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Spatial and seasonal organisation of a darkling beetle (Coleoptera, Tenebrionidae) community inhabiting a Mediterranean coastal dune system a
Giuseppe M. Carpaneto & Simone Fattorini
b
a
Dipartimento di Biologia , Università degli Studi “Roma Tre” , viale Marconi 446, I‐00146, Roma, Italy E-mail: b
Dipartimento di Biologia Animale e dell'Uomo (Zoologia) , Università di Roma “La Sapienza” , viale dell'Università 32, I‐00185, Roma, Italy E-mail: Published online: 28 Jan 2009.
To cite this article: Giuseppe M. Carpaneto & Simone Fattorini (2001) Spatial and seasonal organisation of a darkling beetle (Coleoptera, Tenebrionidae) community inhabiting a Mediterranean coastal dune system, Italian Journal of Zoology, 68:3, 207-214, DOI: 10.1080/11250000109356410 To link to this article: http://dx.doi.org/10.1080/11250000109356410
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Ital. J. Zool., 68: 207-214 (2001)
Spatial and seasonal organisation of a darkling beetle (Coleoptera, Tenebrionidae) community inhabiting a Mediterranean coastal dune system GIUSEPPE M. CARPANETO Dipartimento di Biologia, Università degli Studi "Roma Tre" viale Marconi 446, I-00146 Roma (Italy) e-mail:
[email protected]
SIMONE FATTORINI
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Dipartimento di Biologia Animale e dell'Uomo (Zoologia), Università di Roma "La Sapienza", viale dell'Università 32, I-00185 Roma (Italy) e-mail:
[email protected]
ABSTRACT Darkling beetle communities were studied on the coastal dune system which borders a protected area (Castelporziano Presidential Estate) along the Tyrrhenian Sea. Monthly samplings were conducted in three plant associations along a transect from the seaward slope of the dune to the innermost one. Within a bulk of common species found in all three plant associations, some of them showed quantitative differences at the habitat level. Most species showed similar phenology with a summer drop, only one being a temporal specialist solely active in summer. As a whole, plant cover seems to influence species abundance, while phenology is probably moulded by climatic changes like late summer rainfalls. KEY WORDS: Tenebrionidae - Diversity - Habitat distribution Seasonal variations - Central Italy. ACKNOWLEDGEMENTS The present work is based on materials collected during a more comprehensive field research on the sand dune invertebrate communities of Mediotyrrhenian coastal ecosystems performed by one of us (G.M.C.) with the help of Luca Bertolaccini (prematurely dead), Lucia Altobelli, Paolo Battaglia and Donatella Cagiotti. We are also very grateful to Luca Salvati and three anonymous referees for their helpful comments on the manuscript. The research was supported by a grant from the Italian Ministero dell'Universita e della Ricerca Scientifica e Tecnologica ("Variazione geografica e diversita a livello di specie, faune e zoocenosi: cause storiche ed ecologiche"). (Received 1 January 2000 - Accepted 16 May 2001)
INTRODUCTION
The insect communities inhabiting coastal dunes and sandy beaches of the Mediterranean Sea have been investigated by several Authors (e.g., Therond & Bigot, 1964; Dajoz, 1987; Chelazzi et al, 1990; Colombini et al, 1991; Contarini, 1992; Fallaci et al, 1994). Owing to the relatively simple structure of these ecosystems, characterised by a scarce and discontinuous vegetation cover, such communities of insects show a low diversity of species when compared with adjacent inland ecosystems (cf. McLachlan, 1991). Such relative simplicity facilitates habitat comparison and quantitative research on the ecological role of the species and their population dynamics. On the other hand, the sand dunes are seriously threatened by the human pressure on coastal lands and are usually transformed into spoiled flat beaches and tourist settlements. Although darkling beetles (Coleoptera, Tenebrionidae) are a prominent component of Mediterranean coastal areas, there is a scarce literature on their ecology in such habitats (De los Santos et al, 1988; Martin Cantarino & Seva Roman, 1991; Colombini et al, 1994; Fallaci et al, 1994, 1997). Nevertheless, the knowledge of abundance, seasonal changes and habitat distribution of adult sand dwelling beetles could be of great importance in the study of the structure and dynamics of these threatened ecosystems. The knowledge of the life cycles of the species may supply precious information for a more complete understanding of these topics, especially for the study of the numerical fluctuations of species. Unfortunately, information on the darkling beetle life cycles in Mediterranean areas is almost completely lacking. However, the larvae of soil dwelling darkling beetles are fossorial (e.g., Thomas, 1979; Allsopp, 1980), and their biology is quite different from that of the adults, which are active on the surface. Thus, almost all the literature on the community ecology of these insects is focused on adults (see Wise, 1981; Krasnov & Shenbrot, 1997; Faragalla, 1999; and references therein). Adult darkling beetles are an ideal subject for community ecology research in coastal dune systems, as the evolution of these beetles is clearly related to the colonisation of arid environments, and their life histories are highly tuned to the environmental variability in these habitats (e.g., De los Santos et al, 2000). In particular, darkling beetles inhabiting arid environments like deserts and coastal dunes share a number of adaptations to such habitats, at both morphological and behavioural level (e.g., Colombini et al, 1994). The aim of this paper is to study the species composition and the seasonal dynamics of the darkling beetle community living on a Mediterranean dune system to give an answer to the following questions: (1) How the general structure of a beetle community can be characterised from a zoogeographical point of view? (2) What is the microhabitat distribution and diversity of the darkling beetle assemblages in the different phytocoenoses (plant associations) of the dune system? (3)
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Can be this distribution related to plant cover and structure? (4) What are the seasonal changes of the darkling beetle populations? (5) What are the possible environmental factors influencing both spatial and temporal patterns? (6) What are the major adaptations of beetles to this environment?
MATERIALS AND METHODS
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Study area and sampling techniques The present study was carried out on the dune system stretching along the Castelporziano Presidential Estate. This protected area is located in Central Italy (Tyrrhenian coast) and is bordered by about 25 km of coastal sand dunes (normally 10-15 m of elevation; maximum 27 m). Sampling was made on a dune site extending about 300 m in length and 50 m in width. Along a transect from the seaward slope of the most recent dune to the innermost one (where the evergreen scrub begins), the following phytosociological associations are recognisable (Napoleone, 1970; Gratani et al., 1983; Acosta et al., 2000): (1) Echinophoro spinosae-Elymetum farcti (EE); (2) Echinophoro spinosae-Ammophiletum arundinaceae (EA); (3) Loto cytisoidis-Crucianelletum maritimae (LC). The first association (EE), formerly named Agropyretum mediterraneum, is the most exposed to the salt winds blowing from the sea and covers about 30-35% of the soil. It forms the boundary between the spoiled seashore and the proper dune. The second association (EA), contiguous to EE, is the most characteristic plant guild of stabilised sand dunes and covers about 30%. The reference species for this association, Ammophila arenaria (L.), is very successful in stabilising dunes (cf. Slobodchikoff & Doyen, 1977). The third association (LC), linked to a relatively abundant humus deposited among sand dunes, covers up to 70% of the soil. It extends inland up to the maquis dominated by the prickly juniper, Juniperus oxycedrus L. A total of 17 plant species was recorded (three species in EE, nine in EA, and nine in LC). In order to study differences in beetle species composition and diversity among habitats, monthly sampling were performed in each plant association. Samplings were made from March 1983 to February 1984, by sieving sand and detritus collected at the base of each plant species occurring in each association from the surface to 10-cm depth. A total amount of 31,667 cm3 of sand and detritus was collected every month from ten well-spaced tufts of each plant species. Because the number of plant species was different in each phytocoenosis, a different volume of substrate was analysed in each plant association. In particular, the volume of detritus from both EA and LC was three times much as the volume from EE. Therefore, when the abundance of beetle species was compared among the three plant associations, data were standardised dividing by three the data from EA and LC. Although European coastal dunes are strongly affected by anthropogenic impacts (e.g., Desender et al., 1991), the study area appeared to be well preserved due to the lack of tourist settlements. As confirmed by recent surveys, no habitat changes occurred from the study period to the present time. Moreover, a research on the ecology of the insects inhabiting the dunes at Castelporziano was performed from 1998 to 1999 by monthly sampling based on sand sieving (De Salvo et al., pers. commun.): the analysis, still in progress, of these data clearly revealed that no variations occurred in the darkling beetle community composition. Therefore, data reported in the present paper are actually consistent with the present situation of this area. Monthly values of mean temperature and total rainfall for the study period (Fig. 1) were obtained from the meteorological sta-
I IT1 [ T l 1 I I I J F M A M J J A S O N D I
-A--T(°C)
—•—R(mm)
Fig. 1 - Monthly values of mean temperature (T) and total rainfall (R) for the study period.
