TY  - JOUR
A1  - Bauer, Barbara
A1  - Sommer, Ulrich
A1  - Gaedke, Ursula
T1  - High predictability of spring phytoplankton biomass in mesocosms at the species, functional group and community level
JF  - Freshwater biology
N2  - 1. Models aim to predict phytoplankton dynamics based on observed initial conditions and a set of equations and parameters. However, our knowledge about initial conditions in nature is never perfect. Thus, if phytoplankton dynamics are sensitive to small variations in initial conditions, they are difficult to predict. 2. We used time-series data from indoor mesocosm experiments with natural phyto- and zooplankton communities to quantify the extent to which small initial differences in the species, functional group and community biomass in parallel treatments were amplified or buffered over time. We compared the differences in dynamics between replicates and among all mesocosms of 1year. 3. Temperature-sensitive grazing during the exponential growth phase of phytoplankton caused divergence. In contrast, negative density dependence caused convergence. 4. Mean differences in biomass between replicates were similar for all hierarchical levels. This indicates that differences in their initial conditions were amplified to the same extent. Even though large differences in biomass occasionally occurred between replicates for a short time, dynamics returned to the same path at all hierarchical levels. This suggests that internal feedback mechanisms make the spring development of phytoplankton highly predictable.
KW  - divergence
KW  - hierarchical level
KW  - mesocosms
KW  - predictability
KW  - replicates
Y1  - 2013
U6  - https://doi.org/10.1111/j.1365-2427.2012.02780.x
SN  - 0046-5070
VL  - 58
IS  - 3
SP  - 588
EP  - 596
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Massie, Thomas Michael
A1  - Ryabov, Alexei
A1  - Blasius, Bernd
A1  - Weithoff, Guntram
A1  - Gaedke, Ursula
T1  - Complex transient dynamics of stage-structured populations in response to environmental changes
JF  - The American naturalist : a bi-monthly journal devoted to the advancement and correlation of the biological sciences
N2  - Stage structures of populations can have a profound influence on their dynamics. However, not much is known about the transient dynamics that follow a disturbance in such systems. Here we combined chemostat experiments with dynamical modeling to study the response of the phytoplankton species Chlorella vulgaris to press perturbations. From an initially stable steady state, we altered either the concentration or dilution rate of a growth-limiting resource. This disturbance induced a complex transient response-characterized by the possible onset of oscillations-before population numbers relaxed to a new steady state. Thus, cell numbers could initially change in the opposite direction of the long-term change. We present quantitative indexes to characterize the transients and to show that the dynamic response is dependent on the degree of synchronization among life stages, which itself depends on the state of the population before perturbation. That is, we show how identical future steady states can be approached via different transients depending on the initial population structure. Our experimental results are supported by a size-structured model that accounts for interplay between cell-cycle and population-level processes and that includes resource-dependent variability in cell size. Our results should be relevant to other populations with a stage structure including organisms of higher order.
KW  - chemostat experiments
KW  - Chlorella vulgaris
KW  - environmental changes
KW  - population dynamics
KW  - stage structure
KW  - transient dynamics
Y1  - 2013
U6  - https://doi.org/10.1086/670590
SN  - 0003-0147
SN  - 1537-5323
VL  - 182
IS  - 1
SP  - 103
EP  - 119
PB  - Univ. of Chicago Press
CY  - Chicago
ER  -