Model Of Trophic Interactions Research Articles

Addressing the Eltonian shortfall with trait‐based interaction models

We have very limited knowledge of how species interact in most communities and ecosystems despite trophic relationships being fundamental for linking biodiversity to ecosystem functioning. A promising approach to fill this gap is to predict interactions based on functional traits, but many questions remain about how well we can predict interactions for different taxa, ecosystems and amounts of input data. Here, we built a new traits-based model of trophic interactions for European vertebrates and found that even models calibrated with 0.1% of the interactions (100 out of 71k) estimated the full European vertebrate food web reasonably well. However, predators were easier to predict than prey, especially for some clades (e.g. fowl and storks) and local food web connectance was consistently overestimated. Our results demonstrate the ability to rapidly generate food webs when empirical data are lacking-an important step towards a more complete and spatially explicit description of food webs.

Effects of enhanced productivity of resources shared by predators in a food-web module: Comparing results of a field experiment to predictions of mathematical models of intra-guild predation.

We compared the response to resource enhancement of a simple empirical model of intra‐guild predation (IGP) to the predictions of published, simple mathematical models of asymmetric IGP (a generalist IG Predator that feeds both on a specialist IG Prey and a Resource that it shares with the IG Prey). The empirical model was a food‐web module created by pooling species abundances across many families in a speciose community of soil micro‐arthropods into three categories: IG Predator (large predatory mites), IG Prey (small predatory mites), and a shared Resource (fungivorous mites and springtails). By pooling abundances of species belonging to broadly defined functional groups, we tested the hypothesis that IGP is a dominant organizing principle in this community. Simple mathematical models of asymmetric IGP predict that increased input of nutrients and energy to the shared Resource will increase the equilibrium density of Resource and IG Predator, but will decrease that of IG Prey. In a field experiment, we observed how the three categories of the empirical model responded to two rates of addition of artificial detritus, which enhanced the food of fungivores, the Resource of the IGP module. By the experiment's end, fungivore densities had increased ~1.5× (ratio of pooled fungivore densities in the higher‐input treatment to plots with no addition of detritus), and densities of IG Predators had increased ~4×. Contrary to the prediction of mathematical models, IG Prey had not decreased, but instead had increased ~1.5×. We discuss possible reasons for the failure of the empirical model to agree with IGP theory. We then explore analogies between the behavior of the empirical model and another mathematical model of trophic interactions as one way to gain insights into the trophic connections in this community. We also propose one way forward for reporting comparisons of simple empirical and mathematical models.

Mass balance model of Lake Volta fisheries: The use of Ecopath model

AbstractA mass balance model of trophic interactions among ten key functional producer and consumer groups in Lake Volta was constructed using the Ecopath model to study the energy flows and species interactions in the lake. The present study was based on secondary and primary data on fish catch, diet composition, phytoplankton and zooplankton biomasses, collected in 2015 and 2016. Additional information on growth parameters of major species required for balancing the Ecopath model was obtained from sampling and FishBase. The functional groups were detritus, phytoplankton, zooplankton, benthos, prey fish, Tilapia, Bagrus, Chrysichthys, Alestes and Synodontis species. Four trophic levels were identified in the Lake Volta ecosystem, with the energy flow occurring mainly within the first three trophic levels. The calculated ecotrophic efficiency value of the primary producers (phytoplankton: 0.17; detritus: 0.22) indicated they were least exploited, compared to the secondary producers, zooplankton (0.80) and benthos (0.50). All secondary consumers had ecotrophic efficiency values higher than the primary producers, indicating they are exploited in the ecosystem. The main energy flows in the lake were from phytoplankton and detritus at trophic level I, and Bagrus species, the top predator, at a level of 3.30. The network analysis, illustrating a connectance index of 0.43 and an omnivory index of 0.06, in the lake system indicated the ecosystem is unstable, somewhat immature and still in a developing stage.

Stable-isotope probing and metagenomics reveal predation by protozoa drives E. coli removal in slow sand filters.

