Content
Topic Introduction
In this topic, we will look at some more interactions between species. We have chosen two areas: facilitation and interactions across multiple trophic levels. Facilitation is defined differently by various authors, but is best seen as an interaction (0 +) where the activities of one species benefits another. For example, a large tree can cast shade that benefits other species. A nitrogen-fixing plant generally benefits non-nitrogen fixing neighbours. Trees are so obviously involved in facilitation that they are sometimes called foundation species. A related concept is ecosystem engineers: species that modify the environment in ways that make it more or less favourable for other species. A key aspect of this is the immediate effects: the concept is restricted to benefits accruing to a neighbouring species.
It is possible to argue that facilitation includes trophic cascades. If the presence of grass benefits a herbivore, then it also indirectly benefits the carnivores that prey on the herbivores. These types of interactions are addressed here in the second presentation, which deals with interactions across multiple trophic levels.
By the end of this topic, you should be able to:
- Describe and name the different types of species interaction that involve either mutual benefit, or benefit to one and no effect on the other.
- Define facilitation, and give examples of different types.
- Distinguish facilitation from symbiosis.
- Define and give examples of ecosystem engineers.
- Explain the differences between food webs and trophic cascades.
- Using examples, describe how the loss of keystone species might affect forest ecosystems.
Topic Readings
Required Readings
- Ghazoul, J. and Sheil, D. 2010. Tropical Rain Forest Ecology, Diversity, and Conservation. Oxford, Oxford University Press, 516 pp. Section 13.3.
Optional Readings
- Crawley, M.J. (ed.) 1997. Plant Ecology. 2nd Oxford, UK: Blackwell Scientific. 717 pp. Chapter 16.
- Terborgh, J. and Estes, J.A. (eds.) 2010. Trophic cascades. Predators, prey and the changing dynamics of nature. Washington, DC, USA: Island Press. 464 pp.
Mutualism and facilitation
- Mittelbach, G.G. and McGill, B.J. 2019. Community ecology. 2nd Oxford, UK: Oxford University Press. 409 pp. Chapter 9.
- Rockwood, L.L. 2015. Introduction to population ecology. 2nd Chichester, UK: Wiley-Blackwell. 363 pp. Chapter 8.
Trophic Interactions
- Mittelbach, G.G. and McGill, B.J. 2019. Community ecology. 2nd Oxford, UK: Oxford University Press. 409 pp. Chapters 10 and 11.
- Morin, P.J. 1999. Community Ecology. 2nd Oxford, UK: Blackwell Science. 407 pp. Chapter 8.
- Price, P.W., Denno, R.F., Eubanks, M.D., Finke, D.L. and Kaplan, I. 2011. Insect Ecology: Behavior, populations and communities. Cambridge, UK: Cambridge University Press. 801 pp. Chapter 13.
- Reagan, D.P. and Waide, R.B. (eds.) 1996. The food web of a tropical rain forest. Chicago, Illinois, USA: University of Chicago Press. 616 pp.
- Rockwood, L.L. 2015. Introduction to population ecology. 2nd Chichester, UK: Wiley-Blackwell. 363 pp. Chapter 12.
- Shorrocks, B. and Bates, W. 2015. The biology of African savannahs. 2nd Oxford, UK: Oxford University Press. pp. 237-257.
Self-check Quiz (For certificate learning only)
After viewing topic presentations, take this self-check quiz to check your own progress. This quiz is designed to see how well you remember some of the issues presented in the topic. There are five questions, and each has a potential of 4 answers, only one of which is correct. When you are ready, click the link Self-check Quiz 4.3 to start taking the quiz.
Pre-readings and Discussion (For certificate learning only)
Once you have read Sections 13.3 of Ghazoul, J. and Sheil, D. 2010. Tropical Rain Forest Ecology, Diversity, and Conservation, choose to post one thought provoking question related to the material that you have read, and answer/respond to at least one other student’s question on Module 4 discussion board Module 4 Discussion.
Graded Assignments (For certificate learning only)
Six Sentence Answer #10
Please refer to the course pages on graded assessments to see details of the Six-sentence Answers (6SA) exercise. You should not attempt to do this assessment until you have read and fully understood the requirements.
The Case
You are a member of a major international forest consultancy firm that specializes in doing surveys of forests around the world. Your company is working on a contract looking at the effects of past and present management practices on the forests and savannahs of East Africa. This area is very diverse, including many different forest types. They range from grass and tree savannahs through seasonally dry woodlands and forests to Afromontane rain forest.
Riparian forests in your study appear to be experiencing extensive damage from elephants. The government has suggested that you should remove the elephants, either by killing them or transporting them to another area. This of course has triggered a vigorous and emotional debate. Using the 6SA approach, argue why the complete removal of elephants could have adverse effects on the ecosystem.
Remember to follow the structure of the 6SA outlined in the section on graded assessments.
Formatting:
- Double-space the text.
- 12-point font in New Times Roman or Calibri.
- Put your name (Family or last name, followed by your first name), student number, the title “Topic 1.1 assignment”, and the date at the top of the first page.
- Name the e-file: your Family or last name_your first name_ Topic 1.1_Assignment.doc (or .docx). Example: Innes_John_Topic 1.1_Assignment (or .docx).
- Standard English usage, clear writing style.
- All assignments should be submitted through Canvas before the deadline.
Topic Summary
In this topic, we examined to other forms of interaction among species. In the first, we looked at facilitation, which is usually a (0 +) relationship. We also looked at similar relationships, including mutualism, commensalism and amensalism. While these can be readily distinguished in words, in a tropical forest, some of the relationships are not so easily evaluated. For example, do the Duroia hirsuta trees found in Devil’s gardens, discussed in the previous topic, benefit from the interactions with ants, or suffer? Facilitation may actually be one of the commonest forms of inter-specific relationship, and is widespread in tropical forests.
Many of the relationships between species can be visualized in the form of food webs. These have been of interest to ecologist for decades, as not only to they enable the links between species to be considered, but they are often quantified in terms of the energy transferred from one trophic level to another. Such webs were first designed for much simpler temperate ecosystems, and their application to tropical forests has been problematic, simply because of the diversity of species involved. With so many invertebrates remaining undescribed, the food webs are far from complete. Even with the vertebrates, many interactions remain undescribed or poorly understood. This will continue to be a rich area for tropical forest research for many years.
Topic Self-review (For self learning)
To review what you have learned in the topic, you are encouraged to use the following reflection questions as a study guide to do a self-review for the topic:
- What are the names of the different types of species interaction that involve either mutual benefit, or benefit to one and no effect on the other? Can you describe each?
- How is facilitation defined, and what are some examples of different types of facilitation?
- How is facilitation distinguished from symbiosis?
- How is ecosystem engineering defined, and what are some examples of this phenomenon?
- What are the differences between food webs and trophic cascades?
- How might the loss keystone species affect forest ecosystems, and are there examples of such effects?
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