Excelsior Biology Unit 2 (Test A ONLY)

Competitive Exclusion Principle

States that no two species can occupy exactly the same niche in exactly the same habitat at exactly the same time. If that happens, one will be better at obtaining the resources and will exclude the other species.

Primary Succession

Succession that begins in an area with no remnants of an older community. This happens after extreme natural disasters such as volcanoes or retreating glaciers. The barren rock is exposed, then a series of changes occurs that eventually leads to a forest


The different types of biomes are tropical rain forest with its canopy of trees, tropical dry forest with deciduous trees, tropical grassland/savanna, desert, temperate grassland, temperate woodland, temperate forest with coniferous trees, northwest conif

Population Growth

The factors that can affect population size are birthrate, death rate, and the rate at which individuals enter or leave the population. Populations grow if more individuals are born than die in any period of time, or if the birthrate is higher than the de

Freshwater Ecosystems

Freshwater ecosystems can be divided into three main categories: rivers and streams, lakes and ponds, and freshwater wetlands.

Human Population Growth

The human population, like populations of other organisms, tends to increase. The rate of that increase has changed dramatically over time mostly dramatically reduced death rates.

The Effect of Human Activity

Humans affect regional and global environments through agriculture, development, and industry in ways that have an impact on the quality of Earth's natural resources, including soil, water, and the atmosphere. As the human population grows, it uses more a

Acid Rain

When we burn fossil fuels, we release nitrogen and sulfur compounds which combine with the water vapor in the air and eventually fall as acid rain or acid snow or fog. In some areas, acid rain kills plants by changing the chemistry of the soil and surface

Biological Magnification

Occurs if a pollutant, such as DDT, mercury, or a PCB, is picked up by an organism and is not broken down or eliminated from its body. Instead, the pollutant collects in body tissues and is passed up the food chain in higher concentrations.

Ozone Layer

Between 20 and 50 kilometers above Earth's surface, the atmosphere contains a relatively high concentration of ozone. When CFC's were used on propellants in aerosol cans and coolants, the ozone layer began to thin out, and more ultraviolet light is now ab

Greenhouse Effect

The phenomenon of the atmosphere allowing visible light to enter but trapping the heat inside. As greenhouse gas concentrations rise, they trap more heat, so Earth warms.

Heat transport in the Biosphere

The unequal distribution of heat across the globe has important effects on Earth's climate regions by creating wind and ocean currents which transport heat and moisture throughout the biosphere.


The kind of symbiotic relationship between species in which both benefit.

Succession after Human-Caused Disturbances

Ecosystems may or may not recover from extensive human-caused disturbances such as clearing and farming of tropical rain forests which can change the microclimate and soil enough to prevent regrowth of the original community.

Photic Zone

The sunlit region near the surface of water in which photosynthesis can occur. It may be as deep as 200 meters in tropical seas, but just a few meters deep or less in rivers or swamps.


The scientific study of human populations. It examines characteristics of human populations and attempts to explain how those populations will change over time.


The practice of clearing large areas of land to plant a single highly productive crop year after year. It enables efficient sowing, tending, and harvesting of crops using machines, but impacts fresh water, fertile soil, and consumes large amounts of fossi


The total of all the genetically based variation in all organisms in the biosphere. It includes ecosystem, species, and genetic diversity.

Ecological Footprints

According to one data set, the average American has an ecological footprint over four times larger than the global average. To determine this, researchers calculate the footprint for a typical citizen and then multiply that by the size of the population.