Download Theory of Habitat Selection

CHAPTER 4
Factors affecting Distribution and Abundance :
2) Habitat
Selection
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Learning Outcome
1. Define habitat
2. Acquire knowledge on selecting habitat
based on behavior mechanism
3. Describe the hierarchical decision
making
4. Explain the habitat choice in bird (Cody,
1985)
5. Explain the Theory of Habitat Selection
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Habitat selection and behaviour
• Even though some organisms can occupy
certain habitats they choose not to do
• their distribution is thus limited by their
behavior
• E.g.: Anopheles culicifacies
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Definition of Habitat
• any part of the biosphere where
a particular species can live
either
temporarily
or
permanently
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Two (2) Approaches to study
Habitat Selection
• Proximal approach– behavioral mechanism of
how animals choose habitat
• Ultimate approach – evolutionary approach –
adaptive reasons for habitat choice and
evolutionary significance of the behavior –
conferring survival value and high fitness
- e.g.: aphid
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• Habitat selection between animals
(behavioral mechanisms - choice) and
• plants (dispersal affected by chemical
and physical factors – no choice) are
different
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Mechanisms of Habitat
Selection
-Environmental gradient
-Chemical
-Behavior
-Body Size
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1. Simple Habitat Selection – Based on
Environmental Gradient
• Habitat selection for the isopod, Porcellio scaber is
dependent on moisture gradients (dry-wet)
• It moves randomly and as it finds moist air it
slows down and comes to rest
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2a. Simple Habitat Selection – Based on
Chemical cues
• Some use chemical cues to select habitats –
corn borer females, oviposit on corn
because attracted by volatile odors
(chemicals) from corn plants
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2b. Simple Habitat Selection – Based on
Chemical Cues
• Leaf beetle (Family: Coleoptera)
select their habitat on
cucurbitans (squash, melons,
cucumber) due to the chemical
cucurbitacins.
• 1500 sp. of Coleoptera also do
the same
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3. Habitat Selection Based on Behavior –
Dancing oviposit Mosquito
• Some organisms do not select a
habitat even though it is suitable
for its developing stages
• In India Anopheles culicifacies
(a malaria vector) is not found
in rice fields after the plant
grows to a height of 12 inches
(20 cm).
• These rice field supports
other Anopheles sp.
• Russel & Rao (1942) could not
find eggs of the mosquito but
when they transplanted eggs
to older rice fields, the eggs
survived and produced
normal adults
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•The absence the mosquito is due to the
selection of oviposition by females.
•Mechanical obstruction by the rice stalks
was the limiting factor – the female does
a dance before ovipositing and the rice
plants prevents this action - barrier
•In this way it restricts the species to a
habitat range less than that which it could
occupy
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Habitat selection in relation to Body
Size
•
•
i.
ii.
In desert area - larger species of rodents
(Dipodomys merriami) prefer open habitats
while smaller species (Chaetodipus
penicillatus) prefer covered/sheltered
habitats
Experimental results (Thompson 1982) show
habitat types to body size:
Larger species in open habitats have
enlarged hind legs – speedy locomotion and
well developed hearing – reduce risk of
predation
Smaller species live in sheltered habitats to
hide -reduces predation
Dipodomys merriami
Chaetodipus penicillatus
•
Habitat selection as a result of body size to
reduce predation
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Hierarchical decision making
• Habitat selection operates at the level of
the individual animal.
• Decisions are made in hierarchical manner
from a large scale to a microhabitat scale –
eg. for a migratory bird.
• Example- Hierarchical decision process by
Mexican bird
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Hierarchical
decision making
west
woodland
south
shrub
which of tree types?
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Conceptual model of the variables
that influences habitat choice.
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Hunting
behavior
Song dialect
Habitat Choice in Birds
(Cody, 1985)
Idiosyncratic
behavior
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1. Birds of prey - habitat selection
involves Perch sites
•3 species of hawks in which their habitat choice depends on their
foraging behavior – all feed on the same kind of food
i.
