Changes in Population Size

• In a population of turtles, 78 new turtles were born and 12 turtles died, resulting in a change in population size.
• The population’s growth rate (gr) is the change in the number of individuals in a population (ΔN) over a specific time (Δt).
• The Banff Springs Snail population was estimated to be 3800 in 1997 and about 1800 two years later, indicating a rate of growth of -40%.
• Capita growth rate (cgr) takes into consideration the initial size of the population.
• A town with a population of 1000 people at the beginning of the year and a population of 1020 at the end of the year has a per capita growth rate of 2%.
• Biotic Potential is the highest possible per capita growth rate for a population.
• Factors that determine biotic potential include the number of offspring per reproductive cycle, survival of offspring, age of reproductive maturity, number of times an individual reproduces in a lifetime, and lifespan.
• An exponential growth pattern is exhibited by a population that is growing at its biotic potential.
• A logistic growth pattern is exhibited by a population for which growth is limited by carrying capacity or limited availability of resources.
• Carrying capacity is the maximum population size that a habitat can sustain over an extended period of time.
• Limiting factors are abiotic or biotic factors that limit the size of a population, such as disease, predation, and competition.
• The best life strategy is to reach sexual maturity at a young age, have a long life span, produce large numbers of offspring, and provide offspring with a high degree of paternal care.
• r-selected strategies are used by populations that live close to their biotic potential, have short life spans, become sexually mature at a young age, produce large numbers of offspring at once, and provide little to no paternal care.
• k-selected strategies are used by populations that live close to the carrying capacity of their habitats, have relatively long life spans, become sexually mature later in life, produce few offspring per reproductive cycle, and provide high level of paternal care.
• Most populations are somewhere between the two groups.
• To make a decision on which life strategy is in effect, you have to compare one population to another, such as rabbits vs mosquitoes, or rabbits vs humans.
• change in population size = (number of births + immigrants) - (number of deaths + emigrants)
• gr (growth rate) = change in number of individuals / time period
• change in number of individuals = N final - N initial (N is the number of individuals)
• cpr (capita growth rate) = change in number of individuals / initial population size