Can top-down and bottom-up forces explain phytoplankton structure in a subtropical and shallow groundwater-connected lake?

Bottom-up and top-down control of phytoplankton is one of the most important hypothesis that explains and predicts the structure of aquatic community. Our aim was to elucidate whether predation and resource limitation can control phytoplankton composition and abundance in a subtropical shallow lake with groundwater connection to the river system. During 12 months, the lake was sampled at three points. Physico-chemical parameters, phytoplankton and zooplankton were sampled fortnightly, whereas fish were sampled every 3 months. The results showed that Euglenophyta dominated the total biovolume, followed by Dinophyta and Cryptophyta. As for the species composition, Chlorophyta was the dominant group (80 species recorded), followed by phylum Cyanobacteria (26 species recorded). Redundancy analysis (RDA) indicated that temperature and nitrate + nitrite concentration mainly explained biovolume changes, with zooplankton predation not having any measurable effect on phytoplankton during the high-water (HW) period. During low-water (LW) period top-down by fish was more important. At higher taxonomic resolution (species biovolume), phosphorus was another controlling factor. We concluded that phytoplankton in this lake is mainly regulated by hydrological changes as a macrofactor that affects nutrient availability and other environmental conditions. Even though bottom-up top-down forces do not have a central effect, we found evidence of positive nutrient influences at the HW period and fish effect at the LW period.

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Assessing the relevance of top-down and bottom-up effects as phytoplankton structure drivers in a subtropical hypereutrophic shallow lake

Aquatic Ecology ◽

10.1007/s10452-019-09687-3 ◽

2019 ◽

Vol 53 (2) ◽

pp. 265-280 ◽

Cited By ~ 1

Author(s):

Diego Frau ◽

Yamila Battauz ◽

Patricio Francisco Alvarenga ◽

Pablo Augusto Scarabotti ◽

Gisela Mayora ◽

...

Keyword(s):

Shallow Lake ◽

Top Down ◽

Bottom Up ◽

Phytoplankton Structure

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Selection Method of Dendritic River Networks Based on Hybrid Coding for Topographic Map Generalization

ISPRS International Journal of Geo-Information ◽

10.3390/ijgi9050316 ◽

2020 ◽

Vol 9 (5) ◽

pp. 316

Author(s):

Chengming Li ◽

Wei Wu ◽

Pengda Wu ◽

Yong Yin ◽

Zhaoxin Dai

Keyword(s):

River System ◽

River Network ◽

River Networks ◽

Map Generalization ◽

Topographic Map ◽

Top Down ◽

Bottom Up ◽

Hybrid Coding ◽

Coding Systems ◽

Selection Of

As the coding of a dendritic river system can be used to represent the stream order and spatial-structure of a river network, it is always used in river selection, which is a key step in topographic map generalization. There are two categories of conventional hydrological coding systems, one is the top-down approach, and the other is the bottom-up approach. However, the former does not accurately reflect the hierarchies of a dendritic river network, which is produced by catchment relationships, and it is not appropriate for the stream selection of river networks with uniform distributions of tributaries. The latter cannot directly indicate the subtree depth of a stream, and it is not favorable to stream selection of river systems that have topologically deep structures. Therefore, a selection method for dendritic river networks based on hybrid coding is proposed in this paper. First, the dendritic river network is coded through classical top-down Horton coding. Second, directed topology trees are constructed to organize the river network data, and stroke connections are calculated to code the river network in the bottom-up approach. Third, the river network is marked through hybrid usage of the top-down approach and bottom-up approach, and based on the spatial characteristics of the river network, the river network is classified into three kinds of subtrees: deep branch, shallow branch and modest branch. Then, appropriate coding is assigned automatically to different subtrees to achieve river selection. Finally, actual topographic map data of a river system in a region of Hubei Province are used to comparatively validate the hybrid coding system against two existing isolated coding systems. The experimental results demonstrate that the hybrid coding method is very effective for river network selection, not only in highlighting hierarchies formed by catchment relationships but also in the uniform distribution of tributaries.

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Upgraded Masculinity: A Gendered Analysis of the Debriefing in the Israeli Air Force

Gender & Society ◽

10.1177/0891243217750106 ◽

2018 ◽

Vol 32 (2) ◽

pp. 228-251 ◽

Cited By ~ 2

Author(s):

Varda Wasserman ◽

Ilan Dayan ◽

Eyal Ben-Ari

Keyword(s):

Air Force ◽

New Technologies ◽

Human Life ◽

Dominant Group ◽

Top Down ◽

Bottom Up ◽

Gender Ideals ◽

Improved Performance ◽

The Military

This article examines the importation of new gender ideals into a highly masculine organization through top-down and bottom-up processes. We analyze how a dominant group of men undo and redo gender to reproduce their supremacy and create a new, “improved” form of masculinity. Based on qualitative research on the practice of debriefing in the Israel Air Force, we explore how new practices of masculinity are incorporated into a hegemonic masculinity by introducing so-called “soft” organizational practices and thus constructing a new form of “upgraded” masculinity. We show that pilots are involved in two continual and dialectical processes of performing masculinity. The first includes top-down practices neutralizing opportunities to execute exaggerated masculine performances, including new technologies allowing recording and documenting of all flights, a safety discourse emphasizing the protection of human life, and organizational learning based on self- and group critiques aimed at improved performance. The second, a bottom-up process enacted by pilots, is aimed at restoring and mobilizing masculinity and includes rationalized professionalism, competitiveness, and patronizing. Taken together, these constitute a hybrid, “upgraded” masculinity where “soft” characteristics are appropriated by men to reinforce a privileged status and reproduce their dominance within and outside the military. Our case study focuses on the debriefing, a process in which air teams formally reflect on their performance after a particular task/event to improve it.

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Food chains and food webs: controlling factors and cascading effects

Community Ecology ◽

10.1093/oso/9780198835851.003.0011 ◽

2019 ◽

pp. 206-230

Author(s):

Gary G. Mittelbach ◽

Brian J. McGill

Keyword(s):

Trophic Level ◽

Resource Limitation ◽

Trophic Levels ◽

Joint Control ◽

Top Down ◽

Bottom Up ◽

Cascading Effects ◽

Natural Systems ◽

Ecosystem Size ◽

Community Theory

This chapter uses simple theory and experiments to address the fundamental question of what determines the biomass (abundance) of different trophic levels (plants, herbivores, carnivores) in a community. Theory predicts joint control of trophic-level abundance by bottom-up effects (resources) and top-down effects (predation), with the relative strengths of top-down and bottom-up effects depending on the number of trophic levels and species composition within a trophic level. Observations and experiments support these predictions. Trophic cascades provide evidence for the importance of top-down processes, but the existence of a trophic cascade says little about the relative importance of predator limitation versus resource limitation. Cascading effects result from either the consumptive or non-consumptive effects of predators, or both. Natural systems contain as few as three and as many as six trophic levels, but what determines this number is unknown. Evidence suggests that both productivity and ecosystem size, perhaps in combination, are the primary factors.

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