scholarly journals Aggregating a Plankton Food Web: Mathematical versus Biological Approaches

Mathematics ◽  
2018 ◽  
Vol 6 (12) ◽  
pp. 336 ◽  
Author(s):  
Ferenc Jordán ◽  
Anett Endrédi ◽  
Wei-chung Liu ◽  
Domenico D’Alelio

Species are embedded in a web of intricate trophic interactions. Understanding the functional role of species in food webs is of fundamental interests. This is related to food web position, so positional similarity may provide information about functional overlap. Defining and quantifying similar trophic functioning can be addressed in different ways. We consider two approaches. One is of mathematical nature involving network analysis where unique species can be defined as those whose topological position is very different to others in the same food web. A species is unique if it has very different connection pattern compared to others. The second approach is of biological nature, based on trait-based aggregations. Unique species are not easy to aggregate with others because their traits are not in common with the ones of most others. Our goal here is to illustrate how mathematics can provide an alternative perspective on species aggregation, and how this is related to its biological counterpart. We illustrate these approaches using a toy food web and a real food web and demonstrate the sensitive relationships between those approaches. The trait-based aggregation focusing on the trait values of size (sv) can be best predicted by the mathematical aggregation algorithms.

2015 ◽  
Vol 70 (1) ◽  
pp. 24-42 ◽  
Author(s):  
Pietro Beritelli ◽  
Federica Buffa ◽  
Umberto Martini

Purpose – The purpose of this paper is to present an alternative perspective on understanding the coordinating role of destination management organizations. Destination Management Organizations (DMOs) are known to have a coordinating role within a destination. Many qualitative case studies discuss this role in the institutional context, assuming that the DMO is supposed to coordinate the network of the organizations and stakeholder groups in the destination. By contrast, this paper analyzes the coordinator role of DMOs by focusing primarily on the prominent individuals (directors and board members) affiliated with it. In so doing, it proposes an alternative perspective on these organizations. Looking at the influential individuals in the destination, in particular those affiliated with the DMO, reveals new insights into what the DMO alternatively could be from an individual’s perspective. Design/methodology/approach – Using social network analysis, the coordinator role of the actors affiliated with the DMO for six destination cases in Switzerland, Italy and Austria was measured. First, the network of the most salient individuals in the destination was identified. Second, the coordinator score with the help of the Gould and Fernandez measure was measured. Third, the coordinator scores of individuals affiliated with the DMO were compared against those of the other actors in the network. Fourth, the scores of actors affiliated with the DMO and other actors were compared to the coordinator role attributed to the whole organization by those individuals (i.e. how they see the DMO as coordinator). Fifth, the analysis of the results with case-specific information was completed. Findings – In each of the six destinations, there are actors affiliated with the DMO as top scorers; these are usually the president of the board and other board members, as well as the director. Additionally, the analysis identifies further board members of the DMO among the tourist elite in the destination. The DMO as an organization is generally seen as an important coordinating institution. In particular, the actors affiliated with the DMO attribute a higher coordinating role to the organization than do the other respondents. Practical implications – In their board constellation, DMOs support the formation of interlocking directorships through the representation of various stakeholder groups. They increase the concentration of power in favor of a small group (elite), but they can also increase the effectiveness of decisional processes. In so doing, a DMO serves as a valuable platform for leaders in its destination. Social implications – This study affords a surprising insight into the difference between the overall image actors have of DMOs and the organizations’ self-images, expressed by the actors affiliated to the organizations – the former is always lower than the latter. The study also clearly demonstrates that the role of an institution largely depends on the actors affiliated to it and hence points to the constantly adapting coordinating role of DMOs within destinations. Originality/value – A DMO can be seen as an organization constituted by individuals who join and leave its board or its management. This paper proposes an actor-based analysis of these often small, but controversially discussed organizations. We do it with a combination of quantitative measures from network analysis and qualitative information. The alternative perspective (actors of the DMOs inside the elite) and the application of social network analysis for this purpose have not been used in studies before. Further research points to two new research streams, namely, to understanding the role attributed to the DMO by different actors in the destination and the reasons for joining/leaving the organization and the shift of the self-concept of the DMO.


2018 ◽  
Author(s):  
Charles W Martin ◽  
John F Valentine

Estuaries of the northern Gulf of Mexico contain an abundance of habitat-forming submerged aquatic vegetation (SAV) that provide refuge and protection for a variety of freshwater, estuarine, and marine organisms. However, many of these estuaries now contain numerous exotic species, the ultimate impacts of which are unclear. In the Mobile-Tensaw Delta, located in the upper portion of Mobile Bay, Alabama (USA), Eurasian milfoil (Myriophyllum spicatum, hereafter referred to as Myriophyllum) is now the most dominant submerged macrophyte. Myriophyllum is a structurally-complex macrophyte with the potential to dramatically alter estuarine food webs through reduced encounter rates between predators and their prey and other mechanisms. Previously, we surveyed faunal communities using throw traps, trawls, cores, and suction sampling to compare milfoil assemblages with other native macrophytes to explore the interactive role of hydrology, diel periodicity, and macrophyte presence in influencing community structure. Here, we use this previously collected data to generate a preliminary food web analyses to determine if milfoil, due to its high complexity, creates a "trophic dead end" and limits higher trophic level production. We found the number of nodes, links, linkage density, and connectance to all be greater in milfoil than Vallisneria americana (hereafter referred to as Vallisneria), indicating that a diverse, productive, and highly connected food web exists in this invasive habitat.


