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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.
Feeding Depth
15
Depth (cm)
10
5
0
-5
Yellowlegs
Plover
Sandpiper
-10
-15
Species
Dunlin
Dowitcher
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 Blueheaded 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.