Hydrobiologia 324 : 209-217, 1996 . 209 © 1996 Kluwer Academic Publishers . Printed in Belgium .

Distribution and associations of the aquatic of the Balearic Islands (Spain)

J. Garcia-Aviles l , M. A. Puig 2 & A. G. Soler 3 1 Centro de Investigacidn de Espacios Naturales Protegidos, C/San Sebastian 71, 28791 Soto del Real (Madrid), Spain 2 Centre d' Estudis Avancats, Cam( Sta. Barbara s/n, 17300 Blanes (Gerona), Spain 3 Departamento de Biologla y Ecologla, Facultad de Biologla, Universidad de Murcia, Campus de Espinardo, 30071 Murcia, Spain

Received 1 March 1995 ; in revised form 18 October 1995 ; accepted 6 December 1995

Key words : Heteroptera, distribution, associations, Balearic Islands

Abstract

Twenty-five species of aquatic Heteroptera were collected from the Balearic Islands . Five are first records ( nigrolineata, Micronecta scholtzi, Ranatra linearis, Notonecta meridionalis and Hebrus pusillus) . Previous records are also discussed. The spatial structure of the communities on the Islands is analysed . The different abundance of species and their characteristic habitats are identified. The species associations for each island are established through factorial analysis (correspondence analysis) ; a total of 8 associations are defined . They represent permanent habitats, with the exception of one, characteristic of seasonal ponds of Mallorca. Within the permanent lentic habitats, a clear difference occurs between artificial habitats ('albercas' : stone or cemented man-made irrigation ponds) and natural pond habitats .

Introduction Material and methods

The Heteroptera of the Balearic Islands are relative- A total of 246 sites (120 in Mallorca, 68 in Menorca, ly well known, with studies published since the last 41 in Ibiza and 17 in Formentera) were sampled in (Ramis, 1814 ; Bolfvar & Chicote, 1879 ; Moragues, winter (February and March 1988) and spring (May 1894) as well as in the present century (Saunders, 1901 ; and June 1988) (Garcfa-Avilt s, 1990) using a 30 cm Royer, 1906 ; Garcfas, 1907 ; Torre, 1911 ; S'anchez, square net with 100 ,am mesh size . Figure 1 shows the 1918 ; Eidmann, 1927 ; Villarrubia & Espanol, 1933 ; geographical location of the Balearic Islands ; Table Espanol, 1935 ; Tamanini, 1948, 1949 ; Palau, 1949 ; 1 provides a summary of the types of habitat of the Margalef, 1951, 1952, 1953 ; Bigot, 1958 ; Compte, sampling sites. 1960 ; Ribes, 1965, Compte, 1968 ; Tamanini, 1971 ; Specimens were identified using the keys of Ribes, 1977, 1978, 1984 ; Pons, 1987 ; Nieser & Tamanini (1979), Jansson (1986), Poisson (1957), Montes, 1988) . Macan (1976), Murillo (1985) and Milldn et al. (1987) . Yet, most deal only with single islands and do not In order to define species associations, a multi- discuss habitat preferences . In this study, we provide a ple correspondence factorial analysis, version SPAD .N synoptic information and describe species associations (Lebart et al ., 1987), was applied to each of the islands . and ecological preferences . In this analysis presence/absence data were used . Sta- tions lacking Heteroptera were not eliminated from the analysis.

