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RESEARCHPAPER

Nestedness in sessile and periphytic rotifercommunities: A meta-analysis

Phuripong Meksuwan1, Pornsilp Pholpunthin1, Elizabeth J. Walsh2, Hendrik Segers3 andRobert L. Wallace4

1 Department of Biology, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla, Thailand2 Department of Biological Sciences, University of Texas at El Paso, El Paso, TX, USA3 Belgian Biodiversity Platform, Royal Belgian Institute of Natural Sciences, Brussels, Belgium4 Department of Biology, Ripon College, Ripon, WI, USA

The freshwater littoral comprises a mosaic of habitats structured at several scales by acombination of hydrophyte architecture and physiology. Within this complex environmentlittoral invertebrates should distribute themselves to maximize tness: that is, for sessileanimals selection of permanent substrata is critical, while distribution of motile (periphytic)animals should follow predictions of Ideal Free Distribution theory. Here we explore therelationships between littoral rotifers and hydrophytes by conducting nestedness analyses on10 published datasets (7 sessile; 3 periphytic); one dataset each of microcrustaceans andinsects were included for comparison. We used four metrics to assess nestedness: meanmatrix temperature (T); counts of discrepancy shifts and species segregation; and percentsingletons. Six sessile rotifer datasets exhibited nestedness (T9.2530.2, supported by2 null models; the other metrics varied widely). Our results indicate that distribution ofsessile rotifers and periphytic insects was highly structured, but until more data is availablelittle can be said about the distribution of the periphytic rotifer or microcrustacean communitystructure. Sessile rotifer species possessing idiosyncratic temperatures (T>T 1.5 SD)

exhibited a trend toward a record of cosmopolitanism. Important idiosyncratic hydrophytesincludedCeratophyllum, Chara, andUtricularia. Two of the three periphytic, rotifer datasetsexhibited nestedness (T19.2, 39.9), but each was supported by only one of the four nullmodels. The periphytic microcrustaceans did not show nestedness, while the insects did(T15.5; supported by four null models). The three other metrics varied considerablyamongthe periphytic datasets, showing no discernable pattern.

Received: January 13, 2013Revised: September 3, 2013

Accepted: September 25, 2013

Keywords:

Habitat dependent survival / Hydrophyte / Ideal free distribution theory / Nestednessanalysis / Substratum selection

1 Introduction

Why does an animal live where it does?What is the nature of the ties that bind it to itsworld?

Rachel Carlson

Hydrophytes of the freshwater littoral have the capacityto alter their habitatin striking ways [1]. At thelargest scale,they alter physical characteristics of the water column byslowing water movement thus increasing sedimentation

Correspondence:Dr. Robert L. Wallace, Department of Biology,Ripon College, Ripon, WI 54971, USAE-mail: wallacer@ripon.eduFax: 1-920-748-7243Abbreviations: a, mean species richness per hydrophyte; bp,Betaproportional diversity;IFD, Ideal Free Distribution theory;S,species richness;T, mean matrix temperature

International Review of Hydrobiology2014, 99, 4857 DOI 10.1002/iroh.201301703

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and by reducing light penetration, which in turn keepswater temperature lower and may affect oxygen levels [24]. At intermediate scales, hydrophytes modify waterchemistry by altering pH, and changing concentrations ofcompounds important to plant physiology (e.g., inorganiccarbon, nitrogen, and phosphorus), as well as changinglevels of O2and dissolved organic carbon [57]. Aroundindividual plants, small-scale effects dominate. Herehydrophyte architecture modies water ow among thefoliage [8, 9] and provides structural complexity [1012]that can conceal predators and prey from one another [1315]. Also at this scale, plant physiology can markedly alterwater chemistry within the Prandtl boundary: the thin layerin the immediate vicinity of the plant in which all ow islaminar [16, 17]. Accordingly, the freshwater littoral shouldbe recognized as a mosaic of distinct habitats whosestructure and function depend on hydrophyte density anddiversity. As a result, tness of littoral rotifers will be

determined, in part, by the dominant hydrophytes in thehabitat.

