Growth

Homework

Homework Review 2a).12 2b) c) d) e) 0 3) When r is positive, the population is growing. When r is negative, the population is shrinking. When r is 0, the population is stable. 4a).2, larger. 4b) -.1, population’s shrinking. 4c) 0. 4d) 150.

Homework Review 5) If birth rate exceeds death rate, the population grows. If death rate exceeds birth rate, the population shrinks. If birth rate equals death rate, the population is stable. 6a).25 6b) c) d) 0 6e) 2.2 7) 66 elephants.

Recap A population is a group (all same species) that share a habitat Growth rate is the rate at which a population size is changing. –Two equations. The first is better for change that already happened, the second is better for predicting. –r = (Pe-Ps)/Ps = B - D + I - E Populations of all living things follow an exponential pattern of growth. –The bigger the population, the higher its growth rate. The equation for exponential population growth is ∆N = rN.

Yeast Lab Complete question 5, then take a final yeast measurement. –When you’re done, clean all of your materials and place them back on the counter. Yeast suspensions can be safely poured down a (working) drain. Please make sure they wash down entirely, don’t leave a yeasty film in the sink. Complete graph (I have paper if you don’t want to use the space) of your data. –Don’t answer the last questions yet. –Also come give me your new data, I’ll adjust the class graph.

Yeast Lab With your partner, then to share with the class: Why did some growth curves “stop”?

Growth Curves This is the “exception” to exponential growth that I mentioned, but this is an “exception” that applies to all living things: Initially, they follow exponential growth. But eventually, they get into logistic growth.

Logistic Growth Logistic (or “S-curve”) growth is a growth pattern in which the population initially increases exponentially, but the rate of growth slows and eventually becomes zero as the population nears carrying capacity.

Logistic Growth Carrying capacity is the largest population size that the habitat can stably support over a long period of time. The carrying capacity depends on different limiting factors, things that inhibit or stop population growth. –What could be some limiting factors? –What do you think was the limiting factor/s for your yeast populations?

Carrying Capacity Limiting factors can be density-independent, like physical space. –The square footage of the forest doesn’t depend upon how many rabbits are in it. Or they can be density-dependent, factors that depend upon the size of the population. –For instance, disease. In a small population, there’s little contact between the animals and the disease doesn’t spread or have much of an impact. In a crowded population, it can be a serious limiting factor. –More on these limiting factors later.

Carrying Capacity Carrying capacity determines how many individuals can live in that habitat, and it affects their chances of survival, too. –If a population shoots up above carrying capacity, it will soon rapidly plunge down well below carrying capacity. –If the carrying capacity of the space is small, this plunge could be the end of that population.

Carrying Capacity When doing the math, carrying capacity is denoted K, and is typically drawn right on the graph like this.

Recap Who can recap for me the main points about: –What is a population? –Equations for growth? –Exponential growth? –Logistic growth? –Carrying capacity?

Yeast Lab Finish your yeast lab for tomorrow. Tomorrow, weather permitting, we’re going outside. Dress appropriately.

Logistic Growth

Homework

Recap

Logistic Growth The Elk Game. –The class will be an elk population. Each of you will be an elk family. You’ll need to keep track of how many are in your family. –You begin as 1 elk. There will be food in a bowl. You need 2 pieces to survive. You must grab pieces one at a time, and carry them back to your “home” spot. –At the end of the season, half the class will reproduce and your family will gain a juvenile elk. Juveniles grow up after 1 year. They only need 1 piece of food to live. –At the end of the next season, the other half will reproduce. –Don’t eat the candy! Put it back in the bowl at the end of each season.

Logistic Growth Elk Game sheet due tomorrow.

Growth Curves This is a graph of the human population of the planet. What kind of growth is this?

Growth Curves Knowing what you now do about growth, what does this imply about the future?

Growth Curves The planet Earth must have a K for humanity. –What limiting factors might be in play that will determine what K is for us? –What happens if we reach K? –What happens if we exceed it?

Human Population Growth Go to and determine your household’s “ecological footprint.” –It will compare your footprint to the national average, and identify which activities or habits are most and least responsible for advancing the globe towards K. Your assignment, due when we return from break, is to write an action plan for things you can do to reduce your footprint. –The website has suggestions. –The reason why you have so long is because most of these things require discussion with family, it’s difficult or at least less effective to implement on your own without the rest of the household.

Human Population Growth Fair disclosure! –Ms. Stang’s footprint: acres. (Carbon: 65.5, Food: 76.5, Housing: 11.8, Goods: 43.9) –Earths needed if everybody lived like her: 5.1 :( –Her current action plan: Eat more organic food, choose food with less packaging, try to get recycling service at home