# Population Dynamics The change in the size, density, dispersion, and age distribution of a population in response to changes in environmental conditions.

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Population Dynamics The change in the size, density, dispersion, and age distribution of a population in response to changes in environmental conditions.

Healthy Populations A healthy population will grow and die at a steady rate unless it runs out of food or space or is attacked by disease or predators.

How are populations studied?
Introduced into study areas with abundant resources. Tracked in their natural environment. Population Counts – Determine if a population is healthy and growing. Population Density – Population per Area

What difficulties can occur when trying to measure a wildlife population?
Wildlife can look alike, move, and hide resulting in animals being missed or counted more than once.

So, how do you measure a population?
Trap-Mark-Release Animals are trapped, marked, and released and then trapped a second time. By comparing the number of marked and unmarked animals in the second sampling, the population size can be estimated.

So, how do you measure the size of a population?
Sample Counts Used to estimate the size of a population scattered over a large area by sampling a smaller area.

How fast do populations grow?
Population size is affected by the birth rate, death rate, immigration rate, and emigration rate of a population. Birth Rate + Immigration > Death Rate + Emigration = Increase Birth Rate + Immigration < Death Rate + Emigration = Decrease

Population Curves A population curve graphs the size of a population (number of individuals) on the y-axis over time on the x-axis.

Population Growth Populations show exponential growth, not linear growth. The population growth starts out slow and then increases rapidly with the increasing population size until the carrying capacity is reached. Unlimited exponential growth results in an J-shaped population curve.

Carrying Capacity (K) The largest number of individuals of one species that an ecosystem can support indefinitely. When a population reaches carrying capacity, some organism must either die off or find new resources.

Temporary Overshoot of Carrying Capacity
Before a population reached carrying capacity, it is not affected by limiting factors and can grow exponentially and can overshoot the carrying capacity.

Temporary Overshoot of Carrying Capacity
After the carrying capacity is exceeded, the resources for the population are limited and unless other resources are found, the population will suffer a crash and fall to a new lower carry capacity for the population. This results in an S-shaped population curve.

Life-History Pattern An organism’s reproduction pattern.
Can vary between two extremes. Rapid life-history patterns Slow life-history patterns

Slow Life History Patterns
Produce a few, often large offspring, which they care for over a long period of time. Maintain stable population sizes near the carrying capacity. Populations typically follow an S-shaped curve.

Rapid Life History Patterns
Have a high rate of population growth (r) (Many offspring in a short time period.) Reproduce hordes of offspring early in life. Offspring are usually small, short-lived, and mature rapidly with little to no parental care.

Rapid Life History Patterns
Usually opportunists, reproducing rapidly when conditions are favorable and crashing when conditions are not. Examples: insects, rodents, bacteria

Biotic Potential Highest rate of reproduction under idealistic conditions. The larger the number of offspring produced by parent organisms, the higher the biotic potential of the species.

Limiting Factors and Dispersal
3 Patterns of Dispersal Random Clumped (most common) Uniform (least common)

Population Controls Density-dependent Population Controls
Limiting Factors which become more influential as the population increases. Examples: disease, competition, predators Density-independent Population Controls Effect population regardless of population size or dispersal. Examples: temperature, storms, drought

How do interactions between organisms limit population size?
Predator-Prey Relationships Predators limit the size of prey populations, which can then limit the size of the predator population. Competition Usually the most intense within the same species. Overcrowding and Stress

Human Populations Demography Doubling Time
The study of human population size, density and distribution, movement, and birth and death rates. Doubling Time The time needed for a population to double in size.

Human Populations Age Structure
The proportions of the population that are in different age levels. Can be used to determine stability.

Will humans ever reach their carrying capacity?

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