Topic Introduction

The animal fraction of the total biomass in a tropical forest is a tiny proportion (<0.05%) of the total biomass present. Yet animals exert a significant influence on the forest, and the forest exerts a significant influence on the animals. The result is the evolution of complex interdependencies.

As indicated in the previous module, dispersal of seeds by animals is important in tropical forests – as many as 90% of tropical tree species may require an interaction with animals (pollination, seed dispersal) to reproduce. Plants evolved fruit to attract animals to disperse their seeds, and many species have evolved specialized flowers that encourages pollination by animals.

There are many different types of interactions among and between species. The interactions can be positive, negative or neutral. In mutualism, both species benefit: pollination by animals is a good example. In commensalism, one species benefits and the impacts on the other are neutral. Many epiphytes benefit from their host without adversely affecting it. With herbivory, predation and parasitism, one species benefits and the other loses. In competition, it is widely accepted that both species lose, although one may lose more than the other.

By the end of this topic, you should be able to:

• Describe how plants in tropical forests defend themselves against herbivory.
• Discuss the role of domatia in plant protection.
• Compare different strategies used by plants to limit the impacts of herbivory.
• Describe under what circumstances insectivores can have an impact on insect populations.
• Evaluate the advantages and disadvantages for ungulates living in large groups.
• Assess the role of mesopredators in the ecosystem.
• Describe the importance of diseases in regulating animal populations.
• Contrast the role of parasites with other factors affecting the life strategies of animals.
• Distinguish between the fundamental niche and the ecological niche of an organism.
• Define and explain sympatry.
• Explain how niche partitioning occurs, using examples.
• Summarize Lotka-Volterra models and how they have been applied in competition studies.

Topic Readings

Required Readings

• Ghazoul, J. and Sheil, D. 2010. Tropical Rain Forest Ecology, Diversity, and Conservation. Oxford, Oxford University Press, 516 pp. Section 13.1 and 13.4.

Optional Readings

• Shorrocks, B. and Bates, W. 2015. The biology of African savannahs. 2^nd Oxford, UK: Oxford University Press. 330 pp. Chapter 5.

 Herbivory

• Crawley, M.J. (ed.) 1997. Plant Ecology. 2^nd Oxford, UK: Blackwell Scientific. 717 pp. Chapters 10 and 13.
• Dublin, H.T. 1995. Vegetation dynamics in the Serengeti-Mara ecosystem: The role of elephants, fire, and other factors. In: Sinclair, A.R.E. and Arcese, P. (eds.) Serengeti II. Dynamics, management, and conservation of an ecosystem. Chicago, Illinois, USA: University of Chicago Press. pp. 71–90.
• McNaughton, S.J. 1979. Grassland-herbivore dynamics. In: Sinclair, A.R.E. and Norton-Griffiths, M. (eds.) Dynamics of an ecosystem. Chicago, Illinois, USA: University of Chicago Press. pp. 46–81.
• McNaughton, S.J. and Banyikwa, F.F. 1995. Plant communities and herbivory. In: Sinclair, A.R.E. and Arcese, P. (eds.) Serengeti II. Dynamics, management, and conservation of an ecosystem. Chicago, Illinois, USA: University of Chicago Press. pp. 49–70.
• Norton-Griffiths, M. 1979. The influence of grazing, browsing, and fire on the vegetation dynamics of the Serengeti. In: Sinclair, A.R.E. and Norton-Griffiths, M. (eds.) Dynamics of an ecosystem. Chicago, Illinois, USA: University of Chicago Press. pp. 310–352.
• 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 4.
• Rockwood, L.L. 2015. Introduction to population ecology. 2^nd Chichester, UK: Wiley-Blackwell. 363 pp. Chapter 11.
• Scholes, R.J. and Walker, B.H. 1993. An African savannah. Synthesis of the Nylsvley study. Cambridge, UK: Cambridge University Press. 306 pp. Chapters 9 and 15.
• Scogings, P.F. and Sankaran, M. (eds.) 2020. Savanna woody plants and large herbivores. Chichester, UK: John Wiley & Sons. 756 pp.
• Sinclair, A.R.E. 1995. Equilibria in plant-herbivore interactions. In: Sinclair, A.R.E. and Arcese, P. (eds.) Serengeti II. Dynamics, management, and conservation of an ecosystem. Chicago, Illinois, USA: University of Chicago Press. pp. 91–113.

Predation

• Bertram, B.C.R. 1979. Serengeti predators and their social systems. In: Sinclair, A.R.E. and Norton-Griffiths, M. (eds.) Dynamics of an ecosystem. Chicago, Illinois, USA: University of Chicago Press. pp. 221–248.
• Fryxell, J.M. 1995. Aggregation and migration by grazing ungulates in relation to resources and predators. In: Sinclair, A.R.E. and Arcese, P. (eds.) Serengeti II. Dynamics, management, and conservation of an ecosystem. Chicago, Illinois, USA: University of Chicago Press. pp. 257–273.
• Mittelbach, G.G. and McGill, B.J. 2019. Community ecology. 2^nd Oxford, UK: Oxford University Press. 409 pp. Chapters 5 and 6.
• Morin, P.J. 1999. Community Ecology. 2^nd Oxford, UK: Blackwell Science. 407 pp. Chapters 4 and 5.
• 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 7.
• Rockwood, L.L. 2015. Introduction to population ecology. 2^nd Chichester, UK: Wiley-Blackwell. 363 pp. Chapter 10.
• Schaller, G.B. 1972. The Serengeti lion. A study of predator-prey relations. Chicago, Illinois, USA: University of Chicago press. 480 pp.
• Scheel, D. and Packer, C. 1995. Variation in predation by lions: Tracking a movable feast. In: Sinclair, A.R.E. and Arcese, P. (eds.) Serengeti II. Dynamics, management, and conservation of an ecosystem. Chicago, Illinois, USA: University of Chicago Press. pp. 299–314.
• Sinclair, A.R.E. 1995. Population limitation of resident herbivores. In: Sinclair, A.R.E. and Arcese, P. (eds.) Serengeti II. Dynamics, management, and conservation of an ecosystem. Chicago, Illinois, USA: University of Chicago Press. pp. 194–219.

