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Journal of Ornithology ISSN 0021-8375 J OrnitholDOI 10.1007/s10336-011-0803-1

Breeding land birds across the Greekislands: a biogeographic study withemphasis on faunal similarity, species–arearelationships and nestedness

Stylianos Michail Simaiakis, MichailDretakis, Christos Barboutis, ThanosKatritis, Danae Portolou & StavrosXirouchakis

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ORIGINAL ARTICLE

Breeding land birds across the Greek islands: a biogeographicstudy with emphasis on faunal similarity, species–arearelationships and nestedness

Stylianos Michail Simaiakis • Michail Dretakis •

Christos Barboutis • Thanos Katritis •

Danae Portolou • Stavros Xirouchakis

Received: 8 June 2011 / Revised: 28 October 2011 / Accepted: 16 December 2011

� Dt. Ornithologen-Gesellschaft e.V. 2012

Abstract We investigated the biogeography of 102

breeding land bird species reported on 77 islands in the

Aegean archipelago. For the first time, we prepared a

complete as possible dataset concerning the land birds of

the Aegean islands. The overall insular avifauna has been

treated as a unit to find out certain ecological patterns. We

examined the faunal similarity using recent distribution

data, studied the species–area relationships (SARs) and

tested land bird biotas for nested patterns. A significant

SAR was identified for land bird species richness of the

Aegean islands and for most of the island subdivisions. The

surface area of the available Aegean islands explained 79%

of the variance in species richness and the overall z value

was 0.305, in general suggesting a high degree of island

isolation. The z values of the log–log species–area

regression varied significantly among island groups and

ranged between 0.100 and 0.329. We found that the overall

slope of the species–area curve was steeper than those of

terrestrial invertebrates (i.e., centipedes, darkling beetles).

The land bird fauna on the Aegean islands was nested,

whereas Crete and its satellite islands was the least-nested

island group. Insectivores and seedeaters contributed dif-

ferently to land bird assemblages with the former showing

a more reliable nested arrangement than the latter. In most

cases, the rank of breeding bird species, as determined by

the nestedness metric, was negatively correlated with

island area and/or maximum altitude.

Keywords Aegean archipelago � Crete � Insectivores �Nested assemblages � Seedeaters � Singletons

Zusammenfassung

Brutende Landvogel auf den griechischen Inseln: eine

biogeografische Studie mit Schwerpunkten auf Fau-

nenahnlichkeit, Arten-Areal-Beziehungen und gehauf-

tem Auftreten

Wir haben die Biogeografie von 102 Landvogelarten

untersucht, die auf 77 Inseln des agaischen Archipels

nachgewiesen wurden. Zum ersten Mal haben wir ein

moglichst vollstandiges Inventar der Landvogel der agai-

schen Inseln erstellt. Die Gesamt-Avifauna aller Inseln

zusammen war als eine Einheit betrachtet worden, um

bestimmte okologische Muster zu finden. Wir untersuchten

die Faunenahnlichkeit unter Verwendung aktueller

Verbreitungsdaten sowie die Arten-Areal-Beziehungen

(AAB) und testeten Landvogelgemeinschaften auf Kon-

zentrationen in ihren Auftretungsmustern. Sowohl fur den

Communicated by T. Gottschalk.

Electronic supplementary material The online version of thisarticle (doi:10.1007/s10336-011-0803-1) contains supplementarymaterial, which is available to authorized users.

S. M. Simaiakis (&) � M. Dretakis � C. Barboutis �S. Xirouchakis

Natural History Museum of Crete, University of Crete,

Knossos Av., P.O. Box 2208, 714 09 Heraklion, Crete, Greece

e-mail: simaiakis@biology.uoc.gr

Present Address:S. M. Simaiakis

Natural History Museum of Crete, University of Crete,

Knossos Av., P.O. Box 2208, 714 09 Heraklion, Crete, Greece

S. M. Simaiakis

Department of Biological Sciences, University of Cyprus,

New Campus, P.O. Box 20537, 1678 Nicosia, Cyprus

T. Katritis � D. Portolou

Hellenic Ornithological Society, Kastritsiou 8,

546 23 Thessaloniki, Greece

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DOI 10.1007/s10336-011-0803-1

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Landvogelartenreichtum der Agaischen Inseln insgesamt,

als auch fur den der meisten Insel-Untergruppen konnten

signifikante AAB identifiziert werden. 79% der Varianz im

Artenreichtum wurde uber die Oberflache der verfugbaren

Agaisinseln erklart und der Gesamt-z-Wert lag bei 0.305,

was generell einen hohen Isolationsgrad der Inseln nahe-

legt. Die z-Werte der doppelt logarithmischen Arten-Areal-

Regression variierten signifikant uber die Inselgruppen und

reichten von 0.100 bis 0.329. Wir fanden heraus, dass die

Steigung der Arten-Areal-Kurve steiler war, als die terrest-

rischer Evertebraten (d.h. Tausendfusser, Schwarzkafer).

Die Landvogelfauna der agaischen Inseln zeigte Konzent-

rationen im Auftreten, wahrend Kreta und seine Satelliten-

inseln die Inselgruppe mit der geringsten Konzentrierung

war. Insektivore und granivore Vogelarten trugen

unterschiedlich zu den Landvogelgemeinschaften bei,

wobei erstere verlasslicher ein Konzentration in ihrem

Auftreten zeigten als letztere. In den meisten Fallen war

der Rang an Brutvogelarten, bestimmt durch das Maß der

Konzentrierung, negativ mit der Inselflache und/oder der

Maximalhohe uber Null korreliert.

