Population EcologyPopulation Ecology

Mrs. GamariMrs. Gamari

EcologyEcology The study of the interaction between The study of the interaction between

organisms and their environment (living organisms and their environment (living and non-living).and non-living).

Biotic – living factorsBiotic – living factors Example: living organisms in the environment and Example: living organisms in the environment and

their effects on other living thingstheir effects on other living things

Abiotic – non-living factorsAbiotic – non-living factors Example: water, oxygen, light, temperature, Example: water, oxygen, light, temperature,

inorganic and organic nutrientsinorganic and organic nutrients

Organization in the Living Organization in the Living EnvironmentEnvironment

Ecologists often study a group of organisms in a Ecologists often study a group of organisms in a particular environment.particular environment.

PopulationPopulation All individuals of a All individuals of a single speciessingle species that live within a certain area that live within a certain area

EXAMPLE: All of the bullfrogs in a pond = populationEXAMPLE: All of the bullfrogs in a pond = population

CommunityCommunity A group of different populations/organisms in a certain area.A group of different populations/organisms in a certain area.

Example: The bullfrogs, fish, algae, plants, etc. in that same pondExample: The bullfrogs, fish, algae, plants, etc. in that same pond

EcosystemEcosystem A community and its physical environment; made of abiotic and biotic A community and its physical environment; made of abiotic and biotic

factors.factors. Continual exchange between all parts (living and nonliving) of the Continual exchange between all parts (living and nonliving) of the

ecosystemecosystem

Population SizePopulation Size The number of individuals that a population The number of individuals that a population

contains.contains.

Can be difficult to measure directly, especially Can be difficult to measure directly, especially if there are too many organisms over a large if there are too many organisms over a large area, and they are very mobile.area, and they are very mobile.

Therefore, an ecologist may need to ESTIMATE the Therefore, an ecologist may need to ESTIMATE the number of individuals in a populationnumber of individuals in a population

CRITICAL THINKINGCRITICAL THINKING An ecologist counts 25 oak trees in a An ecologist counts 25 oak trees in a

small patch of forest. S/he needs to small patch of forest. S/he needs to estimate how many oak trees would be in estimate how many oak trees would be in an area that is 10x larger than the small an area that is 10x larger than the small patch.patch.

How many oak trees could be in that larger How many oak trees could be in that larger area? Explain your reasoning.area? Explain your reasoning.

Population DensityPopulation Density Measures how crowded a population is.Measures how crowded a population is.

Number of individuals per unit of areaNumber of individuals per unit of area

Some areas are Some areas are sparselysparsely populated, populated, while others are very while others are very denselydensely populated. populated.

Why do you think this may be?Why do you think this may be?

Measuring the Number of Measuring the Number of Individuals in a Individuals in a PopulationPopulation

Random Sampling – count the number of Random Sampling – count the number of individuals in a small area. Extrapolate to find individuals in a small area. Extrapolate to find the number of individuals in a larger area.the number of individuals in a larger area.

Mark and Recapture – mark a sample of Mark and Recapture – mark a sample of individuals and return them to the wild. Come individuals and return them to the wild. Come back and capture another sample to see how back and capture another sample to see how many have already been marked. Use a many have already been marked. Use a formula to estimate population sizeformula to estimate population size

DispersionDispersion The spatial distribution of individuals within The spatial distribution of individuals within

the populationthe population

http://www.uwyo.edu/dbmcd/popecol/feblects/lect06.html

• The distribution of a population may be impacted by availability of resources, social behavior, or habitat conditions.

Age StructureAge Structure Total number of people

Females

Percentage of individuals within a particular age range

Age ranges

The Regional Institute © 2007

Western New York Age Pyramid, 2000

http://www.uwyo.edu/dbmcd/popecol/feblects/lect06.html

Males

Population DynamicsPopulation Dynamics A population will change in A population will change in

size depending on how many size depending on how many organisms are organisms are addedadded to it and to it and how many organisms are how many organisms are removedremoved from it. from it.

If resources are not limited, If resources are not limited, then the population will grow then the population will grow when the number of new when the number of new individuals added to the individuals added to the population (births) is greater population (births) is greater than the number of individuals than the number of individuals who leave the population who leave the population (deaths).(deaths).

Immigration vs. EmigrationImmigration vs. Emigration

J- Shape CurveJ- Shape Curve The population keeps The population keeps

growing over time. growing over time. Starts slowly, but then Starts slowly, but then rapidly increases.rapidly increases.

Number of individuals Number of individuals coming into the coming into the population exceeds the population exceeds the number leaving the number leaving the populationpopulation

The Biology Cornerhttp://www.biologycorner.com/bio4/notes/popgrowth.php

Carrying CapacityCarrying Capacity The maximum population that can be The maximum population that can be

supported by resources in the supported by resources in the environment. environment.

In reality, resources are not “unlimited.”In reality, resources are not “unlimited.”

S- Shape CurveS- Shape Curve Shows how a Shows how a

population becomes population becomes limited by limited by environmental factorsenvironmental factors

The “plateau” is the The “plateau” is the carrying capacity for the carrying capacity for the area – the maximum area – the maximum number of individuals number of individuals that the environment that the environment can support.can support.

The Biology Corner

http://www.biologycorner.com/bio4/notes/popgrowth.php

Factors That Limit Factors That Limit Population GrowthPopulation Growth

NutrientsNutrients WaterWater DiseaseDisease CompetitionCompetition PredationPredation SpaceSpace

Population RegulationPopulation Regulation Density-Independent FactorsDensity-Independent Factors

Weather, floods, firesWeather, floods, fires Reduce the size of populations, regardless of the original Reduce the size of populations, regardless of the original

size or density of a particular population.size or density of a particular population.

Density-Dependent FactorsDensity-Dependent Factors Resource limitations, shortage of food, habitats (competition, Resource limitations, shortage of food, habitats (competition,

predation, disease, parasitism and disease)predation, disease, parasitism and disease) Triggered by increasing populationsTriggered by increasing populations An individual’s chance of surviving depends on the number of An individual’s chance of surviving depends on the number of

other individuals in that area.other individuals in that area.

PredationPredation

CompetitionCompetition Intraspecific competition: competition within a Intraspecific competition: competition within a

species for resources (food, light, space, species for resources (food, light, space, nutrients, habitats)nutrients, habitats)

Interspecific competition: competition between Interspecific competition: competition between members of different species. HUGE impact members of different species. HUGE impact on evolutionary change because survival rates on evolutionary change because survival rates can be affected over time.can be affected over time.