Transcript What is a Community? - Midlands State University

Introduction to Ecology
Midlands State University
Session 3 – Community Ecology
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Why is This Field Important?
• Useful for conserving entire communities
• Repopulating barren lands
• Determining most important species to
conserve
• Predicting how communities will recover,
after disturbance
• Predicting community resilience to
disturbance
• Quantifying what is present for
conservation and where it would be
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Community Definition
• “an association of
interacting populations,
usually defined by the
nature of their
associations or the habitat
they use”
• Key features:
– Several species
– One area
What is a Community?
A community is any assemblage of
populations in an area or habitat.
Communities differ dramatically in their
species richness and relative abundance.
- species richness: number of species
contained
- relative abundance: number of different
species
What is a Community?
Individualistic hypothesis: a community is a
chance assemblage of species found in
the same area because they have similar
abiotic requirements.
Interactive hypothesis: assemblage of
closely linked species, locked into
association by biotic interactions.
What is a Community?
Interspecific Interactions
and Community Structure
Interspecific interactions: interactions
belonging between populations of
different species under one community
Competition
Interspecific competition for resources can
occur when resources are in short supply
What Structures a
Community?
• Abiotic
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Climate
Latitude
Proximity to Ocean
Disturbances (abiotic)
• Biotic
– Interspecific Interactions
• Keystone Species
– Disturbances (biotic)
– (Intraspecific Interactions?)
Interspecific Interactions
and Community Structure
Interspecific interactions: interactions
belonging between populations of
different species under one community
Competition
Interspecific competition for resources can
occur when resources are in short supply
Interspecific Interactions
Interspecific Interactions
and Community Structure
Parasitism is the symbiotic interaction in
which the parasite derives its nourishment
from the host
- commensalism: interaction that
benefits only one of the species involved
in the interaction
Interspecific Interactions
Mutualism
Interspecific Interactions
Interspecific Interactions
and Community Structure
Predation
- includes the killing of one animal by
another, herbivory, and parasitism
- predator adaptations
- plant defenses against herbivores
- animal defenses against predators
+ / - = more than just predation
 Species #1 / Species #2 = Interaction
+/ 0
= Commensalism
+/ +
= Mutualism
+/ –
= Parasitism (particularly w/o host death)
+/ –
= Herbivory (eating of parts of plant)
+/––
= Parasitoidism (host killed by larvae)
+/––
= Predation (prey killed by predator)
utrient Deficiencies (plants
echanical Deficiencies (plants
Production of Poisons
Mechanical Defenses (animals)
Running Away and Hiding
Fighting Back
Cryptic Coloration
Cryptic Coloration
Coevolution
 Coevolution represents the evolutionary modification of
organisms in response to other organisms, particularly when
two organisms are mutually modified in response to
modifications displayed by the other.
 "Despite the problems in assessing cause and effect in the
evolution of complex ecological relationships, biologists agree
that the adaptation of organisms to other species in a
community is a fundamental characteristic of life. Put another
way, interactions of species in ecological time often translate
into adaptations over evolutionary time.“
 Strictly, coevolutionary relations may be limited to interactions
between two species rather than modifications that affect a
suite of species; for example, an ability to run faster in order to
escape predators is not quite the same thing as an ability to
run faster in order to escape one predator species (which, if it
wants a meal, would then be exposed to selection to run even
faster).
 This narrowing limits the applicability of the idea of coevolution
since it creates a criteria that is stricter then simply more
effectively interacting with other species in terms of survival
and reproduction.
Parasite-Host Coevolution
Interspecific Interactions
and Community Structure
- aposematic
coloration: animals
with effective
chemical defenses
are brightly
colored to act as a
warning
Aposematic (warning)
Coloration
Interspecific Interactions
and Community Structure
- batesian mimicry:
a species of prey
will gain protection
through mimicry
Batesian Mimicry
Müllerian Mimicry
Interspecific Interactions
Interspecific Competition
•An interaction between members of two or more species that, as a consequence either of
exploitation of a shared resource or of interference related to that resource, has a negative
effect on fitness-related characteristics of at least one of the species (Wiens 1989).
