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The Habitable Planet: A Systems Approach to Environmental Science 


Why are there so many living organisms on Earth, and so many different species? How do the characteristics of the nonliving environment, such as soil quality and water salinity, help determine which organisms thrive in particular areas? These questions are central to the study of ecosystems—communities of living organisms in particular places and the chemical and physical factors that influence them. Learn how scientists study ecosystems to predict how they may change over time and respond to human impacts.

Interactive Labs

Ecology Lab (Units 4, 7, 9, 13)

As you learned in Unit 4, ecosystems are a complex and delicate balancing game. The addition or removal of any species affects many other species that might compete for or provide food. In this lab you will get a chance to “build your own” ecosystem, and explore the effects of these interrelationships.launch lab




Unit 4: Ecosystems // Glossary

The increase in concentration of a chemical in organisms that reside in environments contaminated with low concentrations of various organic compounds.

Broad regional areas characterized by a distinctive climate, soil type, and biological community.

carrying capacity
The number of individuals an environment can support without significant negative impacts to the given organism and its environment.

carbon dioxide fertilization
Increased plant growth due to a higher carbon dioxide concentration.

Simultaneous evolution of two or more species of organisms that interact in significant ways.

competitive exclusion principle
The hypothesis stating that when organisms of different species compete for the same resources in the same habitat, one species will commonly be more successful in this competition and exclude the second from the habitat.

Process of reducing nitrate and nitrite, highly oxidised forms of nitrogen available for consumption by many groups of organisms, into gaseous nitrogen, which is far less accessible to life forms but makes up the bulk of our atmosphere.

fundamental niche
The full range of environmental conditions (biological and physical) under which an organism can exist.

gross primary productivity (GPP)
The rate at which an ecosystem accumulates biomass, including the energy it uses for the process of respiration.

Those species that invest more heavily in fewer offspring, each of which has a better chance of surviving to adulthood.

keystone species
A single kind of organism or a small collection of different kinds of organisms that occupy a vital ecological niche in a given location.

latitudinal biodiversity gradient
The increase in species richness or biodiversity that occurs from the poles to the tropics, often referred to as the latitudinal gradient in species diversity.

life history strategy
An organism’s allocation of energy throughout its lifetime among three competing goals: growing, surviving, and reproducing.

Evolving to appear similar to another successful species or to the environment in order to dupe predators into avoiding the mimic, or dupe prey into approaching the mimic.

Refers to an interaction between two or more distinct biological species in which members benefit from the association. Describes both symbiotic mutualism (a relationship requiring an intimate association of species in which none can carry out the same functions alone) and nonsymbiotic mutualism (a relationship between organisms that is of benefit but is not obligatory: that is, the organisms are capable of independent existence).

net primary productivity (NPP)
The rate at which new biomass accrues in an ecosystem.

niche partitioning
The process by which natural selection drives competing species into different patterns of resource use or different niches. Coexistence is obtained through the differentiation of their realized ecological niches.

nitrogen fixing
The conversion of nitrogen in the atmosphere (N2) to a reduced form (e.g., amino groups of amino acids) that can be used as a nitrogen source by organisms.

primary producers
Organisms that produce organic compounds from atmospheric or aquatic carbon dioxide, principally through the process of photosynthesis. Primary production is distinguished as either net or gross. All life on earth is directly or indirectly reliant on primary production.

realized niche
The ecological role that an organism plays when constrained by the presence of other competing species in its environment

Species with a reproductive strategy to produce many offspring, each of whom is, comparatively, less likely to survive to adulthood.

species richness
A type of approach to assessing biodiversity that examines the distribution of all resident terrestrial vertebrates: amphibians, reptiles, birds, and mammals.

A fundamental concept in ecology that refers to the more or less predictable and orderly changes in the composition or structure of an ecological community.

trophic cascades
Occur when predators in a food chain suppress the abundance of their prey, thereby releasing the next lower trophic level from predation (or herbivory if the intermediate trophic level is an herbivore). Trophic cascades may also be important for understanding the effects of removing top predators from food webs, as humans have done in many places through hunting and fishing activities.

trophic level
A feeding level within a food web.


Series Directory

The Habitable Planet: A Systems Approach to Environmental Science 


Harvard Smithsonian Center for Astrophysics in association with the Harvard University Center for the Environment. 2007.
  • Closed Captioning
  • ISBN: 1-57680-883-1