PDS AP Environmental Science 8th Period 2011-12

This is a good example of a parasitic relationship between organisms–

http://news.yahoo.com/zombie-fly-parasite-killing-honeybees-230200867.html

Tags: news

I have a question regarding predation. In class we’ve been categorizing predation into three groups: True predators parasitoids and pathogens. We’ve said that pathogens are synonymous for disease, but in the book it says that pathogens are disease that infect a host via parasite. My question is two part: Is a disease that infects a population that is not transmitted via a parasite still considered a pathogen? And if so, is these diseases also a part of predation?

On the Study Guide for the test, question number 15 asks what species relationships can be deduced from population graphs. I’m wondering if these relationships are the predator-prey type graphs, and if so, what other relationships are there? I have a feeling that this has to do with the coevolution idea, but I’m not sure.

Ok, so I get that a fundamental niche is “the suite of ideal environmental conditions for a species” and that a realized niche is “the range of abiotic and biotic conditions under which a species actually lives” but my really quest has to do with niche generalists versus niche specialists. Are generalists found in both fundamental and realized niches or only in various realized niches because they can live with abiotic/biotic conditions variations? And vice versa with specialists. Sorry, I’ve sort of really confused myself on the matter.

I was looking over the Chapter 5 study guide and question 5 is confusing me. I have the diagram but I was wondering if someone could explain the diagram and the idea about phylogenis and phylogenetic trees in more detail than the book did? Also, question 16 asks about realized and fundamental niches. Do organisms live in fundamental niches or are these just for a comparison to what the organisms ideal environment would be? Thanks!

Tags: community, ecology, succession

Since I made a slidedeck to go with the homework, I took scribe duties. BONUS: Below the slides is a short YouTube clip that explains how the elephant could be a keystone species. -W

Tags: ecology, keystone species

The two population growth models we discussed in class were:

• Exponential Growth
• Logistic Growth

Exponential Growth Curve:

When a population is growing without limits at a fixed rate, numbers will climb over time creating a J-Curve. This assumes no limiting factors or resource depletion at the rate of typical exponential growth.

Logistic Growth Curve:

This model is the logistic curve of a population. Overtime births decrease and deaths increase creating an inflection point in the graph where the line will start to level out at K, the carrying capacity. This curve is called an S-Curve. This model assumes that all individuals in a population have the same needs and that the environmental conditions are constant. This is hardly possible in today’s world.

In class we discussed population dynamics between r and K populations. While “r” species have a higher rate of growth and shorter lifespans like bacteria or mice, “K” species have slower growth rates and longer lifespans, like Blue Whales or African elephants. Other animals have traits from both spheres, like a cockaroach because it produces rapidly but has a longer life time. These models could measure either one of the species but it depends on the fixed growth rate and resources. It is more likely for a “r” population to experience exponential growth and have an intrinsic growth rate and approach a carrying capacity easier while a “K” species who has a lower intrinsic growth rate may reach a carrying capacity over a longer period of time.

There are positives negatives with both of these models in that they each have assumptions. The J curve is assuming unlimited resources which is not realistic and the S curve indicates that a population may naturally find its carrying capacity when in reality it may overshoot it (as we saw in the Island Royale simulation.) Since no species exist in isolation, they have producers and predators, predicted populations using models are not always accurate. Models can be used for a basic outline of a populations growth but should not be used as a primary source to predict populations.

Here is the slidedeck from today’s lesson about species interactions. We discussed many examples of coevolution that produced these relationships and the population dynamics that result. You can play them within the blog or go to my Slideshare page to play them full size. I don’t like to use Power Point often, but it provides a nice place to park all the pictures/videos of examples from today’s lesson.

Tags: ecology, evolution, population

Today in class we started talking about population biology. Scientists can study nature at 5 different levels of complexity: individual, population, community, ecosystem, and biosphere. Today, we focused on populations.

The image below (thanks Mr. Willard) displays the levels of complexity.

A population contains all organisms and species of a particular area. It’s important to remember that when we talk about adaptations that are taking place, the populations are adapting as a whole, not the individuals. Scientists monitor populations for research, but there’s always “flux”. One equation that was highlighted today was the way to calculate changes in population size: (births + immigration) – (deaths + emigration) = change in population size. The four factors that affect population size are (obviously the four in the equation) births, deaths, immigration, and emigration.

We also discussed the 5 population characteristics. Size (N), density, distribution, sex ratio, and age structure, all of which are important in determining the traits of any population. The size is the total number of individuals with in a certain area, or how many species exist. Density is the number of individuals per unit area at a particular time. This factor helps scientists estimate if the species are rare or abundant in this area. Distribution can be expressed in three ways: random, uniform, and clumped. Random distribution has no pattern to where individuals live and grow, and uniform is evenly spaced (typical for territorial animals). Clumped distribution will be observed in animals or plants that have a higher survival rate traveling/growing in a group, whether helping to get food or just increasing protection. Sex ratio is simply the ratio of males to females, which should be 1:1, but is not always. Age structure is how many individuals fit into particular age categories, and it helps scientists guess how rapidly a population will grow. Depending on which generations have the most organisms, there might be large declines, or inclines, in population size.

We also went over growth models, where we specified the two things that every population has: a maximum potential for growth and a carrying capacity. Maximum potential for growth will only be fulfilled given ideal conditions and unlimited resources. It is known as the intrinsic growth rate (r), and the graph that it produces has a “J” shape, known as the exponential growth model. The Carrying capacity (K) is the limit of how many individuals a food supply or area can support. When growth reaches it’s carrying capacity, it slows, as shown in the logistic growth model. It has an “S” shape curve.

Exponential Growth Model                                                               Logistic Growth Model                    

Next, we touched on the two reproductive strategies. It is important to remember that whichever strategy a species utilizes, it is because they have evolved, not by choice. The two are r-selected species and K-selected species. r-selected have a high intrinsic growth rate and reproduce quickly and often (examples: mosquitoes and dandelions). K-selected have low intrinsic growth rates and do not produce many offspring very often (examples: elephants, whales, and humans).

Tags: population