scholarly journals Climate-induced changes in bottom-up and top-down processes independently alter a marine ecosystem

2012 ◽  
Vol 367 (1605) ◽  
pp. 2962-2970 ◽  
Author(s):  
Malte Jochum ◽  
Florian D. Schneider ◽  
Tasman P. Crowe ◽  
Ulrich Brose ◽  
Eoin J. O'Gorman
Keyword(s):  
Body Size ◽  
Body Mass ◽  
Nutrient Enrichment ◽  
Size Structure ◽  
Marine Ecosystem ◽  
Shore Crab ◽  
Top Predator ◽  
Top Down ◽  
Microalgal Biomass ◽  
Bottom Up

Climate change has complex structural impacts on coastal ecosystems. Global warming is linked to a widespread decline in body size, whereas increased flood frequency can amplify nutrient enrichment through enhanced run-off. Altered population body-size structure represents a disruption in top-down control, whereas eutrophication embodies a change in bottom-up forcing. These processes are typically studied in isolation and little is known about their potential interactive effects. Here, we present the results of an in situ experiment examining the combined effects of top-down and bottom-up forces on the structure of a coastal marine community. Reduced average body mass of the top predator (the shore crab, Carcinus maenas ) and nutrient enrichment combined additively to alter mean community body mass. Nutrient enrichment increased species richness and overall density of organisms. Reduced top-predator body mass increased community biomass. Additionally, we found evidence for an allometrically induced trophic cascade. Here, the reduction in top-predator body mass enabled greater biomass of intermediate fish predators within the mesocosms. This, in turn, suppressed key micrograzers, which led to an overall increase in microalgal biomass. This response highlights the possibility for climate-induced trophic cascades, driven by altered size structure of populations, rather than species extinction.

Trophic Relationships in Freshwater Pelagic Ecosystems

1986 ◽  
Vol 43 (8) ◽  
pp. 1571-1581 ◽  
Author(s):  
Donald J. McQueen ◽  
John R. Post ◽  
Edward L. Mills
Keyword(s):  
Food Web ◽  
Trophic Status ◽  
Size Structure ◽  
Trophic Relationships ◽  
Top Down ◽  
Eutrophic Lakes ◽  
Bottom Up ◽  
Coefficients Of Variation ◽  
Step Down ◽  
Pelagic Ecosystems

Relative impacts of bottom-up (producer controlled) and top-down (consumer controlled) forces on the biomass and size structure of five major components of freshwater pelagic systems (piscivores, planktivores, zooplankton, phytoplankton, and total phosphorus availability) were estimated. Predictions that emerge are (1) maximum biomass at each trophic level is controlled from below (bottom-up) by nutrient availability, (2) this bottom-up regulation is strongest at the bottom of the food web (i.e. phosphorus → phytoplankton) and weakens by a factor of 2 with each succeeding step up the food web, (3) as energy moves up a food web, the predictability of bottom-up interactions decreases, (4) near the top of the food web, top-down (predator mediated) interactions are strong and have low coefficients of variation, but weaken with every step down the food web, (5) variability around the bottom-up regressions can always be explained by top-down forces, and (6) interplay between top-down and bottom-up effects changes with the trophic status of lakes. In eutrophic lakes, top-down effects are strong for piscivore → zooplankton, weaker for planktivore → zooplankton, and have little impact for zooplankton → phytoplankton. For oligotrophic lakes, the model predicts that top-down effects are not strongly buffered, so that zooplankton → phytoplankton interactions are significant.

