Lab II-2.pdf

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CLJ7SS

Observing Succession in

Aquarium Microcosms

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EQUIPMENT AND MATERIALS

Youll need the following items to complete this lab session (The standard kit for this hook,

available from wo

_{fhehoricscie,jtsteorn, includes the items listed in the first group.)}

MATERIALS FROM KIT

Copes Shdes.tOt

Stain. eosrn Y

• fvlethylcellulose _{Stain: methylene blue}

• oHOst oup r • Thermometer

• m-’rptte,

MATERIALS YOU PROVIDE

• Ginve _{Pondlife reference material(s) (see text)}

• Aquariummicrocosms(from preceding lab) _{Watch or clock with second hand}

• Par ticuiate masks, N100 (see text)

BACKGROUND

Si:’

1

lundamental concept in ecology, is the process by which a community

pi

1’/ transforms itself from an arbitrary starting point to the steadystate equilibrium of

.1

2

trtinunity. The point at which that equilibrium is reached depends on environmental

i

md the types of organisms present at the starting point, although not necessarily

ti

numbers.

‘:rCrccO5iTiS_{reiresent srbifr;i y comrnuntiew}

- itthose communities are‘icry similar, but we

that they are identical For us rnpie. one at the

-;might contain a few examples of a rare organism,

,-;[her contains none of that or ganisrn. If that organism uwdator upon another specir.s that is present in both

.: ..cts, the

succession

we observe n the two rsiicrocosms ary different. In the tirst microcosm, stable populations

predator and prey organisms wili likely develop, while n secondmicrocosmthe absence of the predator may result

a cocoon oiled growth of the prey organism. Or a third organism

may step rn to assume the ecological role of predator.

In short, mimi ucosms like ours are soiri”what predictable

in terms of succession, but even very small changes in

the curnmiuiuity makeup may cause drurnatir: changes in sijccessmoii In the extreme case. one microcosm nay lourish

over a perid if veeks to months of not indetirimtely). while

another apparently tent ical. microcosm Play quickly approach ‘enescence and die oft, That’s one of the reasonssicsuggest

bculding several of these microcosm’; rite other reason is that

in the next lab session we’ll intentionally liter the environmental

characteristics of sortie microcosms and compare their succession to those of a control microcosm.

In terms of sublect matter, these rrimcrocosrn lab sessions

actually belong with the ecology group. However, because ;ve’ll be observing the microcusnis regularly over a period of several weeks to several months, we needed to get the mnicrocosins

star tori early, so we elected to place thriso lab sessions in their own groi p early in the book,

lit this lab session we’ll observe and catalog sonic of the

microscopic life present in our .iquai muminicrocosins,

Obviously, detailed observations require inure time than casual otiservations. Doing detailed observations arid counts requires

‘igniti’ant commitment of time arid effort, particularly if

you have several n’ricrocosms. If time ‘s limited, simply do the ;et ‘iou can, keeping in mind that changes are likely to occur

I lore r apidly at first arid more slowly later n the life cycle of the

ricrocusms.

tsaml’j. you should perform this procedure initially on the day

‘jou create the microc osrns, repeat this procednre for each of

your aquarium microcosms every day for the trst week, then

every two to three days once the microcc’smns begin to stabilize, and then once a week after frill equilibrium has been reached (which may occur at different times for different rnicrocusins).

1 Put on your gloves and goggles,

2. Observe the color and degree of turbidity of the microcosm

andioemd your observations in your I ib notebook.

F’

ti

PROCEDURE 11-2-1: OBSERVE SUCCESSION IN MICROCOSMS

With

regard

to microcosms, sLiccession is just another word for changes, and

much

of the

educotional value in microcosms comes from observing and documenting those changes

em

a

regular (and frequent) schedule. Changes can be observed on many levels, from simple

observations of gross changes such as the color arid turbidity of the water to detailed

observations of the types, nLirnberg, and other characteristics of the various microorganisms

pi esent in the microcosm and how they change over time.

3 t drills iiruu tIe’ lid from rh’ rricmr,srn rlisforhiric’

tim contents 3 tIe l:j’u oil So. If’s not ririsoinmon for

—ti,irti iI,irl,,iffrr haveit ihitoil fur several days oi longer—so irke sure

YOUhave adequate ye itilatiu i

4 Measure tho fi’niperature of the water and record itin

your lab riothouk (Do not stir the microcosm: simply dip the thermometer into the water and withdrawitonce it registers the temperature.)

