Type 1 errorThe rejection of a true null hypothesis.
Type 2 errorThe acceptance of a false null hypothesis.Unstable equilibriumThe state of a system at which forces are precisely balanced,
but away from which the system moves when displaced.VariableA characteristic or measure of the natural world that may take on any of a
number of different values.
VectorAn organism that acquires, transports, and delivers an infectious agent to
a host. Sometimes there is development or multiplication/replication of the infec-
tious agent in a vector but this is not obligatory. (See also intermediate host).Watershed(i) In North America, the drainage basin of a stream or river. (ii) In Europe
and elsewhere, the line demarcating different drainage basins.
WildlifeWild animals, usually terrestrial vertebrates whose populations are moni-
tored and managed for exploitation or conservation.XericReferring to habitats where water is in short supply to plants. (Cf. mesic.)ZoonosisA parasite occurring naturally in animals and naturally transmitted
between animals and humans.400 GLOSSARY
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