Introduction

The Mediterranean basin shows a wide range of habitats

(e.g., maquis and phrygana formations) determined by

climatic features and modified by human activities

(Margaris 1981; Rackham and Moody 1997; Blondel and

Aronson 1999). Palaeogeographic events contributed to the

progressive fragmentation of coastal landscapes of Greece

(Dermitzakis and Papanikolaou 1981; Anastasakis and

Dermitzakis 1990; Dermitzakis 1990) into the present-day

landbridge islands of the Aegean archipelago. Researchers

have shown that the species communities on the Aegean

islands have been shaped not only by the geotectonic his-

tory of the area (e.g., Beerli et al. 1996; Douris et al. 1998;

Trichas et al. 2008) but also through more recent eustatic

sea level changes (e.g., Bittkau and Comes 2005). More-

over, humans have modified the natural ecosystems

resulting in increased fragmentation of habitats.

The Aegean archipelago is characterized by high envi-

ronmental and topographical heterogeneity (Dafis et al.

1996; Blondel et al. 2010), long-term isolation of many

islands (Triantis et al. 2008), high levels of species diver-

sity, high percentage of endemism (Sfenthourakis and

Legakis 2001), and a complex geological and geographic

history (Anastasakis and Dermitzakis 1990). It comprises

floral and faunal species with different biogeographic

affinities originating from Asia, Europe, and Africa

(Triantis et al. 2008). Numerous biogeographic studies on

vertebrate and invertebrate terrestrial taxa (Foufopoulos

and Ives 1999; Sfenthourakis et al. 1999; Dennis et al.

2000; Parmakelis et al. 2006; Triantis et al. 2008) have

contributed significantly to the investigation of the evolu-

tionary history of the area. However, there are many dis-

crepancies among them due to taxon-orientated biological

attributes (see Parmakelis et al. 2006). Consequently, more

thorough studies are needed for a number of unexplored

taxonomic groups (e.g., land birds), and that makes the

Aegean archipelago an excellent geographic region for

studying biogeographic patterns.

Despite the high ornithological value (i.e., numerous

islands, heterogeneity of habitats, idiosyncratic island his-

tories) of the Mediterranean basin (Covas and Blondel

1998), studies of avian ecology in the region generally, and

Greece especially, are relatively few (e.g., Sgardelis and

Margaris 1992; Katsimanis et al. 2006) when compared to

studies of other taxa and their distribution (Sfenthourakis

1996; Panitsa et al. 2006). Nevertheless, Watson (1964),

based on three scientific excursions from 1954 to 1961,

presented a monograph on the distribution, habitat prefer-

ences, and systematics of the land birds of the Aegean

archipelago and discussed the effects of area, habitat

diversity, and geological history on bird assemblages. He

also attempted to enrich the knowledge of breeding passe-

rines in the Aegean islands, to determine the origin of the

avifauna, and to detect factors that influence passerine

distribution. Although Watson (1964) included a large

number of islands in his dissertation, breeding passerines

were occasionally not determined precisely due to scattered

visits on many islands over a long period of time. Moreover,

the total insular avifauna was not treated as a unit or as part

of smaller island subsets (e.g., the Cyclades island group),

small islands (less than 5 km2) were excluded from species–

area relationship (SAR) analyses, and most islets lying off

the coast of large islands were not studied, underestimating

the species richness of the region (e.g., Crete).

This research aimed to improve our understanding of the

biogeography of the Aegean islands by focusing on the

patterns or mechanisms that underlie land bird species

distributions. We selected breeding land birds because (1)

the majority of species have similar ecological require-

ments, (2) many species are quite philopatric and are related

to particular island sites for breeding (Watson 1964), (3)

species mostly depend on the islands for feeding, and (4)

due to their small size, most species have relatively low

dispersal ability. Therefore, breeding land birds are a group

of great interest in biogeography.

This is the first time that we have indexed a large dataset

of land birds coming from numerous scientific sources (e.g.,

the recent catalogue of the Hellenic Ornithological Society,

see ‘‘Methods’’). Furthermore, the total insular avifauna has

been treated as a unit in order to correct previous scientific

inconsistencies and reveal patterns that land birds present in

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this area. To address this challenge, we used modern

methodological approaches (for further details, see

‘‘Methods’’), and we tried to answer three critical issues in

relevance to biogeographic theory and community ecology.

1. We wanted to know if the land bird fauna shows

biogeographic relationships relevant to the geological

history of the Aegean archipelago. To achieve this

goal, we investigated the faunal similarity within and

between island groups, and we explained clusters of

islands with respect to the geography and the palae-

ogeography of the Aegean region (for further discus-

sion, see Dermitzakis and Papanikolaou 1981;

Dermitzakis 1990; Anastasakis and Dermitzakis 1990).

2. There are currently many candidate models to describe

the species–area relationship (Tjørve 2009 for review).

