It is usually thought that unlike terrestrial plants, phytoplankton will not show a significant response to an increase of atmospheric CO 2 . Here we suggest that this view may be biased by a neglect of the effects of carbon (C) assimilation on the pH and the dissociation of the C species. We show that under eutrophic conditions, productivity may double as a result of doubling of the atmospheric CO 2 concentration. Although in practice productivity increase will usually be less, we still predict a productivity increase of up to 40% in marine species with a low affinity for bicarbonate. In eutrophic freshwater systems doubling of atmospheric CO 2 may result in an increase of the productivity of more than 50%. Freshwaters with low alkalinity appeared to be very sensitive to atmospheric CO 2 elevation. Our results suggest that the aquatic C sink may increase more than expected, and that nuisance phytoplankton blooms may be aggravated at elevated atmospheric CO 2 concentrations.
Dispersaland habitat connectivity in complex heterogeneous landscapes: an analysis with a GIS-based random walk model. -Ecography 19: 97-106.A grid-based random walk model has been developed to simulate animal dispersal, taking landscape heterogeneity and linear barriers such as roads and rivers into account. The model can be used to estimate connectivity, and has been parameterized for the badger in the central Netherlands. The importance of key parameters was evaluated by meilns of sensitivity analysis. Results agree with field observations. and give interesting insight into the isolation of populations and potential populations. The model can be applied to obtain knowledge about dispersal processes in complex landscapes.
P. Schippers und J . P. Knuupen. Winund Sturing Centre for Integrured Land, Soil undWutrr Rrseurcli (SC-DLO), P.O. Box 12s. N L -6 7 0 A C Wugeningen. The Nerlierlunds. -1. Verhoom cvtd R. C. vun Apekloorn. Inst. for Forestry mid Nuture Reseurch (IBN-DLO).
A systematic theoretical evaluation has been made of three important plant life history traits: adult longevity, seed longevity and seed mass, where seed mass is interpreted as being indicative of dispersal distance and seedling vigour. This model study examined the role of these three traits in relation to environmental disturbance. We chose temperate grasslands, widespread in north Western Europe and northern and eastern America, as our reference system for our simulations. Eight plant strategies were defined by allowing two levels in each of the three and combining them in all eight possible ways. A simple, spatially explicit model was developed to simulate competition among individuals with these eight trait combinations at different levels of disturbance. Simulation results were compared with the actual occurrence over a disturbance gradient of species with similar plant trait combinations in a large database from the Sheffield area (UK). This showed that with increasing disturbance level, non‐dormant perennials, dormant perennials, non‐dormant annuals and dormant annuals, respectively, became dominant but only if small‐seeded, indicating the relative viability of these particular strategies with respect to disturbance. A new prediction from the model was that stable coexistence occurs between plant strategies with dormant and with non‐dormant seeds over a range of levels of disturbance. Plant strategies with large seeds were inferior to small‐seeded ones if competitive ability of seedlings is proportional to seed weight. This difference was highest at low seed densities and low germination probabilities, indicating that large‐seeded species secure no advantage from being dormant (i.e. having a low germination probability). Finally, the results indicated that dormancy is superior to dispersal as a method of coping with disturbance.
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