Stable-isotope probing and metagenomics were applied to study samples taken from laboratory-scale slow sand filters 0.5, 1, 2, 3 and 4 h after challenging with (13)C-labelled Escherichia coli to determine the mechanisms and organisms responsible for coliform removal. Before spiking, the filters had been continuously operated for 7 weeks using water from the River Kelvin, Glasgow as their influent source. Direct counts and quantitative PCR assays revealed a clear predator-prey response between protozoa and E. coli. The importance of top-down trophic-interactions was confirmed by metagenomic analysis, identifying several protozoan and viral species connected to E. coli attrition, with protozoan grazing responsible for the majority of the removal. In addition to top-down mechanisms, indirect mechanisms, such as algal reactive oxygen species-induced lysis, and mutualistic interactions between algae and fungi, were also associated with coliform removal. The findings significantly further our understanding of the processes and trophic interactions underpinning E. coli removal. This study provides an example for similar studies, and the opportunity to better understand, manage and enhance E. coli removal by allowing the creation of more complex trophic interaction models.

Parameterizing and operationalizing zooplankton population dynamic and trophic interaction models

Abstract Plourde, S., and Browman, H. I. 2014. Parameterizing and operationalizing zooplankton population dynamic and trophic interaction models. – ICES Journal of Marine Science, 71: 234–235. This themed set (TS) of articles was motivated by the need for modellers and biologists–ecologists to work more closely together to produce more realistic simulation models of zooplankton population dynamics and trophic interactions. The TS was intended to cover a broad range of subjects and potential approaches, including identifying crucial gaps in our knowledge and parameterization of biological/physiological processes, experimental/fieldwork aimed at quantifying the response of key physiological and behavioural processes to variations in the environment, identifying novel modelling approaches that would enable the development of simulation models that would minimize the need for species-specific (and stage-specific) model parameterization, etc. Five articles were accepted for inclusion in the TS. They cover the majority of these themes. TSs are intended to be instrumental in focusing attention, triggering opinions, and stimulating ideas, discussion and activity in specific research fields. We hope that this TS has achieved that.

Predicted responses of invasive mammal communities to climate‐related changes in mast frequency in forest ecosystems

Predicting the dynamics and impacts of multiple invasive species can be complex because ecological relationships, which occur among several trophic levels, are often incompletely understood. Further, the complexity of these trophic relationships exacerbates our inability to predict climate change effects on invaded ecosystems. We explore the hypothesis that interactions between two global change drivers, invasive vertebrates and climate change, will potentially make matters worse for native biodiversity. In New Zealand beech (Nothofagus spp.) forests, a highly irruptive invasive mammal community is driven by multi-annual resource pulses of beech seed (masting). Because mast frequency is predicted to increase with climate change, we use this as a model system to explore the extent to which such effects may influence invasive vertebrate communities, and the implications of such interactions for native biodiversity and its management. We build on an established model of trophic interactions in the system, combining it with a logistic probability mast function, the parameters of which were altered to simulate either contemporary conditions or conditions of more or less frequent masting. The model predicts that increased mast frequency will lead to populations of a top predator (the stoat) and a mesopredator (the ship rat) becoming less irruptive and being maintained at appreciably higher average abundances in this forest type. In addition, the ability of both current and in-development management approaches to suppress invasive mammals is predicted to be compromised. Because invasive mammals are key drivers of native fauna extinction in New Zealand, with the additional loss of associated functions such as pollination and seed dispersal, these predictions imply potentially serious adverse impacts of climate change for the conservation of biodiversity and ecosystem function. Our study also highlights the importance of long-term monitoring data for assessing and managing future impacts of global change drivers.

On the “strict homeostasis” assumption in ecological stoichiometry

Multiple elements including carbon (C), nitrogen (N) and phosphorus (P) are required for organismal growth, reproduction, and maintenance. Newly emerging mathematical models linking population dynamics with stoichiometric relationships among these key elements improve historic trophic interaction models and resolve some existing paradoxes. The degree to which organisms maintain a constant chemical composition in the face of variations in the chemical composition and availability of their environmental resources is referred to as “stoichiometric homeostasis”. Most of these models so far have assumed constant nutrient contents in heterotrophs, called “strict homeostasis”, and varied nutrient contents in autotrophs, called “non-homeostasis”, due to the fact that the stoichiometric variability of heterotrophs is often much less than that of autotrophs. Our study suggests that the “strict homeostasis” assumption is reasonable when the stoichiometric variability of herbivores is less than a threshold. This threshold is independent of algal stoichiometric variability, thus the above historic reasoning for strict homeostasis in heterotrophs is not convincing. We find that the “strict homeostasis” assumption seems valid for many herbivores except for herbivores with small mortality rates. The results are nearly same in both one-nutrient and two-nutrient models, and robust to perturbation of parameter values and environmental nutrient status. Finally, the two-nutrient model shows that herbivore's survival needs higher variation in the more potentially limiting of the two elements.