We used the logarithmically transformed equation of

the power model S = c Az (see Arrhenius 1921), where

S is the number of species, A is the surface area (km2),

and z and c are model parameters. The power model,

proposed by Arrhenius (1921), is the most frequently

applied, mainly due to the fact that it consists of

parameters with biological meaning (see Brown and

Lomolino 1998). Parameter c reflects the patterns of the

species richness in the study area and varies with taxon,

climate, and biogeographical region (MacArthur and

Wilson 1967; Whittaker and Fernandez-Palacios 2007),

whereas z is the slope of the straight line reflecting the

degree of isolation for each island group (MacArthur

and Wilson 1967; Connor and McCoy 1979). Accord-

ing to their predictions, the slope of the species–area

curve would be higher for distant or isolated archipel-

agoes (MacArthur and Wilson 1967). In addition, a low

slope means that there is less sensitivity to island area

than for a group of islands of high slope (Whittaker and

Fernandez-Palacios 2007). To search these assump-

tions, we calculated regression slopes (z values) and

intercepts (c values) for land birds and we compared

slopes with other taxa from the same region.

3. In natural ecosystems, species assemblages among true

islands often show a nested pattern (Lomolino et al.

2006) in which biotas of islands with low species

richness are nonrandom subsets of biotas of richer sites

(Patterson and Atmar 2000). In a nested geographic

system, isolates are ranked in order of decreasing

species richness and species are sorted in order of

decreasing occurrence with some deviations from

perfect nestedness (e.g., unexpected presences or

absences) (Patterson and Atmar 1986). Regarding the

biology of land birds and the history of the Aegean

islands, what does a nested assemblage imply about the

evolutionary and ecological processes (e.g., immigra-

tion, extinction) generating this pattern? A substantial

fraction of land bird species are singletons (rare species

only known from a single island). How can singletons

affect nestedness? Moreover, to figure out the causality

of nestedness we investigated the effect of area,

elevation, and degree of isolation in the study islands.

We also analyzed the insectivores and seedeaters guilds

to detect idiosyncratic similarities or differences and

look for characteristic species assemblages.

Methods

Study area

Data sources and summary geographic data for the Aegean

area are given in Fig. 1 and Table 1. The total insular

avifauna has been divided into four separate geographic

sectors according to the geography and the palaeogeo-

graphic history of the Aegean region: (1) North Aegean

island group (NA), with Lesvos being the largest out of 12

islands, (2) Crete and its satellite islets (CR), consisting of

19 islands, with Crete being the largest, (3) Cyclades island

group (CY), with Naxos being the largest out of 27 islands,

and (4) Dodecanese island group (DO), with 17 islands,

with Rhodes being the largest (see Table 1).

Sources of data

Island features (e.g., size, elevation, distance from main-

land) were calculated using the ESRI ArcGis Desktop

(Redlands, CA, USA) and the Google Earth platform. We

used the presence/absence of breeding land bird species

occurring on the 77 islands rather than island population

size. We determined the current distribution of land birds

of the Aegean islands from the existing literature (Watson

1964; Spinthakis et al. 1993; Papakonstantinou et al. 1999;

Handrinos and Akriotis 1997) and the Standard Data Forms

of the updated inventory of the important bird areas (IBAs)

of Greece (HOS 2010). This dataset was further refined by

mining the databases of the Hellenic Ornithological Soci-

ety (HOS) and the Natural History Museum of Crete

(NHMC) for bird records from field expeditions carried out

in the Aegean archipelago during the last two decades and

by evaluating all unpublished reports. Relevant information

from the latest edition of the Greek Red Data Book of

threatened animals (Legakis and Maragkou 2009) and the

Fauna Europaea (v.2.2, 2010) were also included. In total,

we constructed a checklist of 102 breeding land bird spe-

cies distributed throughout 77 Aegean islands (Appendix 1

in Supplementary 1 v1). Moreover, we studied the species

composition of the insectivores and seedeaters guilds (see

also Appendix 1 in Supplementary 1 v1).

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Fig. 1 Study area and

distribution of 77 examined

islands of the Aegean

archipelago. 1–12 North Aegean

island group (NA), 14–40Cyclades island group (CY),

42–58 Dodecanese island group

(DO), 59–77 Crete and its

satellite islets (CR). 1 Thasos,

2 Samothraki, 3 Limnos, 4 Agios

Efstratios, 5 Lesvos, 6 Skyros,

7 Chios, 8 Psara, 9 Antipsara,

10 Samos, 11 Ikaria, 12 Fournoi,

13 Kythira, 14 Astypalaia,

15 Andros, 16 Tinos, 17 Syros,

18 Mykonos, 19 Kea,

20 Kythnos, 21 Serifos,

22 Sifnos, 23 Milos, 24 Paros,

25 Naxos, 26 Amorgos, 27 Ios,

28 Sikinos, 29 Folegandros,

30 Thira, 31 Anafi, 32 Antimilos,

33 Polyaigos, 34 Antiparos,

35 Donousa, 36 Hrakleia, 37 Ano

Koufonisi, 38 Schoinousa,

39 Kato Koufonisi, 40 Keros,

41 Antikythira, 42 Leipsoi,

43 Leros, 44 Kalymnos,

45 Telendos, 46 Kalolimnos,

47 Kinaros, 48 Levitha,

49 Patmos, 50 Kos, 51 Nysiros,

52 Tilos, 53 Symi, 54 Chalki,

55 Rhodes, 56 Saria,

57 Karpathos, 58 Kasos,

59 Crete, 60 Agria Gramvousa,

61 Imeri Gramvousa,

62 Pontikonisi, 63 Elafonisi,

64 Kolokytha, 65 Chrysi,

66 Agioi Theodoroi, 67 Gavdos,

68 Gavdopoula, 69 Paximadi,

70 Dia, 71 Elasa, 72 Dragonada,

73 Gianisada, 74 Paximada,

75 Kavalli N, 76 Kavalli S,

77 Koufonisi Crete

Table 1 The identity of the Aegean islands and the smaller island groups (geographic position as in Fig. 1)

