© Sociedad Española de Malacología Iberus, 15 (2): 25-34, 1997 Phenological patterns and life history tactics of Helicoidea (Gastropoda, Pulmonata) snails from Northern Greece Patrones fenológicos y estrategias de vida en Helicoidea (Gastropoda, Pulmonata) del Norte de Grecia Maria LAZARIDOU-DIMITRIADOU and Stefanos SGARDELIS* Recibido el 8-I-1996. Aceptado el 31-VII-1996 ABSTRACT The present study mainly concerns with the differences in the biological cycles and strategies adopted by different Helicoidea snail species. In Northern Greece the climatic conditions are not very uniform. Some snails breed during the same period as in Northern Europe but most breed in autumn, as species from Southern Europe do. Breeding may take place in all sea- sons except in winter, and seems to be species-specific. Long-lived snails of big size differ from short-lived species of small size as to the time of their breeding period. The climatic con- ditions affect the time of the breeding season and their whole life cycle and phenologies. En- vironmental variables in Northern Greece are strongly seasonal and thus Helicoidea snails exhibit predictable oscillations in their activity patterns, which can be interpreted by the de- mographic response of the populations. Terrestrial snails seem to follow two different pheno- logic curve types: the semelparous and short-lived species populations show a more stable phenological pattern than the biennial and pluriennial ones, who mature after the first year of their lives, being more plastic trying to face the climatic differences from one year to another. RESUMEN El presente estudio trata de las diferencias en los ciclos biológicos y a las estrategias adopta- das por diferentes especies de Helicoidea. En el norte de Grecia, las condiciones climáticas no son muy uniformes. Algunas especies crían durante el mismo periodo en que lo hacen en el N de Europa, pero la mayoría lo hacen en otoño, como sucede en especies del S del con- tinente. La cría puede tener lugar durante casi todas las estaciones, excepto el invierno, y el periodo parece ser específico para cada especie. Las especies longevas y de gran talla di- fieren de las de pequeño tamaño y vida más corta en la duración de su ciclo de cría. Las condiciones climáticas afectan al momento de la temporada de cría y a todo su ciclo vital y fenología. Las variables ambientales son fuertemente estacionales, así que aparecen oscila- ciones predecibles en los patrones de actividad, que pueden ser interpretadas por la res- puesta demográfica de las poblaciones. Las babosas parecen seguir dos tipos de curvas fe- nológicas distintas. Las especies semelpáricas y de corta vida muestran un patrón fenológico más estable que el de especies bianuales y prurianuales, que maduran tras el primer año de vida y son más flexibles a la hora de enfrentarse a las diferencias climáticas interanuales. KEY WORDS: Biological cycle, phenology, Northern Greece, Helicoidea, Helix, Eobania, Helicella, Monacha, Bradybaena. PALABRAS CLAVE: ciclo biológico, fenología, N Grecia, Helicoidea, Helix, Eobania, Helicella, Monacha, Bradybaena. * Departments of Zoology and Ecology, School of Biology, Aristotle University of Thessaloniki, 54006 Thessaloniki, Macedonia, Greece. 25 Iberus, 15 (2), 1997 INTRODUCTION 1995; LAZARIDOU-DIMITRIADOU AND KATTOULAS, 1981, 1985, 1991; STAIKOU, Greece has a Mediterranean climate LAZARIDOU-DIMITRIADOU AND FARMA- which is differentiated mainly along a KIS, 1988; HATZIIOANNOU, ELEUTHERIA- northern-southern gradient. In Northern DIS AND LAZARIDOU-DIMITRIADOU, 1989; Greece climate is transient from STAIKOU, LAZARIDOU-DIMITRIADOU AND Mediterranean (mostly coastal areas) to PANA, 1990; STAIKOU AND LAZARIDOU- temperate (inland areas). A typical cha- DIMITRIADOU, 1990, 1991). racteristic of this climate type is the coincidence of high temperatures and low precipitations during summer (las- MATERIALS AND METHODS ting from June to October). The wet sea- son is divided by a cold winter which is Data used derived from monthly milder in the coastal areas. Drought is a quantitative samplings of Helicoidea strong agent controlling population dy- snails from different parts of Northern namics and activity of most soil inverte- Greece. The following species were brates as it imposes a pause in most studied: Family Bradybaenidae, Brady- physiological activities. Low temperatu- baena fruticum (Müller, 1774); Family res during winter are also important for Helicidae, Cepaea vindobonensis (Férus- population dynamics and activity as sac, 1821), Eobania vermiculata (Müller, they impose hibernation in some of the 1774), Helix lucorum Linnaeus, 1758, invertebrates e. g. terrestrial gastropods. Helicella (Xerothracia) pappi (Schüt, 1962), So observed discontinuities in popula- Helix figulina (Rossmässler, 1839), Helix tion development during the transition pomatia rhodopensis Kobelt, 1906, Theba from the favourable to the unfavourable pisana (Müller, 1774); Family Hygromii- seasons and vice-versa may be attribu- dae, Cernuella virgata (Da Costa, 1778), ted to