Biology 213 Chapter 54

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Biology 213 Chapter 54

• Community Ecology

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Please turn in any Bird books Tree I.D.
books Stopwatches Or any field trip items that
you forgot to turn in already. Keep your science
fees to zero, Thank you.
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You will be able to

• Define and give examples of niches
• Describe various types of interactions within a
• community
• Compare contrast how dominant and
• keystone species influence a community

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Dining In

• Wasps and Pieris caterpillars form an unusual
  three-step food chain
• The 4-mm-long wasp Apanteles glomeratus stabs
  thru skin of Pieris rapae
  caterpillar
  lays her eggs
• caterpillar is destroyed
• when wasp larvae hatch
• nourish themselves
• on its internal organs

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• Ichneumon wasps can detect when a Pieris
  caterpillar contains Apanteles larvae

Female ichneumon will pierce caterpillar and
deposit her own eggs inside of Apanteles larvae
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• Finally, another wasp, a chalcid, may lay its
  eggs inside the ichneumon larvae

• Usually, only the chalcids will emerge from the
  dead husk of the caterpillar

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• Biological community interactions
  interdependence of organisms living in it.

• Ecosystem functioning depends on complex
  interactions btwn its community of organisms and
  the physical environment

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A community all organisms inhabiting a
particular area

• Several factors characterize every community
• Biodiversity
• Prevalent form of vegetation ( its levels)
• Response to disturbances
• Trophic structure (feeding relationships)

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• Biodiversity variety of different kinds of
  organisms that make up a community

• two major components
• Species richness, or total of different species
  in the community
• Relative abundance of different species

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• Interspecific interactions (), (-), neutral
• Competition (-)/(-) occurs btwn 2 populations if
  
• they both require same limited resource

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• Interspecific interactions (), (-), neutral
• Predation ()/(-) one species kills eats other
  
• species

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Symbiosis

• A symbiotic relationship is an interaction
  between two or more species that live together in
  direct contact
• 3 main types of symbiotic relationships within
  communities

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• Symbiosis
• Mutualism
• Both partners benefit
• Commensalism
• One partner benefits and the other is unaffected
• Parasitism
• One partner benefits while the other is harmed

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• Interspecific interactions (), (-), neutral
• Parasitism ()/(-) one species is nourished by
• another species harms other species.

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• Parasitism type of predator-prey relationship

• parasite benefits and host is harmed
• parasite obtains food at expense of host
• Parasites are typically smaller than their hosts

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Worldwide, 25 of all deaths result from parasite
infections
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• Interspecific interactions (), (-), neutral
• Mutualism ()/() both species benefit

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• Examples of mutualism
• Nitrogen-fixing bacteria and legumes

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• Mutualism can be
• Obligate
• one species cannot
• survive without the
• other
• Facultative
• both species can
• survive alone

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Mutualism
Algae in coral
polyps give C and N compounds,
get N in return (NH3) from coral waste. Obligate
or Facultative?
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Pollination is mutualism e.g. Milkweed
(Asclepias) is pollinated by butterflies
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mutualism often demonstrates coevolution
Each party evolves features that
take advantage of the association, but
also provides them with an encouraging reward.
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• Interspecific interactions (), (-), neutral
• Commensalism ()/(0) only 1 species
• benefits other species is not harmed

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• Commensalism - symbiotic relationship where one
  partner benefits and other is unaffected

• e.g. of commensalism
• Algae growing on shells of sea turtles
• Barnacles that attach to whales
• Birds that feed on insects flushed out of grass
  by grazing cattle

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Commensalism
Spanish moss and southern trees (e.g. Golden
Larch)
One benefits, the other isnt helped or
harmed
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Competitive exclusion principle
Populations of 2 species cannot co-exist in a
community if their niches are nearly identical
Resource partitioning or character displacement
occurs (or extinction of one species)
Hightide
Chthamalus
Balanus
Ocean
Lowtide
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• Competition btwn species with identical niches
  has two possible outcomes

• One population survives
• more efficient using resources
• reproductive advantage,
• may eventually eliminate other (difficult to
  observe).
• resource partitioning

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• Ecological niche
• Distinctive lifestyle role of an organism in a
  community
• all abiotic and biotic aspects
• E.g. organisms habitat is one parameter used to
  describe the niche

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Various community niches interact How does a
bumper crop of acorns relate to a human disease?
Increase in human exposure to Lyme bacterium
Public health hazard
Deer attracted to forest
Tick population increases
Healthier forest