Island

group

n Ar (km2) Alt (m) Dm (km) Di (km) Sp

AE 77 0.004–8,264 (237.1 ± 965.8) 19–2,456 (513.6 ± 426.6) 0.1–147.0 (51.6 ± 47.2) 0.05–106.7 (15.1 ± 19.6) 2–81

NA 12 4.498–1,632 (380.5 ± 465.1) 134–1,611 (857.6 ± 474.2) 1.5–86.7 (38.4 ± 27.9) 1.5–61.5 (21.9 ± 20.1) 12–81

CR 19 0.004–8,264 (438.3 ± 1,895.2) 19–2,456 (238.3 ± 543.4) 0.1–95.0 (12.7 ± 22.1) 0.1–95.0 (10.2 ± 22.1) 2–66

CY 27 3.898–430 (94.6 ± 106.0) 118–1,001 (526.6 ± 237.7) 11–146.5 (96.8 ± 43.1) 0.4–106.7 (16.8 ± 21.7) 11–35

DO 17 1.912–1,407 (147.5 ± 336.9) 116–1,216 (566.2 ± 320.2) 4.5–85.2 (35.9 ± 27.0) 0.05–45.6 (12.3 ± 11.5) 13–42

AE Aegean islands (1–77), CR Crete and satellite islets (59–77), CY Cyclades islands (14–40), DO Dodecanese (42–58), NA North Aegean

islands (1–12). n number of islands, Ar range of area, Alt range of altitude, Dm range of the distance to the closest mainland, Di range of the

distance to the closest larger island or mainland, Sp range of species richness. Mean value and standard deviation is given in brackets. Due to

uncertain biogeographic affinities Kythira (n. 13) and Antikythira (n. 41) were not included in any of the aforementioned subgroups

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Data analysis

Faunal similarity

A binary matrix was created for the land bird species

occurring on each island. Phi’s similarity coefficient was

used to investigate faunal similarity among islands. Phi’s

euclidean coefficient of association is a non-metric formula

(range -1.0 to 1.0) and is not influenced by frequency of

occurrence (Jackson et al. 1989). Multivariate analyses

were conducted using NTSYS numerical taxonomy pack-

age (Rohlf 1993). We used the unweighted pair group

method with arithmetic mean (UPGMA) to construct

dendrograms (Sneath and Sokal 1973). It is a simple

agglomerative clustering technique for the creation of

phenograms.

Species-area relationship (SAR)

We applied the commonly used power model, log S = log

c ? z log A (Arrhenius 1921; Preston 1962), where S is the

species richness (number of species in a given sample), A is

the sample area, z is the slope of the line, and c is the

intercept. We made all regression tests with Statistica 6

(StatSoft 2001). For the comparison of slopes (z value) and

intercepts (c), we followed the basic statistical tests pro-

posed by Gould (1979) and Zar (2009).

Measure of nestedness

We used the nestedness metric based on overlap and

decreasing fill, hereafter NODF to measure the total pres-

ence-absence matrix nestedness (Almeida-Neto et al.

2008). NODF is well suited to check separately nestedness

between islands (Nrow) or species (Ncolumn). We used the

ANINHADO C?? program (see Guimaraes and Guimar-

aes 2006 for review) to compute the degree of nestedness.

Nestedness causality was explored based on the rank of

islands produced by NODF and its correlation with certain

parameters such as area, altitude range, distance to the

closest mainland, and distance to the nearest larger island

(see Appendix 2 in Supplementary 2 v1). We carefully

addressed singletons (species only known from a single

island) that are often considered to be evenly dispersed

between islands. We used the software package R 2.8.0

(R Development Core Team 2008) to calculate the Pearson

product-moment correlation coefficients and checked for

any colinearity effect among independent variables by

using VIF (variation inflation factor). In all other tests, we

used SPSS v.15 (SPSS, 1989–2006). Measurements are

presented as mean ± standard deviation.

Results

Species richness and faunal similarity

The study area consisted of 77 islands supporting 102 land

bird species, belonging to 60 genera (Fig. 1; Appendix 1 in

Supplementary 1 v1). Concerning each individual island

group, North Aegean islands support 91 species belonging

to 56 genera, of which 15 are singletons (16%). The

Cyclades islands support 48 species belonging to 30 gen-

era, of which 11 are singletons (23%). Dodecanese islands

have 61 species belonging to 39 genera, of which 17 are

singletons (28%). Crete and its surrounding islands have 66

species belonging to 41 genera, of which 53 are singletons

(80%) (see Appendix 1 in Supplementary 1 v1).

The dendrogram revealed two well-defined island

groups: (1) all satellite islands of Crete (18 islands), and

(2) the rest of the Aegean islands (59 islands) (Fig. 2). The

second group can be split into three subgroups: (1) the

northern Aegean islands of Thasos and Samothraki, (2)

three large islands of the eastern Aegean (Lesvos, Samos,

Kos), and (3) mostly the Cyclades and the Dodecanese

islands. This latter group can be further split into three

smaller subgroups: (1) most of the larger Cyclades islands,

(2) most of the Dodecanese islands, and (3) the smaller

Cyclades islands (Fig. 2).