210

Table 1 . Location and characteristics of the sampling sites

Habitat Sites Mallorca Menorca Ibiza Formentera

Stream 2, 3, 6, 7, 8, 9, 10, 11, 12, 125, 126, 132, 136, 137, 190, 191, 208, 209, 213, 237, 238, 239 . 14, 15, 26, 27, 28, 31, 34, 138, 139, 140, 142, 145, 216, 223. 36, 37, 38, 39, 62, 63, 65, 147, 148, 149, 151, 157, 66, 69, 72, 73, 81, 83, 84, 158, 159, 160, 161, 164, 85, 86, 88, 90, 92, 94, 100, 165, 167, 168, 171, 172, 103, 104, 105, 108, 109, 174, 175, 181, 182, 183, 111, 112, 119. 184, 186 . Pond 4, 13, 17, 18, 19, 20, 21, 121, 122, 124, 131, 134, 201, 207, 229 . 234, 240, 241, 243, 244, 22, 23, 24, 25, 47, 48, 50, 135, 141, 143, 144, 150, 246. 52, 53, 54, 55, 57, 58, 61, 152, 154, 155, 156, 162, 93, 116, 117 . 176, 178, 185 . 'Alberca' 16, 43, 51, 56, 59, 60, 67, 153, 166, 173, 188 . 189, 192, 195, 196, 197, 242. 71, 77, 78, 79, 80, 89, 95, 200, 203, 205, 210, 212, 96, 97, 99, 106, 110, 114, 214, 215, 217, 218, 219, 120 . 220, 221, 222 . Marsh 29, 30, 35, 40, 41, 42, 44, 123, 127, 128, 129, 130, 202, 226 . 230, 231, 232, 235, 236, 45, 46, 101 . 133, 146, 169, 177 . 245 . Spring 1, 5, 32, 33, 49, 64, 68, 163, 170, 179, 180, 187 . 193, 194, 198, 199, 204, 233 . 70, 76, 82, 87, 91, 98, 102, 206, 211, 224, 225, 227, 107, 113, 115, 118 . 228. Reservoir 74, 75 .

Table 2. Definitions of Abundance of each MENORC ;, species on each island

Abundance Proportion of sites from which recorded

Very abundant > 50% Abundant 30%-50% IBIZA Common 15%-29% Scarce 5%-14% Rare <5% 0 30 km (~ Very rare Only 1 site FORMENTERA

Figure 1 . Geographical location of the Balearic Islands

Based on the scores of the multiple correspondence analysis, a cluster of 20 fixed groups was formed for preferred habitats, and other factors are mentioned cases considered in each analysis . These were orga- below. nized into five classes in order to maximize objectivity. Corixa affinis Leach, 1817 Mallorca: Scarce (sites: 17, 20, 22, 23, 55, 57, 58, 61) . Species Menorca: Abundant (sites: 121, 124, 126, 130, 131, 132, 134, 135, 137, 138, 140, 141, 147, 150, 154, 155, A total of 25 species were captured, five of wich 156, 160, 161, 162, 172, 175, 176, 185, 186) . Ibiza : (Sigara nigrolineata, Micronecta scholtzi, Ranatra lin- Very rare (site : 197). earis, Notonecta meridionalis and Hebrus pusillus) In ponds and streams (with slow or almost no cur- are first records for the Islands . The species, islands, rent), usually with aquatic vegetation and fresh or recording sites, abundance on each island (Table 2), slightly brackish water. 21 1

Corixa panzeri (Fieber, 1848) Sigara stagnalis (Leach, 1817) Mallorca: Very rare (site: 89). Menorca: Common Menorca: Scarce (sites : 129, 130, 136, 139, 150, 176, (sites: 121, 124, 125, 131, 132, 135, 136, 137, 139, 182, 185). 140, 141, 154, 155, 175, 182, 183, 186) . First record Always in lentic habitats (marshes, ponds and the for Mallorca . mouths of streams), mainly in brackish water, with or In ponds and streams (with slow or almost no cur- without vegetation. rent), always with aquatic vegetation and fresh or Cited for Mallorca by Moragues (1894) and Bigot slightly brackish water. (1958). Because of the destruction or disappearance of recording habitats and a lack of subsequent records Parasigara perdubia (Rey, 1894) since then, its current presence is in need of confirma- Mallorca: Scarce (sites : 9, 16, 81, 91, 104, 105) . tion. Menorca: Scarce (sites : 137, 140, 159, 160, 161, 174, 183, 188) . First record for Mallorca . Micronecta scholtzi (Fieber, 1860) Mainly in streams with slow to moderate current, Mallorca : Rare (sites : 74, 75, 117) . Ibiza: Scarce (sites: with or without vegetation and fresh water . 192, 203, 210, 221, 222). New for the fauna of the Cited for Ibiza (Nieser & Montes, 1988) in a stream Balearic Islands. formed by the Broils d'es Bosquetell spring . During In great numbers in the Cuber and Gorg Blau reser- our study, this stream had completely dried up . voirs in Mallorca. In Ibiza, always in small numbers in 'albercas' with or without aquatic vegetation and fresh Sigara lateralis (Leach, 1817) or slightly brackish water. Mallorca : Scarce (sites : 17, 18, 19, 20, 23, 52, 53, 54, 55, 57, 58, 61, 79) . Menorca : Common (sites : 122, Naucoris maculatus Fabricius, 1798 123, 124, 129, 130, 135, 137, 138, 141, 147, 150, 154, Mallorca: Rare (sites : 89, 90, 102) . Menorca : Rare 155, 156, 162, 175, 176, 182, 185) . Formentera : Rare (sites: 160, 174) . (sites: 238, 239) . First record for Formentera . Always in permanent lentic habitats, with abundant Mainly in ponds with or without vegetation and aquatic vegetation and fresh or very slightly brackish with fresh or brackish water . water. Cited for Ibiza by Ribes (1984) and Nieser & Sigara nigrolineata (Fieber, 1848) Montes (1988) . Mallorca : Rare (sites : 52, 109) . Ibiza: Scarce (sites : 192, 200, 217) . New for the fauna of the Balearic Nepa cinerea Linnaeus, 1758 Islands. Mallorca : Scarce (sites: 9, 21, 22, 62, 63, 88, 102, 108, Mainly in lentic habitats, with or without vegetation 115). Menorca : Scarce (sites: 138, 139, 140, 151, 155, and fresh water. In Ibiza always in 'albercas' (small 161, 176, 184, 186, 187). Ibiza: Very rare (site: 190). man-made ponds for irrigation made of cement or stone First record for Ibiza . walls); in Mallorca, in a pond and in a seasonal stream On banks of streams and ponds, usually in areas with almost no current . with vegetation and fresh or slightly brackish water .

