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Unformatted text preview: The Structure of Ecosystems The Structure of Ecosystems Trophic categories Producers Consumers Detritus feeder / decomposers Trophic relationships: food chains, food webs, trophic levels. Nonfeeding relationships: symbiosis Autotrophs = Producers = Self feeders Autotrophs = Producers = Self feeders Producers: Autotrophs (auto = self, troph = feeding) Producers: Autotrophs Primary producers Photosynthetic (green things) Chemosynthetic (deepsea vents) Photosynthesis (chlorophyll) organic compounds Photosynthesis 6 CO2 + 6 H20
Water Carbon dioxide C6H12O6 + 6 O2
Glucose Atmospheric oxygen Respiration C6H12O6 + 6 O2
Glucose Atmospheric oxygen 6 CO2 + 6 H20
Carbon dioxide Water Consumers: Heterotrophs (hetero = other, troph = feeding) Primary consumers = herbivores e.g., caribou eat plant material Secondary consumers = predators e.g., wolves eat caribou Predation – one species feeds on another enhances
fitness of predator but reduces fitness of prey (+/– interaction) Types of predation
Carnivores – kill the prey during attack Herbivores – remove parts of many prey, rarely lethal. Parasites – consume parts of one or few prey, rarely lethal. Diet breadth
consumes only one prey type
narrow diet specialist broad diet generalist consumes many prey types A verbal model of predatorprey cycles: A verbal model of predatorprey cycles: Predators eat prey and reduce their numbers Predators go hungry and decline in number With fewer predators, prey survive better and increase Increasing prey populations allow predators to increase And repeat… Lotka-Volterra models describe predator and prey population cycling. Real world predator and prey populations can cycle in size. Detritus feeder and decomposers Feed on dead organisms and organism waste Biomass Pyramid Biomass Pyramid Interrelationships in food chains create Interrelationships in food chains create food webs Predation has strong influences on evolution Adaptations to avoid being eaten:
spines (cactii, porcupines) hard shells (clams, turtles) toxins (milkweeds, some newts) bad taste (monarch butterflies) camouflage aposematic colors mimicry Camouflage – blending in Aposematic colors – warning Mimicry – look like something that is dangerous or tastes bad Mimicry – look like something that is dangerous or tastes bad
Mullerian mimicry – convergence of several unpalatable species Mimicry – look like something that is dangerous or tastes bad
Batesian mimicry – palatable species mimics an unpalatable species
model mimic mimics model Symbiotic Relationships Symbiotic Relationships
Feeding Parasitism: (+,) One species derives nutrients directly from another. Lamprey and shad No feeding Mutualism: (+,+) Both species benefit by the interaction between the two species. Honey bee and flower Commensalism: (+, 0) One species benefits from the interaction and the other is unaffected. Remora fish and Shark Competition Competition Interspecific competition: competition among individuals of different species Intraspecific competition: competition among individual of the same species Inter-specific: causes
a narrowing of the resource base Intra-specific: causes
an expansion in the resource base Resource base Resource base Competition Competition Competition for resources Competition for resources Zebra Impala Kudu Giraffe Vertical position of vegetable
Resource base Competition for resources Competition for resources Zebra Impala Kudu Giraffe Vertical position of vegetable
Resource base Competition for resources Competition for resources Sp. A Sp. B Sp. C Sp. D Resource base Reducing competition Reducing competition Resource Resource Partitioning: the spatial and or temporal division of resources among different species Reducing competition Reducing competition Competitive exclusion: if shared resources are Competitive not partitioned the less competitive species will be excluded (i.e., extirpation or extinction) be i.e., Keystone species affect community structure
Predators can allow coexistence of competing prey competitors Barnacles Balanus Mussels Mytilus (Paine 1966) Keystone species affect community structure
Predators can allow coexistence of competing prey predator Starfish Pisaster competitors Barnacles Balanus Mussels Mytilus (Paine 1966) How can we test the effect of a predator on community structure? Experiment - Remove the predator
Starfish Pisaster Barnacles Balanus Mussels Mytilus Removal experiment
- mussels are the dominant competitor - competitive exclusion of barnacles
starfish removed % of intertidal zone mussels barnacles time What is the effect of the predator on the structure of this community?
- starfish allow coexistence of competitors
starfish removed % of intertidal zone mussels barnacles time How do starfish promote coexistence?
Starfish Pisaster Barnacles Balanus Mussels Mytilus Starfish are picky – they prefer mussels (dominant competitor), which allows barnacles (weaker competitor) to coexist. Keystone species affect community structure disproportionately to their abundance. Picky predators can promote coexistence among competing prey species. Competitive exclusion is prevented when the dominant competitor is the preferred prey. The Human Presence The Human Presence Three revolutions Neolithic Industrial Environmental Red Sky in the Morning by James Gustave The Inconvenient Truth by Al Gore ...
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This note was uploaded on 02/17/2011 for the course BIOL 270 taught by Professor Jones during the Spring '06 term at South Carolina.
- Spring '06