SARs: comparison of slopes and intercepts

The Arrhenius model in its logarithmic form showed that

the area of the 77 Aegean islands explained 79% of the

variance in species richness. Moreover, we calculated a

slope of 0.305 for the land birds of the Aegean islands

(Table 2). For the four main island subgroups, the

respective z values were: (1) 0.329 for the north Aegean

islands, (2) 0.215 for Crete and its satellite islets, (3) 0.257

for the Cyclades islands, and (4) 0.100 for Dodecanese

islands (see Table 2).

Before examining the z values of the power regression

lines for differences, we checked for differences in inter-

cepts (c). However, there was no case where the intercepts

showed statistically significant differences among the four

principal island groups (Table 3). In addition, we com-

pared intercepts c among the four subsets of the islands

only when the z values showed no statistical difference.

The regression slope of the Cretan islands was significantly

lower from that of the north Aegean islands and the Cyc-

lades islands, but significantly higher than that of Dodec-

anese island group (Table 3). In contrast, there were no

significant differences between the z values of the Cyclades

and the Dodecanese islands or between the north Aegean

islands and that of the Cyclades islands and Dodecanese

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islands (Table 3). Due to statistically indistinguishable

slopes, the Dodecanese islands showed a higher intercept

C than that of the Cyclades islands and north Aegean

islands (Tables 4, 5).

Nestedness

The entire community of land birds showed a significantly

nested pattern (NODF = 73.2, P \ 0.05) (Table 4). Apart

from the north Aegean islands, NODF showed that entire

matrices were less nested than those without singletons

(Table 4). The distribution of land birds in the Cyclades

islands and the north Aegean island group showed more

Fig. 2 UPGMA tree based on the similarity matrix obtained by

applying Phi’s index to the binary data matrix. The number of land

bird species on each island is given in parentheses. Black arrows

show the three largest islands (Crete, Lesvos, Rhodes) of the study

area. Black dots indicate the three islands with the highest species

richness (Lesvos, Crete, Samos)

Table 2 Results of least squares linear regressions for all island

groups and regression models discussed in the text

Island groups C z R2 P

AE (77) 0.754 0.305 0.789 \0.001

NA (12) 0.786 0.329 0.835 \0.001

CR (19) 0.616 0.215 0.666 \0.001

CY (27) 0.856 0.257 0.814 \0.001

DO (17) 1.161 0.100 0.271 \0.05

AE Aegean islands, CR Crete and satellite islets, CY Cyclades islands,

DO Dodecanese, NA North Aegean islands. C intercept of the island

range, z slope of island range, R2 the maximum variance explained,

P values of the regression. The number of islands in each group is

given in parentheses

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nested assemblages than Crete and Dodecanese. Crete with

its satellite islands showed the lowest NODF value with the

highest increase when singletons where excluded from the

analysis. The degree of nestedness between the islands of

the north Aegean, the Cyclades, and Dodecanese was

higher than the Cretan island group.

Insectivores and seedeaters across the Aegean islands

were strongly nested according to NODF (Table 5).

Insectivores showed slightly higher degrees of nestedness

than seedeaters in the Aegean islands. When we separately

calculated the degree of nestedness between insectivores

and seedeaters for the four island subgroups, insectivores

were less nested in the north Aegean islands, Crete, and

Dodecanese islands (Table 5).

Regarding the causality of nestedness, the pearson

product-moment coefficient indicated that the island order,

as determined by NODF metric for all the 77 Aegean

islands, was strongly correlated with the logarithm of area

Table 3 Test for difference in

regression coefficients (z slope

and intercept C) among the four

island subgroups

CR Crete and satellite islets,

CY the Cyclades, DO the

Dodecanese, NA north Aegean

islands. P \ 0.05 represents

significant difference

Island groups t test for slope z P t test for intercept C P

NA—CR t = 3.470 [ t0.05(2),27 = 2.052 \0.05 t = 0.750 \ t0.05(2),28 = 2.048 [0.05

NA—CY t = 1.295 \ t0.05(2),35 = 2.030 [0.05 t = 1.277 \ t0.05(2),36 = 2.028 [0.05

NA—DO t = 0.710 \ t0.05(2),25 = 2.060 [0.05 t = 1.381 \ t0.05(2),26 = 2.056 [0.05

CR—CY t = 4.862 [ t0.05(2),42 = 2.018 \0.05 t = 1.470 \ t0.05(2),43 = 2.017 [0.05

CR—DO t = 3.526 [ t0.05(2),32 = 2.037 \0.05 t = 0.426 \ t0.05(2),33 = 2.035 [0.05

CY—DO t = 0.016 \ t0.05(2),40 = 2.021 [0.05 t = 0.947 \ t0.05(2),41 = 2.020 [0.05

Table 4 Measure of nestedness for the Aegean islands and all four smaller Island groups

