Ecology of Tigriagrion Aurantinigrum calvert in response to variations in environmental conditions (Zygoptera: Coenagrionidae)

Ecology of Tigriagrion aurantinigrum Calvert in response to variations inenvironmental conditions

(Zygoptera:

Coenagrionidae)

P. DeMarco+Jr.¹* and M.V.C. Vital²

ReceivedAugust 1, 2006 / RevisedandAccepted February 13,2007 1Laboratorio EcologiaTeoricaeSintese, DepartamentodeBiologia Geral, Universidade Federal deGoias, BR-74001-970, Goiania, GO, Brazil;- pdemarco@icb.ufg.br

2

Programade_{Pos-graduagao}emEntomologia,DBA,Universidade Federal deVigosa, BR-36570-000, Vigosa, MG, Brazil;— mvcvital@hotmail.com

*

CorrespondingAuthor

The_{daily activity patterns,}behaviourandpopulation dynamicsinZygopteraare

thoughttobe affectedbythephysicalconditions of the environment. How andwhy

the_sp.reacts tothose conditions is determinedmainly byits bionomic characteris-tics.Here,anauto-ecological studyisperformedofT.aurantinigrum,in anattempt

toclarifyits responses tophysicalconditions. It issuggestedthat T.aurantinigrum couldfit,withafewassumptions,in the “female-control”classification of odon.

mat-ingsystem. Some interactions wereobserved between individuals,but it is assumed that theseplayarole insexrecognition,rather thanin territorial contests. The results indicate that this_sp.is affected_bythe_{following physical}conditions: the_monthlyrain fall,which hasapositiveeffectonthe abundance (withthepossible exceptionof the

heavyrainmonths);thewaterflowvelocity,which seemstodefinealimit of its occur-rence;and thedailyvariation intemperature,whichseemstoinduce the_sp.torestrict its_activitytothe hottest_periodof theday,asexpectedfroma“thermal conformer”.

T.aurantinigrumappearstobeaffectedbysmallscalevariations of environmental variables,asobservedbythe differences of its abundanceatthe 3 different sites of this

study.Under conditionsof thecurrent“forest-to-pasture”conversion that iscommon in the Brazilian Atlantic Forestregion,thesp.isexpectedtoincrease its abundance and to broaden itsgeographicalrange,althoughwaterbodyalterations could limit

2 P. DeMarco,Jr & M.V.C. Vital

INTRODUCTION

Serious pressure duetohabitat destruction caused

_by,

_e.g.

_{damming large}

and medium size

_rivers,

_seweragewaste instreamsand

_{deforestation,}

has resulted in serious threattomuch ofthe

_aquatic

faunain manyareasof southeastern Bra-zil

_(MITTERMEIER

etah,

1999).

Most of thisareais consideredas

regionally

outstanding

in

biological

value and must be

_priorized

in conservation actions (BIODIVERSITY SUPPORT PROGRAM etah,

_1995).

Recent studies have demonstrated that_some

_species,

such _asHetaerinarosea

(Calopterygidae),

may be favoured

by

theconversionof

_gallery

forest to pasture,

although

other

spe-cies,

e.g.

Heteragrion

aurantiacum

_{(Megapodagrionidae),}

_{may become}rarer or

completely disappear (FERREIRA-PERUQUETTI

& DEMARCO,

2002).

The

possible

causeof these results may be understandableintermsof bionomicchar-acteristics of the

_respective

_{species. Thus,}

H.rosea is a

‘sun-species’

that could

alsooccurin the forest but doesnot

require

any

special

substrate for

oviposition

(DE MARCO &PE1XOTO, 2004),whereas H. aurantiacum is_a

_{shadow-species}

whose habitat is

_closely

relatedtoforest and which

_oviposits

in trunksorstems oftreesin streams,asdosomeother

_species

_{in this genus}

(GONZALEZ-SORI-ANO & VERDUGO,

1982). Unfortunately,

there is _a

verylimited amount of information_on

_ecological

traits in

_{neotropical species}

that could be usedto

un-derstand and also

_predict

which

_species

could be_morethreatened under the im-pactof deforestation.

