© 2009 Delmar, Cengage Learning Chapter 12 Population Ecology.

© 2009 Delmar, Cengage Learning

Chapter 12

Population Ecology


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


Population Ecology

• Population ecology – is the study of organisms at the population level instead

of just individuals


Population Characteristics

• Several measures describe populations– density

– distribution

– birthrates and death rates

– age structure

– sex ratio

– fecundity (reproductive rate)


Population Density

• Number of individual organisms living within a defined area– number of prairie dogs per square mile

– number of students per classroom


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


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


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


Birthrates and Death Rates

• Death rate– Number of deaths in comparison with the number of

individuals per year


Factors Affecting Birthrate

• Three main factors influence a population’s birthrate– age structure

– mating systems

– sex ratio


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


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


Fecundity of a Population

• Number of eggs produced per female

• Fertility

• Production


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


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


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


Causes of Extinction

• Several factors affect extinction– habitat destruction or degradation

– introduced or non-native species

– low numbers

– pesticides

– illegal killing


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


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


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


Aquatic Biomes

• Among the many biomes found in or around water are– freshwater

• lotic environment

• lentic environment

• wetlands

– marine


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


Freshwater Biome

• Abiotic factors that shape the freshwater biome– water temperature

– light intensity

– concentration of dissolved materials

– flow rate of a stream


Freshwater Biome

• Two different kinds of habitat in freshwater biome– lotic habitats

– lentic habitats


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


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


Wetlands

• Evidence shows wetlands are difficult to restore– Several groups are attempting to restore wetlands


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


Marine Biome

• Great diversity of environments– intertidal zone

– continental shelf

– oceanic zone

– estuaries


Terrestrial Biomes

• Biomes found on land include– desert

– tundra

– grassland

– temperate forest

– coniferous forest


Desert

• Temperatures– Daytime temperatures usually high

– Nights usually cold

• Biome with less than 10 inches of precipitation a year


Desert

• Desert organisms must be specially adapted to dry conditions– plants

• taproots, short growing seasons

– animals• get water from food, lap up dew


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


Tundra

• Plants and animals– adapted to cold and limited vegetation


Grassland

• Treeless biome often found in interior of continents– warm to hot summers

– cold, freezing winters

– periodic droughts

– frequent fires


Grassland

• Vegetation includes grasses and other plants adapted to this environment


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


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


Coniferous Forest

• Dominated by coniferous trees– produce seeds in cones

– needle-shaped leaves

© 2009 Delmar, Cengage Learning Chapter 12 Population Ecology.

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