ecology’ communityecology’ - biology -...
TRANSCRIPT
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Ecology Community Ecology
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Community Ecology
Populations are linked by interspecific interactions that impact the survival & reproduction
of the species involved
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Community Structure • Community−an assemblage of
populations living close enough together for potential interaction
• Dominant Species−most abundant, highest biomass, powerful control over occurrence and distribution of other species… VA Sugar Maple
• Keystone Species−NOT necessarily most abundant, exert strong control due to their ecological roles or niches… Sea Otters!!!
• Richness number of species & abundance
• Species diversity older = greater diversity larger areas = greater diversity climate = solar input & H2O available
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Biodiversity
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• Communities with higher diversity are – More productive and more stable regarding
their productivity – Better able to withstand and recover from
environmental stresses – More resistant to invasive species, organisms
that become established outside their native range
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Species Diversity
Species Richness
(# of different species)
Species Diversity = + Rela9ve abundance
5
(propor9on each different species represents of all the individuals in the community)
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Species Richness
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Which community is richer?
A
B
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Sample Data
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The data below represents the abundance of macro-invertebrates taken from three different river communities in Georgia. A variety of diversity indices may be used to calculate species diversity. Based on the data below, which community has the greatest diversity?
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Observa9on Of Sea O>er Popula9ons And Their Preda9on
Food chain before killer whale involve- ment in chain
(a) Sea otter abundance
(b) Sea urchin biomass
(c) Total kelp density
Num
ber p
er 0
.25
m2
1972 1985 1989 1993 1997 0 2 4 6 8
10
0
100
200
300
400 G
ram
s pe
r 0.2
5 m
2 O
tter n
umbe
r (%
m
ax. c
ount
)
0
40
20
60
80
100
Year
Food chain after killer whales started preying on otters
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Killer Whales vs. Sea O>ers Predator-‐Pray Energe9cs
The daily caloric requirements for male versus female killer whales (orcas) is shown below:
• Male killer whale: 308,000 kcal/day
• Female killer whale: 187,000 kcal/day
Calculate the average caloric value of a sea o>er assuming a male orca consumes five sea o>ers each day to meet its caloric requirement.
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Killer Whales vs. Sea O>ers Predator-‐Pray Energe9cs
Calculate the average caloric value of a sea o>er assuming a male orca consumes five sea o>ers each day to meet its caloric requirement.
Using dimensional analysis or simple arithme9c:
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Killer Whales vs. Sea O>ers Predator-‐Pray Energe9cs
Assume a popula9on of 4 male orcas feed solely on sea oSers. How many oSers are lost to the community over a 6-‐year period?
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Why the change? – Some fish popula9ons have declined in recent decades
– Shortage of seals and sea lions resulted in killer whales preying on smaller sea oSers
– Shortage of certain fish caused substan9al declines in harbor seals and sea lions
Interes9ngly, The Sea O>er Is Not Usually The Orca’s Food of Choice
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Why Should We Care About Declining Numbers of Sea O>ers?
• Sea oSers are an important part of the coastal community
• The loss of sea oSers affects the community directly and indirectly
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A keystone species is one that has a strong effect on the composi9on of the community
– Removal of keystone species causes a decrease in species richness
– Sea oSers eat sea urchins which are fierce compe9tors having a diet of kelp
Indirect Effect on the Community
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Sea Urchin Popula9on vs. Kelp Density
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Early Hypotheses of Community Structure Individualistic
Individualis9c Hypothesis − a chance group of species is linked & distributed according to its tolerance ranges for abio9c factors
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Early Hypotheses of Community Structure Individualistic
Interac9ve hypothesis -‐ states that the community is an integrated unit comprised of closely-‐related species associa9ng with each other due to bio9c interac9ons.
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Early Hypotheses of Community Structure Individualistic
Community composi9on seems to change con9nuously, with each species independently distributed
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Factors that Impact Communities 1. Disease 2. Interspecific Interac9ons:
• Compe99on
• Preda9on • Symbiosis
! Mutualism − mycorrhizae ! Commensalism
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Defense Mechanisms Mullerian-Two or more unpalatable, aposematically colored species resemble each other
Cryptic-camouflage Aposematic-warning
Batesian-palatable/ harmless species mimics an unpalatable/ harmful model
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Ecological Niches An organism’s niche is the specific role it plays in its environment…its job!
• All of its uses of biotic and abiotic resources in its environment
• Ex: oak tree in a deciduous forest ! Provides oxygen to plants,
animals ! Provides a home for
squirrels ! Provides a nesting ground
for blue jays ! Removes water from the
soil
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The Niche
• Ecological niche is the total of an organism’s use of biotic and abiotic resources in its environment
Ex: Barnacle species on the coast of Scotland
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Competition Between Organisms Of Different Species Can Be Direct Or Indirect
• Interference−Directly figh9ng over resources
• Exploita9ve− Indirectly compe9ng by consuming a common limi9ng resource (space)
• Apparent-‐ Indirectly between 2 species both preyed upon by the same predator.
Example: Species A and species B are both prey of predator C. The increase of species A will cause the decrease of species B because the increase of As would increase the number of predator Cs which in turn will hunt more of species B.
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Competitive Exclusion Principle
Some9mes referred to as Gause's law of compe99ve exclusion states that two species compe9ng for the same resources cannot coexist if other ecological factors are constant. • The compe9ng species that has even the slightest advantage will dominate in the long term and emerge the victor.
• The loser will either relocate or become ex9nct. • The principle has been paraphrased as "complete compe9tors cannot coexist".
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Competition Between Organisms Of Different Species
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Solutions to Competitive Exclusion
• Resource partitioning− sympatric species consume slightly different foods or use resources in different ways
Ex: Anolis lizard sp. perching sites in the Dominican Republic
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Solutions to Competitive Exclusion
Character displacement− sympatric species tend to diverge in the characteristics that overlap
Ex: Darwin’s finch beak size on the Galapagos Islands
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Succession • Ecological succession−
transi9on in species composi9on over ecological 9me
• Pioneer organisms = bacteria, lichen, algae
• Climax community = stable • Primary− begun in lifeless
area; no soil, perhaps volcanic ac9vity or retrea9ng glacier.
• Secondary an exis9ng community has been cleared by some disturbance that leaves the soil intact
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Human Impact on Ecosystems
• Humans are the most widespread agents of disturbance – Reduces diversity – Prevent some naturally
occurring disturbances
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Human Impact on Ecosystems
• Combus9on of Fossil Fuels
– Leads to acid precipita9on
– Changes the pH of aqua9c ecosystems and affects the soil chemistry of terrestrial ecosystems
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Increasing Carbon Dioxide Concentra9on in the Atmosphere
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Created by:
Susan Ramsey VASS Notable contribu9ons by S.Meister