Oaks thrive bumper crop of acorns
White-footed Mouse population increase
Decrease in gypsy moth pupae
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• Fundamental niche
• Potential ecological niche for an organism
• Realized niche
• Niche an organism actually occupies
• Limiting factors
• Environmental resources and components that
  restrict an organism to a realized niche

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Competition effect on organisms realized niche
Brown anole introduced species
Out-competes native green anole
where 2 niches overlap
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Fig. 54-3a
EXPERIMENT
High tide
Chthamalus
Chthamalus realized niche
Balanus
Balanus realized niche
Ocean
Low tide
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Fig. 54-3b
RESULTS
In terms of their niches, what do the results
tell you about Chthamalus? And about Balanus?
High tide
Chthamalus fundamental niche
Ocean
Low tide
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• Competition
• Two or more individuals attempting to use same
  resource
• Intraspecific competition
• Among individuals within a population
• Interspecific competition
• Between different species

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Interspecific competition between protists
Grown together P. aurelai excludes P. caudatum
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• Some species reduce competition by resource
  partitioning
• Competition among species is reduced by character
  displacement
• Structural, ecological, behavioral
  characteristics diverge
  where ranges overlap (sympatric)
• Spatial Temporal Food

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Character Displacement
Characteristics tend to be divergent in sympatric
populations of 2 species than in allopatric
populations of same 2 species
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Fig. 54-4
G. fuliginosa
G. fortis
Character Displacement
Beak depth
Los Hermanos
60
40
G. fuliginosa, allopatric
20
0
Daphne
60
40
Percentages of individuals in each size class
G. fortis, allopatric
20
0
Sympatric populations
Santa María, San Cristóbal
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More divergent
40
20
0
8
10
12
14
16
Beak depth (mm)
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Resource partitioning
Galapagos finches Ancestral finches diverged
to partition limited resources insects, seeds,
etc. Character displacement structural changes
occur
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Resource partitioning different life stages
Adults feed differently from larvae. Different
Adult species avoid direct competition feed on
different parts of plants, select different
microhabitats
Agraulis vanillae
Heliconius charitonius
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• Predation
• Consumption of one species
• (the prey) by another (the predator)
• Coevolution
• Predator and prey both evolve more efficient ways
  to interact.
• Prey changes to escape predation
• Predator becomes more efficient at predation

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Coevolution in sea shell studies

• Modern shells show scars from molluscivore crab
  predation
• Ancient shells from similar environment show
  scars too, but crab claws have evolved to be
  stronger with bigger teeth
• Shells have evolved more thickness, larger size,
  rigid calcification, quick scarring, and
  variations in shape.

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• As predators adapt to prey, sometimes natural
  selection also shapes prey's defenses

• process of reciprocal adaptation is known as
  coevolution
• Example Heliconius passionflower vine

Eggs
females avoid phony eggs.
Sugardeposits
Ants wasps also attracted to sugar deposits
prey upon butterflys eggs.
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• Defenses
• Mechanical chemical defenses
• Associating in groups
• Cryptic coloration
• Aposematic (warning) coloration
• Müllerian Batesian mimicry

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• Prey gain protection against predators thru
  variety of defense mechanisms

• Mechanical defenses, e.g.quills of a porcupine

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Associating in groups
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Chemical defenses widespread very effective

• Animals with effective chemical defenses often
  brightly colored to warn predators
• e.g. poison-arrow frog Skunk

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• Camouflage - very common defense in animal kingdom

• Example gray tree frog

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Cryptic coloration
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• Batesian mimicry when a palatable or harmless
  species mimics an unpalatable or harmful one

• Mimicry can even involve behavior
• This hawkmoth larva puffs up its head to mimic
  the head of a snake

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These butterflies are not Batesian mimicry but
are Müllerian mimicry
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• Müllerian mimicry 2 unpalatable species that
  inhabit same community mimic each other -

• Example cuckoo bee and yellow jacket

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Predation can maintain diversity in a community

• keystone species exerts strong control on
  community structure due to its ecological role
• A keystone predator may maintain community
  diversity by reducing s of strongest
  competitors in a community
• e.g. sea star is a keystone predator

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• Seals over-hunted normal food for Orcas
• Predation by Orcas (Killer whales) on sea otters,
  allowing sea urchins to overgraze on kelp
• Sea otters represent the keystone species

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Fig. 54-16
100
80
Otter number ( max. count)
60
40
20
0
(a) Sea otter abundance
400
300
Grams per 0.25 m2
200
100
0
(b) Sea urchin biomass
10
8
Number per 0.25 m2
6
4
2
0
1972
1985
1997
1989
1993
Year
(c) Total kelp density
Food chain
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• Keystone species
• Present in small numbers but are crucial in
  determining species composition and ecosystem
  functioning
• Dominant species
• Affect the community because they are so commonly
  found
• Largest biomass

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Dominant species

• One hypothesis dominant species most competitive
  in exploiting resources
• Another hypothesis dominant species most
  successful at avoiding predators
• Invasive species, introduced to a new environment
  by humans, often lack predators or disease.
• What are some invasive species in our region?

