Dragonfly assemblage correlation with environmental variables

2.5 Spatial trends

2.5.5 Dragonfly assemblage correlation with environmental variables

The list of dragonfly species sampled in 2001 and 2002 and their codes used in the multivariate analyses are given in Table 2.1a/b . only data from 2001 and 2002 was used in multivariate analyses as data trends for 2000 and very similar to those in 2001. CA of sites and dragonfly species showed that the three sites had clearly different patterns that are similar to the Bray-Curtis clusters in Fig. 2.6. While the Open reservoir (Opp) assemblage formed a separate assemblage of several dragonfly species, the waterfall/forested river (Wffr) and shaded reservoir and small stream (Shps) sites appeared to form another assemblage of closely similar species. The two CA ordinations representing data collected in 2001 (Fig. 2.7a) and 2002 (Fig. 2.7b) showed that SUs Opp40I and Wffrl 0 1 shared some similar species with the shaded reservoir and small stream (Shps) site. However, two species still maintained a high preference for the Shps biotope. In the 2002 ordination, open reservoir (Opp) site species were clearly distinct due probably to biotope modification.This ordination, like the one for 2001 also showed typical species associated with SUs Wffr3 and Wffr4.

CCA revealed the patterns of relationships between the measured environmental variables, sampling units and dragonfly species in tri-plot ordinations. In the 2001 ordination (Fig.8a), the open reservoir biotope appeared to be dominated by increasing gradients of floating and submerged vegetation as opposed to Wffr and Shps biotopes, which appeared to occur along increasing gradients of Flow, Mhsr; Mfor and %shade. The Exposed rock and Flow gradients were vital biotope components of the waterfall/forested river (Wffr) site that attracted typical dragonfly species like Platycypha caligata, Zygonyx natalensis and Paragomphus cognatus. The shaded reservoir and stream (Shps) site also shared some important characteristics of the waterfall/forested river (Wffr) site but attracted only typical species like Chlorolestes tessellatus and Notiothemis jonesi. Some species e.g.Pseudagrion hageni preferred the forested water edges of shaded reservoir and stream (Shps) and waterfall/forested river (Wffr) sites.The 2.002 ordination (Fig. Sb), produced similar results, except at the open reservoir (Opp) site

Table 2.4 ANOVA results of mean dragonfly species richness~and abundance Nand measured site variables collected at all three sites (Wffr, Shps, and Opp) along the dragonfly trail during the study. Means followed by the same letter across rows are not significantly different at 5% level of probability.

Site

Variables"

···S···:··· ···· ···}6:-f~~··· ~:jP·~---···-···----?t~--·· ..- -..-.. ---.--.----r~;·~·!·~··--·---·--·-K:;:-~~~f" " -" " "

N

76c 347d 377d 4.15 0.027

Mhsr 78.4a 30.4b 52.6a 64.17 <0.001

Mgra 33.3a 29.6a 12.8b 3.46 0.046

Fsv 18.3a 62. 8b 26.7a 90.67 <0.001

pH 7.2a 6.54b 7.15a 72.28 <0.001

Tu 66.42 40.83 59.92 1245.44 <0.29 (ns)

At 26.02 25.21 28.8 45.21 <0.38 (ns)

% Sh 38.3b 50.2b O.4a 14.76 <0.001

Wd 6.29a 4.24a 15.80b 65.06 <0.00 1

as

= Mean number of species; N = number of individuals; Mhsr = Marginal herbs, sedges and reeds; Mgra= Marginal grasses; Fsv = Floating/submerged vegetation; Tu = Turbidity; %Sh = Percentage shade; Wd = Water depth and At = Atmospheric temperature.

Table 2.5Two-way ANOVA results of site-by-year interaction for species richness~, abundance N and measured site variables along the dragonfly trail during the whole sampling period (Jan 2000 - Dec 2002). Means followed by the same letter in a row are not significantly different at 5% level of probability.

Site varial>les*

. .. . ... ..... . ... . . . ...... .

_!.\:'ry.~ _.!.\:'ry.~ !.\:'rY.~

- . .

_~.!~.Y..! _~.~.Y.~ _~~~y~ .Q.l~x.~ .QJ>.y~ -.Q.P.Y..~ ¥.::I:.:lt.~~ ~~.y.?~1.~I.e ^.

