BIOLOGY 1101 LAB 10: ECOLOGICAL SUCCESSION

[Pages:10]BIOLOGY 1101 LAB 10: ECOLOGICAL SUCCESSION

READING: Please preview pages 428-432 and pages 435-437 in your textbook before starting this lab. Pay special attention to discussions of species interactions and disturbance.

Background

We often view an ecosystem as something stable in which populations of various organisms live in equilibrium--nature in balance. This view is incomplete because it overlooks the fact that it took time to establish that apparent stability, and changes continue to occur over time.

Community structure (patterns of species abundance and the relationships between populations) is not static, but changes over time. In other words, communities are dynamic, a quality that makes them interesting to study. Two of the fundamental processes driving these changes are disturbance and succession.

The term succession refers to the series of changes observed in a community following a disturbance event. A disturbance event, such as a wildfire, flood, landslide, or hurricane, is an event that alters ecosystem structure through changes in resource availability or other aspects of the physical environment. For example, think of a severe forest fire that kills most of the standing vegetation. What was once a closed canopy forest with very little light reaching the ground is now a very open and bright place. Plants and seeds that were in the shade can take advantage of the new available resources, including sunlight. The plant species that will thrive in the new, open environment may be different from those that grew under the closed forest canopy. These plants are called early successional plants because they thrive in recently disturbed environments. They are also called pioneers, ruderals, or weeds. Over time, as early successional plants grow, they change the environment again (by providing shade or changing soil conditions, etc.), which creates opportunities for a different set of plant species. These plant species that establish after the early successional species are called late successional species. They are generally less tolerant of disturbance events, for example a late successional species might thrive in low light conditions. Sometimes these species simply grow more slowly and live longer than early successional species and only become prevalent a while after the disturbance event. Plant communities can be thought of as going through cycles of disturbance followed by succession followed by disturbance and so on. This is not to say that these cycles, and the resulting communities, are ever identical or exactly repeatable.

In this lab, you will explore the dynamics of plant communities, that is, how plant communities change over time and space as a result of interactions between organisms, their biotic (e.g., herbivores or neighboring competitors) and abiotic (e.g., precipitation) environment, and disturbance regimes (the frequency, intensity, and extent of disturbance events). The concepts of succession and disturbance are

1

timely given the extent to which human-caused disturbances, such as logging and land development, are influencing global ecosystems and the extent to which natural disturbances, such as fires and floods, are actively managed by humans (and are themselves changing in response to climate change). Informed voters and citizens should know about disturbance and succession in ecological communities. Knowledge of these processes will help them make decisions about land conservation, wildlife habitat restoration and natural resource management practices.

INTRODUCTION TO THE LAB

Today you will explore how plant communities change over time following a disturbance. In the first part of the lab, you will play an interactive online game to develop a mature plant community through the process of ecological succession. You will play the game multiple times to learn how the presence of some species affects the growth of others and how the process of succession is influenced by the type of disturbance. In the second part of the lab, you will learn a bit about the ecology at Yellowstone National Park and then you will generate data to observe how the structure of a model forest community changes during the time following a severe forest fire.

LEARNING OBJECTIVES

After studying this material, you should be able to: 1. Describe and distinguish between the processes of primary and secondary succession; give some real-world examples of each. 2. Describe how biotic components in an ecosystem change abiotic components during succession. 3. Explain why different plants respond differently to changes in their environment. 4. Describe biotic and abiotic factors that influence the way a plant community changes over time. 5. Explain the role of disturbance in ecosystems and its relationship to succession in plant communities.

Exercise 1: Succession Online Interactive Game

[1] Go to OR go to and click on the Ecology link and then the Succession Interactive link.

[2] Click Start a new Game! and then select Primary Succession from the Main Menu. ? After a short introduction, during which a volcano will erupt and you will be given important instructions for how to proceed, you will see a panel with different groups of organisms which you can add to a newly formed volcanic island. ? Note that the game includes both Producers and Consumers. Please feel encouraged to play around with both, however this lab activity will focus on the plant community.

[3] First click on "grasses" and "Add Grasses to My Island". (3.1) Why can grasses not survive on the island yet?

2

[4] Return to the panel of organisms to read about the various plant groups and start building your ecosystem. (4.1) Record the progression of your ecosystem starting with the early successional, or colonizing, species and ending with the "climax" community. Note the characteristics of each group that determine which successional stages it emerges in, dominates, and if applicable, when it diminishes or declines. The template below is one possible to record succession visually.

Colonizer Species

[5] Be sure you are able to answer the following questions. (5.1) Which group, or groups, is composed of pioneer species? (5.2) What role do lichens play in the environment during primary succession? (5.3) After you add mosses to the island, is it possible to add grasses? Why, what changed? (5.4) What happens to the mosses during the colonization of grass species? Why? (5.5) What traits do early successional plants share? What traits do late successional plants share?

[6] Return to the Main Menu and select Secondary Succession. [7] After the introduction but before you start the process of succession, answer the following question.

(7.1) How are starting conditions different between Primary and Secondary succession? [8] Try adding Lichens and/or Mosses to the island first.

? You will see a text box appear that tells you secondary succession does not need to start with lichens or mosses... but why won't the game let you do it anyway?

