A community is best described as a group of organisms of a variety of species that coexist in a defined area (immediate region). Thus, community ecology is the study of the ways in which members of these diverse species interact. Community ecology encompasses not only the manner of relationships between living factors (biotic), but between nonliving factors as well (abiotic). Biotic factors consist of producers (autotrophs), consumers (heterotrophs), and Decomposers. The producers in the community are widely categorized as plants… but bacteria can be autotrophs as well. The two subcategories of producers are Photosynthetic autotrophs and chemoautotrophs. Chemoautotrophs (bacteria) use external energy derived from chemical compounds to create their own food through the process of chemosynthesis. Photosynthetic autotrophs (plants) use sunlight as their catalyst for food production (hence the name producers) for photosynthesis. Heterotrophs feed on producers in order to get their energy (which is why they’re called consumers… I think ya get it). Heterotrophs can be divided into three subcategories: Carnivores, omnivores, and herbivores. Herbivores eat only plants (autotrophs). Some examples would be deer, grasshoppers, mice, etc. Carnivores have a strictly meat-based diet, so they feed exclusively on other consumers (Scavengers, a division of carnivores, feed on dead carcasses). Prime examples of carnivores would be Big Cats, Birds of Prey, and sharks. And Omnivores strike a balance between the two, eating both autotrophs and their fellow heterotrophs. Common-place organisms with an omnivore nature would be bears (grizzlies), humans, and raccoons. Decomposers are organisms (fungi and bacteria) that dissolve corpses into organic matter, thus cycling the nutrients back into the ecosystem. These feeding relationships determine the flow of energy & cycling of nutrients from autotrophs to heterotrophs. Coevolution is key—it determines community stability. Though it may not appear helpful, predation causes the prey to adopt defensive adaptations with each successive generation.
Four Main Species:

Ø Keystone: A species that is critical to the ecological framework of a community, and has a huge impact on the community
Ø Indicator: A species that reflects the biological condition (health, etc) of an ecosystem. These species would be the first to have their population decline if there was a negative impact on the environment
Ø Native: Species that are naturally in that habitat. It naturally lives in thrives in the area. (indigenous to the area)
Ø Alien: Species introduced to the ecosystem by unnatural means (human introduction). NOT indigenous to the area. Often-times competes with native species for resources, resulting in the decline of native populations.
Energy Pyramid:
In an ecosystem, nutrients are recycled… energy is not. The energy pyramid depicts how energy travels between the organisms of an ecosystem. The initial source of energy to EVERY ecosystem/community is the sun. The sun’s energy is received directly by autotrophs, who when consumed, pass their energy on to heterotrophs known as primary (1st level) consumers. The primary consumers are devoured by secondary consumers (2nd level), and those are then eaten by tertiary consumers (3rd level). Each level of energy-using organisms forms what is known as a trophic level. Each time energy is transferred to each successive trophic level, only 10 % of the energy is transferred (producers
à 100%, primary consumers à 10%, secondary consumers à .1%, tertiary consumersà .01%). Due to this, most ecosystems can only support 3 levels of consumers.
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Symbiotic Relationships:

Ø Mutualism: A symbiotic relationship in which both organisms involved benefit.
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Ø Commensalism: A symbiotic relationship in which one organism benefits and the other is unaffected (neither helped not harmed).
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Ø Parasitism: A symbiotic relationship in which one organism benefits, and the other is harmed.
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Misc:

Ø Predation: One organism eats another (owl preys on mouse). Results in evolution; mouse develops defensive adaptations; owl develops “offensive” adaptations.
Ø Competition: Two species compete for resources for survival. Results in both future adaptations (evolution to gain advantage), and the decline of one species. (Bobcat and Coyote both use rabbit population as a resource).
Competition: Species in an ecosystem compete for limited supplies—so the flourishing of one species results in the vulnerability of another.

v Intraspecific competition (between individuals of the same species): Members of the same species both rely on the same resource, so it’s a competition of who attains it first. Examples include neighboring wolf packs that both hunt caribou, cougars that both eat jackrabbits, etc.
v Different Types of Interspecific Competition (between various species):
Ø Interference Competition: 1 species directly interferes with the survival of another by physically preventing the species from establishing itself in the habitat (preventing access to resources, etc)
Ø Exploitative Competition: Indirect competition in which both species depend on a limited resource. One species’ use of the resource depletes its ability to the other species.
Ø Apparent Competition: Indirect competition in which both species are literally competing for survival—both are the prey of the same predator. The survival of one species results in the decline of the other, since the predator will prey on the species that is less capable.
Questions!:
1. Explain why most ecosystems can’t support more than 3 trophic levels of consumers.
2. Explain how competition and predation contribute to evolution.
3. A clownfish living in a sea anemone is an example of what kind of symbiotic relationship?
a) Parasitism b) Commensalism c) Mutualism d) Predation
4. What are the paths of energy and nutrients in an ecosystem?
a) Nutrients are recycled, energy is not b) Both are recycled
c) Both are nonrenewable d) Energy is recyled, nutrients are not



Community Interactions Crossword










Question Answers:

  1. Since only 10 % of the energy from each level is transferred to each level of consumers, the number of organisms that need to be consumed increases closer towards the top of the pyramid. Eventually, it becomes impossible for an organism to sustain itself with enough food/energy—or to find enough resources.
  2. Competition and evolution cause the prey to develop defensive adaptations to protect themselves from their predators. Predators then develop adaptations in turn to maintain access to their prey and counter the defensive adaptations.
  3. Answer Choice "B"
  4. Answer Choice "A"
Community Interactions Crossword Answers:
1. PARASITISM, 2. INTERSPECIFIC, 3. HETEROTROPH, 4. TROPHIC LEVEL, 5. HERBIVORE, 6. DECOMPOSER, 7. MUTUALISM, 8. PREDATION, 9. PHOTOSYNTHESIS, 10 (DOWN). NATIVE, 10 (ACROSS). NUTRIENTS, 11. COMPETITION, 12. AUTOTROPH, 13. INTRASPECIFIC, 14. CARNIVORE, 15. OMNIVORE, 16. ENERGY, 17. COMMENSALISM, 18. ALIEN, 19. INDICATOR, 20. CHEMOSYNTHESIS, 21. KEYSTONE

Sources:
www.mansfield.ohio-state.edu

What I learned from Environmental Systems =)
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