Ecosystem and Community Dynamics Unit 4: The Biosphere

Levels of Organization Organism Population (of one species) Biological community (interacting, living populations) Ecosystem (living and non-living) Biome (many ecosystems – similar climate) Biosphere (all biomes on earth)

Ecosystem Interactions Chances for survival are increased when any one species uses the available resources in different ways. Habitat – area where an organism lives Niche – role or position that an organism has in its environment Competition (resources) v. predation (plants too!)

Symbiotic Relationships All examples of symbiosis – two (or more) species living closely together Mutualism – two or more organisms that benefit from each other. Commensalism – one organisms benefits, the other neither benefits nor is harmed (Nemo!). Parasitism – one organism benefits, the other is harmed. Mutualism – coral. Coral protects, algae provides nutrients!

Flow of Energy in an Ecosystem Autotroph – collects energy from the sun to produce food Heterotroph – gets its energy by consuming other organisms Herbivore Carnivore Omnivores Scavengers Detritivores or decomposers – eat and break down parts of dead organisms and retain their nutrients so they can be reused What would happen if decomposers didn’t exist?

Wood louse decomposing dead plants!

Models of Energy Flow Food chains and food webs Have different trophic levels Each step in the food chain/web Arrows represent the flow of energy Why would we use webs instead of chains?

Energy and Biomass Pyramids

How do the two relate?

Communities (From earlier) A group of interacting populations that occupy the same area at the same time. Living things only Organisms adapt to the conditions under which they live. What factors might influence tropical fish community?

Limiting Factors and Tolerance Limiting factor – restricts the…of organisms Numbers Reproduction Distribution Could be biotic (ex. competition for food) or abiotic (temperature) Range of tolerance – upper and lower limit of a particular limiting factor Example: 9-25 oC for steelhead trout Conditions under which they can live (might not necessary thrive)

Ecological Succession How might an ecosystem respond to a drastic change in biotic/abiotic factors? Example: forest fire

Primary Succession The establishment of a community in an area of exposed rock that does not have any topsoil Example: Solidified lava flow First step: Lichens (a mutualistic relationship between a fungus and an algae) and mosses As they die, make first layer of soil Pioneer species Later: Weedy plants (grasses and ferns) Much later: Shrubs and trees

Secondary Succession A process that occurs after a disturbance has taken place, but the soil remains Example: forest fires What’s different about the time scale? Thought question: notice the species at the start and at the finish

When does succession “end?” Unclear. (hard to tell) Climax community – when a stable community has formed What role might humans play?