The

_physical

conditions ofa

given

environmentare

important

factors in

de-termining

the

_ecology

and behaviour of the

_species

_present

_(CORBET,

_1999),

and the

knowledge

of how these

_{species respond}

to_{these conditions may lead}to

predictions

ontheir

distribution, population

size and

dynamics.

Conditions that

might

be

_important

in the

_regulation

of odonate

_populations

and communitiesare

air temperatureandwater current

_{velocity (in}

lotic

environments). Temperature

seems tobe adeterminant of

_{daily activity}

and behaviour

_{(MAY, 1991;}

HEIN-RICH, 1993; POLCYN, 1994;DE MARCO & RESENDE,

2002)

and of therate of

_development

of the larvae

_(BAKER

&FELTMATE, 1987;PRITCHARDet

ah,

1996).

Thecombinedeffect of

_growth

and

_efficiency

underdifferent thermal

regimes

mayalso determine the range of distribution of a

given species

and

ex-plain

the

_relationship

between

_species

richness and _temperatureina

large

scale view

_{(EVERSHAM& COOPER, 1998; CORBET, 1999).}

Watercurrent

velocity

may also

play

an

important role, especially

in

_species

with

_{endophytic oviposition,}

that may show

preferences

for

_specific

velocities

_(GIBBONS

&

_PAIN,

_1992).

Tigriagrion

isa

monotypic

genus of small-sized damselflieswhose

biology

and distribution_are

_{poorly known,}

and which

appeartooccurinstreamsin the South

American continent. So far T._{aurantinigrum}is known from

_Paraguay,

Bolivia and central and southern

_{Brazil) (COSTA}

&SANTOS,

2001).

In this

_study

we

rec-ognizes

the

importance

of scale

(both spatial

and

_temporal)

tothe

_knowledge

of the natural

_history

of_a

_{given species.}

STUDY AREA

This workwasconductedatthree different sites(1,2and 3)of the Sao Bartolomeu stream,asmall waterbodyin theVigosaregion,MinasGerais,Brazil. Theregionhasawetsub-tropicalclimate (Kop-penCWbclassification),with thedryseasonfromMaytoSeptemberinclusive (GOLFARI, 1975).

Themeanannual rainfallrangesbetween 1500and 2000mm,themeanannual temperaturebetween

14,0and26,1°Cand the relative humidityis about 80%(VALVERDE, 1958).Inall the three sites the

streamwidth varies fromonetothree meters.

At site 1,thestream cutsthroughapasturearea,withminimum seweragedischargeand with the

impactofsomecattlegrazing activity nearby.Afew bushes arescatteredalongitsmargins, some-timesreachingmorethanonemetertall. Thewaterflowvelocityin therainyseason(whichwe meas-ured witha current metermodel 1210,Scientific Instruments, Inc.)wasthehighestfrom the three sites(mean=_{0,596 m/s;}s.d.=±0,292).Site2 is locatedapproximately50maway,and isvery

simi-lar, exceptfor the lowervelocity (0,261 m/s;s.d.=_±0,147).In additiontobushes,therearealsosome treesnearthemarginsof thestream.Site3,located ca500mfrom the other two,near asmallurban concentration,therefore it issubjecttosomeseweragedischarge.Like the othersites,it is located ina

pasturearea,with somebushes and smalltreesnearthe stream’smargins.Thewater currentvelocity

is_verysimilartothatatsite2(0,260 m/s;s.d.=_±0,115).Dataonthis sitewascollecteda_yearbefore westartedtoworkonsites1and 2.

METHODS

BEHAVIOUR ANALYSIS- The behavioural datawascollectedonlyatsites1and2, always

be-tween09:00 and 14:00. After_havingobtainedanestimate of abundance (see below),wesearched for individuals onwhichtoperformananalysisof the_species’temporal budget, usingafocal observa-tion methodasdescribedbyDEMARCOetal.(2002).Each individualwasobserved foroneminute and the time spent in each behaviourwasrecorded. For T.aurantinigrum,theonlybehavioural

cat-egoriesobservedwereflight activity, aggressiveorterritorial defense andperching.Additional data werecollected inJanuary2004 withspecialemphasisonthe observation of interactions.