~

^9.2 ¹¹ ¹⁰ ^8.8 ^7.2 ⁶ ^12.2 ^12.2 ^10.2 ^0.10 ^0.98 ^(ns)

.b[ 71a 96a 62a 491d 350c 200b 589d 356c 185b 9.54 0.038

Mhsr 82.8a 76.2a 76.2a 65a 21.2b 5c 75a 63a 19b 11.20 <0.001 Mgra 32.5b 31.2b 36.2b 23.8b 30b 35b 34.2b 3c 1.2c 13.56 <0.00 1

Fsv 63.2 62.5 62.5 16.2 11.2 27.5 36.2 36.2 7.5 8.57 <0.001

pH 7.1a 7.1a 7.4a 6.6b 5.92b 7.1a 7.25a 7.05a 7.15a 16.28 <0.00 1

Tu 60.5 73.75 65 30 22.5 70 45 59.75 75 503.38 0.213 (ns)

At 26.35 26.1 25.6 27.07 24.27 24.2 29.62 29.5 28.15 2.12 0.105 (ns)

'%Sh 33.8 37.5 43.8 57.5 53.8 39.5 1.2 0.0 0.0 0.39 0.81 (ns)

- . . '!!..~ -.-~-:~ - .-.-.~-:~ ..---- §.:.~Z_ _._L?~ _ . _ .. ~.:.s..? ._ _ ._.~:._~_~._ - !?:?? _~ ..s.:.?.Z . . U. :.~ . ._ ~:._ _ Q:.Q.

^(ll.S.)

*Abbreviation asinTable 4

(Y)

Peal 0

Peog

8

Wffrl02

•

Znat

Wffr302

• o

Aleu

Sfon 0

o

⁰

Afal O

Eelo Tdor

Shps402

•

Wffr202

•

Wffr402

•

, Cglm

:0 Shps302

•

Opp302

Plup : Psal

...o ^io ^.

Aimp

Pmas

808 o

Njon

o

Ctes

o

Lplg Phag

...0

•

_Shps202

•

Shpsl02

o

Aglm

o

Ojul

Opp202

• o

Tbas Nfar

o

Opp402.

o

Isen Oppl02 0

• Pker ~

• Tsti

o

Cery

Pfla Uass Tart

U) 0

Aspe N

-2.5 +3 .0

Fig. 2.7a CA biplot of dragonfly species (open circles) and site sampling units (closed circles) along the dragonfly trail in 2001. Species codes are as in Table 2.1alb.Site and sampling unit abbreviations are: Wffr= Waterfall and forested river (Wffrl 01; Wffr20 1;

Wffr301; Wffr401), Shps = Shaded reservoir and stream (ShpslOl; Shps201; Shps301;

Shps401), Opp

=

Open reservoir (OpplOl; Opp201; Opp301; Opp401).

(Y)

Peal 0

Pcog

8

Wffrl02

•

Znat

Wffr302

• o

Aleu

Sfon 0

o

⁰

Afal O

Eelo Tdor

Shps402

•

Wffr202

•

Wffr402

• :0

Cglm ^Shps302

• o

Njon

o o

Ctes Lplg

•

_Shps202

•

_Shpsl02

o

Aglm

o

Ojul

Opp202

Tbas

o

Nfar

• Tsti

o

Opp302

Cery

Pfla Uass Tart

: Phag

. Plup ^I Psal 0

--- --- - ----0---- -- -- -- - --

p - -- - - - - -- -- - - - - - -- - --- - - - - - -- - - - - -- -

0 '

O ^Opp402 _• ^:_I

Isen Oppl02 0 :

Aimp • Pker:

Pmas 0

8 •

t..f) 0

Aspe 0J

- 2. 5 _+3.0

Fig.2.7b CA biplot of dragonfly species(opencircles) and sites sampling units (closed circles) alo ngthe dragonfl ytrailin2002. Species codesare as in Table 2.1a/b.Site and sampling unitabbreviat ionsare:Wffr

=

^Waterfall and forested river (Wffr l02; Wffr202;

Wffr302;Wffr402), Shps= Shaded reservoir and stream(Shpsl02; Shps202; Shps302; Shps402), Opp = Openreservoir (Opp 102;Opp202; Opp302; Opp402)

Peal

•

+ ^Egla^Znat ^P

-

^eog ^{Sfo n}

^o

^VVffr201

Afal Plu l • •

Njan

•

Ctes

Mfor

Pl1ag

O/OSh' .

o

Shps2 01

•

Piri Aleu

•

Shps401 Mhsr

•

Oj ul

•

Aglm

Flow

Opp40 1

Fsv

Pfla •

VVffr301 E rock CD

pH ^VVffr301

Tart Plum Tdor

Isen • • Aimp

Nfar

•

^Aela

•

^{Opp30 1}

• •

Plup

Cery 0

Opp201 0 ^{Opp10 1}

Thti

• _• _• •

Pm as Aspe

•

dF.::::::::::::::-...,..,..,..,~ ~.._~. '::':":_ ~~ ..__ __ .._. .

