A community is all the organisms that live within a given area. This type of study usually focuses on interaction between species. All ecosystems have producers, consumers, and decomposers. Producer – an organism that makes its own food Plants do this by participating in photosynthesis (energy obtained from light) Other organisms do this by participating in chemosynthesis (energy obtained from chemicals)

Consumer – an organism that obtains energy by eating other organisms Herbivores eat plants Carnivores eat other animals Omnivores eat plants and other animals Ecologists construct food chains and food webs Food chain – a linear diagram that shows trophic levels (how energy flows from one organism to another) Ex: grass  antelope  lion grass – producer antelope – primary consumer lion – secondary consumer

Food chains always begin with a producer and end with a consumer and it shows predator/prey relationships. Predator – an organism that kills and feeds on another organism Prey – an organism that gets killed and consumed by another organism The predator at the end of the food chain is the top predator A food web displays all of the food chains in an ecosystem. It shows how different species competes for food. Plants are the lowest trophic level (producers) and foxes, hawks, and snakes are the highest tropic levels (top predators) It also displays the symbiosis of a community.

Symbiosis is the interaction of two species at live in close proximity to one another. Three types of symbiotic relationships: Parasitism – an interactive relationship in which one species is benefited and the other is harmed (cuckoos and warblers) Commensalism – an interactive relationship in which one species is benefited with no effect on the other (remoras and sharks) Mutualism – an interactive relationship in which both species benefit from one another (bees and clover)

The energy in most ecosystems comes from the Sun. Producers convert that energy to organic molecules. Primary productivity – the rate at which an ecosystem’s producers build organic matter (biomass) What has a greater primary productivity – tropical rain forests or deserts? Once biomass is created in producers, it can be passed along to primary consumers, secondary consumers, etc. As energy moves up the food chain, much of it is lost to the consumer. Only about 10% makes it to the next level to be used to make biomass (growth and reproduction) The other 90% gets unused because: Some food sources never get eaten, so energy decomposes back into ground Some food that gets eaten is used for basic functioning (maintenance) Some food gets digested and excreted (feces) Result: An ecosystem always has less and less biomass as you move up a food chain (more grass than zebras, more zebras than lions) It is a diagram that shows the energy at different levels of a food chain. It shows that you lose energy as you move to the top of the chain. Primary Succession – the onset of simple, hearty producers in a pristine habitat. Ex: When new rock is exposed (lava flow, glacial retreat), the first producers to grow are mosses and lichens (pioneer plants). They work to break down rock to form soil for the establishment of small plants and shrubs. Secondary Succession – the onset of new producers in an area where an event has destroyed a previous ecosystem Ex: After a natural disaster (forest fire, tsunami, etc.) it doesn’t take too long for species to move in. The pioneer plants can be more complex because soil has already been established. It just needs to be repopulated. Succession stops when a climax community is achieved. Climax community – the stable group of species that eventually occupies an ecosystem.