PDS AP Environmental Science 8th Period 2011-12

I am still a little confused about feedback loops. I know that you shouldn’t associate positive with good and negative with bad and I understand the different things that cause the feedback loops. For example, jobs and sanitation lead to positive feedback loops and crime and pollution lead to negative feed back loops. So does that mean that in a positive feedback loop those good things are brought to the city causing more people to move in? And that then the city is accelerating too quickly which can be a bad thing? And in a negative feedback loop those bad things take place in the city which causes people to move out but it could be a good thing because then it is able to self correct itself? This is kind of confusing but I just want to make sure that I am understanding this right so if some one could clarify that would be great.

In class on Wednesday, we discussed the ten principles of smart growth. But before that, we discussed reasons urban areas tend to sprawl. Today we discussed how cities usually get to a point where crime, pollution, unemployment can trigger a negative feedback loop  which causes people to leave and the population to decrease. That leads to the suburbs growing because of things like an increase in jobs available, less pollution and less crowding. As the suburbs grow, there is a transition into a positive feedback loop triggered by the Highway Trust Act which leads to an acceleration in urban sprawl. In the book, figure 10.15 is a good example of this positive feedback loop; as the city sprawls outward–>leads to longer commutes to work–>leads to more money spent on gas–>leads to more money gather in taxes by government–>leads to more money for more highways—>leads to more urban sprawl…

The next thing we did in class was go over the ten principles of smart growth (can be found on pages 276-277 in the book)

Smart Growth Principles: An attempt to battle urban sprawl and make attractive, livable, sustainable urban/suburban areas.

1. mixed land uses: mixing residential, education, recreation, etc. in one area. Leads to easy accessibility and less automobile dependency.

2. range of housing opportunities and choices: provides housing for people of all incomes.

3. walkable neighborhoods: encourages walking which leads to less automobile use.

4. community and stakeholder collaboration: involve all stakeholders in the planning of determining how neighborhood will appear and be constructed.

5. compact building design: multistory buildings and parking lots to take up less land (spread up instead of out).

6. communities with a sense of place and distinct character (ex. Dilworth and Phillips Place).

7. preserve open space, farmland, natural beauty: to keep some green space and have access to fresh, local produce and recreation.

8. variety of mass transportation choices: convenient alternatives to driving.

9. strengthen existing communities (infill): infill construction in existing communities. The process of buying land and tearing down the old houses and buildings on that land and replacing them with new and bigger houses. Instead of going outside of the city, you take land that is not being used from inside the city and reuse it.

10. predictable, fair, and cost effective development decisions.

*Note: you can check the book on these 10 if you need or are unclear on any of these or want to clarify them for the reader.

After going over these principles, we watched a video that talked about how a city, Boulder, Colorado, created a new community. As we watched the video, we were asked to look for how many smart growth principles they incorporated into this community. We concluded that they included every one of the ten principles. This shows that it is possible to create a community that uses all ten of these principles.  Here is one source that you can look at that shows the Holiday Neighborhood in Boulder.  http://www.terrain.org/articles/16/wann.htm

Tags: sustainability, urban areas, urban planning

In class on Friday, we discussed Darwin’s theory of natural selection. This lesson goes over questions 10-13 in the study guide. So first, we said that natural selection is the engine that drives changes in species, but there are misconceptions. The first is that “survival of the fittest” is not based on physical strength but it’s based on survival and reproductive success. And second, there is no goal in the process and then end state is not perfection, it’s just survival.

Then we talked about the four things that are needed in Darwin’s theory of natural selection. As you can see in the diagram, natural selection is the biggest arrow that leads to more species.

1. Genetic variation: there have to be some variations in individuals within a population. For example, in a hummingbird species, there has to be some hummingbirds with short beaks and some with long beaks.

2. Overproduction of offspring: the rate of reproduction is surpassing the amount of supplies, which leads to competition.

3. A struggle of existence: the competition for food and space created from the overproduction of offspring creates a struggle for survival.

4. Differential survival and reproduction: those organisms that win the struggle are able to reproduce more offspring with successful genes/traits, so over time the population changes.

Next, we went over the three different types of natural selection. These are also written on a handout that we got in class on Friday.

1. Directional: this shifts the range of variation, meaning that the species moves from one specific genotype and phenotype towards towards a different genotype and phenotype.

2. Stabilizing: this is when extreme forms of this species are eliminated and the intermediate phenotypes become dominant. For example, if there are three different colors of butterfly, white, red, and pink, the extremes of red and white will show up less than the intermediate of pink.

3. Diversifying: this is the opposite of stabilizing natural selection and the extremes become dominant over the intermediate. So, in the butterfly example, there would be more red and white butterflies instead of pink ones.

As you can see in the diagram, there is a smaller arrow below the one for natural selection that says random processes. Changes in species can also arise through random processes and there are four types.

1. Mutation: a mutation can arise by mistakes in the copying process of genes that changes the genetic code and if they are not lost, then they may increase in frequency in the population.

2. Genetic Drift: in large populations genetic composition stays the same, while in a smaller population it takes less time for the composition to change.

3. Bottleneck effect: when there is a drastic decrease in size within a population, genotypes will be lost.

4. Founder effect: when a small group of individuals are isolated from the population, genetic variety will be lost.

Now to go over the diagram in more detail. One important thing to notice is that over time, changes can lead to different species. But you can also have change that does not create new species. We have already gone over the bigger arrow (natural selection) and the smaller arrow (random processes). Those two arrows make up microevolution which occurs within one population. The splitting arrow represents macroevolution which is changes between populations that gives rise to new species. Written inside the splitting arrow are two types of isolation that lead to these two different species. One type is reproductive isolation, also known as sympatric isolation. And the second is geographic isolation, also known as allopatric isolation. (To see an example of how geographic isolation can lead to two different species, click on the link below and view the short video on salamanders.) To conclude, through natural selection, random processes, and isolation, population A, species X can split into population A, species X and population B, species Y and they can not interbreed.

http://www.youtube.com/watch?v=GIGXLNYV9kc&list=FLaYd3aYbrHaG3CL5iElnbHw&index=55&feature=plpp_video

Click to Enlarge

Tags: biodiversity, evolution

I was listing the biomes in order of how much precipitation they had and I saw that prairies had the least amount. But that confused me because it still has a good amount of biodiversity and has very rich soil. I don’t really understand how that is possible considering there is barely any precipitation there and that is one of the most important factors. And in class today we said that the more precipitation there was, the more consumers and there are a lot of consumers (even secondary) in prairies. Is it just because of the moderate temperatures that enable the grass to grow?

I believe that the biggest environmental problem that we face today is conservation. I’m not necessarily talking about just saving trees but other issues such as trying to prevent animal extinction and also getting rid of invasive species. And the destruction that is happening to the coral reefs could also try to be prevented and we should try to conserve them as well.