scholarly journals Mechanisms of trophic niche compression: evidence from landscape disturbance

2018 ◽  
Author(s):  
Francis J. Burdon ◽  
Angus R. McIntosh ◽  
Jon S. Harding
Keyword(s):  
Food Web ◽  
Food Webs ◽  
Agricultural Land ◽  
Trophic Position ◽  
Resource Scarcity ◽  
Trophic Niche ◽  
Isotopic Niche ◽  
List Type ◽  
Landscape Disturbance ◽  
Trophic Diversity

AbstractNatural and anthropogenic disturbances commonly alter patterns of biodiversity and ecosystem functioning. However, how food webs respond to these changes remains poorly understood. Here, we have described aquatic food webs using invertebrate and fish community composition, functional traits, and stable isotopes from twelve agricultural streams along a landscape disturbance gradient.We predicted that excessive inputs of fine inorganic sediment (sedimentation) associated with agricultural land uses would negatively influence stream trophic diversity (e.g., reduced vertical and horizontal trophic niche breadths).Food-web properties based on Bayesian analyses of stable isotope data (δ13C and δ15N) from consumers showed that increasing sediment disturbance was associated with reduced trophic diversity, indicated by the whole community (fish and invertebrates combined) occupying a smaller area in isotopic niche space. Reductions in trophic diversity were best explained by a narrowing of the consumer δ13C range, and to a lesser extent, consumer δ15N range along the sedimentation gradient.We hypothesized that multiple mechanisms associated with sedimentation may have caused trophic niche ‘compression’. Decreased niche partitioning, driven by increasing habitat homogeneity, environmental filtering, and resource scarcity seemingly lead to a greater similarity in trophic roles. These pathways may have contributed to a reduction in trophic diversity, whereas increased resource homogeneity was seemingly less important.Our results also indicate downward shifts in the vertical trophic position of benthic meospredators and invertebrate prey relative to higher consumers. This ‘trophic decoupling’ suggests that terrestrial resource subsidies may offset reductions of aquatic prey for larger stream fishes.Sedimentation was associated with reduced trophic diversity, which may affect the functioning and stability of stream ecosystems. Our study helps explain how multiple mechanisms can influence food-web properties in response to this type of disturbance.

scholarly journals fluxweb: a R package to easily estimate energy fluxes in food webs

2017 ◽  
Author(s):  
Benoit Gauzens ◽  
Andrew Barnes ◽  
Darren Giling ◽  
Jes Hines ◽  
Malte Jochum ◽  
...  
Keyword(s):  
Steady State ◽  
Food Web ◽  
Food Webs ◽  
Ecosystem Functioning ◽  
R Package ◽  
Estimation Methods ◽  
List Type ◽  
Energy Fluxes ◽  
Flux System ◽  
Primary Output

AbstractUnderstanding how changes in biodiversity will impact the stability and functioning of ecosystems is a central challenge in ecology. Food-web approaches have been advocated to link community composition with ecosystem functioning by describing the fluxes of energy among species or trophic groups. However, estimating such fluxes remains problematic because current methods become unmanageable as network complexity increases.We developed a generalisation of previous indirect estimation methods assuming a steady state system [1, 2, 3]: the model estimates energy fluxes in a top-down manner assuming system equilibrium; each node’s losses (consumption and physiological) balances its consumptive gains. Jointly, we provide theoretical and practical guidelines to use the fluxweb R package (available on CRAN at https://bit.ly/2OC0uKF).We also present how the framework can merge with the allometric theory of ecology [4] to calculate fluxes based on easily obtainable organism-level data (i.e. body masses and species groups -eg, plants animals), opening its use to food webs of all complexities. Physiological losses (metabolic losses or losses due to death other than from predation within the food web) may be directly measured or estimated using allometric relationships based on the metabolic theory of ecology, and losses and gains due to predation are a function of ecological efficiencies that describe the proportion of energy that is used for biomass production.The primary output is a matrix of fluxes among the nodes of the food web. These fluxes can be used to describe the role of a species, a function of interest (e.g. predation; total fluxes to predators), multiple functions, or total energy flux (system throughflow or multitrophic functioning). Additionally, the package includes functions to calculate network stability based on the Jacobian matrix, providing insight into how resilient the network is to small perturbations at steady state.Overall, fluxweb provides a flexible set of functions that greatly increase the feasibility of implementing food-web energetic approaches to more complex systems. As such, the package facilitates novel opportunities for mechanistically linking quantitative food webs and ecosystem functioning in real and dynamic natural landscapes.