Effects of Set Bagnet fisheries on the shallow coastal ecosystem of the Bay of Bengal

The coastal ecosystem of the Bay of Bengal (BOB) is described using a mass-balance model of trophic interactions to understand the effects of Set Bag Net on the ecosystem. The BOB model had 14 functional ecological groups; 13 living and one dead (detritus). The result showed that the fishery was heavily exploited and operated at a mean trophic level of 2.45. The SBN fishery was characterized with high fishing mortality rates and large omnivory indices for most of the commercially exploited demersal and pelagic groups. The total primary production requirement for sustainable catch was estimated at 15.11%. However, results of Ecosim simulations elucidated that the key resources, like small demersal, small to medium pelagic fish groups and penaeid shrimps, were likely to show a rapid decline in yields within five years with a twice increase in fishing effort and pressure. In contrast, the palaemonidae and sergested shrimp yields showed an increasing trend as they seem to be able to sustain the high fishing pressure, since their predators are also harvested. In addition to that, cephalopod, which is a non-targeted group for this fishery, is also likely to increase in yield for the time being. The two most drastically affected groups in both fisheries were likely to be shark and small demersal. Continuously increasing fishing effort using SBN will lead to a rapid decline of most of the commercial marine resources and predicted to have a serious effect on the ecosystem functioning of BOB.

A simultaneous test of trophic interaction models: which vegetation characteristic explains herbivore control over plant community mass?

Predicting herbivore control over plants (i.e. changes in plant mass due to herbivore damage) is a central goal of ecology. Progress has been limited, however, because the vegetation characteristics thought to influence herbivore control are naturally correlated and typically experimentally confounded. To address this problem, we defined eight conventional models that predict herbivore control over plant community mass, each model based on a different vegetation characteristic (i.e. host concentration, tissue nitrogen, growth rate, size, tolerance of herbivory or net primary productivity). We then used structural equation modelling to test each model against two field experiments. Our results clearly rejected all models except for a tolerance of herbivory mechanism; stems with greater access to limiting resources better tolerated herbivory, regardless of where herbivore activity was greatest. Consequently, herbivore reductions of plant community mass were greatest at low resource availability. This adds to evidence that herbivore activity poorly predicts herbivore control.

A stoichiometrically derived algal growth model and its global analysis

Organisms are composed of multiple chemical elements such as carbon, nitrogen, and phosphorus. The scarcity of any of these elements can severely restrict organismal and population growth. However, many trophic interaction models only consider carbon limitation via energy flow. In this paper, we construct an algal growth model with the explicit incorporation of light and nutrient availability to characterize both carbon and phosphorus limitations. We provide a global analysis of this model to illustrate how light and nutrient availability regulate algal dynamics.

Assessment of impacts of invasive fishes on the food web structure and ecosystem properties of a tropical reservoir in India

A network model of trophic interactions in a tropical reservoir in India was developed with the objective to quantify matter and energy flows between system components and to study the impact of invasive fishes on the ecosystem. Structure of flows and their distribution within and between trophic levels were analysed by aggregating single flows into combined flows for discrete trophic levels. The trophic flows primarily occurred in the first four trophic level (TL) and the food web structure in this reservoir ecosystem was characterized by the dominance of low TL organisms, with the highest TL of only 3.57 for the top predator. Highest system omnivory index (SOI) was observed for indigenous catfishes (0.422), followed by the exotic fish Mozambique Tilapia (0.402). Nile Tilapia and Pearl spots show the highest niche overlap which suggests high competition for similar resources. The mixed trophic impact routine reveals that an increase in the abundance of the African catfish would negatively impact almost all fish groups such as Indian major carps, Pearl spots, indigenous catfishes and Tilapines. The other invasive fish Mozambique Tilapia adversely affects the indigenous catfishes. The most interesting observation in this study is that the most dominant invasive fish in this reservoir, the Nile Tilapia does not negatively impact any of the fish groups. In fact it positively impacts the Indian major carps. The direct and indirect effects of predation between system components (i.e. fish, invertebrates, phytoplankton and detritus) are quantitatively described and the possible influence and role in the ecosystem's functioning of the invasive fish species are discussed.

