Communities, Food Chains/Webs and Succession (Chap. 46)

Communities interacting plants and animals forming a identifiable group (doesn’t include abiotic environment) –Open communities gradually blend into others forests –Closed communities have more definite borders and therefore few organisms pass between communities pond, caves

Succession – species or groups in a community give way to the next Autogenic succession –the change is because of the current species involved aspen and cherry create shady conditions that are unfavorable to themselves but good for maple and oak seedlings Allogenic succession –external forces cause the change ponds become nutrient rich because of runoff and plants begin to proliferate

Primary succession –the establishment of a community where no community previously existed –takes a very long time rocky ground  lichens, moss, plants  field  forest Secondary succession –the establishment of a new community where a previous community had been –more rapid than 1º succession fields  small plants, shrubs  forests

Ecosystems consists of all the species AND components of the physical environment (abiotic factors) of a particular site components of an ecosystem –Ecologists categorize organisms into three categories/trophic levels based on their metabolism and role within the community

1. Autotrophs (Producers) –convert energy from sunlight or inorganic molecules into organic molecules –producers start all food chains 2. Heterotrophs (Consumers) –organisms that use energy in organic matter obtained from other organisms –can be subdivided into primary, secondary, tertiary, quaternary consumers ex. rabbit, snake, hawk, lion

3. Detritivores (Decomposers) feed off dead organic matter by ingesting it. ex. worms, dung beetles, bacteria 4. Saprotrophs (Decomposers) feed off dead organic matter by secreting digestive enzymes into it and absorbing the products of digestion. ex. bread mold, mushrooms Both are very important to break down nutrients in complex organic compounds that otherwise would be permanently locked up in dead organic matter

Food Chain a sequential path of food consumption the table below gives one example of a food chain and the trophic levels represented in it. Grass → Grasshopper → Toad → Snake → Hawk → Bacteria of decay In general, Autotro phs (Produc ers) → Herbivores (Primary Consumers) → Carnivores (Secondary, tertiary, etc. consumers) → Decompo sers

Food Web a diagram that shows all the feeding relationships in a community more realistic than a food chain and much more complicated