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Institute
- Theodor-Boveri-Institut für Biowissenschaften (44) (remove)
Freshly cut beech deadwood was enriched in the canopy and on the ground in three cultural landscapes in Germany (Swabian Alb, Hainich-Dun, Schorfheide-Chorin) in order to analyse the diversity, distribution and interaction of wood-inhabiting fungi and beetles. After two years of wood decay 83 MOTUs (Molecular Operational Taxonomic Units) from 28 wood samples were identified. Flight Interception Traps (FITs) installed adjacent to the deadwood enrichments captured 29.465 beetles which were sorted to 566 species. Geographical 'region' was the main factor determining both beetle and fungal assemblages. The proportions of species occurring in all regions were low. Statistic models suggest that assemblages of both taxa differed between stratum and management praxis but their strength varied among regions. Fungal assemblages in Hainich-Dun, for which the data was most comprehensive, discriminated unmanaged from extensively managed and age-class forests (even-aged timber management) while canopy communities differed not from those near the ground. In contrast, the beetle assemblages at the same sites showed the opposite pattern. We pursued an approach in the search for fungus-beetle associations by computing cross correlations and visualize significant links in a network graph. These correlations can be used to formulate hypotheses on mutualistic relationships for example in respect to beetles acting as vectors of fungal spores.
Assoziationen von Ameisen mit Pflanzen (und oft noch mit pflanzensaugenden Insekten als drittem Partner) dürften eine Ursache des Artenreichtums und der hohen Abundanzen tropischer Formicidae sein. Die von den Ameisen genutzten Pflanzen bieten entweder Nahrung an, über extraflorale Nektarien und/oder Nährkörperchen, oder aber - bei den eigentlichen Myrmekophyten - Nistraum und z.T. auch Nahrung. Diese Beziehungen zeichnen sich durch unterschiedliche Nutzungsweisen und Nutzungsintensitäten und damit stark differierende Abhängigkeit der Partner voneinander aus. Ein besonders breites Spektrum von Ameisen-Pflanzen-Assoziationen finden wir in der paläotropischen Baumgattung Macaranga (Euphorbiaceae), die sich daher als Modellsystem für vergleichende Untersuchungen hervorragend eignet. Die Grundfrage unserer Untersuchungen an diesem System lautet: Verläuft aufgrund der ausgeprägt mosaikartigen Verteilung der von den myrmekophilen Pflanzen angebotenen Nahrungs- und Nistraumressourcen die Neu- und Wiederbesiedlung von Habitaten durch die Ameisen in Form von Zufallsprozessen? Oder werden, im Gegenteil, durch diesen Umstand Spezialisierungen seitens der Ameisen gefördert und die Zusammensetzung der Lebensgemeinschaften dadurch stärker deterministisch geprägt? Unsere bisherigen Untersuchungen zeigen, daß beide Prinzipien wirken. Bei der alleinigen Nutzung von Nahrungsressourcen fehlen spezialisierte Beziehungen weitgehend und stochastische Ereignisse dürften sehr häufig die Pflanzen-Ameisen-Assoziation bestimmen. Bei den eigentlichen Myrmekophyten hingegen ist die Auswahl der assozierten Ameisen viel stärker determiniert, ganz besonders dann, wenn der Wohnraum, den die Pflanze offeriert, nur durch aktives Öffnen seitens der Ameisen erschlossen werden kann.
The pioneer tree Macaranga in SE Asia has developed manyfold associations with ants. The genus comprises all stages of interaction with ants, from facultative relationships to obligate myrmecophytes. Only myrmecophytic Macaranga offer nesting space for ants and are associated with a specific ant partner. The nonmyrmecophytic species are visited by a variety of different ant species which are attracted by extrafloral nectaries (EFN) and food bodies. Transitional Macaranga species like M. hosei are colonized later in their development due to their stem structure. Before the colonization by their specific Crematogaster partner the young plants are visited by different ant species attracted by EFN. These nectaries are reduced and food body production starts as soon as colonization becomes possible. We demonstrated earlier that obligate ant partners can protect their Macaranga plants against herbivore damage and vine cover. In this study we focused on nonspecific interactions and studied M. tanarius and M. hosei, representing a non-myrmecophyte and a transitional species respectively. In ant exclusion experiments both M. tanarius and M. hosei suffered significantly higher mean leaf damage than controls, 37% versus 6% in M. hosei, 16% versus 7% in M. tanarius. M. tanarius offers both EFN and food bodies so that tests for different effects of these two food rewards could be conducted. Plants with food bodies removed but with EFN remaining had the lowest mean increase of herbivore damage of all experimental groups. Main herbivores on M. hosei were mites and caterpillars. Many M. tanarius plants were infested by a shootborer. Both Macaranga species were visited by various ant species. Crematogaster spp. being the most abundant. We found no evidence for any specific relationships. The results of this study strongly support the hypothesis that non-specific, facultative associations with ants can be advantageous for Macaranga plants. Food bodies appear to have lower attractive value for opportunistic ants than EFN and may require a specific dietary adaptation. This is also indicated by the fact that food body production in the transitional M. hosei does not start before stem structure allows a colonization by the obligate Crematogaster species. M. hosei thus benefits from facultative association with a variety of ants until it produces its first domatia and can be colonized by its obligate mutualist.
To highlight human impact on biodiversity in the Lamto region, termites were studied with regard to their use as bio-indicators of habitat change in the tropics. Using a standardized method, termites were sampled in the three most common habitat types, i.e., in semi-deciduous forest, savanna woodland, and annually burned savanna, all inside Lamto Reserve and its surrounding rural domain. Termite species richness fell from 25 species in the Lamto forest to 13 species in the rural area, involving strong modification in the species composition (species turnover = 59 %). In contrast, no significant change in diversity was found between the Lamto savannas and the rural ones. In addition, the relative abundance of termites showed a significantly greater decline in the rural domain, even in the species Ancistrotermes cavithorax (Sjostedt) (Isoptera: Termitidae), which is known to be ecologically especially versatile. Overall, the findings of this study suggest further investigation around Lamto Reserve on the impact of human activities on biodiversity, focusing on forest conversion to land uses (e.g. agricultural and silvicultural systems).