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that fish lacking pelvic girdles evolved from normal fish during this
period. The pelvic fin structures associated with the girdle also function
in courtship displays and appear to result in patterns of selective mating
among fish with and without these structures. Reimchen (1980) noted
similar variation in pelvic girdle and spines, together with its relation to
the predation regime, in the threespine stickleback in Canada.
Rapid Evolutionary Adaptation by Terrestrial
Ve r tebrate Predators
Character displacement is frequently observed on oceanic islands where
colonizations have brought close competitors together. In a few cases,
character displacement has resulted from recent colonization events. Off
the northeast coast of New Guinea, a mid-seventeenth century volcanic
explosion and caldera collapse created modern Long Island and probably
destroyed the biota of other nearby small islands.These islands have since
been recolonized by plants and animals, all arrivals being across ocean
gaps.Two honeyeaters, insectivorous and nectar-feeding birds, have estab-
lished populations on the island (Diamond et al. 1989). These closely
related species, Myzomela pammelaena and M. schlateri , occur on many
islands of the surrounding ocean but do not occur together except in the
Long Island group. Both species appear to be effective colonizers of iso-
lated islands, a species group termed “supertramps” by island biogeogra-
phers. On the Long Island group, these species show increased divergence
in body size; their weight ratio is 1.52 on Long Island compared to 1.43
in areas where they are not sympatric. Diamond et al. (1989) concluded
that the increased size difference evolved after contact on the Long Island
group and is probably related to partitioning of insect foods.
Similar rapid evolutionary adjustments to new biotic environments
can be seen in mammal invaders of oceanic islands, particularly in body
size (Case 1978; Dayan and Simberloff 1998). Yom-Tov et al. (1999)
examined relationships between morphology of various rat (kiore, Rattus
exulans ;black rat, R. rattus ; Norway rat, R. norvegicus ) and mouse (house
mouse, Mus musculus ) species on Pacific Islands, where these species had
all been introduced by humans.They found that the kiore was largest on
islands where it was the only species and smallest on islands where all four
species were present. The black rat tended to be smaller in body size on
islands where both the kiore and the house mouse were present. Norway
rats showed no difference in body size depending on the presence or
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