5. Use the tip of the thermometer to transfer one drop of the

niicrocosrn water to a pieceofpH test paper. Record the

pH vOlue in your lab notebook

6 Use a clean pipette to withdrawitdrop of water from the surtar;e ot the microcosm. Transfer it to a flat shde. add a drop of rriethylcetulose to slow dcwrr the fast movers, arid put acover slipiiip0cc.

7 trio _{vu thu ‘ilidc at low mnapnifi’ ‘of ion (‘lOX). md into}

n 1 anydrifrrr’mit orm’ariisu sirs possible. Even it ow

‘if ii slr—p_’mi’jinern Iti: staterjttOe ni

if snot uirusiirltoobservi’ r fo,’r’u or mont’ mli’iori’fe species, noi isif _{unusual to see only a few. Scan tli full}

area under tin’ coverslip to make sure you don f miss any Species.

3’ Using a porrrl hfe reference nr urnual or Internet resources,

,ittempt to identify each species present, or at leist the

0 Scan the entire populated area of the slde anrf record your impressions of the relative numbers of each species present as “very abundant,” “abundant,” “moderate,” “rare,” or “very rare,”

10 Center a populated area of the slide under the objective arid perform an actual count of each species visible in the

fir’ld of view, beginning with those species that move slowly

or riot at all For motile species, do a 15-second count of each species If an individual swims into the field of view during the 15-second period, increment your count by one:

ifan individual swims out of the field of view, decrement your count by one. After you complete the count, center another random populated area under the oblectrve and

ii sit 3ou .“ si:sis0.ohnsu.,isroissash Mi::

thr.i’ sam so h:i ioom:sund, level a nil tmmectiomi ot lig[ I,

so a:. Si iii) with r’u°nsil ,tim ..if yooca n disable tile

flash:, do so. (III erwise, hold a tinier ovrir ft0tii’•i ‘whM

to nnivemit oufii’ti usfiisns it

,t:t:slsofii

Remnernbr’r ffn:if you don t know ‘xsrotiy whit’s urnwii’n in those rimicri ‘en stirs. Its rmnir,rfiIy nottileAnidrorriod,i Strain. but firer e nmiglrt he a real twisty growing in tfirare. rriavbe even several nitsties.

Use full irsepiri, precautror to moms Ii fir rio you open a microcosrir Wear gloves, goggles, arid (if you really want to he fully protected) an NI00 particle mask Wash the gloves rn soap and water before rernovirrg and discarding theni, and then wash your hands thoroLrghly

irr soap and wafer When you nnmnove specimens, sterilize

them before discarding them. Always replace the lid of

thr’ incr ocosmn imnriiedafoly when you re net actually

isbtar.rrrg s,iirrples froni it

.,.s’ f.’ it..,rI,iitirtnis,nir.S

r..’pit iism ii.: S .‘.S im e.’srnnil,it 00 arr’oelm,m is

iire.sent arid von e certain it ii..4nrioeba proteus. resord

is nr iso nce lo vs’urlab notebook by genus armd sriecies,

On the other timid, if there’s an amoeba present but

100 are. uncertum mias to :ts species, record It as 51 ri’ iy .Pmoeha up.. oritoevera clearly rfifferent arnoe.bs’e a rresermt, iOenit,.{ me muftiniei,n..0iiis asAmm.si.:’b,:i so i

‘em: so’ ImiOmrr_n tail, thoseo

ietenim ‘;i’imlitsr Simmt Si iii,iee,if

liti’rrah’i,tut n’.trote tiecarocuirston tue

ii’ is’s iii Urn, sirlumatnnm if _{:rriy). SiOiI.me,}appnn’inmaio

sos land isnimp’ it rlitferetit mndrviduitls are differ emit sizes), whetisu Ui notthe specmes is motile (and,ifso, how fast.),a ridi..nnyunusual features. Forexample, yoLr rnsthtPeson:tm a euglenaas “shape aiternatirmg, between.

rcuiar and ‘.vnrni: like suithalmmiosf invisible whip U

L’im”th 3() inn ijbuuf five tiniies’,:idth) granul.ir

I rr .,mom’meiti:n5’ inst

iO itii oCt s’t Mn,r-,

repeat the count. Do that again, for a total of three counts.

and average the number of individuals in each species for

the total sample.

