(1922, rev. ed. 1959), Osmotic Regulation in Aquatic
Animals(1939), and Comparative Physiology of Respi-
ratory Mechanisms(1941). He died on September 13,
1949, in Copenhagen.
krummholz Trees that grow near the tree line and
that are profoundly shaped by wind and ice, often
twisted and flaglike or stunted. Krummholzliterally
means “crooked wood.”
K-selection Natural selection, or pattern of repro-
duction, that occurs in populations at or near the car-
rying capacity (K) of a normally stable environment.
Characteristics of these populations are slow reproduc-
tion, increased longevity of individuals, delayed maturi-
tyof offspring, or reduction in the number of offspring,
with increased level of parental care. In effect, the K-
selection strategy is to ensure maximum survival of the
individual over that of reproductive capacity. A prime
example is humans.
See alsoR-SELECTION.
k-T boundary Atransitional stage in geology from
the end of the Cretaceous (k) to the beginning of the
Tertiary (T), approximately 65 million years ago. Also
pertains to a site or area showing evidence of rocks and
other materials from both periods. There is a super-
abundance of iridium and osmium isotopes typical of
meteorites in this zone, and this has led some to suggest
that the mass extinction of species including dinosaurs
was caused by a large Earth collision with asteroids or
meteorites.kuru(trembling disease) A slowly progressive and
fatal disease of the brain; a human transmissible
spongiform encephalopathy (TSE) caused by a prion.
Found in New Guinea and transmitted when people
handled and ate the brains of their dead relatives, a
cannibalistic ritual in Papua New Guinea.kuru 193