Population+dynamics+notes


 * //November 8th, 2011//**
 * //Notes by Melissa Quinn//**

**Measuring Population Charachteristcs**
Today in class we did some activties in order to demonstrate the different ways to estimate a size of the population. We did this by going to difrferent stations and trying out the measuring estimation procedures on sample populations such as cards, a picture of bacteria, a picture of people, and a picture of trees. The two possible methods are :

- Using quadrants is a common technique for stationary small animals, suchs as plants and insects. A small defined area is isolated by a quadrant and the samples of the population are counted found within this quadrant. Population size can then be estimated through calculations based on counts within the area multiplied by the number of quadrants. As stated above, quadrant sampling is the most effective for stationary species.


 * //-//** The mark-recapture method is a sampling technique used for estimating population size and density by comparing the proportion of marked and unmarked anuimals captured in a given area. It is sometimes called caprutre- recapture. An example of this method is as follows : assume a lakec is home to a popualtion of 3000 pickeral . If 300 pickeral are caprutred and marked and then released back into the lake, then the proportion of fish marked in the population would be 0.10 or 10%. The marked fish would then be mixed randomly back into the environment . If another sample was then taken you would expect 10% to be marked. The proprotion of marked fish in the entire population is expected to equal the proportion of marked recaptures in a samples. It can be measured by using the following equation:

total # makred ( M) # of recaptures (m) _______________ = _________________ total population ( N) size of second sample ( n)


 * //November 10, 2011//**
 * // Notes by Rachael Kitchen //**

2. Density-Independent Factors
 * Factors affecting Population Change **
 * 1) Density-Dependent Factors
 * 2) As density changes, the effect on these factors change
 * 3) High density
 * Intraspecific competition: competition between people or animals of the same species
 * Ex: Too many deer, decreases the amount of food for deer which decreases the reproductive success ( the deer may not even reach sexual maturity)
 * Ex: Harp Seals must get big and fat to be sexually mature; they don’t have a specific age at which they become sexually mature. The reproductive success would decrease with an increased density of seals, resulting in a decrease in the amount of food per seal meaning they do not reach sexual maturity.
 * Ex: Predation: Predators regulate the number of prey. An increase of sharks decreases the number of fish, which decreases the amount of food for sharks, which decreases the number of sharks, which increases the number of fish…… It is a cycle that keeps of recurring.
 * Disease
 * Disease spreads quickly and to more people in a dense population
 * Ex: You want to be in the country where there are less people when there is a SARS outbreak, you do not want to be in a densely populated area where there is more change of you becoming infected.
 * 1) Low Density
 * Allee effect
 * Some species cannot mate without a pack, this decreases the population
 * If the animals cannot find a mate, the population decreases
 * If the population continues to decrease lower and lower, the species will probably not survive
 * Ex: If tigers can’t find each other, their genes cannot be passed on, and the population decreases.
 * Some sharks, when the females cannot find a mate, can fertilize themselves and produce female baby sharks. These would have the same DNA.
 * Minimum Viable Population Size: The lowest number of individuals needed to keep the population alive. Scientists can estimate this value.
 * If there are only a few individuals, inbreeding occurs because there isn’t a lot of choice
 * Genetic variation gets lost (For example Hemophilia in the royal family
 * 1) These factors will influence a species regardless of their population
 * Ex: Extreme weather: too hot or too cold. Animals will not be inclined to start a family with these extreme conditions because they are trying to survive themselves (they may not have enough food in the conditions).
 * Ex: Human factors: insecticides, herbicides etc. Biomagnification: the concentration of pesticide increases in larger animals because the larger animals eat so many smaller animals, who eat a lot of the pesticide/herbicide etc.
 * Limiting Factor: whatever resource is in the shortest supply is the limiting factor.
 * Ex: a species needs carbon dioxide, water, and nitrogen to survive and nitrogen is not present. Nitrogen is the limiting factor: the population can decreases or disappear.

Fluctuations occur in population sizes all the time, hopefully the species will be able to survive them. Further Reading: section 14.3 in the textbook