Size Spectrum Theory

2019 ◽  
pp. 15-37
Author(s):  
Ken H. Andersen
Keyword(s):  
Body Size ◽  
Power Law ◽  
Clearance Rate ◽  
Size Structure ◽  
Prey Size ◽  
Marine Ecosystem ◽  
Size Spectrum ◽  
Predator Prey ◽  
Predation Mortality ◽  
Size Preference

This chapter follows the size-structure of the entire marine ecosystem. It shows how the Sheldon spectrum emerges from predator–prey interactions and the limitations that physics and physiology place on individual organisms. How predator–prey interactions and physiological limitations scale with body size are the central assumptions in size spectrum theory. To that end, this chapter first defines body size and size spectrum. Next, it shows how central aspects of individual physiology scale with size: metabolism, clearance rate, and prey size preference. On that basis, it is possible to derive a power-law representation of the size spectrum by considering a balance between the needs of an organism (its metabolism) and the encountered prey, which is determined by the spectrum, the clearance rate, and the size preference. Lastly, the chapter uses the solution of the size spectrum to derive the expected size scaling of predation mortality.

scholarly journals Abundance and size structure of planktonic protist communities in a Neotropical floodplain: effects of top-down and bottom-up controls

2017 ◽  
Vol 29 (0) ◽  
Author(s):  
Bianca Ramos de Meira ◽  
Fernando Miranda Lansac-Tôha ◽  
Bianca Trevizan Segovia ◽  
Felipe Rafael de Oliveira ◽  
Paulo Roberto Bressan Buosi ◽  
...  
Keyword(s):  
Heterotrophic Bacteria ◽  
Size Structure ◽  
Information Criterion ◽  
Heterotrophic Flagellates ◽  
Control Mechanisms ◽  
Linear Regression Models ◽  
Top Down ◽  
Bottom Up ◽  
Upper Paraná River Floodplain ◽  
Predation Effects

Abstract: Aim: We aimed to assess the influence of bottom-up and top-down control mechanisms on the abundance and size structure of protist communities (heterotrophic flagellates and ciliates). We formulated the following hypothesis: bottom-up control mechanisms, related to the availability of resources in the environment, are responsible for structuring the abundance of these communities, whereas top-down control mechanisms, related to predation effects, determine the size pattern of these organisms. Methods Samples for planktonic organisms were taken in 20 shallow lakes belonging to the upper Paraná River floodplain. We evaluated linear regression models to select the best model which predicts the patterns observed according to Akaike Information Criterion. Results The best models selected to explain the abundance of heterotrophic flagellates included negative relations with picophytoplankton abundance and positive with rotifers abundance, while for their size structure, negative relationships were found with heterotrophic bacteria, ciliates and rotifers biovolumes. In relation to the ciliates, their abundances were positively related to the rotifers and picophytoplankton abundances and negatively with the heterotrophic bacteria abundance. On the other hand, for the size structure, the best models selected strong negative relations with the microcrustaceans biovolumes, in addition to relations with the different fractions of the phytoplankton. Conclusion For both flagellates and ciliates, their abundance is being mainly regulated by a bottom up control mechanism, whereas for the size structure the results showed that both food resources and predators were important, indicating that bottom-up and top-down mechanisms act simultaneously in determining the size of these microorganisms.

Short Note: Paradigms need hypothesis testing: no evidence for top-down forcing on Adélie and emperor penguin populations

2008 ◽  
Vol 20 (4) ◽  
pp. 391-392 ◽  
Author(s):  
Christophe Barbraud ◽  
Cedric Cotte
Keyword(s):  
Southern Ocean ◽  
Species Interactions ◽  
Research Effort ◽  
Marine Ecosystem ◽  
Short Note ◽  
Emperor Penguin ◽  
Ecological Research ◽  
Top Down ◽  
Bottom Up ◽  
Ecosystem Interactions

In their recent review article “Paradigm lost, or is top-down forcing no longer significant in the Antarctic marine ecosystem?” Ainley et al. (2007) questioned why Southern Ocean marine ecologists apparently have shifted to a central paradigm where bottom-up forcing by physics and climate change has become the single most important driver of food web dynamics in the Southern Ocean. Ainley et al. (2007) suggest that top-down forcing (forcing by biotic processes) is no longer considered in the interpretation of ecological research results aimed at understanding ecosystem processes of the Southern Ocean. Based on two examples from the literature they suggest that population trends could better be explained by including species interactions in the modelling rather than by changes in climate related physical processes alone. Nicol et al. (2007) questioned the paradigm shift proposed by Ainley et al. (2007) and made a broad review of the ecological research conducted in the Southern Ocean ecosystems. They concluded that there has been considerable research effort into ecosystem interactions over the last 25 years in the Southern Ocean, and that there seems little evidence that there has been an almost complete shift in paradigms; rather both bottom-up and top-down processes are recognized to govern ecosystems functioning.

