PDS AP Environmental Science 5th Period 2010-11

So this wasn’t exactly asked in the simulation but why did the shorter seasons cause a smaller variation in the moose population?

In a predator/prey relationship during an extended growing season, what are the biological reasons for the extinction of the predator (wolf), and does the prey always become extinct first?

The Paradox of Enrichment is when the population swings are to erratic to be sustainable right? Does a predator need to be present for extermination to take place? Or can competition alone take out a species?

Also how does sympatric speciation work? I know it’s the reproductive isolation of a population living in the same region, but what are some examples of this?

thanks

I’m afraid I do not quite understand Stabilizing Selection. Can someone explaine to me how itermediate traits are changing but the status quo is still maintained?

Note: This was posted by WillW in the other class-might be helpful as we did not assign a scribe that day.
The Isle Royale simulation in class points out the significance of free population growth, the presence of predators, and the availability of food in an ecosystem. The three simulations that we did focus on each of these and their effects on the populations of moose and wolves.

Exercise 1

This exercise focused on the population of moose when there are no predators present. We ran the simulation for about fifty years. The resulting graph looks similar to an S curve with a slight rise and fall before it reaches carrying capacity. This is an example of a population overshooting its carrying capacity, which then results in a dieback, also called correction, in the population until the carrying capacity is achieved.

A couple important things to note.

1 – A population grows fastest when it is medium sized.

2 – No population can sustain a J curve indefinitely. There is always a carrying capacity.

3 – The moose overshoot their carrying capacity because they have no natural predators. The dieback is then caused by the resulting food shortage when the moose are placed in direct competition with each other.

4 – The point of greatest population growth is called the inflection point.

Exercise 2

In this exercise, wolves were introduced to the island.

Ok. I have two questions.

The first one is with the paradox of enrichment, I know the overshoot comes sooner and is greater, so there’s a greater dieback. Does one animal start dying first and that is what leads to the other dying, or do they die in unison or what?

My other question is that Mr. Willard said that at some point the the population of mooses was at its most unstable…but I didn’t write down what that point was. Would it be the beginning of the overshoot or at the peak or on the downside of the overshoot or something else?

Population biologists/ecologists rarely have the luxury of counting every organism in an ecosystem or biome, but they still have to try in order to monitor relative biodiversity or determine if a population is threatened or endangered. Today we simulated a popular sampling technique known as mark and recapture. While we used pretzel goldfish as tagged fish, in reality a typical fish tag looks more like this:

See the blue tag (click to enlarge)?

Image Source: http://www.greenalgaecontrol.com/GAC%20Private%20Lakes.html

Of course, we make some assumptions when we use this method. I think the professor that created this page does a nice job explaining the method and limitations of using it: Estimating the Size of Animal Populations (might be a useful read before finishing your lab write-up).

Finally, here is our class data for today. Please analyze it before reaching and writing your conclusion:

Class Data (click to enlarge)

Of course, I’m available by email if you have any questions. -W

In class on Tuesday we learned about species populations. A population is a group of individuals of a species that live in a particular area. Populations coevolve based off of the five relationships we learned about in the previous unit (mutualism, comensalism, parasitism, predation, and competition). All populations of any species contain these five characterisitics:

1. Size: Population sizes increase, decrease, or are stable, and  follow patterns

Equation: (Births + Immigration) – (Deaths + Emigration) = Change in size

2. Density: The number of individuals per unit of area

Increase in Density-

Pros: acccess to mates increases, safety increases

Cons: intraspecific competition increases, rescources decrease, predation increases, rate of infectious disease  spreading increases

3. Distribution:

1-Clumped Distribution:herds, school of fish, humans(urbanization)

2-Uniformed Distribution: organisims evenly spaced

3-Random Distribution: trees (seed travel)

4. Age/Sex Stucture:

Sex Ratio-porportion of males to females

Age Structure-describes relative numbers of organisms of each age within a population

Age Structure Diagram

5. Growth Rate:

-annual growth in percentage form

-grows exponentially, yet with limits, which is why graphs have a logistic growth   curve

- all populations have theoretical limit (carrying capacity)

Growth Rate Graph

Age Structure Diagram: http://images-mediawiki-sites.thefullwiki.org/08/3/8/3/25099082503828593.png

Growth Rate Graph:

http://www.cdli.ca/courses/biol2201/unit04_org01_ilo02/BI300002.gif

According to our text, biological evolution is the genetic change in populations of organisms across generations. But to begin our discussion on evolution, we had to first consider how biodiversity is calculated. Speciation – Extinction = Biodiversity. Speciation is the only method known to add species and increase biodiversity, and extinction–the disappearance of a species–decreases biodiversity. In class today, we focused on speciation. So let’s imagine a certain population of a species and call them Population A. Within the population, natural selection occurs, which drives change in the population. The change is seen in the changing allele frequencies of the gene pool. This is termed microevolution. Microevolution usually occurs over just several generations.

Now, there are 4 Factors of Natural Selection:

1. Genetic Variation (Sources of variation include mutation and sexual reproduction/meiosis.)
2. Overproduction of Offsprings
3. Struggle for Existence
4. Differential Rate of Survival and Reproduction

Genetic variation allows different combinations of genes to produce offsprings with different traits through sexual reproduction. Furthermore, overproduction of offsprings via sexual reproduction allows many offsprings with all sorts of different combinations of genes. Due to the limited amount of resources, the large number offsprings will struggle to survive, and only the offsprings with the best traits for survival and reproduction will pass on it’s genes. These four factors are all interconnected and essential in driving change within populations. These populations change in order to survive, thus certain traits are favored. There are 3 Types of Natural Selection that illustrate the different ways that a population can change.

1. Directional Selection – One extreme trait is favored over the other extreme trait.
2. Stabilizing Selection – An intermediate trait is favored over the two extremes.
3. Disruptive (Diversifying) Selection – The extreme traits are favored over the intermediate trait.

This site has great graphs that can help visualize the three types: http://www.tutorvista.com/biology/types-of-natural-selection.

As populations change, they can become so different that Population A becomes Population A1 and Population A2. Once these two populations are so dramatically different that they cannot reproduce together, they are classified as two completely different species. Reproductive Isolation essentially determines if a species has diverged or not. This is termed speciation or macroevolution. Unlike microevolution, macroevolution occurs after millions of generations. Furthermore, speciation is often triggered by geographic isolation.

There are 2 Types of Speciation:

1. Allopatric – Speciation is due to geographic seperation.
2. Sympatric – Speciation occurs in the same location, but for some reason, a species separates.

This site illustrates the difference between the two modes of speciation: http://scienceblogs.com/evolvingthoughts/2007/03/basic_concepts_allopatry_and_s.php.

*From Mr. W, here is the brief video example on allopatric speciation shown in class: