Ábrahám Levente: Válogatott tanulmányok II. - Natura Somogyiensis 9. (Kaposvár, 2006)

Ábrahám Levente: Pit building ant-lion larvae effect to the distribution of the substrate particles in their microhabitats - Tölcsérépítő hangyaleső lárvák hatása a szubsztrát szemcsék eloszlására élőhelyeiken

168 NATURA SOMOGYIENSIS where sunrays, the rain and wind have a direct influence, the area with vegetation and with the open sandy surfaces alternate giving a mosaic-like patterns. The geographical distribution of the species dwelling in protected habitats cannot be related to the quality of the bedrock (sand, loess, clay, adobe etc.), the larvae only occur in dry warm microhabitats (WHEELER 1930, GEPP and HÖLZEL 1989). The common features of this type of habitats that they are small and protected from the wind, from the rain and in most cases from direct sunrays as well. The protected microhabitats distributed in a mosaic-like pattern in the habitat and their vegetation coverage is close to 0%. These kinds of microhabitats form on scarps, drop-offs, at the foot of artificial building sides and under cliff ledges. In order to understand the habitat preference and the distribution pattern of the ant-lion larvae, the geographical distribution of the substrate needs to be compared to the substrate of the two characteristic habitats. The experiments with different types of substrates suggested that the particle sizes are significantly influencing the habitat preferences of the larvae, and therefore effecting on the predator activity and on the interactions (SIMBERLOFF et al. 1978, GATTI and FARJI-BRENNER 2002). On the other hand, direct observations revealed that the larvae also have an effect on the particle size distribution in their pit's environment (GEPP and HÖLZEL 1989). The particle size preference of the ant-lion larvae observed in laboratories has been the subject of several publications. During their experiments, YOUTHED and MORAN 1969 came to the conclusion that Myrmeleon obscurus which lives in open habitats in South Africa prefers the size of sand fraction between 0.211-0.295 mm. KITCHING (1984) during his experiments with the larvae of Myrmeleon pictifrons which occurs in protected habitats in Australia found the particle size preferences of this larvae between 0.125-0.5 mm. ALLEN and CROFT'S (1985) experiments carried out also in Australia gave more specific information on the ant-lion larvae. They divided the sand particles into three fractions (fine 0.3 mm, medium 0.3-0.6 mm, coarse 0.6-1.2 mm) and they realized that Myrmeleon diminutus living in open habitats and Myrmeleon pictifrons occurring in protected habitats prefer the finest substrate fraction. In the United States LUCAS (1982,1986, 1989a) has carried out laboratory experiments to examine the influencing factors on the behavior of the ant-lion larvae. He tested pitbuilding ant-lion larvae living in open {Myrmeleon carolinus) and in protected habitats {Myrmeleon crudelis) and he divided the substrate into seven fractions. He pointed out that the larvae both from protected and open habitats chose the fine (fine 0.125-0.250 mm) fraction from the substrate. According to his studies (LUCAS 1989b) no significant differences can be found between the particle size preferences of the larvae living in open or protected habitats. In Hungary SIPOS (1986) has studied the particle size preferences of Euroleon nostras occurring in protected microhabitats in experiments with seven fraction sizes as well. As a result he stated that during the experiment most third instar (L3) larvae (80%) built their pits in sand of 0.2-0.4 mm fraction size. During the laboratory experiments in Slovenia with ant-lion larvae of Euroleon nostras DEVETAK et al. (2005) got similar results. Those laboratory experiments which used flour, iron-filings or glass-dust as substrate cannot be evaluated from behavioral ecology point of view since they do not reflect nature like circumstances. From earlier experiments it is known that there is an overlap between the particle size preferences of the larvae living in the two different kinds of habitat. The quality of the substrate is different in the two characteristic habitats of the ant-lion larvae. The environmental factors are different in the open and the protected habitats (ÁBRAHÁM 2003). The aim of the present study is to investigate the particle size preferences of the pitbuilding ant-lion larvae living in open or protected microhabitats.