11. Repeat your observations at medium (LOOX) and high-dry

(400X) magnification, noting and recording any species

that become visible at higher magnification.

If you have time, repeat this procedure for each of your other

aquarium microcosms to establish baseline population

estimates for each of them. Don’t make the mistake of focusing

on plentiful species md ignoring organisnis that are nut present

in large numbers. Relative population counts will probably

change over time, and those changes may (or may not) be

dramatic.

At •U)fl’<;‘;

p.

iihrui.ii. .1 vi’

in

.mi i.‘ty.iiii. i’’t.i

‘.il

.p’‘..;.‘•.

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y:saI,’

4’i. ik”’.iiii .iti’’,;qJtit.1.iq’iiikIi’ii:. ii

‘iJ’’” ii’i i”.’’iI;‘t’iu’i.i

l•tiit ‘I’:

iicii’’il:’ii i’.i ii)(..’a.’ii’,.

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oil, lnr.

ut

uiiytlui

1:1 othni sr..’ .i‘u’ri.ii iiiiliiitinui

:3i’’.ti.iit’’.’ .iuiilti.’’ii i,’i.uti’h’ ii ‘i:uiui.ui”r

12. To document the original status of the microcosm, label

and date a clean microscope slide, transfer another drop of

water from the surface of the microcosm to the slide, and

spread the drop across the central area of the slide. Flame

the slide to kill the microorganisms present and affix them

to the slide. Stain the slide with methylene blue and then

with eosin V. Dry the slide and observe

it

to ensure that all

species you noted are present on the slide.

u ‘II

,‘.,‘.‘,lru I

n’.’’ u’ .‘,.‘u ,iq’‘(‘i _ti.i’,u’’fc’u,’n,‘‘ .iitin:.u’i.’

‘.‘..ui’,’i.;ntt.Iuv.uk,...iI.’i;.. uik’i’iiiu,,uuuii

ti. I Jung clean pipettes, repeat the preceding steps using

specimens from near the vegetation and from near the

bottom sediment. You will probably find that the relative

abundance of species changes significantly. Some species

may be present in abundance or entirely absent in different

.ireas of the microcosm.

Schedule follow-up observations now. II possible, observe

them daily (or the first week, ideally at the same time of day

each time. Follow-up observations needn’t be as detailed

or time-consuming as this first observation. Just do quick

population estimates for as many species as possible, looking

for obvious changes and trends. For example, a species that

was initially present in sniall numbers may increase its numbers

significantly over the first few days. while the population of

another that was plentiful initially may deer ease noticeably.

If time is limited, focus your attention on only one of your

microcosms. which you can designate as your control

microcosm. You should be able to dna follow up observatmun

on

the surface, vegetation. aiicl sediment of your control microcosm

in

perhaps 15 minutes. If you have inure tinie

and

particularly if the initial state of one

ni

moie of your other microcosms differed noticeably liom your control inicmcusnm. it’s useful to do follow tip observ,itiuns aimitor them

as

well.

As time posses. you

can change

the frequency ol your tollow’up observations depending on wh,it changes you see occurring, ,ind how quickly. During the first

few

(lays .hiaiiges are likely to occur quickly. Alter a week, you can pioh.mhly induce lIme frequency of follow-tip obset vations to oimce

evei

y two or fhree

days

without nmissing intich. As the iniciocosimms begin

to

settle

down and

near equilibrium, you’ll piohably find that

few

clm.iimges

occur from one week to the next.

Do not he surprised if

one

or more of yourmic’incosiiisdies off. [hat’s why we nmacfe spares.

Q

I,:

What gross changes did you observe in your microcosms as they aged?

REVIEW QUESTIONS

Q2:

Did you iiotnn any cli.,,iwn in tim

ictative

i.’ts ciimrhcular

types

of

orgzinr.ins

as the imuclIw.inn.IgQmi’

Q

3:

Asyommi ilusucusin p. oi i’Sses toward eqti’iibi111111 what ehmnies did

you

observeiii terms ofthe types of organisms present

and (lvii it’iativi’lx)IiiititiOtIS’

Q

4:

in terms of the spuciesitii._{diii you notice .mny :.igniti•.ii’t rliangns as the microco.n, matured}

Q

5:

Why is it important to observe aseptic proceciLires when working with water

from

a microcosm?

Q6:

What

safety procedures

should you use when working with microcosms?