Landscapes Forest and Global Change - ESA - Escola Superior ...

E.S. Meier et al. 2010. Projections of shifts in species distributions
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target species to reach such habitats given constraints of the landscape (fragmentation, climate,
competing species). By this, we were able to simulate realistic tree migration patterns across
Europe at a comparably fine spatial resolution of 1km for the ongoing century.
3. Results
The variation partitioning approach showed, that over all climatic conditions, the joint
contribution of biotic and abiotic predictors to explain deviance in SDMs was relatively small
(~9%) compared to the contribution of each predictor set individually (~20% each). The
influence of biotic predictors was higher for mid to late succession species than for early
succession species.
The results of the correlation analysis were in line with the ‘stress-gradient hypothesis’ for F.
sylvatica: towards favourable growing conditions, its abundance was strongly linked with the
abundance of its competitors, while this link weakened considerably towards unfavourable
growing conditions. This resulted in a North-South and an elevation gradient throughout Europe,
with stronger correlations in the South and at low elevations. The sensitivity analysis showed a
potential spatial segregation of currently competing species with changing climate and a
pronounced shift of zones where co-occurrence patterns may play a major role, but also a
general reduction in interaction strength.
Results from the sensitivity analysis of migration rates point to one effect that may help to
explain aspects of the ‘stress gradient-hypothesis’; the higher the biotic interactions (i.e.,
increased number of species occurring in a cell) towards species-specific favourable growing
conditions, the more migration rates are limited. Climate seems to be directly limiting migration
and finally constraining species’ distributions only where biotic interactions were low.
Landscape fragmentation further lead to considerable time lags in range shifts for some species.
In summary, the projected distributions by 2100 predicted from limiting migration rates
dynamically with SDMs was rather in agreement with assumptions of “unlimited dispersal” for
early succession species, while it matched rather with the assumption of “no migration” for
medium and late succession species.
4. Discussion
The influence of biotic variables on SDM performance may indicate that community
composition and other local abiotic factors or biotic processes strongly influence species
distributions. However, the importance of species co-occurrence patterns for calibrating reliable
species distribution models for use in climate effects projections does not seem to be equally
crucial under all possible climatic conditions; in our correlation approach we were able to
localise European areas (mostly low elevations, more southern part of the range) where
inclusion of biotic predictors is recommended. Further we demonstrated, that implementing
more realistic migration rates might substantially alter projections, and reduce the uncertainty in
projections of species distributions under climate change scenarios.
During recent climate change, many slow reproducing mid to late successional species
may not be able to keep pace according to our analysis. Biotic interactions may mainly limit
migration rates towards species-specific favourable growing conditions, while climate seems to
be directly limiting primarily where biotic interactions are low. Landscape fragmentation may
further lead to considerable time lags in range shifts, which may bring migration to a halt where
migration is already relatively slow. Assessing the effects of interlinked processes such as
climate, inter-specific interactions and landscape-fragmentation on migration rates and species
distributions in a dynamic and compound model reduces the uncertainty in projections of
species distributions under climate change scenarios. If standard SDMs should be used in the
future because of simplicity or where insufficient information on dynamic migration rates is
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.