Chapter 23*Ecology and the Environment
The Organization of Ecological SystemsThe smallest living unit is the individual organism. Populations are groups of organisms of the same species.Communities are interacting groups of populations of different species.An ecosystem consists of all the interacting organisms in an area and their interaction with their abiotic surroundings.
EnvironmentEcology study of relationships between organisms and environment.Factors:Biotic livingAbiotic nonliving
EcosystemsThose organisms that trap sunlight for photosynthesis are called producers, since they produce organic material from inorganic material. They include green plants, algae, and cyanobacteria. They convert sunlight energy into the energy contained within the chemical bonds organic compounds.The organisms that obtain energy in the form of organic matter are called consumers. All animals are consumers. They either eat plants directly or eat other sources of organic matter derived from plants.Each time the energy enters a different organism it is said to enter a different trophic level. It is a step or stage in the flow of energy through an ecosystem.
Trophic LevelsPlants are producers and occupy the first trophic level.Animals that are herbivores are primary consumers and occupy the second trophic level.Animals that eat other animals are secondary consumers or carnivores. They can be subdivided into trophic levels depending on what animals they eat.Animals that eat herbivores occupy the third trophic level and are primary carnivores.Animals that feed on the primary carnivores are known as secondary carnivores and occupy the fourth trophic level.A human can eat a fish that ate a frog that ate a spider that ate an insect that consumed plants for food.The sequence of organisms feeding on one another is known as a food chain.Omnivores are animals that are both carnivores and herbivores.
Trophic LevelsIf an organism dies the energy in the organic compounds of its body is released to the environment as heat by organisms that decompose the dead body into carbon dioxide, ammonia, and other simple organic molecules. These organisms are called decomposers. Decomposers include bacteria and fungi. The simple inorganic compounds can now be used by producers to trap energy again.
Ecological systemsThe food chain
Energy Flow in EcosystemsThere is about a 90% loss of available energy as we proceed from one trophic level to the next higher level. When the energy in producers is converted to the energy of herbivores much of the energy is lost as heat to the surroundings. The same is true for all the other levels.
Energy flow in EcosystemsSun is primary source of energy for most living things.
Higher trophic levels lose ~90% of energy to space due to 2nd law of thermodynamics.
Community InteractionsFood chains are interwoven into a food web. In a community the interacting food chains usually result in a relatively stable combination of populations.Most ecosystems are not constant. As one population increases another decreases. This can occur because the there are differences in rainfall throughout the year or changes in the amount of sunlight and in the average temperature.Some communities, like tropical rainforests, have large numbers of different kinds of organisms present. Such communities have high biodiversity. Others, like tundra communities, have low biodiversity. If a specific kind of organism is eliminated form a region there is a loss of biodiversity.
Terrestrial CommunitiesTerrestrial communities are determined primarily by climatic factors of precipitation patterns and temperature ranges. They are called biomes. Biomes include:Temperate Deciduous Forest-found in parts of the world that have a lot of rainfall and cold weather for a significant part of the year. Predominant plants lose their leaves more or less completely during the year. In much of this region the natural vegetation has been removed to allow for agriculture.Grasslands or Prairie-Common in western North America and parts of Eurasia, Africa, Australia and South America. The dominant vegetation is various species of grasses. The rainfall is not adequate to support the growth of dense forests. Most have been converted to agricultural uses.Savanna-Found in tropical regions that have pronounced rainy and dry seasons. Fires during the dry seasons prevent the establishment of forests. Found in Central Africa and parts of South America. Consist of grasses with scattered trees.
Terrestrial CommunitiesDesert-Very dry areas and are found throughout the world wherever rainfall is low and irregular. Some are extremely hot and others can be quite cold during the year. Animals avoid the hottest part of the day by staying in burrows or other shaded, cooler areas. Almost no vegetation.Boreal Forest-Also known as taiga-Found in parts of southern Canada and northern US and much of northern Asia. Evergreen trees are the predominant vegetation like spruces and firs. Long, cold winters, abundant rainfall.Temperate Rainforest-The coastal areas of northern California, Oregon, Washington, British Columbia and Alaska. Ample precipitation, fertile soil and mild temperatures result in lush growth of plants like spruce and fir which are evergreens. There are trees as old as 800 years.
DesertBoreal Forestor TaigaTemperateRainforest
Terrestrial CommunitiesTundra-North of the boreal forest. Extremely long, severe winters and short, cool summers. The deeper layers of the soil are permanently frozen-permafrost. Very few plants and animals and no trees survive. Tropical Rainforests-Primarily in the equator in Central and South America, Africa, parts of southern Asia and some Pacific Islands. High temperatures, daily rain, and many species of plants.
Carbon cycle essential for the organic compounds
Nitrogen cycle essential for formation of amino acids. Often the limiting factor in terrestrial ecosystems.
Population CharacteristicsA population is a group of organisms of the same species located in the same place at the same time, like the rat population in the sewers of your city, the number of people of New York City, etc..The people of the world constitute the human population. A species is the largest population of a particular kind of organism.A population usually implies a place and a time.
PopulationsA local population is a small portion of a species and local populations of the same species will show some differences.Gene frequency is a difference that populations could show. For example, the genes for tallness in humans is greater in certain African tribes.
The allele for type B blood is not evenly distributed in the world. This map showsthat the type B allele is most common in parts of Asia and has been dispersed to the Middle East and parts of Europe and Africa. There has been very little flowof the allele to the Americas.
Age DistributionsAnother difference in population is its age distribution. If the majority of a population is prereproductive then a baby boom should be anticipated in the future. If it is reproductive then the population should be growing rapidly. If it is post reproductive then a population decline should be anticipated.Populations can also differ in their sex ratios. (female: male). The larger this ratio is the faster the population grows.
Population GrowthKenya-large prereproductive population will grow rapidly in the future. US-large reproductive population, low prereproductive. Will continue to grow for a time but will Stabilize in the future. Germany-large post reproductive. Population is beginning to fall.
The Population Growth CurveThere is a tendency for populations to grow if environmental conditions permit. The change in in population size over time is known as a population growth curve. The change in the size of a population depends on the rate at which new organisms enter the population compared to the rate at which they leave.The number of new individuals added to the populations by reproduction per thousand individuals is called natality. The number of individuals leaving the population by death per thousand individuals is called mortality.When a small number of organisms, e.g., two mice, first invade an area there is a period of time before reproduction takes place when the population remains small and relatively constant. This is called the lag phase.The exponential growth phase is when active reproduction is occurring and the mortality rate is low because the population is young.Eventually conditions such as food, water, or nesting sites will be in short supply, or predators or disease may kill many individuals. Then the number of individuals entering the population by reproduction or immigration will come to equal the number of individuals leaving it by death or migration and the population size becomes stableDuring the stable equilibrium phase there is a decrease in natality and an increase in mortality.
Population growth curveNatality added to population by reproduction
Mortality leaving population by death.First introducedNatality and mortality low.High natalityNatality equals mortality
Limiting Factors to Human Population GrowthThe curve of population growth over the past several thousand years for humans shows that the human population remained low and constant for thousands of years but has increased rapidly in the past few hundred years.
When Columbus discov