Sigara selecta (Fieber, 1848) Ranatra linearis (Linnaeus, 1758) Mallorca : Scarce (sites : 41, 42, 43, 44, 45, 48, 77) . Menorca: Very rare (site: 174). New for the fauna of Menorca: Very rare (site : 127). the Balearic Islands . Always in stagnant brackish waters, whether they In the La Vall stream, near its mouth, in an area are natural (marshes, coastal lagoons, etc .) or artificial of permanent and fresh waters, with almost no current ('albercas'), with or without vegetation . and abundant macrophytes . Cited by Ribes (1984) for Ibiza, based on records by Gasull in 1945, in an area long dried up or altered . Anisops debilis perplexa Poisson, 1929 Because of this and the lack of subsequent records, its Mallorca : Rare (sites : 51, 80, 89, 105). Ibiza : Scarce current presence in Ibiza is in need of confirmation . (sites: 203, 210, 215, 217, 219) . Formentera: Very rare (site: 242). First record for Formentera . 2 12

Always in 'albercas', with or without vegetation 222). Formentera: Very rare (site: 233). First record and fresh or slightly brackish water. for Formentera. In very diverse habitats (from streams to sources or Anisops sardea Herrich-Schaffer, 1850 marshes), always in lentic areas with abundant aquatic Mallorca: Scarce (sites : 19, 20, 51, 52, 80, 89, 114, vegetation . 117) . Menorca : Abundant (sites: 121, 122, 123, 130, 131, 134, 135, 140, 141, 145, 147, 150, 154, 155, 156, Aquarius najas (De Geer, 1773) 162, 166, 172, 176, 178, 182, 185, 186) . Ibiza : Rare Mallorca: Scarce (sites: 2, 9, 81, 82, 91, 92) . Menorca : (sites: 203, 217) . Rare (sites : 159, 160) . Mainly in ponds and 'albercas', with or without Always in permanent fresh waters (sources and vegetation and fresh or brackish water. In Menorca, streams) with or without vegetation and with or without also in stream still-waters . current.