ABUNDANCE ESTIMATION-Afixed-areascanmethod (FERREIRA-PERUQUETTI& DE

MARCO, 2002)was usedin ordertoestimate themonthlyabundanceof_{Tigriagrionaurantinigrum}

ateach site.Wedivided the stream,ateachstudy site,intotwo meterlinearsegments (50 segmentsat

sites 1 and2,and 49atsite3).An estimate of abundancewasobtainedby countingthe number of T.aurantinigrumindividuals ineach segmentatsites1 and 2atleastthreedayseachmonth,always

between 10:00 and 14:00, Thecountstook,on_average, 15 minutes andnosegmentwasscanned for

morethantwominutes. Sites1and2wereinvestigatedbetween September2001 andAugust2002.

Themonthlyabundance ofT.aurantinigrumwasnotinvestigatedatsite3;thisarea wasused inthe estimation ofdailyvariations of thespecies’abundance (see below).

DAILY ACTIVITY—In 30 minuteintervals,between 8:00 and17:00,the numbers of individu-alswereestimated with thesamemethodasstatedabove,duringthree daysin the_rainyseason(all

sites)and duringthreedaysin thedryseason(onlysites1 and2).The airtemperaturein ashaded areawasmeasured in30 minute intervals.

STATISTICAL ANALYSIS- For_analysisof the_dependencyof T.

aurantinigrumoccurrencein relationto streamvelocity,alogistic regression accordingtoHOSMER & LEMESHOW(1989)was

appliedusingthequasi-Newtonmethod. To examine therelationshipbetween Tigriagrionabundance and rainfall,alinearregression analysis(SNEDECOR&COCHRAN, 1980)wasused.

4 P. DeMarco,Jr & M.V.C. Vital

RESULTS

Based_{on a}

_sample

size of50

observations,

it is clear thatnear its

reproduc-tive

_habitats,

T.

_{aurantinigrum spends}

mostof its time

_perched,

and thisseems

toholdtrueforboth

_dry

and

_rainy

_seasons.

_During

_a

_single

observation_an

indi-Fig, 1. Mean abundance of_{Tigriagrionaurantinigrum}between 8:00 and 17:30atsite 1(Afor_rainy and B for_dryseason),site2(Cfor_rainyand D for_dry)and site3(E,rainyseasononly);themean temperatures(°C) duringthestudyareshownfor bothseasons(F).Meanabundance is measured by themeannumber of individuals in the2 metersegments.Bars showstandard deviations.

vidualwas seen

pursuing

anotheronethat_gotclose toit

_{(but only}

forone

sec-ond);

this_wasrecorded_as defense behaviour.

Dur-ing

another two

obser-vations,

two individuals

facing

each other

_flying

upand downwere seen.

This_seems tobe _a terri-torial defense

_behaviour,

although

it could also be relatedtosex

recognition.

Thesame behaviourwas

noticed six _more

times,

but outside the

time-budget analysis.

Intwoof thesecases therewasthe

impression

oneindividual

pursued

the other_onefor

ashort distance

(<1 m).

The

_oviposition

behav-iourwasnoticed ina

sin-gle

female; itwas

perched

on an

aquatic plant

close

tothewater

surface,

then

submerged

and

_stayed

un-derwater for 90 s,

bend-ing

the abdomen

_(while

still

_holding

the

_plant),

with the

_{tip touching}

the

vegetation.

In

_spite

of the_greatamountof time

spentatthe

_reproductive

habitats,

wedid not

ob-Tigriagrion

auran-tinigrum

Fig.2.Logisticregressionof the presenceof

onwater current

veloc-ity(measuredinm/s)for sites 1 (A),2(B)and 3(C). Bars show standarddeviations. Trendline showsastatistically significant relationship.

P.DeMarco,Jr & M.V.C. Vital 6

serveany other behav-iour associated with

re-production.

The

_daily

_activity

patterns varied

dra-matically

between sites 1 and2

_(Fig.

_{1, A-E).}

During

the

_rainy

sea-son, the abundance of T.

_{aurantinigrum}

was

much

higher

at site

2,

although

individuals left site 1 later in the

day. Also,

there_{was a}

period

in the middle of the

_day

when the abun-dances decreasedatall three sites. The

timing

varied littlebetween thesites: 11.00-12.30atsite

_1,

10.30--11.30atsite 2 and 11.30-12.30at site 3.