Matrix NODF Er P(Er) Ce P(Ce) S n

AE 73.19 20.90 \0.001 32.07 \0.001 102 77

AEsing 75.47 25.12 \0.001 36.81 \0.001 83 77

NA 76.80 42.72 \0.001 52.21 \0.001 91 12

NAsing 75.16 55.92 \0.001 63.79 \0.001 76 12

CR 37.51 12.56 \0.001 25.58 \0.001 66 19

CRsing 72.18 36.60 \0.001 46.90 \0.001 13 19

CY 76.32 43.25 \0.001 54.67 \0.001 49 27

CYsing 82.01 53.38 \0.001 64.30 \0.001 38 27

DO 66.06 37.42 \0.001 46.96 \0.001 61 17

DOsing 72.49 47.91 \0.001 57.72 \0.001 44 17

AE Aegean islands, NA north Aegean islands, CR Crete and its satellite islands, CY Cyclades islands, DO Dodecanese islands, sing without

singletons

NODF total matrix nestedness, Er nestedness of null model where presences are randomly assigned to any cell within the matrix, P(Er)

significance of NODF based on this null model, Ce nestedness of null model where the probability of a cell aij show a presence is (Pi/C ? Pj/R)/

2, in which Pi is the number of presences in the row i, Pj is the number of presences in the column j, C is the number of columns and R is the

number of rows, P(Ce) significance of NODF based on this null model, S species richness, In number of islands, sign without singletons

Table 5 Measure of nestedness

for insectivores and seedeaters

across the Aegean islands

Abbreviations follow Table 4

Matrix NODF Er P(Er) Ce P(Ce) S n

Insectivores AE 80.49 22.65 \0.001 35.45 \0.001 35 71

Insectivores NA 78.66 43.76 \0.001 53.50 \0.001 30 12

Insectivores CR 41.07 15.89 \0.001 28.39 \0.05 26 13

Insectivores CY 81.31 44.07 \0.001 55.60 \0.001 16 27

Insectivores DO 70.19 34.17 \0.001 44.05 \0.001 23 17

Seedeaters AE 77.00 32.40 \0.001 44.22 \0.001 24 76

Seedeaters NA 83.71 52.94 \0.001 61.65 \0.001 22 12

Seedeaters CR 51.62 14.96 \0.001 27.20 \0.001 19 18

Seedeaters CY 70.27 55.74 \0.001 64.58 \0.05 15 27

Seedeaters DO 74.55 51.97 \0.001 61.44 \0.001 15 17

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(r = -0.88) and the altitudinal range (r = -0.76;

Table 6). All other variables were not correlated with

island rank. In contrast, for the north Aegean islands, the

island order was negatively correlated with altitudinal

range (r = -0.78; Table 6). In the Cyclades group, the

island position was negatively correlated with the loga-

rithm of area (r = -0.84; see Table 6). For Crete and its

satellite islands, there was no variable correlated to island

rank. In the Dodecanese islands, distance to nearest

mainland was positively associated with the rank of islands

(r = 0.73; see Table 6).

Discussion

Faunal similarity and biogeographic patterns

The cluster analysis separated clearly the small islets around

Crete and the rest of the Aegean islands. This occurs

because all islets harbor specific taxa such as Alectoris

chukar, wild Columba livia, Corvus corax, Motacilla alba,

Monticola solitarius, and Sylvia melanocephala, as well as

due to the striking absence of many other species found on

small islands with similar phryganic ecosystems further

north (e.g., Carduelis cannabina, Emberiza caesia,

Galerida cristata). In the eastern region, almost all the

Dodecanese islands were linked together at higher simi-

larity values than the Cyclades islands (Fig. 2). This pattern

is caused by land bird species of the genera Acrocepha-

lus, Anthus, Cercothrichas, Certhia, Cisticola, Clamator,

Coracias, Garrulus, Merops, Muscicapa, Phoenicurus,

Pica, Poecile, and Upupa, occurring in the Dodecanese but

not in the Cyclades islands. In contrast, species from the

genera Alauda, Cuculus, Oriolus, Petronia, and Serinus

were found to breed and forage in the Cyclades islands but

not in the Dodecanese. In the north Aegean, Thasos, and

Samothraki offer a variety of habitats suitable for breeding

and foraging. Thus, Dendrocopus syriacus, Monticola

saxatilis, Phoenicurus ochruros, Sylvia atricapilla, and

Tichodroma muraria breed in the two aforementioned

islands but not in the southern islands (Fig. 3).

SARs and comparison of slopes and intercepts

The significant correlation detected between species rich-

ness and area (logarithmic power model), generally fits

within the range of species–area relationships for island

groups (Connor and McCoy 1979). However, this finding

disagrees with the demonstration that z is lower for tem-

perate archipelagoes than for tropical archipelagoes

(Schoener 1976). When we amassed the data to plot the

species–area curves of the Aegean land birds on the four

island groups, apart from the Dodecanese, all slopes ranged

from 0.215 to 0.329, similar to values estimated in studies

of several island archipelagoes (Diamond and May 1977;

Wilcox 1978; Ricklefs and Bermingham 2004; Begon et al.

2006). Slope range was also congruent with Rosenzweig’s

(1995) typical z values for islands.