Defining yield policies in a viability approach

Mullon et al. [Mullon, C., Curry, P., Shannon, L., 2004. Viability model of trophic interactions in marine ecosystems. Nat. Resour. Model. 17 (1), 27–58] proposed a dynamical model of biomass evolution in the Southern Benguela ecosystem, including five different groups (detritus, phytoplankton, zooplankton, pelagic fish and demersal fish). They studied this model in a viability perspective, trying to assess, for a given constant yield, whether each species biomass remains inside a given interval, taking into account the uncertainty on the interaction coefficients. Instead of studying the healthy states of this marine ecosystem with a constant yield, we focus here on the yield policies which keep the system viable. Using the mathematical concept of viability kernel, we examine how yield management might guarantee viable fisheries. One of the main practical difficulties up to now with the viability theory was the lack of methods to solve the problem in large dimensions. In this paper, we use a new method based on SVMs, which gives this theory a larger practical potential. Solving the viability problem provides all yield policies (if any) which guarantee a perennial system. We illustrate our main findings with numerical simulations.

Effects of fisheries on the Cantabrian Sea shelf ecosystem

The Cantabrian Sea shelf ecosystem is described using a mass-balance model of trophic interactions, in order to understand the effects of the different fisheries that operate in this area. The study was based on a database of bottom trawl surveys, ICES stock assessment working groups, stomach analyses, fisheries research and was supplemented by published information. The model had 28 trophic groups corresponding to pelagic, demersal and benthic domains, also including detritus and fishery discards. The results indicated that the biomass and production of some groups would be unrealistic if they were independently estimated by single-species assessment approaches. Summaries are given to illustrate the flow distributions between groups. Strong relationships existed between the pelagic, demersal and benthic domains due to key groups, like zooplankton suprabenthic and horse mackerel, that transferred the flow from primary production to the upper trophic levels. Feeding pressure on phytoplankton was low and detritivorous species were an important component of the ecosystem. Estimations of the trophic level of the fisheries, transfer efficiency between trophic levels and mixed trophic impact analysis, that consider the fishery both as an impacting and as an impacted component, were also included. The results indicated a fisheries impact level in the Cantabrian Sea comparable to that in the most intensively exploited temperate shelf ecosystems of the world. The fishery was operating at a mean trophic level of 3.7. The importance of discards as food in the ecosystem was low, in comparison with detritus, primary producers or other low trophic levels. The negative trophic impact of trawling on the different groups of the system was high and much stronger than the other gears studied. All fishing gears, except the purse seine, had negative impact on fish feeders and elasmobranchs. The mean trophic level of Cantabrian Sea fisheries declined from 1983 to 1993 but has remained steady since then.

Are lemmings prey or predators?

Large oscillations in the populations of Norwegian lemmings have mystified both professional ecologists and lay public. Ecologists suspect that these oscillations are driven by a trophic mechanism: either an interaction between lemmings and their food supply, or an interaction between lemmings and their predators. If lemming cycles are indeed driven by a trophic interaction, can we tell whether lemmings act as the resource ('prey') or the consumer ('predator')? In trophic interaction models, peaks of resource density generally have a blunt, rounded shape, whereas peaks of consumer density are sharp and angular. Here we have applied several statistical tests to three lemming datasets and contrasted them with comparable data for cyclic voles. We find that vole peaks are blunt, consistent with their cycles being driven by the interaction with predators. In contrast, the shape of lemming peaks is consistent with the hypothesis that lemmings are functional predators, that is, their cycles are driven by their interaction with food plants. Our findings suggest that a single mechanism, such as interaction between rodents and predators, is unlikely to provide the 'universal' explanation of all cyclic rodent dynamics.