A sessile (epiphytic) rotifer becomes bound to itssubstratum when the mobile juvenile (larva) encounters asurface and undergoes metamorphosis that ends inpermanent attachment. Consequently, while habitat-de-pendent survival and subsequent reproduction determinestness, the outcome is initiated by the act of substratumselection [1820]. On the other hand, periphytic speciesare motile as adults and can move among hydrophytes,and of course they also may be residents of open waters.For example reporting on hydrophyte dominated waters of

the Yamuna River (India) Arora and Mehra [21] haveshown that of the 90 motile rotifers present, 57 wereperiphytic (found in association with Eichhornia and/orSalvinia) and 48 were both pelagic and periphytic. Yetthere are some characteristics that set periphytic speciesapart from those that are truly pelagic. While not attachedto a specic plant, periphytic rotifers occur near enough tohydrophytes to be exposed to a distinct milieu, many feedwithin the aufwuchs, and some species deposit their eggson plants or at least release them within the littoralzone [13, 2224]. For those species that deposit their eggson hydrophytes tness of the embryo is determined insimilar ways as for sessile taxa. However, as mobileadults, periphytic species should distribute themselvesaccording to Ideal Free Distribution (IFD) theory: that is,tness is maximized by exploiting the available habitatsbased on the aggregate of positive (e.g., resources) andnegative (e.g., predators) assets associated with each [25].Unfortunately, we know almost nothing about the relativetness of either sessile or periphytic rotifers as a function oftheir habitat [20, 26].

While the species richness [27] and abundance [28] inthe littoral rotifer community appears to be as least asgreat, and often greater, than that of open waters [29]

(cf. [30]), these taxa remain an understudied component ofaquatic systems. Here we present a retrospective analysisof sessile and periphytic rotifer community structure vianestedness analysis, using datasets on littoral micro-crustaceans and insects for comparative purposes.Recognizing differences in diversity and composition ofthe littoral rotifer community offers us opportunity tounderstand the importance of the hydrophytes in structur-ing this habitat.

2 Methods

We compiled 12 published datasets (Table 1) of sufcientdetail that listed sessile or periphytic invertebrates that hadassociations with hydrophytes: sessile rotifers (n7),periphytic rotifers (n3), periphytic microcrustaceans(n1), and periphytic insects (n1). For simplicity we

refer to these species as colonists; in this context the termcolonist should not be confused with colony, as in colonialrotifers (e.g.,Floscularia conifera). These are species thatform intra- and interspecic aggregates by attaching to oneanother [31]. In our analysis we included colonial rotifers,but only in those instances of their being attached directlyto a hydrophyte. Of course, our study cannot beconsidered exhaustive, neither in the literature we selectednor in the thoroughness of each study (e.g., in parity ofplant surface area examined). For the rotifers we alteredspecies designations to conform to recent efforts tostabilize rotifer nomenclature [32, 33].

In our analysis we tested the hypothesis that colonistsof hydrophytes exhibited nestedness. In this case,nestedness indicates that colonists comprising smallerspecies assemblages on some hydrophytes are a nestedsubset of those hydrophytes with larger assemblages. Wedeveloped an initial data matrix comprising presenceabsence data of S rows of rotifers and H columns ofhydrophytes. The matrix is rearranged (packed) usingalgorithms so that it achieves the densest grouping of Sand H[34, 35]. While at least 10 metrics have been used toassess whether species assemblages exhibit nested-ness [36], we simplied our analyses by using fournestedness metrics. (1) Matrix temperature (T) i s ameasure of disorder in a data matrix ranging from perfectnestedness (T0) to maximum disorder (T100), withintermediate temperatures indicating a combination oforder and disorder of the species assemblage [37]. TocalculateTof the packed matrix we used ANINHADO [38,39]. Using this application all datasets were tested againstfour null models with 1000 simulations for each null model:(a) species presences are randomized within columns; (b)species presences are randomized within rows; (c)presence in a cell is randomized within the wholematrix; (d) presences are assigned by a function

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Table

1.

Summaryofnestednes

smetricsfordatasetsofinvertebrate

colonists(sessileorperiphyticspecie

s)andtheirhydrophytesa)

Location;Referenceb);

[#ofsitesinthestudy]

Biod

iversityc)

#of

hydrophytes

Mean

matrixT

(#ofnull

model

support)d)

Discrepancy

shifts

(colonists;

hydrophytes)

Species

segregation

Singlet

ons

(%)

Idiosyncraticspec

iese)

S,a,

bp

Colonists

Hydrophyte

Sessilerotifers

A.