Swainson’s
hawk
Swainson’s hawk – open areas with less trees –are the best
at soaring and hunt from the air much more than percheswings suited for soaring and hunt from air
ii. Ferruginous hawk– open areas with less trees
– wings intermediate for soaring
Ferruginous hawk
iii. Red tailed hawk – select many perch trees or cliffs – wings
less suited for soaring - so, it will sit on perches and look for
prey
•In all 3 cases, habitat selection is tied to their hunting
behaviour/methods
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The red tailed hawk
2. Pipit – Idiosyncratic Behavior
• Pipit:
i. Tree pipit (Anthus trivialis) – found only in areas that
has trees
ii. Meadow /ground pipit (A. pratensis) – in treeless
areas
• For the tree pipit the tree is important for landing after
it sings it song while flying, but for the
meadow pipit it finishes its song on the ground
• Both have similar requirements – both feed
on the same type of organisms
• Thus the tree pipit is excluded from the habitat of
meadow pipit because it needs a perch to land after
singing. In this way their behaviour limits their range.
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3. Song Dialects
• Song birds have many dialects that distinguish
subpopulations and also influence habitat selection.
• Habitat selection in birds is partly a genetic trait but can
be modified by learning and experience
• Song birds (sparrows) in California are subdivided into
4 dialects – their habitat is homogeneous yet they have
distinct boundaries based on the dialect types
• Dialects are learned and culturally transmitted from
parent to offspring – birds mate with birds of same
dialect – thus socially determined dialect boundaries
also are genetic boundaries restricting gene flow
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shrub/wetland
Yellowthroat
forest opening
Hooded Warbler
Deciduous/conifer trees
Ovenbird
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Evolution of Habitat
Preference
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Habitat recognition
Habitat recognition may be exacting (Making great demands on
one's skill, attention, or other resources) :
• salmon returning to spawn in the same stream in
which they hatched due to olfactory cues (sense of
smell).
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Habitat recognition may be imprecise
:
(Lacking
exactness and accuracy of expression or detail)
• aphids landing on plants – taste the chemical
suitability of the plant to feed
- if suitable, it feeds
- if not found, they fly away and find suitable
plants
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• Generally organisms that have
specific
habitat
predictability
(salmon) are exacting in their habitat
selection
• While those faced with habitat
unpredictability (aphids) must adopt
more flexible habitat selection
behavior
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Theory of Habitat Selection
(Fretwell, 1972)
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Theory of Habitat Selection
(Fretwell, 1972)
1. Habitat is assumed to have a suitability for
any species.
2. Suitability = fitness = assume females produce
more offspring.
3. Suitability is not constant but affected by:
(i) food supply, shelter and predators
(ii) function of density of other individuals
and such that overcrowding reduces suitability
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Predictions of the Model
• Habitat type: good, intermediate and poor
• When sp. density is high
- good, intermediate and poor habitats would
have almost equal suitability (but different
densities of sp.)
• Individuals would be crowded in the good
habitats and at low density in the poor habitat
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Ideal Free Distribution (IFD)
• The term "ideal" means that animals are
"ideal" in their assessment of patch
quality; they know how profitable each
available patch is.
• The term "free" means that animals are
capable of moving unhindered from one
patch to another.
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Ideal Free Distribution (IFD)
• An ecological term that describes the way in which
animals distribute themselves between several patches
of resources.
• The theory states that individual animals will aggregate
in various patches proportionately to the amount of
resources available in each.
• The IFD theory predicts the distribution of animals that
compete for resources that are distributed in patches
(Fretwell, 1972 ; Fretwell and Lucas, 1970 ).
• Example: if patch A contains twice as much food as
patch B, there will be twice as many individuals foraging
in patch A as in patch B.
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Evidence for the ModelFretwell 1972,
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• Studies on yellow legged gulls – on Medes Island in
Spain (Bosch and Sol, 1998) – nest in shrubby and grassy
meadows
• Gulls prefer shrubby areas and occupy them first.
Shrubby habitats are good for nesting, where it provides
some protection (hiding places) from predators and also
shade to reduces heat stress
• Gulls in the shrubby habitats laid 2.8 eggs on average
while those from grassy areas laid 2.9 eggs
• Fitness/suitability is nearly equal in both habitats – as
predicted by Fretwell (1972). Both site can favour the
gulls to produce more offsprings
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