Notonecta meridionalis Poisson, 1926 Gerris argentatus Schummel, 1832 Menorca: Scarce (sites : 126, 141, 150, 156, 157, 176, Menorca: Rare (sites: 160, 174) . 185). New for Balearic Island fauna . In stream still-waters with abundant emerging In ponds and two streams with slow current ; always macrophytes and fresh water . in areas with macrophytes and fresh or slightly brackish water. Gerris thoracicus Schummel, 1832 Mallorca : Rare (sites : 3, 16, 51, 55, 78) . Menorca : Notonecta maculata Fabricius, 1794 Common (sites : 126, 132, 135, 136, 137, 138, 140, Mallorca : Common (sites : 2, 6, 9, 11, 12, 16, 17, 18, 141, 147, 151, 155, 156, 158, 162, 175, 176, 182, 183, 19, 20, 31, 43, 51, 52, 56, 57, 60, 61, 63, 73, 80, 185, 186). 85, 88, 89, 91, 93, 97, 105, 106, 110, 114) . Menorca : In very diverse habitats (mainly in streams, ponds Common (sites : 121, 126, 137, 140, 141, 147, 149, and 'albercas') with fresh and brackish water and 150, 155, 160, 166, 172, 175, 178, 183, 184, 185, aquatic vegetation. 186). Ibiza : Common (sites : 189, 190, 192, 200, 203, 210, 215, 216, 218, 219). Formentera : Very rare (site : Hebrus pusillus (Fallen, 1807) 242). First record for Formentera. Mallorca : Very rare (site: 102). New for the fauna of In very diverse habitats (mainly 'albercas', ponds the Balearic Islands . and stream still-waters), with or without vegetation and In the Estany de la Fuente de Sant Joan, a small fresh or slightly brackish water . lagoon with a coverage of the alga Enteromorpha Several authors (Ribes, 1965 ; Nieser & Montes, intestinales in pleustonic form (Martinez Taberner, 1988) regard notes of Notonecta glauca for Mallorca 1988) and abundant emerging riparian vegetation . (Moragues, 1894; Garcias, 1907 ; Compte, 1960) as belonging to N. maculata . Hydrometra stagnorum (Linnaeus, 1758) Mallorca : Common (sites: 2, 3, 7, 10, 12, 21, 22, 62, Notonecta viridis viridis Delcourt, 1909 63, 72, 73, 81, 83, 86, 88, 91, 106, 120) . Menorca : Menorca: Scarce (sites : 121, 135, 137, 141, 150, 156, Common (sites : 132, 137, 138, 140, 142, 155, 157, 157). 161, 172, 175, 178, 179, 183, 184, 185, 186, 187) . In ponds and stream still-waters with abundant Ibiza: Scarce (sites: 190, 194, 201, 204, 223, 224) . aquatic vegetation and fresh or slightly brackish water . On the banks of permanent aquatic habitats with or without vegetation and fresh or very slightly brackish Plea minutissima Leach, 1817 waters. Mainly in streams on Mallorca and Menorca Mallorca : Common (sites : 12, 16, 17, 18, 20, 21, 22, and in springs on Ibiza . 47, 52, 53, 60, 81, 83, 89, 90, 93, 116, 117) . Menorca : Abundant (sites : 121, 131, 132, 134, 135, 136, 137, Mesovelia vittigera Horvath, 1895 139, 140, 141, 145, 146, 147, 150, 154, 155, 156, 160, Mallorca : Rare (sites : 47, 90, 102, 114, 117) . Menorca: 161, 162, 165, 167, 174, 175, 176, 182, 183, 186, 187, Scarce (sites : 132, 155, 175, 176, 182). Ibiza: Very rare 188). Ibiza : Scarce (sites : 190, 201, 203, 216, 220,

213 C. affinis (site: 208) . Formentera: Rare (sites: 233, 246). First OS. lateralis + 1 .5 record for Ibiza and Formentera. Mainly in permanent fresh water habitats (large S. nigrolineata ponds, and still-waters and mouths of streams) with • emerging vegetation . • A. sardea S. selecta M. scholtzi • • Microvelia pygmaea (Dufour, 1833) G . thoracicus I Mallorca : Scarce (sites : 21, 47, 60, 61, 81, 88, 89, .4 M vittigera 2 +0 .6 • • • N. maculates 93, 97, 117, 120). Menorca : Common (sites: 140, 147, P . minutissima • C panzeri 150, 151, 163, 165, 166, 176, 178, 186, 188) . Ibiza : N. maculatus Abundant (sites : 190, 191, 192, 193, 194, 197, 201, A . debilis perplexes M. pygmaea V hoberlandti • 204, 207, 216, 222, 223, 224, 229) . H. pusilius _-1 .0 In stagnant waters and those of little current, mainly H. stagnorum • II in areas with emerging or floating vegetation and fresh N. cinerea •• •A . najas water. P. perdubia Figure 2 . Plot of the first two axes of the multiple correspondence Velia hoberlandti Tamanini, 1949 analysis for the Heteroptera of Mallorca . Mallorca : Scarce (sites: 1, 5, 6, 7, 9, 27, 34, 62, 67, 68, 69, 71, 82, 104, 105, 107) . Menorca : Scarce (sites : 141, 142, 163, 183, 187) . Endemic species of the Balearic Islands. 0 0 In permanent habitats (springs and stream still- waters), usually with fresh water and with or without vegetation . Records of V rivulorum for the Balearic Islands antidate to the description of V hoberlandti (Tamanini, 1949), and presumably belong to V hoberlandti . Notes of V caprai caprai by Ribes (1965) and Pons (1987) for Mallorca and Menorca are based on exter- nal taxonomical characters, and probably belong to V hoberlandti . Notes of V caprai caprai by Nieser & Montes (1988) for Mallorca and Menorca are identification errors and belong to V hoberlandti (Nieser, in litt.) . Hence, the only species of Velia present on the 11 A Islands is V hoberlandti . 0 --0 .60 0 O E A~ II Associations of species Figure 3 . Ordination of the sampling sites on Mallorca on the first two axes of the multiple correspondence analysis. The symbols used for each of the habitat types are : A springs, 0 streams, • 'albercas', MALLORCA 0 ponds, + marshes, 0 reservoirs .

