Populations
description
Transcript of Populations
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Population DynamicsPopulation Dynamics
AP Environmental ScienceAP Environmental Science
Chapter 9, 12 & 13Chapter 9, 12 & 13
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Characteristics of a PopulationCharacteristics of a Population• Population - individuals inhabiting the same area
at the same time
• Population Dynamics: Populations change due to– Population Size - number of individuals– Population Density - population size in a certain
space at a given time– Population Dispersion - spatial pattern in habitat– Age Structure - proportion of individuals in each age
group in population
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Population SizePopulation Size• Natality
– Number of individuals added through reproduction– Crude Birth Rate - Births per 1000– Total Fertility Rate – Average number of children
born alive per woman in her lifetime
• Mortality– Number of individuals removed through death– Crude Death Rate Deaths per 1000
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Population DensityPopulation Density
• Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area– Some species exist in high densities - Mice– Some species exist in low densities - Mountain lions
• Density depends upon– social/population structure– mating relationships– time of year
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Population DispersionPopulation Dispersion
Population dispersion is the spatial pattern of distribution
There are three main classifications
Clumped: individuals are lumped into groups ex. Flocking birds or herbivore herds due to resources that are clumped or social interactions most common http://www.johndarm.clara.net/galleryphots/
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Population DispersionPopulation DispersionUniform: Individuals are regularly spaced in the environment - ex. Creosote bush due to antagonism between individuals, or do to regular spacing of resources rare because resources are rarely evenly spaced
http://www.calflora.net/bloomingplants/creosotebush2.html
www.agry.purdue.edu/turf/ tips/2002/clover611.htm
Random: Individuals are randomly dispersed in the environment ex. Dandelions due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals rare because these conditions are rarely met
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Age StructureAge Structure• The age structure of a population is usually
shown graphically
• The population is usually divided up into prereproductives, reproductives and postreproductives
• The age structure of a population dictates whether is will grow, shrink, or stay the same size
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Age Structure DiagramsAge Structure DiagramsPositive Growth Zero Growth Negative Growth (ZPG)Pyramid Shape Vertical Edges Inverted Pyramid
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• Biotic Potential– factors allow a population to increase
under ideal conditions, potentially leading to exponential growth
• Environmental Resistance – affect the young more than the elderly
in a population, thereby affecting recruitment (survival to reproductive age)
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Biotic PotentialBiotic Potential• Affect the ability of populations of a given
species to increase in size– Abiotic Contributing Factors:
• Favorable light
• Favorable Temperatures
• Favorable chemical environment - nutrients
– Biotic Contributing Factors:• Reproductive rate
• Generalized niche
• Ability to migrate or disperse
• Adequate defense mechanisms
• Ability to cope with adverse conditions
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Environmental ResistanceEnvironmental Resistance• Affect the ability of populations of a given
species to increase in size– Abiotic Contributing Factors:
• Unfavorable light
• Unfavorable Temperatures
• Unfavorable chemical environment - nutrients
– Biotic Contributing Factors:• Low reproductive rate
• Specialized niche
• Inability to migrate or disperse
• Inadequate defense mechanisms
• Inability to cope with adverse conditions
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Population GrowthPopulation Growth• Population growth depends upon
– birth rates– death rates– immigration rates (into area)– emigration rates (exit area)
Pop = Pop0 + (b + i) - (d + e)
ZPG (b + i) = (d + e)
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Population GrowthPopulation Growth• Populations show two types of
growth– Exponential
• J-shaped curve• Growth is independent of population
density
– Logistic • S-shaped curve• Growth is dependent on population
density
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Exponential GrowthExponential GrowthOne female will produce 6 young over her 100 year life span. In a population,
this amounts to a growth rate of 2%
How many elephants could result from one male and one female after 750
years?
19,000,000 elephants!!!19,000,000 elephants!!!
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Exponential Growth GraphExponential Growth Graph
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Carrying CapacityCarrying Capacity
• Basic Concept: Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths)– There is a dynamic balance between
biotic potential and environmental resistance
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Carrying Capacity (K)Carrying Capacity (K)
• Exponential curve is not realistic due to carrying capacity of area
• Carrying capacity is maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability)
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Logistic GrowthLogistic Growth• Because of Environmental Resistance,
population growth decreases as density reaches carrying capacity
• Graph of individuals vs. time yields a sigmoid or S-curved growth curve
• Reproductive time lag causes population overshoot
• Population will not be steady curve due to resources (prey) and predators
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Population Growth
• As a population levels off, it often fluctuates slightly above and below the carrying capacity.
