Journal articles: 'Trophic interaction strengths'

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Pawar, Samraat, Anthony I. Dell, and Van M. Savage. "Dimensionality of consumer search space drives trophic interaction strengths." Nature 486, no. 7404 (May 30, 2012): 485–89. http://dx.doi.org/10.1038/nature11131.

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Gibert, Jean P., and John P. DeLong. "Phenotypic variation explains food web structural patterns." Proceedings of the National Academy of Sciences 114, no. 42 (October 2, 2017): 11187–92. http://dx.doi.org/10.1073/pnas.1703864114.

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Food webs (i.e., networks of species and their feeding interactions) share multiple structural features across ecosystems. The factors explaining such similarities are still debated, and the role played by most organismal traits and their intraspecific variation is unknown. Here, we assess how variation in traits controlling predator–prey interactions (e.g., body size) affects food web structure. We show that larger phenotypic variation increases connectivity among predators and their prey as well as total food intake rate. For predators able to eat only a few species (i.e., specialists), low phenotypic variation maximizes intake rates, while the opposite is true for consumers with broader diets (i.e., generalists). We also show that variation sets predator trophic level by determining interaction strengths with prey at different trophic levels. Merging these results, we make two general predictions about the structure of food webs: (i) trophic level should increase with predator connectivity, and (ii) interaction strengths should decrease with prey trophic level. We confirm these predictions empirically using a global dataset of well-resolved food webs. Our results provide understanding of the processes structuring food webs that include functional traits and their naturally occurring variation.

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Kordas, Rebecca L., and Steve Dudgeon. "Dynamics of species interaction strength in space, time and with developmental stage." Proceedings of the Royal Society B: Biological Sciences 278, no. 1713 (November 24, 2010): 1804–13. http://dx.doi.org/10.1098/rspb.2010.2246.

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Quantifying species interaction strengths enhances prediction of community dynamics, but variability in the strength of species interactions in space and time complicates accurate prediction. Interaction strengths can vary in response to density, indirect effects, priority effects or a changing environment, but the mechanism(s) causing direction and magnitudes of change are often unclear. We designed an experiment to characterize how environmental factors influence the direction and the strength of priority effects between sessile species. We estimated per capita non-trophic effects of barnacles ( Semibalanus balanoides ) on newly settled germlings of the fucoid, Ascophyllum nodosum , in the presence and absence of consumers in experiments on rocky shores throughout the Gulf of Maine, USA. Per capita effects on germlings varied among environments and barnacle life stages, and these interaction strengths were largely unaltered by changing consumer abundance. Whereas previous evidence shows adult barnacles facilitate fucoids, here, we show that recent settlers and established juveniles initially compete with germlings. As barnacles mature, they switch to become facilitators of fucoids. Consumers caused variable mortality of germlings through time comparable to that from competition. Temporally variable effects of interactors (e.g. S. balanoides ), or spatial variation in their population structure, in different regions differentially affect target populations (e.g. A. nodosum ). This may affect abundance of critical stages and the resilience of target species to environmental change in different geographical regions.

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Cuthbert, Ross N., Tatenda Dalu, Ryan J. Wasserman, Cristián J. Monaco, Amanda Callaghan, Olaf L. F. Weyl, and Jaimie T. A. Dick. "Assessing multiple predator, diurnal and search area effects on predatory impacts by ephemeral wetland specialist copepods." Aquatic Ecology 54, no. 1 (November 29, 2019): 181–91. http://dx.doi.org/10.1007/s10452-019-09735-y.

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AbstractPredator–prey interaction strengths can be highly context-dependent. In particular, multiple predator effects (MPEs), variations in predator sex and physical habitat characteristics may affect prey consumption rates and thus the persistence of lower trophic groups. Ephemeral wetlands are transient ecosystems in which predatory copepods can be numerically dominant. We examine the interaction strengths of a specialist copepod Paradiaptomus lamellatus towards mosquito prey in the presence of conspecifics using a functional response approach. Further, we examine sex variability in predation rates of P. lamellatus under circadian and surface area variations. Then, we assess the influence of a co-occurring heterospecific predatory copepod, Lovenula raynerae, on total predation rates. We demonstrate MPEs on consumption, with antagonism between conspecific P. lamellatus predatory units evident, irrespective of prey density. Furthermore, we show differences between sexes in interaction strengths, with female P. lamellatus significantly more voracious than males, irrespective of time of day and experimental arena surface area. Predation rates by P. lamellatus were significantly lower than the heterospecific calanoid copepod L. raynerae, whilst heterospecific copepod groups exhibited the greatest predatory impact. Our results provide insights into the predation dynamics by specialist copepods, wherein species density, diversity and sex affect interaction strengths. In turn, this may influence population-level persistence of lower trophic groups under shifting copepod predator composition.

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Cuthbert, Ross N., Rana Al-Jaibachi, Tatenda Dalu, Jaimie T. A. Dick, and Amanda Callaghan. "The influence of microplastics on trophic interaction strengths and oviposition preferences of dipterans." Science of The Total Environment 651 (February 2019): 2420–23. http://dx.doi.org/10.1016/j.scitotenv.2018.10.108.

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Barabás, György, and Stefano Allesina. "Predicting global community properties from uncertain estimates of interaction strengths." Journal of The Royal Society Interface 12, no. 109 (August 2015): 20150218. http://dx.doi.org/10.1098/rsif.2015.0218.

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The community matrix measures the direct effect of species on each other in an ecological community. It can be used to determine whether a system is stable (returns to equilibrium after small perturbations of the population abundances), reactive (perturbations are initially amplified before damping out), and to determine the response of any individual species to perturbations of environmental parameters. However, several studies show that small errors in estimating the entries of the community matrix translate into large errors in predicting individual species responses. Here, we ask whether there are properties of complex communities one can still predict using only a crude, order-of-magnitude estimate of the community matrix entries. Using empirical data, randomly generated community matrices, and those generated by the Allometric Trophic Network model, we show that the stability and reactivity properties of systems can be predicted with good accuracy. We also provide theoretical insight into when and why our crude approximations are expected to yield an accurate description of communities. Our results indicate that even rough estimates of interaction strengths can be useful for assessing global properties of large systems.

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Riley, Leslie, Mark Dybdahl, and Robert Hall, Jr. "Invasive Species Impact: Direct and Indirect Interactions Between Two Stream Snails and Their Algal Resources." UW National Parks Service Research Station Annual Reports 28 (January 1, 2004): 61–69. http://dx.doi.org/10.13001/uwnpsrc.2004.3577.

