Dr. Tim Baker - Human impact & global change
The macroecology of Amazonian forests: understanding current and future trends in a changing ecosystem

Amazonian forests contain approximately 40 % of the biomass stored in terrestrial ecosystems and more than half of global biodiversity. Predicting the effects of global environmental change on these forests requires an understanding of the ecological mechanisms that determine current patterns of forest composition, structure and dynamics. For example, is resource availability, or disturbance, more important for determining variation in forest turnover and growth rates? What role does species composition have in determining ecosystem properties? These questions have been addressed using long term data from a network of forest inventory plots across Amazonia. These plots show that there are regional scale spatial patterns in species and functional composition, aboveground biomass, wood productivity, tree mortality and recruitment rates, and the stocks and decomposition rates of coarse woody debris. Edaphic, rather than climatic, conditions correlate with higher rates of forest turnover and growth rates in western Amazonia, and compositional patterns determine variation in forest biomass.

These spatial patterns are important because they have provided the context for concerted increases in tree mortality, recruitment and growth rates, and forest biomass. Overall, these trends indicate that Amazonian forests have increased in productivity and carbon storage and are most plausibly explained by increasing resource levels. The known spatial variation in forest productivity, structure and composition therefore provides a range of predictions about the future of intact Amazonian forests. In particular, increases in the abundance of species with low wood density as a result of elevated rates of tree turnover, may reverse currently observed increases in forest biomass. The ecological processes and changes in intact forests need to be considered alongside more direct alteration of tropical forests from logging, land use and climatic changes, to determine effective conservation strategies and the future contribution of these biomes to the global carbon cycle.

Prof. Paulo S. Oliveira - Organism interactions
Dual seed dispersal systems: Interactions between ants and fleshy diaspores in the tropics

In tropical forests nearly 90% of the shrubs and trees bear fleshy fruits and rely on vertebrate frugivores for seed dispersal. Thus most studies on seed dispersal of tropical species have hitherto focused on fruit consumption and seed deposition patterns generated by primary, vertebrate seed dispersers. However, large amounts of the fruit crop produced by tropical trees can reach the forest floor intact, spontaneously or dropped by vertebrate frugivores. Because tropical ground-dwelling ants are remarkably abundant and diverse, a wide range of interactions between ants and fallen fleshy diaspores is expected to occur in tropical habitats. These ant-diaspore interactions can affect seed biology (germination), modify seed fate, and markedly affect patterns of recruitment (distribution and survival of seedlings) in primarily vertebrate-dispersed species lacking adaptations for ant-dispersal. Such an influence of secondary dispersers enhances the complex, two-phase nature of the dispersal ecology of tropical tree species. Untangling the complexity of such dispersal systems (with sequentially-connected phases) is crucial for understanding the evolutionary relationship between frugivores and plants, and plant regeneration pathways. Mutualisms are less conspicuous in dispersal systems than in more tightly coevolved systems, and interactions between ants and fleshy diaspores are highly unpredictable and variable. Indeed, the intricacy of the mutualistic networks within such dispersal systems may underlie the biotic complexity and high diversity of tropical ecosystems.

Prof. Robbert Gradstein - Biodiversity
Bryophyte assemblages of tropical rain forests - responses to forest modification and global warming

Tropical rain forests because of their structural complexity and favorable microclimatic conditions are a rich habitat for bryophytes. Owing to the lack of a protective cuticle, solutions and gases may enter freely into the living tissues of these plants causing sensitive reactions of these plants to changes in the environment. Because of this, bryophytes are good ecological indicators. Based on results of our work in tropical America and Asia I will discuss spatial patterns of bryophyte diversity in different rain forest types, responses to forest modification, and the possible impact of global warming on bryophyte diversity. Evidence from bryophytes allows for recognition of new, hitherto overlooked type of rainforest: the Tropical Lowland Cloud Forest (TLCF) with record-high diversity. Analysis of bryophyte assemblages along disturbance gradients shows that old-growth primary forests are not necessarily more diverse than secondary ones. Diversity in plantations and on remnant trees, however, is significantly reduced. Canopy closure is an important parameter influencing bryophyte diversity along the disturbance gradient. Similarity in species composition of secondary and primary forests increases with forest age but after 40 years of succession many primary forest species had not re-established in secondary forest, indicating that long time is needed for recovery of bryophyte communities. The possible impact of global warming on tropical bryophyte diversity was studied by translocation of bryophyte assemblages along temperature gradients in the Andes. The results show species-specific responses to transplantation after two years and indicate that community structure and species composition of bryophytes in tropical rain forests may be significantly modified as a result of future temperature increases of two or more degrees.