• Reproductive Lag-
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Reproductive StrategiesReproductive Strategies• Goal of every species is to produce as many
offspring as possible• Each individual has a limited amount of
energy to put towards life and reproduction• This leads to a trade-off of long life or high
reproductive rate• Natural Selection has lead to two strategies for
species: r - strategists and K - strategists
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r - Strategistsr - Strategists• Spend most of
their time in exponential growth
• Maximize reproductive life
• Minimum life expectancy
K
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R StrategistsR Strategists• Many small offspring• Little or no parental care and protection of offspring• Early reproductive age• Most offspring die before reaching reproductive age• Small adults• Adapted to unstable climate and environmental
conditions• High population growth rate – (r)• Population size fluctuates wildly above and below
carrying capacity – (K)• Generalist niche• Low ability to compete• Early successional species
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K - StrategistsK - Strategists
• Maintain population at carrying capacity (K)
• Maximize lifespan
K
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K- StrategistK- Strategist• Fewer, larger offspring• High parental care and protection of offspring• Later reproductive age• Most offspring survive to reproductive age• Larger adults• Adapted to stable climate and environmental
conditions• Lower population growth rate (r)• Population size fairly stable and usually close to
carrying capacity (K)• Specialist niche• High ability to compete• Late successional species
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Survivorship CurvesSurvivorship Curves• Late Loss: K-strategists that produce few young
and care for them until they reach reproductive age thus reducing juvenile mortality
• Constant Loss: typically intermediate reproductive strategies with fairly constant mortality throughout all age classes
• Early Loss: r-strategists with many offspring, high infant mortality and high survivorship once a certain size and age
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Conservation BiologyConservation Biology
• Careful and sensible use of natural resources by humans
• Originated in 1970s to deal with problems in maintaining earth's biodiversity
• Dedicated to protecting ecosystems and to finding practical ways to prevent premature extinctions of species
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Conservation BiologyConservation Biology• Three PrinciplesThree Principles
1. Biodiversity and ecological integrity are useful and necessary to all life on earth and should not be reduced by human actions
2. Humans should not cause or hasten the premature extinction of populations and species or disrupt vital ecological processes
3. Best way to preserve earth’s biodiversity and ecological integrity is to protect intact ecosystems that provide sufficient habitat
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Habitat FragmentationHabitat Fragmentation• Process by which human activity
breaks natural ecosystems into smaller and smaller pieces of land
• Greatest impact on populations of species that require large areas of continuous habitat
• Also called habitat islands
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1949 1964
Habitat fragmentation
in northern Alberta
1982 1991
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Human ImpactsHuman Impacts
• Fragmentation and degrading habitat
• Simplifying natural ecosystems
• Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides
• Elimination of some predators
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Human ImpactsHuman Impacts• Deliberately or accidentally
introducing new species
• Overharvesting potentially renewable resources
• Interfering with the normal chemical cycling and energy flows in ecosystem
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Working with NatureWorking with Nature
• Learn six features of living systems– Interdependence– Diversity– Resilience– Adaptability– Unpredictability– Limits
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Basic Ecological LessonsBasic Ecological Lessons1. Sunlight is primary source of energy
2. Nutrients are replenished and wastes are disposed of by recycling materials
3. Soil, water, air, plants and animals are renewed through natural processes
4. Energy is always required to produce or maintain an energy flow or to recycle chemicals
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Basic Ecological LessonsBasic Ecological Lessons5. Biodiversity takes many forms because it has
evolved over billions of years under different conditions
6. Complex networks of + and – feedback loops exist
7. Population size and growth rate are controlled by interactions with other species and with abiotic factors
8. Organisms generally only use what they need
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Four Principles for SustainabilityFour Principles for Sustainability
1. We are part of, not apart from, the earth’s dynamic web of life.
2. Our lives, lifestyles, and economies are totally dependent on the sun and the earth.
3. We can never do merely one thing (first law of
human ecology – Garret Hardin).
4. Everything is connected to everything else; we are all in it together.