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We measured the strength of direct and indirect interactions in order to develop a standardized estimate of the impact of an invasive snail on its resource and a competitor. The freshwater New Zealand snail, Potamopyrgus antipodarum, an invasive species in the western U.S., is the most abundant benthic macroinvertebrate grazer in several rivers, where it overlaps with several threatened endemic snails. In one watershed, Potamopyrgus coexists with the snail, Pyrgulopsis robusta, which may be affected by resource competition with Potamopyrgus. In field enclosure experiments, we quantified the direct grazing effect of snails on algae and the indirect effects between consumers. Potamopyrgus significantly limited growth of Pyrgulopsis. In contrast, Pyrgulopsis appeared to facilitate growth of the invasive snail (Potamopyrgus). In natural populations, snail densities were positively correlated over five sites, but negatively correlated at two downstream sites. Interaction strengths between snails and algae were equivalent for both snails at both sites, indicating that invasion success could not be attributed to differences in resource acquisition. However, the overall impact of the invader was much higher at the downstream site when both snail abundance and interaction strengths were considered. Negative individual effects of Potamopyrgus at two trophic levels in conjunction with high Potamopyrgus abundance demonstrated a significant impact of the invader in this lotic community.

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Pinkerton, Matthew H., and Janet M. Bradford-Grieve. "Characterizing foodweb structure to identify potential ecosystem effects of fishing in the Ross Sea, Antarctica." ICES Journal of Marine Science 71, no. 7 (February 13, 2014): 1542–53. http://dx.doi.org/10.1093/icesjms/fst230.

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AbstractThe potential ecosystem effects of fishing for Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region were investigated. Mixed trophic impact analysis was applied to a model of the Ross Sea foodweb and used to calculate the relative trophic importances of species and trophic groups in the system. The trophic impact of toothfish on medium-sized demersal fish was identified as the strongest top-down interaction in the system based on multiple-step analysis. This suggests a potential for a strong predation-release effect on some piscine prey of toothfish (especially grenadiers and ice-fish on the Ross Sea slope). However, Antarctic toothfish had moderate trophic importance in the Ross Sea foodweb as a whole, and the analysis did not support the hypothesis that changes to toothfish will cascade through the ecosystem by simple trophic effects. Because of limitations of this kind of analysis, cascading effects on the Ross Sea ecosystem due to changes in the abundance of toothfish cannot be ruled out, but for such changes to occur a mechanism other than simple trophic interactions is likely to be involved. Trophic importances were highest in the middle of the foodweb where silverfish and krill are known to have a key role in ecosystem structure and function. The six groups with the highest indices of trophic importance were (in decreasing order): phytoplankton, mesozooplankton, Antarctic silverfish, small demersal fish, Antarctic krill and cephalopods. Crystal krill and small pelagic fish also had high trophic importance in some analyses. Strengths and limitations of this kind of analysis are presented. In particular, it is noted that the analysis only considers trophic interactions at the spatial, temporal and ecological scale of the whole Ross Sea shelf and slope area, averaged over a typical year and in 35 trophic groups. Interference and density-dependent effects were not included in this analysis. Effects at smaller spatial and temporal scales, and effects concerning only parts of populations, were not resolved by the analysis, and this is likely to underestimate the potential risks of fishing to Weddell seals and type-C killer whales.

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Li, Xiaoxiao, Wei Yang, Ursula Gaedke, and Peter C. Ruiter. "Energetic constraints imposed on trophic interaction strengths enhance resilience in empirical and model food webs." Journal of Animal Ecology 90, no. 9 (May 10, 2021): 2065–76. http://dx.doi.org/10.1111/1365-2656.13499.

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Schmitz, Oswald J., and Jessica R. Price. "Convergence of trophic interaction strengths in grassland food webs through metabolic scaling of herbivore biomass." Journal of Animal Ecology 80, no. 6 (July 1, 2011): 1330–36. http://dx.doi.org/10.1111/j.1365-2656.2011.01882.x.

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11

Novak, Mark. "Trophic omnivory across a productivity gradient: intraguild predation theory and the structure and strength of species interactions." Proceedings of the Royal Society B: Biological Sciences 280, no. 1766 (September 7, 2013): 20131415. http://dx.doi.org/10.1098/rspb.2013.1415.

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Intraguild predation theory centres on two predictions: (i) for an omnivore and an intermediate predator (IG-prey) to coexist on shared resources, the IG-prey must be the superior resource competitor, and (ii) increasing resource productivity causes the IG-prey's equilibrium abundance to decline. I tested these predictions with a series of species-rich food webs along New Zealand's rocky shores, focusing on two predatory whelks, Haustrum haustorium , a trophic omnivore, and Haustrum scobina , the IG-prey. In contrast to theory, the IG-prey's abundance increased with productivity. Furthermore, feeding rates and allometric considerations indicate a competitive advantage for the omnivore when non-shared prey are considered, despite the IG-prey's superiority for shared prey. Nevertheless, clear and regular cross-gradient changes in network structure and interaction strengths were observed that challenge the assumptions of current theory. These insights suggest that the consideration of consumer-dependent functional responses, non-equilibrium dynamics, the dynamic nature of prey choice and non-trophic interactions among basal prey will be fruitful avenues for theoretical development.

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Calizza, Edoardo, Loreto Rossi, Giulio Careddu, Simona Sporta Caputi, and Maria Letizia Costantini. "A novel approach to quantifying trophic interaction strengths and impact of invasive species in food webs." Biological Invasions 23, no. 7 (March 13, 2021): 2093–107. http://dx.doi.org/10.1007/s10530-021-02490-y.

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AbstractMeasuring ecological and economic impacts of invasive species is necessary for managing invaded food webs. Based on abundance, biomass and diet data of autochthonous and allochthonous fish species, we proposed a novel approach to quantifying trophic interaction strengths in terms of number of individuals and biomass that each species subtract to the others in the food web. This allowed to estimate the economic loss associated to the impact of an invasive species on commercial fish stocks, as well as the resilience of invaded food webs to further perturbations. As case study, we measured the impact of the invasive bass Micropterus salmoides in two lake communities differing in food web complexity and species richness, as well as the biotic resistance of autochthonous and allochthonous fish species against the invader. Resistance to the invader was higher, while its ecological and economic impact was lower, in the more complex and species-rich food web. The percid Perca fluviatilis and the whitefish Coregonus lavaretus were the two species that most limited the invader, representing meaningful targets for conservation biological control strategies. In both food webs, the limiting effect of allochthonous species against M. salmoides was higher than the effect of autochthonous ones. Simulations predicted that the eradication of the invader would increase food web resilience, while that an increase in fish diversity would preserve resilience also at high abundances of M. salmoides. Our results support the conservation of biodiverse food webs as a way to mitigate the impact of bass invasion in lake ecosystems. Notably, the proposed approach could be applied to any habitat and animal species whenever biomass and diet data can be obtained.

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Sentis, Arnaud, Julie Morisson, and David S. Boukal. "Thermal acclimation modulates the impacts of temperature and enrichment on trophic interaction strengths and population dynamics." Global Change Biology 21, no. 9 (May 19, 2015): 3290–98. http://dx.doi.org/10.1111/gcb.12931.