environmental thresholds. Monacha cartusiana (Müller, 1774), Xero- Although the association between lenta obvia (Menke, 1828), Xeropicta climate and life history phenomena is arenosa Ziegler, 1836, Xerotricha conspur- self evident, it can vary among terres- cata (Draparnaud, 1801). Sampling trial molluscs, even between popula- lasted two or four years depending on tions of the same species. Phenology the species and their life span (LAZARI- reflects certain aspects of the demo- DOU-DIMITRIADOU, 1981, 1995; LAZARI- graphy of a population, that is the DOU-DIMITRIADOU AND KATTOULAS, timing of its life cycle characteristics in a 1981, 1985, 1991; STAIKOU ET AL., 1988; given environment. The classification of STAIKOU ET AL., 1990; STAIKOU AND phenological patterns into categories or LAZARIDOU-DIMITRIADOU, 1990, 1991). types (WOLDA, 1988) is better by using Details regarding the sites and the sam- phenological models (VAN STRAALEN, pling procedures are given in previous 1982; STAMOU, ASIKIDIS, ARGYROPOULOU studies on these species (LAZARIDOU- AND SGARDELIS, 1993). Using a phenolo- DIMITRIADOU, 1981, 1995; LAZARIDOU- gical model, complex phenograms can DIMITRIADOU AND KATTOULAS, 1985, be classified into types considering their 1991; STAIKOU ET AL., 1988). Ombrother- skewness, curtosis, phase and period. mic data for Northern Greece from 1980 The aim of the present study was to to 1990 are given in Figure 1. Data were find out whether terrestrial gastropods provided by Mahairas P., Professor of adopt a general phenological pattern if Climatology from the Aristotle Univer- they are differentiated according to their sity of Thessaloniki. origin, or their biotopes (inland and Fischer’s exact test for independence coastal areas) or life spans. The present in 2 x 2 contingency tables (ZAR, 1984) study is a part of an extensive research was used for comparisons between the done on the distribution and ecology of different categories, e. g. snails with Helicoidea gastropods in Northern autumnal and vernal-estival reproduc- Greece (LAZARIDOU-DIMITRIADOU, 1981, tive periods, long-lived (> 3 years) and 26 LAZARIDOU-DIMITRIADOU AND SGARDELIS: Phenology of Helicoidea in N Greece 40 80 30 60 °C C ° 20 40 Precipitation (mm) 10 20 Prec. (mm) 0 0 JFMAMJJASOND Months Figure 1. Ombrothermic diagram from Northern Greece. Temperature: open squares; Precipitation: solid rhombus. Figura 1. Diagrama ombrotérmico del Norte de Grecia. Temperatura: cuadrados abiertos; Precipitación: rombos sólidos. short-lived snail species (up to 3 years), f (ET) = EXP(α+b x COS(2π x (ET-ϕ/T)) (1) large (largest shell diameter > 25 mm) and small sized snails. where the independent variable ET, The phenological pattern of Helicoi- termed Ecological time, is a function of dea species was studied by using the standard clock time (ST), ET = f (ST). In phenological model applied for the the course of standard time, ecological study of microarthropods (STAMOU ET time is going faster during periods of AL., 1993). In short, in this model when sharp changes in abundance and slower asymmetries and discontinuities are dis- during periods of abundance stability. played the scales of the time-axis were Thus, the proposed equation describing adjusted. Changing time scales results the length of the Ecological time unit in the definition of a new variable (∆ET) as a function of Standard time ST termed ecological time (ET), which is a is: function of a standard clock time (STAMOU ET AL., 1993). This technique is ∆ET= f (ST) = EXP(α1+b1 x COS(2π x based upon the following considera- (ST-ϕ1)/T1)) (2) tions: 1) the timing of a population in the field is determined by the sequence The model has eight parameters of of demographic events and/or beha- which the period T and the phase ϕ of vioural characteristics (i. e. migratory), the phenogram, as well as period T1 and and 2) the rate of the demographic the phase ϕ1 of the function relating ET events depends on the fluctuations of to ST, are the most important. The environmental variables. period T and the phase ϕ of the pheno- In this model it is assumed that the grams are expressed formally in ET phenology of any population inhabiting units. For convenience they could be a seasonal environment can be descri- expressed in ST units (as T’ and ϕ’) by bed by a symmetric periodic curve: using equation (2) for the calculation of 27 Iberus, 15 (2), 1997 the Standard time T’ or ϕ’ which corres- (ϕj in Table I). X. obvia from Karvali ponds to T or ϕ units in the Ecological peaked in July. Helix lucorum displayed time-scale (see STAMOU ET AL., 1993: fig. a similar interannual instability. In both 1). For the comparison of phenograms cases the shift in phase seems to be asso- two more parameters can be derived: a) ciated with an unexpected change of the an estimation of the sharpness (curtosis) weather, an extended dryness (STAIKOU of the phenogram C=(R2-R1)/T’, where ET AL., 1988: fig. 2) which provoked an (R2-R1) is the time interval around the overall decline of the population density phase ϕ’, during which the abundance is (Fig. 2).