PUBLIKATIONEN

Vorträge mit Bezug zur Tropenstation

Joint Meeting of the society for Tropical Ecology & the Association for Tropical Biology and Conservation
27 - 30 July 2009, Marburg, Germany

The Tropical Station La Gamba/Costa Rica ("Tropenstation La Gamba") - 
a place for scientific studies in the Neotropics
A. Weber (held by David Bröderbauer)

In this lecture, the Tropical Station La Gamba ("Tropenstation La Gamba") and its surroundings are presented in more detail. The Station , run by a private association but being closely connected to the University of Vienna, serves three main purposes: (1) Research in tropical biology and other scientific disciplines, (2) Teaching of university students (excursions, courses and lectures), (3) Teaching of biologically interested laymen. The surroundings of La Gamba host a broad spectrum of natural habitats in terrestrial and aquatic settings, which are embedded in a matrix of different land use. Therefore, the station could develop as base for studying the impact of global change and the effects of complex interactions between rainforests and the adjacent cultural landscape on tropical ecosystems.

Anton Weber (Department of Palynology and Structural Botany, Centre of Biodiversity, Faculty of Life Sciences, University of Vienna. A-1030 Wien, Rennweg 14, Austria)
anton.weber@univie.ac.at  

Impact of climate change on the performance of tropical lowland forests in SW Costa Rica
W. Wanek, S. Drage, F. Hofhansl, N. Hinko, E.M. Pölz, A. Richter

Recent studies on the impact of rainfall seasonality and annual climate fluctuations will be presented and interpreted in terms of future responses of rainforests to climate change. El Nino Southern Oscillation (ENSO) strongly affects precipitation patterns in SW Costa Rica, with mean annual precipitation (MAP) ranging between 4700 mm (1997 El Nino) to 6500 mm (2007 La Nina) at the Tropical Station La Gamba. Seasonality was not affected by ENSO. Effects of MAP on net primary production i.e. wood increment and litterfall in the Esquinas rainforest were assessed. The effect was most pronounced in leaf litterfall in primary rainforests in valley bottom positions (primary ravine forest) being positively related to annual precipitation and in residual litterfall being inversely correlated. In contrast total fine litterfall was unaffected in primary ravine forests. Since leaf litter is more nutrient rich than residual litter (mostly woody debris) one can assume that aboveground nutrient cycling may be strongly positively affected in wet years promoting net primary production as a whole. This is though not evident in stem increments indicating lower woody biomass production in wet years. Moreover, major effects of land-use and topography on biomass pools, primary production and nutrient use efficiency will be demonstrated.

Wolfgang Wanek (Department of Chemical Ecology and Ecosystem Research, Centre of Ecology, Faculty of Life Sciences, University of Vienna. A-1090 Wien, Althanstraße 14, Austria)
wolfgang.wanek@univie.ac.at, +431 4277 54254

Neotropical lowland rainforests: nutrient export by rainforest streams
F. Schiemer, M. Fordinal (held by Wolfgang Wanek)

The paper provides a survey of the overall hydro-geochemical conditions of the Esquinas river catchment in context of its complex geology and land use pattern. The geochemical signatures of the different tributaries show a close spatial relationship with the geology. A similar pattern is evident with regard to plant nutrients, nitrate, phosphate and silicate. A more detailed analysis of nutrient dynamics shows clear differences in the retention of P and N by the rainforest system. The relationship between nutrient concentrations and flow was analysed for two streams of different stream order. These analyses allow the calculation of the total nutrient loss from the catchment and a discussion of the potential consequences of the change in runoff patterns due to climate changes.

Friedrich Schiemer (Department of Limnology and Hydrobotany, Centre of Ecology, Faculty of Life Sciences, University of Vienna. A-1090 Wien, Althanstraße 14, Austria) 
friedrich.schiemer@univie.ac.at,  +431 4277 54340

Mycelial carton galleries of Azteca brevis (Formicidae) in Southern Costa Rica and the impact of global change
V.E. Mayer, H. Voglmayr and G. Windischbauer

Azteca brevis (Formicidae, Dolichoderinae), an arboricolous ant living on branches of Tetrathylacium macrophyllum (Flacourtiaceae) cultivate fungi for reinforcement of the walls of nest constructions or of tunnel-shaped runway galleries. These fungi are grown on organic material like bark, epiphylls or trichomes forming stable "carton structures". The molecular investigation of the fungi found on the Azteca brevis carton shows, that a complex association of several fungi is involved. All fungi isolated were unequivocally placed within the Chaetothyriales. Whereas the New World Attini with their highly specialised one-to-one (one ant species - one fungal cultivar) pattern, and temperate Lasius with a one-to-two (one ant species - two mutualists) or many-to-one (different ant species share the same mutualist) system, the Azteca brevis-fungi association is a one-to-many multi-species network.
Experiments with Atta workers placed on T. macrophyllum branches covered with a carton tunnel inhabited by A. brevis revealed that the numerous small holes which perforate the carton tunnels allow a highly advanced group ambush strategy to chase prey and to defend the colony.
Field observations showed that the construction of the galleries is declining during dry periods and dependent on regular precipitation.

Veronika Mayer (Dept. of Palynology and Structural Botany, Faculty Centre of Biodiversity, Faculty of life Sciences, University of Vienna, Rennweg 14, A-1030 Wien, Austria)
veronika.mayer@univie.ac.at 

The importance of gallery forests in the tropical lowlands of Costa Rica for understorey forest birds
B.S. Seaman & C.H. Schulze

Rivers and streams lined by narrow forest strips are common in the lowland countryside of Southwestern Costa Rica. We studied the importance of these gallery forests for birds, especially forest species. Using mist-nets, we captured 1110 birds belonging to 90 species between June and September 2007 at sixteen sites spread equally over four habitat types: forest interior, forest margin, gallery forest connected to closed forest, and isolated gallery forest. Though isolated gallery forests had the greatest number of expected species in total, they supported the lowest number of forest specialist species, lower even than connected gallery forests. The studied habitats differed from each other in their faunal composition. There was no significant difference in the proportion of birds with brood patches or of recaptures across the studied habitat types, leading to the assumption that birds, at least for a small fraction of forest species gallery forests constitute an important secondary habitat. Furthermore, they can form corridors of stepping stones that allow movements within the matrix of human-dominated habitats, and benefit total bird species richness in the Costa Rican countryside.

Benjamin Seaman (Department of Population Ecology, Faculty Centre of Biodiversity, Faculty of life Sciences, University of Vienna, Rennweg 14, A-1030 Wien, Austria)
benjamin.seaman@gmx.at