8 research outputs found
Genotype-by-temperature interactions may help to maintain clonal diversity in Asterionella formosa (Bacillariophyceae)
No full textMarine and freshwater phytoplankton populations often show large clonal diversity, which is in disagreement with clonal selection of the most vigorous genotype(s). Temporal fluctuation in selection pressures in variable environments is a leading explanation for maintenance of such genetic diversity. To test the influence of temperature as a selection force in continually (seasonally) changing aquatic systems we carried out reaction norms experiments on co-occurring clonal genotypes of a ubiquitous diatom species, Asterionella formosa Hassall, across an environmentally relevant range of temperatures. We report within population genetic diversity and extensive diversity in genotype-specific reaction norms in growth rates and cell size traits. Our results showed genotype by environment interactions, indicating that no genotype could outgrow all others across all temperature environments. Subsequently, we constructed a model to simulate the relative proportion of each genotype in a hypothetical population based on genotype and temperature-specific population growth rates. This model was run with different seasonal temperature patterns. Our modeling exercise showed a succession of two to several genotypes becoming numerically dominant depending on the underlying temperature pattern. The results suggest that (temperature) context dependent fitness may contribute to the maintenance of genetic diversity in isolated populations of clonally reproducing microorganisms in temporally variable environments.
Challenges and opportunities for integrating lake ecosystem modelling approaches
No full textA large number and wide variety of lake ecosystem models have been developed and published during the past four decades. We identify two challenges for making further progress in this field. One such challenge is to avoid developing more models largely following the concept of others (‘reinventing the wheel’). The other challenge is to avoid focusing on only one type of model, while ignoring new and diverse approaches that have become available (‘having tunnel vision’). In this paper, we aim at improving the awareness of existing models and knowledge of concurrent approaches in lake ecosystem modelling, without covering all possible model tools and avenues. First, we present a broad variety of modelling approaches. To illustrate these approaches, we give brief descriptions of rather arbitrarily selected sets of specific models. We deal with static models (steady state and regression models), complex dynamic models (CAEDYM, CE-QUAL-W2, Delft 3D-ECO, LakeMab, LakeWeb, MyLake, PCLake, PROTECH, SALMO), structurally dynamic models and minimal dynamic models. We also discuss a group of approaches that could all be classified as individual based: super-individual models (Piscator, Charisma), physiologically structured models, stage-structured models and trait-based models. We briefly mention genetic algorithms, neural networks, Kalman filters and fuzzy logic. Thereafter, we zoom in, as an in-depth example, on the multi-decadal development and application of the lake ecosystem model PCLake and related models (PCLake Metamodel, Lake Shira Model, IPH-TRIM3D-PCLake). In the discussion, we argue that while the historical development of each approach and model is understandable given its ‘leading principle’, there are many opportunities for combining approaches. We take the point of view that a single ‘right’ approach does not exist and should not be strived for. Instead, multiple modelling approaches, applied concurrently to a given problem, can help develop an integrative view on the functioning of lake ecosystems. We end with a set of specific recommendations that may be of help in the further development of lake ecosystem model
The good, the bad and the plenty: interactive effects of food quality and quantity on different Daphnia species
No full textEffects of food quality and quantity on consumers are neither independent nor interchangeable. Although consumer
growth and reproduction show strong variation in relation to both food quality and quantity, the effects of food quality or
food quantity have usually been studied in isolation. In two experiments, we studied the growth and reproduction in three
filter-feeding freshwater zooplankton species, i.e. Daphnia galeata x hyalina, D. pulicaria and D. magna, on their algal food
(Scenedesmus obliquus), varying in carbon to phosphorus (C:P) ratios and quantities (concentrations). In the first experiment,
we found a strong positive effect of the phosphorus content of food on growth of Daphnia, both in their early and late
juvenile development. Variation in the relationship between the P-content of animals and their growth rate reflected
interspecific differences in nutrient requirements. Although growth rates typically decreased as development neared
maturation, this did not affect these species-specific couplings between growth rate and Daphnia P-content. In the second
experiment, we examined the effects of food quality on Daphnia growth at different levels of food quantity. With the same
decrease in P-content of food, species with higher estimated P-content at zero growth showed a larger increase in threshold
food concentrations (i.e. food concentration sufficient to meet metabolic requirements but not growth). These results
suggest that physiological processes such as maintenance and growth may in combination explain effects of food quality
and quantity on consumers. Our study shows that differences in response to variation in food quality and quantity exist
between species. As a consequence, species-specific effects of food quality on consumer growth will also determine how
species deal with varying food levels, which has implications for resource-consumer interactions.
Warming accelerates termination of a phytoplankton spring bloom by fungal parasites
No full textContains fulltext :
157042.pdf (Publisher’s version ) (Open Access
State of the art review on climate change impacts on natural ecosystems and adaptation
No full textClimate change has become unavoidable and the Netherlands has started to adapt the water systems and coastal defense to reduce vulnerability to the effects of climate change. These strategies to make the Netherlands climate-proof will also have its impact on nature and ecosystem functioning, in addition to the direct impacts of climate change. This report provides a state-of-the-art review of national and international research with respect to climate change impacts and adaptation, relevant to natural ecosystems in the Netherlands. This review is intended to serve as a reference of current available knowledge and will assist in programming new research required for climate-proofing the Netherland
Warming advances top-down control and reduces producer biomass in a freshwater plankton community
No full textContains fulltext :
175485.pdf (Publisher’s version ) (Open Access)16 p
Plankton dynamics under different climate conditions in tropical freshwater systems (a reply to the comment by Sarmento, Amado & Descy, 2013)
No full textContains fulltext :
117159.pdf (Publisher’s version ) (Open Access
The Ecology and Palaeoecology of Diatom – Duckweed Relationships
No full textThis thesis focuses on the ecology and palaeoecology of diatom-duckweed relationships and utilises a combined experimental, ecological and palaeoecological approach. In particular, the study sought to determine the potential of the epiphytic diatom Lemnicola hungarica to be utilised as a proxy indicator of past dominance of duckweed (Lemna) in small ponds. To this end, contemporary sampling of epiphytic diatom assemblages from a variety of macrophytes (including multiple samples of free-floating plants) were collected from around the world and analysed for diatom epiphytes. In this study, even despite significant environmental gradients, L. hungarica showed a significant association with free-floating plants (including Lemna spp.) as did Sellaphora seminulum. To determine whether this relationship might be used to infer Lemna-dominance in sediment cores, diatom assemblages were analysed in surface sediments from English Lemna and non-Lemna covered ponds and in a core from a pond (Bodham Rail Pit, eastern England) known to have exhibited periods of Lemna-dominance in the past. In both cases, the data suggested that both L. hungarica and S. seminulum were excellent predictors of past Lemna-dominance. Finally, to infer the consequences of Lemna-dominance for the long-term biological structure and ecosystem function of the Bodham Rail Pit, the sedimentary remains of diatoms, plant pigments, and plant and animal macrofossils were enumerated from two sediment cores. These stratigraphic data were compared with the diatom Lemna-indicator metric which indicated three distinct Lemna cycles. Sediment core analyses suggested major compositional, structural and ecological changes brought about by the Lemna cycles, especially in the submerged macrophyte community and in fish-invertebrate relationships. These data reveal that duckweed proliferation, often brought about by eutrophication and terrestrialisation in ponds, can result in dramatic ecological changes due to a strong physical ecosystem engineering effect