tion of "Ufficio Centrale di Ecologia Agraria" at Pomezia, near the study area. Data analysis The zoogeographic composition of the community was studied by the analysis of the species ranges. In such analysis, species ranges were coded using the distribution types proposed by Vigna Taglianti et al. (1999). To study the incidence of flightlessness, several specimens of each species were dissected, and wing conditions examined. Then, species were classified as: apterous, brachypterous and macropterous. The numerical importance of each species in the structure of the whole community (i.e., the overall dominance of species) was computed as a percentage of the total number of a given species collected in the three habitats on the total darkling beetles sampled. Also, species were ranked according to their body size, and their abundance was correlated with the size by using Spearman's rank correlation test. As measures of the species body size (total length) we used mean values obtained from the ranges reported by Fattorini & Carpaneto (in press). Although species richness is generally the most relevant component of beetle diversity, due to the scarce number of species occurring in the study area and the substantial uniformity of the beetle assemblages in the three habitats, diversity indices which include a measure of equitability were used. We used Shannon's diversity index as a measure for community diversity, H' = - X p ; • lnpj, where pj is the proportion of individuals belonging to species i in a collection. Community evenness was estimated by Pielou's index J' = H1 / lnS, where S is the number of species in the habitat. Monthly values of both indexes were calculated for each habitat and differences tested by the Kruskal-Wallis ANOVA test. The x 2 test was used to verify if the differences in darkling beetle species abundance among the three plant associations were significant. The null hypothesis was formulated considering a uniform distribution by species abundance at the habitat level. Temporal variations in species abundance in the three plant associations were studied considering the dominance of each species in a given month as its percentage on the total number of darkling beetles collected in that month.
DARKLING BEETLES ON A MEDITERRANEAN DUNE
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X. pellucidus) or brachypterous {Phaleria acuminata, Ph. provincialis, Ps. normandi). Because the actual numbers of collected specimens are affected by differences in the volume of the substrate analysed, the ratios between specimens and volume were calculated in order to estimate the number of beetles per m3 of substrate. As a whole, the beetle density decreased from the external to the innermost plant association, the number of beetles per m3 of substrate being 930.7 in EE, 713.7 in EA and 606.7 in LC. With the exception of X. pallidus (which was represented in our samplings by only four specimens, and absent from EE) no differences in species composition RESULTS was observed among the three habitats. Also, due to the scarce numbers of T. aphodioides and X. pallidus, Species composition and abundance in different habitats data on these two species were excluded from %2 test Ten species of darkling beetles were collected during and Spearman's correlation among species phenologies. Looking at the yearly abundance of each species in the this study (Table I). All species showed distribution significant differences ranges restricted to Mediterranean areas: six species three different plant associations, siculus (%2 = 6.1, df = 2, P < 0.05), showed a Mediterranean distribution, three appeared to were observed for E. 2 be restricted to the western part of the Mediterranean Ph. acuminata (% = 479-5, df = 2, P < 0.0001), Ph. (y} = 19.9, df = 2, P < 0.0001), Ps. normandi basin, and only one showed an East Mediterranean dis- provincialis 2 tribution. However, some of these species seem to be (X = 10.5, df = 2, P < 0.01). By contrast, no