In general, the slopes (z values) of the power model

suggest a remarkable degree of island isolation for each

island group. With the exception of Crete and its adjacent

islets, the evidence suggests that the majority of the island

subgroups were relatively recently formed (Perissoratis and

Conispoliatis 2003). Besides the recent formation of the

north Aegean islands and the Cyclades islands (Dermitza-

kis and Papanikolaou 1981; Dermitzakis 1990), both can be

characterized as the most distant island clusters (highest

mean distance from the nearest mainland and highest mean

distance from the larger nearest islands) (see Table 1). This

could also explain the higher z values compared to the rest

of the island groups. Conversely, lower values are typical

for the less distant islands in the southernmost Aegean

region. Thus, the relatively low z values in Dodecanese

could be attributed to the recent formation of the island

group (Perissoratis and Conispoliatis 2003). Here, the

Dodecanese islands behave as part of a continuous land

mass (i.e., Anatolia peninsula) with high numbers of land

bird species independent of island size. This pattern agrees

with the tenebrionid beetles in the south Aegean region

(Trichas et al. 2008). Moreover, the Dodecanese islands

have the highest intercept (c) compared to the other sub-

groups. This is in accordance with the aspect that less

isolated islands should retain higher immigration rates that

Table 6 Correlation (Pearson product-moment correlation coeffi-

cient—r) between the rank of islands after packing to maximal

nestedness using NODF and island order based on particular features

of all 77 islands (AE) as well as of 12 north Aegean islands (NA), 19

Cretan islands (CR), 27 Cyclades islands (CY), and 17 Dodecanese

islands (DO)

r AE r NA r CR r CY r DO

Rank and log(area) -0.881** – – -0.838** n.s.

Rank and alt -0.755* -0.781* n.s. n.s. n.s.

Rank and distm n.s. - n.s. n.s. 0.733*

Rank and disti n.s. n.s. – n.s. n.s.

Island features include area, altitudinal range (alt), distance from closest mainland (distm), and distance from nearest larger island (disti)

* P \ 0.05, ** P \ 0.001, n.s. non significant, dash excluded correlation values due to significant colinearity of independent variables

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depend on the dispersal ability (Wilcox 1978), and there-

fore higher diversities (see also Rosenzweig 1995).

In comparison to other taxonomic groups, the slope

(z value) of the species–area regression of terrestrial iso-

pods of the central Aegean islands was lower (z = 0.23)

(Sfenthourakis 1996) than that of land birds. The same

pattern was seen in centipedes of the Aegean islands

(z = 0.12) Simaiakis et al. (2012), as well as in land snails

of the central Aegean islands (z = 0.27) (Mylonas 1982).

Regarding tenebrionid beetles of the Aegean region, the

slope of the species–area relationship according to Trichas

et al. (2008) was 0.28, or 0.26 as proposed by Fattorini

(2002), but still lower than the z value for land birds in the

same broad region. The land birds and reptiles in the

Aegean islands show the greatest slopes of the power

regression model, 0.30 and 0.32, respectively. Though this

relatively high z value is in contrast with the low degree of

isolation of the Aegean islands, it agrees with the territorial

character of land birds and their relatively low dispersal

ability (Watson 1964), and the trophic–rank theory, where

species high up in the food web can cause higher z values

(Holt et al. 1999).

Fig. 3 Species–area regression curves. AE Aegean islands, CR Cretan islands, CY the Cyclades islands, DO the Dodecanese islands, NA north

Aegean islands. The number of islands on each geographic region is given in parentheses

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Nestedness

Islands have often been found to exhibit highly nested set

of species assemblages (Fischer and Lindenmayer 2002).

NODF metric found a high degree of nestedness for the

land birds of all the 77 Aegean islands (see Table 4). The

large number of singletons in Crete might explain the low

degree of nestedness. The paradigm of Crete has been

described by Almeida-Neto et al. (2008) as ‘‘nested pattern

minimally filled’’, in which there is only one fully filled

row (Crete) and numerous fully filled columns (land bird

species such as Motacilla alba, Columba livia, and Mon-

ticola solitarius). For the Dodecanese islands, the prox-

imity to Turkey and the recent geological formation

(Perissoratis and Conispoliatis 2003) result in higher

disorder, because colonization by particular species (e.g.,

Oenanthe oenanthe, Sylvia cantillans, Sylvia atricapilla,

Lanius collurio, Emberiza hortulana, Upupa epops) seems

to be a stochastic process compared to more distant island

groups.

When we excluded singletons, all subgroups except the

north Aegean islands were more nested. In most island

assemblages, singletons do not significantly decrease

nestedness because land bird species with single presence

tend to occur on higher ranked islands (see Appendix 1 in

Supplementary 1 v1). Instead of this, unexpected land bird

singletons (e.g., Prunella collaris and Pyrrhocorax pyr-

rhocorax) tend to occur on medium ranked islands, such as

Samothraki and Chios in the northernmost Aegean islands

(see Appendix 1 in Supplementary 1 v1). Whether or not

singletons are excluded, the Cyclades islands and the north

Aegean islands showed the highest degree of nestedness

(Table 4), and this pattern fits with the remote character of

these two groups. Both aforementioned geographic subdi-

visions showed the highest mean distance from the closest

mainland and the highest mean distance from the nearest

larger island, respectively (see Table 1). Hence, the

movement of land birds from nearby continents to the north

Aegean islands or the Cyclades islands, and vice versa,

may be more limited than that in the Cretan and Dodeca-

nese islands. Abbott (1978) stressed the idea that a stretch

of water could be a barrier or a filter to the dispersal of land

birds to islands.

Regarding nestedness, there are congruencies and dif-

ferences between the two major land bird guilds, namely

insectivores and seedeaters. Both insectivores and seed-

eaters showed a considerable degree of nestedness (see

Table 5). Matrices remained highly ordered with signifi-

cant nested patterns in all island groups, with the exception

of Crete. Overall, while it is suggested that the effect of

species exchange between any adjacent continental region

(pool of species) and the islands tends to weaken the effect

of extinction in producing a nested structure (Wright et al.

