This graph depicts the growth of a hypothetical population over time. The population has no limits to survival and reproduction and simply grows at a constant growth rate. The constant growth rate results in exponential growth of the population.
Such a population will have a J-shaped curve if plotted on a graph with time on the x axis and population size on the y axis.
The J curve shows a slight lag at first and then a rapid increase. This is due to the fact that the larger the population, the faster it grows, even at the same growth rate.
Think of it this way: If the population doubles every year, the doubling of a small number yields a number that is still small, but the doubling of a larger number, on the other hand, produces a much larger gain in the number of individuals.
Actual populations in nature can't grow exponentially for long. As a population begins to fill its environment, resistance factors kick in to decrease the population growth rate.
For instance, predators may find the more numerous prey easier to track and capture. Competition for resources may leave some individuals without food or habitat, and crowding may also bring about an increase in disease and aggression.
This kind of growth—in which as population size increases, growth rate decreases—is called logistic growth. A population that grows logistically will produce an S-shaped curve. As the population approaches its maximum sustainable population size, the population size levels off.
The population size that a particular environment can support indefinitely—without long-term damage to the environment—is called its carrying capacity, signified as K in population models.
Identify the main features of exponential and logistic growth. Drag the terms and descriptions to their correct locations.
Complete these sentences about population growth. Drag the terms to their correct locations.