•Often these competitive effects have population consequences as well.
•Exploitation (scramble) competition: individuals have free access to resources and use of
those resources by some individuals diminishes their availability to other individuals.
•Interference (contest) competition: Some individuals are denied access to resources by the
(often aggressive) actions of others. Usually incorporates a spatial component.
•Intensity of competition is the proximate, physiological, behavioral effect on individuals.
•Importance of competition is the ecological or evolutionary consequences of those effects.
Defense against – / –
Interference Competition
 Fighting back
 Running away
 Avoidance
 Losing
Exploitative Competition
 Competitive exclusion
 Resource partitioning
 Character displacement
Fundamental vs. Realized Niche
Interspecific Interactions
and Community Structure
Gause’s Competitive exclusion principle:
- two species are so similar that they
compete for the same limiting resources
- one will use the resources more
efficiently and reproduce more
- this will lead to local elimination of the
competitor
Competitive Exclusion
Interspecific Interactions
and Community Structure
Resources partitioning:
- species will evolve to use a different set
of resources
- leads to a differentiation of niches
Resource Partitioning
Character displacementCharacter displacement- Brown and Wilson (1956)
 Two overlaping species with overlapping ranges
 Parts of the range where one species occur alone , populations of
that species is similar to the other species and may be diffiicult to
distinguish from it
 In the area of overlap, where to species occur together, the
population are more divergent and easily distinguished i.e , they
“displace” one onether in one or more charactersics
 These charactersics involved can be
morphological,ecological,behavioral,or physiological; they are
assumed to be genetically based
Character displacementIt has two adaptive values
• Enhances niches displacement thus reducing competetion
• Enhances genetic segregation by maintaining species
distinctiveness (i.e. , preventing hybridization) and thereby maintains
a greater species diversity in the community (than would be the case
if one species eliminated the other, or if they hybridized into one
species)
Character displacement
Dual nature of this pattern show character displacement when:
• Species that occur in different geography regions or separated by
a spatial barrier- allopatric
• Species occurring in the same area but not necessarily the same
niche are said to sympatric
Character displacementExamples and Explanation
• Brown and Wilson (1956) -2 species of nuthatches (Sitta)
• Where the 2 species are allopatric- each is similar to the other-can
only be distinguished by a bird taxonomist
• Sympatric- striking divergence in morphology-distinguished at a
glance- in one species the bill and black facial stripe become
enlarged, whilst reduced in the other
• Accentuated difference in bill size reduces food niche overlap
• Conspicuous difference in facial stripe enhances species
recognition and prevents interbreeding-cut down on energy wasted
in unsuccessful and unfruitful mating with wrong species
Character displacementDarwin’s finches on Galapagos islands
• Two species of ground finches (Geospiza) occurring together on
the larger , differ in body size and beak proportions
• On some smaller one or the other species may occur alone , in
which case each species is almost exactly intermediate in size and bill
configuration ( so much so that they were to be hybrids)
• Thus, each allopatric species converged towards the other, partially
filling, as it were, the other niche
• MacAthur and Levins (1967) suggested that character
convergence instead of displacement, might occur when a third
competing species invades the territory occupied by two species
already competing in overlapping niches
Character Displacement
Natural selection: allopatric and sympatric speciation
• Species- natural biological unit tied together by sharing of common
gene pool
• Speciation-formation of new species and development of species
diversity, occurs when gene flow within the common is interpreted by
an isolated mechanism
– Allopatric speciation -isolation occurs through geographic separation of
populations descended from common ancestor
– Sympatric spepiation- isolation occurs through ecological or genetic means
within the same area
Natural selection: allopatric and
sympatric speciation
• Allopatric speciation-generally assumed to be primary mechanism
by which species arise
– Two interbreeding population become separated spatially (as
on an island or separated by a mountain range)
– In time sufficient genetic differences accumulate in isolation so
that the segments will not interchnage genes (interbreed) when
they come together again, they co-exist asdistinct species in
different niches or perhaps these differences are further
accentuated by additional process of character displacement
