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| ecology | the scintific study of interactions among organisms and between organisms and their environment, or surroundings. |
| biosphere | combined portions of the planet in which all of life exists, including land, water, and air, or atmosphere. |
| species | a group of organisms so similar to one another that they can breed and produce fertile offspring. |
| populations | groups of individuals that belong to the same species and live in the same area |
| communities | assemblages of different populations that live together in a defined area. |
| ecosystem | a collection of all the organisms that live in a particular place, together with their nonliving, or physical, environment |
| biome | a group of ecosystems that have the same climate and similar dominant communities |
| autotroph | organism that can capture energy from sunlight or chemicals and use it to produce its own food from inoranic compounds; also called a producer |
| producer | organism that can capture energy from sunlight or chemicals and use it to produce its own food from inoranic compounds; also called an autotroph |
| photosynthesis | autotrophs that use light energy to power chemical reactions that convert carbon dioxide and water into oxygen and energy-rich carbohydrates such as sugars and starches |
| chemosynthesis | when organisms use chemical energy to produce carbohydrates |
| heterotrophs | organisms that rely on other organisms for their energy and food supply |
| consumers | organisms that rely on other organisms for their energy and food supply |
| herbivores | obtain energy by eating only plants. |
| carnivores | animals that eat primarily only other animals |
| omnivores | eat both plants and animals |
| detritivores | eat remains of life called detritus |
| decompsers | break down organic matter |
| food chain | a series of steps in which organisms transfer energy by eating and being eaten |
| food web | network of complex interactions formed by the feeding relationships among the various organisms in an ecosystem |
| tropic level | each step in a food chain or food web |
| ecological pyramid | diagram that shows the relative amounts of energy or matter contained within each trophic level in a food chain or food web. |
| biomass | the total amount of living tissue within a given trophic level |
| biogeochemical cycle | process in which elements, chemica compounds, and other forms of matter are passed from one organism to another and from one part of biosphere to another |
| evaporation | the process by which water changes from liquid form to an atmospheric gas |
| transpiration | the process that water can also enter the atmosphere by evaporting from the leaves of plants |
| nutrients | all the chemical substances that an organism needs to sustain life |
| nitrogen fixation | a process that converts nitrogen gas into ammonia |
| denitrification | a process where other soil bacteria convert nitrates into nitrogen gas |
| primary productivity | the rate at which organic matter is created by producers |
| limiting nutrient | when an ecosystem is limited by a single nutrient that is scarce or cycles very slowly |
| algal bloom | an immediate increase in the amount of algae and other producers that results from a large input of a limiting nutrient |
| population density | the number of individuals per unit area |
| immigration | the movement of individuals into an area |
| emigration | the movement of indiviuduals out of an area |
| exponential growth | occurs when the individuals in a population reproduce at a constant rate |
| logistic growth | occurs when a populations' growth slows or stops following a period of exponential growth |
| carrying capacity | largest number of individuals of a population that a given environment can support |
| limiting factor | a factor that causes population growth to decrease |
| density-dependant limiting factor | a limiting factor that depends on a population size |
| predator-prey relationship | mechanism of population control in which a population is regulated by predation |
| densit independent limiting factors | unusual weather, natural disasters, seasonnal cycles, and certain human activities-such as damming rivers and clear-cutting forests |
| demography | the scientific study of human populations |
| demographic transition | a dramatic change in birth and death rates |
| age structure diagrams | population profiles |
