Monika Winder - Academia.edu (original) (raw)

Papers by Monika Winder

ABSTRACT Background/Question/Methods The distribution of organisms along a body-size axis can rev... more ABSTRACT Background/Question/Methods The distribution of organisms along a body-size axis can reveal whether neutral or niche processes lie behind community structure: the neutral hypothesis for example predicts that such a distribution should be continuous, whereas organisms grouped in lumps can be indicative of the presence of niche-based processes. Recent studies of both aquatic and terrestrial communities have revealed discontinuous body-size distributions, indicating niche processes drive community structure. Identifying patterns in community-structure and their drivers is an important step towards distinguishing resilient from vulnerable communities, as changes in community structure could serve as indicators of an impending regime shift. However, while some of these studies conclude that these discontinuities are exogenously driven through discontinuities in the physical environment, other studies point towards endogenous drivers of community structure, arguing that competition alone can explain the observed body-size distributions. The methods used, their assumptions and the levels of data aggregation that lead to these contrasting conclusions differ considerably, making it difficult, if possible at all, to understand where exogenous or endogenous processes act or to make cross-comparisons between studied communities. Results/Conclusions We here compare four commonly used methods – the body-mass difference index, a kernel density estimator, the DIP-test and a latent class analysis – to produce a systematic framework to study discontinuities in community body-size distributions. We apply these models to two 20-year phytoplankton time-series from the Baltic Sea and analyze the results obtained in the context of each model’s assumptions and the levels of data aggregation. We find that niche processes drive the phytoplankton community structure in the Baltic Sea, that the effect of endogenous versus exogenous effects on structure are related to the scale of observation and that the patterns observed are not constant over time. We relate changes in community structure to environmental changes in the Baltic Sea, opening the door to further studies on indicators of system resilience.

Ecology letters, 2014

Scale is a key to determining which processes drive community structure. We analyse size distribu... more Scale is a key to determining which processes drive community structure. We analyse size distributions of phytoplankton to determine time scales at which we can observe either fixed environmental characteristics underlying communities structure or competition-driven size distributions. Using multiple statistical tests, we characterise size distributions of phytoplankton from 20-year time series in two sites of the Baltic Sea. At large temporal scales (5-20 years), size distributions are unimodal, indicating that fundamental barriers to existence are here subtler than in other systems. Frequency distributions of the average size of the species weighted by biovolume are multimodal over large time scales, although this is the product of often unimodal short-term (<1 year) patterns. Our study represents a much-needed structured, high-resolution analysis of phytoplankton size distributions, revealing that short-term analyses are necessary to determine if, and how, competition shapes t...

ABSTRACT Background/Question/Methods Our present understanding of climate warming on marine organ... more ABSTRACT Background/Question/Methods Our present understanding of climate warming on marine organisms is often restricted to the temperature dependence of individual species, while consequences for food web interactions and energy transfer efficiency are still unknown. The variety of diverse species responses might prevent extrapolation to the community and ecosystem level, because biotic interactions might lead to a dampening or amplification of single species effects. Here we investigate effects of increased temperature on energy (carbon) and nutritional transfer efficiency from primary producers to terminal zooplankton consumers using a natural microbial community from Espegrend Fjord, Bergen and two focal zooplankton groups: copepods and filter-feeding appendicularians. The cycling of organic matter was investigated using 13C labeled bicarbonate added to all mesocosms to follow the transfer of carbon from dissolved inorganic carbon (DIC) into phytoplankton, heterotrophic bacteria, and zooplankton. In addition to carbon flow, the biochemical (fatty acid, FA) composition as an index of seston food quality was investigated, as there is an increasing awareness of food quality as a limiting factor for consumers. The conversion of phytoplankton into mesozooplankton consumer biomass for carbon and production rates measured using combined FA-specific 13C isotope analysis (CS-SI). Results/Conclusions Enrichment of mesocosm with 13C indicated both exchange and drawdown over time, which was strongest at increased temperature. Phytoplankton FAs were enriched after one day of label addition, whereas the signal appeared later in bacteria and zooplankton consumers and differed between temperature treatments. Taxon-specific FA markers showed that phytoplankton groups differed in their response to warming. Along with shifts in phytoplankton community composition, the FA profile of seston and zooplankton changed, suggesting that in synchrony with altering species composition food quality changes for primary consumers can be expected under climate change. CS-SI analyses indicate that carbon flow to copepods and appendicularians varied with increased temperature. While overall bulk biomass did not change with temperature, turnover rates increased at higher temperature, suggesting that climate warming largely affects carbon transfer rates. This study suggests that CO2-induced shifts alter carbon flow through the planktonic food web, which will have significant effects on trophic transfer, particle sedimentation and nutrient cycling.