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Galapagos islands-classic example of allopatric speciation
From a common ancestry a whole group of species evolved in isolation on the on the
different islands and adatively radiated so that a variety of potential niches was
eventually on re-invasion
Species available include; slender-billed insect eaters, ground and tree feeders, and
thick billled seed eaters, ground and tree feeders, large and small bodied finches,
wood pecker finch
Natural selection: allopatric and
sympatric speciation
• Sympatric speciation-more wide spread and important as previous
believed
• Demonstrated in higher plants- genetic isolation mechanism such as
polyploidy(duplication of chromosomes sets), hybrization, self
fertilization, and asexual reproduction
• E.g great salt invasion of Britain- geographical breakdown caused
by man- followed by hybridization and polyploidy
• Spartana alterniflora was introduced and it cross breeed
S.maritima to produce a polyploidy species S.townsendii
Interspecific Interactions
and Community Structure
Ecological niche
- sum total of a species’ use of biotic and
abiotic resources in its environment
- how a species “fits into” an ecosystem
- where it is and what it does
-defn- main unit of ecological distribution
within which the species is restricted by its
own structural and behavioural limitations
Interspecific Interactions
and Community Structure
Ecological niche
- Multidimensional volume with which viable population can be
maintened (Hutchison, 1958)
The volume can be defined in terms of:
• Conditions- abiotic factors- Temprature, Humidity, Ph
• Resources- Biotic limits; quantity and quality of feed, availability of
mating partners
• - Various conditions and resources which affect the organisms or
populations resulting in the multi-dimensional nature of ecological
niche
• -Niche- defined by many factors
– Specialist organism narrower niches compared to generalist
Niches
• Definition?
• 1. The ecological
role played by a
species in a
community
• 2. An n-dimensional
hypervolume
– Huh?
Niche =
N-dimensional Hypervolume
• Dimensions are the
limiting factors
pH
• pH, soil type,
humidity, temperature,
nesting space, mates,
parasites, etc.
• Niche use determines
community formation
pH
temperature
Niche concept
Fundamental niche- includes the total range of environmental
conditions and resources that are suitable without influence of
interspecific competition or predation from other species
-species express potential
Realised niche- limited conditions and resources
-Maintain viable populations
-presecnce of competitors
Niches and resource partitioning
•Niche: environmental factors that influence the growth, survival, and reproduction of a
species
•Niche theory has focused on resource partitioning, niche overlap and competition among
species in communities.
(from Wiens 1989)
•Gause’s competitive exclusion principle states that ecologically similar species
using shared limiting resources cannot coexist at equilibrium
Fundamental & Realized
Niches
Interspecific Interactions
Types of Interspecific Interactions
No interaction
Allelopathy
Commensalism
Mutualism
Competition
Predation
Parasitism
Species 1
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Species 2
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– sharp boundaries
– abrupt ecotones
– distinct associations
between species
• Open
– boundaries are vague,
gradual
– little or no association
between species
abundance
• Closed
abundance
General Types of
Communities
Abundance of
a single species
geographic range
geographic range
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Island Biogeography
• : “Equilibrium Theory of Island
Biogeography” Full Title
• Assertions re: # species:
– Near > Far
– Bigger > Smaller
– There is an equilibrial number of
species
• Advocates for CAR?
Island Biogeography Research
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Florida Keys - mangrove islands
Gassed several islands to kill all insects on mangroves
Observed return rates of species
Counted number and trophic type
Occurred in early 1970’s
Island Biogeography Results
• Size of Island (longhorn beetles)
– Species-Area
Relationship
• Equilibrial
Theory (insects)
Island Biogeography
Conclusions
• Supported main assertions
• Assertions re: # species:
– Near > Far
– Bigger > Smaller
– There is an equilibrial number of
species
• Spawned a great deal of
additional research by many others
– One of two main proponents
(Simberloff) no longer agrees with
equilibrial assertion
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species –before-PRACT
HANDOUT
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Keystone Species
• The most important species
– Structures the community
• Contributes greatest amount to ecosystem
functioning
– Controlling herbivores
• Terminal Predators are most commonly thought of here
– Decomposition
– Produces greatest amount of biomass?