Author(s):  
Kevin S. McCann

This chapter examines food webs at the landscape scale by focusing on the large-scale food web architecture that is deeply constrained by space. It begins with a discussion of how variability in space, time, and food web structure, coupled with the ability of organisms to rapidly respond to variation, affect the maintenance of the food web and its functions. It then explains how individual traits such as body size and foraging behavior relate to food web structure in space and time. It also considers the role of spatial constraints on food webs and how the existence of fast–slow pathways coupled by mobile adaptive predators gives rise to spatial asynchrony in the resources. The chapter concludes with a review of some empirical examples to show that some food webs display the bird feeder effect and that resource coupling of distinct habitats appears to stabilize food webs.


2018 ◽  
Vol 593 ◽  
pp. 61-72 ◽  
Author(s):  
M Corry ◽  
D Harasti ◽  
T Gaston ◽  
D Mazumder ◽  
T Cresswell ◽  
...  

2010 ◽  
Vol 278 (1713) ◽  
pp. 1886-1893 ◽  
Author(s):  
Eoin J. O'Gorman ◽  
Jon M. Yearsley ◽  
Tasman P. Crowe ◽  
Mark C. Emmerson ◽  
Ute Jacob ◽  
...  

Functionally unique species contribute to the functional diversity of natural systems, often enhancing ecosystem functioning. An abundance of weakly interacting species increases stability in natural systems, suggesting that loss of weakly linked species may reduce stability. Any link between the functional uniqueness of a species and the strength of its interactions in a food web could therefore have simultaneous effects on ecosystem functioning and stability. Here, we analyse patterns in 213 real food webs and show that highly unique species consistently tend to have the weakest mean interaction strength per unit biomass in the system. This relationship is not a simple consequence of the interdependence of both measures on body size and appears to be driven by the empirical pattern of size structuring in aquatic systems and the trophic position of each species in the web. Food web resolution also has an important effect, with aggregation of species into higher taxonomic groups producing a much weaker relationship. Food webs with fewer unique and less weakly interacting species also show significantly greater variability in their levels of primary production. Thus, the loss of highly unique, weakly interacting species may eventually lead to dramatic state changes and unpredictable levels of ecosystem functioning.


2016 ◽  
Vol 335 ◽  
pp. 87-100 ◽  
Author(s):  
Laura E. Koehn ◽  
Timothy E. Essington ◽  
Kristin N. Marshall ◽  
Isaac C. Kaplan ◽  
William J. Sydeman ◽  
...  

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Zachariah G. Schonberger ◽  
Kevin McCann ◽  
Gabriel Gellner

AbstractModular food web theory shows how weak energetic fluxes resulting from consumptive interactions plays a major role in stabilizing food webs in space and time. Despite the reliance on energetic fluxes, food web theory surprisingly remains poorly understood within an ecosystem context that naturally focuses on material fluxes. At the same time, while ecosystem theory has employed modular nutrient-limited ecosystem models to understand how limiting nutrients alter the structure and dynamics of food webs, ecosystem theory has overlooked the role of key ecosystem interactions and their strengths (e.g., plant-nutrient; R-N) in mediating the stability of nutrient-limited ecosystems. Here, towards integrating food web theory and ecosystem theory, we first briefly review consumer-resource interactions (C-R) highlighting the relationship between the structure of C-R interactions and the stability of food web modules. We then translate this framework to nutrient-based systems, showing that the nutrient-plant interaction behaves as a coherent extension of current modular food web theory; however, in contrast to the rule that weak C-R interactions tend to be stabilizing we show that strong nutrient-plant interactions are potent stabilizers in nutrient-limited ecosystem models.


2018 ◽  
Author(s):  
Charles W Martin ◽  
John F Valentine

Estuaries of the northern Gulf of Mexico contain an abundance of habitat-forming submerged aquatic vegetation (SAV) that provide refuge and protection for a variety of freshwater, estuarine, and marine organisms. However, many of these estuaries now contain numerous exotic species, the ultimate impacts of which are unclear. In the Mobile-Tensaw Delta, located in the upper portion of Mobile Bay, Alabama (USA), Eurasian milfoil (Myriophyllum spicatum, hereafter referred to as Myriophyllum) is now the most dominant submerged macrophyte. Myriophyllum is a structurally-complex macrophyte with the potential to dramatically alter estuarine food webs through reduced encounter rates between predators and their prey and other mechanisms. Previously, we surveyed faunal communities using throw traps, trawls, cores, and suction sampling to compare milfoil assemblages with other native macrophytes to explore the interactive role of hydrology, diel periodicity, and macrophyte presence in influencing community structure. Here, we use this previously collected data to generate a preliminary food web analyses to determine if milfoil, due to its high complexity, creates a "trophic dead end" and limits higher trophic level production. We found the number of nodes, links, linkage density, and connectance to all be greater in milfoil than Vallisneria americana (hereafter referred to as Vallisneria), indicating that a diverse, productive, and highly connected food web exists in this invasive habitat.


2020 ◽  
Vol 37 (3) ◽  
pp. 351-363
Author(s):  
Michel Iskin da S Costa ◽  
Lucas Dos Anjos

Abstract In food webs, fishery can play the role of top predator, competing thus with other top predators for valuable food resources. In this view, it has been claimed in fisheries management that culling of top predators can be a means to improve fishery yield. To investigate this hypothesis, we use theoretical population models to assess in a multispecies context how fishery yield from target species harvest responds to top predator cull. Defying crisp summary, the four analysed food web models show that this response may be either positive or negative or both, indicating that in terms of multispecies fishery management the harvest yield may not accrue as a consequence of predator removal. In addition, this multitude of behaviours points also to the fact that the response of fishery yield to top predator cull may be difficult to assess.


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