significant were found in the abundance polytypic, with localised populations. Particularly, at differences among habitats 2 A. rufus (%2 least three species occur in the study area with sub- of P. bipunctata (% = 5.4, df = 2, P = 0.07), 2 (% = 5.28, df = 2, P species restricted to Tyrrhenian Italy: Erodius siculus = 2.7, df = 2, P = 0.25), H. pellucida 2 ssp. neapolitanus Solier, 1834; Pimelia bipunctata ssp. = 0.07), and X. pellucidus (x = 2.9, df = 2, P = 0.24). In papii Canzoneri, 1963, and Pseudoseriscius normandi particular, E. siculus and Ps. normandi were increasing from EE to LC, while Ph. acuminata and Ph. provincialis ssp. pacificii Leo, 1982. Out of a total of 5577 specimens, 1061 were collected showed an opposite pattern (Table I). As to the overall dominance of each species, A. rufus, in EE, 2441 in EA and 2075 in LC. With the exception of Trachyscelis aphodioides (a macropterous species), all H. pellucida, Ph. acuminata, and Ps. normandi species are apterous (E. siculus, P. bipunctata, Ammo- reached high values, while T. aphodioides and X. palbiusrufus, Halammobia pellucida, Xanthomus pallidus, lidus showed very low values. As with the dominance
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Temporal frequencies (F) were calculated on 12 samples considering each month as a sample. Species were thus classified as constant (F > 50%), accessory (25% < F < 50%), accidental (10% S F < 25%) and sporadic (F < 10%) (cf. Fallaci et al., 1994). Species phenologies were studied by Spearman's rank correlation test. Comparisons were made to study the phenology of the same species in the three different habitats as well as the correlations between the total phenologies of the different species. In all tests, significant level was fixed to P < 0.05. A hierarchical clustering strategy was used to study similarity between temporal darkling beetle assemblages. Based on Euclidean distances, clustering was conducted by Ward's method. Statistical analyses were performed using STATISTICA software (version 4.5, 1993).
TABLE I - Darkling beetle general distribution, abundance and dominance. EME, E Mediterranean; WME, W Mediterranean; MED, Mediterranean; EE, Echinophoro spinosae-Elymetum farcti; EA, Ecbinophoro spinosae-Ammophiletum arundinaceae; LC, loto cytisoidisCrucianelletum maritimae.
Species
Geographic range
Erodius siculus Solier, 1834 Pimelia bipunctata Fabricius, 1781 Ammobius rufus Lucas, 1849 Trachyscelis aphodioides Latreille, 1809 Phaleria acuminata Kuster, 1852 Phaleria provincialis Fauvel, 1901 Halammobia pellucida (Herbest, 1799) Pseudoseriscius normandi (Espanol, 1949) Xanthomus pallidus (Curtis, 1830) Xanthomus pellucidus (Mulsant, 1856)
EME WME MED MED MED MED MED WME WME MED
Total number of collected specimens
Overall dominance
70 59 2688 12 659 104 1476 413 4 92
1.26 1.06 48.20 0.22 11.82 1.87 26.47 7.40 0.07 1.65
Habitat abundance" EE
EA
LC
3.00 9.33 13.00 2.00 9.67 9.33 409.00 395.67 364.00 6.00 1.00 1.00 377.00 83.67 10.33 35.00 14.33 8.67 179.00 225.33 207.00 36.00 56.33 69.33 0.00 1.00 0.33 14.00 17.33 8.67
Habitat dominance*** EE
EA
LC
0.28 1.15 1.88 0.19 1.19 1-35 38.55 48.63 52.63 0.57 0.12 0.15 35.53 10.28 1.49 3.30 1.76 1.25 16.87 27.70 29.93 339 6.92 10.02 0.00 0.12 0.05 1.32 2.13 1.25
* Overall dominance = species abundance / total number of darkling beetles (5577) x 100. ** Habitat abundance = number of specimens per standard volume of substrate (1140012 cm3). *** Habitat dominance = species abundance /number of darkling beetles (1061 in EE, 2441 in EA, 2075 in LC) x 100.
Body size (mm)
10.0-11.0 14.0-18.5 2.5-3.8 3.0-4.0 5.0-8.0 5.3-8.1 3.8-4.5 4.0-9.0 6.9-11.0 6.0-9.0
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in the different plant associations, A. rufus was clearly dominant in all associations, followed by H. pellucida; Ph. acuminata was an important element in EE and EA, but not in LC; Ps. normandi was an important element in EA and LC, but not in EE. All other species showed lower values (