During

the

dry

season, the abundance decreasedat site 1

_(between

12.30 and

_13.30)

and there is _someindication that it didsoalsoatsite 2. In thisseasonindividualswereactive

only during

the hot-testpartof the

_{day (Fig.}

_1F).

At site

_1,

the

_activity

started when the_temperature reached _ca22°C in both_seasons, i.e.at9.00 in the

rainy

season andat 12.00 in the

_dry

_seasonand

_ceased,

in the

_dry

_seasonat

_least,

when it fell below_ca21,5°C. A

_{logistic regression}

was

performed

between thestream

_velocity

and the abun-dance

_(using

the

_{daily activity data)}

of T.

_{aurantinigrum}

in the

_rainy

seasonfor each site. The

_relationship

wasnot

_significant

for site 2

_(\

2=

0,027,

df=

1,

p=

0,870)

norforsite 3

(\

2 =

1,932.

df= _1, p=

0,164),

but itwassofor site 1

_(x

2=

5,819,df=_1, p=

0,016).

In the lastcase,the

probability

of

_Tigriagrion

occurrence

in_a

2m-segment

of thestreamdecreases with the increasedwater flow

_velocity

(Fig. 2).

It is

_important

that site 1wastheonewith the_greateststandard devia-tion in

_{velocity, suggesting}

that the

_relationship

wasnot

significant

atthe other sites

_only

because

_they

didnot havea broad

enough

variationfor this variable. A

_{significant relationship}

wasalso found when

pooling together

the

_Tigriagrion

abundanceacrossall

sample

sites

_(x

2= _10,234,df = _1,

p=

_0,001).

Asatsite

_1,

the

_probability

of _occurrence decreased_asthewater current

velocity

increased

(Fig. 3).

The

_changes

in

_monthly

abundance of T.

_{aurantinigrum}

seemtobe similar be-tweensites 1 and

_{2, although}

itwasalmost

always higher

atsite 2

_{(Fig. 4).}

A

sig-nificant

_relationship

wasfound

by

the linear

_regression

of themean

monthly

abun-danceonthemean

monthly

rain fall for both sites

_(p

=_0,047and R2

=_0,30for site

1,

and p=_0,028and R2=

0,37

for site2),

showing

that the abundance rises when Tigriagrion

aurantini-grum

Fig. 3.Logistic regressionof the_presence of

onwatercurrentvelocity(measuredinm/s)for thedata of all sitestogether.Bars show standard deviations. Trend line showsa

the rain fall is

_{higher (Fig. 5).}

However,

the abundanceat thetwosites decreased when themean

monthly

precipita-tion exceeded_ca8 _mm;this occurred

_during

the

_heavy

rains of

_January

and

Febru-ary.

DISCUSSION

CONRAD & PRITCH-ARD

₍₁₉₉₂₎

_presented

a

comprehensive

review of odonate

_mating

_systems,

de-scribing

aseries of

strategies

thatresult from the

predict-ability

of male-female en-counters and the

_ability

of

males to control the female

access to

_oviposition

re-sources. One of the

simplest

strategies,

knownas

“female-control”,

occurswhen the

fe-males’ presence is

predictable,

but the malesarenotableto control

_oviposition

resourc-es. Thiscan occur when

ovi-position

sites_{are numerous}and

_widely

distributed within_alimited

area,hence males have little chancetocontrol femaleaccess to them. The authors_suggest thattwomain

_strategies

_are

_thought

toevolve in such situation: the control of the female

_{by grasping it,}

and the

_{submerged oviposition. Tigriagrion}

appears tofit in_{this category, as}femalesare

predictably

encounterednearwaterandthe

ovi-position

resources arefarmoreabundant than the males. However,CONRAD & PRITCHARD

₍₁₉₉₂₎

also

_predicted

that the

_copula

shouldoccurfar from the water, which doesnotseemtobe thecasein

_{Tigriagrion (since}

males and females

are

predictably

found in the

margin

of thestream). We think that female control mayalsooccur nearwaterbodies with the

only assumption

that the

_availability

of_resources should be much

_larger

than the number of males in thearea.This is

reinforcedbecause CONRAD & PRITCHARD

₍₁₉₉₂₎

_suggestthat males under this_strategymay

_actively

seek formatesormaintaina

position

that increase their

ability

to

intercept

females

_approaching

thewater. The

_probably

most efficient Tigriagrion aurantinu-grum

Fig.4. Meanmonthlyabundance of

in 2metersegmentsatsites 1(A)and 2(B).Mean abun-dance is measuredbythemeannumber of individuals in the 2metersegments.Bars show standard deviations. Letterson x-axis indicate months from_SeptembertoJuly.

8 P. DeMarco,Jr & M.V.C. Vital

place

to

intercept

females

ap-proaching oviposition

sitesare

the

_margins

of thewater

body

and this_seems tobean

incipi-ent

_phase

inthe evolution of

territoriality.

In

_Zygoptera,

the male

rec-ognition

of their

conspecif-ic females is

_thought

to occur

mainly by

visual _cues

(COR-BET,

1999),

so sexual

dimor-phism

should be

_important

in male-femaleencounters. T.

au-rantinigrum, however,

doesnot show any

degree

of sexual

di-morphism,

and it is

_suggested

that theinteractions observed

during

this

_study

_{are a} mech-anismof behavioural_sex

rec-ognition.

Further observations

arestill needed in orderto

clar-ify

this

_subject,

since these in-teractions could be associated with the

_{territoriality}

in this

species.

As

_expected

from such a

small-sized

_damselfly,

T.

au-rantinigrum activity

seems to

depend

on the airtemperature,

allowing

to

classi-fy

it_asa“thermal

_{conformer”,}

_sensuMAY

_(1976;

_1991).

_However,it should be

emphasized

that there is_acontinuumbetween the thermal conformer and the heliotherm

_classes,

with

_body

size

_playing

a

significant

role in

_determining

the

position

ofa

given species

in this scale. The_conceptismost

_powerful

ifwe

con-sider it

_{comparatively.}

Asan

example,

Hetaerina_rosea

_{(Calopterygidae).}

which has both

greater

body

size and broader

period

of

_activity

atsite 3

_(DE

MARCO &PEIXOTO, 2004),could be

_placed

further in the heliotherm direction than T.

aurantinigrum.

Small-sized

_species

are

probably

affected

_by

small-scalevariationsinconditions andresources

(ZIV, 2000).

In these

_species,

a small

gradient

in_{temperatureor} water flow may represent the entire scale fromworst,

sub-optimal

and

_optimal

habitats. This distinction may be very

important

hereassomeof the studied ar-eas mayrepresent

sub-optimal

habitats for T.

aurantinigrum,

asmeasured

by

the

meanabundances. This is alsoa

warning

about the need of

_replication

on behav-

Ti-griagrion aurantinigrum

Fig. 5.Linear regressionof themeanabundance of on meanrain fallfor each month

of the studyfor sites1(A)and 2(B).Meanabundance is measured bythemeannumber of individualsin the 2 me-tersegments.

ioural and

_activity

_patternstudiestoavoid conclusions drawn from

_analysis

of_a

sub-optimal

habitat.

The_greatvariation in the

_activity

_patternof T.

_{aurantinigrum}

thatwasfound between the three

_{sites, despite}

the

_proximity

of sites 1 and

_2,

_suggeststhat its abundance is

_strongly

affected

_by

local

_conditions,

such_asthewater current

ve-locity.

In

_fact,

thisvariablecan

easily explain

thedifferencesbetweensites1 and

2,

since the firstonehasa

higher

current

velocity

and lower T.aurantinigrum abun-dance.

_However,

site3hasaflow

velocity

similartosite

_2,

but holds the smallest

population

abundance.Thus,other local conditionsor resources we wereunable

to_measure

_(e.g.

_some

_reproductive

_resource, like_an

_{aquatic plant)}

_are

_probably

important

tothe

species.

Ofcourse, the lower abundance in site 3 could also be

caused,

directly

or

indirectly, by

the

_higher

sewer

discharge

in thestreamat this

point.

Although

weobserved

_only

one

reproductive

event,webelieve that the under-water

_ovipositon

could becommonin T.

