Book of Abstracts

Uncertain ecosystems: the ecology of open, non-forested vegetation
William J. Bond, Botany Department, University of Cape Town, Private Bag, Rondebosch, 7701, South Africa;
william.bond@uct.ac.za
46
Climate has long been considered the prime factor determining the distribution of major vegetation formations
implying that there is a single stable vegetation state for a given climate. However this is not true for large parts of
the world where strikingly different vegetation states, such as forests and grasslands, occur in the same landscapes
under the same climate. For most of the last century the non-forested (‘open’) ecosystems were thought to be
secondary vegetation produced by deforestation and anthropogenic burning. However open ecosystems include
some of the world's richest biodiversity hotspots, implying a long evolutionary history. Recent fossil and
phylogenetic evidence supports their antiquity while Quaternary studies are showing that some open ecosystems
were even more extensive before the rise of human populations. Recognition of the age and extent of open
ecosystems challenges traditional ecological concepts. Succession, driven by competition for resources and
especially light, should result in dominance of taller- shade-tolerant growth forms where resources permit. Yet open
ecosystems dominated by low-growing plants have persisted for millions of years. Recurrent disturbance, especially
by fire, but also by large vertebrate herbivores, is important in maintaining open ecosystem states. Though
understanding of the global importance of fire has grown rapidly in the last decade, there are still many uncertainties
about the importance of mammals in creating and maintaining open ecosystems, both now and in the past.
Recognition of the global extent of uncertain ecosystems, and of factors maintaining open ecosystems, is essential
for understanding future global change of terrestrial vegetation.
Fragmentation and biodiversity patterns in fragmented semi-arid landscapes
Yoni Gavish; Ben-Gurion University of the Negev, POB 653, Beer-Sheva, 84105, Israel; gavishyoni@gmail.com
Yaron Ziv; Ben-Gurion University of the Negev, POB 653, Beer-Sheva, 84105, Israel; yziv@bgu.ac.il
Two main processes that drive the current global biodiversity crisis are global climate change and the transformation
of natural habitats into human dominated land-uses (habitat loss). As human settlements and agricultural practice in
desert environments are relatively scarce, the world’s deserts have experienced relatively low levels of habitat loss.
As such, the effects of habitat loss and fragmentation on desert systems are relatively unexplored. In contrast, semiarid
landscapes, which lie at the edge of the world’s desert belt, have already been subjected to high levels of habitat
loss and fragmentation. We have sampled spiders in three fragmented semi-arid landscapes along the sharp climatic
gradient of Israel. Various methods to decouple fragmentation from habitat loss reveal that fragmentation actually
maximizes diversity. We explain this result using an occupancy-based null model for the species-area relationship.
The null-model reveals that rare species are found on small patches more than expected by chance. We further
develop the link between occupancies and species-area relationship to theoretically explore the effect of
fragmentation on species diversity. This exploration reveals that when the evenness of the distribution of area
between patches is low, fragmented landscapes will sustain higher species diversity than continuous landscapes. We
suggest that if we wish to understand how climate change and human effects influence biodiversity, we should apply
quantitative models and methods in order to recognize underlying mechanisms.
Elimination of predators is a sufficient condition for steppification
Lauri Oksanen 1,2 - lauoks@utu.fi, Tarja Oksanen 1,2 and Risto Virtanen 3
1 Department of Biology, section of Ecology, University of Turku, FI-20014 Turku, Finland
2 Section of Sciences, Finnmark University College, Alta, NO-9504 Alta, Norway
3 Department of Biology, University of Oulu, FI-90014 Oulu, Finland
During the last three millennia, vast forested areas have changed into treeless communities, dominated by
graminoids or prostrate dicots. Sometimes the vegetation has become scanty enough to warrant the term
desertification, but in most cases, steppification is a more appropriate term, since even in the new state, > 50% of
ground is covered by plants.