A b exponential growth predict a growth curve for a

This preview shows 13 out of 16 pages.

scale, suburbanites “dust” their lawns. (a) (b) Exponential Growth: Predict a growth curve for a population.
Image of page 13

Subscribe to view the full document.

500 C HAPTER 15 Population Ecology: How Do Organisms Interact to Form Populations? Number of individuals Time (months) Figure 15-9 Some populations grow exponentially, at least for a time.After a period of relatively slow growth, the population size soars. is still 0.4 (although not necessarily constant, a population’s “little r” may remain so) and that the gardener has left them alone (probably not a reasonable assumption). Now, in just two weeks, the population increases by 40. By late October, the population is approximately 1000 (under the same assumptions). In just two weeks, the population increases by 400.In just one year,our slug population could,if left to its own devices,jump from 10 to 45,000! The flowers never had a chance. Note: With exponential growth, where the larger the population, the faster it grows. Growth of Most Populations Follows an S-shaped Curve Obviously, in nature, populations are seldom “left to their own devices.” If the gardener hadn’t discovered the slugs and interfered with their exponential growth, something else would have—snakes or shrews perhaps (Figure 15-10). Predators are one of the factors Chapman had in mind when he spoke of environmental resistance. 1 dN/dt 2 rN , Figure 15-10 Shrews are mouse- sized friends to gardeners.These voracious predators can eat an amount of slugs and other garden pests equal to their own weight each day. Emerald Ash Borer: Observe the effect of this exponential growth.
Image of page 14
15-3 How Do Populations Grow? 501 Logistic Population Growth Number of individuals Time (months) Logistic Population Growth Figure 15-11 Most populations do not grow exponentially for long.After a period of such growth, environmental resistance limits further growth. What would have happened to the population of Salvia in our garden if there had been no slugs? We can guess that, through the first few growing seasons, their numbers would have behaved as the slug numbers did.Then, after a period of little change, num- bers would increase rapidly, as predicted by the exponential equation. But gardens fill. There is, after all, only so much space for plants. For these flowers, environmental resis- tance is measured in terms of available space. When all spaces are filled, a population can increase no further. Similarly, although factors other than space may be key, a gar- den filled with Salvia can support only so many slugs. Notice that the growth of both of these populations, when graphed, would follow an S-shaped curve (Figure 15-11). Rapid growth would be followed by a flattening off. Numbers would not increase beyond an upper limit. In other words, each population has a carrying capacity , defined as the number of individuals the environment can support.
Image of page 15

Subscribe to view the full document.

Image of page 16
You've reached the end of this preview.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern