Geography Reference
In-Depth Information
dif ering because of past competitive interactions; the places where they live
and nest, the foods they eat, and their morphology may all have been visited
by what community ecologist Joseph Connell calls the ghost of competition
past. When humans disrupt the barriers that evolution has put in place to re-
duce competition, the specters of competition present and future pay a visit
and shock subirdia's ecological web.
Noisy miners are indigenous Australian birds with bright yellow beaks
and black masks. They are about as big as a robin and somewhat resemble
a myna bird with scalloped gray, black, and olive plumage. Like Bewick's
wrens in Seattle, in the town of Crows Nest, Australia, noisy miners are bul-
lies. In this part of Queensland, about one hundred miles west of Brisbane,
agriculture and some urban development fracture and reduce native eucalypt
woodlands and the dense understory of shrubs. This modii cation suits the
miner well, and its abundance has increased greatly throughout eastern Aus-
tralia. A host of other woodland-dependent songbirds whose numbers have
declined are being revisited by the ghost of competition past, and it has a big
yellow beak.
Noisy miners aggressively defend their territories from other species. Pre-
sumably through evolutionary time, species excluded by miners settled in
habitats where these aggressors were rare, such as expanses of eucalypt woods
where native shrubs were dense. Urbanization and agriculture have degraded
the shrubs that many forest birds need in order to coexist with miners. Smaller
birds move more easily through the shrubs than do the larger miners, i nding
food and nesting space ample within them. Miners forage in open ground and
remain bit-part players in the bird community where shrubs predominate.
But competition is back at work in Australian suburbs, pitting miners against
birds such as the superb fairy-wren and silvereye. This time these small song-
birds have few shrubs in which to hide. Competition may force some birds to
evolve new distinctions that again remove them from the miner's tyranny.