The trophic role of Octopus insularis at a pristine tropical atoll in southwest Atlantic: a potential keystone predator?

2019 ◽  
Author(s):  
Renato Junqueira de Souza Dantas ◽  
Tatiana Silva Leite ◽  
Cristiano Queiroz de Albuquerque
Keyword(s):  
Food Web ◽  
Trophic Position ◽  
Feeding Strategy ◽  
Isotope Analysis ◽  
Carbon Sources ◽  
Trophic Levels ◽  
Isotopic Niche ◽  
Southwest Atlantic ◽  
Trophic Role

In the present study, we evaluated the trophic role of Octopus insularis Leite and Haimovici, 2008 in the food web of Rocas Atoll, a preserved insular territory in the southwest Atlantic. Using stable isotope analysis of C and N, we showed that the local trophic web comprises at least four trophic levels, where the octopus presents d13C values from -12.1 to -6.1‰, d15N values from 6.4 to 11.0‰ and occupies a trophic position (TP) between the second and third trophic levels (mean ± SD TPadditive = 3.08 ± 0.36; TPBayesian = 3.12 ± 0.17). Among other benthic/reef-associated consumers, this cephalopod stood out for its much wider isotopic niche (SEAB = 4.7890), pointing to a diet diversified in carbon sources, but focused on prey in lower TPs. Time-minimizing feeding strategy seemed almost permanent throughout the life cycle, given the great niche overlap between small and large octopuses (large: SEAB = 4.59, small: SEAB = 4.03) and their very similar trophic positions (TPadditive/TPBayesian: large = 3.27/3.26; small = 2.89/2.99). Also, as a prey, O. insularis composed 16%-24% of the diet of some benthic/demersal predators. Overall, exerting great predatory pressure on bottom-associated organisms and serving as a relevant food source for top and mesopredators, O. insularis represented a top consumer of the benthic portion of the food web and an important link between its benthic and demersal strata with potential for keystone species.

scholarly journals Loss of functionally unique species may gradually undermine ecosystems

2010 ◽  
Vol 278 (1713) ◽  
pp. 1886-1893 ◽  
Author(s):  
Eoin J. O'Gorman ◽  
Jon M. Yearsley ◽  
Tasman P. Crowe ◽  
Mark C. Emmerson ◽  
Ute Jacob ◽  
...  
Keyword(s):  
Food Web ◽  
Food Webs ◽  
Ecosystem Functioning ◽  
Trophic Position ◽  
Interaction Strength ◽  
Natural Systems ◽  
Interacting Species ◽  
Weakly Interacting ◽  
Taxonomic Groups ◽  
Unique Species

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.

Depth-specific patterns in benthic–planktonic food web relationships in Lake Superior

2006 ◽  
Vol 63 (7) ◽  
pp. 1496-1503 ◽  
Author(s):  
Michael E Sierszen ◽  
Gregory S Peterson ◽  
Jill V Scharold
Keyword(s):  
Great Lakes ◽  
Food Web ◽  
Food Webs ◽  
Water Column ◽  
Trophic Position ◽  
Lake Superior ◽  
Benthic Algae ◽  
Isotope Ratios ◽  
Food Sources ◽  
Large Lakes

