Chapter 13: Ecology, Communities and the Environment

Ecology

Ecology

Ecology:

• Study of the interactions between organisms and their environment

Levels of Ecology

Level of ecology:

• Organism:
  • Individual living entity
• Population:
  • All the organisms of a species within an area
• Community:
  • All the distinct populations within an area
• Ecosystem:
  • System of communities and the abiotic systems with which they interact
• Biosphere:
  • All the ecosystems on earth

Habitat, Niche

Habitat

Habitat:

• Area where an organism lives

Niche

Niche:

• An organism’s “place” within its environment
  • Includes all the ways the organism interacts with its environment - where it lives, what it eats, its role within its ecosystem, etc.

Competitive exclusion principle:

• Two species cannot occupy the same niche; one will inevitably outcompete the other

Niche Partitioning:

• Two species coexisting in a niche by partitioning the niche
  • Example: Two species of birds occupying different parts of a tree

Interactions

Competition

Organisms in an ecosystem compete for resources - such as food, space, mates

Intraspecific Competition:

• Competition within a species

Interspecific Competition:

• Competition between two distinct species

Predation

Predators eat prey.

Symbiosis

Symbiotic Relationship:

• Extended interactive relationship between different species
• Mutualism:
  • Both organisms benefit
    • Example: sea anemone and clown fish
• Commensalism:
  • One organism benefits and the other is unaffected
    • Example: whale and barnacle
• Parasitism:
  • One organism benefits and the other is harmed
    • Example: dog and flea

Food Chain

Organic Material

Organisms obtain energy by consuming organic material.

The organic material needs to be synthesized from inorganic material.

Trophic Categories

Autotroph:

• Organism that synthesizes its own organic material
• Photosynthesis:
  • Process by which plants synthesize organic material using sunlight
• Chemosynthesis:
  • Process by which select organisms synthesize organic material using energy obtained from oxidative reactions

Heterotroph (Consumer):

• Organism that obtains organic material by consuming other organisms

Types of Consumers

Consumer:

• Organism that obtains organic molecules by consuming other organisms

Types of consumers:

• Herbivore:
  • Eats plants
• Carnivore:
  • Eats animals
• Omnivore:
  • Eats both plants and animals
• Detritivore:
  • Eats dead organisms
• Decomposer:
  • Secretes enzymes that decompose organic material back into inorganic material
  • Includes bacteria, fungi

Food Chain

Food Chain:

• Linear representation of the progression of food, from the organism that synthesizes it, up to the organism that eats it, etc.

Food Web:

• Non-linear representation of the food progression; takes into account that organisms may eat others on their level, or others more than one level below, etc.
• More complex than a food chain; generally more realistic

Trophic Level:

• An organism’s level within a food chain
  • Producer:
    • Bottommost, autotroph
  • Primary Consumer ($1 ^\circ$):
    • Eats the producer
  • Secondary Consumer ($2 ^\circ$):
    • Eats the primary consumer
  • Tertiary Consumer ($3 ^\circ$):
    • Eats the secondary consumer
  • Quaternary Consumer ($4 ^\circ$):
    • Eats the tertiary consumer
• In a food web, an organism can have multiple trophic levels; for example, it can be both a primary and secondary consumer

Food Chain Pyramids

Food Chain Pyramid:

• Demonstrates a variables variation at each trophic level
• Food Chain Energy Pyramid:
  • The food chain’s energy pyramid is always largest at the bottom and smaller as it goes up
  • Each trophic level has less energy than the previous level
  • Each transformation of energy between levels loses energy to entropy
• Other food chain pyramids include pyramid of numbers - demonstrating the number of organisms at each level, and pyramid of biomass - demonstrating the total biomass at each level.
• The pyramid of biomass is typically largest on bottom and smaller as it goes up, however, the pyramid of numbers can assume varied shapes.

Abiotic Cycles

Abiotic Resources

Abiotic - non living - resources, such as water and nutrients, are finite.

Essential elements are cycled between biotic and abiotic states.

Water Cycle

In the water cycle, water cycles between the atmosphere and the geosphere:

• Precipitation:
  • Water falls from clouds as rain or snow
• Evaporation:
  • Open water evaporates into the atmosphere
• Transpiration:
  • Water in leaves evaporates into the atmosphere
• Condensation:
  • Water in the atmosphere condenses into clouds

Carbon Cycle

• Atmospheric $CO_2$ is absorbed by plants during photosynthesis
• $CO_2$ is released into the atmosphere by:
  • Decomposition
  • Respiration
  • Burning fossil fuels such as coal, oil and gasoline

Nitrogen Cycle

• Atmospheric nitrogen is not directly usable
• Nitrogen Fixation:
  • Various bacteria convert atmospheric nitrogen to a usable form
• Assimilation:
  • Plants absorb nitrate from the soil
  • Other organisms obtain nitrogen by eating plants, etc.
• Decomposition:
  • Biotic organisms die, decompose, and the nitrogen is returned to the soil
• Decomposed nitrogen can be recycled, or denitrified by bacteria and returned to the atmosphere.

Phosphorous Cycle

• Phosphorous is needed for ATP, DNA, RNA, phospholipids, bones, and other organs.
• The phosphorous cycle does not have a gaseous phase, and takes much longer than other cycles.

Schematics

• Food chain

  

• Food web

  

• Energy Level Pyramid

  

• Pyramid of Numbers