Prof. Timm Hoffman - Biodiversity
Global change and human impacts on biodiversity in Namaqualand, South Africa

TIMM HOFFMAN, Institute for Plant Conservation, Botany Department, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa. Tel: +27-21-650-2440. thoffman@botzoo.uct.ac.za

RICK ROHDE, Centre for African Studies, Edinburgh University, Edinburgh. Tel: +27-21-461-5921. rick.rohde@ed.ac.uk

Two perceived threats face the biota of Namaqualand. Firstly, recent modelling efforts suggest that climate change will impact heavily on the diversity and agricultural production of the region as a result of a reduction in rainfall and an increase in temperature over the next 50 years. Secondly, the expansion of communal land under South Africa's land reform programme could lead to higher stocking rates over a significant portion of Namaqualand on a scale not seen in the region since the 1950s. This trend could be exacerbated as a result of the downscaling of mining operations in the region and the retrenchment of workers who use their severance packages to invest in livestock production. To investigate these issues we take an historical perspective. We look at historical trends in rainfall over the last 100 years and incorporate recent interpolation studies carried out by colleagues within the BIOTA South research programme. Evidence for the impact of climate change is investigated for two long-lived tree Aloe species growing in the broader Namaqualand region. The apparently contradictory results suggest that responses to drought and high rainfall events are complex and the life history dynamics of long-lived species need to be better understood. The historical impact of human society in the region from pre-colonial to recent times is also outlined. Changes in the area cultivated and stocking rate for communal and private land suggests that the last two decades has seen a significant decline in the agricultural use of the land. While the low-lying bottom lands continue to be the most heavily exploited, increased urbanisation in the region has drawn a large number of people off the land, particularly in the last few decades. Improved infrastructural development in the rural areas of Namaqualand has also meant that people are now less reliant on natural resources for their day-to-day activities. Firewood production in a recently-electrified rural village, for example, has seen a 75% reduction in fuelwood consumption. The strong environmental history and repeat photography approach undertaken in this analysis suggests that Namaqualand's landscapes are similar to what they have looked like in the last 100 years. If anything, there is more vegetation cover today than there was 50 years ago and there is little evidence of widespread desertification in the region. Land use impacts were probably greatest in the first half of the 20th century and have declined in the last 50 years.

Prof. Teja Tscharntke - Human impact & conservation
Plant-insect diversity and ecosystem functioning in human-dominated tropical landscapes

The modification of tropical landscapes through human exploitation of the environment continues to reduce biodiversity on a global scale. This decline in biodiversity has led to concern over the potential loss of major ecosystem processes. Further, agricultural land use and biodiversity conservation have been traditionally viewed as incompatible, but only recently, recognition has increased that a restriction of conservation efforts to natural, undisturbed ecosystems is of limited value. Agriculture can make important contributions to high diversity of landscapes, while it also benefits from sustainable ecosystem services provided by agricultural conservation management at local and regional scales. For example, enhanced biological pest control and improved crop pollination may directly increase the farmers' income.

In this presentation, I will refer to results on patterns of biodiversity and plant-insect interactions, changing with spatial and temporal scales considered, from the Collaborative Research Centre "Stability of Rainforest Margins in Indonesia" (STORMA, SFB 552) and the BioTEAM (BMBF) research program on the "Evaluation of biological diversity of land-use systems in a mega-diverse region of Ecuador" (Bio-Sys).

References:

Klein, A, Steffan-Dewenter, I., Tscharntke, T. (2003): Fruit set of highland coffee increases with the diversity of pollinating bees. Proceedings of the Royal Society of London, Series B 270: 955-961.

Olschewski, R., Tscharntke, T., Benítez, P. C., Schwarze, S., Klein, A. M. (2006): Economic valuation of pollination services and pest management comparing coffee landscapes in Ecuador and Indonesia. Ecology and Society.

Tscharntke T., Klein, A.M., Kruess, A., Steffan-Dewenter, I., Thies, C. (2005): Landscape perspectives on agricultural intensification and biodiversity-ecosystem service management. Ecology Letters 8: 857-874.

Tylianakis, J., Klein, A.-M. , Tscharntke, T. (2006): Spatiotemporal variation in the diversity of Hymenoptera across a tropical habitat gradient. Ecology (in press).