Understand population growth - AP Biology

A clumped pattern of dispersion occurs when individuals aggregate in patches. For example, a herd of cows all graze in a field together, as it is their only source of food within five miles. Uniform dispersion is when organisms are evenly spaced throughout a given area. This results from territoriality, or when organisms defend their physical space against other organisms. Random dispersion is the unpredictable spacing of organisms throughout a given area. There are no strong attractions or repulsions among individuals that would result in clumped or uniform dispersion; the animals are scattered randomly.

Life tables are summaries of the survival patterns of a population. They are constructed using cohorts (groups of individuals of similar age). By following and observing these individuals from birth until death, researchers can make life tables and plot survivorship cures, showing the number of cohorts alive over their lifetimes.

Iteroparity refers to an organism's reproductive strategy that involves multiple reproductive cycles. Adults are likely to survive and breed, each time producing few offspring. They care for their young, who grow to adulthood and also reproduce. In these kinds of environments, competition for resources is very intense. Semelparity refers to an organism's reproductive strategy that involves a single reproductive cycle over the course of its lifetime. Semelparity in associated with mass reproduction, and is favored in highly variable and unpredictable environments. Offspring usually have a low survival rate, and reach sexual maturity quickly.

Negative feedback inhibition prevents populations from continually increasing in size. Without these such factors, population sizes would not be controlled. For example, perch feed on and find shelter in kelp. Where there are too many perch, there is not enough kelp to sustain them all (for food and shelter), and the fish population decreases in size. When there are less perch, there is enough kelp for them to feed on and hide in. Because conditions are favorable, the perch numbers increase. This negative feedback inhibition is density dependent and controls population size dynamics.

K-selection is density dependent selection, while r-selection is density independent selection; the two are opposites. While all the answer choices are related, only one displays the same (opposite) relationship: semelparous and iteroparous. Semelparous refers to the “one shot” reproductive trend, producing many offspring only once during an organism's lifetime. Iteroparous refers to organisms that breed multiple times, producing few offspring each time. For semelparous organisms, survival is low and the environment is generally unpredictable. For iteroparous organisms, survival rates are high and the environment is stable and dependable.

The logistic growth model shows that population size levels off as it approaches its carrying capacity. In this situation, as the population increases and resources are used, the population approaches its carrying capacity, which is the maximum population size that the environment can support. The exponential growth model is unrealistic, as it shows a population’s growth when resources are abundant, but this there is no environment where resources are always in abundance. Survivorship curves show the life patterns of species; rather than comparing the relationship between resources and population size, these types of graphs compare age and population size.

“Resilience” is the term used to describe the speed at which an ecosystem can re-establish equilibrium after a disturbance.

In exponential growth, the growth rate is modeled as the reproductive rate times the number of individuals . By adding the term , we arrive at the equation for logistic growth. As increases, the value of (and thus of the entire equation) will decrease to the point where . After this, the growth rate will become negative! The result is that the population will be limited to a size of . This limit is known as the carrying capacity.

“Resilience” is the term used to describe the speed at which an ecosystem can re-establish equilibrium after a disturbance.

Disease is a biotic factor, while the other choices are abiotic factors. Density-dependent factors are biotic in nature, and may involve things such as mating, food, competition, and disease. Density dependent factors will affect different populations differently depending on how many organisms are present in a given area. In the case of disease, consider that the flu will spread more easily in a densely-populated city than it will in a loosely-populated desert.

The other answer options will affect a population the same, regardless of density, because they affect large areas with the same magnitude.

A clumped pattern of dispersion occurs when individuals aggregate in patches. For example, a herd of cows all graze in a field together, as it is their only source of food within five miles. Uniform dispersion is when organisms are evenly spaced throughout a given area. This results from territoriality, or when organisms defend their physical space against other organisms. Random dispersion is the unpredictable spacing of organisms throughout a given area. There are no strong attractions or repulsions among individuals that would result in clumped or uniform dispersion; the animals are scattered randomly.

Life tables are summaries of the survival patterns of a population. They are constructed using cohorts (groups of individuals of similar age). By following and observing these individuals from birth until death, researchers can make life tables and plot survivorship cures, showing the number of cohorts alive over their lifetimes.

Iteroparity refers to an organism's reproductive strategy that involves multiple reproductive cycles. Adults are likely to survive and breed, each time producing few offspring. They care for their young, who grow to adulthood and also reproduce. In these kinds of environments, competition for resources is very intense. Semelparity refers to an organism's reproductive strategy that involves a single reproductive cycle over the course of its lifetime. Semelparity in associated with mass reproduction, and is favored in highly variable and unpredictable environments. Offspring usually have a low survival rate, and reach sexual maturity quickly.

Negative feedback inhibition prevents populations from continually increasing in size. Without these such factors, population sizes would not be controlled. For example, perch feed on and find shelter in kelp. Where there are too many perch, there is not enough kelp to sustain them all (for food and shelter), and the fish population decreases in size. When there are less perch, there is enough kelp for them to feed on and hide in. Because conditions are favorable, the perch numbers increase. This negative feedback inhibition is density dependent and controls population size dynamics.

K-selection is density dependent selection, while r-selection is density independent selection; the two are opposites. While all the answer choices are related, only one displays the same (opposite) relationship: semelparous and iteroparous. Semelparous refers to the “one shot” reproductive trend, producing many offspring only once during an organism's lifetime. Iteroparous refers to organisms that breed multiple times, producing few offspring each time. For semelparous organisms, survival is low and the environment is generally unpredictable. For iteroparous organisms, survival rates are high and the environment is stable and dependable.

The logistic growth model shows that population size levels off as it approaches its carrying capacity. In this situation, as the population increases and resources are used, the population approaches its carrying capacity, which is the maximum population size that the environment can support. The exponential growth model is unrealistic, as it shows a population’s growth when resources are abundant, but this there is no environment where resources are always in abundance. Survivorship curves show the life patterns of species; rather than comparing the relationship between resources and population size, these types of graphs compare age and population size.

In exponential growth, the growth rate is modeled as the reproductive rate times the number of individuals . By adding the term , we arrive at the equation for logistic growth. As increases, the value of (and thus of the entire equation) will decrease to the point where . After this, the growth rate will become negative! The result is that the population will be limited to a size of . This limit is known as the carrying capacity.

Disease is a biotic factor, while the other choices are abiotic factors. Density-dependent factors are biotic in nature, and may involve things such as mating, food, competition, and disease. Density dependent factors will affect different populations differently depending on how many organisms are present in a given area. In the case of disease, consider that the flu will spread more easily in a densely-populated city than it will in a loosely-populated desert.

The other answer options will affect a population the same, regardless of density, because they affect large areas with the same magnitude.

A clumped pattern of dispersion occurs when individuals aggregate in patches. For example, a herd of cows all graze in a field together, as it is their only source of food within five miles. Uniform dispersion is when organisms are evenly spaced throughout a given area. This results from territoriality, or when organisms defend their physical space against other organisms. Random dispersion is the unpredictable spacing of organisms throughout a given area. There are no strong attractions or repulsions among individuals that would result in clumped or uniform dispersion; the animals are scattered randomly.