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LABORATORY TWO COMMUNITY ECOLOGY
OVERVIEW: Ecologists often begin their studies of communities by attempting to identify and list the species of organisms present. This can be a daunting task for a single individual, and so ecologists often turn to specialists called systematists or taxonomists for help. Taxonomists are specialists in particular groups of plants or animals, who have intensively studied the diversity of such a group and are familiar with the information so far published on the group. In addition to aiding other biologists with their research efforts, taxonomists do their own research, documenting biodiversity and constructing hypotheses about the history of plant and animal species. Taxonomists may name and describe newly discovered species, reclassify those already named, and construct diagrams showing how the species in a group might be related. An important measure of a habitat's richness and complexity is the number of species it can support. This is an entirely different idea from the number of individual organisms a habitat can support. In the Arctic, for example, there are few species, but those species that are present can occur in huge numbers, for example, mosquitoes. In tropical rain forests, thousands of species can be found in a small area, but each species may be represented by only a few individuals. For most communities, it would not be feasible to try to take a complete inventory of every species present. Instead, we must take samples—measurements of parts of the whole—that, ideally, will provide an accurate picture of the whole. A number of sampling techniques are available for obtaining quantitative information concerning the structure and composition of forest communities. The most widely applicable technique, however, is that of sampling with quadrats or plots of standard size. Quadrat sampling techniques may be adapted for use in all major types of plant communities, and for the study of communities of sessile or sedentary animals as well. The details of quadrat sampling procedure, including the size, shape, number, and arrangement of the sample plots, must be determined for the particular type of community being sampled and on the basis of the type of information desired. In this lab, we will sample the local litter-animal community structure so that we can use that information next week to calculate species diversity in a community. Litter is the layer of material that rests on the surface of a forest floor. It includes leaves, seeds, bits of decaying wood, microorganisms, and many different animal species, most of which you cannot see unless you observe carefully. The diversity of animal species corresponds roughly to the diversity of plant species in the forest, and it can vary depending on local environmental conditions, such as moisture, sunlight, and temperature. You will use litter animals as a measure of biodiversity.
OBJECTIVES OF LABORATORY: •To understand the value of sampling studies in describing communities. •To examine the factors that determine community composition, such as microclimate and competition •To learn appropriate sampling and field techniques for forest analysis (e.g., collecting litter animals)
DEFINE: Community, species, biodiversity, sampling, litter, dichotomous key
SIZE AND SHAPE OF SAMPLING PLOTS: Plot size should be determined on the basis of the size and density of the organisms being sampled. Plots should be large enough to contain significant numbers of individuals, but small enough that the individuals present can be separated, counted, and measured without confusion leading to duplication and omission of individuals. For vegetation, suggested plot sizes are 1 square meter for herbaceous vegetation, 10-20 square meters for communities of shrubs or saplings up to about 3 meters in height, and 100 square meters for mature tree communities. Because we will be sampling small animals, mostly invertebrates such as insects, small plots are sufficient. We will use plots with an area of ¼ square meter—that is, squares with ½ meter-long sides. Plot shape is important in relation to the ease of laying out plots and to the efficiency of sampling. Square or rectangular plots are preferred in this survey work, and such plots have come to be called “quadrats”.
NUMBER AND ARRANGEMENT OF PLOTS: The number of plot samples must, at a minimum, be sufficient to turn up the bulk of the species present in the stand. This number may be determined in a semiobjective manner by plotting a species-area curve as the sampling is being carried out. This curve consists of the number of samples taken plotted against the cumulative species total. A species-area curve usually rises sharply at first, since the first samples reveal many new species, but eventually levels off, indicating that additional samples are revealing few new species. An adequate sample number usually should be well into the latter portion of the curve. Here is an example of such a species-area curve: On the X axis, plot the sequence of plots, such as plot 1, plot 2, plot 3 etc. On the Y axis, plot the cumulative number of species encountered. Plot 1 has 5 species. Plot X=1, Y=5 Plot 2 has 2 new species. Plot X=2, Y = (5+2) or 7 Plot 3 has 1 new species. Plot X=3, Y + (7+1) or 8 etc.
