Final answer:
If a water hyacinth population has an r value of zero, the population size would not change over time.
Step-by-step explanation:
The value 'r' can be positive, meaning the population is increasing in size; or negative, meaning the population is decreasing in size; or zero, where the population's size is unchanging, a condition known as zero population growth. In the case of a water hyacinth population with an 'r' value of zero, the population size would not change over time. This means that the number of births and deaths in the population would balance each other, resulting in a stable population size.