PDS AP Environmental Science 8th Period 2010-11

I’m a little confused about how a climax community fits in with the idea of succession. I know that biodiversity is greatest in the middle stage of succession, but climax community makes it seem like it is the climax of biodiversity. So what exactly is a climax community, and when does it happen in succession? Thanks!

When thinking about population ecology, it is important to remember that populations evolve, not individuals. We’ve learned that populations do not operate independently of each other, but are connected and intertwined within communities. Therefore, we say that populations evolve together; they coevolve. In population ecology, there are 5 major relationships:

1. predation
2. mutualism
3. commensalism
4. competition
5. parasitism

Most of that is review from previous units, though. The main new stuff we learned involved characteristics of populations.

5 CHARACTERISTICS OF POPULATIONS:

1. Size: The size of a population can either increase, decrease, or stay the same. It can also move in patterns. It can be expressed as an equation:  (births+immigrations) – (deaths+emigrations) = size.

This is an example of a population size graph. It illustrates how populations can change size in patterns or cycles. It also demonstrates the idea that populations affect each other and do not operate independently… a key idea in population ecology.

2.  Density: Density is defined as the number of individuals per unit of area. A high density of individuals can have both pros and cons depending on the situations:

+ safety in numbers                                                                     – more intraspecific competition

+easily find mates                                                                         - infectious disease is more easily spread

- high density could actually attract predators (buffet)

<– high density of organisms in a population

3.  Distribution:  There are 3 types of distribution:

clumped- (picture on the left) all the birds are distributed together in a cluster/bunch

uniform- (picture in the center) the penguins are evenly spaced out

random- (picture on the right) the different species of trees are mixed in randomly

4.  Age Structure/Sex Ratios:  these are based off of age and sex “cohorts”; they are illustrated by histograms

5.  Growth Rates:  growth rates are expressed in percentages. There are 2 common situations: exponential growth and logistic growth. Exponential growth (constant growth rate) is sometimes called a J Curve. Logistic growth (unregulated growth rate) is sometimes called an S Curve. Their graphs may look something like this:

The graph on the left shows exponential growth, while the graph on the right shows logistic growth. Notice that in logistic growth, the curve levels off at a certain point “K”. This point is called the carrying capacity. These graphs might look simple, but growth rates are rarely this simple in the real world, they just tend to follow these two basic trends/stereotypes.

That’s basically it.

P.S. Always be on the lookout for the NAP ZONE:

Nap Zone: The Movie

I think our biggest environmental problem right now is our reliance as a country on fossil fuels. Most Americans tend to think that these resources will last forever, but they are actually nonrenewable. This dependency is not something that we can sustain for much longer. I know that people are trying to come up with alternative options for transportation, including cars that require less gas or ones that have fewer emissions, but it has been tough to make these options completely attractive or affordable. The burning of fossil fuels results in a huge amount of air pollution and carbon dioxide emission that is destroying the atmosphere. For these reasons, I think it is the most significant environmental problem we have to deal with right now.