In a rain forest, the line keeps increasing. In a pine stand, the line levels off almost immediately. In a hardwood forest, the line increases at first but then levels off when no new species are encountered. It takes a lot of effort to do plots. A few would do in a pine stand and maybe a hundred in a rain forest. We will sample three plots in our forest. Generally, you want to sample plots according to the ten percent rule—you have enough plots when a ten-percent increase in area results in less than a ten-percent increase in species. Often, ecologists will then add a few plots just to “make sure.”
LAB EXERCISE: In this lab exercise, we will sample one habitat, rich forest litter, and attempt to identify as many of the kinds of animals found there as possible. The animals will be collected from your litter samples by a device called a Berlese funnel, which is illustrated in the figure below. The Berlese funnel is basically a hot incubator that dries out forest litter samples and collects the animals living in the samples in a reservoir. A light bulb provides heat and light, and the funnel channels animals trying to escape the heat and light into a reservoir containing preservative.
90 Watt bulb, keep at least 3” Berlese Funnel
Leaf Litter Sample
Funnel must be clean and slippery
Preservative Fluid
1. To store and carry the leaf litter, each team should have a large plastic bag. In addition, two or three teams should bring meter sticks to the sampling location.
2. When you arrive at the sampling location, your instructor will assign areas for each team’s sampling. Mark off a ¼-meter square plot. Remember, this means ½-meter per side. Stake out your site with four corner pegs and some string.
3. Off to the side of your plot, examine the structure of the litter layer and make a sketch documenting your observations. If you are careful, you should be able to observe this year’s leaf layer distinct from the previous year’s layer. This year’s layer will be much thicker and less compact. Next, gently brush away the leaves and observe the surface of the soil. What materials rest directly on the soil surface? Finally, observe the soil structure by gently scraping back a thin layer of soil and then moving progressively deeper (to a final depth of about 3cm). Notice the color of the soil at the surface versus the color as you go deeper.
4. At your plot, remove only the layer of dry leaves near the top and discard it to one side of the plot. Be careful NOT to discard the decaying material closer to the surface of the soil. Now remove all the remaining litter, down to the surface of the soil, and place the sample in the plastic bag.
5. Load your sample into a Berlese funnel, being careful not to allow too much material to fall through the mesh. Placing the larger litter materials on the mesh first will help limit the amount of small litter that falls through. When you finish loading your sample, add any material that has fallen through to the floor back onto the top of the material in the funnel.
6. Place a reservoir of Ethanol/Glycerin under the outlet of the funnel. This will catch, kill, and preserve the animals that fall from the litter above.
7. Turn on the light, replace the lid, and allow your sample to incubate overnight. The laboratory technician will store your sample until next week.
8. A sample of litter animals will be provided. First, separate the animals into groups of similar organisms. Next, use the dichotomous key to practice identifying each group of organisms in preparation for next week’s lab. Note: Do not merely try to match animals with the pictures. The drawings are provided to aid in identifying key features.
9. After you have correctly keyed out six groups, allow the instructor to check your work before you leave lab.
Assignment Read next week’s lab and familiarize yourself with the calculations for Simpson’s Index.
KEY TO MACROSCOPIC SOIL ANIMALS FROM FOREST LITTER IN THE EASTERN U.S.
1a. Body covered with a hard or leathery exoskeleton or a calcified shell; legs, if any, jointed, at least on the anterior end of the body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.
1b. Body soft, usually worm like; legs, if any, not jointed . . . . . . . . . . . . . . . . . . . . . . . . . .34.
2a. With a calcified shell, usually spirally coiled . . . . . . . . . . . . . . . . .Phylum MOLLUSCA, Class GASTROPODA, Snails.
2b. With a chitinous exoskeleton and usually with jointed appendages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phylum ARTHROPODA, 3.
3a. Walking legs more then six . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.
3b. Walking legs six . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Class INSECTA, 16.
4a. Eight walking legs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.
4b. More than eight walking legs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.