Heteroptera were present in 77 of the 120 sampled sites on Mallorca, totalling 20 species . 2 is associated at its positive end with Corixa affi- The first two axes of the correspondence analysis nis and Sigara lateralis and with Hydrometra stagno- account for 14.94% and 11 .77% of the total variance, rum, Nepa cinerea, Parasigara perdubia andAquarius respectively. Axis 1 is defined by Sigara selecta at its najas at its negative end (Figure 2) . positive end and by Anisops sardea, Mesovelia vittig- The distribution of sampling sites (Figure 3) shows era, Corixa panzeri, Naucoris maculatus and Anisops almost all ponds in the upper left quadrant (-/+) and debilis perplexa at its negative end (Figure 2) . Axis all marshes at the positive end of Axis 1 . Axis 2 sep- arates lentic ecosystems (in particular temporal ponds

214

G. argenratus r1, MALLORCA A. najas N. maculatus R. linearis • • • P. pcrduh;a +2.25

CLASS 2 q -- 7 101 CLASS 3 i22, 13 1 CLASS 4 C 1617 CLASS5 9~ 1 20

I MENORCA CLASS 1 3 C CLASS 2[ 5 1 I 7 CLASS 3 [ t0 - P. minutissima • • N macalara r z 1 3 affinis 14 H. stagnonmr •C . CLASS 4 16 obertaidti e• a • panzeri n •C 1a I • •N. viridis CLASS 5 1 C Zp M. pygmaea •+ 1 .0 G. thoracicus -0 .25 A. sardea • '1. vittigera . lateralis Figure 4. Dendrograms based on the scores of multiple correspon- • S . selecta S • •N. meridionalis II dence analyses . •s stagnalis Figure 5. Plot of the first two axes of the multiple correspondence analysis for the Heteroptera of Menorca . at its positive end) from lotic habitats (in particular spring and permanent streams at its negative end) . 0 0 0 On the whole, the negative and positive ends of +0 .6 Axis 1 are defined by species characteristic of perma- nent lentic fresh water ecosystems and of permanent 0 F71 n lentic ecosystems with brackish waters, respectively . 0 The positive and negative ends of Axis 2 are defined by species characteristic of temporal lentic ecosys- tems and of permanent lotic ecosystems, respectively . O D Remaining axes are associated only with stations with - 0 .3 A r'0+ 0.~~ 0 1 one species present, and cannot be defined. 1 A j 00 0 O A cluster analysis was made based on the resulting On ,o 0~00 0 O O A 0 .2 scores of the preceding factorial analysis (Figure 4) 0 DO 0 and groups obtained were divided into five classes **0 11 (Table 3) . Class 1 corresponds to sites which lacked Figure 6 . Ordination of the sampling sites on Menorca on the first species distinctive of the remaining groups and where two axes of the multiple correspondence analysis . The symbols used only accidental species were present (Table 3) . for each of the habitat types are : A springs, O streams, • 'albercas', In general, the following associations can be O ponds, * marshes . defined for Mallorca : 1 . Permanent lotic habitats (springs and streams) : Class 2 with Aquarius najas and Parasigara per- MENORCA dubia as the characteristic species . 2. Seasonal lentic habitats (ponds and `albercas' ). Heteroptera were present in 53 of the 68 sampled sites Class 3 with Sigara lateralis, Corixa affinis and on Menorca, totalling 21 species . Plea minutissima . The first two axes of the multiple correspondence 3. Permanent 'albercas' . Class 4 with Anisops debilis factorial analysis account for 21 .81% and 15.65% of perplexa, Anisops sardea and Notonecta maculata . the total variance, respectively . Figure 5 shows the 4. Permanent ponds . Class 5 with Mesovelia vittigera, species associated with both axes . These are Notonec- Micronecta scholtzi and Naucoris maculatus . ta viridis viridis, Mesovelia vittigera and Notonecta