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Cuthbert, Ross N., Ryan J. Wasserman, Tatenda Dalu, Horst Kaiser, Olaf L. F. Weyl, Jaimie T. A. Dick, Arnaud Sentis, Michael W. McCoy, and Mhairi E. Alexander. "Influence of intra‐ and interspecific variation in predator–prey body size ratios on trophic interaction strengths." Ecology and Evolution 10, no. 12 (June 2020): 5946–62. http://dx.doi.org/10.1002/ece3.6332.

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McCluney, Kevin E., and John L. Sabo. "Animal water balance drives top-down effects in a riparian forest—implications for terrestrial trophic cascades." Proceedings of the Royal Society B: Biological Sciences 283, no. 1836 (August 17, 2016): 20160881. http://dx.doi.org/10.1098/rspb.2016.0881.

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Despite the clear importance of water balance to the evolution of terrestrial life, much remains unknown about the effects of animal water balance on food webs. Based on recent research suggesting animal water imbalance can increase trophic interaction strengths in cages, we hypothesized that water availability could drive top-down effects in open environments, influencing the occurrence of trophic cascades. We manipulated large spider abundance and water availability in 20 × 20 m open-air plots in a streamside forest in Arizona, USA, and measured changes in cricket and small spider abundance and leaf damage. As expected, large spiders reduced both cricket abundance and herbivory under ambient, dry conditions, but not where free water was added. When water was added (free or within moist leaves), cricket abundance was unaffected by large spiders, but spiders still altered herbivory, suggesting behavioural effects. Moreover, we found threshold-type increases in herbivory at moderately low soil moisture (between 5.5% and 7% by volume), suggesting the possibility that water balance may commonly influence top-down effects. Overall, our results point towards animal water balance as an important driver of direct and indirect species interactions and food web dynamics in terrestrial ecosystems.

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Wang, Rong, John A. Dearing, and Peter G. Langdon. "Critical Transitions in Lake Ecosystem State May Be Driven by Coupled Feedback Mechanisms: A Case Study from Lake Erhai, China." Water 14, no. 1 (January 3, 2022): 85. http://dx.doi.org/10.3390/w14010085.

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Critical transitions between ecosystem states can be triggered by relatively small external forces or internal perturbations and may show time-lagged or hysteretic recovery. Understanding the precise mechanisms of a transition is important for ecosystem management, but it is hampered by a lack of information about the preceding interactions and associated feedback between different components in an ecosystem. This paper employs a range of data, including paleolimnological, environmental monitoring and documentary sources from lake Erhai and its catchment, to investigate the ecosystem structure and dynamics across multiple trophic levels through the process of eutrophication. A long-term perspective shows the growth and decline of two distinct, but coupled, positive feedback loops: a macrophyte-loop and a phosphorus-recycling-loop. The macrophyte-loop became weaker, and the phosphorus-recycling-loop became stronger during the process of lake eutrophication, indicating that the critical transition was propelled by the interaction of two positive feedback loops with different strengths. For lake restoration, future weakening of the phosphorus-recycling loop or a reduction in external pressures is expected to trigger macrophyte growth and eventually produce clear water conditions, but the speed of recovery will probably depend on the rates of feedback loops and the strength of their coupling.

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Zhong, Zhiwei, Xiaofei Li, Dean Pearson, Deli Wang, Dirk Sanders, Yu Zhu, and Ling Wang. "Ecosystem engineering strengthens bottom-up and weakens top-down effects via trait-mediated indirect interactions." Proceedings of the Royal Society B: Biological Sciences 284, no. 1863 (September 20, 2017): 20170894. http://dx.doi.org/10.1098/rspb.2017.0894.

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Trophic interactions and ecosystem engineering are ubiquitous and powerful forces structuring ecosystems, yet how these processes interact to shape natural systems is poorly understood. Moreover, trophic effects can be driven by both density- and trait-mediated interactions. Microcosm studies demonstrate that trait-mediated interactions may be as strong as density-mediated interactions, but the relative importance of these pathways at natural spatial and temporal scales is underexplored. Here, we integrate large-scale field experiments and microcosms to examine the effects of ecosystem engineering on trophic interactions while also exploring how ecological scale influences density- and trait-mediated interaction pathways. We demonstrate that (i) ecosystem engineering can shift the balance between top-down and bottom-up interactions, (ii) such effects can be driven by cryptic trait-mediated interactions, and (iii) the relative importance of density- versus trait-mediated interaction pathways can be scale dependent. Our findings reveal the complex interplay between ecosystem engineering, trophic interactions, and ecological scale in structuring natural systems.

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DeRoy, Emma M., Steven Crookes, Kyle Matheson, Ryan Scott, Cynthia H. McKenzie, Mhairi E. Alexander, Jaimie T. A. Dick, and Hugh J. MacIsaac. "Predatory ability and abundance forecast the ecological impacts of two aquatic invasive species." NeoBiota 71 (January 27, 2022): 91–112. http://dx.doi.org/10.3897/neobiota.71.75711.

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Characterising interspecific interaction strengths, combined with population abundances of prey and their novel predators, is critical to develop predictive invasion ecology. This is especially true of aquatic invasive species, which can pose a significant threat to the structure and stability of the ecosystems to which they are introduced. Here, we investigated consumer-resource dynamics of two globally-established aquatic invasive species, European green crab (Carcinus maenas) and brown trout (Salmo trutta). We explored the mediating effect of prey density on predatory impact in these invaders relative to functionally analogous native rock crab (Cancer irroratus) and Atlantic salmon (Salmo salar), respectively, feeding on shared prey (Mytilus sp. and Tenebrio molitor, respectively). We subsequently combined feeding rates with each predator’s regional abundance to forecast relative ecological impacts. All predators demonstrated potentially destabilising Type II functional responses towards prey, with native rock crab and invasive brown trout exhibiting greater per capita impacts relative to their trophic analogues. Functional Response Ratios (attack rates divided by handling times) were higher for both invasive species, reflecting greater overall per capita effects compared to natives. Impact projections that incorporated predator abundances with per capita effects predicted severe impacts by European green crabs. However, brown trout, despite possessing higher per capita effects than Atlantic salmon, are projected to have low impact owing to currently low abundances in the sampled watershed. Should brown trout density increase sixfold, we predict it would exert higher impact than Atlantic salmon. Such impact-forecasting metrics and methods are thus vital tools to assist in the determination of current and future adverse impacts associated with aquatic invasive species.

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Rossberg, A. G., Å. Brännström, and U. Dieckmann. "How trophic interaction strength depends on traits." Theoretical Ecology 3, no. 1 (April 22, 2009): 13–24. http://dx.doi.org/10.1007/s12080-009-0049-1.

