Fall2011_Lab11

=Lab 11 - Population=

Help on worksheet:
- When calculating survivorship curve percents, use the percent, don't add a zero to the end. Plot it on the semi-log paper, and write in the correct numbers for the y-axis (the up and down axis). You will fill in a zero on the y-axis, for the numbers after the first 9. So your last number on the y-axis is "100" - For the x-axis, when you plot both bubble populations, don't use the actual ages, but come up with a percent for each age, just like you did for the y-axis. Take each age and divide it by the max age, and then use this "percent of max age" to plot both bubble populations on the same graph. - Use a K=100, and an r=1 when calculating the plant population -

DUE DATE: This worksheet will be due on Wed 16th, not Monday the 14th. We'll also have a quiz on Wed the 16th over Population and Community structure stuff (community structure stuff from the first 2 days, Nov. 7th and 9th).

Mini-lecture:
- Population growth can be unlimited, and so for example, each population doubles in size each generation, and this continues unlimited. But in the real world, there is a limit to growth (only so many places to live, only so much food, etc.). When this happens, you have to take into the carrying capacity of the environment, which is how many individuals the environment can hold. As the population approaches this limit to growth, growth rates start to slowdown. So in respect to the earlier example, the population does not double each time, maybe it only grows by half.

- Survivorship curves give you a snapshot in time of the population with respect to the different age groups. If you compare different species and the proportion of ages in the species, you might see differences (more younger individuals, more older individuals). This can be explained somewhat by the growth and development of the different species. These development stages and life stages are called life history. (life history is not the fossil record)

- Survivorship is called that, because it measures what proportion of a population "survives" to the next age class. High survivorship for early age classes (youth) means that most of the population survives the younger age classes. Inevitably, in this case, there will be low survivorship at the older age classes. This is typified by a "type 1" curve, such as in primates. Alternatively, you could have low survivorship at early age classes, and this means that very few young individuals "survive" to middle-age. With this example, there will then be high survivorship at older ages. An example of this is oak trees -- one tree produce tens of thousands of possible offpring (acorns), but usually only 1 or 2 of them reach 20 or 30 years old (middle age for oak trees). This is a "type 3" curve. A "type 2" curve is a species that has no different survivorship rates among the different age classes. An example of this is squirrels.

- The surivivorship curves are plotted with a logarithmic y-axis (% of survivors out of the different age classes), and this is because in natural, real-world populations, the "type 2" populations will have changes between age classes that are logarithmic (if you are going from young ages classes to old age classes). So if there is 1000 individuals in age class 3, a type 2 curve will see 100 individuals in age class 4, and 10 individuals in age class 5. Each change is a smaller number, but it's not a linear change, it's based on "10 times some-number". 1000=10 times 3, 100=10 times 2, 10=10 times 1, etc. So the type 2 curve is a constant logarithmic change, and when you plot this on a logarithmic y-axis it will look like a straight line. Type 1 or 3 curves are not straight lines, and so their rate of change between age classes is not the same. So the rate of change between younger age classes will be less than when you compare the young survivorship to the older individuals. Fewer youths survive to the next age classes than older individuals (fewer deaths in old age when you compare to the deaths in young ages). This is like a type 1 curve. Oak trees resemble this. The opposite is true with type 3 curves. Many young individuals survive to the next age classes, but not many older individuals survive in the older age classes. There are more deaths in old age than compared to the deaths at young ages. This is like primates, especially since they have parental care to protect the individuals at the young age classes.