Regional ecosystem variability drives the relative importance of bottom-up and top-down factors for zooplankton size spectra

2007 ◽  
Vol 64 (3) ◽  
pp. 516-529 ◽  
Author(s):  
Kerri Finlay ◽  
Beatrix E Beisner ◽  
Alain Patoine ◽  
Bernadette Pinel-Alloul
Keyword(s):  
Pareto Distribution ◽  
Size Structure ◽  
Fish Predation ◽  
Top Down ◽  
Lake Productivity ◽  
Size Spectra ◽  
Bottom Up ◽  
Zooplankton Size ◽  
Fish Species Composition ◽  
Zooplankton Communities

The relative effects of top-down and bottom-up drivers of zooplankton size structure were examined in three limnologically diverse regions of Quebec, Canada. Lake productivity drove biomass of small-sized zooplankton (300–1000 µm) in the Eastern Townships and Laurentian regions, which have high total phosphorus gradients, but was not significant in the low-productivity region, Gouin. Fish species composition was found to affect biomass of large-sized (>1000 µm) zooplankton and was the primary factor affecting zooplankton size structure in the low productivity region. When size structure of the zooplankton communities were described as normalized biomass size spectra, only bottom-up factors were significant, as increasing productivity resulted in higher curve peaks and increased parabola curvature. No factors were significantly related to any parameter of the Pareto distribution to describe size spectra. Overall, bottom-up forces were stronger drivers of zooplankton size structure, particularly in regions with wide ranges in lake trophy, while fish predation was more important in regions with low productivity variability.

scholarly journals Bottom-up and top-down effects of temperature on body growth, population size spectra and yield in a size-structured food web

2021 ◽  
Author(s):  
Max Lindmark ◽  
Asta Audzijonyte ◽  
Julia Blanchard ◽  
Anna Gårdmark
Keyword(s):  
Food Web ◽  
Growth Rates ◽  
Temperature Effects ◽  
Size Structure ◽  
Metabolic Effects ◽  
Young Fish ◽  
Top Down ◽  
Bottom Up ◽  
Effects Of Temperature ◽  
Size At Age

AbstractResolving the combined effect of climate warming and exploitation in a food web context is key for predicting future biomass production, size-structure, and potential yields of marine fishes. Previous studies based on mechanistic size-based food web models have found that bottom-up processes are important drivers of size-structure and fisheries yield in changing climates. However, we know less about the joint effects of ‘bottom-up’ and ‘top-down’ effects of temperature: how do temperature effects propagate from individual-level physiology through food webs and alter the size-structure of exploited species in a community? Here we assess how a species-resolved size-based food web is affected by warming through both these pathways, and by exploitation. We parameterize a dynamic size spectrum food web model inspired by the offshore Baltic Sea food web, and investigate how individual growth rates, size-structure, relative abundances of species and yields are affected by warming. The magnitude of warming is based on projections by the regional coupled model system RCA4-NEMO and the RCP 8.5 emission scenario, and we evaluate different scenarios of temperature dependence on fish physiology and resource productivity. When accounting for temperature-effects on physiology in addition to on basal productivity, projected size-at-age in 2050 increases on average for all fish species, mainly for young fish, compared to scenarios without warming. In contrast, size-at-age decreases when temperature affects resource dynamics only, and the decline is largest for young fish. Faster growth rates due to warming, however, do not always translate to larger yields, as lower resource carrying capacities with increasing temperature tend to result in declines in the abundance of larger fish and hence spawning stock biomass – the part of the population exposed to fishing. These results show that to understand how global warming impacts the size structure of fish communities, both direct metabolic effects and indirect effects of temperature via basal resources must be accounted for.

Psychology and Culture: Top Down Versus Bottom Up?

PsycCRITIQUES ◽  
2005 ◽  
Vol 50 (19) ◽  
Author(s):  
Michael Cole
Keyword(s):  
Top Down ◽  
Bottom Up
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