2 populations
TRANSCRIPT
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Populations
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Populations
• All individuals of a given species in a particular habitat
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Communities
• All the organisms in a defined area• Ecosystem
– A community plus all the non-living (abiotic) components in a habitat
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Populations
• Measuring Populations• How populations are regulated
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Measuring Populations
• Population Density–Number of individuals per unit area
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Population Density
• Influenced by
– Mortality– Emigration
– Natality– Immigration
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Population Growth
• Population density fluctuates
• Natality + immigration = mortality + emigration
• Mortality is usually high
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Types of Populations
• Open
– Natality, mortality, immigration and emigration affect population size
• Closed
– Only natality and mortality affect population size
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Exponential Growth
• Under favourable conditions
• No predators, parasites or competition
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Sigmoid Growth• Natural conditions• Curve flattens because
of– Competition– Predators– Parasites – Environmental resistance– Carrying capacity
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Closed Population Growth
• No immigration or emigration
• Population slowly kills itself– Lack of
• Food• Space• Oxygen• Water
– Poisons itself
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J Curve
• Closed population• Upper limit
– Seasonal conditions• Never reaches carrying capacity
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Survivorship
• The chance of remaining alive to pass on your genes to the next generation
• Life expectancy
• Life span
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Survival of the species
• Most energy is put into survival of species
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Age Group structure
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Population Distribution
• Clumped • Random• Evenly spread out
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Clumped Populations
• Increases competition for food and space
• Reduces drying out• Greater defence• Easier to find mates• May also be due to
substrate
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Evenly Spread
• Animals– By competition or
aggression– Defended territories– Limits population
density
• Plants– Shading– Competition– Allelopathy
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Population Regulation
• Abiotic– Tolerance– Acclimation– Geographical Barriers – Liebig’s Law of Minimum
• Biotic– Predation, paracitism– Disease, toxic wastes– Competition, Humans
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Tolerance
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Acclimation
• When tolerance limits for an organism change they acclimatise– Slow process– Usually to seasons
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Liebig’s Law
• The functioning of an organism in limited or controlled by whatever essential environmental factor is in the least favourable amount
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Geographical Barriers
• Mountain ranges• Seas and oceans• Rivers
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Predation
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Humans
• Over-hunting– Extinction
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• Destroy habitats– Draining swamps– Clearing forests
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• Over-use of pesticides
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• Toxic wastes