Population Biology. Summary Slide Population DynamicsPopulation Dynamics Human Population GrowthHuman Population Growth.

Population Population BiologyBiology

Summary SlideSummary Slide

• Population DynamicsPopulation Dynamics

• Human Population GrowthHuman Population Growth

Population DynamicsPopulation Dynamics

Principles of Population Principles of Population GrowthGrowth

• Population Growth: an increase Population Growth: an increase in the size of a population over in the size of a population over timetime

• Scientists can observe Scientists can observe population growth most easily population growth most easily with microorganisms in a Petri with microorganisms in a Petri dish with adequate nutrient dish with adequate nutrient supplysupply

How fast do populations growHow fast do populations grow

• Populations do not grow steadily Populations do not grow steadily (linear) instead they grow (linear) instead they grow exponentially (j-shaped) exponentially (j-shaped) according to limiting factorsaccording to limiting factors

• Exponential Growth: As a Exponential Growth: As a population gets larger it also population gets larger it also grows faster and results in a grows faster and results in a population explosionpopulation explosion

Limits of the environmentLimits of the environment

• Population growth does have Population growth does have limitslimits

• A limiting factor for population A limiting factor for population growth includes availability for growth includes availability for food and space (s-shaped curve)food and space (s-shaped curve)

• Carrying capacity: The number of Carrying capacity: The number of organisms of one species that an organisms of one species that an environment can supportenvironment can support

Patterns of population growthPatterns of population growth

• Scientists study population Scientists study population growth based on an organism’s growth based on an organism’s reproductive capabilitiesreproductive capabilities

• Two examples include: Two examples include: mosquitoes and elephantsmosquitoes and elephants

MosquitoesMosquitoes

• Mosquitoes reproduce rapidly in a short Mosquitoes reproduce rapidly in a short period of timeperiod of time

• Mosquitoes do well in an unpredictable Mosquitoes do well in an unpredictable environment and are generally small, mature environment and are generally small, mature rapidly, reproduce early, and live short livesrapidly, reproduce early, and live short lives

• Mosquito populations increase rapidly and Mosquito populations increase rapidly and decrease rapidly with sudden changes in decrease rapidly with sudden changes in the environmentthe environment

• When the conditions for the mosquitoes are When the conditions for the mosquitoes are in a more favorable environment then the in a more favorable environment then the populations will once again risepopulations will once again rise

ElephantsElephants

• Elephants reproduce very slowly over Elephants reproduce very slowly over a long period of time (with 2 years a long period of time (with 2 years gestation)gestation)

• Elephants are very different because Elephants are very different because they are large, reproduce and mature they are large, reproduce and mature slowly and are long-livedslowly and are long-lived

• Elephants maintain a population very Elephants maintain a population very close to their carrying capacity of close to their carrying capacity of their environmenttheir environment

Environmental limits to Environmental limits to population growthpopulation growth

• Limiting factors regulates the Limiting factors regulates the size of a population through food size of a population through food supply, extreme temperatures, supply, extreme temperatures, and even weather eventsand even weather events

• There are two main types of There are two main types of limiting factors: density limiting factors: density dependent and density dependent and density independent factorsindependent factors

Limiting FactorsLimiting Factors

• Density Dependent Factors: The larger the Density Dependent Factors: The larger the population the more impact on the population the more impact on the population population

• Examples of density dependent factors Examples of density dependent factors include: Disease, competition, parasites and include: Disease, competition, parasites and foodfood

• Density Independent Factors: No matter Density Independent Factors: No matter what the population or population size all what the population or population size all are affectedare affected

• Examples of density independent factors Examples of density independent factors include: temperature, storms, floods, include: temperature, storms, floods, drought, and habitat disruption, pollutiondrought, and habitat disruption, pollution

Predation affects population Predation affects population sizesize

• Populations of predators and prey Populations of predators and prey change over time and effect each of change over time and effect each of the populationsthe populations

• Generally, it is the young, old, injured Generally, it is the young, old, injured and diseased organisms in a prey and diseased organisms in a prey population which are huntedpopulation which are hunted

• Therefore, it is the predator-prey Therefore, it is the predator-prey relationship which helps to controls relationship which helps to controls populations.populations.

The effects of competitionThe effects of competition

• Competition within a population are Competition within a population are also very important and can serve as also very important and can serve as a limiting factor for a populationa limiting factor for a population

• When resources are low then When resources are low then competition within a population competition within a population increases therefore leading to a increases therefore leading to a decrease in population as a resultdecrease in population as a result

The effects of crowding and The effects of crowding and stressstress

• When a population increases to When a population increases to overcrowding then the population suffers overcrowding then the population suffers emotionallyemotionally

• This emotional issue helps to control the This emotional issue helps to control the populations numberspopulations numbers

• Emotion issues for a population include: Emotion issues for a population include: aggression, decrease in parental care, aggression, decrease in parental care, decreased fertility, and decreased decreased fertility, and decreased resistance to diseaseresistance to disease

• All of these factors will help to limit the size All of these factors will help to limit the size of the population in one way shape or formof the population in one way shape or form

Human Population Human Population GrowthGrowth

Demographic TrendsDemographic Trends

• Demography: The study of human Demography: The study of human population growth characteristics like population growth characteristics like growth rate, age structure and growth rate, age structure and geographic distributiongeographic distribution

• The world population has increased The world population has increased exponentially over the past several exponentially over the past several hundred yearshundred years

• This is probably due to the fact that This is probably due to the fact that humans can eliminate competition, humans can eliminate competition, increase food supply and control increase food supply and control diseasesdiseases

Effects of birthrates and death Effects of birthrates and death ratesrates

• Population growth= birth rate-Population growth= birth rate-death ratedeath rate

• In order to determine the rate of In order to determine the rate of population growth three factors population growth three factors must be known: fertility rate, must be known: fertility rate, birth rate and death ratebirth rate and death rate

• Population growth in the US is Population growth in the US is declining due to several factorsdeclining due to several factors

Effects on the PopulationEffects on the Population

• The fertility rate is decreasing The fertility rate is decreasing because people are waiting longer to because people are waiting longer to have children (generally in their 30’s)have children (generally in their 30’s)

• People are having fewer children than People are having fewer children than they have in the past decadesthey have in the past decades

• In populations where the death rate is In populations where the death rate is high due to disease in the population high due to disease in the population then the population growth is lowthen the population growth is low

Does age affect population Does age affect population growth?growth?

• Age structure: proportion of the Age structure: proportion of the populations that are at different populations that are at different age levelsage levels

• Discuss DistributionsDiscuss Distributions

Mobility has an effect on Mobility has an effect on population size?population size?

• The movement of the human The movement of the human population makes it hard for population makes it hard for demographers to predict human demographers to predict human population growthpopulation growth

Types of MobilityTypes of Mobility

• Immigration: The movement of Immigration: The movement of individuals into a populationindividuals into a population

• Emigration: The movement of Emigration: The movement of individuals from a populationindividuals from a population

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