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Donadi, S., Å. N. Austin, U. Bergström, B. K. Eriksson, J. P. Hansen, P. Jacobson, G. Sundblad, M. van Regteren, and J. S. Eklöf. "A cross-scale trophic cascade from large predatory fish to algae in coastal ecosystems." Proceedings of the Royal Society B: Biological Sciences 284, no. 1859 (July 19, 2017): 20170045. http://dx.doi.org/10.1098/rspb.2017.0045.

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Trophic cascades occur in many ecosystems, but the factors regulating them are still elusive. We suggest that an overlooked factor is that trophic interactions (TIs) are often scale-dependent and possibly interact across spatial scales. To explore the role of spatial scale for trophic cascades, and particularly the occurrence of cross-scale interactions (CSIs), we collected and analysed food-web data from 139 stations across 32 bays in the Baltic Sea. We found evidence of a four-level trophic cascade linking TIs across two spatial scales: at bay scale, piscivores (perch and pike) controlled mesopredators (three-spined stickleback), which in turn negatively affected epifaunal grazers. At station scale (within bays), grazers on average suppressed epiphytic algae, and indirectly benefitted habitat-forming vegetation. Moreover, the direction and strength of the grazer–algae relationship at station scale depended on the piscivore biomass at bay scale, indicating a cross-scale interaction effect, potentially caused by a shift in grazer assemblage composition. In summary, the trophic cascade from piscivores to algae appears to involve TIs that occur at, but also interact across, different spatial scales. Considering scale-dependence in general, and CSIs in particular, could therefore enhance our understanding of trophic cascades.

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O'Gorman, Eoin J., Jon M. Yearsley, Tasman P. Crowe, Mark C. Emmerson, Ute Jacob, and Owen L. Petchey. "Loss of functionally unique species may gradually undermine ecosystems." Proceedings of the Royal Society B: Biological Sciences 278, no. 1713 (November 24, 2010): 1886–93. http://dx.doi.org/10.1098/rspb.2010.2036.

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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.

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Emmerson, Mark, T. Martijn Bezemer, MarkD Hunter, T. Hefin Jones, GregoryJ Masters, and Nicole M. Van Dam. "How does global change affect the strength of trophic interactions?" Basic and Applied Ecology 5, no. 6 (December 2004): 505–14. http://dx.doi.org/10.1016/j.baae.2004.09.001.

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Guichard, Frédéric. "Recent advances in metacommunities and meta-ecosystem theories." F1000Research 6 (May 2, 2017): 610. http://dx.doi.org/10.12688/f1000research.10758.1.

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Metacommunity theory has provided many insights into the general problem of local versus regional control of species diversity and relative abundance. The metacommunity framework has been extended from competitive interactions to whole food webs that can be described as spatial networks of interaction networks. Trophic metacommunity theory greatly contributed to resolving the community complexity-stability debate by predicting its dependence on the regional spatial context. The meta-ecosystem framework has since been suggested as a useful simplification of complex ecosystems to apply this spatial context to spatial flows of both individuals and matter. Reviewing the recent literature on metacommunity and meta-ecosystem theories suggests the importance of unifying theories of interaction strength into a meta-ecosystem framework that captures how the strength of spatial, species, and ecosystem fluxes are distributed across location and trophic levels. Such integration predicts important feedback between local and regional processes that drive the assembly of species, the stability of community, and the emergence of ecosystem functions, from limited spatial fluxes of individuals and (in)organic matter. These predictions are often mediated by the maintenance of environmental or endogenous fluctuations from local to regional scales that create important challenges and opportunities for the validation of metacommunity and meta-ecosystem theories and their application to conservation.

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Schweiss, Virginia R., and Chet F. Rakocinski. "Destabilizing effects on a classic tri-trophic oyster-reef cascade." PLOS ONE 15, no. 12 (December 15, 2020): e0242965. http://dx.doi.org/10.1371/journal.pone.0242965.

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How interactions among multiple predators affect the stability of trophic cascades is a topic of special ecological interest. To examine factors affecting the stability of the classic tri-trophic oyster reef cascade within a different context, configurations of three predators, including the Gulf toadfish, Gulf stone crab, and oystershell mud crab, were manipulated together with either oyster shell or limestone gravel substrate within a multiple predator effects (MPE) experiment. Additionally, a complimentary set of trait-mediated-indirect interaction (TMII) experiments examined the inhibition of oyster consumption relative to mud-crab size and top predator identity in the absence of other cues and factors. The classic tri-trophic cascade formed by the toadfish-mud crab-oyster configuration was potentially weakened by several interactions within the MPE experiment. Consumption of oysters and mud crabs by the intraguild stone crab was undeterred by the presence of toadfish. Although mud crab feeding was inhibited in the presence of both toadfish and stone crabs, estimated non-consumptive effects (NCEs) were weaker for stone crabs in the MPE experiment. Consequently, the total effect was destabilizing when all three predator species were together. Inhibition of mud crab feeding was inversely related to direct predation on mud crabs within the MPE experiment. Complimentary TMII experiments revealed greater inhibition of mud crab feeding in response to stone crabs under sparse conditions. TMII experiments also implied that inhibition of mud crab feeding could have largely accounted for NCEs relative to oysters within the MPE experiment, as opposed to interference by other mud crabs or top predators. An inverse relationship between mud crab size and NCE strength in the TMII experiment disclosed another potentially destabilizing influence on the tri-trophic-cascade. Finally, although habitat complexity generally dampened the consumption of oysters across MPE treatments, complex habitat promoted mud crab feeding in the presence of toadfish alone. This study underscores how ecological interactions can mediate trophic cascades and provides some additional insights into the trophic dynamics of oyster reefs for further testing under natural conditions.

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Luhring, Thomas M., and John P. DeLong. "Trophic cascades alter eco-evolutionary dynamics and body size evolution." Proceedings of the Royal Society B: Biological Sciences 287, no. 1938 (November 4, 2020): 20200526. http://dx.doi.org/10.1098/rspb.2020.0526.

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Trait evolution in predator–prey systems can feed back to the dynamics of interacting species as well as cascade to impact the dynamics of indirectly linked species (eco-evolutionary trophic cascades; EETCs). A key mediator of trophic cascades is body mass, as it both strongly influences and evolves in response to predator–prey interactions. Here, we use Gillespie eco-evolutionary models to explore EETCs resulting from top predator loss and mediated by body mass evolution. Our four-trophic-level food chain model uses allometric scaling to link body mass to different functions (ecological pleiotropy) and is realistically parameterized from the FORAGE database to mimic the parameter space of a typical freshwater system. To track real-time changes in selective pressures, we also calculated fitness gradients for each trophic level. As predicted, top predator loss generated alternating shifts in abundance across trophic levels, and, depending on the nature and strength in changes to fitness gradients, also altered trajectories of body mass evolution. Although more distantly linked, changes in the abundance of top predators still affected the eco-evolutionary dynamics of the basal producers, in part because of their relatively short generation times. Overall, our results suggest that impacts on top predators can set off transient EETCs with the potential for widespread indirect impacts on food webs.