(8.1) Read the descriptions for Lichens and Mosses and write down one or more ecological explanations for why these groups are not allowed to kick off secondary succession.

[9] Now you can play around with adding different groups of producers (and consumers, if you like). (9.1) What characteristic(s) of grasses (or wildflowers) make them good early colonizing species in secondary succession? (9.2) Why are trees the last thing to become established on the island?

[10] One last thing before you move on. Perhaps you noticed in the simplified interactive game that the "climax" community that exists at the end of secondary succession was identical to the one that existed before the disturbance. In reality, there are factors, some random and some predictable that make it hard to know the end result of succession. Think about our island examples carefully. In order for succession to occur, our island was dependent on seeds and spores coming in from other

3

islands or nearby continents (either on the wind, ocean currents, or animal carriers), but if those source locations had continued to go through succession on their own, then the seeds and spores available now would be quite different than what was available at some previous time. Succession could not possibly result in the same climax community if the available species are different, right? Furthermore, not all ecosystems reach a true "climax" community since they could be hit by repeated, minor disturbance events or another major disturbance that permanently alters the biotic and abiotic communities. For more information on this you can visit .

Exercise 2: Fire Disturbance in Yellowstone

Yellowstone National Park contains both shrubland and grasslands in the northern parts of the park and lodgepole pine forests in the central part. Many of the species in these communities are fireadapted (unlike in the Amazon Forest), and the communities depend on periodic burns to persist.

Historically, the shrub and grasslands burn every 25 to 60 years and the lodgepole pine forests burn every 150 to 300 years. Prior to 1972, a policy of fire suppression in the US reduced the occurrence of all forest fires (park managers instituted a natural fire management plan in 1972 that would allow some naturally occurring fires to burn). In 1988, however, Yellowstone experienced the driest summer in its recorded history, and over 36% of the park burned in massive fires... for months.

The Yellowstone forest communities that existed right before the 1988 fires were the product of over a century of ecological succession following the last catastrophic fires to consume the area back in the 1700s.

[1] Look at Table 1, showing a series of photos taken after the 1988 fires. The first photo was taken just after the fire, and the only sign of life is the scattering of pinecones on the ground. Lodgepole pines produce pinecones that remain closed with resin until heated by fire. It is an adaptation to frequent fires and allows lodgepole pine seedlings to take advantage of the drastically different growing conditions following a fire disturbance (namely open space). By 1991, small grasses and a few forbs (small flowering plants) cover the ground, and little seedlings of lodgepole pine have sprouted from cones that opened during the fire. Nearly 10 years after the fire (see the 1997 photo), there is a thick layer of green vegetation and wildflowers appear among the growing pine seedlings.

4

1988

1991

1997

1998

1988

1989

1991

1992

Table 1 Post-fire succession in Yellowstone National Park. National Park Service photos taken at Point 169, 2.85 miles east of the west gate by Bob Stevenson and Jim Peaco, 1988-1998 (top row). Series of four taken after the 1988 fires at Point 181, six miles east of road & just south of Tower Falls store parking area; Bob Stevenson; 1988-1992 (bottom row).

5

The photo sequence from Yellowstone covered fewer than 10 years post-fire. What will happen over the longer-term? In this part of the lab, you will act as a surveyor gathering data on the changing plant community in a lodgepole pine forest after a fire. You will observe by counting the number of individuals of different types of plants that grow in the experimental plot 5, 8, 10, 20, 40, 60, and 100 years after the fire.

[2] Figure 1 below represents an aerial view of a forest plot in Yellowstone. It has remained more or less in equilibrium for the last 100 years and has not been subjected to a major disturbance event for at least 200 years. One year after this survey was complete, a severe fire burned through the area. (2.1) Describe the composition of the plant community in the plot before the fire (shown in Fig. 1).

Figure 1. Forest Plot one year before the fire.

Taxa

# of plants % of Total

Grasses

Annuals

Forbs

Shrubs Pine

Total # ______

[3] For Figures #2 ? 9, count the number of each type of plant found in the plot. Use the key provided in the table as a guide.

6

Figure 2. Forest Plot from Year 0 to Year 4.

Figure 3. Forest Plot at Year 5.

Taxa

# of plants % of Total

Grasses

Annuals

Forbs

Shrubs Pine

Total # ______

Figure 4. Forest Plot at Year 8.

Taxa

# of plants % of Total

Grasses

Annuals

Forbs

Shrubs Pine

Total # ______

Figure 5. Forest Plot at Year 10.

Taxa

# of plants % of Total

Grasses

Annuals

Forbs

Shrubs Pine

Total # ______

Taxa

# of plants % of Total

Grasses

Annuals

Forbs

Shrubs Pine

Total # ______

7

Figure 6. Forest Plot at Year 20.

Figure 7. Forest Plot at Year 40.

Taxa

# of plants % of Total

Grasses

Annuals Forbs

Shrubs

Pine

Total # ______

Figure 8. Forest Plot at Year 60.

Taxa

# of plants % of Total

Grasses

Annuals Forbs

Shrubs

Pine

Total # ______

Figure 9. Forest Plot at Year 100.

Taxa

# of plants % of Total

Grasses

Annuals

Forbs

Shrubs

Pine

Total # ______

Taxa

# of plants % of Total

Grasses

Annuals

Forbs

Shrubs

Pine

Total # ______

8

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download