ABSTRACT Terrestrial plants have a life history that has evolved to a circannual rhythm in concer... more ABSTRACT Terrestrial plants have a life history that has evolved to a circannual rhythm in concert with the seasonal climate system and overall biomass follows a regular cycle of growth and senescence having a period of 1 year. Consistency in phase and amplitude render terrestrial plant activity an effective tool to observe shifts in the seasonal life cycle in response to climate change. The other half of Earth’s primary production occurs in aquatic systems, dominated by unicellular algae having the capacity to divide daily under optimal conditions and population changes can, in principle, occur any time within a year. Given that periods of life cycles differ on land compared to aquatic systems, it can be expected that patterns of seasonal variability might differ between terrestrial and pelagic plants. We compiled 121 phytoplankton biomass time series with a median length of 16 years from estuarine-coastal and lake ecosystems in the temperate and subtropical zone and address three questions: Do aquatic pelagic plants follow the canonical seasonal pattern of terrestrial plants? What are the dominant periodicities of aquatic primary producers? How recurrent are cyclical patterns from year to year? We applied wavelet analysis to extract the phase and amplitude of these long-term phytoplankton time series. The data revealed that in about 45 % of the aquatic sites an annual cycle of 12-month periodicity was strongest expressed, corresponding to one peak per year. In about 20 % the 6-month periodicity dominated, characteristic of two peaks within a year, and about 35 % showed a pattern best attributed to the 2-5 month band periodicity and for 2 % no consistent periodicity emerged. The reoccurrence of the seasonal fluctuations varied however greatly from year to year, ranging from more predictable patterns to irregular patterns in other sites. These findings suggest that seasonal activity of chlorophyll a can be unpredictable and variable. We propose drivers that give rise to the broad pattern of seasonal phytoplankton fluctuations and discuss advantages and limitations of using phytoplankton phenology as indicators of climate change.

ABSTRACT Background/Question/Methods Degradation of carrying capacity and consequent food limitat... more ABSTRACT Background/Question/Methods Degradation of carrying capacity and consequent food limitation has been proposed as one of the key factors driving the recent decline of pelagic fishes in the upper San Francisco Estuary. Dramatic drop in fish biomass, however, was not accompanied by equivalent decrease in zooplankton carbon, the key food source for threatened and endangered fish species. It is hypothesized that shifts in zooplankton species composition associated with the establishment of invasive species has reduced the nutritional prey quality for secondary consumers. We tested whether essential nutrient concentrations vary among native and introduced zooplankton species. Fatty acid (FA) associated food quality is a critical factor that regulates the energy transfer between primary producers and consumers, and plays an important role in growth, development and reproduction success in heterotrophs. We compared the fatty acid profiles of seven dominant native and invasive zooplankton species collected in the Estuary. Lower concentrations of essential FAs in invasive species would suggest negative changes in the food quality for fish. Results/Conclusions Our analyses show substantial differences in long-chain polyunsaturated FAs (PUFAs) across zooplankton taxa. The invasive cyclopoid Limnoithona that currently dominates plankton communities had the lowest concentration of eicosapentaenoic acid (EPA). We also detected substantially lower accumulation of monounsaturated fatty acids (MUFAs) by Limnoithona, potentially associated with their carnivorous diet. Higher accumulation of EPA but no accumulation of docosahexaenoic acid (DHA) in cladocerans was confirmed in our analysis of Daphnia. These taxonomical differences in the FA composition altered nutritional quality of the whole community, because native cladocerans significantly declined and invasive Limnoithona increased after their introduction in the early 1990s. Observed shifts in the essential FAs of the whole zooplankton community likely modified growth and survival of secondary consumers. Temporal dynamics in the zooplankton nutritional status is calculated and compared to the observed declines of pelagic fishes in the Estuary. Our study highlights the importance of nutritional quality to fully understand the underlying processes that limit production at higher trophic levels.

Annual Review of Ecology, Evolution, and Systematics, 2012

Water Research, 2004

Temporal variability in lake phytoplankton is controlled largely by a complex interplay between h... more Temporal variability in lake phytoplankton is controlled largely by a complex interplay between hydrodynamic and chemical factors, and food web interactions. We explored mechanisms underlying phytoplankton interannual variability in Lake Washington (USA), using a 25-yr time series of water quality data (1975-1999). Time-series analysis and PCA were used to decompose chlorophyll data into modes of variability. We found that phytoplankton dynamics in Lake Washington were characterized by four seasonal modes, each of which was associated with different ecological processes. The first mode coincided with the period when the system was light limited (January-March) and phytoplankton patterns were driven by the amount of available solar radiation. The second mode (April-June) coincided with the peak of the spring bloom and the subsequent decline of phytoplankton biomass, and was largely controlled by total phosphorus levels and grazing pressure from cladoceran zooplankton. Evidence of co-dependence and tight relationship between phytoplankton and cladoceran dynamics were also found from July to October when a large portion of the phosphorus supply in the mixed layer was provided by zooplankton excretion. The fourth mode (November-December) was associated with the transition to thermal and chemical homogeneity and the winter phytoplankton minima (2-2.5 microg/l). Finally, we examined the effects of meteorological forcing and large-scale oceanic climate fluctuations (ENSO and PDO) on phytoplankton dynamics and assessed the significance of their role on the interannual variability in the lake.

Proceedings of the Royal Society B: Biological Sciences, 2009

Philosophical Transactions of the Royal Society B: Biological Sciences, 2010

Marine Ecology Progress Series, 2013