radioactive

Atoms that spontaneously emit subatomic particles and/or energy. (Chapter 22)

radioactive half-life

The time it takes for half of the radioactive isotopes in a sample to decay to a new form. (Chapter 22)

radiative forcer

Anything that alters the balance of incoming solar radiation relative to the amount of heat that escapes out into space. (Chapter 21)

random distribution

A distribution in which individuals of a population are spread out over the environment irregularly, with no discernable pattern. (Chapter 9)

range of tolerance

The range, within upper and lower limits, of a limiting factor that allows a species to survive and reproduce. (Chapter 8)

receptor

A structure on or inside a cell that binds to a particular molecule, thus allowing the molecule to affect the cell. (Chapter 3)

reclamation

Restoring a damaged natural area to a less damaged state. (Chapter 18)

recycle

The fourth of the waste-reduction four Rs: Return items for reprocessing into new products. (Chapter 7)

reduce

The second of the waste-reduction four Rs: Make choices that allow you to use less of a resource by, for instance, purchasing durable goods that will last or can be repaired. (Chapter 7)

reduced-tillage cultivation

Planting crops in soil that is minimally disturbed and that retains some plant residue from the previous planting. (Chapter 17)

refuse

The first of the waste-reduction four Rs: Choose not to use or buy a product if you can do without it. (Chapter 7)

remediation

Restoration that focuses on the cleanup of pollution in a natural area. (Chapter 13)

renewable energy

Energy from sources that are replenished over short time scales or that are perpetually available. (Chapter 1, 23)

replacement fertility rate

The rate at which children must be born to replace those dying in the population. (Chapter 4)

reservoirs (or sinks)

Abiotic or biotic components of the environment that serve as storage places for cycling nutrients. (Chapter 8)

reservoir

Abiotic or biotic components of the environment that serve as storage places for cycling nutrients. (Chapter 8); An artificial lake formed when a river is impounded by a dam. (Chapter 14)

resilience

The ability of an ecosystem to recover when it is damaged or perturbed. (Chapter 10)

resistance factors

Things that directly (predators, disease) or indirectly (competitors) reduce population size. (Chapter 9)

resource partitioning

A strategy in which different species use different parts or aspects of a resource rather than compete directly for exactly the same resource. (Chapter 10)

restoration ecology

The science that deals with the repair of damaged or disturbed ecosystems. (Chapter 10)

reuse

The third of the waste reduction four Rs: Use a product more than once for its original purpose or for another purpose. (Chapter 7)

riparian areas

The land areas close enough to a body of water to be affected by the water’s presence (for example, areas where water-tolerant plants grow) and that affect the water itself (for example, provide shade). (Chapter 15)

risk assessment

The process of weighing the risks and benefits of a particular action in order to decide how to proceed. (Chapter 3)

r-selected species

Species that have a high biotic potential and that share other characteristics, such as short life span, early maturity, and high fecundity. (Chapter 9)