© 2009 Delmar, Cengage Learning
Population Ecology
• Ecology – is the study of interactions
– Used to get the most accurate picture of the environment
• Management decisions are based on what is happening to the total population, not individual organisms
© 2009 Delmar, Cengage Learning
Population Ecology
• Population ecology – is the study of organisms at the population level instead
of just individuals
© 2009 Delmar, Cengage Learning
Population Characteristics
• Several measures describe populations– density
– distribution
– birthrates and death rates
– age structure
– sex ratio
– fecundity (reproductive rate)
© 2009 Delmar, Cengage Learning
Population Density
• Number of individual organisms living within a defined area– number of prairie dogs per square mile
– number of students per classroom
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Population Density
• Important to scientists– especially when several years’ worth of data are
available
– allows interpretation
– can assess whether population is growing, shrinking, or stabilized
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Population Distribution
• A measure of how far apart population members live from each other (space)– Prairie dogs vs Mountain lions
• Distribution is seldom uniform– Organisms usually concentrate near resources
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Birthrates and Death Rates
• Both birthrate and death rate are gauges of overall population health
• Birthrate– Number of births in comparison with number of
individuals per year
© 2009 Delmar, Cengage Learning
Birthrates and Death Rates
• Death rate– Number of deaths in comparison with the number of
individuals per year
© 2009 Delmar, Cengage Learning
Factors Affecting Birthrate
• Three main factors influence a population’s birthrate– age structure
– mating systems
– sex ratio
© 2009 Delmar, Cengage Learning
Factors That Affect Birthrate
• Age structure– makeup in terms of maturity
– number of animals in each age group
• A population loses many mature males– likely to have a high proportion of young males
– can reduce birthrate
© 2009 Delmar, Cengage Learning
Factors That Affect Birthrate
• Mating systems
• Sex ratio– number of males compared to females
• A sufficient number of males must be available– Low number of males would decrease birthrate
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Fecundity of a Population
• Number of eggs produced per female
• Fertility
• Production
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Population Growth
• Several factors affect a population’s growth– birthrate versus death rate
– age of maturity and gestation period
– adaptability
– emigration and immigration
– availability of resources or carrying capacity• J – shaped Curve vs S – shaped Curve
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Movement of Organisms
• Some wild animals are quite mobile– emigration
• an individual’s movement out of a population
– immigration• an individual’s movement into a population
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Availability of Resources
• Resources in any environment are limited– Population growth is related to the availability of
resources
• Carrying capacity– maximum number of individual organisms that the
environment is capable of sustaining
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Causes of Extinction
• Several factors affect extinction– habitat destruction or degradation
– introduced or non-native species
– low numbers
– pesticides
– illegal killing
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Adaptability and Extinction
• Most species that survive through time have the common trait of adaptability
• Species that are capable of changing as their environments change have better chances of survival– Adaptable species can adjust
– Specialized species are vulnerable
© 2009 Delmar, Cengage Learning
Why Worry About Extinction?
• Extinction is a natural process– Then why worry about species extinction?
• The current rate at which species are going extinct is far from natural– Human activity has put most species in trouble
– Many organisms may someday benefit humans
© 2009 Delmar, Cengage Learning
Biomes
• Climate is related to latitude and altitude– Ecosystems at similar latitudes and elevations have
similar characteristics• temperature and precipitation similar
• Biomes are ecosystems with similar types of vegetation and similar climate
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Aquatic Biomes
• Among the many biomes found in or around water are– freshwater
• lotic environment
• lentic environment
• wetlands
– marine
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Freshwater Biome
• Biome contains organisms adapted to living in or near water that is not salty– Wide variety of environmental conditions found in
freshwater ecosystems
• Producers– phytoplankton
– zooplankton
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Freshwater Biome
• Abiotic factors that shape the freshwater biome– water temperature
– light intensity
– concentration of dissolved materials
– flow rate of a stream
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Freshwater Biome
• Two different kinds of habitat in freshwater biome– lotic habitats
– lentic habitats
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Freshwater Biome
• Lotic habitats– flowing water
– support little plant growth
– detritus-based food webs
• Lentic habitats– standing water such as ponds, lakes, swamps
– regions of differing light and temperature
© 2009 Delmar, Cengage Learning
Wetlands
• Land areas that are flooded during all or part of the year
• Great amount of concern about wetlands– Total area of wetlands in North America has declined
© 2009 Delmar, Cengage Learning
Wetlands
• Evidence shows wetlands are difficult to restore– Several groups are attempting to restore wetlands
© 2009 Delmar, Cengage Learning
Marine Biome
• The world’s largest biome is characterized by its salt content or salinity– oceans, bays, estuaries
• Abiotic factors shaping the marine biome– light intensity
– temperature
– pressure
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Marine Biome
• Great diversity of environments– intertidal zone
– continental shelf
– oceanic zone
– estuaries
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Terrestrial Biomes
• Biomes found on land include– desert
– tundra
– grassland
– temperate forest
– coniferous forest
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Desert
• Temperatures– Daytime temperatures usually high
– Nights usually cold
• Biome with less than 10 inches of precipitation a year
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Desert
• Desert organisms must be specially adapted to dry conditions– plants
• taproots, short growing seasons
– animals• get water from food, lap up dew
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Tundra
• Northern biome– permafrost
– no trees
– temperatures below freezing most of year
– less than 10 inches of precipitation a year
– summer months produce wet and spongy environment
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Grassland
• Treeless biome often found in interior of continents– warm to hot summers
– cold, freezing winters
– periodic droughts
– frequent fires
© 2009 Delmar, Cengage Learning
Grassland
• Vegetation includes grasses and other plants adapted to this environment
© 2009 Delmar, Cengage Learning
Temperate Forest
• Biome dominated by broad-leaved deciduous trees– approximately 30 inches of rain a year
– four distinct seasons
• Climate is less uniform than other biomes– produces variety of plant species
© 2009 Delmar, Cengage Learning
Coniferous Forest
• Evergreen forest forms broad northern belt across North America– precipitation mostly in form of snow
• ranges from 15 inches to 40 inches per year
– winters long and cold
– summers moderate with cool nights