5a. Body divided into two regions by a distinct constriction; spinning-organs at the end of the abdomen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Order ARANEA, Spiders.
5b. Body not divided by a constriction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.
6a. Body not segmented, or at most divided into two or three areas by sutures . . . . . . . . . . .7.
6b. Body segmented, at least in the posterior part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.
7a. Body hard, brown or black, heavily sclerotized or partially covered with sclerotized plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8.
7b. Body soft, pink, red, or white, often furry-looking, or ornamented with long (or fan-like) setae . . . . . . . . . . . Order ACARINA, Suborder TROMBIDIFORMES, Soft mites and adults of chiggers.
8a. Body with a number of dorsal and ventral plates, but with at least some exposed white or tan areas between them; legs rarely concealed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Order ACARINA, Suborder MESOSTIGMATA, Parasitiform mites.
8b. Body more or less completely covered with very hard, often highly ornamental or arched plates; legs sometimes concealed between clamshell-like valves or wing-like extensions from the body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Order ACARINA, Suborder SARCOPTIFORMES, Clam and Beetle Mites (Orbatid mites).
9a. With the pedipalps formed into large pincers; eyes at the sides of the head or absent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Order PSEUDOSCORPIONIDA, Pseudoscorpions.
9b. With the pedipalps similar to walking legs, but smaller; eyes on either side of a central, raised tubercle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Order OPILIONES, Harvestmen.
10a. Only the first 3 pairs of appendages jointed, the following ones stump-like and ending in rows of comb claws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class INSECTA, Order LEPIDOPTERA, larvae of moths or butterflies.
10b. All appendages jointed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.
11a. Seven pairs of legs; abdomen with ventral flaps (pleopods) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class CRUSTACEA, Order ISOPODA, Pillbugs or Sowbugs.
11b. More than 7 pairs of legs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12.
12a. Nine or 10 pairs of legs; antennae 3-branched, usually very small; some with five brown dorsal plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Class PAUROPODA, Pauropods.
12b. More than 10 pairs of legs; antennae not branched . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.
13a. Twelve pairs of legs . . . . . . . . . . . . . . . . . . . . . . . .Class SYMPHYLA, White centipedes.
13b. Thirteen pairs of legs . . . Class DIPLOPODA, Order POLYXENIDA, Tufted Millipedes.
13c. More than 13 pairs of legs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.
14a. Antennae with 6 or 7 segments . . . . . . . . . . . . . . . . . . . . Order DIPLOPODA, Millipedes.
14b. Antennae with more than 7 segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.
15a. Fifteen pairs of legs (fewer in immature forms); often turning blue or purple in alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class CHILOPODA, Order LITHOBIOMORPHA, Rock Centipedes.
15b. Twenty-one or 23 pairs of legs; last pair sometimes enlarged; color orange, yellow, or white . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class CHILOPODA, Order SCOLOPENDROMORPHA, Lurking Centipedes.
15c. More than 23 pairs of legs; body extremely long and slender; color usually yellow or red . . . . . . . . . . . . Class CHILOPODA, Order GEOPHILOMORPHA, Burrowing Centipedes.
16a. Thorax and abdomen connected by a thin waist; ant-like or wasp-like . . . . . . . . . . . . . . . . Order HYMENOPTERA, Ants and Wasps. (Note: The thin waist or pedicel of an ant bears a large, erect scale which is not present in wasps.)
16b. Thorax and abdomen broadly joined . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.
17a. Winged . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.
17b. Wingless . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26.
18a. Forewings developed as a hard cover over hindwings . . . . . . . . . . . . . . . . . . . . . . . . . . 19.
18b. Forewings membranous or leathery; or only one pair of wings . . . . . . . . . . . . . . . . . . . 20.
19a. A pair of prominent pincers at the end of the abdomen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Order DERMAPTERA, Earwigs.
19b. No such pincers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Order COLEOPTERA, Beetles.
20a. One pair of wings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.
20b. Two pairs of wings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.
21a. Posterior wings vestigial, modified to form a pair of club-shaped organs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Order DIPTERA, Flies.
