Chapter 4 Population Biology

Why don’t populations of organisms grow indefinitely?
Limiting factors affect survival rates. Exceeding carrying capacity reduces populations.

The number of organisms of one species that an environment can support is called its _____.
Carrying capacity

If the number of organisms in a population is _____ the environment’s carrying capacity, births _____ deaths and the population _____.
Under; exceed; grows

If the number of organisms rises _____ the carrying capacity of the environment, _____ will exceed _____.
Above; deaths; births

This pattern will continue until the population is once again at or _____ the carrying capacity.
Below

The most important factor that determines population growth is the organism’s _____.
Reproductive pattern

Organisms that follow a rapid life-history pattern _____.
Have short life spans, have small bodies, and reproduce early.

Organisms that follow a slow life-history pattern _____.
Reproduce slowly

A limiting factor that has an increasing effect as population size increases is _____.
Competition

The snowshoe hare is a primary source of food for the Canadian lynx. Explain how the lynx population size changes when the hare population increases.
Hare population goes up which means more food for the lynx population. The lynx population then goes up as well.

Explain how the change in the lynx population size affects the hare population.
The lynx population goes up which causes the hare population to go down.

What is the relationship between the lynx and the hare called?
Predator-prey relationship

When does competition decrease the size of a population?
When demand for resources exceeds supply.

What can cause an organism to exhibit stress, and what symptoms of stress can lead to a decrease in population size?
When populations of organisms because over crowded, individuals may exhibit stress. As populations increase in size, individual animals begin to exhibit a variety of symptoms including aggression, decrease in parental care, decreased fertility, and decreased resistance to disease.

What is a population?
A group of organisms of one species that interbreed and live in the same place at the same time.

What is a simple way for a biologist to study population growth?
Bacterial cultures in a petri dish.

How is population growth different than growth of job income?
No linear growth, grow exponentially first.

What is exponential growth?
Rapid growth as population increases which doubles in a fixed period of time.

Can biological populations grow exponentially?
Yes, slow at first but then the population gets larger and the growth explodes.

What does a graph of an exponentially growing population look like?
J- sleep, creep, leap

What is carrying capacity?
Population size the environment can support.

Name 4 abiotic factors that affect carrying capacity:
Water, sunlight, nutrients, and oxygen.

Name 4 biotic facts that affect carrying capacity:
Food, predation, competition, and parasites.

How does birth rate compare to death rate when a population is under carrying capacity? Over carrying capacity?
When births are lower than deaths under carrying capacity, the population increases. When births are over deaths over carrying capacity, the population decreases.

Describe organisms that have a rapid life history? Give 2 examples.
Rapid life-history patterns are found in organisms from unpredictable environments. Typically, these organisms have a small body size, mature rapidly, reproduce early, and have a short life span. Bacteria and rabbits would be two examples of this. (R-strategists)

Describe organisms that have a long life history. Give 2 examples.
Species that live in more stable environments, such as elephants, often have a different life-history pattern. Humans, bears, whales, and long-lived plants are large, reproduce and mature slowly, and are long-lived. These organisms maintain population sizes near the carrying capacities of their environments. Elephants and humans would be two examples of this. (K-strategists)

What is a density-dependent factor? Give 3 examples.
It includes disease, competition, parasites, and food. These have an increasing effect as the population increases. Food supply, competition, and parasites would be 3 examples of this.

What is a density-independent factor? Give 3 examples.
They affect all populations, regardless of their density. Most are abiotic factors, such as temperature, storms, floods, drought, and habitat disruption. Another examples would also be pollution. Temperature, storms, floods, and drought are some examples of this.

How does predation affect population. Give an example.
When a predator consumes prey, it can affect the population size of the prey population. An examples would be a swarm of locusts eats and destroys acres of lettuce on a farm. (Lynx and hare)

How does competition affect population? Give an example.
When only a few individuals compete for resources, no problem arises. When a population increases to the point at which demand for resources exceeds the supply, the population size decreases.

How does crowding and stress affect population? Give an example.
As populations increase in size, individual animals begin to exhibit a variety of symptoms, including aggression, decrease in parental care, decreased fertility, and decreased resistance to disease.

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