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Animal Communities. Factors that influence community composition: Species interactions History (biogeography) Physical environment Habitat/ vegetation. Species Interactions: Competition.
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Animal Communities Factors that influence community composition: • Species interactions • History (biogeography) • Physical environment • Habitat/ vegetation
Species Interactions: Competition • Tinian Monarch (above) vs. Rufous Fantail (below): two species of tropical island birds that both feed on flying insects: • On islands where both species co-occur, the more aggressive Tinian Monarch occupies the forest canopy, whereas the smaller Rufous Fantail uses the forest understory. • Where only the Rufous Fantail occurs, the species uses the entire forest profile, from canopy to understory.
Species Interactions: Mutualism • Golden White-eye (above) and Rufous Fantail (below, searching for food): these tropical forest species interact in ways that benefits both. • The larger white-eye hops along branches in search of leaf-dwelling insects. As it searches, it flushes flying insects from branches. The Rufous Fantail follows closely behind and captures the disturbed insects in mid-air. • The presence of the loudly vocal fantail alerts the white-eye to potential dangers, such as the presence of predators. Hence, both species benefit from the relationship.
Biogeography • Definition- the historical reasons behind the global distribution of plants and animals. • Example: The Eastern Mud Turtle has never colonized appreciably north of Long Island’s terminal moraine (debris hills left by melting glaciers), despite the 17,000 years that have passed since glaciers retreated from the region.
Communities I: Shorebirds of Tidal Flats Shorebirds are species that migrate along the New England coast in spring and fall, but spend the breeding season in the high arctic. They feed in tidal mud- and sand flats. The species present have differing niches. Species may differ in such niche dimensions as: the time at which they use the habitat (temporal habitat subdivision) the space they occupy (spatial habitat subdivision) the substrate (mud, sand, rocks) they use the feeding strategy they employ.
Temporal Habitat Subdivision In southern New England, the Semipalmated Sandpiper migrates primarily in late summer (August), whereas the very similar western sandpiper migrates principally in early fall (September). The Semipalmated (above) and Western sandpipers are typical fall migrants on coastal sand and gravel flats (left).
Spatial Habitat Subdivision • Vertical subdivision: The chart below shows the depth (or height) to which different species of shorebirds can probe in tidal flats for food (0 = surface). • Horizontal subdivision: Species like the stilt (right) are comparatively large, and can feed in portions of the tidal flat that have deeper water than can smaller species.
Substrate Subdivision • Different species prefer different substrates to feed in. • The Ruddy Turnstone (above right) prefers feeding from intertidal rocks. • The Red Knot (below right) prefers feeding in tidal mudflats.
Feeding Strategy • Species like the oystercatcher (above right) have specially designed beaks that permit them to open clams. • Other species like the red knot (below right) probe into tidal mudflats to find marine invertebrates. They time their spring migration to coincide with the laying of horseshoe crab eggs- a highly nutritious and abundant food.
Communities II: Forest Birds • More three-dimensional habitats like forests support many species, because many ecological niches (ways of making a living) are available to fill. • The species present have differing niches. Species may differ in such niche dimensions as: • time of habitat use • habitat space occupied • vegetation type used • feeding strategy • moisture regime (e.g. wet or dry areas) • forest successional stage
Temporal Habitat Subdivision • Species may differ in the time of day they use a habitat. • The Long-eared Owl (left) is the nocturnal version of the Cooper’s Hawk (above). Both species are forest predators.
Seasonal Changes • Species also may change their use of habitats seasonally. • In summer (above center), the Tufted Titmouse (left) is a forest generalist and occurs over most of eastern Connecticut. • In winter (above right), it moves toward coastal areas where it occupies primarily deciduous forest.
Spatial Habitat Subdivision • Species may subdivide the habitat horizontally or vertically. • The Rose-breasted Grosbeak (above right) and Gray Catbird (below right) both occupy forest gaps (openings in the forest canopy). • The grosbeak inhabits treetops, whereas the catbird inhabits understory shrubs.
Vegetation Subdivision • Species may subdivide the habitat based on vegetation type. • Both the Red-eyed Vireo (above right) and Blue-headed Vireo (below right) live in the same forests where they occupy the forest canopy (treetops). • However, the Red-eyed Vireo prefers areas where deciduous trees predominate, whereas the Blue-headed Vireo prefers areas where conifers are common.
Feeding Strategy • Species may differ in the type of food they eat, where they search for food, or in the manner in which they procure it. • Both the Ruby-throated Hummingbird (left; female) and Canada Warbler are inhabitants of the understory of forested wetlands. • The hummingbird feeds on nectar in this environment, whereas the warbler feeds on insects.
Moisture Regime • Species may choose areas with differing moisture levels. • The closely related Hermit Thrush (above right) and Veery (below right) are inhabitants of the forest floor. • The Hermit Thrush occupies dry forest, whereas the Veery occupies moist to wet areas.
Forest Successional Stage • Species may choose forests at different stages of maturity. • The Least Flycatcher (above right) occupies young forests dominated by “pole” timber. As New England forests have matured, its populations have dropped. • The Ovenbird (below right) occupies mature forest. In the mature forests that dominate the New England landscape, it is among the most abundant of species present.