In an investigation of the spatial characteristics of Laurentian Great Lakes food webs, we examined the trophic relationship between benthic amphipods (Diporeia) and plankton in Lake Superior. We analyzed the carbon and nitrogen stable isotope ratios of Diporeia and plankton at stations in water column depths of 4–300 m. Neither δ15N nor δ13C of plankton from the upper 50 m of the water column varied significantly with station depth. Diporeia isotope ratios exhibited depth-specific patterns reflecting changes in food sources and food web relationships with plankton. Diporeia was 13C enriched at station depths of <40 m, reflecting increased dietary importance of benthic algae. There was a systematic increase in Diporeia δ15N with depth, which appeared to result from a combination of dietary shifts in the nearshore and decompositional changes in Diporeia's principal food, sedimented plankton, in deep habitats. Diporeia δ13C and δ15N together described changes in food web isotope baseline with depth. They also discriminated three depth strata representing photic, mid-depth, and profundal zones. These findings have implications for our understanding of Great Lakes food webs and analyses of trophic position within them, the ecology of zoobenthos and plankton communities, and sampling designs for large lakes.

Trophic positions and predator–prey mass ratio of the pelagic food web in the East China Sea and Sea of Japan

2016 ◽  
Vol 67 (11) ◽  
pp. 1692 ◽  
Author(s):  
Seiji Ohshimo ◽  
Hiroshige Tanaka ◽  
Koh Nishiuchi ◽  
Tohya Yasuda
Keyword(s):  
Food Web ◽  
Food Webs ◽  
East China Sea ◽  
Sea Of Japan ◽  
Trophic Position ◽  
Mass Ratio ◽  
The East China Sea ◽  
Predator Prey ◽  
Prey Mass ◽  
Scaled Models

Size-based food webs analysis is essential for understanding food web structure and evaluating the effects of human exploitation on food webs. We estimated the predator–prey mass ratio (PPMR) of the pelagic food web in the East China Sea and Sea of Japan by using the relationships between body mass and trophic position. Trophic position was calculated by additive and scaled models based on nitrogen stable isotope ratios (δ15N). The PPMRs based on additive and scaled models were 5032 (95% confidence interval (CI) 2066–15506) and 3430 (95% CI 1463–10083) respectively. The comparatively high PPMRs could reflect low ecosystem transfer efficiency and high metabolic rate.

scholarly journals Multidimensional trophic niche revealed by complementary approaches: gut content, digestive enzymes, fatty acids and stable isotopes in soil fauna

2020 ◽  
Author(s):  
Anton M. Potapov ◽  
Melanie M. Pollierer ◽  
Sandrine Salmon ◽  
Vladimír Šustr ◽  
Ting-Wen Chen
Keyword(s):  
Fatty Acids ◽  
Stable Isotopes ◽  
Food Web ◽  
Digestive Enzymes ◽  
Species Coexistence ◽  
Trophic Niche ◽  
List Type ◽  
Gut Content ◽  
Additional Value ◽  
Trophic Niches

AbstractThe trophic niche of an organism is tightly related to its role in the ecosystem and to interactions with other species. Thousands of species of soil animals feed on detritus and co-exist with apparently low specialisation in food resource use. Trophic niche differentiation may explain species coexistence in such a cryptic environment. However, most of the existing studies provide only few and isolated evidence on food resources, thus simplifying the multidimensional nature of the trophic niches available in soil.Focusing on one of the most diverse soil taxa – springtails (Collembola) – we aimed to reveal the additional value of information provided by four complementary methods: visual gut content-, digestive enzyme-, fatty acid- and stable isotope analyses, and to demonstrate the multidimensional nature of trophic niches.From 40 studies, we compiled fifteen key trophic niche parameters for 125 species, each analysed with at least one method. Focusing on interspecific variability, we explored correlations of trophic niche parameters and described variation of these parameters in different Collembola species, taxonomic groups and life forms.Correlation between trophic niche parameters of different methods was weak in 45 out of 64 pairwise comparisons, reflecting the complementarity of the multidimensional trophic niche approach. Gut content and fatty acids provided comparable information on fungivory and plant feeding in Collembola. Information provided by digestive enzymes differed from that gained by the other methods, suggesting its high additional value. Stable isotopes were mainly related to plant versus microbial feeding. Many parameters were affected by taxonomic affiliation but not life form. Furthermore, we showed evidence of bacterial feeding, which may be more common in Collembola than usually assumed.Different methods reveal different feeding dimensions, together drawing a comprehensive picture of the trophic niche in taxa with diverse feeding habits. Food web studies will benefit from simultaneously applying several joint approaches, allowing to trace trophic complexity. Future studies on the multidimensional trophic niche may improve understanding of food-web functioning and help to explain species coexistence in cryptic environments such as soil.