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Foundation Species (Ecosystem Engineers)

• ecosystem engineers
• cause physical Ds in environment
• affecting community structure

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Biology 213 Chapter 54

• Community Ecology
• Part 2

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You will be able to

• Compare and contrast various types of
• symbiosis
• Explain the concept of biodiversity and its
• importance in studying ecosystems.
• Compare contrast 1o 2o succession
• Explain types of disturbances (man-made
• natural ) that can cause succession.

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Biodiversity

• Ecological measurement of an ecosystems
• health
• Measures interactions within a community
• and interdependence of various species.
• Describes a communitys ability to survive
• various types and degrees of disturbance

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• Species richness
• of species within a community
• Species diversity
• Relative importance of each species within a
  community

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Effect of community complexity on species richness
Complexity of chaparral communities based upon
density and height of foliage. Higher complexity
is reflected in larger variety of bird
species more variety in food and shelter.
Reflects drier habitat in Chile.
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Species richness

• Related to solar E H2O (autotrophs)
• Evolutionary history age of an area
• Related to isolation
• islands, mountain tops
• replacements vs extinction

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Fig. 54-27
Islands can be any isolated region
Immigration
Immigration
Extinction
Extinction
Immigration
Extinction
(small island)
(near island)
(far island)
(large island)
Immigration
Extinction
Rate of immigration or extinction
Rate of immigration or extinction
Rate of immigration or extinction
(large island)
(far island)
Extinction
Immigration
(near island)
(small island)
Equilibrium number
Far island
Near island
Small island
Large island
Number of species on island
Number of species on island
Number of species on island
(a) Immigration and extinction rates
(b) Effect of island size
(c) Effect of distance from mainland
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Species richness

• One major dominant species reduces richness
  (think city fauna)
• Community margins overlapping
• Ecotones or Edge Zones
• Enrich a communitys diversity

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Edge Zones Ecotones
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Species richness stability

• Older, moderately disturbed communities often
  richer in species
• Glaciated regions vs rain forests
• Less diverse habitats more prone to
• devastation by one event or agent
• Planted field vs diverse natural field
  responding to pests

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Older moderately disturbed communities richer
in species
Frequently or recently disturbed area shows
less diversity in some cases.
But is that always true?
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• Intermediate disturbance hypothesis
• Disturbance affects succession and species
  richness
• Species richness is greatest at moderate levels
  of disturbance

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Intermediate disturbance hypothesis
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• The nature of communities
• Organismic model
• Views a community as a super-organism that goes
  through stages of development (succession)

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• The nature of communities
• Individualistic model
• Abiotic environmental factors are primary
  determinants of species composition
• Organisms are separate from each other
  communities can rearrange independently of each
  species

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• Ecological succession
• Primary succession
• Occurs in an area not previously inhabited
• Secondary succession
• Occurs where there is a pre-existing community
  and well-formed soil

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• Ecological succession is a transition in species
  composition of a community following a disturbance

• Primary succession
• is gradual colonization of barren rocks,
  gravel, or sand by living organisms
• Secondary succession
• occurs after a disturbance has removed
  vegetation but left soil intact

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Primary succession
Starts without soil. No organic matter, only
mineral material sand, bare rock, gravel from
glacial outwash, volcanic ash lava, man-made
structures or severe erosion
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Primary succession
Volcanic regions Pioneer plants must establish
themselves in tiny crevices that collect some
moisture and infinitesimal bits of organic
detritus
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Secondary succession
Starts with soil. Pioneer plants start from
roots or seeds in soil or transported seeds (by
wind or animals) from surrounding areas. Faster
than primary succession.
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Some regions are periodically disturbed by
natural phenomena

• Floods
• Blizzards avalances
• Hurricanes
• Are these disturbances actually part of the
  areas ecosystem?
• What happens when these disturbances are
  eliminated? e.g. flooding on damned rivers /
  fires in our region?

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Some regions are periodically disturbed by
man-made phenomena

• Logging
• Agriculture land clearing, pests encouraged
• Alien species introduced accidentally
  purposefully
• Grazing
• Building
• How do communities react to disturbances?
• How can humans minimize impact on local
  communities?