21b. Posterior wings completely absent; abdomen with a pair of small, dorsal tubular appendages; mouthparts a coiled tube . . . . . . . . . . . . . . . . .Order HOMOPTERA, Aphids.
22a. Anterior wings leathery, at least in part. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.
22b. Anterior wings not leathery; either broad and membranous or narrow, style-like and fringed with hairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.
23a. Only the proximal half of the forewings leathery . . . . . . . . . . Order HEMIPTERA, Bugs.
23b. Forewings entirely leathery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Order ORTHOPTERA, Roaches, Grasshoppers, etc.
24a. Mouthparts for chewing, directed somewhat anteriorly; animals ant-like, but white . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Order ISOPTERA, Termites.
24b. Mouthparts for chewing or for sucking, but directed ventrally; not very ant-like, gray, black, red or yellow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25.
25a. Wings broad; mouthparts for chewing . . . . . . . . . . . . Order CORRODENTIA, Barklice.
25b. Wings style-like or rod-like, fringed with long hairs; mouthparts conical, head frequently elongate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Order THYSANOPTERA, Thrips. (Note: strangely enough, the word "thrips" is both singular and plural.)
26a. Body worm-like, abdomen more than 10 times longer than thorax, mouthparts for chewing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Order COLEOPTERA, Larvae of beetles.
26b. Body more typically insectan; mouthparts for sucking or chewing. . . . . . . . . . . . . . . . .27.
27a. Wingpads usually present; mouthparts a jointed sucking-tube. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HEMIPTERA, Larvae of bugs.
27b. Wingpads absent; mouthparts for chewing, or if for sucking, then not a jointed tube . . . 28.
28a. Mouthparts a coiled tube; two short, tubular dorsal appendages on the abdomen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Order HOMOPTERA, Aphids.
28b. Mouthparts for chewing or for sucking, but not a coiled tube . . . . . . . . . . . . . . . . . . . . .29.
29a. Mouthparts for sucking, short and conical, ventrally directed, head often peculiarly elongated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Order THYSANOPTERA, Thrips.
29b. Mouthparts for chewing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30.
30a. Antennae absent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Order PROTURA, Subinsects.
30b. Antennae present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31.
31a. Abdomen with terminal pincers, long, jointed filaments, or short, flap-like cerci. . . . . . 33.
31b. Cerci or filaments not present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.
32a. Mouthparts directed anteriorly; ant-like . . . . . . . . . . . . . . . . .Order ISOPTERA, Termites.
32b. Mouthparts directed ventrally; not ant-like . . . . . . . . . .Order CORRODENTIA, Barklice.
33a. Antennae of 10 or more segments; abdomen with pincers or with filaments made up of many joints . . . . . . . Order THYSANURA, Japygids (with pincers) and Bristletails.
33b. Antennae of 8 or fewer segments; abdominal cerci fused into a furcula for jumping that can be folded beneath the abdomen; abdomen either cylindrical or globular . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Order COLLEMBOLA, Springtails.
33c. Antennae very long, multisegmented; cerci flaplike, of a single joint; body much flattened . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Order ORTHOPTERA, Roaches.
34a. Body with 8 stumpy claw-tipped legs; usually from moss, exceedingly small (protozoan-sized) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phylum TARDIGRADA, Waterbears.
34b. Body legless, although unpaired appendages or appendages terminal on the abdomen may be present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35.
35a. With a flattened, ventral creeping foot; eyes sometimes borne on tentacles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phylum MOLLUSCA, Class GASTROPODA, Slugs.
35b. No such creeping foot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36.
36a. Body long, thin, unsegmented . . . . . . . . . . . . . . . . . Phylum NEMATODA, Roundworms.
36b. Body stouter, segmented . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37.
37a. Without a consolidated head region, lacking hard mouthparts, segments all similar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phylum ANNELIDA, Class OLIGOCHAETA, Earthworms.
37b. With a sclerotized head capsule and hard, sometimes concealed mouthparts, segments often dissimilar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wormlike larvae of insects (DIPTERA, HYMENOPTERA, or COLEOPTERA).
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