_{aurantinigrum,}

also

_explaining

the

dif-ficulty

toobserve such behaviour. This

oviposition

habit could be

_important

to

protectthe

eggs from

desiccation,

since thewater level of the smallstreamsthat

are

usually

the habitat of this

species

often fall

drastically during

the

dry

season.

However,if T.

_{aurantinigrum}

is

_really

restrictedtounderwater

_endophytic

ovipo-sition,

it would be reasonabletoexpecttoavoid the fastcurrents

(as

it is shown in

our

results),

since

they

could be harmful

given

its small size. The underwater

ovi-position

is knowntobe

potentially

harmful

_manly

dueto water current

(CORBET,

1999), although

itseemsthatno one

suggested

that the

_body

size could limit the maximumcurrent

_velocity

thata

given species

couldendure. On the other

_hand,

some

species,

as

Calopteryx splendens

xanthostoma

_{(Calopterygidae),}

_{may seek} for fastercurrentat

_{oviposition sites,}

asthis maypreventthe

_growth

of

_algae

on

the eggs that decreases its survival

(SIVA-JOTHY

et

_{al., 1995).}

The

_{population dynamics}

of T.

aurantinigrum

appearstofollowapattern com-monin other

species

found in thisareawith

higher

abundances in the

_rainy

season

(DE

MARCO &

_{PEIXOTO, 2004).}

In H. _roseait is

_suggested

that the

_dynamics

is

_adjusted

tohave

_higher

adult abundance in monthswith

longer photoperiod

duration and lower

_{evapotranspiration,}

_{which may}

_provide

the

_opportunity

to increase the total time_spentin

_{reproduction. However,}

T.

_{aurantinigrum}

abun-dance

_peak

_occurs earlier in the

_rainy

_seasonthan in H.roseaand other

species

thatwe have observed in the

_region.

It is

possible

that the

_heavy

rains thatare commonin

_January

and

_February

couldcause agreat

mortality

in those months

that, otherwise,

show climatic conditions similartothose

_during

the

_population

peaks.

These

_heavy

rains could

_play

an

important

role in

_{synchronizing}

_the pop-ulations where the larval

_period

lasts aboutoneyear.

A

_special

feature of

_{population dynamics}

in this and other

_species

found in the Atlantic Forest

_(cf.

DE MARCO &FURIERI, 2000;DE MARCO &PEIXOTO,

2004)

is the_apparent

_general

trend towards univoltinism. This is believedtobe

P. DeMarco,Jr &M.V.C. Vital 10

dueto seasonal constraints that wouldovercomethe

potential

of these

_species

for_a faster larval

_development

_(CORBET,

_1999).

CORBET

₍₁₉₉₉₎

also notes that

_{tropical-centered species}

that

_reproduce

in

_upland

streams

usually

are

uni-voltine and their emergence

commonly

takes

_{place just}

before

_heavy

rains,that could make thewater coursehazardoustothe larvae. If this isso,the

heavy rains,

aside of

_increasing

the

_{Tigriagrion mortality}

(as

suggested above),

would

_actually

controlling

its

_{population dynamics.}

T.

_{aurantinigrum}

_appearswell

_adapted

toareaswhere the forestcover is

with-drawn,and_we

_predict

that this

_species,

_asH.rosea,should increase its

abundance,

and

_possibly

its

_geographical

_{range, under the conversion of forest}topasturethat is the dominant

_{landscape change}

in the Brazilian Atlantic Forest. On the other

hand,

T.

_{aurantinigrum requirement}

of intermediatewater flowvelocities could be a restriction, since the

_regulation

of the streams,

by

canalization intomore

straight

and fastwater systems or

by changing

themintoa

complete

lentic

envi-ronment, isa commonfeature ina_pasturedominated

_landscape.

ACKNOWLEDGEMENTS

Wearegreatlyindebted toP.E.C. PEIXOTO for the massivehelpin the field work and for sugges-tions onthemanuscript.Wearealso_verythankfulltoD.C. RESENDE for valuable commentsand suggestionsonthemanuscript.This workwas_{partially supported by}the Institute dePesquisasda

Mata Atlantica(IPEMA).

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