2 15

Table 3 . Associations of characteristic species resulting from the classification (centroid) in classes, obtained with the scores defined in the correspondence factorial analysis . Classes cited as `without defined association' include those sites without the common species that are characteristic of the associations, but which contain accidental species instead .

Island Class Groups Sites Association

Mallorca 1 1, 2, 3, 4, 5, 6, 7. 1, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 21, 24, 25, Without defined association 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 48, 49, 50, 56, 59, 60, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 76, 77, 78, 83, 84, 85, 86, 87, 8 8, 93, 94, 95, 96, 97, 98, 99, 100, 101, 103, 104, 106, 107, 108, 109, 110, 111, 112 , 113, 115, 116, 118, 119, 120 . 2 8, 9 . 2, 9, 81, 82, 91, 92. A . najas, P perdubia 3 10, 11, 12, 13, 14. 16, 17, 18, 19, 20, 22, 23, 52, 53, 54, 55, 57, 58, 61, S. lateralis, C. affinis, P 79. minutissima 4 15, 16. 51, 80, 89, 105 . A . debilis perplexa, A, sardea, N. maculata 5 17, 18, 19, 20. 47, 74, 75, 90, 102, 114, 117 . M. vittigera, M. scholtzi, N. maculatus Menorca 1 1, 2, 3, 4 . 121, 126, 135, 137, 141, 150, 156, 157, 185 . N. viridis viridis, N. meridionalis, C. affinis 2 5, 6, 7 . 132, 155, 175, 176, 182 . M. vittigera, G . thoracicus 3 8, 9, 10, 11, 12 . 138, 140, 142, 147, 151, 161, 163, 172, 178, 183, H. stagnorum, N. cinerea, V hober- 184, 186, 187 . landti, M. pygmaea 4 13, 14, 15, 16, 17, 122, 123, 124, 125, 127, 128, 129, 130, 131, 133, Without defined association 18 . 134, 136, 139, 143, 144, 145, 146, -148, 149, 152, 153, 154, 158, 159, 162, 164, 165, 166, 167, 168, 169, 170, 171, 173, 177, 179, 180, 181, 188 . 5 19, 20 . 160, 174. G. argentatus, N. maculatus, P perdubia

