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Community Ecology
IB: 2.1.6, 2.1.7Ch. 8
Videos – extinction clip on exotics, clip on coral reefs
Syllabus Statements
• 2.1.6: Define the terms species, population, community, niche and habitat with reference to local examples
• 2.1.7: Describe and explain population interactions using examples of named species
Vocabulary
• Community
• Competition
• Mutualism
• Niche
• Parasitism
Definitions
1. Population a group of individuals of a certain species in a given area at a given time: blue crabs in the Halifax river
2. Community interacting groups of populations in an area: the scrub community on campus
3. Species a group of individuals who can interbreed to produce fertile, viable offspring: FL panthers
4. Niche The role of an organism in its environment (multidimensional): nocturnal predator of small mammals in the forest
5. Habitat Where an organism typically lives: mangrove swamps
Community Structure
• Consider the spatial distribution of organisms
• Physical appearance: Size, stratification, distribution of populations and species
• Species diversity and richness: number of different species
• Species abundance: number of individuals of each species
• Niche structure: number, uniqueness and interaction of niches available
mft
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50
20
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Tropicalrain forest
Coniferousforest
Deciduousforest
Thornforest
Tall-grassprairie
Short-grassprairie
Desertscrub
Thornscrub
Comparison of types, sizes and stratification of species in different terrestrial communities (complexity)
Community Differences
• Aquatic systems deep ocean, sandy beach, lakes, rivers, wetlands
• Physical structure varies– Most habitats are mosaics, vegetation patches– Sharp edges or broad ecotones (transition zones)– Physical properties differ at edges = edge effect– Forest edge may be sunnier, drier, warmer
• different species at the edge• Many wild game species found here• Edges can fragment habitat vulnerability & barriers
What is a niche
• The organisms role in its environment• How it responds to the distribution of
resources• Many dimensions to it – therefore an n-
dimensional hypervolume• No two species can occupy the same
niche for any period of time• If a niche is vacant organisms will quickly
adapt to fill it
• Fundamental Niche Everything that the organism could possibly do given a competitor free environment
• Realized Niche Everything the organism does after competition limits them
Biodiverse Communities
• Top species rich environments are tropical rainforests, coral reefs, deep sea, large tropical lakes
• Usually high diversity but low abundance• Factors for increased diversity
1. Latitude: most diverse near equator2. Depth: marine communities peak about 2000m3. Pollution: more pollution less speciesOn land increases in solar radiation, precipitation,
seasonal variation, decreased elevation
Sp
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1,000
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Latitude
80ºN 60 40 20 0
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90ºN 60 30 0 30ºS 60
Latitude
Effects of Latitude
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00 2,000 4,000 6,000
Depth (meters)
0 2,000 4,000 6,000
Depth (meters)
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Coast Deep Sea Coast Deep Sea
Snails Tube worms
© 2004 Brooks/Cole – Thomson Learning
Effects of Depth
Number of individuals per diatom species
Nu
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iato
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pec
ies Unpolluted
stream
Pollutedstream
The Island Effect
• Isolated ecosystems studied by MacArthur and Wilson in 1960’s
• Diversity effected by island size & degree of isolation
• Island Biogeography theory: diversity effected by – Rate of species immigration to island– Rate of extinction on island– Equilibrium point = species diversity
High
Low
Rat
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f im
mig
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exti
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Equilibrium number
Immigration and extinction rates
Number of species on island
(a)
© 2004 Brooks/Cole – Thomson Learning
Island Biogeography
• Immigration and Extinction Effected by1. Size:
– small island has less immigration (small target), – Small island has fewer resources, more extinction
2. Distance from mainland:– Closer to mainland more chance of immigration
• Applied in conservation for “habitat islands” like national parks surrounded by development
High
Low
Rat
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mig
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exti
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Small island
Effect of island size
Number of species on island
(b)
Large island
© 2004 Brooks/Cole – Thomson Learning
Island Biogeography Data
• South Pacific Islands study looked at bird diversity as distance from New Guinea increased
• Caribbean Island study found bigger islands had more species diversity than smaller islands which were otherwise similar
100
50
25
12.5
6.250 2,000 4,000 6,000 8,00010,000
Distance from New Guinea (kilometers)
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sam
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NEW GUINEA
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1 10 100 1,000 10,000 100,000Area (square miles)
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sp
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SABAMONTSERRAT CUBAHispaniola
Puerto Rico
JamaicaCuba
MontserratSaba
Redonda
© 2004 B
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Learn
ing
Communities have different “Types” of Species
• Native species = species that normally live and thrive in a particular community
• Nonnative species = species that are accidentally introduced into an area
• Keystone species = species that are more important than their abundance or biomass suggest
• Indicator species = species that serve as early warnings of damage in a community
Nonnative Species
• Also called exotics, aliens, or introduced sp.