Parasitism

• Goater, T.M., Goater, C.P. and Esch, G.W. 2014. Parasitism: The diversity and ecology of animal parasites. 2^nd Cambridge, UK: Cambridge University Press. 497 pp.
• Heide-Jørgensen, H.S. 2008. Parasitic flowering plants. Leiden, The Netherlands: Koninklijke Brill NV. 438 pp.
• Hudson, P.J., Rizzoli, A., Grenfell, B.T., Heesterbeek, H. and Dobson, A.P. (eds.) 2001. The ecology of wildlife diseases. Oxford, UK: Oxford University Press. 197 pp.
• 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 8.
• Rockwood, L.L. 2015. Introduction to population ecology. 2^nd Chichester, UK: Wiley-Blackwell. 363 pp. Chapter 9.
• Schmid-Hempel, P. 2011. Evolutionary parasitology. The integrated study of infections, immunology, ecology and genetics. Oxford, UK: Oxford University Press. 516 pp.

Competition

• Crawley, M.J. (ed.) 1997. Plant Ecology. 2^nd Oxford, UK: Blackwell Scientific. 717 pp. Chapters 8, 12 and 14.
• Jarman, P.J. and Sinclair, A.R.E. 1979. Feeding strategy and the pattern of resource-partitioning in ungulates. In: Sinclair, A.R.E. and Norton-Griffiths, M. (eds.) Dynamics of an ecosystem. Chicago, Illinois, USA: University of Chicago Press. pp. 130–613.
• Mittelbach, G.G. and McGill, B.J. 2019. Community ecology. 2^nd Oxford, UK: Oxford University Press. 409 pp. Chapters 7 and 8.
• Morin, P.J. 1999. Community ecology. 2^nd Oxford, UK: Blackwell Science. 407 pp. Chapters 2 and 3.
• 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 5.
• Rockwood, L.L. 2015. Introduction to population ecology. 2^nd Chichester, UK: Wiley-Blackwell. 363 pp. Chapter 7.
• Scholes, R.J. and Walker, B.H. 1993. An African savannah. Synthesis of the Nylsvley study. Cambridge, UK: Cambridge University Press. 306 pp. Chapter 14.

Fundamental Concepts

PPT Presentations

This topic contains four presentations:

4.1.1 Interactions - Herbivory.pptx Download 4.1.1 Interactions - Herbivory.pptx

4.1.2 Interactions - Predation.pptx Download 4.1.2 Interactions - Predation.pptx

4.1.3 Interactions - Parasitism.pptx Download 4.1.3 Interactions - Parasitism.pptx

4.1.4 Interactions - Competition.pptx Download 4.1.4 Interactions - Competition.pptx

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 more important 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 4.1 to start taking the quiz.

Pre-readings and Discussion (For certificate learning only)

Once you have read Sections 13.1 and 13.4 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 #8

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.

In the forested corridors that you have been planting, the post-planting surveys that your team has been conducting reveal that there is significant mortality of seedlings. Using the 6SA format, argue why this may only be a problem under certain circumstances.

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

This topic has covered a large number of interactions that occur in tropical forests. These take many different forms, but in those presented in this topic, there is normally a winner and a loser. Very often, the relationship is very asymmetric. Examples of beneficial relationships do exist, and some of these are examined in the next topic.

Predator–prey, herbivore–plant and parasite–host relationships all generally involve a (+ -) relationship between species. In some cases it may be within species, as infanticide occurs quite commonly, and is being documented in an ever-widening range of species, including felines, canids, primates and others. Competition also occurs both within and between species, although this generally involves a (- -) relationship.

It has only been possible to touch on some of these complex relationships in this module. However, we hope that you have gained an idea of some of the types of relationship that exist, and how they can influence the structure and composition of ecosystems.

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:

• How do plants in tropical forests defend themselves against herbivory?
• What is the role of domatia in plant protection?
• What are the different strategies used by plants to limit the impacts of herbivory?
• Under what circumstances can insectivores can have an impact on insect populations, and how common is this?
• What are the advantages and disadvantages for ungulates living in large groups? Do the advantages outweigh the disadvantages?
• What is the role of mesopredators in forest ecosystems?
• In what ways can disease regulate animal populations? Does the same apply to plant populations?
• How does the role of parasites compare with other factors affecting the life strategies of animals?
• What is the difference between the fundamental niche and the ecological niche of an organism?
• What is sympatry, and how does it work?
• How does niche partitioning occur? Can you give examples from different types of forest?
• What are Lotka-Volterra models, and how have they been applied in competition studies?