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Succession study Abandoned Field to Oak Forest

• Dwight Billings in 1930s
• Succession of plant species on abandoned
  agricultural fields in N. Carolina.
• Deserted from a few years to 150 years.

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First stage of secondary succession

• Pioneer plants
• Annual species lichens
• Colonize bare ground and nutrient poor soils

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Second stage

• Annuals quickly replaced in dominance the next
  year by biennial plants and grasses
• Two year life cycle
• Usually reproduce in 2nd year

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Perennials and Shrub stage

• After about 3 to 4 years
• biennial grass species gave way to perennial
  herbs and shrubs
• Perennial plants
• live for many years
• reproduce several times over their life spans.

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Softwood tree species take over

• After about 5 to 15 years
• Loblolly, Shortleaf, and Virginia pines Sweet
  Gum trees colonize the area (Note S.E. U.S.)

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Softwood tree species take over

• Forest canopy starts to form
• canopy reduces light reaching forest floor
• shaded understory excludes light loving perennial
  herb and shrub species
• low light perennial herb and shrub species take
  over ground cover

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Canopy changes habitat

• Canopy changed microclimate of habitat near
  ground level.
• more humid
• moderated temps
• less wind
• rain drops cushioned

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Canopy changes habitat

• Low light conditions inhibited germination of
  pine seedlings.
• Development of a soil litter layer humus
• Soil chemistry changes

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Forest composition changes slowly

• Shade, humidity, humus and leaf litter, low light
• germination of hardwood species
• oak (Quercus spp.)
• hickory (Carya spp).
• 50 to 75 years after pioneer species hardwoods
  start to replace softwood species
• pines max heights 25 meters
• oaks hickories average 10 meters tall

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Climax Community

• Softwoods shorter life span 50 yrs
• Gap created filled by subdominant hardwood trees
• Oak and hickory, can live for more than 100 years
• Sites more than 100 years old were found to be
  dominated by mature oak forests

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This succession takes 120 yrs from pioneer
stage to climax community.
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• With infrequent disturbance a stable climax
  community consisting of plants and animals that
  can reproduce themselves in the existing
  conditions will become established.
• Disturbance of the ecosystem will start the
  process of succession anew.

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Remember succession isnt usually uniform

• In one area - usually small patches in different
  stages of succession
• Depends on time severity of last disturbance
• Adds diversity in types of vegetation and animals
  living in the greater region.

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Agriculture, overgrazing, and logging affect a
regions succession
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Fig. 54-24
Disturbance of ocean floor by trawling removes
5 to 25 of an area's seabed life on a single
run.
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The role of fire in ecosystems

• key abiotic factor in many ecosystems
• Grasslands so dependent on fire its absence is
  considered a disturbance
• Allelopathic chemicals burnt off
• Accumulated debris reduced and nutrients released

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Fire Ecology

• Fire Dependence effects of fire make environment
  more hospitable for regeneration growth.
• Fire History fire frequency occur in an area.
• Record fire scars or charcoal layer in tree
  rings
• Fire Regime (characteristics) intensity,
  severity, frequency, and vegetative community.

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Fire Ecology

• 4. Fire Adaptation special traits to survive
  fires at various stages of plant life cycles
• serotinous cones
• fire resistant bark
• fire resistant foliage
• rapid growth and development

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Fire maintains ecotones small fires
create many edges
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• Clicker Question 2 on succession
• A small fire burns through a Douglas-fir old
• growth forest. What type of succession would
• occur on the forest floor, and what would the
• dominant plant species be several months after
• the fire?
• 2o succession mature Douglas-fir trees
• 1o succession grasses
• 2o succession oak and madrone trees
• 1o succession mosses lichens
• 2o succession grasses

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Rogue valley succession

• Depends upon
• Climate
• Local physical factors
• Slope what does that do?
• Water run-off angle direction of sun
• Altitude
• Fires, storms, floods

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Rogue valley succession

• Depends upon
• Communities
• Composition of plants type, age,
• distribution
• Animals grazing, soil
• compaction/fertilization, others?

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Rogue valley succession

• Depends upon
• Human activities
• Alien plant animal species introduced
• Logging, agriculture, grazing,
• building houses roads
• Fire suppression

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Successional stages in our area

• Grasses
• White oak savanna
• Chaparral
• Black oak and Madrone
• Ponderosa pine (may be mixed)
• Douglas-fir and other trees
  (e.g. Incense cedar)

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