Bio 004,CH19, College of the Desert
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Collection of interacting organisms of different species within an ecosystem.
- The variety of different kinds of organisms.
- 1. Species richness
- 2. Relative abundance
- 3. Species diversity
Total number of different spp in the community
Size of populations of different spp in the community
The number and relative abundance of spp in a community.
Other Properties of a Community
- 1. Prevalent Form of Vegetation.
- 2. Stability.
- 3. Trophic Structure.
Encounters be-tween members of different species.
Three main types of interspecific interactions: Competition, Predation, Symbiosis
Competitive Exclusion Principle
Populations of two spp cannot coexist in a community if their niches are nearly identical. Usually results in one spp dying out, moving out, or adapting to occupy another niche. Possible mechanism for natural selection.
- When populations of two or more spp in a community rely on similar limiting resources.
- 1. Niche
- 2. Resource partitioning
Sum total of spp use of biotic and abiotic resources in the environment (eco-logical role in nature - job). Example: birds of prey - diurnal v. nocturnal.
Differentiation of niches that enables similar spp to co-exist in a community (Darwin’s finches).
- Predator: Organism that eats another.
- Prey: Organism that gets eaten by another (food).
- 1. Acute senses
- 2. Ability to catch and subdue prey.
- 3. Fast and agile (pursuit).
- 4. Camouflage (ambush).
Plant Defenses v.
- 1. Chemical weapons: Poisonous (nicotine) or distasteful (peppermint).
- 2. Mechanical weapons: Spines or thorns.
Animal Defenses v. Predators
- 1. Hiding, fleeing (passive).
- 2. Alarm calls distraction (active).
- 3. Cryptic coloration (camouflage).
- 4. Mechanical, chemical defenses.
Defenses v. Predators
- 1. Aposematic coloration: Bright-color warning. Frog.
- 2. Batesian mimicry: Copy a harmful spp. Camouflage.
- 3. Mullerian mimicry: Shared copies of distasting spp. Monarch taste bad so Bisoroy (spelling) must taste bad because they look similar.
- Interaction between two or more spp that live in close contact.
- 1. Parasitism: Parasite, Host
- 2. Mutualism
Organism that lives on or in another organism – usually smaller; benefits.
Organism supporting another organism living on or in it –usually bigger; harmed.
Interaction between two or more species in which both benefit. Methanogens & N-fixing bacteria, Acacia trees and ants, Coevolution usually occurs between mutualistic spp.
Episodes that damage biological communities temporarily or long term by destroying organisms and affecting the availability of resources. Examples: storms, fires, floods, droughts, & humans.
Transition in spp composition of a community following an ecological disturbance.
Occurs in a virtually lifeless area where no original organisms exist; no soil is present.
Occurs where an existing community has been cleared by a disturbance, but the soil is left in tact.
Trophic Levels and
- 1. Trophic level
- 2. Food chain
- 3. Producers
- 4. Consumers
- 5. Omnivores
- 6. Decomposers
Logical sequence of food transfer from one trophic level to another.
Organisms that use sunlight for photosynthesis and produce organic molecules from inorganic molecules. Examples: cyanobacteria, algae, & plants.
- Organisms that obtain energy as organic material from other organisms. Examples: herbivores (plant eaters - primary) & carnivores (meat eaters - secondary).
Organisms which feed on both plants and animals.
Organisms which feed on dead and decaying material.
A system of interwoven food chains creating a more stable community.
- 1. Pyramid Base; Producers.
- 2. 1st Level: 1° Consumers.
- 3. 2nd Level: 2° Consumers
Dry weight of all organisms at a specific trophic level.
- Include carbon, nitrogen, phosphorous, and water.
- 1. All cycles have an abiotic reservoir and can bypass the biotic components.
Chemical Cycles –
- 1. Certain cycles (N) require microorganisms in order to enter biotic components.
- a)80% of atmosphere is N, but plants cannot utilize N directly (N-fixing bacteria).
- b)Animals obtain N from their diet.
Large regional communities primarily determined by climate (temperatures & rainfall as well as altitude and latitude (terrestrial).
Aquatic Biomes –
- 1. Standing bodies of water (lakes & ponds).
- 2. Flowing water (rivers & streams).
Where freshwater merges with salt. Marine life distributed according to depth, degree of light penetration, distance from shore & surface, and temperature.
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