scholarly journals NetworkExtinction: an R package to explore the propagation of extinctions through complex ecological networks

2020 ◽  
Author(s):  
M. Isidora Ávila-Thieme ◽  
Derek Corcoran ◽  
Simón P. Castillo ◽  
Fernanda S. Valdovinos ◽  
Sergio A. Navarrete ◽  
...  
Keyword(s):  
Food Web ◽  
Food Webs ◽  
Degree Distribution ◽  
Null Model ◽  
Biodiversity Loss ◽  
R Package ◽  
List Type ◽  
Food Web Structure ◽  
Species Extinction ◽  
Species Extinctions

AbstractBiodiversity loss is one of the current drivers of global change with an acute impact on community structure. Different measures and tools (e.g., simulations of extinction events) have been developed to analyze the structure of ecological systems and their stability under biodiversity loss, especially in complex settings with multiple interacting species, such as food webs. However, there remains the need for tools that enable a quick assessment of the ensuing impacts on food webs structure due to species extinction. Here, we develop an R package to explore the propagation of species extinctions through food webs, measured as secondary extinctions, according to user-defined node removal sequences.In the NetworkExtinction package, we seek the integration between theory and computational simulations by developing six functions to analyze and visualize the structure and robustness of food webs represented as binary adjacency matrices. Three functions simulate the sequential extinction of species; a fourth function compares food web metrics between random and non-random extinction sequences; a fifth function visualizes the change in a given network metric along with the steps of sequential species extinction; a sixth function allows the user to fit and visualize the degree distribution of the network, fitting linear and non-linear regressions. We illustrate the package’s use and its outputs by analysing a Chilean coastal marine food web.By using the NetworkExtinction package, the user can estimate the food web robustness after performing species’ extinction routines based on several algorithms. Moreover, the user can compare the number of simulated secondary extinctions against a null model of random extinctions. The visualizations allow graphing topological indexes that the deletion sequences functions calculate after each removal step. Finally, the user can fit the degree distribution of the food web.The NetworkExtinction R package is a compact and easy-to-use package to visualize and assess the food web structure (degree distribution) and robustness to different sequences of species loss. Therefore, this package is particularly useful to evaluate the ecosystem response to anthropogenic and environmental perturbations that produce non-random species extinctions. In that way, it also allows us to assess the contribution of central nodes to food webs stability.

scholarly journals Trophic position and isotopic niche of mangrove fish assemblages at both sides of the Isthmus of Panama

2020 ◽  
Vol 96 (3) ◽  
pp. 449-468 ◽  
Author(s):  
Lara E Stuthmann ◽  
Gustavo A Castellanos-Galindo
Keyword(s):  
Food Webs ◽  
Environmental Conditions ◽  
Fish Assemblages ◽  
Trophic Position ◽  
Mangrove Ecosystem ◽  
Accurate Estimation ◽  
Isotopic Niche ◽  
Bocas Del Toro ◽  
The Pacific ◽  
The Caribbean

