Ecology
|
Blog Alert: Explain the difference between a ecosystem, species, community, population. |
What is a population?
A population is a group of interacting individuals of the same species. Examine the growth curves below. Which curves are the students likely to see in nature and at their restoration sites? Which two are impossible to sustain for long peri- ods of time and why? (see Forms of Population Growth handout for students)
The linear curve (A) is characterized by a constant rate of popula- tion growth; the exponential curve (B) is characterized by an ac- celerating rate of population growth. If the linear or exponential growth curves continued indefinitely, the earth would be covered with every species because their growth would never slow down. A population has to stop growing at some point. The logistic (C) and cyclical (D) curves are the most likely curves to be seen in nature. Within both of these curves is an exponential curve at the very beginning. When a population first begins to es- tablish, it is subject to a lot of “stochasticity,” which is the scientific term for randomness. This means that random mortality, caused by a flood, a predator, disease, or other disaster can have a big impact on the population because there are so few individuals. This period is represented at the beginning of the graphs, where the total population growth rate is really slow, even though the per capita reproductive rate is at its maximum because resources are abundant. Gradually, the population will reproduce and sustain a positive growth rate. At this point, the population will contain enough individuals so that losing a few will not affect the overall population growth rate very much. The population will continue to grow rapidly until suppressed by a limiting factor. This phenom- enon is known as density dependence. The maximum population size of a species in a given ecosystem is known as its carrying capacity. Disease, predation, parasites, limited habitat, and limited resourc- es are some of the factors that keep populations of animals from covering the entire planet.
A population is a group of interacting individuals of the same species. Examine the growth curves below. Which curves are the students likely to see in nature and at their restoration sites? Which two are impossible to sustain for long peri- ods of time and why? (see Forms of Population Growth handout for students)
The linear curve (A) is characterized by a constant rate of popula- tion growth; the exponential curve (B) is characterized by an ac- celerating rate of population growth. If the linear or exponential growth curves continued indefinitely, the earth would be covered with every species because their growth would never slow down. A population has to stop growing at some point. The logistic (C) and cyclical (D) curves are the most likely curves to be seen in nature. Within both of these curves is an exponential curve at the very beginning. When a population first begins to es- tablish, it is subject to a lot of “stochasticity,” which is the scientific term for randomness. This means that random mortality, caused by a flood, a predator, disease, or other disaster can have a big impact on the population because there are so few individuals. This period is represented at the beginning of the graphs, where the total population growth rate is really slow, even though the per capita reproductive rate is at its maximum because resources are abundant. Gradually, the population will reproduce and sustain a positive growth rate. At this point, the population will contain enough individuals so that losing a few will not affect the overall population growth rate very much. The population will continue to grow rapidly until suppressed by a limiting factor. This phenom- enon is known as density dependence. The maximum population size of a species in a given ecosystem is known as its carrying capacity. Disease, predation, parasites, limited habitat, and limited resourc- es are some of the factors that keep populations of animals from covering the entire planet.
Two general categories of niches that ecologists use to sort species are r-selected and k-selected spe- cies. R-selected species tend to be poor competitors and have high growth and reproductive rates, but invest relatively little energy in each individual offspring. K-selected species have low growth and reproductive rates, but invest a lot of energy in each individual off- spring. For example, an r-selected species could be a weed, while a K-selected species could be a redwood. The r-selected strategy is successful when resources are abundant and random mortality is high, such as in an area of high disturbance, while the K-selected strategy is successful when resource competition is high and ran- dom mortality is low.
Level 3-Guiding Question: What makes population grow? Answer each of the questions underneath each of the short power points and in addition write your answers on index cards and post them under the question on the board.
" What factors limit populations and their ability to survive?"
|
|
Level 3-Investigation: Prey and Predator Dynamics
Read the lab activity below (Instructions for Predator-Prey Simulation) and graph your results (Predator-Prey Activity Data Chart and Predator-Prey Activity Fluctuation Graph). When complete each team will present their result to 2-3 other teams.
After reading the instruction please print out the Predator-Prey Activity Data Chart and the Predator-Prey Fluctuation Graph by clicking on t he buttons below. Check out the image on the left to help you collect the data needed. To enlarge it please click on the image.
"Prey vs Predator" sample line graph
Level 3-Videos:Predator-Prey Dynamics and Invasive Species
How will limiting factors affect or not affect invading species? What impacts might an invasive species have on its new environment? What pressures might an invasive species place on native species? Based on what we know about population growth, invasive species will negatively impact the resources (nutrients, food, space, etc) available to native species in the environment. By definition, invasive species must be doing something better than native species since they are successfully competing for space and resources. Invasive species may also become new predators or parasites in their non-native ecosystem. Because native species did not evolve with these new predators or parasites, they will be ill suited to deal with them and their populations are likely to suffer.
|
|
Click on the audio icon to hear your assignment after you have watched the videos 10 achievement points |
Invasive Species Report
Level 3-Elaborate: Writing Prompt for next field experience after reading the instructions please write the following:
Write an email to your SLEWS Coordinator recommending WHY he or she should monitor the project over time and HOW he or she should go about collecting data. In your email please include:
Reasons why it is important to monitor the restoration site
- Choose 1 biotic and 1 abiotic factor to monitor and describe why you chose those factors
- Describe how you will collect data to monitor these factors over time
- Describe how you expect those factors to change over time
Level 3-Review: What is a Population & what limits it's size?
Level 3-Summary: Students will understand the ecological definition of a population and the different ways that populations can grow. Take the following test to help you practice and prepare the unit final.
Assignments for this Unit
-Blog Alert: Explain the difference between a ecosystem, species, community, population. Click the "Blog Page" button to post your comments!
-Level 3-Elaborate: make an audio file by listening to the audio file and make your own impression of the growth of invasive species in California.
-Level 3-Review: Monitoring the health of habitats, Write an email to your SLEWS Coordinator recommending WHY he or she should monitor the project over time and HOW he or she should go about collecting data.
-Level 3-Elaborate: make an audio file by listening to the audio file and make your own impression of the growth of invasive species in California.
-Level 3-Review: Monitoring the health of habitats, Write an email to your SLEWS Coordinator recommending WHY he or she should monitor the project over time and HOW he or she should go about collecting data.