Transcript Habitat Selection

Habitat Selection
• Animals that move freely across habitats and
exercise selectivity in their location can
influence community patterns through habitat
selection
Habitat Selection
• Habitat selection provides one possible
explanation for the conspicuous absence of
highly mobile, readily dispersing species from
an apparently suitable community
• As with most community patterns, chance
evens or exclusions caused by direct
interactions with other species produce
similar patterns
Habitat Selection
• Habitat selection can function
like a selective filter between
a developing community and
the species pool of potential
members by sorting among
species that can actively avoid
or choose to colonize a
particular place
Habitat Selection
• Those choices often depend on the kinds of
interactions that are likely to occur with other
species that are already present in the
community
• Factors that influence habitat selection
include the avoidance of physiological stress,
the availability of prey or the necessary
resources, and the avoidance of competitors
and enemies
Habitat Selection
• Animals respond to combinations of these
factors in complex ways, and there is some
evidence that some animals make relatively
sophisticated choices by weighing foraging
advantages against mortality risks in particular
sites
Habitat Selection
• Although much of the research to
date has focused on higher
vertebrates (birds), field
observations and experiments
show that even animals with
modest sensory abilities appear to
show strong preferences for
favorable habitats
Habitat Selection
• Evidence for habitat selection comes from
studies using a variety of approaches
• One approach draws on natural history
observations to associate the presence of
particular species with biotic or abiotic
features of the habitat
Habitat Selection
• Correlative studies linking the
presence/absence of organisms to habitat
features can be determined through statistical
analysis (e.g. logistic regression) or the
abundance can be modeled against multiple
habitat features (multivariate analysis)
Habitat Selection
• These are correlative as they assume the
association displayed by highly mobile
organisms is an active decision
• Others have used direct experimental
manipulation of the
factors thought to
influence habitat choice
Habitat Selection: Correlations
• The observation that some mobile organisms
are found in certain habitats and not in others
is de facto evidence for habitat selection
• Early work by MacArthur (1958) on
microhabitat use by coexisting warblers is one
of the examples of this approach
Habitat Selection: Correlations
Habitat Selection: Correlations
• There are patterns of correlation between
habitat complexity and species diversity
Habitat Selection: Correlations
• There have been more detailed studies
showing the correlation between actual
species composition of forest vegetation and
of birds (with respect to particular foraging
guilds and vegetation)
Habitat Selection
• Different groups of
birds species
responded to
aspects of variation
in plant species
composition in
northern hardwood
forest
Habitat Selection
• Wiens and Rotenberry (1981) examined avian
community structure in a simpler shrubsteppe habitat and found the community
relatively species poor and relatively weak
habitat associations
Habitat Selection: Cues and
Consequences
• Sebens (1981) documented an interesting
example of habitat selection by settling larvae
of the large Pacific sea anemone (Anthopleura
xanthogrammica)
• The adults are sessile sit-and-wait predators,
typically eating bi-valve mollusks
• Junvenile Anthopleura tend to occur
selectively in dense patches of the bivalve
mollusk Mytilus
Habitat Selection: Cues and
Consequences
• Habitat selection based upon prey availability
Habitat Selection: Cues and
Consequences
• Grosberg (9181) has experimentally shown
that several species of settling invertebrates
will discriminate among substrates based
upon density of potential competitors that
may encounter
Habitat Selection: Cues and
Consequences
• The dominant competitor in
the fouling community (MA) is
a small tunicate (Botryllus)
• It tends to overgrow and
displace many of the other
sessile species
• Grosberg coaxed different
densities of Botryllus larvae to
settle on small glass plates
Habitat Selection: Cues and
Consequences
• He then looked at how potential competitors
settled after the different Botryllus densities
were established
• One group actively discriminated against
plates with high densities (suggesting strong
ability to detect competitors) the others did
not (although consisted mostly of species able
to elevate feeding structure above Botryllus)
• Avoidance (A) or
tolerance (B) of
the competitor
Botryllus
Habitat Selection: Cues and
Consequences
• A number of species, both vertebrates and
invertebrates, appear to select against
habitats that contain predators
• Sih (1982) looked at habitat use by different
size classes of the predatory aquatic bug
Notonecta (which are cannibals)
Habitat Selection: Cues and
Consequences
• Use of different portions of the stream pools
by large and small Notonecta appears to
reflect compromises between selecting
habitats with abundant food and avoiding
cannibalistic predation by adults
• Instars 1-3 avoid adults and forage at the edge
while adults forage at the center of pools (and
upon removal, smaller instars moved to the
center)
Habitat Selection
• Site dependent
patterns of habitat
use by different
instars of Notonecta
in pools with and
without cannibalistic
adults
Habitat Selection
• Other kinds of organisms appear to make
similar ontogenetic shifts in habitat use that
depend on the presence of predators.
• Although the costs of predator avoidance
seem slight, Morin (1986) observed that
tadpoles of the spring peeper spent the first 2
weeks after hatching hidden in the bottom
litter layer of artificial ponds
Habitat Selection
• As they grew, they moved off the bottom to
forage in more conspicuous locations (but
only in ponds without predators)
• In ponds containing predators (newts), they
remained hidden at the bottom during the
entire 2 month larval period
Habitat Selection
• Holomuzki (1986) studied patterns of
microhabitat use by larvae of the tiger
salamander, Ambystoma tigrinum, in
ephermeral ponds in AZ.
Habitat Selection
• Ambystoma changed their diel patterns of
microhabitat use in ponds with an important
predator Dytiscus
• Dytiscus tend to forage
primarily at night in shallow
water; at which time
Ambystoma move into
deeper water
Habitat Selection
Habitat Selection: Conflicting Demands
• Some studies have shown that adults of some
species can detect the presence of potential
competitors and predators of their offspring
and can select sites for their offspring to
minimize some of those risks
Habitat Selection: Conflicting Demands
• Experimental manipulation
of the abundance of
potential predators and
competitors that interact
with larvae of the southern
gray tree frog Hyla
chrysoscelis
Habitat Selection: Conflicting Demands
• Using artificial small ponds, they counted the
number of calling males at ponds containing
different risks (species)
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1) no predators or competitors
2) intraspecific comp
3) intersp. Comp
4) adult salamander
5) larval salamander
6) fish
7) dragonfly larvae
Habitat Selection: Conflicting Demands
• Males avoided ponds
with conspecific larvae
or fish
• Females avoided any
predator
• Both male and female
appear to select
against
comp/predation
Habitat Selection: Conflicting Demands
• Other studies have explored the trade-offs
between opportunities for foraging and
predation risk
• Consider blue-gill sunfish; small fish forage
most efficiently in open
water on zooplankton but
are also vulnerable to
largemouth
large-mouth bass in those
same habitats
Habitat Selection: Conflicting Demands
• Consequently, small bluegills preferentially
use nearshore vegetated habitats, because
these habitats greatly reduce the risk of
predation by bass
Habitat Selection: Conflicting Demands
• Effects of +/- of
predator
(largemouth bass)
on habitat use and
growth rates
Habitat Selection
Habitat Selection