... ---_.-.. . .. --- -..- ---..-- .- ---.. . .---. -... .- -..'f'- ---- .. ..--. - ...-- -.b

Shps301 0

Shp s10 1

r l I

- 1. 5 +2 .5

Fig.2.8a CCA triplot of dragonfly species (closed circles);site samplingunits(open circles) and environmentalvariables(arrows) in 2001.Axis 1 is horizontaland axis 2 vertical. Species codes are as in Tables 2.1aJb.Sub-site abbreviations are :Waterfall

=

waterfall and forested river;Shps = shaded reservoir and stream;Opp = open reservoir.

Environmental variable abbreviations:Fsv = floating and submergedvegetation;%Sh= percentage shade;Mfor

=

margin alforest; Mgra = margin algrasses;Mhsr

=

marginal herbs, sedg esand reeds;Erock

=

exposed rock.

Lf)

N+

Pea l

•

Znat: Peog

V\lffr102

o

•

Aleu

V\lffr202

o

V\lffr302

o

^Flow^: ^Mhsr

%Sh

•

Phag

Mfor

Njo n

0 Shps202

• o

Shps102

• •

•

Ctes

Agl m NCar

Fsv

•

_Oj_ul

Shps302

o

Pker Tdor

Opp102

• o o

^V\lff^r402

• Opp402

Aspe Opp202

• Thas Ael o

•

Plup

•

Ise n

• • •

Aimp • • 0

."

Ta r t MOPB

Pmas Afal Plu l

•

Pfla Sfon

Tsti Cery Lplg

Opp302 Erock

.-1 I

- 1 . 5 +2 .5

Fig.2.8b CCA triplot of drago nfly species(clos ed circles); site sampling units (open circles) and environmental variables (arrows) in 2002.Axis 1 is horizont al and axis 2 vertical. Species codes are as in Tables 2.1a/b. Sub-site abbreviations are :Waterfall = waterfalland fore st ed river; Shps

=

shadedreservoir andstream; Opp

=

open reservoir.

Environmentalvariable abbreviations:Fsv= floating and submerged vegetation;%Sh

=

percentage shade; Mfor

=

marginal forest; Mhsr

=

marginalherbs, sedges and reeds;

Exrock

=

exposed rock;Mop

=

marginal ornamental plants. Only important variable

gradients have appeared on the ordination .

Table2.6a Summary of weightings of the first two axesof CA and CCA for Odonat~

samp ling ye a rs of 2001 and2002 along thedragonflytrail in PietermaritzburgNational Botanical Ga rdens.Variancesexplained by thetwo axesaregiv en. Monte-Carlo

probabilitytests of sign ifi cance are sh ow n for the first canonical axis(A X1)and all four axes. *P<0.05; **P<O.Ol.

2001 2002 Year

..._--_._----------_...-..----_...----- _..

--------------_ ----_..----_..----_ _-.-.._._.---

_._-_...---_....----------------_._--------....-- ....----_ ---_ ----_ _-------

AXES AXl AX2 AXl AX2

Eigenvalues 0.460 0.349 0.448 0.368 0.990 0.986 Axes

Weightings

SP-ENC'

CPVS-EN3 F-Ratio P-value

30.3 CA

53.3 29.5 35.5 1.258 0.01*

CCA

53.8 64.1

All4 AU4

axes CA CCA axes

AXI AX2 AXI AX2

0.450 0.315 0.442 0.310 0.991 0.987 35.7 60.7 34.7 59.1

39.5 67.2

1.860 1.596 2.721

0.01* 0.tH5* 0.005**

, Species-environmentcorrelations; 2Cmnulative species variance of speciesdata; 3Cumulativespecies varianceofspecies-environmentrelations

Table 2.6b Intra-setcorrelations between eachof the environmental variables and Canonical Correspondence Analysis axes durin g both years (2001 and 2002)for Odonata sampled alongthe dragon flytrail in the Pietermaritzburg National Botanical Gardens.

