Chapter 5: PopulationsChapter 5: Populations

5.1 How Populations Grow?5.1 How Populations Grow?Describing PopulationsDescribing Populations

How do ecologists study populations?Populations are studied by

Geographic range Density and distribution Growth rate Rate structure

Geographic RangeGeographic Range

Area inhabited by a population Can vary in size depending on the

species

Density & DistributionDensity & Distribution The number of individuals of a particular species at a specific

place. The number of individuals per unit area. Distribution refers to how individuals in a population are

spaced out across the range of the population. Random, Uniform, Clumped Refer to Fig 5-2

For Example: the number of alligators per square mile of the everglades

population = individuals = 400 alligators = 10 alligators density unit area 40 km2 km2

By measuring the population density of a specific species can give us a better idea of the effects of the environment in a specific area.

Patterns of DistributionPatterns of Distribution

Growth RateGrowth Rate Indicates whether the size of a population

increases, decreases or is sustained.

Age StructureAge Structure The number of males and females of each

age contained in a population.

Population GrowthPopulation GrowthWhat factors affect population What factors affect population

growth?growth? The factors that can affect population size.

birthrate death rate immigration & emigration rates

It depends on how many individuals are added or removed.

Exponential GrowthExponential Growth

Is the growth of a population by a constant factor at constant time intervals.

Unlimited resources and absence of predation and disease, population will grow exponentially.

Logistic GrowthLogistic Growth When a population’s growth slows and then

stops following a period of exponential growth.

Phases of GrowthPhases of Growth Phase 1: Exponential Growth Phase 2: Growth Slows Down Phase 3: Growth Stops

The Logistic Growth CurveThe Logistic Growth Curve

It occurs when a population’s growth slows and then stops, following a period of exponential growth.

Carrying CapacityCarrying Capacity Maximum number of organisms in a population

that an environment can maintain. When birthrate and the death rate are the same. When immigration equals emigration.

Carrying CapacityCarrying Capacity The population of seals

before the early 1900’s kept this population below its carrying capacity. After the hunting was reduced, the seal population increased exponentially until it reached its carrying capacity. This S-shaped curve indicates a rapid increase in population for a period of time that will stabilize after reaching carrying capacity of the environment.

Carrying Capacity Video

5.2 Limits to Growth5.2 Limits to Growth

Condition that restricts a population's growth, such as space, disease, and food availability.

What factors determine carrying capacity?What factors determine carrying capacity?

Density-Dependent Limiting Density-Dependent Limiting FactorsFactors

Factor that limits a population more as population density increases. Competition Predation Herbivory Parasitism Disease Stress from overcrowding

CompetitionCompetitionWhen populations become crowded, individuals compete for:FoodWaterSpaceSunlightTerritoriesOther essentials

Predation and HerbivoryPredation and Herbivory• Predator-

Prey Relationships

• Herbivore Effects

• Humans as Predators

Refer to pages 138-139

Parasitism and DiseaseParasitism and DiseaseParasites and disease causing organisms feed at the expense of their host, weakening them and often causing disease or death.

Stress From OvercrowdingStress From OvercrowdingHigh level of stress can weaken the body’s ability to resist disease or it can cause females to neglect, kill, or even eat their own offspring.

Limiting Factor video

Density-Independent Density-Independent FactorsFactors

Unusual weather such as hurricanes, droughts, floods.

Natural disasters such as wildfires.

Fig. 5-10

What limiting factors do not typically depend on What limiting factors do not typically depend on population density?population density?

Limiting Factors Video

5.3 Human Population 5.3 Human Population GrowthGrowth

The human population, like populations of other organisms, tend to increase.

How has human population size changed over time?How has human population size changed over time?

Historical OverviewHistorical Overview The human population has increased explosively. Wide-scale farming began to replace hunting and gathering,

providing a more plentiful food supply. More food meant people reproduced more and lived longer, and the population began to climb.

In the past few centuries, death rates have continued to decline because of improvements in nutrition, sanitation, and health care.

Predicting Future Population Predicting Future Population GrowthGrowth

A city population's demands for food, water, energy and other supplies can strain resources far from the city.

New technology, especially in agriculture and medicine, enabled more people to survive and reproduce.

Patterns of Human Patterns of Human Population GrowthPopulation Growth

Read Page 144

Refer to Fig 5-12

OverPopulationvideo