteria. Nitrogen is brought back into the food chain by nitrogen-fixing bacteria that exist on the roots of plants called legumes (peas, beans, alfalfa, and clover). The bacteria trap the nitrogen, form ammonium ions, and make these ions available to plants for amino-acid synthesis.

Biosphere

The biosphere is the blanket of living things that surrounds the substratum of Earth. The biosphere is composed of living organisms, as well as the physical environment. The physical environment includes the rocky material of Earth’s crust, the water on or near Earth’s surface, and the thin blanket of gas surrounding Earth. All life is confined to a five-mile vertical space around Earth’s surface.

Ecologists study the living components of the biosphere in subunits called biomes. A biome is a group of communities with stable ecosystems dominated by a particular climax community. Deserts, forests, and prairies are examples of biomes. Other examples are the tundra, taiga (the southern edge of the tundra), and temperate forests. Each biome represents a unique situation where the ecosystem is defined by the environment. The broad diversity of living things that characterizes Earth exists in the biome. Each type of living thing is adapted to its own habitat and niche within the biome. The general composition of a biome remains uniform, but local differences arise as a result of population fluctuations, floods, fire, and other ecological factors.

Populations

Ecology is the discipline of biology that is concerned primarily with the interaction between and among organisms and their environments. There are many levels of organization in the world of living things, and each level has features not displayed by any other. The important levels of organization are population, community, ecosystem, biosphere, and biome.

A population is a group of individuals belonging to one species usually occupying a defined area at a defined time. Populations of living things interact with other populations of their own kind, with populations of other species, and with physical aspects of their environment.

A population’s growth proceeds until reaching certain environmental limits. When a population has reached the maximum size that the environment can support indefinitely, assuming consistent conditions, the population is said to have reached its carrying capacity. The growth of a population cannot exceed the carrying capacity of its environment forever.

The growth of a population passes through stages. There is an initial lag period of minimal growth, followed by an exponential growth period of maximum population growth. The curbs that limit population growth may include the crowding of a population to the point that resources like food and water become scarce, an example of a density-dependent factor affecting population size. Density-dependent factors include disease, competition, predation, and territoriality. Density-independent factors that affect population size include weather-related events, for example.