• FL examples include fire ants, hydrilla, potato vine, peacock bass, …– Occupy niches excluding native organisms– Reproduce rapidly in absence of natural
predators– Usually are very adaptable to human disturbed
environments
Common Florida Exotics
Indicator Species
• Mostly species that respond quickly to changes in the environment
• Birds indicate tropical forest destruction• Trout indicate pollutant presence in water• Amphibians are a classic indicator
– Frogs case study p 170– Frog decline and deformities
Keystone Species
• Strong interactions with other species affect the health and survival of those species
• They process material out of proportion to their numbers
• Roles include: pollination, seed dispersion, habitat modification, predation by top carnivores, efficient recycling of animal waste
Sea Otters
Keystone Species II
• Habitat modification– Elephants – knock over trees in savannah to
promote grass growth & recycle nutrients– Bats & birds – regenerate deforested areas
by depositing plant seeds in their droppings– Beavers – create ponds forming habitats for
many pond dwelling species like fish, ducks, & muskrats
Keystone Species III
• Top predators exert stabilizing effect by feeding on and regulating certain species– Wolves, leopards, lions, gators, sharks, otters
• Over 300+ species are found on the wolf kills made in Yellowstone
Waste removal
•Dung beetles – remove bury and recycle animal waste•Establish new plants•Aerate soil•Reduce disease causing microorganisms
Species Interactions
• Interactions may be harmful, beneficial, or have no effect at all
• Competition: Intraspecific or Interspecific
• Predation, Mutualism (Symbiosis), Commensalism, Parasitism
Intraspecific Competition
• Competition between members of the same species for a common resource
• Resource: food, space, mates, etc.
• Territoriality – Organisms patrol or mark an area– Defend it against others– Good territories have
• Abundant food, good nesting sites, low predator pop.
– Disadvantage = Energy, Reduce gene pool
Territoriality Examples
Interspecific Competition
• 2 or more different species involved• Competing for food, space, sunlight, water,
space, nesting sites or other limited resource• If resources abundant, they can be shared but in
nature they are always limited• If fundamental niches overlap competition• One of the species must…
1. Migrate if possible2. Shift feeding habits or behavior = Evolve3. Suffer a sharp population decline4. Become extinct
Connell’s Barnacles
Methods of competition
1. Interference• One species limits access of others to a
resource, regardless of its abundance• Hummingbird territoriality, Desert plant
allelopathy
2. Exploitation• Species have equal resource access, differ
in speed of use• Quicker species = more of it & hampers
growth, reproduction and survival of other species
Allelopathy
Competitive Exclusion Principle
• One species eliminates another in an area through competition for limited resources– Two Paramecium species– Identical conditions grown apart both do well– Grown together one eliminates the other
• The niches of two species cannot overlap significantly for a long period of time
High
Low
Rel
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0 2 4 6 8 10 12 14 16 18
Days
Each species grown alone
Parameciumaurelia
Parameciumcaudatum
High
Low
Rel
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0 2 4 6 8 10 12 14 16 18
Days
Both species grown together
Parameciumaurelia
Parameciumcaudatum
Avoiding Competition
• Resource partitioning = dividing of scarce resources to species at different– Times– Methods of use– Different locations
• Species occupy realized niche, a small fraction of their fundamental niches– Lions vs leopards, hawks vs. owls
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Resource use
Resource use
Species 1 Species 2
Regionof
niche overlap
Species 1 Species 2
© 2004 Brooks/Cole – Thomson Learning
Predation
• Members of one species feed directly on all or part of a living organism of a different species
• Individuals predator benefits, prey harmed
• Population prey benefits: take out the weak, greater resource access, improved gene pool
• Predator plays important ecological role
Predation
Predation strategies
1. Herbivores – sessile prey, no need to hurry
2. Pursuit – speed (cheetah), eyesight (eagles), cooperation (wolves)
3. Ambush – camouflage for hiding (praying mantis), lures (anglerfish)
Ambush Predators
Prey defenses
• Camouflage – change color, blend with environment,
• Chemical warfare – produce chemicals which are poisonous, irritating, bad smelling or tasting
• Warning coloration – bright colors advertise inedibility (mimics take advantage of this)
• Behavioral strategies – Puffing up, mimicking predators, playing dead, schooling
Warning coloration
Batesian mimicry
Mullerian mimicry
Span worm Bombardier beetle
Viceroy butterfly mimicsmonarch butterfly
Foul-tasting monarch butterfly
Poison dart frog When touched, the snake caterpillar changes shape to look like the head of a snake
Wandering leaf insect
Hind wings of io mothresemble eyes of a much larger animal
Parasitism
• One species feeds on part of another organism (the host) without killing it
• Specialized form of predation
• Parasite Characteristics1. Usually smaller than the host
2. Closely associated with host
3. Draws nourishment from & slowly weakens host
4. Rarely kills the host
• Examples = Tapeworms, ticks, fleas, fungi
Parasites
Malaria
According to the World Health Organization there are 300 to 500 million clinical cases of malaria each year resulting in 1.5 to 2.7 million deaths
The disease kills more than one million children - 2,800 per day - each year in Africa alone. In regions of intense transmission, 40% of toddlers may die of acute malaria.
In the early 1960s, only 10% the world's population was at risk of contracting malaria. This rose to 40% as mosquitoes developed resistance to pesticides and malaria parasites developed resistance to treatment drugs. Malaria is now spreading to areas previously free of the disease.
Mutualism
• Symbiotic relationship where both species benefit
• Pollination, Nutrition, Protection are main benefits
• Not really cooperation, both benefit by exploiting the other
Mutualism II
Examples
1. Lichens – fungi & algae living together food for one, structure for the other
2. Plants and Rhizobium bacteria one gets sugars the other gets nitrogen
3. Oxpeckers and Rhinos food for one, less parasites for the other
4. Protists and termites break down wood for one, nutrients for the other
Oxpeckers and black rhinoceros
Clown fish and sea anemone
Commensalism• One species benefits the
other is neither harmed nor helped
– Examples1. Herbs growing in the shade
of trees
2. Birds building nests in trees
3. Epiphytes = “Air plants” which attach themselves to the trunk or branches of trees-they have a solid base to grow on
and better access to sunlight & rain
What interaction is this?
What interaction is this?
What interaction is this?