CCA axis 2 0.368 0.413 2 0.3184 0.858 0.8 174 2002

CCA axis 1 0.448 0.78 89 0.9103 -0.003 0.1918

Year 2001

Variab les" CCAaxisI CCAaxis 2

Eig envalues 0.442 0.310

pH -0.5463 0.6815

%Sh 0.96 17 0.0267

Flow 0.2857 0.7372

Mhsr 0.5683 0.7385

Mgra' 0.0556 0.1133

Mfor 0.9515 0.0916 0.9299 0.1341

Fsv -0.1190 -0.8844 0.4374 -0.7903

Ero ck -0.0034 0.8583 -0.6153 0.3349

... ~gJ? = :: ~ ~g.:.~ .. ?

^{} .!} ^_^{_ _}

~.9.:.~.??..9. _ _ .

n SeeMethods.' Marginalgrassesonly measured inyear200I2Marginalornamentalplantsonlymeasured

IIIyear 2002.Notethat onlyimportantenvironmentalvariablesareincluded inthe table.

which underwent major physical changes to its biotope.Marginal vegetation diversity was replaced by two alien ornamental plants:Agapanthus orientalis and Watsonia spp. along the reservoir edges. The marginal ornamental plant (Mop) gradient was important in this regard, as was probably variation in water levels, both affecting dragonfly richness and diversity.

The eigenvalues of axes one and two of CCA for each of the two ordinations (using 2001 and 2002 species 'and environmental variable data) are given in Table 2.6a. Intra-set correlations of environmental gradients with axes (Table 2.6b) showed that percentage shade, pH and marginal forest were highly correlated with axis one for both years.

Floating and submerged vegetation (Fsv) and Exposed rock (Exrock) were correlated with axis one for year 2002 only. Flow was highly correlated with axis two for both years and marginal herbs, sedges and reeds (Mhsr) was highly correlated with axis two of year 2002. Marginal ornamental plant (Mop) was only slightly correlated with axis two of year 2002. Axis one for the two ordinations was therefore important in accounting for the observed species distribution in both years. The species-environment correlation coefficients were also very strong for the two ordinations (always greater than 0.96). Measured environmental variables were therefore responsible for the main variations in species patterns as indicated by cumulative percentage variances for species and species- environment relations (2001 CCA: 82%; 2002 CCA: 70.3%). Monte-Carlo probability tests (first axis) were significant for 2001 ordination (F

=

1.258; P

=

0.01) and 2002 ordination (F

=

1.596; P

=

0.015).These tests were significant for all four ordination axes in 2001, (F

=

1.860;P

=

0.01) and highly significant for all four ordination axes in 2002, (F= 2.721;P = 0.005).

Dalam dokumen Dragonfly assemblage dynamics and conservation at small reservoirs in KwaZulu-Natal, South Africa. (Halaman 63-70)

Dragonfly assemblage correlation with environmental variables

2.5 Spatial trends

2.5.5 Dragonfly assemblage correlation with environmental variables

···S···:··· ···· ···}6:-f~~··· ~:jP·~---···-···----?t~--·· ..- -..-.. ---.--.----r~;·~·!·~··--·---·--·-K:;:-~~~f" " -" " "

N

as

. .. . ... ..... . ... . . . ...... .

- . .

~

- . . '!!..~ -.-~-:~ - .-.-.~-:~ ..---- §.:.~Z_ _._L?~ _ . _ .. ~.:.s..? ._ _ ._.~:._~_~._ - !?:?? _~ ..s.:.?.Z . . U. :.~ . ._ ~:.~~_ _ Q:.Q.~~

8

•

•

o

o

•

•

•

•

...o io .

808

o

o

o

•

•

o

o

•

o

o

o

o

=

8

•

•

o

o

•

•

•

:0

•

o

o o

•

•

o

o

o

o

p - -- - - - - -- -- - - - - - -- - --- - - - - - -- - - - - -- -

8 •

=

•

-

o

•

•

o

•

•

•

•

•

•

• •

• • • •

•

=

=

=

=

•

o

•

o

o

•

- . . '!!..~ -.-~-:~ - .-.-.~-:~ ..---- §.:.~Z_ _._L?~ _ . _ .. ~.:.s..? ._ _ ._.~:._~_~._ - !?:?? _~ ..s.:.?.Z . . U. :.~ . ._ ~:._ _ Q:.Q.

...o ^io ^.

^o

• _• _• •