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Deacy, William W., Jonathan B. Armstrong, William B. Leacock, Charles T. Robbins, David D. Gustine, Eric J. Ward, Joy A. Erlenbach, and Jack A. Stanford. "Phenological synchronization disrupts trophic interactions between Kodiak brown bears and salmon." Proceedings of the National Academy of Sciences 114, no. 39 (August 21, 2017): 10432–37. http://dx.doi.org/10.1073/pnas.1705248114.

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Climate change is altering the seasonal timing of life cycle events in organisms across the planet, but the magnitude of change often varies among taxa [Thackeray SJ, et al. (2016) Nature 535:241–245]. This can cause the temporal relationships among species to change, altering the strength of interaction. A large body of work has explored what happens when coevolved species shift out of sync, but virtually no studies have documented the effects of climate-induced synchronization, which could remove temporal barriers between species and create novel interactions. We explored how a predator, the Kodiak brown bear (Ursus arctos middendorffi), responded to asymmetric phenological shifts between its primary trophic resources, sockeye salmon (Oncorhynchus nerka) and red elderberry (Sambucus racemosa). In years with anomalously high spring air temperatures, elderberry fruited several weeks earlier and became available during the period when salmon spawned in tributary streams. Bears departed salmon spawning streams, where they typically kill 25–75% of the salmon [Quinn TP, Cunningham CJ, Wirsing AJ (2016) Oecologia 183:415–429], to forage on berries on adjacent hillsides. This prey switching behavior attenuated an iconic predator–prey interaction and likely altered the many ecological functions that result from bears foraging on salmon [Helfield JM, Naiman RJ (2006) Ecosystems 9:167–180]. We document how climate-induced shifts in resource phenology can alter food webs through a mechanism other than trophic mismatch. The current emphasis on singular consumer-resource interactions fails to capture how climate-altered phenologies reschedule resource availability and alter how energy flows through ecosystems.

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Robson, Belinda J. "Habitat architecture and trophic interaction strength in a river: riffle-scale effects." Oecologia 107, no. 3 (August 1996): 411–20. http://dx.doi.org/10.1007/bf00328458.

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Ovadia, Ofer, and Oswald J. Schmitz. "Weather variation and trophic interaction strength: sorting the signal from the noise." Oecologia 140, no. 3 (June 4, 2004): 398–406. http://dx.doi.org/10.1007/s00442-004-1604-5.

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Spiller, David A., and Thomas W. Schoener. "Climatic control of trophic interaction strength: the effect of lizards on spiders." Oecologia 154, no. 4 (October 31, 2007): 763–71. http://dx.doi.org/10.1007/s00442-007-0867-z.

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Sentis, Arnaud, Charlène Gémard, Baptiste Jaugeon, and David S. Boukal. "Predator diversity and environmental change modify the strengths of trophic and nontrophic interactions." Global Change Biology 23, no. 7 (November 25, 2016): 2629–40. http://dx.doi.org/10.1111/gcb.13560.

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POTAPOV, ANTON M. "Multifunctionality of soil food webs." Zoosymposia 22 (November 30, 2022): 54. http://dx.doi.org/10.11646/zoosymposia.22.1.23.

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Soil food webs regulate functioning, ensure stability and support biodiversity both below and above ground. Structure of feeding interactions in soil food webs is shaped by complex size and spatial organization of soil life, and diverse adaptations of soil-dwelling consumers. Strengths of the feeding interactions between consumers and their resources can be quantitatively expressed in ‘energy fluxes’, reflecting trophic functions such as herbivory, microbivory, or predation. Multiple energy fluxes support multiple trophic-related functions and thus support multiple functions at the ecosystem level. I will show how we can use traits of soil consumers to reconstruct network topology of soil food webs and quantify energy fluxes along their resource, size, and spatial dimensions (Potapov 2022). I will then introduce “trophic multifunctionality” i.e. simultaneous support of multiple trophic functions by the food web (analogous to ecosystem multifunctionality) as an approach to calculate a number of quantitative food-web indicators and compare them across systems. With further validation, trait and energy flux approaches would allow to embrace functioning of soil communities from microorganisms to large animals and in perspective use this knowledge to actively manage soil functioning.

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Otto, Sonja B., Eric L. Berlow, Nathan E. Rank, John Smiley, and Ulrich Brose. "PREDATOR DIVERSITY AND IDENTITY DRIVE INTERACTION STRENGTH AND TROPHIC CASCADES IN A FOOD WEB." Ecology 89, no. 1 (January 2008): 134–44. http://dx.doi.org/10.1890/07-0066.1.

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Chen, M., Y. Si, L. Han, X. Liu, B. Huang, and CK Kang. "Effect of prey selectivity and trophic cascades induced by mesozooplankton on the dynamics of phytoplankton." Marine Ecology Progress Series 662 (March 18, 2021): 35–51. http://dx.doi.org/10.3354/meps13627.

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Mesozooplankton are key components in the marine environment, linking the microbial food web and the classic food chain. Yet uncertainties remain on how mesozooplankton mediate the dynamics of prey communities through their complex feeding patterns. To examine mesozooplankton-mediated trophic interactions, we performed shipboard incubations using food removal and dilution methods during 4 cruises in the Pearl River estuary (PRE), Southern China. Our results revealed that mesozooplankton had diverse effects on different size fractions and taxonomic groups of phytoplankton via a combination of strong feeding selectivity and trophic cascades. High ingestion rates by mesozooplankton suppressed the accumulation of microphytoplankton (>20 µm), whereas low ingestion rates by mesozooplankton and resultant trophic cascades promoted the biomass of nano-sized (2-20 µm) and pico-sized (0.7-2 µm) phytoplankton. Among phytoplankton groups, diatoms were passively selected by mesozooplankton despite their high concentrations in natural seawater, whereas dinoflagellates and cryptophytes were actively preferred by mesozooplankton in spring and autumn. Similarly, ciliates were also preferred by mesozooplankton despite their lower biomass compared to phytoplankton, which induced a trophic cascade that indirectly increased the biomass of smaller phytoplankton. The overall feeding effect of mesozooplankton on phytoplankton was determined by the balance between direct grazing rates and indirect compensation with trophic cascades. The degrees of carnivory of the mesozooplankton, which determined the strength of trophic cascades, varied among seasons, resulting in weak control of algal blooms by mesozooplankton. Our findings provide insights into the complex trophic interactions between mesozooplankton and other plankton groups in dynamic natural ecosystems.

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Gibert, Jean P., and John P. DeLong. "Temperature alters food web body-size structure." Biology Letters 10, no. 8 (August 2014): 20140473. http://dx.doi.org/10.1098/rsbl.2014.0473.

