Topic Introduction

Tropical ecologists face a huge dilemma. We know that the vast majority of animals in tropical forests are invertebrates, and that the biodiversity of tropical forests mainly comprises invertebrates. Yet, most of those species are undescribed, and our knowledge of the ecology of most invertebrates is at best rudimentary. Most invertebrates are small and inconspicuous and pass unnoticed. Some of the larger or more obvious groups are better known: the butterflies is a good example. However, the butterflies are only a small segment of the Lepidoptera, with the majority being moths. Moths are much less known than butterflies, primarily because identification is so much more difficult. Some other groups have received also received a disproportionate amount of attention. There are numerous guides to dragonflies and damselflies, again largely because they are a visible component of tropical forest ecosystems. Katydids have also received some attention in the popular literature, but these insects are surprisingly difficult to find, despite being common and relatively large. This is because they rely on camouflage that is effective against humans as it is against predators.

A number of invertebrates make themselves known. Anyone working in tropical forests has probably encountered a range of these. They include leeches, schistosomes, chiggers, the unrelated jiggers, mosquitoes, black flies, tsetse flies and a range of other animals that treat the human body as a feeding opportunity. Some of these pass on diseases that can fatal. While most of these parasites are readily apparent to humans, it is worth remembering that most evolved to feed on other mammals, and many also infest non-mammalian hosts.

Some of the invertebrates encountered in tropical forests are extraordinary, such as the flatworms and unrelated velvet worms. The giant earthworms of Borneo are amazing, but even more surprising are the giant leeches that prey on them. These headline-grabbing animals are often featured in documentaries about tropical forests, but it is the vast majority of small to minute animals that are really important, primarily because of the role that they play in the breakdown of organic matter.

In this introductory topic, we look at the complex world of invertebrates. With such variety, it is impossible to do justice to them. However, our intention is to introduce to the variety of invertebrate life in tropical forests. It is worth remembering that the previous module in this course (Module 4) was devoted to vertebrates, of which there are about 68,000 described species. Module 3 was devoted to plants: there are about 310,000 seed plants. Module 3 also included a single topic dealing with fungi – there are about 52,000 described species of fungi. Today, there are about 1,300,000 described invertebrate species, although only a fraction of these are terrestrial, and the vast majority of invertebrates have yet to be described.

We place a lot of emphasis on protecting biodiversity, yet it is difficult to see how this can be done effectively when so many species remain undescribed. About 10,300 species of prokaryotes have been described, out of a total estimated ar 10 million or more. Estimates of the numbers of undescribed eukaryotes range from 3–8 million (definitely too low) to over 100 million. Understanding the ecological roles of all these organisms is an insurmountable task. This module will, however, introduce to the complex world of the terrestrial invertebrates.

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

• Explain why a knowledge of invertebrates is important for tropical forest ecology
• Evaluate the roles of different types of invertebrates in tropical forests
• Describe the diversity of insects in tropical forests
• Assess why insects are an important component of the tropical forest ecosystem.

Topic Readings

Required Readings

• Ghazoul, J. and Sheil, D. 2010. Tropical Rain Forest Ecology, Diversity, and Conservation. Oxford, Oxford University Press. pp 71–74, and Section 5.2.3.
• Optional Readings

• Brusca, R.C., Moore, W. and Shuster, S.M. 2016. Invertebrates. 3^rd Sunderland, Massachusetts, USA: Sinauer Associates. 1104 pp.
• Corlett, R.T. and Primack, R.B. 2011. Tropical Rain Forests. An ecological and biogeographical comparison. 2^nd Chichester, UK: Wiley-Blackwell. Chapter 7.
• 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.

Fundamental Concepts

PPT Presentations

5.1. Overview - Tropical forest invertebrates.pptx Download 5.1. Overview - Tropical forest invertebrates.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 5.1 to start taking the quiz.

Pre-readings & Discussion (For certification)

Once you have read the introduction to Chapter 5 and Section 5.1.4 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 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 #8

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.

Your CEO has seen these developments and is enthusiastic. It will be a significant draw for tourists. However, possibly inspired by the film Jurassic Park and its sequels, it has been suggested that even more tourists might be attracted to the island if you were to introduce Komodo Dragons (Varanus komodoensis). The 175,000 tourists who visit Komodo annually are now being asked to pay up to $1000 each, and this has been suggested as a major source of income for the island’s government. Using the 6SA format, please indicate how you argue for or against this idea.

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

Topic Summary

This topic provides a brief introduction to the invertebrates. Invertebrates are often dealt with very superficially in accounts of tropical ecology and, with the exception of a few groups such as the butterflies and dragonflies, they generally receive little attention. This is reflected in the availability of field guides, which are limited not only because of the lack of widespread interest in invertebrates, but because most invertebrates are difficult to observe, and their extraordinary diversity makes the development of field guides very difficult.

As a forest manager, you need to be aware of invertebrates for a number of reasons. Firstly, you may be parasitized by them. Diseases such as Dengue fever, river blindness, malaria, yellow fever, Chagas disease, sleeping sickness and chikungunya virus are all caused or transmitted by invertebrates. Ticks, leeches, and a large number of biting flies may make life unpleasant for you when working in a tropical forest. Secondly, the conservation status of most invertebrates is unknown. While it will normally require a specialist to identify a rare invertebrate species, you should at least know what sort of animal is being described. Most people would be able to describe a butterfly, moth or mosquito, but a lot fewer will be able to describe a velvet worm or flatworm, and even fewer are likely to know the difference between a collembolan and a tardigrade.

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:

• Why is a knowledge of invertebrates so important for tropical forest ecology?
• What roles do different types of invertebrates play in tropical forests?
• How would you go about describing the diversity of insects in tropical forests?
• Why are insects such an important component of the tropical forest ecosystem?