Keystone Species
• Usually thought of as Strong interactors
– Tightly woven into the fabric of the food web
– The species that is the very strongest
interactor
• Definition #2:
– The species that, when removed, leads to a
total breakdown of the food web
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Succesion
• Ordely and progressive sequence of
replacment of one community by another
on an area until a relatively stable
community often called a climax occupies
the area (Clementsian model, F.E
Clements, 1916)
Succession Types
Primary succession
• New habitat from barren ground e.g. lava and ash from volcanic
eruptions
• No previous vegetation, no seeds, organic matter from prior
vegetation
• Seeds from other areas colonize the new substrate there by
initating vegetation changes
• Begins with colonization and establishment of pioneer species.
water-submerged aquatic plants
Floating aquatic plants
Reed Swamp
Sedge meadow
Woodlands
Rockcrutose lichen
Foliose lichen
Mosses
Herbaceous plants
Shrubs
Climatic forest
Hydrosere
Very wet
Mesosere
Moderate conditions
Typical primary succession from a rock and a body water
Xerosere
Very dry
Succession Definitions
• Chronological
distribution of
organisms within an
area
• The sequence of
species within a
habitat or community
through time
• Shared:
– Time
– Single area
Succession Types – by Habitat
• Primary
– New habitat from
barren ground
•Secondary
–Modified habitat in already
areas with biotic growth
Secondary succesion
Replacement of pre-existing vegetation,
disturbance that disrupts vegetation
composition and functioning
-well developed soil and a biological legacy
Sucession
• End of succession is called climax
• This due to:
- Climatic limitations- climax climaxes e.g. Brachystegia woodland
-Soil limitations- edaphic climaxes e.g. Somabhula grasslands-raised
water table preventing trees from growing
- Sporobolus ioclados- sodic soils
- Fire limitations- pyric climaxes e.g nyanga where fire keeps natural
vegetation (forest) from re-establishing itself
- Man’s activities- anthropogenic climaxes- change in vegetation at
Nyanga following settlement
Succession Types – by Process
• Degradative
– Consumption of a finite resource
Succesion may be progressive and move towards
climax conditions due to:
• Allogenic
– Requires ongoing extrinsic environmental changesother factors not due to plants
• Autogenic
– Intrinsic factors within the community-factors due
to plants
Allogenic factors
• Other factors not due to plants
Allogenic factors may cause succesion to
be retrogressive
Still debatable wther this constitutes a
sucession
Six stages to classical vegetation development (Clements,
1916)
First three stages constitute invasion
1. Migration-movement of germplasm into an area from out side-wind,
animals, man, water
2. Ecesis –establishment of plants from germplasm
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Germination,establishment,growth, reproduction
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Eventually results in mixed composition of vegetation
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For limiting resource-light, water, nutrients, space
Aggregation-establishment of daughter plants around parent
germplasm
Composition (same or different species)
Biotic reaction-effect of living organism on their environment
Stabilisation-plants of different species within the community are
able to co-exist with one another in a balance
Alternatives to the classical succesion model
Critism againist Clements’s model
• Assumed vegetation changes
– Climatic climax, regardless of other factors e.g. soil
• Viewed succesion as a highly orderly, unidirectional and predictable
process
– Absolute stability or lack of change in species composition is
unlikely
TANSLEY 1935
o Polyclimax theory
o Climax vegetation- mosaic vegetation climaxes contolled
by soil moisture, soil nutrients, topography, fire,slope
exposure, animal activity
Alternatives to the classical succesion model
Connell and Slatyer (1977)
• 3 different models of plant succession
• Facilitation,inhibition, tolerance
– Facilitation model
• Clementsian approach-succession autogenic
• Early stage species modify environment and prepare site
for late stage species-facilities their success
– Inhibition model
• No species is competively superior to the other
• Ultimate winners-long lived plants even though early later
stage species for a long time
• Sucession-not ordely and less predictable
Alternatives to the classical succesion model
Tolerance model
• Intermediate between facilitation and inhibition