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The increased temperature associated with climate change may have important effects on body size and predator–prey interactions. The consequences of these effects for food web structure are unclear because the relationships between temperature and aspects of food web structure such as predator–prey body-size relationships are unknown. Here, we use the largest reported dataset for marine predator–prey interactions to assess how temperature affects predator–prey body-size relationships among different habitats ranging from the tropics to the poles. We found that prey size selection depends on predator body size, temperature and the interaction between the two. Our results indicate that (i) predator–prey body-size ratios decrease with predator size at below-average temperatures and increase with predator size at above-average temperatures, and (ii) that the effect of temperature on predator–prey body-size structure will be stronger at small and large body sizes and relatively weak at intermediate sizes. This systematic interaction may help to simplify forecasting the potentially complex consequences of warming on interaction strengths and food web stability.

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Michel, Nicole L., Thomas W. Sherry, and Walter P. Carson. "The omnivorous collared peccary negates an insectivore-generated trophic cascade in Costa Rican wet tropical forest understorey." Journal of Tropical Ecology 30, no. 1 (November 11, 2013): 1–11. http://dx.doi.org/10.1017/s0266467413000709.

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Abstract:Insectivorous birds and bats often protect plants through density- and trait-mediated cascades, but the degree to which insectivores reduce herbivorous arthropods and leaf damage varies among systems. Top-down interaction strength may be influenced by the biotic and abiotic context, including the presence of vegetation-disturbing animals. We tested two hypotheses: (1) insectivorous birds and bats initiate trophic cascades in tropical rain-forest understorey; and (2) the native, omnivorous collared peccary (Pecari tajacu) negates these cascades via non-trophic effects. We studied the top-down effects of birds and bats on understorey plants in north-eastern Costa Rica using 60 netted exclosures within and outside existing peccary exclosures. Excluding birds and bats increased total arthropod densities by half, both with and without peccaries. Bird/bat exclosures increased Diptera density by 28% and leaf damage by 24% without peccaries, consistent with a trophic cascade. However, bird/bat exclosures decreased Diptera density by 32% and leaf damage by 34% with peccaries, a negation of the trophic cascade. Excluding peccaries increased leaf damage by 43% on plants without birds and bats. This is the first study, to our knowledge, to demonstrate that the non-trophic activity of an omnivorous ungulate can reverse a trophic cascade.

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Moreau, Gaétan, and Christer Björkman. "Nonadditive interactions between trophic levels bias the appraisal of the strength of mortality factors." Population Ecology 54, no. 1 (September 27, 2011): 125–33. http://dx.doi.org/10.1007/s10144-011-0289-y.

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Sanders, Dirk, Elisa Thébault, Rachel Kehoe, and F. J. Frank van Veen. "Trophic redundancy reduces vulnerability to extinction cascades." Proceedings of the National Academy of Sciences 115, no. 10 (February 21, 2018): 2419–24. http://dx.doi.org/10.1073/pnas.1716825115.

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Current species extinction rates are at unprecedentedly high levels. While human activities can be the direct cause of some extinctions, it is becoming increasingly clear that species extinctions themselves can be the cause of further extinctions, since species affect each other through the network of ecological interactions among them. There is concern that the simplification of ecosystems, due to the loss of species and ecological interactions, increases their vulnerability to such secondary extinctions. It is predicted that more complex food webs will be less vulnerable to secondary extinctions due to greater trophic redundancy that can buffer against the effects of species loss. Here, we demonstrate in a field experiment with replicated plant-insect communities, that the probability of secondary extinctions is indeed smaller in food webs that include trophic redundancy. Harvesting one species of parasitoid wasp led to secondary extinctions of other, indirectly linked, species at the same trophic level. This effect was markedly stronger in simple communities than for the same species within a more complex food web. We show that this is due to functional redundancy in the more complex food webs and confirm this mechanism with a food web simulation model by highlighting the importance of the presence and strength of trophic links providing redundancy to those links that were lost. Our results demonstrate that biodiversity loss, leading to a reduction in redundant interactions, can increase the vulnerability of ecosystems to secondary extinctions, which, when they occur, can then lead to further simplification and run-away extinction cascades.

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Stein, Roy A., Dennis R. DeVries, and John M. Dettmers. "Food-web regulation by a planktivore: exploring the generality of the trophic cascade hypothesis." Canadian Journal of Fisheries and Aquatic Sciences 52, no. 11 (November 1, 1995): 2518–26. http://dx.doi.org/10.1139/f95-842.

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The trophic cascade hypothesis currently being tested in north temperate systems may not apply to open-water communities in lower latitude U.S. reservoirs. These reservoir communities differ dramatically from northern lakes in that an open-water omnivore, gizzard shad (Dorosoma cepedianum), often occurs in abundance. Neither controlled by fish predators (owing to high fecundity and low vulnerability) nor by their zooplankton prey (following the midsummer zooplankton decline, gizzard shad consume detritus and phytoplankton), gizzard shad regulate community composition rather than being regulated by top-down or bottom-up forces. In experiments across a range of spatial scales (enclosures, 1–9 m2; ponds, 4–5 ha; and reservoirs, 50–100 ha), we evaluated the generality of the trophic cascade hypothesis by assessing its conceptual strength in reservoir food webs. We reviewed the role of gizzard shad in controlling zooplankton populations and hence recruitment of bluegill, Lepomis macrochirus (via exploitative competition for zooplankton), and largemouth bass, Micropterus salmoides (by reducing their bluegill prey). Reservoir fish communities, owing to the presence of gizzard shad, appear to be regulated more by complex weblike interactions among species than by the more chainlike interactions characteristic of the trophic cascade.

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Miele, Vincent, Christian Guill, Rodrigo Ramos-Jiliberto, and Sonia Kéfi. "Non-trophic interactions strengthen the diversity—functioning relationship in an ecological bioenergetic network model." PLOS Computational Biology 15, no. 8 (August 29, 2019): e1007269. http://dx.doi.org/10.1371/journal.pcbi.1007269.

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Carney, Heath J. "A general hypothesis for the strength of food web interactions in relation to trophic state." SIL Proceedings, 1922-2010 24, no. 1 (December 1990): 487–92. http://dx.doi.org/10.1080/03680770.1989.11898785.

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South, Josie, Monica McCard, Dumisani Khosa, Lubabalo Mofu, Takudzwa C. Madzivanzira, Jaimie T. A. Dick, and Olaf L. F. Weyl. "The effect of prey identity and substrate type on the functional response of a globally invasive crayfish." NeoBiota 52 (November 7, 2019): 9–24. http://dx.doi.org/10.3897/neobiota.52.39245.

