Understanding patterns and processes in models of trophic cascades

Heath, Michael R.; Speirs, Douglas C.; Steele, John H.

doi:10.1111/ele.12200

Cited by 134 publications

(156 citation statements)

References 79 publications

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“…Similar observations have been made in models specifically developed for the study of virus-host interactions in the oceans (for example, the Kill-the-Winner model; Thingstad and Lignell, 1997;Thingstad, 2000). However, within food-web models, the nature of trophic cascade depends on the type of regulation and even the functional response of consumers to resources (Heath et al, 2014), suggesting that similar analysis of variations in the present model are warranted.…”

Section: Resultssupporting

confidence: 68%

A multitrophic model to quantify the effects of marine viruses on microbial food webs and ecosystem processes

et al. 2015

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Viral lysis of microbial hosts releases organic matter that can then be assimilated by nontargeted microorganisms. Quantitative estimates of virus-mediated recycling of carbon in marine waters, first established in the late 1990s, were originally extrapolated from marine host and virus densities, host carbon content and inferred viral lysis rates. Yet, these estimates did not explicitly incorporate the cascade of complex feedbacks associated with virus-mediated lysis. To evaluate the role of viruses in shaping community structure and ecosystem functioning, we extend dynamic multitrophic ecosystem models to include a virus component, specifically parameterized for processes taking place in the ocean euphotic zone. Crucially, we are able to solve this model analytically, facilitating evaluation of model behavior under many alternative parameterizations. Analyses reveal that the addition of a virus component promotes the emergence of complex communities. In addition, biomass partitioning of the emergent multitrophic community is consistent with well-established empirical norms in the surface oceans. At steady state, ecosystem fluxes can be probed to characterize the effects that viruses have when compared with putative marine surface ecosystems without viruses. The model suggests that ecosystems with viruses will have (1) increased organic matter recycling, (2) reduced transfer to higher trophic levels and (3) increased net primary productivity. These model findings support hypotheses that viruses can have significant stimulatory effects across whole-ecosystem scales. We suggest that existing efforts to predict carbon and nutrient cycling without considering virus effects are likely to miss essential features of marine food webs that regulate global biogeochemical cycles.

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Section: Resultssupporting

confidence: 68%

A multitrophic model to quantify the effects of marine viruses on microbial food webs and ecosystem processes

et al. 2015

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“…The largely non-experimental nature of regime shift requires creative methods to increase understanding of mechanisms that both initiate and maintain regimes [2,4,[6][7][8][9][10][11]32,43,57], as the range of spatial scales in which key regime shift drivers operate and may be detected vary by more than five orders of magnitude (figure 1), while within-system spatial heterogeneity has long been identified as a potentially important factor in analyses of regime shifts [1,10]. As the above examples have demonstrated, recent examinations of the roles of spatial heterogeneity and the movement of marine populations have implications for the initiation and detection of regime shifts, and some common features emerge.…”

Section: Resultsmentioning

confidence: 99%

The importance of within-system spatial variation in drivers of marine ecosystem regime shifts

Fisher

Casini

Frank

et al. 2015

Phil. Trans. R. Soc. B

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Comparative analyses of the dynamics of exploited marine ecosystems have led to differing hypotheses regarding the primary causes of observed regime shifts, while many ecosystems have apparently not undergone regime shifts. These varied responses may be partly explained by the decade-old recognition that within-system spatial heterogeneity in key climate and anthropogenic drivers may be important, as recent theoretical examinations have concluded that spatial heterogeneity in environmental characteristics may diminish the tendency for regime shifts. Here, we synthesize recent, empirical within-system spatio-temporal analyses of some temperate and subarctic large marine ecosystems in which regime shifts have (and have not) occurred. Examples from the Baltic Sea, Black Sea, Bengula Current, North Sea, Barents Sea and Eastern Scotian Shelf reveal the largely neglected importance of considering spatial variability in key biotic and abiotic influences and species movements in the context of evaluating and predicting regime shifts. We highlight both the importance of understanding the scale-dependent spatial dynamics of climate influences and key predator–prey interactions to unravel the dynamics of regime shifts, and the utility of spatial downscaling of proposed mechanisms (as evident in the North Sea and Barents Sea) as a means of evaluating hypotheses originally derived from among-system comparisons.

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“…Much of this can be found in literature from marine, aquatic and invertebrate systems (Heath et al, 2014;Meadows et al, 2017), or systems and models where bottom-up processes are relatively predictable, stable and controllable. Reliable work on MRH, TCH and BMTCH in terrestrial systems is only beginning to catch up to these disciplines.…”

Section: Implications For Large Carnivore Science and Managementmentioning

confidence: 99%

Can we save large carnivores without losing large carnivore science?

Allen

Allen²,

Andrén

et al. 2017

Food Webs

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a b s t r a c t a r t i c l e i n f oLarge carnivores are depicted to shape entire ecosystems through top-down processes. Studies describing these processes are often used to support interventionist wildlife management practices, including carnivore reintroduction or lethal control programs. Unfortunately, there is an increasing tendency to ignore, disregard or devalue fundamental principles of the scientific method when communicating the reliability of current evidence for the ecological roles that large carnivores may play, eroding public confidence in large carnivore science and scientists. Here, we discuss six interrelated issues that currently undermine the reliability of the available literature on the ecological roles of large carnivores: (1) the overall paucity of available data, (2) reliability of carnivore population sampling techniques, (3) general disregard for alternative hypotheses to top-down forcing, (4) lack of applied science studies, (5) frequent use of logical fallacies, and (6) generalisation of results from relatively pristine systems to those substantially altered by humans. We first describe how widespread these issues are, and given this, show, for example, that evidence for the roles of wolves (Canis lupus) and dingoes (Canis lupus dingo) in initiating trophic cascades is not as strong as is often claimed. Managers and policy makers should exercise caution when relying on this literature to inform wildlife management decisions. We emphasise the value of manipulative experiments and discuss the role of scientific knowledge in the decision-making process. We hope that the issues we raise here prompt deeper consideration of actual evidence, leading towards an improvement in both the rigour and communication of large carnivore science.

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Understanding patterns and processes in models of trophic cascades

Cited by 134 publications

References 79 publications

A multitrophic model to quantify the effects of marine viruses on microbial food webs and ecosystem processes

A multitrophic model to quantify the effects of marine viruses on microbial food webs and ecosystem processes

The importance of within-system spatial variation in drivers of marine ecosystem regime shifts

Can we save large carnivores without losing large carnivore science?

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