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

ÁBRAHÁM L.: PIT BUILDING ANT-LION LARVAE 183 The analysis of the samples taken from the natural habitats of the ant-lion larvae has proved that the particle size of the substrate is converted by the larvae during their pit building and sand throwing activity (Figure 8) and this result corresponds with the earlier experimental observations of the pit building activity (BÍRÓ 1885a, 1885b REDTENBACHER 1883, 1884). The spatial distribution of the particle size of the substrate can be influenced by the chitin bristles and teeth of the mandibles and head of the larvae. The larvae gather the finer fraction particles inside the pit and they throw out the coarser particles in the neighborhood of the pit (GEPP and HÖLZEL 1989). This pattern is suitable for the effective predator activity which comes from the physical characteristic of the substrate (LUCAS 1982, FARJI-BRENER 2003). In protected habitat the larvae live in populations of higher density than in open habitats therefore they sift through the substrate of their microhabitats several times for many years. In the process of arranging the larger size particles towards the edge, the substrate is getting finer (Figures 12, 14). In open habitats the larvae being under unfavorable conditions (e.g. lack of food, high temperature) leave their pits and rebuild them somewhere else consequently the particle size of the substrate is not as differentiated as in the cases of the species living in protected habitat (Figures 9, 10). Because of the prevailing exogenic processes, such as wind, rain and other disturbing effects in open habitats, a more homogenous mixture of particles is formed on the spatial scale of the microhabitats. In their case study, LOIREITON and MAGRATH (1996) emphasize the important role the particle size plays in the predator activity. In the case of finer particle size, the pray has less chance to escape, which was proved by a measurement series as well. Therefore it can be stated that in both types of habitats the ant-lion larvae try to gather the finer particles in their pits by their sand throwing activity. There are more significant differences in the particle size distribution between the habitats which are geographically are far from each other than between the different types of microhabitats (Figure 3). In the microhabitats of the ant-lion larvae, the particle distribution of the substrate is the result of the activity of the larvae. The larvae gather the particle size which they prefer the most. The particle size of 0.2-0.3 mm seems to be the most typical in the case of the Myrmeleon species regardless of the type of the habitat and the quality of the substrate. In three cases out of two, the highest figure of preference of the larvae of Euroleon nostras was 0.1-0.2 mm under natural circumstances. In general it can be established that the quality of the substrate is reflected in the particle size preferences of the larvae dwelling in different habitats rather than in the difference of the species and the ages of the larvae. The present and the earlier studies (ÁBRAHÁM 2003) suggest that Euroleon nostras, and very likely other pit-building species living in protected microhabitat, chose their habitats providing less food besides optimal particle size and thermal conditions. On the other hand, the species occurring in open habitats such as Myrmeleon bore, live in habitats with bigger food supply but with extreme thermal conditions and coarser particle size. Acknowledgement The author would like to express their sincere thanks to Dr. Viktor Marko (Corvinus University, Department of Entomology, Budapest and Dr. Sándor Farkas (Kaposvár University) for their valuable remarks made by reading the manuscript which improved the quality of printed version of the study.