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Biological invasions threaten biodiversity on a global scale, therefore, developing predictive methods to understand variation in ecological change conferred is essential. Trophic interaction strength underpins community dynamics, however, these interactions can be profoundly affected by abiotic context, such as substrate type. The red swamp crayfish (Procambarus clarkii) has successfully invaded a number of freshwater ecosystems. We experimentally derive the Functional Response (FR) (density dependent predation) of the red swamp crayfish preying upon both a benthic prey; chironomid larvae, and a pelagic prey; Daphnia magna, on a no substrate control, sand, and gravel substrates to determine whether (1) there is a higher impact on prey that are benthic, and (2) whether the presence of different substrate types can dampen the interaction strength. We apply and demonstrate the utility of the Functional Response Ratio (FRR) metric in unravelling differences in ecological impact not obvious from traditional FR curves. Procambarus clarkii is capable of constantly utilising high numbers of both benthic and pelagic prey items, showing a Type II functional response under all scenarios. The presence of gravel and sand substrate each independently decreased the magnitude FR upon D. magna. Though, with regards to chironomid larvae the FR curves showed no difference in magnitude FR, the FRR reveals that the highest impact is conferred when foraging on sand substrate. This reinforces the need for impact assessments to be contextually relevant.

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Di Capua, Giorgia, Jakob Runge, Reik V. Donner, Bart van den Hurk, Andrew G. Turner, Ramesh Vellore, Raghavan Krishnan, and Dim Coumou. "Dominant patterns of interaction between the tropics and mid-latitudes in boreal summer: causal relationships and the role of timescales." Weather and Climate Dynamics 1, no. 2 (October 15, 2020): 519–39. http://dx.doi.org/10.5194/wcd-1-519-2020.

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Abstract. Tropical convective activity represents a source of predictability for mid-latitude weather in the Northern Hemisphere. In winter, the El Niño–Southern Oscillation (ENSO) is the dominant source of predictability in the tropics and extratropics, but its role in summer is much less pronounced and the exact teleconnection pathways are not well understood. Here, we assess how tropical convection interacts with mid-latitude summer circulation at different intra-seasonal timescales and how ENSO affects these interactions. First, we apply maximum covariance analysis (MCA) between tropical convective activity and mid-latitude geopotential height fields to identify the dominant modes of interaction. The first MCA mode connects the South Asian monsoon with the mid-latitude circumglobal teleconnection pattern. The second MCA mode connects the western North Pacific summer monsoon in the tropics with a wave-5 pattern centred over the North Pacific High in the mid-latitudes. We show that the MCA patterns are fairly insensitive to the selected intra-seasonal timescale from weekly to 4-weekly data. To study the potential causal interdependencies between these modes and with other atmospheric fields, we apply the causal discovery method PCMCI at different timescales. PCMCI extends standard correlation analysis by removing the confounding effects of autocorrelation, indirect links and common drivers. In general, there is a two-way causal interaction between the tropics and mid-latitudes, but the strength and sometimes sign of the causal link are timescale dependent. We introduce causal maps that show the regionally specific causal effect from each MCA mode. Those maps confirm the dominant patterns of interaction and in addition highlight specific mid-latitude regions that are most strongly connected to tropical convection. In general, the identified causal teleconnection patterns are only mildly affected by ENSO and the tropical mid-latitude linkages remain similar. Still, La Niña strengthens the South Asian monsoon generating a stronger response in the mid-latitudes, while during El Niño years the Pacific pattern is reinforced. This study paves the way for process-based validation of boreal summer teleconnections in (sub-)seasonal forecast models and climate models and therefore works towards improved sub-seasonal predictions and climate projections.

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Ludlam, John P., Brandon T. Banks, and Daniel D. Magoulick. "Density-dependent effects of omnivorous stream crayfish on benthic trophic dynamics." Freshwater Crayfish 21, no. 1 (December 31, 2015): 165–70. http://dx.doi.org/10.5869/fc.2015.v21-1.165.

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Abstract Crayfish are abundant and important consumers in aquatic food webs and crayfish invasions have demonstrated strong effects of crayfish on multiple trophic levels. Density may be an important factor determining the role of omnivorous crayfish in benthic communities, especially if density alters the strength of trophic interactions. The effect of crayfish density on a simple benthic food web using ceramic tiles was examined in three treatments (crayfish exclusion cage, cage control (open to crayfish), and exposed ceramic tiles) in mesocosms stocked with 6, 12, or 18 crayfish·m-2. We hypothesized that at low densities crayfish consumption of herbivorous chironomids would increase algal abundance, but at high densities crayfish would reduce both periphyton and invertebrates. In the experiment, periphyton and chironomid abundance increased with declining crayfish biomass on day 30 but not day 15. The magnitude of crayfish effects on day 15 periphyton chlorophyll a abundance increased with crayfish biomass, but crayfish effects on day 30 periphyton chlorophyll a or chironomid biomass did not increase with crayfish biomass. In this experiment there was little evidence for a trophic cascade at low crayfish densities and strong omnivory by crayfish dominated trophic dynamics.

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Fábián, Virág. "Predicting the sign of trophic effects: individual-based simulation versus loop analysis." Community Ecology 22, no. 3 (October 2021): 441–51. http://dx.doi.org/10.1007/s42974-021-00068-1.

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AbstractFood web research needs to be predictive in order to support decisions system-based conservation. In order to increase predictability and applicability, complexity needs to be managed in such a way that we are able to provide simple and clear results. One question emerging frequently is whether certain perturbations (environmental effects or human impact) have positive or negative effects on natural ecosystems or their particular components. Yet, most of food web studies do not consider the sign of effects. Here, we study 6 versions of the Kelian River (Borneo) food web, representing six study sites along the river. For each network, we study the signs of the effects of a perturbed trophic group i on each other j groups. We compare the outcome of the relatively complicated dynamical simulation model and the relatively simple loop analysis model. We compare these results for the 6 sites and also the 14 trophic groups. Finally, we see if sign-agreement and sign-determinacy depend on certain structural features (node centrality, interaction strength). We found major differences between different modelling scenarios, with herbivore-detritivore fish behaving in the most consistent, while algae and particulate organic matter behaving in the least consistent way. We also found higher agreement between the signs of predictions for trophic groups at higher trophic levels in sites 1–3 and at lower trophic levels in site 4–6. This means that the behaviour of predators in the more natural sections of the river and that of producers at the more human-impacted sections are more consistently predicted. This suggests to be more careful with the less consistently predictable trophic groups in conservation management.

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Gehrke, PC, and JH Harris. "The role of fish in cyanobacterial blooms in Australia." Marine and Freshwater Research 45, no. 5 (1994): 905. http://dx.doi.org/10.1071/mf9940905.

