Ecology

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Ecology

• GHSGT REVIEW

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What is Ecology?

• The scientific study of
• Interactions among organisms
• Interactions between organisms and their
  environment
• Biosphere portions of the Earth where life
  exists (land, water, and air)

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Levels of Organization

• Species group of organisms that can breed and
  produce fertile offspring
• Population a group of individuals of the same
  species that live in the same area
• Community different populations that live in
  the same area
• Ecosystem all the organisms plus the nonliving
  environment
• Biome group of ecosystems with the same climate
  and similar communities

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Levels of Organization
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Energy Flow

• Sunlight is the main energy source for life on
  Earth.
• Autotrophs (producers) organisms that make
  their own food
• Photosynthesis use light energy to make food
• Chemosynthesis use chemical energy to make food

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Energy Flow

• Heterotrophs (consumers) organisms that must
  feed on other organisms for energy
• Herbivores eat only plants
• Carnivores eat other animals
• Omnivores eat both plants and animals
• Detrivores feed on dead matter
• Decomposers break down organic matter

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Feeding Relationships

• Energy flows through an ecosystem in one
  direction (sun ? producers ? consumers)
• Food chain a series of steps in which organisms
  transfer energy by eating and being eaten

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Feeding Relationships

• Food web a network of complex feeding
  interactions
• Trophic levels each step in a food chain or
  food web
• 1st producers
• 2nd primary consumers
• 3rd secondary consumers
• 4th tertiary consumers

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Ecological Pyramids

• Energy Pyramid shows the amount of energy
  available at each trophic level
• Only about 10 of the energy is transferred to
  the next level
• Biomass Pyramid shows the amount of living
  tissue within each trophic level
• Pyramid of numbers shows the number of
  organisms at each trophic level

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Ecological Pyramids
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Biotic and Abiotic Factors

• Biotic factors the living things that influence
  organisms
• Abiotic factors the nonliving things that
  influence organisms
• Light
• Soil
• Wind
• Water
• Temperature

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Habitat and Niche

• Habitat the area where an organism lives
• Niche the role an organism plays in its habitat
• No two species can share the same niche in the
  same habitat

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Community Interactions

• Symbiosis any relationship in which two species
  live closely together
• Mutualism both species benefit (flowers
  insects)
• Commensalism one species benefits while the
  other is neither helped nor harmed (orchids in a
  rainforest)
• Parasitism one organism benefits while the
  other is harmed (fleas on a dog)

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Symbiosis
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Populations

• Population density the number of individuals
  per unit area
• Population growth increase in size of a
  population
• Population size can be affected by
• Number of births
• Number of deaths
• Immigration organisms moving into an area
• Emigration organisms moving out of an area

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Exponential Growth

• Under ideal conditions with unlimited resources,
  a population will grow exponentially
• J-shaped curve

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Logistic Growth

• As resources become less available, the growth of
  a population slows or stops
• S-shaped curve

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Limiting Factors

• A factor that causes population growth to
  decrease
• The population size will usually remain constant
• Creates the s-shaped curve
• Two kinds of limiting factors
• Density-dependent
• Density-independent

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Density-Dependent Factors

• A limiting factor that depends on population size
• Competition organisms compete for resources
• Between members of the same species
• Between members of different species
• Parasitism and disease

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Density-Dependent Factors

• Predation when one species feeds on another
• Predator the organism that feeds on the prey
• Prey the organism being eaten

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Density-Independent Factors

• Affects all populations, regardless of the
  population size
• Unusual weather heavy storms
• Natural disasters tornado, volcanic eruption
• Seasonal cycles insects die during winter
• Human activities clear-cutting forests

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Evolution of Populations

• Directional selection - form of natural selection
  in which the entire curve moves occurs when
  individuals at one end of a distribution curve
  have higher fitness than individuals in the
  middle or at the other end of the curve

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Evolution of Populations

• Stabilizing selection - form of natural selection
  by which the center of the curve remains in its
  current position occurs when individuals near
  the center of a distribution curve have higher
  fitness than individuals at either end

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Evolution of Populations

• Disruptive selection - form of natural selection
  in which a single curve splits into two occurs
  when individuals at the upper and lower ends of a
  distribution curve have higher fitness than
  individuals near the middle

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Human Population Growth

• At first the human population grew slowly
• About 500 years ago it started increasing rapidly
• Resembles the J-shaped curve

US World Populations
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Ecological Succession

• The series of changes that occurs in a community
  over time
• Primary succession occurs on surfaces where no
  soil exists (no previous life)
• Pioneer species the first species to populate
  the area
• Lichens ? mosses ? grasses ? shrubs ? trees

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Primary Succession
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Ecological Succession

• Secondary Succession when a disturbance changes
  the existing community without removing the soil
• Tornadoes, fire, clear cutting
• Occurs much quicker than primary succession
• Climax community the relatively stable final
  community