Transcript 14.1 Habitat And Niche

14.1 Habitat And Niche
Ecological niches
 Niches: fundamental and realized
 Principle of competitive exclusion
 Realized niche as competitive refuge
 Niche crossovers
 Character displacement
 Adaptive radiation
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Ecological niche concept
Habitat occupance =
Ecological niche =
“Where are you from?”
“What’s your address?”
“What do you do?”
“Do you eat meat?”
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Specialized habitat occupance
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Niche breadth:
generalist vs.
specialist
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Categorizing niches
Niche overlap?
Junco
Chickadee
Douglas squirrel
Deer mouse
Deer
Coyote
Cougar
Main food
source
seeds
seeds & insects
seeds
seeds
generalist/
specialist
? specialist
? generalist
? specialist
? specialist
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The principle of competitive exclusion
“Two species requiring approximately the same
resources are not likely to remain long evenly
balanced in numbers in the same habitat.”
J. Grinnell (1915)
Also known as “Gause’s principle” after mathematical
formulation by Gause in 1930.
In consequence, the loser is excluded, at least locally,
unless…
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1. There are refuges from competition;
the potential loser hangs on in marginal
habitats; or
2. The loser can re-immigrate from
elsewhere; or
3. Disturbances in the environment
prevent the winner from gaining a
complete monopoly.
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Categorizing niches:
dietary segregation amongst local granivores
Species
Habitat
Other foods?
thrush
floor
berries, insects (esp. ants
and beetles)
warbler
canopy
insects
Dusky squirrel
canopy
insects, mushrooms,
flowers, birds’ eggs
mouse
floor
insect larvae (esp. moths)
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Reducing niche overlap through
habitat segregation
upper canopy
lower canopy
shrub
floor
resource overlap?
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Fundamental
vs. realized
niche
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Flour Beetle Experiments
•
•
What’s a niche? Collective environmental factors that influence growth, survival,
and reproduction.
Tribolium beetles infest stored grain products.
– Park studied interspecific competition between T. confusum and T.
castaneum under varied environmental conditions.


Had similar fundamental niches; when
grown alone the abiotic constraints
were similar.
Growing the two species together
suggested interspecific competition
restricts the realized niches (adds
biotic influences) of both species to
fewer environmental conditions.
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Competition and Niches of Small Rodents
• Brown studied competition among rodents in Chihuahuan
Desert.
– Predicted if competition among rodents is mainly for
food, then small granivorous rodent populations would
increase in response to removal of larger granivorous
rodents.
Insectivorous rodents would show little or no response.
Results supported hypothesis.
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Competition and Niches of Small Rodents
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Niche compression
 Realized niches are narrower than
fundamental niches, therefore the
species occupies a narrower range of
habitats than it would in the absence
of competition.
 The realized niche can be regarded as
a ‘competitive refuge’.
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Determining niche compression
Natural experiments
Allopatric speciation results when a population is separated by a physical barrier (geographic speciation)
. Sympatric speciation occurs without physical separation of members of the population.
compression
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Niche compression:
barnacles on Scotland’s rocky shores
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Habitat
And
Niche
Overlap
andNiche
Competition Between
Barnacles
• Connell discovered
interspecific competition in
barnacles. Balanus plays a
role in determining lower
limit of Chthamalus within
intertidal zone.
– Did not account for all
observed patterns.
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Sedge niches: Fraser delta
high tide
low
tide
Daily
Inundation
Rare
H1: realized = fundamental
Daily
Inundation
Rare
H2: Scirpus occupies refuge
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Determining niche compression
A. Field experiments: reciprocal transplants
high
tide
low
tide
Two-year transplant experiment was
inconclusive. Both species grew well
in other species zone.
(Mike Pidwirny)
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Dominance hierarchy
dominant sp.
subdominant sp.
in the absence of competition
resource gradient
A
B
C
with competition
refuge exclusion refuge
zone
resource gradient
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Character displacement
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Character
Displacement
= evolution of niche
divergence by
competition
•
•
•
The degree of competition is assumed
to depend upon degree of niche
overlap,
Interspecific competition has been
predicted to lead to directional selection
for reduced niche overlap.
Galapagos finch size versus seed size.