Estimating diel, depth-specific foraging opportunities with a visual encounter rate model for pelagic piscivores

We developed a visual foraging model for piscivores that predicts search volume as a function of light and turbidity. We combined this model with diel hydroacoustic measurements of depth-specific prey fish densities during summer stratification in Lake Tahoe, Lake Washington, and Strawberry Reservoir to examine differences in diel, depth-specific visual encounter rates of prey. These study sites were selected to represent gradients of increasing limnetic prey fish density and declining transparency. The model predicted over a 30-fold difference in maximum depth-specific diel encounter rates among the three lakes. Lake Washington, which was characterized by intermediate transparency and moderate limnetic prey density, had the highest predicted prey encounter rates. The pattern of prey encounter rates among the three lakes was similar to the proportional contribution of limnetic prey fishes observed in the diet of piscivores from these waters. This approach may be used to construct temporally and spatially explicit trophic interaction models for examining mechanisms underlying predator and prey distributions or to predict the response of existing or introduced predators to changing environmental conditions, prey abundance, or distribution.

Trophic network model of a shallow water area in the northern part of the Lagoon of Venice

A network model of trophic interactions within Palude della Rosa, a shallow water area in the northern part of the Lagoon of Venice, was developed with the objective to coherently quantify state variables as well as matter and energy flows between system components. Structure of flows and their distribution within and between trophic levels were analysed by aggregating single flows into combined flows for discrete trophic levels. Ninty-eight percent of total throughput is confined to the 1st and 2nd trophic level with the overall system strongly depending on the consumption of detritus. The distribution of energy and the poor structure of the flows suggest that the network is able to reflect prominent features of the ecosystem as, for example, effects produced by eutrophication processes, validated by field observations. Direct and indirect effects and dependencies between system components such as nekton, zoobenthos and detritus are quantitatively described. Predation pressure amongst system components is discussed. Nektonic fauna emphasising commercially exploited species was included in the model to also show the potential use of the trophic network for purposes of fisheries and of sanitary management. The present model is considered to be a first step in mapping the entire Lagoon through trophic networks for different areas in the Lagoon of Venice, along a gradient of hydrodynamic characteristics and levels of pollution. A large amount of ecological and biological information on the lagoon ecosystem may thus be summarised in a coherent framework. Information on fish stocks and other nektonic fauna present in the lagoon are one of the main gaps in the database. Such lack of information should be covered by additional field investigations to obtain more reliable knowledge on the exchanges of matter and energy also within higher trophic levels.

Planktonic microbes: Tiny cells at the base of the ocean's food webs

Phytoplankton in the size range 5–100 μm was originally thought to be the primary source of food for most life in the sea. However, smaller planktonic microbes, down to 0.2 μm in size, have been the focus of intensive investigation by marine scientists during the past two decades. These microbes attain high abundance and biomass in all parts of the world ocean. They include non-photosynthesizing bacteria, at least two types of photosynthesizing prokaryotes, and eukaryotic phototrophs. The new information has resulted in a greatly revised concept of how pelagic ecosystems in both marine and freshwater environments function. The original idea of a basically linear food chain from diatoms to copepods to fish has given way to an extremely complex model of trophic interactions within a microbial food web, which supports metazoan food webs via biomass production of both heterotrophic and autotrophic cells.

A trophic continuum derived from plant structure, animal size and a detritus cascade

A new model of trophic interactions in large many species ecosystems is presented. This trophic continuum model is defined by organisms harvesting resources from an environment. Animal size classes, a classification of plant products and detritus initiates the resource descriptions of ecosystems. Strategic trophic models are reviewed. Trophic interactions are Markovian. The Lindeman trophic level concept is criticized for its dependence on the history of energy flow rather than an assessment of the present resource state. Criteria for a strategic model of ecosystem energetics are specified as the indivisibility of herbivore and detritovore chains; the non-equivalence of different trophic transfers; and that the plant is not a single reference point to scale trophic space. Elton's pyramid of number met these criteria. The trophic continuum model points to closer links between theories of energy flow, species diversity and ecosystem heterogeneity.