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Background A population is a group of organisms of the same…

Background A population is a group of organisms of the same species that live in a particular geographic location. For example, people living in Phoenix, Arizona, are considered a population of humans.  Biologists estimate the number of organisms in a population (population size) to know whether a species has become too rare or too abundant. Knowing a population’s size also enables biologists to manage the resources needed to sustain the population. For example, biologists have estimated how many people will live in Phoenix during the next 40 years to know whether the current water supply will support the future population. A population grows when the number of organisms born exceeds those that die. Conversely, a population shrinks when the number of organisms that die exceeds the number born. If the population of humans in Phoenix grows from one year to the next, the number of people born must have exceeded the number of people who died.  The growth rate measures how a population’s size changes over time. A positive growth rate means the population size increases over time (i.e., the population grows). A negative growth rate means the population size decreases over time (i.e., the population shrinks). A zero growth rate means that the population size does not change over time (i.e., the population neither grows nor shrinks but remains stable). Population size increases yearly if its growth rate is greater than 0. For example, if the growth rate for Phoenix for the last 10 years were 0.16, the population size would have increased by 16% (a mean of 1.6% per year). If the nearby town of Sierra Vista experienced a growth rate of -0.05 during the same period, its population size decreased by 5% over 10 years (a mean of -0.5% per year). The growth of a population depends on many variables, like the abundance of food. Organisms rely on matter and energy in food to survive and reproduce. Predators, such as owls (see figure above), consume other organisms as food, referred to as prey. Prey density is the number of prey living in an area. The greater the prey density, the more prey exists in an area. A population of predators requires a sufficient prey density to persist over time.    

To which population should the biologist supply additional p…

To which population should the biologist supply additional prey? Recall that the biologists want to add prey to the population growing more slowly based on their respective typical prey densities and the relationship between prey density and growth rate (if both have negative growth rates – the population with the more negative or lower growth rate).