The document discusses the periodic cycling of a bacterial disease affecting a population of wild coyotes every three years. It evaluates several explanations for this pattern, determining that the correct one is the periodic immigration of coyotes from other populations that have already recovered from the disease. Other factors, such as birth rates, natural deaths, and recovery rates, do not adequately explain the periodicity of the epidemics.

1. Correct option: 4.
You are studying a population of wild coyotes and notice that every three years there is an
epidemic of a bacterial disease. Which of the following best explains this periodic cycling of the
disease?
1. New coyotes are continuously born into the population.
The statement is true but not the correct explanation.
The population must have new offspring continuously so that the it remains existing after
periodic epidemics each after 3 years.
2. Coyotes are dying from other causes over time.
The statement is true but not the correct explanation.
It may happen as a natural death, prey-predator relationships, other diseases, etc.
3. During an outbreak, the proportion of coyotes who are sick with the disease slowly falls as
they recover.
The statement is true but not the correct explanation.
Since, the immunity of one coyotes may work differently from others; some may fall sick early
while some may get sick late. However, epidemics can occur anytime once a sufficiently large
pathogen load has been established by the infected (sick) members. Thus, this case does not
show periodicity, most probability.
4. Coyotes from other populations, who have already caught and recovered from the disease,
immigrate into the study population.
The statement is true and is the correct explanation.
Immigration (periodic) of recovered coyotes from other community into the study area may be
responsible for the periodic appearance of epidemic in the study area.
Solution
Correct option: 4.
You are studying a population of wild coyotes and notice that every three years there is an
epidemic of a bacterial disease. Which of the following best explains this periodic cycling of the
disease?
1. New coyotes are continuously born into the population.
The statement is true but not the correct explanation.
The population must have new offspring continuously so that the it remains existing after
periodic epidemics each after 3 years.
2. Coyotes are dying from other causes over time.

2. The statement is true but not the correct explanation.
It may happen as a natural death, prey-predator relationships, other diseases, etc.
3. During an outbreak, the proportion of coyotes who are sick with the disease slowly falls as
they recover.
The statement is true but not the correct explanation.
Since, the immunity of one coyotes may work differently from others; some may fall sick early
while some may get sick late. However, epidemics can occur anytime once a sufficiently large
pathogen load has been established by the infected (sick) members. Thus, this case does not
show periodicity, most probability.
4. Coyotes from other populations, who have already caught and recovered from the disease,
immigrate into the study population.
The statement is true and is the correct explanation.
Immigration (periodic) of recovered coyotes from other community into the study area may be
responsible for the periodic appearance of epidemic in the study area.