Eightstates,

USA[194]

33,16.4,

2.0

9f)

21.2

(4)

33;27

10

3(9.1

%)

Collothecacampanulata;

Limniasshiawasseensis;

Ptyguramucicola

Rootedplantswith

large,

flat,

floatingleaves

B.

Twostates,

USA

28,12.4,

2.3

8g)

23.2

(4)

21;21

10

7(35.7

%)

Collothecacampanulata;

Cupelopagisvorax;

Flosculariaringens;

Limniasshiawasseensis

Chara

C.

Ponds,

Germany

[22]

15,

4.1,

3.6

17

15.8

(4)

26;22

8

4(26.7

%)

Ptygurabrachiata

Alg

ae,

Utriculariasp.

D.

Bogpond,

NH,

USA[1]

19,

8.6,

2.1

7

30.2

(2)

17;15

2

6(31.6

%)

Beauchampiacrucigera;

Ptygurabarbata

U

triculariagibba

E.

Bogs,

Germany[10]

13,

4.0,

3.3

7

9.5

(3)

6;7

7

4(30.8

%)

Beauchampiacrucigera;

Ptyguralongicornis

Utriculariaintermedia

F.

Bogsandlakes,

France[7]

14,

9

38.4

(0)

NA

NA

2(14.3

%)

G.

ThaleNoiLake,

Thailand[1]

40,12.3,

3.3

15

12.3

(4)

47;50

16

11(27.

5%)

Acyclussp.;

Collotheca

heptabrachiata;

Limniasceratophylli

Ceratophyllum

demersum;

U

triculariaaurea

Periphyticrotifers

H.

LakeKisajno,

Poland[4]

99,31.2,

3.2

4f)

39.9

(1)

33;32

13

28(28

.3)

Conochilusnatans;

Eosphoranajas;

Synchaetalongipes;

Synchaetastylata;

Trichocercacapucina;

Trichocercaelongata;

Trichocercastylata

I.Alpond,

Turkey[1]

60,21.3,

0.6

4

19.2

(1)

10;17

7

4(6.7

%)

Lecanenana;

Monommatasp.;

Scaridiumsp.;

Trichocercaobtusidens;

Trichocercarattus

Typhasp.

(continued)

P. Meksuwan et al. International Review of Hydrobiology2014, 99, 4857

50 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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Table

1.(Continued)

Location;Referenceb);

[#ofsitesinthestudy]

Biod

iversityc)

#of

hydrophytes

Mean

matrixT

(#ofnull

model

support)d)

Discrepancy

shifts

(colonists;

hydrophytes)

Species

segregation

Singletons

(%)

Idiosyncraticspec

iese)

S,a,

bp

Colonists

Hydrophyte

J.

Forestponds,

Poland[7]

17,

10

44.7

(0)

NA

NA

8(47.1%)

Periphyticmicrocrustaceans

K.

Alpond,

Turkey[1]

27,

4

39.7

(0)

NA

NA

0%

Aquaticinsects

L.

Streamsand

lakesMI,USA[16]

32,

7.1,

4.5

15

15.5

(4)

40;38

10

11(34.4

%)

Fourinsectspp.

Potamogeton

alpinus,

P.natans,

P.pectinatus

NestednessmetricsafterUlrich[37].

a)Hereweexpandedthedenitionofhydrophytetoincludelamento

usalgae,aswellasbothvascularan

dlarge,non-vascularplants.

b)A.

Table9[66];B.subsetofA(pg4950);C.

Text[80];D.

Table2,

[18]withadditionalunpublisheddata;E.Text[81];F.

Table1[82];G.

Table2[65];H.

TableVIII[83];

I.&K.

Table1[84];J.

Table4[70];L.

Table2[85].

c)S

speciesrichnessofthesite

(gdiversity)andforpackedmatrices

withatleast1nullmodelsupport:a

m

eanSperhydrophyte,

bp

b

proportionaldiversity(g/a).

d)Support(p