• Later succesional species are neither inhibited nor aided by species
of earlier stages
Other alternate theory of sucession
State and Transitional model-Westoby et al, (1989)
• Multi-directional changes in community composition rather than unidirectional changes only
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Transition or process bring about change in the vegetation community
Community-several end results or states
Examples of transitions-overgrazing moderate grazing, light grazing, drought
Possibilty many climaxes depending on biotic and abiotic factor
Alternatives to the classical succesion model
The shifting mosaic steady state model
-rather than achieveing equilibrium, forest vegetation, achieves a statestanding crop (total biomass-living+ dead) flactuates about a mean
Disturbance
-force, agent or process-biotic or abiotic that causes a change in part
or all of a system
-agents of change
-examples-fire, landslides, drought,floods, herbivory
Species diversity
Intermediate disturbance hypothesis
Low disturbance
High disturbance
Frequent
Infrequent
Intermediate disturbance hypothesis of community
organisation
Species composition of a community is seldom in a
state of equilibrium, and high species diversity can
be maintained only at intermediate levels of
disturbance such as fires or windstorms
Intermediate disturbance hypothesis of community
organization
• Most probable mechanism for non equilibrium hypothesis is the IDH
(Cornell, 1978)
• Highest diversity is maintained at intermediate levels of disturbance
• Rationale-at high levels of disturbance e.g when envr variable are
extreme—(lo or hi temp, low rainfall, high wind, high frequency of
fire etc), only good colonists- r-selected species will survive, giving
rise to low diversity
• This gives rise to low diversity- theory predicts, at low rates of
disturbance, competitively dominant species will out compete all other
species and only a few k-selected species will persit again giving low
diversity
• Most diverse lie some somewhere in between
Intermediate disturbance hypothesis of community
organization
• Natural communities seem to fit well into this model e.g tropical rainforest
and coral reefs are both examples of communities with high species diversity
– Coralreefs maintans high species diversity in areas disturbed by hurricanes (Cornell,1978)
– Richest tropical forest occur where disturbance by storm or people has occurred
(Cornell,1978)
• Riece (1994)-disturbances operates in habitats of all types-naturally disturbed
areas nearly always more diverse than undisturbed areas.
• Sousa (1978)-provided elegant verification of IDH in marin intertidal
situation
– Small boulders-easily disturbed by waves•
Mean 1.7 species of sessile plants and animals
– Large boulders-rarely moved by waves
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2.5 mean of species
– Intermediate sized boulders
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3.7 species
Applications of Succession
• Can you think of any?
• Examples:
–Gauging timber harvests or fisheries harvests
–Dating deposits (bog people)
–Forensic Entomology
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Measuring Biodiversity
• Aspects of biodiversity to
measure?
• Possibilities
–Richness
–Abundance
–Diversity (interaction of
richness & abundance)
–Trophic Levels
–Feeding Guilds
–Taxonomic Diversity
Diversity Indices
• Used to compare sites or evaluate a single one
through time
• Many many many types
• Main ones:
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Shannon (diversity)
Simpson (diversity)
Rarefaction (richness)
Sorenson (comparative diversity)
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Global Distribution of
Biodiversity
• Greatest in areas where NPP is greatest
– Terrestrial: toward Equator - Why?
– Aquatic: near shore, marine upwellings – Why?
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Relationship Between Community
Diversity and Stability
• Stability components
– Resistance
– Resilience
– Recovery speed
• Biodiversity has been
thought to influence
Stability
– Croplands – Unstable
– Tropics – Stable
• Jury still out
– preliminary work seems to
support this
Proximate Ecological Fields
- Next Week:
• Trends down pyramid:
– Increase in geographic scale
Population
– From single species to multiple
species
Community
– Increasing number of ecological
factors that may be influential
Ecosystem
– Decreasing certainty in results
Next Week: The Tour of
Ecology Continues
• Population ecology
• Community ecology
• Ecosystem ecology
– Next week’s emphasis
• Conservation Issues