Fishes are important components of marine coastal ecosystems, often represented in food webs as second and third order consumers. Fish trophic positions (TP) in these food webs can vary across ontogeny and accurate estimation can provide insights into the functioning of these ecosystems. Mangrove ecosystem function can also vary depending on local and regional environmental conditions. Panamanian mangroves in the Caribbean Sea and the Pacific Ocean occur under strikingly different environmental conditions after the closure of the Panama Isthmus over 3 mya and likely function differently. Here, we use δ15N and δ13C and Bayesian models to calculate the TP and the Convex Hull Area (TA) of the most common fish species inhabiting mangroves of the Gulf of Montijo and Bocas del Toro on the Pacific and Caribbean coasts of Panama, respectively. Thirteen dominant fishes were used for the estimation of TP, eight in the Pacific and five in the Caribbean. Mean TP of the communities was similar but with significantly larger variations in the Caribbean than in the Pacific. Similarly, the TA was larger for the Caribbean fish assemblage than for the Pacific. Both results indicate that trophic modes in the Caribbean fish assemblages are more varied than in the Pacific. With some exceptions, FishBase TP estimates correlated positively with TP stable isotope estimates. Our results suggest that TP and TA are good proxies for mangrove fish communities' trophic modes and that these metrics may vary depending on mangrove environmental settings.

scholarly journals Food web persistence in fragmented landscapes

2017 ◽  
Vol 284 (1859) ◽  
pp. 20170350 ◽  
Author(s):  
Jinbao Liao ◽  
Daniel Bearup ◽  
Bernd Blasius
Keyword(s):  
Food Web ◽  
Food Webs ◽  
Trophic Position ◽  
Biodiversity Loss ◽  
Habitat Destruction ◽  
Trophic Levels ◽  
Food Web Structure ◽  
Spatially Extended ◽  
Biodiversity Maintenance ◽  
Patch Connectivity

Habitat destruction, characterized by patch loss and fragmentation, is a key driver of biodiversity loss. There has been some progress in the theory of spatial food webs; however, to date, practically nothing is known about how patch configurational fragmentation influences multi-trophic food web dynamics. We develop a spatially extended patch-dynamic model for different food webs by linking patch connectivity with trophic-dependent dispersal (i.e. higher trophic levels displaying longer-range dispersal). Using this model, we find that species display different sensitivities to patch loss and fragmentation, depending on their trophic position and the overall food web structure. Relative to other food webs, omnivory structure significantly increases system robustness to habitat destruction, as feeding on different trophic levels increases the omnivore's persistence. Additionally, in food webs with a dispersal–competition trade-off between species, intermediate levels of habitat destruction can enhance biodiversity by creating refuges for the weaker competitor. This demonstrates that maximizing patch connectivity is not always effective for biodiversity maintenance, as in food webs containing indirect competition, doing so may lead to further species loss.

The Role of Stochastic Simulations to Extend Food Web Analyses

2011 ◽  
pp. 163-196 ◽  
Author(s):  
Marco Scotti
Keyword(s):  
Food Web ◽  
Food Webs ◽  
Trophic Position ◽  
Interaction Strength ◽  
Skewed Distribution ◽  
Stochastic Simulations ◽  
Trophic Chain ◽  
Dominance Relations ◽  
Top Predators ◽  
Secondary Extinction

Food webs are schematic representations of who eats whom in ecosystems. They are widely used in linking process to pattern (e.g., degree distribution and vulnerability) and investigating the roles played by particular species within the interaction web (e.g., centrality indices and trophic position). First, I present the dominator tree, a topological structure reducing food web complexity into linear pathways that are essential for energy delivery. Then, I describe how the dominance relations based on dominator trees extracted from binary food webs may be modified by including interaction strength. Consequences related to the skewed distribution of weak links towards the trophic chain are discussed to explain higher risks of secondary extinction that characterize top predators dominated by basal species. Finally, stochastic simulations are introduced to suggest an alternative approach to static analyses based on food web topology. Ranking species importance using stochastic-based simulations partially contradicts the predictions based on network analyses.

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