Population Biology

Summary Slide Population DynamicsPopulation Dynamics Human Population GrowthHuman Population Growth

Population Dynamics

Principles of Population Growth Population Growth: an increase in the size of a population over timePopulation Growth: an increase in the size of a population over time Scientists can observe population growth most easily with microorganisms in a Petri dish with adequate nutrient supplyScientists can observe population growth most easily with microorganisms in a Petri dish with adequate nutrient supply

How fast do populations grow Populations do not grow steadily (linear) instead they grow exponentially (j-shaped) according to limiting factorsPopulations do not grow steadily (linear) instead they grow exponentially (j-shaped) according to limiting factors Exponential Growth: As a population gets larger it also grows faster and results in a population explosionExponential Growth: As a population gets larger it also grows faster and results in a population explosion

Limits of the environment Population growth does have limitsPopulation growth does have limits A limiting factor for population growth includes availability for food and space (s-shaped curve)A limiting factor for population growth includes availability for food and space (s-shaped curve) Carrying capacity: The number of organisms of one species that an environment can supportCarrying capacity: The number of organisms of one species that an environment can support

Patterns of population growth Scientists study population growth based on an organism’s reproductive capabilitiesScientists study population growth based on an organism’s reproductive capabilities Two examples include: mosquitoes and elephantsTwo examples include: mosquitoes and elephants

Mosquitoes Mosquitoes reproduce rapidly in a short period of timeMosquitoes reproduce rapidly in a short period of time Mosquitoes do well in an unpredictable environment and are generally small, mature rapidly, reproduce early, and live short livesMosquitoes do well in an unpredictable environment and are generally small, mature rapidly, reproduce early, and live short lives Mosquito populations increase rapidly and decrease rapidly with sudden changes in the environmentMosquito populations increase rapidly and decrease rapidly with sudden changes in the environment When the conditions for the mosquitoes are in a more favorable environment then the populations will once again riseWhen the conditions for the mosquitoes are in a more favorable environment then the populations will once again rise

Elephants Elephants reproduce very slowly over a long period of time (with 2 years gestation)Elephants reproduce very slowly over a long period of time (with 2 years gestation) Elephants are very different because they are large, reproduce and mature slowly and are long-livedElephants are very different because they are large, reproduce and mature slowly and are long-lived Elephants maintain a population very close to their carrying capacity of their environmentElephants maintain a population very close to their carrying capacity of their environment

Environmental limits to population growth Limiting factors regulates the size of a population through food supply, extreme temperatures, and even weather eventsLimiting factors regulates the size of a population through food supply, extreme temperatures, and even weather events There are two main types of limiting factors: density dependent and density independent factorsThere are two main types of limiting factors: density dependent and density independent factors

Limiting Factors Density Dependent Factors: The larger the population the more impact on the populationDensity Dependent Factors: The larger the population the more impact on the population Examples of density dependent factors include: Disease, competition, parasites and foodExamples of density dependent factors include: Disease, competition, parasites and food Density Independent Factors: No matter what the population or population size all are affectedDensity Independent Factors: No matter what the population or population size all are affected Examples of density independent factors include: temperature, storms, floods, drought, and habitat disruption, pollutionExamples of density independent factors include: temperature, storms, floods, drought, and habitat disruption, pollution

Predation affects population size Populations of predators and prey change over time and effect each of the populationsPopulations of predators and prey change over time and effect each of the populations Generally, it is the young, old, injured and diseased organisms in a prey population which are huntedGenerally, it is the young, old, injured and diseased organisms in a prey population which are hunted Therefore, it is the predator-prey relationship which helps to controls populations.Therefore, it is the predator-prey relationship which helps to controls populations.

The effects of competition Competition within a population are also very important and can serve as a limiting factor for a populationCompetition within a population are also very important and can serve as a limiting factor for a population When resources are low then competition within a population increases therefore leading to a decrease in population as a resultWhen resources are low then competition within a population increases therefore leading to a decrease in population as a result

The effects of crowding and stress When a population increases to overcrowding then the population suffers emotionallyWhen a population increases to overcrowding then the population suffers emotionally This emotional issue helps to control the populations numbersThis emotional issue helps to control the populations numbers Emotion issues for a population include: aggression, decrease in parental care, decreased fertility, and decreased resistance to diseaseEmotion issues for a population include: aggression, decrease in parental care, decreased fertility, and decreased resistance to disease All of these factors will help to limit the size of the population in one way shape or formAll of these factors will help to limit the size of the population in one way shape or form

Human Population Growth

Demographic Trends Demography: The study of human population growth characteristics like growth rate, age structure and geographic distributionDemography: The study of human population growth characteristics like growth rate, age structure and geographic distribution The world population has increased exponentially over the past several hundred yearsThe world population has increased exponentially over the past several hundred years This is probably due to the fact that humans can eliminate competition, increase food supply and control diseasesThis is probably due to the fact that humans can eliminate competition, increase food supply and control diseases

Effects of birthrates and death rates Population growth= birth rate- death ratePopulation growth= birth rate- death rate In order to determine the rate of population growth three factors must be known: fertility rate, birth rate and death rateIn order to determine the rate of population growth three factors must be known: fertility rate, birth rate and death rate Population growth in the US is declining due to several factorsPopulation growth in the US is declining due to several factors

Effects on the Population The fertility rate is decreasing because people are waiting longer to have children (generally in their 30’s)The fertility rate is decreasing because people are waiting longer to have children (generally in their 30’s) People are having fewer children than they have in the past decadesPeople are having fewer children than they have in the past decades In populations where the death rate is high due to disease in the population then the population growth is lowIn populations where the death rate is high due to disease in the population then the population growth is low

Does age affect population growth? Age structure: proportion of the populations that are at different age levelsAge structure: proportion of the populations that are at different age levels Discuss DistributionsDiscuss Distributions

Mobility has an effect on population size? The movement of the human population makes it hard for demographers to predict human population growthThe movement of the human population makes it hard for demographers to predict human population growth

Types of Mobility Immigration: The movement of individuals into a populationImmigration: The movement of individuals into a population Emigration: The movement of individuals from a populationEmigration: The movement of individuals from a population

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