parasitism
A symbiotic relationship between individuals of two species in which one benefits and the other is negatively affected. (Chapter 10)
particulate matter (PM)
Particles or droplets small enough to remain aloft in the air for long periods of time. (Chapter 20)
passive solar technologies
Technologies that allow for the capture of solar energy (heat or light) without any electronic or mechanical assistance. (Chapter 23)
pathogen
An infectious agent that causes illness or disease. (Chapter 5)
payback time
The amount of time it would take to save enough money in operation costs to pay for the equipment. (Chapter 23)
peak oil
The moment in time when oil will reach its highest production levels and then steadily and terminally decline. (Chapter 19)
peer review
A process whereby researchers submit a report of their work to outside experts who evaluate the study’s design and results to determine whether it is of a high enough quality to publish. (Chapter 2, 3)
perennial crops
Crops that do not die at the end of the growing season but live for several years, allowing them to be harvested annually without replanting. (Chapter 17)
performance standards
Targets set that specify acceptable levels of pollution that can be released or exist in ambient (outdoor) air; industries must act to meet these standards. (Chapter 24)
persistence
The ability of a substance to remain in its original form; often expressed as the length of time it takes a substance to break down in the environment. (Chapter 3)
persistent chemicals
Chemicals that don’t readily degrade over time. (Chapter 3)
pesticide
A natural or synthetic chemical that kills or repels plant or animal pests. (Chapter 17)
pesticide resistance
The ability of a pest to withstand exposure to a given pesticide, the result of natural selection favoring the survivors of an original population that was exposed to the pesticide. (Chapter 17)
petrochemicals
Distillation products from the processing of crude oil such as fuels or industrial raw materials. (Chapter 19)
phosphorus cycle
A series of natural processes by which the nutrient phosphorus moves from rock to soil or water, to living organisms, and back to soil. (Chapter 8)
photosynthesis
The process by which plants and other autotrophs use the energy of sunlight to make energy-rich molecules using carbon dioxide and water. (Chapter 8)
photovoltaic (PV) cells
A technology that converts solar energy directly into electricity. (Chapter 23)
pioneer species
Plant species that move into an area during early stages of succession; these are often r species and may be annuals—species that live 1 year, leave behind seeds, and then die. (Chapter 10)
point source pollution
Pollution from discharge pipes (or smoke stacks) such as that from wastewater treatment plants or industrial sites. (Chapter 15, 20)
policy
A formalized plan that addresses a desired outcome or goal. (Chapter 2, 24)
policy tools
Methods that can be used to enforce or implement regulations or achieve desired outcomes. (Chapter 24)
political lobbying
Contacting elected officials in support of a particular position; some professional lobbyists are highly organized, with substantial financial backing. (Chapter 24)
pollution standards
Allowable levels of a pollutant that can be present in environmental waters or released over a certain time period. (Chapter 15)
polyculture
Farming method in which a mix of different species are grown together in one area. (Chapter 17)
population
All the individuals of a species that live in the same geographic area and are able to interact and interbreed. (Chapter 8, 9)
population density
The number of individuals per unit area. (Chapter 4, 9)
population distribution
The location and spacing of individuals within their range. (Chapter 9)
population dynamics
Changes over time in population size and composition. (Chapter 9)
population growth rate
The change in population size over time that takes into account the number of births and deaths as well as immigration and emigration numbers. (Chapter 4, 9)
population momentum
The tendency of a young population to continue to grow even after birth rates drop to “replacement fertility” (two children per couple). (Chapter 4)
positive feedback loop
Changes caused by an initial event that then accentuate that original event (for example, a warming trend gets even warmer). (Chapter 21)
potable
Clean enough for consumption. (Chapter 14)
precautionary principle
A principle that encourages acting in a way that leaves a margin of safety when there is a potential for serious harm but uncertainty about the form or magnitude of that harm. (Chapter 2, 3, 21, 24)
precipitation
Rain, snow, sleet, or any other form of water falling from the atmosphere. (Chapter 14)
predation
Species interaction in which one individual (the predator) feeds on another (the prey). (Chapter 10)
prediction
A statement that identifies what is expected to happen in a given situation. (Chapter 2)
primary air pollutants
Air pollutants released directly from both mobile sources (such as cars) and stationary sources (such as industrial and power plants). (Chapter 20)
primary sources
Sources that present new and original data or information, including novel scientific experiments or observations and firsthand accounts of any given event. (Chapter 3)
primary succession
Ecological succession that occurs in an area where no ecosystem existed before (e.g., on bare rock with no soil). (Chapter 10)
producer
An organism that captures solar energy directly and uses it to produce its own food (sugar) via photosynthesis. (Chapter 8, 10)
protected areas
Geographic spaces on land or at sea that are recognized, dedicated, and managed to achieve long-term conservation of nature. (Chapter 13)
proven reserves
A measure of the amount of a fossil fuel that is economically feasible to extract from a known deposit using current technology. (Chapter 19)
public health
The science that deals with the health of human populations. (Chapter 5)