Communities biodiversity, issues keystone species habitats, niches Interactions:
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Communitiesbiodiversity, issues keystone specieshabitats, niches
Interactions:competition, predation,mutualism, commensalismco-evolution
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• Wasps and Pieris caterpillars form a food chain
• Wasp eggs layed inside caterpillar
– Caterpillar eaten up by larvae
Dining In
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• A second wasp can detect wasp larvae inside these caterpillars
– and will deposit her own eggs inside of the first wasp’s larvae
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• Finally, yet another wasp, a chalcid, may lay its eggs inside the second wasp’s larvae
• Only the chalcid wasp’s larvae emerge from the caterpillar carcass
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• = All the organisms in a particular area
• Description includes:– Trophic structure (feeding relationships)
-- Vegetation-- Biodiversity -- Response to disturbances
Community
Figure 36.1
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Figure 36.9A
TROPHIC LEVEL
Quaternaryconsumers
Tertiaryconsumers
Carnivore Carnivore
Carnivore Carnivore
Carnivore Carnivore
Herbivore Zooplankton
Plant Phytoplankton
Secondaryconsumers
Primaryconsumers
Producers
A TERRESTRIAL FOOD CHAIN AN AQUATIC FOOD CHAIN
What’s for lunch?
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Figure 36.10
Tertiaryandsecondaryconsumers
Secondaryandprimaryconsumers
Primaryconsumers
Producers
(Plants, algae,phytoplankton)
Detritivores
(Prokaryotes, fungi,certain animals)
Wastes anddead organismsFood webs
oftenmore real thanfood chains
Food webs reveal the flow of energy
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• 170 billion tons of biomass per year
Figure 36.11
Tertiaryconsumers
Secondaryconsumers
Primaryconsumers
Producers
10 kcal
100 kcal
1,000kcal
10,000 kcal
1,000,000 kcal of sunlight
Energy supply limits the length of food chains
Avg. 10% conversion of biomassto next level
Endothermic animals convert only 2% Plants
convert 30-85%
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• Consequences:
• Low density of large carnivores
• a field of corn can support more vegetarians than carnivores.
Figure 36.12
Secondaryconsumers
Primaryconsumers
Producers
Humanvegetarians
Corn
Humanmeat-eaters
Cattle
Corn
TROPHIC LEVEL
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• Chemicals are concentrated in food chains by biological magnification
Figure 38.3B
DDT in water0.000003 ppm
DDT inzooplankton0.04 ppm
DDT insmall fish0.5 ppm
DDT inlarge fish2 ppm
DDT infish-eating birds25 ppm
DDT concentration:increase of10 million times
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• Biodiversity is the variety of organisms that make up a community
• Components:
– Species variety: total number of different species in the community
– relative abundance of different species
– Genetic variation within each species
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Biodiversity - current issues
1. Another mass extinction in progress?
2. Wildlife preserves - do they work? 3. Biodiversity hot spots: Should
conservation efforts focus only on areas of high biodiversity?
4. Alien species
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• Habitat is the environment in which an organism lives.
• A population's niche is its role in the community
– How it uses the biotic and abiotic resources of its habitat
Communities
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• There are four main types of relationships among species within communities
– Competition
– Parasitism, predation
– Commensalism
– Mutualism
Community interactions
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Community interactions
Interspecific competition occurs between
two populations if they both require the same
limited resource
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• The competitive exclusion principle
– Populations of two species cannot coexist in a community if their niches are nearly identical
Figure 36.2
Hightide
Chthamalus
Balanus
Lowtide
Ocean
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• Competition between species with identical niches has two possible outcomes– One population will eventually eliminate the other
– Natural selection may lead to resource partitioning (division)
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• Predation is an interaction where one species eats another
– consumer = predator
– food species = prey
• Parasitism is a form of predation
– Parasite, host
– Not immediately lethal
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• Some plants have evolved parasitic ways of obtaining food from other plants
– Dodder taps into the host’s vascular tissue
Other modes of nutrition for plants:
Figure 32.12A
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– Mistletoe siphons sap from vascular tissue of its host plants
Figure 32.12B
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• As predators adapt to prey, natural selection also shapes the prey's defenses.
• This reciprocal adaptation = coevolution
– Example: Heliconius and the passionflower vine
Figure 36.3A
Eggs
Sugardeposits
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• Carnivorous plants obtain nutrients from animal tissues
– Sundew and Venus flytrap use insects as a source of minerals
– enables them to thrive in highly acidic soil
Figure 32.12C, D
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• Prey gain protection against predators through a variety of defense mechanisms1. Mechanical defenses, such as the quills of a porcupine
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2. Chemical defenses
– Animals are often brightly colored to warn predators
– Example: the poison-arrow frog
Figure 36.3B
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3. Camouflage
Figure 36.3C
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4. Batesian mimicry occurs when a harmless species mimics a harmful one– mimicry can involve behavior
– hawkmoth larva puffs up its head to mimic the head of a snake
Figure 36.3D
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• Eliminates weaker individuals
• keystone predator maintains diversity by reducing numbers of the strongest competitors in a community
- Ex. sea star is a keystone predator
What are effects of predation?
Figure 36.4A
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• Predation by killer whales on sea otters, allowing sea urchins to overgraze on kelp
– Sea otters represent the keystone species
Figure 36.4B
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• Commensalism - one partner benefits and the other is unaffected
• Examples
- Algae that grow on the shells of sea turtles
– Barnacles that attach to whales
– Birds that feed on insects flushed out of the grass by grazing cattle
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• Mutualism:
both partners benefit
Example:
– Acacia trees and the ants of the genus Pseudomyrmex
Figure 36.5B
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• Mutualism
• mycorrhizae
– fungal threads increase plant's absorption of nutrients and water
– fungus receives nutrients from the plant
Figure 32.11
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• nodules in the plant roots contain bacteria that convert N2 gas to soluble NO3-, NH4+
Legumes and certain other plants house nitrogen-fixing bacteria
Figure 32.14A
Shoot
Nodules
Roots
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Figure 32.13
ATMOSPHERE
N2
N2Nitrogen-fixing
bacteria
Ammonifyingbacteria
Organicmaterial
NH4+
(ammonium) Nitrifyingbacteria
NO3–
(nitrate)
Root
NH4+
Aminoacids
Soil
Nitrogen-fixing bacteria and legumes
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• Disturbances include events such as storms, fires, floods, droughts, overgrazing, and human activities – damage biological communities
– remove organisms
– alter the availability of resources
Disturbance is a prominent feature of most communities
Figure 36.6