344 ■ CHAPTER 19 Growth of Populations
ECOLOGY
the total number of individuals in the population.
A population is a group of organisms of the same
species in a defined area. Population size tends to
change over time—sometimes increasing, some-
times decreasing. Whether the size of a population
increases or decreases depends on the number of
births and deaths in the population, as well as on
the number of individuals that enter (immigrate) orinfection (Figure 19.3). Slowing the spread of Zika,
therefore, involves the screening of donated blood
and the proper use of condoms during sex. But
true prevention ultimately requires decreasing the
incidence of mosquito bites, which can be accom-
plished by getting rid of the mosquitoes.
Scientists have taken many approaches to
trying to reduce the mosquitoes’ population size,Figure 19.3
How Zika is transmitted
The CDC produces posters such as this for public health issues including Zika, sexually transmitted diseases, and the flu.
Q1: What is the main way by which someone is infected with the Zika virus?Q2: Judging by the poster and your knowledge of mosquito behavior, what can you do to decrease your risk of being
infected with the Zika virus?Q3: Besides the transmission methods shown on the poster, what are some other ways you could become infected with
the Zika virus?