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Galapagos Finch Character
allopatric Displacement
sympatric
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Character Displacement
• Taper and Case: Necessary criteria for C.D.:
– Morphological differences between sympatric
populations are statistically greater than differences
between allopatric populations.
– Differences between sympatric and allopatric
populations have genetic basis.
– Differences between sympatric and allopatric
populations evolved in place, and are not derived from
different founder groups already differing in the
character.
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Taper and Case: Characteristics
– Variation in the character must have a known effect on
use of resources.
– Must be demonstrated competition for the resource
and competition must be directly correlated with
character similarity.
– Differences in character cannot be explained by
differences in resources available to each of the
populations.
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Placental mammals
Does evolution fill a finite
number of jobs?
(e.g. community wants
burrower?)
Is there a restricted
“guild”?
Australian marsupials
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“woodpecker” “nectar-feeder”
Hawaiian honeycreepers:
seed-eating finch evolves into vacant niches?
http://biology.swau.edu/faculty/petr/ftphotos/hawaii/postcards/birds/
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Galapagos finches: opportunistic evolution
Source: Lack, D. 1966. Darwin’s Finches. Harper, N.Y.
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Parallel (or convergent)
evolution
of animals inhabiting
African (right) and S.
American (left) tropical
forest
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Island invasions and community saturation: plants
New Zealand
~2000 native plants
~2000 naturalized aliens
3 natives extinct
California
~5000 native plants
~1000 naturalized aliens
<30 natives extinct
Brown, JH and Sax, DF 2004. Austral Ecology 29, 530-536.
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Island invasions and community saturation: fish
Hawaii
5 native freshwater fish species
40 naturalized aliens
no extinctions
124 watersheds in temperate
North America
Fish diversity increased in 100; declined in 20
Brown, JH and Sax, DF 2004. Austral Ecology 29, 530-536.
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What is a “community”?*
An ecological (or biological) community refers
to a group of interacting organisms living
together in a specific geographical area or
habitat.
An equivalent (and now somewhat
anachronistic) term is biocenosis (proposed
by Karl Möbius in 1877 to describe the
interacting organisms of the oyster- and
mussel-bearing tidal flats of the North Sea).
*or is it a “commutiny”?
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Community structure
 Closed vs. open communities
 Ecotones (community boundaries)
 The continuum concept
 Biogeoclimatic zones
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Are communities closed, or open?
*community
named after
dominant(s):
e.g. Douglas
fir, hemlockcedar.
*
*
*
E = ecotone
fidelity?
= a continuum?
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Characteristics of open and closed communities
Early proponent
OPEN
H.A. Gleason
CLOSED
F.E. Clements
Organization
Individualistic
Holistic
Boundaries
Diffuse
Distinct
Species ranges
Independent
Coincident
Coevolution
Uncommon
Prominent
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Terrestrial biomes
(plants and animals)
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KEY CONCEPT
Every organism has a habitat and a niche.
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Objectives
• Differentiate between a habitat and a niche
• Differentiate between competitive exclusion and
ecological equivalents
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A habitat differs from a niche.
• A habitat is all aspects of the area in which an organism
lives.
– biotic factors
– abiotic factors
• An ecological niche
includes all of the
factors that a
species needs to
survive, stay healthy,
and reproduce.
– food
– abiotic conditions
– behavior
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Resource availability gives structure to a community.
• Species can share habitats and resources.
• Competition occurs when two species use resources in the
same way.
• Competitive exclusion keeps two species from occupying
the same niche.
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• Competitive exclusion has different outcomes.
– One species is better suited to the niche and the other
will either be pushed out or become extinct.
– The niche will be divided.
– The two species will further diverge.
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• Ecological equivalents are species that occupy similar
niches but live in different geographical regions.
Madagascar
South America
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What are the 3 parts of an organisms ecological niche?
• Food type
• Abiotic conditions
• Behavior
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What does the principle Competitive Exclusion say will
happen when 2 species compete for the same resource?
• One species will be better suited to the niche, and the
other species will either be pushed into another niche or
become extinct
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If a group of mantella frogs were transported to the
ecosystem of the poison dart frogs, what might happen
to the 2 species populations?
• As ecological equivalents, they share a similar niche.
• The population better suited to the niche might deprive
the other of resources, causing the other to die off.
OR
• One population might respond to limitted resources by
altering its niche.