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Potential pathways for interaction between fish and cyanobacteria include fish grazing directly on cyanobacteria, fish preying on grazers of cyanobacteria, fish supplying nutrients through excretion, fish providing nutrients by resuspending sediments, and fish altering the availability of nutrients and light by damaging macrophytes. The dominant interactions in Australia are likely to be through pathways that increase the availability of nutrients at the bottom of the food web. Carp probably contribute to these pathways more than do other species by excreting nutrients, resuspending sediments and damaging macrophytes. Further research, on both alien and native fish species, is needed to quantify these processes. Grazing of cyanobacteria by fish is probably trivial because freshwater fish in Australia lack mechanisms to process cyanobacterial cells effectively. Trophic interactions between planktivorous fish, zooplankton and cyanobacteria require closer study to assess the potential for preventing cyanobacterial blooms by manipulating natural predator communities in Australia. However, the need to protect and strengthen native fish stocks precludes removal of native fish to reduce predation pressure on zooplankton communities. Alternative solutions that combine control of nutrients entering waterways and removal of carp have a higher likelihood of success.

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LaManna, Joseph A., Scott A. Mangan, Alfonso Alonso, Norman A. Bourg, Warren Y. Brockelman, Sarayudh Bunyavejchewin, Li-Wan Chang, et al. "Plant diversity increases with the strength of negative density dependence at the global scale." Science 356, no. 6345 (June 29, 2017): 1389–92. http://dx.doi.org/10.1126/science.aam5678.

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Theory predicts that higher biodiversity in the tropics is maintained by specialized interactions among plants and their natural enemies that result in conspecific negative density dependence (CNDD). By using more than 3000 species and nearly 2.4 million trees across 24 forest plots worldwide, we show that global patterns in tree species diversity reflect not only stronger CNDD at tropical versus temperate latitudes but also a latitudinal shift in the relationship between CNDD and species abundance. CNDD was stronger for rare species at tropical versus temperate latitudes, potentially causing the persistence of greater numbers of rare species in the tropics. Our study reveals fundamental differences in the nature of local-scale biotic interactions that contribute to the maintenance of species diversity across temperate and tropical communities.

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Pan, Ying, Yaoyue Long, Jin Hui, Weiyi Xiao, Jiang Yin, Ya Li, Dan Liu, Qingdong Tian, and Liqiang Chen. "Microplastics can affect the trophic cascade strength and stability of plankton ecosystems via behavior-mediated indirect interactions." Journal of Hazardous Materials 430 (May 2022): 128415. http://dx.doi.org/10.1016/j.jhazmat.2022.128415.

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48

Dobrowsky, Terrence M., Yan Zhou, Sean X. Sun, Robert F. Siliciano, and Denis Wirtz. "Monitoring Early Fusion Dynamics of Human Immunodeficiency Virus Type 1 at Single-Molecule Resolution." Journal of Virology 82, no. 14 (May 14, 2008): 7022–33. http://dx.doi.org/10.1128/jvi.00053-08.

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ABSTRACT The fusion of human immunodeficiency virus type 1 (HIV-1) to host cells is a dynamic process governed by the interaction between glycoproteins on the viral envelope and the major receptor, CD4, and coreceptor on the surface of the cell. How these receptors organize at the virion-cell interface to promote a fusion-competent site is not well understood. Using single-molecule force spectroscopy, we map the tensile strengths, lifetimes, and energy barriers of individual intermolecular bonds between CCR5-tropic HIV-1 gp120 and its receptors CD4 and CCR5 or CXCR4 as a function of the interaction time with the cell. According to the Bell model, at short times of contact between cell and virion, the gp120-CD4 bond is able to withstand forces up to 35 pN and has an initial lifetime of 0.27 s and an intermolecular length of interaction of 0.34 nm. The initial bond also has an energy barrier of 6.7 kB T (where kB is Boltzmann's constant and T is absolute temperature). However, within 0.3 s, individual gp120-CD4 bonds undergo rapid destabilization accompanied by a shortened lifetime and a lowered tensile strength. This destabilization is significantly enhanced by the coreceptor CCR5, not by CXCR4 or fusion inhibitors, which suggests that it is directly related to a conformational change in the gp120-CD4 bond. These measurements highlight the instability and low tensile strength of gp120-receptor bonds, uncover a synergistic role for CCR5 in the progression of the gp120-CD4 bond, and suggest that the cell-virus adhesion complex is functionally arranged about a long-lived gp120-coreceptor bond.

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Fleeger, John W. "How Do Indirect Effects of Contaminants Inform Ecotoxicology? A Review." Processes 8, no. 12 (December 16, 2020): 1659. http://dx.doi.org/10.3390/pr8121659.

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Indirect effects in ecotoxicology are defined as chemical- or pollutant-induced alterations in the density or behavior of sensitive species that have cascading effects on tolerant species in natural systems. As a result, species interaction networks (e.g., interactions associated with predation or competition) may be altered in such a way as to bring about large changes in populations and/or communities that may further cascade to disrupt ecosystem function and services. Field studies and experimental outcomes as well as models indicate that indirect effects are most likely to occur in communities in which the strength of interactions and the sensitivity to contaminants differ markedly among species, and that indirect effects will vary over space and time as species composition, trophic structure, and environmental factors vary. However, knowledge of indirect effects is essential to improve understanding of the potential for chemical harm in natural systems. For example, indirect effects may confound laboratory-based ecological risk assessment by enhancing, masking, or spuriously indicating the direct effect of chemical contaminants. Progress to better anticipate and interpret the significance of indirect effects will be made as monitoring programs and long-term ecological research are conducted that facilitate critical experimental field and mesocosm investigations, and as chemical transport and fate models, individual-based direct effects models, and ecosystem/food web models continue to be improved and become better integrated.

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Froneman, Pierre William. "Predator Diversity Does Not Contribute to Increased Prey Risk: Evidence from a Mesocosm Study." Diversity 14, no. 8 (July 22, 2022): 584. http://dx.doi.org/10.3390/d14080584.

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Predation plays an important organisational role in structuring aquatic communities. Predator diversity can, however, lead to emergent effects in which the outcomes of predator–prey interactions are modified. The importance of predator diversity in regulating predator–prey interactions was investigated during a 9-day mesocosm study conducted in the middle reach of a temporarily open/closed, temperate, southern African estuary. The zooplankton community, comprising almost exclusively (>95% of total counts) calanoid and cyclopoid copepods of the genera Pseudodiaptomus, Paracartia and Oithona, was subject to three different juvenile fish predator treatments at natural densities: 1. predation by Gilchristella aestuaria, (Gilchrist, 1913; SL 15.3 ± 2.4 mm); 2. predation by Myxus capensis (Valenciennes, 1836; SL 12.8 ± 3.7 mm); and 3. a combination of the two predators. The presence of the predators contributed to a significant decline in the total zooplankton abundances, with a concurrent increase in total chlorophyll-a (Chl-a) concentrations, consistent with the expectations of a trophic cascade (ANCOVA; p < 0.05 in all cases). There were no significant differences in the total Chl-a concentration or total zooplankton abundances between the different predator treatments, suggesting that the increase in predator diversity did not contribute to increased prey risk or to the strength of the trophic cascade.

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Journal articles on the topic 'Trophic interaction strengths'

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