1998), this does not agree with the present study. Insecti-

vores and seedeaters proved to be less vagile than expec-

ted, provoking a kind of faunal relaxation in several island

sectors (e.g., the north Aegean islands and the Cyclades

islands) and showing a considerable degree of nestedness.

The Aegean islands have varied in size, elevation, and

proximity since isolation from the two distinct continental

areas (the Balkan peninsula and the Anatolian peninsula),

and present an ideal study area to detect factors that affect

faunal composition (see Foufopoulos and Mayer 2007) (see

also Table 1). Our results showed that for the Aegean

islands the higher the altitudinal range, the richer the island

land bird fauna, and the greater the island surface, the

higher the species richness. As long as elevation can be

viewed as a metric of island size, larger and higher islands

are first in sight from a distance and provide a larger variety

of environmental heterogeneity (Foufopoulos and Mayer

2007). A similar pattern has been observed in the study of

Watson (1964). In regard to the importance of vegetation

structural complexity, Watson (1964) pointed out for the

first time the importance of habitat heterogeneity in

determining avian diversity on the Aegean islands (e.g.,

islands with more complex vegetation harbor more spe-

cies). Hence, in consensus with Watson (1964), there is a

rationale why area and altitude were detected to explain

nested patterns on three out of the four main island groups

studied. Particularly, the area significantly explained nested

patterns in the Cyclades islands. With regard to the cause

of nestedness within the north Aegean islands, only ele-

vation could explain the order in which islands were ranked

by NODF. Regarding the Dodecanese islands, many

islands have been separated from Asia Minor no longer

than 21,000 years (Perissoratis and Conispoliatis 2003).

Fattorini (2002) suggested that the south-eastern islands

(Dodecanese) behave as parts of the Anatolia landmass.

This could explain why the distance to the nearest main-

land identified as the only factor to affect nestedness pat-

tern and support the high numbers of land bird species in

the Dodecanese compared to the other island assemblages.

Unsurprisingly, therefore, the further the distance to the

closest mainland (i.e., Turkey), the lower species richness

on an island.

Although area could explain nonrandom patterns in land

birds, this was not the case for several invertebrate biotas

across the Aegean islands (results not shown) (Sfentho-

urakis et al. 1999; Triantis and Mylonas 2009; Simaiakis

and Martınez-Morales 2010). For the Cyclades islands,

where adequate data were available to calculate nestedness,

terrestrial isopods, land snails, and centipedes showed

considerable similarities in the degree of nestedness, even

though different reasons may account for the causality of

nestedness (for further details, see Hausdorf and Hennig

2005; Simaiakis and Martınez-Morales 2010). Nested

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assemblages of isopods, land snails, and centipedes were

better explained by distance from continental Greece and by

absolute shorter distance from the mainland, and by dis-

tance to the closest continent (degree of isolation), respec-

tively (Sfenthourakis et al. 1999; Simaiakis and Martınez-

Morales 2010). With respect to the ground beetle fauna

from the Cyclades islands, Trichas et al. (2008) found

evidence that nestedness was significantly explained by the

palaeogeography of the area and the degree of isolation.

In conclusion, the results of the biogeographic study

suggest that certain northeastern Aegean islands (e.g.,

Thasos, Samothraki, Lesvos, Samos, Kos), due to their

geographic affinities with major continents (e.g., south-

eastern Europe and Turkey), and their high environmental

heterogeneity, retain idiosyncratic land bird assemblages

compared to southernmost islands. With a few exceptions,

the number of land bird species is better described by the

species–area relationship, whereas the power model

explains the variation of species richness compared to area.

Although we were not able to detect a common factor to

infer causality of nestedness in every group of islands, we

found that area and elevation were mainly related to the

ranking of islands. Here, land birds, both seedeaters and

insectivores, have been identified as an informative taxon

to study biogeographic patterns in the Aegean islands. But

still, there is much work to be done in order to define

habitats based on the biology of the land birds and to

unravel their role in determining the species richness in

highly fragmented environments, such as the Aegean

archipelago with the numerous islands and islets.

Acknowledgments We thank our colleagues, S. Adamandopoulou,

H. Alivizatos, G. Andreou, S. Bourdakis, D. Bousbouras, A. Christidis,

M. Dimaki, T. Dimalexis, P. Dragoumis, A. Evangelidis, J. Fric,

M. Gaetlich, K. Gaganis, A. Galanaki, E. Galinou, Y. Gavalas,

B. Hallmann, Y. Ioannidis, E. Kakalis, N. Kardakari, G. Karris,

T. Kominos, P. Latsoudis, A. Manolopoulos, K. Misiakos,

M. Moschovis, M. Panagiotopoulou, N. Probonas, Y. Rousopoulos,

A. Sakoulis, V. Saravia Mullin, T. Skartsi, K. Stara, R. Tsiakiris,

Y. Tsougrakis, and S. Zogaris, who significantly contributed to the

study of the Important Bird Areas of Greece. We are grateful to

Alexandra Manousaki and Maria Plataki for their valuable contribution

to shape the primary dataset for land birds. We also thank Ian Henshaw

for his critical comments on the manuscript and all linguistic remarks.

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