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A bison and an elk live in the same habitat and feed on
the same grasses. Does this mean that the competitive
exclusion principle does not apply? Expleain.
• The competitive exclusion principle only applies if the 2
species live in the same habitat AND occupy the same
niche
• A niche includes
– Food type
– Abiotic conditions
– Behavior
• These two species use the same food resource but
occupy different niches
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Considering the competitive exclusion principle, why
may it be harmful to transport a species such as a
rabbit, to another habitat where it currently does not
exist?
• If a new species is introduced to an area, it may occupy a
similar niche as a native species and be better adapted
for the niche to have no natural predators.
• This could drive the native species to extinction
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KEY CONCEPT
Organisms interact as individuals and as populations.
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Objectives
• Compare & Contrast interspecfic and intraspecific
competition
• Describe the 3 types of symbiosis
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Competition and predation are two important ways in
which organisms interact.
• Competition occurs when two organisms fight for the
same limited resource.
– Intraspecific
competition
– Interspecific
competition
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• Predation occurs when one organism captures and eats
another.
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• There are three major types of symbiotic relationships.
– Mutualism: both organisms benefit
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• There are three major types of symbiotic relationships.
– Commensalism: one organism benefits, the other is
unharmed
Ø
Human Our eyelashes
are home to tiny mites
that feast on oil
secretions and dead
skin. Without harming
us, up to 20 mites may
be living in one eyelash
follicle.
Commensalism
Ø Organism is not affected
+
+
Organism benefits
Demodicids Eyelash
mites find all they need to
survive in the tiny follicles
of eyelashes. Magnified
here 225 times, these
creatures measure 0.4
mm in length and can be
seen only with a
microscope.
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• There are three major types of symbiotic relationships.
– Parasitism: one organism benefits, the other is harmed
0
Parasitism
+
_
Hornworm
caterpillar
The host hornworm
will eventually die as
its organs are
consumed
by wasp larvae.
_
Organism is not affected
0
Braconid
wasp
Braconid larvae
feed on their
host and
release
themselves
shortly before
reaching
the pupae
stage of
development.
Organism benefits
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• There are three major types of symbiotic relationships.
– Parasitism meet their needs as ectoparasites (such
as leeches) and endopaasites (such as hookworms)
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During the fall spawning of salmon, grizzly bears fight
over space on the banks of a river. What type of
competition is this?
• The bears are fighting amongst themselves so it is
considered intraspecific competition
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Describe and give an example of the 3 types of
symbiosis
• Mutualism
+/+
• Commensalism +/0
• Parasitism
+/-
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How are predation & parasitism similar? How do they
differ?
• Predation & parasitism are both relationships in which
one organism benefits while the other is harmed.
• In predation, the predator needs to kill its prey in order to
benefit
• In parasitism, the parasite benefits by keeping its host
alive
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After a lion has made a kill birds will sometimes arrive to
pick at the carcass. The birds would be considered
_________(A)_________________ while the lions would
be considered _________(B)_____________________
• A) Scavengers
• B) Predators
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KEY CONCEPT
Each population has a density, a dispersion, and a
reproductive strategy.
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Objectives
• Consider density and geographic dispersal as
characteristics of populations
• Describe 3 basic types of survivorship curves in relation
to reproductive strategies.
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Population density is the number of individuals that live
in a defined area.
• Population density is a measurement of the number of
individuals living in a defined space.
• Scientists can calculate population density.
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Geographic dispersion of a population shows how
individuals in a population are spaced.
• Population dispersion refers to
how a population is spread in
Clumped
an area.
dispersion
Uniform
dispersion
Random
dispersion
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• There are three types of dispersion.
– clumped
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• There are three types of dispersion.
– uniform
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• There are three types of dispersion.
– random
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Survivorship curves help to describe the reproductive
strategy of a species.
• A survivorship curve is a diagram showing the number of
surviving members over time from a measured set of births.
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• Survivorship curves can be type I, II or III.
– Type I—low level of infant mortality and an older
population
– common to large mammals and humans
– Type II—survivorship rate is equal at all stages of life
– common to birds
and reptiles
– Type III—very
high birth rate,
very high infant
mortality
– common to
invertebrates
and plants
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An Organism has 10 offspring. Two of these offspring
die each year over a 5 year period. Is this organism
more likely to be a bird or insect? Explain.
