Content

Introduction
Readings
Fundamental Concepts
Self Check
Pre-readings & Discussion
Graded Assignment
Summary
Self Review

Topic Introduction

As the arthropods are such a large group, and are so important for a full understanding of tropical forest ecology, we have split the discussion of them into two topic areas. In this topic, we look at the tardigrades, onychophorans, crustaceans, myriapods and Chelicerata. In the next and final module of this course, we look at the insects.

The arthropods are better known that many other invertebrate phyla. However, knowledge remains very incomplete, and there are vast numbers of arthropods that have never been formally described. We suspect that many of these are being lost as a result of deforestation in the tropics, and so they will never be described. Many are very specific in their feeding habits, for example being dependent on a particular plant species for at least part of their life cycle. This makes them vulnerable, especially in areas with restricted habitat availability. Another concern is climate change, and especially how climate change may affect montane forests. As the climate warms, many montane species may be lost because there is simply nowhere for the species to go.

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

Describe some tardigrades and onchyphorans.
Explain their relationship to other arthropods.
Evaluate the role of tardigrades, crustaceans, millipedes, centipedes and arachnids in tropical forest ecosystems.
Contrast the lifestyles of the main orders of crustaceans.
Evaluate the importance of crustaceans in mangrove forests.
Distinguish between millipedes and centipedes and describe the main lifestyles adopted by these animals.
Describe the range of animals included in the Chelicerata.
Contrast the differing lifestyles of the major families of spiders.

Topic Readings

Required Readings

Ghazoul, J. and Sheil, D. 2010. Tropical Rain Forest Ecology, Diversity, and Conservation. Oxford, Oxford University Press, 516 pp. Chapter 5.2.1

Optional Readings

Assam State Biodiversity Board. 2015. Common Spiders from Selected Protected Areas of Upper Assam. Guwahati, India: Assam State Biodiversity Board. 192 pp.
Brusca, R.C., Moore, W. and Shuster, S.M. 2016. Invertebrates. 3^rd Sunderland, Massachusetts, USA: Sinauer Associates. Chapters 23 and 24.
Gerlach, J. and Marusik, Y. (eds.) 2010. Arachnida and Myriapoda of the Seychelles Islands. Siri Scientific Press. 435 pp.
Hanson, P.E. 2011. Insect diversity in seasonally dry tropical forests. In: Dirzo, R., Young, H.S., Mooney, H.A., and Ceballos, G. (eds.) Seasonally Dry Tropical Forests: Ecology and Conservation. Washington DC, USA: Island Press. pp. 71-84.
Koh, J.K.H., Bay, N. 2019. Borneo Spiders. A Photographic Field Guide. Kota Kinabalu, Malaysia: Sabah Forestry Department. 498 pp.
Lindsey, T. 1998. Green Guide. Spiders of Australia. Sydney, Australia: New Holland Publishers. 96 pp.
Penney, D. 2009. Common Spiders & Other Arachnids of the Gambia, West Africa. Siri Scientific Press. 80 pp.

Fundamental Concepts

PPT Presentations

5.3.1 The Arthropods.pptx

5.3.2 Tardigrades and onychophorans.pptx

5.3.3 Crustaceans.pptx

5.3.4 Myriapods.pptx

5.3.5 Chelicerata.pptx

Self-check Quiz

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 5.3 to start taking the quiz.

Pre-readings & Discussion (For certification)

Once you have read Sections 5.2.1 and 5.2.3 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 remember to answer/respond to at least one other student’s question on the discussion board Online Discussion Module 5.

Graded Assignment (For certification)

Six Sentence Answer #9

If you are not familiar with the Six Sentence Answer (6SA) format, please refer to the course pages on graded assessments to see details of the 6SA exercise. You should not attempt to do this assessment until you have read and fully understood the requirements. The 6SAs are designed to be done in order, staring with topic 1.1. As you work through these, you will be told more and more about the context of the case study.

The case

So far, we presented the situation that you are a member of a major international forest consultancy firm that specializes in doing surveys of forests around the world. You have access to field teams and the latest surveying equipment, including LiDAR. Your company has taken on a contract with the UN-REDD (United Nations Collaborative Programme on Reducing Emissions from Deforestation and Forest Degradation in Developing Countries) to survey the forests on a very large island in South-East Asia, and you not only have the full cooperation of the government but they are also asking your company for advice on a range of other issues.

You have already produced a map of the island’s forests, and assessed the growing stock. Your field teams have done on-the-ground surveys to develop the allometric equations that you needed to produce estimates of the carbon stored in different types of forest on the island. You have found major differences, as you might expect, between the moist tropical forests on the west of the island and the dry forests in the rain shadow of the volcano on the east of the island. You have identified that the trees in the tropical moist forest are much smaller than those on the island of Borneo, located only a few hundred kilometres to the west and you have found a plausible explanation for this.

The government has indicated that it is interested in developing ecotourism on the island and are building an interpretative walk through a section of rain forest on the west of the island. They are still at the initial stages of planning, and have asked your company to help them. You have already indicated how you would prioritize the botanic features along the walk and how the plants got there, and how you would also develop an interpretative sign for the mammals presents on the island.

Some local people have told you that every year, there is an incredible event during which thousands of land crabs migrate from the rain forest to the beaches. This presents both opportunities for the island’s ecotourism ideas, and potential problems if the migration route is disrupted or the crabs are disturbed. Using the 6SA format, please indicate how you would advise your company to deal with this issue.

Remember to follow the structure of the 6SA outlined in the section on graded assessments.

Topic Summary

In this topic, we have examined a number of different orders within the arthropods, concentrating on all the groups other than insects (which we look at in the next topic). Our knowledge of many of these groups is quite limited, but is slowly being amassed. This presents major research opportunities for those studying tropical forest ecology.

The lifestyles adopted by many of these groups differs markedly. Some are predators, others herbivores and quite a few are omnivores. Most have hard exoskeletons, and must moult regularly. Notable exceptions include the tardigrades (which have a thin, uncalcified cuticle) and the onychophorans (velvet worms), which have a soft, thin, flexible and very permeable cuticle.

The Chelicerata are perhaps the best known of the groups covered in this topic. They include a wide variety of animals that have various breathing mechanisms, including book gills, book lungs, tracheae or through the cuticle. Many are predators, but they are also an important source of food for some species. Some have developed various forms of toxin to help defend themselves, but their predators in turn have evolved resistance to those toxins. For example, meerkats (Suricata suricatta; Herpestidae) have considerable immunity to scorpion venom.

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 do tardigrades and onchyphorans look like?
How are tardigrades and onycophorans related to other arthropods?
What are the roles of tardigrades, crustaceans, millipedes, centipedes and arachnids in tropical forest ecosystems?
How do crustaceans differ in their lifestyles?
How important are crustaceans in mangrove forests and what ecological roles do they fulfil?
How do millipedes and centipedes differ?
How many different types of Chelicerata can you describe?
How do spiders differ in their hunting styles?

FODE 008-01