immigration
The movement of people into a given population. (Chapter 4)
incinerators
Facilities that burn trash at high temperatures. (Chapter 7)
independent variable
The variable in an experiment that a researcher manipulates or changes to see if the change produces an effect. (Chapter 2)
indicator species
A species that is particularly vulnerable to ecosystem perturbations, and that, when we monitor it, can give us advance warning of a problem. (Chapter 10, 13)
industrial agriculture
Farming methods that rely on technology, synthetic chemical inputs, and economies of scale to increase productivity and profits. (Chapter 16, 17)
infant mortality rate
The number of infants who die in their first year of life per every 1,000 live births in that year. (Chapter 4)
infectious disease
An illness caused by an invading pathogen such as a bacterium or virus. (Chapter 5)
inferences
Conclusions we draw based on observations. (Chapter 2)
infill development
The development of empty lots within a city. (Chapter 25)
infiltration
The process of water soaking into the ground. (Chapter 14)
information literacy
The ability to find and evaluate the quality of information. (Chapter 3)
integrated pest management (IPM)
The use of a variety of methods to control a pest population, with the goal of minimizing or eliminating the use of chemical toxins. (Chapter 17)
Intergovernmental Panel on Climate Change (IPCC)
An international group of scientists that evaluates scientific studies related to climate change to thoroughly and objectively assess the data. (Chapter 21)
internal cost
A cost—such as for raw materials, manufacturing costs, labor, taxes, utilities, insurance, or rent—that is accounted for when a product or service is evaluated for pricing. (Chapter 6)
instrumental value
An object’s or species’ worth, based on its usefulness to humans. (Chapter 1, 12)
intrinsic value
An object’s or species’ worth, based on its mere existence; it has an inherent right to exist. (Chapter 1, 12)
invasive species
A non-native species (a species outside its range) whose introduction causes or is likely to cause economic or environmental harm or harm to human health. (Chapter 11)
in vitro study
Research that studies the effects of experimental treatment on cells in culture dishes rather than in intact organisms. (Chapter 3)
in vivo study
Research that studies the effects of an experimental treatment in intact organisms. (Chapter 3)
IPAT model
An equation (I = P × A × T) that measures human impact (I), based on three factors: population (P), affluence (A), and technology (T). (Chapter 6)
isotopes
Atoms that have different numbers of neutrons in their nucleus but the same number of protons. (Chapter 22)