Population Dynamics
Populations! Population: a group of organisms of the same species that are living within a certain area Species: a group of organisms that are able to reproduce and produce fertile offspring! Population Size: the number of organisms in a given population The human population size of Tolland is about 16,000
Growth of Populations! No population continues to grow unchecked! Population Growth: the increase of a population with time Under Ideal conditions the size of a population will increase indefinitely showing a growth curve like a J! Ideal Conditions: unlimited food, absence of disease, lack of predators, favorable temperatures, etc.
J-Curve
Growth of Populations! Biotic Potential: the highest rate of reproduction under ideal conditions! Limiting Factors: circumstances that keep organisms from reaching their biotic potential (factors that limit the growth of a population) Examples: disease, predators, lack of food, lack of water, lack of space
S-Curve! Typical population growth curve
Population Growth Rate Curve! Shows how fast a population grows Yeast population growth rate 200 180 160 140 Increase in Cell Number 120 100 80 60 40 20 0 1 2 3 4 5 6 7 8 9 10 Time (hours)
Carrying Capacity! Carrying Capacity: The maximum number of organisms in a certain population that a given environment is capable of sustaining under a specific set of conditions! At carrying capacity, birthrate balances death rate and the population stabilizes! Birthrate: the number of organisms born or produced in a given period of time! Death Rate: the number of organisms that die in a given period of time
Population Density! Population density: the size of a population that occupies a given area at any given point in time! As population density increases, the growth rate of a typical population will decrease As you go up the S-curve, the rate of growth (slope of the line) decreases (levels off)
Limiting Factors! Density-dependent limiting factors: influence of any limiting factor that varies with the population density Examples: food, water, space, predators! Density-independent limiting factors: not related to population density Examples: temperature, natural disaster
Predation and Food! Predation: feeding of one organism on another! Predation is density-dependent The more prey, the more likely a predator is to catch one As population density decreases, predators are less able to catch prey! Predation is a limiting factor for the prey population! Food availability (prey population) is a limiting factor for the predator population
Regulation of Population Size: Predator/Prey Graph
Effects of Predation! Predation maintains population size of the prey near carrying capacity preventing overpopulation Overpopulation of the prey population could damage other populations and in turn damage the prey population! Predation can act as a form of natural selection Example: Wolves will kill the slowest deer
Interacting Populations! Symbiosis: long-term interactions between two species Commensalism! One organism benefits, the other is not affected Mutualism! Both organisms benefit Parasitism Remora & Zebra Shark Clown Fish & Anemone! One organism benefits (parasite), but the other is harmed (host)! Parasite examples: fleas, leaches, tapeworms
Parasitism! Parasitism can be a limiting factor! Density-dependent Likelihood of transferring parasites within a population increases as population density increases
Disease! Density-dependent limiting factor The denser the population, the greater the chance of a disease spreading! Sometimes humans use disease-causing organisms (bacteria) to limit other populations (i.e., pests)
Oxygen! In an open system, oxygen is densityindependent! In a closed system, oxygen is densitydependent trapped in an air-tight space aquatic environments
Interspecific Competition! Competition among populations of DIFFERENT SPECIES! Density-dependent limiting factor! 3 Possible outcomes: Extinction! Example: P. aurelia v. P. caudatum Emigration Adaptation! Example: Finches in the Galapagos Islands
Competition in Paramecium
Competition in Paramecium
Competition in Paramecium P. bursaria
Competition in Paramecium
Competition in Paramecium Competitive exclusion
Competition in Paramecium Resource specialization
Intraspecific Competition! Competition between members of the same species! Density-dependent! Ways species avoid intraspecific competition: Life cycles & life spans Social Hierarchy/Pecking Order (must be reestablished if new members join the population) Role separation Behavioral & physiological changes Emigration Territoriality! Extinction IS NOT an outcome of intraspecific competition
Human Population Without Limits?! The current human population growth is J- shaped (ideal conditions)! Rate of growth is declining slightly
Age Structure Diagrams (aka Population Pyramids)! Show the percentage of a population in each age group! Shape of the pyramid indicates the growth rate
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