0.4 What is biodiversity? a comparison of spider communities

Objectives

To explore through classification of life forms the concept of biological diversity as it occurs at various taxonomic levels.

Procedures

Spiders are a highly species rich group of invertebrates that exploit a wide variety of niches in virtually all the earth'sbiomes. Some species of spiders build elaborate webs that passively trap their prey whereas others are active predatorsthat ambush or pursue their prey. Given spiders' taxonomic diversity as well as the variety of ecological niches breadthalong with the ease of catching them, spiders can represent useful, fairly easily measured indicators of environmentalchange and community level diversity.

This exercise focuses on classifying and analyzing spider communities to explore the concept of biological diversity andexperience its application to decision making in biological conservation. The exercise can be undertaken in three parts,depending on your interest level.

• Level (1)

  You will gain experience in classifying organisms by sorting a hypothetical collectionof spiders from a forest patch and determining if the spider collection is adequate to accurately represent theoverall diversity of spiders present in the forest patch.

• Level (2)

  If you wish to explore further, you can sort spider collections made at four other forestpatches in the same region and contrast spider communities in terms of their species richness, species diversity, andcommunity similarity. You will apply this information to make decisions about the priority that should be given toprotecting each forest patch in order to conserve the regional pool of spider diversity.

• Level (3)

  If you wish to explore the concepts of biodiversity yet further, you will next take intoaccount the evolutionary relationships among the families of spiders collected. This phylogenetic perspective willaugment your decision making about priorities for patch protection by accounting for evolutionary distinctivenessin addition to diversity and distinctiveness at the community level.

Level 1: sorting and classifying a spider collection and assessing its comprehensiveness

Obtain a paper copy of the spider collection for forest patch "1." The spiders were captured by a biologisttraveling along transects through the patch and striking a random series of 100 tree branches. All spiders dislodgedthat fell onto an outstretched sheet were collected and preserved in alcohol. They have since been spread out on atray for you to examine. The spider collection is hypothetical but the species pictured are actual spidersthat occur in central Africa (illustrations used are from Berland 1955 ).

The next task is for you to sort and identify the spiders. To do this you have to identify all the specimensin the collection. To classify the spiders look for external characters that all members of a particular group of spidershave in common but that are not shared by other groups of spiders. For example, leg length, hairiness, relative sizeof body segments, or abdomen patterning and abdomen shape all might be useful characters. Look for groups ofmorphologically indistinguishable spiders, and describe briefly the set of characters unique to each group. Theseoperational taxonomic units that you define will be considered separate species. To assist you in classifyingthese organisms, a diagram of key external morphological characters of beetles is provided ( ). Note that most spider identification depends on close examination of spider genitalia. For thisexercise, however, we will be examining gross external characteristics of morphologically dissimilar species.