• The organism is a bird because the mortality pattern
described is closest to type II.
• Insects tend to be type III, with many offspring and high
mortality early in life stages
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KEY CONCEPT
Populations grow in predictable patterns.
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Objectives
• Describe 4 characteristics that affect population size
• Compare exponential and logistic population growth
• Identify factors that limit population growth
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Changes in a population’s size are determined by
immigration, births, emigration, and deaths.
• The size of a population
is always changing.
• Four factors affect the
size of a population.
– immigration
– births
– emigration
– deaths
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Population growth is based on available resources.
• Exponential growth is a rapid population increase due to an
abundance of resources.
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• Logistic growth is due to a population facing limited
resources.
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• Carrying capacity is the maximum number of individuals in
a population that the environment can support.
• A population crash is a dramatic decline in the size of a
population over a short period of time.
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Ecological factors limit population growth.
• A limiting factor is something that keeps the size of a
population down.
• Density-dependent limiting factors are affected by the
number of individuals in a given area.
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• Density-dependent limiting factors are affected by the
number of individuals in a given area.
– predation
– competition
– parasitism
and disease
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• Density-independent limiting factors limit a population’s
growth regardless of the density.
– unusual weather
– natural disasters
– human activities
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What 4 factors determine the growth rate of a
population?
• Immigration
• Births
• Deaths
• Emigration
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How does carrying capacity affect the size of a
population?
• Carrying capacity limits the size of a population
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Habitat
And Niche
is the main difference between a densitydependant limiting factor and a density-independent
limiting factor? Give an example of each.
Density-Dependant
• A density dependant
limiting fact is affected by
the number of individuals
in a given area
– These are usually BIOTIC
limiting facto=rs such as
Predation
Competition
Disease
Density-Independant
• A density independent
limiting factor is not
affected by population
size/density
– These are usually ABIOTIC
limiting factors such as
Weather
Forrest fires
Natural disasters
Human activities
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What might cause exponential growth to occur only for
a short period when a new species is introduced to a
resource filled environment.
• Eventually, the growing population will consume all the
resources, and the species may experience a population
crash.
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Give an example of how a symbiotic relationship could
cause a population to crash.
• If a parasite or disease spreads in a dense population, it
could cause a population to decline dramatically over a
short period of time.
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KEY CONCEPT
Ecological succession is a process of change in the
species that make up a community.
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Objectives
• Describe the process of primary succession
• Explain the difference between primary and secondary
seuccession
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Succession occurs following a disturbance in an
ecosystem.
• Succession regenerates or creates a community after a
disturbance.
– a sequence of biotic changes
– damaged communities are regenerated
– new communities arise in previously uninhabited areas
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• There are two types of succession.
– primary succession — started by pioneer species
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• There are two types of succession.
– secondary succession — started by remaining species
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How is primary succession different from secondary
succession?
• Primary succession begins with barren rock, worn down
and colonized with a pioneer species
• Secondary succession begins with established soil in
which many different plants can grow
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Why are pioneer species so important for primary
succession?
• Pioneer species such as mosses and lichens can break
down rock into smaller pieces.
• When they die, their remains may mix with the pieces of
rock forming a thin layer of soil
• They change the ecosystem in ways that enable the
support of more diverse species
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Does the process of primary succession take longer in
the tropical or arctic areas? Explain.
• Primary succession takes longer in arctic areas because
– rock is covered in snow part of the year
– the growing season is shorter
– and cold temperatures slow growth and decomposition
• Soil takes much longer to form.
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Which reaches a climax community 1st, an area
undergoing primary or secondary succession? Explain
• Secondary succession takes less time to reach a stable
climax community because the soil is already there
• In primary succession there is no soil and so it will take
longer to reach a climax community
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During succession, what might be the limiting factor for
sun-loving mosses as taller plants begin to grow?
• The amount of sunlight that reaches them
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At what point during primary succession does an
ecosystem provide the fewest habitats for an organism?
Explain.
• There are no habitable areas in the earliest stages of
succession because there is no soil to support
producers..
• Land becomes habitable once rock has weathered
enough to support mosses and lichens
• Over time mosses and lichens will provide the resources
needed to support other organisms
14.1 Habitat And Niche
Redwood forest niches
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Competitive ‘release’ or are niches and habitat occupancy moreor-less fixed?
NB: hypothetical !