meridionalis at the positive end of Axis 1 and Sigara a clay substratum on the north coast : Class 2 with selecta at the negative end. The positive end of Axis Mesovelia vittigera and Gerris thoracicus . 2 is defined by Parasigara perdubia, Naucoris macu- 2. Permanent streams . a) In general : Class 3 with latus, Gerris argentatus, Ranatra linearis and Aquar- Hydrometra stagnorum, Nepa cinerea, Velia ius najas. Distribution of stations related to both axes hoberlandti and Microvelia pygmaea. b) Large (Figure 6) show most ponds in the lower right quadrant still-waters: Class 5 with Gerris argentatus, Nau- (+/-) and marshes and springs in the lower left quadrant coris maculatus and Parasigara perdubia . On the whole, Axis 1 is associated with species characteristic of permanent fresh water lentic habitats on its positive end. Axis 2 separates species charac- IBIZA teristic of permanent streams (at its positive end) from Heteroptera were present in 25 of the 41 sampled sites the remaining habitats . on Ibiza, totalling . l l species . Only Microvelia pyg- A cluster analysis based on the resulting axes of maea and Notonecta maculata have been captured in the correspondence analysis (Figure 4), established over 25% of the sampled sites, whilst the remaining five site classes (Table 3), and their associated species . species con only be found in very few stations . Class 4, with only accidental species, is characterized The first two axes of the correspondence anal- by the absence of species that define the rest. ysis account for 22 .45% and 19 .11% of the total As a whole the following associations can be variance, respectively. Axis 1 is defined by Anisops defined for Menorca : sardea, Anisops debilis perplexa, Sigara nigrolinea- ta, Micronecta scholtzi and Notonecta maculata at its 1 . Permanent lentic habitats . a) In general: Class 1 positive end, and by Corixa affinis and Hydrometra with Notonecta viridis viridis, Notonecta merid- stagnorum at its negative end . Axis 2 is associated at ionalis and Corixa affinis . b) Lentic habitats with its positive end with Nepa cinerea and Plea minutissi- 216 ma, and at its negative end with Mesovelia vittigera. Permanent lotic habitats are found only on Mal- Because of the small number of species and stations lorca and Menorca . Associated with these habitats in where they were found, there is no graphical represen- Mallorca areAquarius najas and Parasigara perdubia . tation of this analysis . In Menorca, Gerris argentatus, Naucoris maculatus The cluster does not define species associations and Parasigara perdubia are associated with the larger but rather divides stations according to the presence streams, while Hydrometra stagnorum, Nepa cinerea, or absence of the two most abundant species on the Velia hoberlandti and Microvelia pygmaea are asso- island (Microvelia pygmaea and Notonecta macula- ciated with the smaller streams with little current and ta) . Notonecta maculata was found mainly in artificial abundant vegetation . lentic habitats ('albercas') and Microvelia pygmaea in As far as the permanent lentic habitats are con- natural lentic habitats (ponds and stream pools) . cerned, there are obvious differences between the 'albercas' and the ponds . In the permanent 'albercas', FORMENTERA wich are considerable both in number and extension Heteroptera were present in 5 of the 17 sampled in Mallorca and in Ibiza particularly (where they form sites on Formentera, totalling 5 species . Sigara lat- the majority of permanent aquatic habitats) there is eralis was found in two pools of a seasonal streams ; an association made up of Anisops debilis perplexa, Anisops debilis perplexa and Notonecta maculata in an Anisops sardea and Notonecta maculata . Menorca, `alberca' ; Plea minutissima in a permanent pond and with fewer 'albercas', has no definite species asso- Mesovelia vittigera in this and another pond. ciation for this habitat . With regard to permanent ponds, in Mallorca one can find an association composed of Mesovelia vittig- Conclusions era as characteristic species and Micronecta scholtzi and Naucoris maculatus as associated species. While A total of 25 species were collected . Five (Sigara in Menorca there are two associations, one including nigrolineata, Micronecta scholtzi, Ranatra linearis, the majority of permanent ponds and which is made Notonecta meridionalis and Hebrus pusillus) are first up by Notonecta viridis and Notonecta meridionalis as records for the Balearic Islands . characteristic species and with Corixa affinis as associ- Only two of all previously cited species have not ated species, and another association which is restrict- been found in our study . Sigara scripta, cited by Mor- ed to ponds with a clay substratum found on the north agues (1894) for Mallorca in a long dried-up site, and coast of the island and made up by Mesovelia vittig- Micronecta leucophala, cited by Tamanini (1948) for era as characteristic species and Gerris thoracicus as Mallorca based on specimens belonging to the Civic associated species. Natural History Museum of Genova and collected by Jorda, probably before 1930 . Due to the dates of these recordings and the lack of subsequent ones, the pres- Acknowledgements ence of both species on the Islands is in need of con- firmation. We thank Dr J . A. Palazon and Dr J. F. Calvo Sendin With the exception of the endemic Velia hober- for help with statistical methods ; Dr N. Nieser and Dr landti, the remaining species are widely distributed A. Millan for help with taxonomical questions, and J . throughout the Mediterranean area, particularly in the Larkin for revision of English manuscript . west. Only Anisops debilis perplexa has a smaller dis- tribution area; in the south of the Iberian Peninsula and the north of Africa (Nieser & Montes, 1984) . References For the Balearic Islands, only permanent habitats show definite species associations, with the exception Bigot, L ., 1958. Elements d'dtude des peuplements a salicornes de file de Majorque (Baleares) . Bol . Soc . Hist. Nat . 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