Musical chairs mortality functions: density-dependent deaths caused by competition for unguarded refuges

Samhouri, Jameal F.; Vance, Richard R.; Forrester, Graham E.; Steele, Mark A.

doi:10.1007/s00442-009-1307-z

Cited by 19 publications

(17 citation statements)

References 54 publications

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“…In contrast, a meta-analysis of reef fish studies found strong evidence for density dependence, even in the subset of studies that individually lacked sufficient statistical power to detect it (Osenberg et al 2002). Subsequent work also indicates that density dependence is important in reef fishes, but most such studies have focused on relatively small, siteattached species (e.g., Johnson 2008, Samhouri et al 2009). The fact that our estimates of the strength of density dependence are, if anything, stronger in the roving grazers and scrapers than in the territorial grazers ( Fig.…”

Section: Discussionmentioning

confidence: 99%

Diversity and stability of herbivorous fishes on coral reefs

Thibaut

Connolly

Sweatman

2012

Ecology

118

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Biodiversity may provide insurance against ecosystem collapse by stabilizing assemblages that perform particular ecological functions (the “portfolio effect”). However, the extent to which this occurs in nature and the importance of different mechanisms that generate portfolio effects remain controversial. On coral reefs, herbivory helps maintain coral dominated states, so volatility in levels of herbivory has important implications for reef ecosystems. Here, we used an extensive time series of abundances on 35 reefs of the Great Barrier Reef of Australia to quantify the strength of the portfolio effect for herbivorous fishes. Then, we disentangled the contributions of two mechanisms that underlie it (compensatory interactions and differential responses to environmental fluctuations [“response diversity”]) by fitting a community‐dynamic model that explicitly includes terms for both mechanisms. We found that portfolio effects operate strongly in herbivorous fishes, as shown by nearly independent fluctuations in abundances over time. Moreover, we found strong evidence for high response diversity, with nearly independent responses to environmental fluctuations. In contrast, we found little evidence that the portfolio effect in this system was enhanced by compensatory ecological interactions. Our results show that portfolio effects are driven principally by response diversity for herbivorous fishes on coral reefs. We conclude that portfolio effects can be very strong in nature and that, for coral reefs in particular, response diversity may help maintain herbivory above the threshold levels that trigger regime shifts.

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Section: Discussionmentioning

confidence: 99%

Diversity and stability of herbivorous fishes on coral reefs

Thibaut

Connolly

Sweatman

2012

Ecology

118

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“…1b-c) that continuously accelerate or decelerate (i.e., the second derivative is never equal to zero). Similar piecewise functions have been used widely to identify thresholds for biological effects of contaminants [25], edge effects on ecological communities [26], phase-dependent dynamics in cyclic populations [27], and density-dependent mortality in fish populations [28], to name just a few examples.…”

Section: Methodsmentioning

confidence: 99%

Identifying Thresholds for Ecosystem-Based Management

2010

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BackgroundOne of the greatest obstacles to moving ecosystem-based management (EBM) from concept to practice is the lack of a systematic approach to defining ecosystem-level decision criteria, or reference points that trigger management action.Methodology/Principal FindingsTo assist resource managers and policymakers in developing EBM decision criteria, we introduce a quantitative, transferable method for identifying utility thresholds. A utility threshold is the level of human-induced pressure (e.g., pollution) at which small changes produce substantial improvements toward the EBM goal of protecting an ecosystem's structural (e.g., diversity) and functional (e.g., resilience) attributes. The analytical approach is based on the detection of nonlinearities in relationships between ecosystem attributes and pressures. We illustrate the method with a hypothetical case study of (1) fishing and (2) nearshore habitat pressure using an empirically-validated marine ecosystem model for British Columbia, Canada, and derive numerical threshold values in terms of the density of two empirically-tractable indicator groups, sablefish and jellyfish. We also describe how to incorporate uncertainty into the estimation of utility thresholds and highlight their value in the context of understanding EBM trade-offs.Conclusions/SignificanceFor any policy scenario, an understanding of utility thresholds provides insight into the amount and type of management intervention required to make significant progress toward improved ecosystem structure and function. The approach outlined in this paper can be applied in the context of single or multiple human-induced pressures, to any marine, freshwater, or terrestrial ecosystem, and should facilitate more effective management.

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“…Although less conventional than other functions (e.g., Gompertz, von Bertalanffy), the bi-phasic piecewise regression models provide more parsimonious descriptions of various metabolic, energetic, and ecological processes-including growth in fish. This is supported by a growing body of theoretical (Quince et al 2008a) and empirical (Post and Lee 1996;Post and Parkinson 2001;Quince et al 2008b;Samhouri et al 2009) literature. Furthermore, piecewise regression provides a convenient method for calculating the change in growth rate (indicated by the change in slope coefficients) and the age at which growth slows (indicated by the value of the independent variable at slope flexure), thereby allowing us to determine whether the change in growth coincided with an increase in energy allocation to storage (see below: "Energy allocation").…”

Section: Growthmentioning

confidence: 71%

Energy allocation in juveniles of a warm-temperate reef fish

et al. 2010

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During the first year of life, organisms are faced with competing demands for energy between growth and storage. Most research on energy allocation in young fishes has focused on cold-temperate species which are subjected to strong seasonal fluctuations in productivity, while few studies have considered those at lower latitudes where seasonality is less pronounced. Gag (Mycteroperca microlepis) of the northeastern Gulf of Mexico settle in coastal seagrass beds in the spring as juveniles and emigrate to offshore reefs in the fall. Upon settlement, these young fish grow at remarkably fast rates, but their growth slows considerably before emigration. Slowed growth can be explained by one of three hypotheses:(1) size-specific emigration times; (2) reduced feeding efficiency associated with declines in primary and secondary productivity; or (3) energetic shifts in allocation from growth to storage. Gag emigrate essentially as a cohort, so slowed growth does not result from differential emigration patterns based on fish size. They also emigrate before seasonal declines in primary and secondary productivity; thus, food remains abundant and feeding efficiency constant. The more plausible hypothesis is that there is an energetic shift from growth to storage. The liver serves as the primary site of lipid storage and the hepatosomatic index of juvenile gag increases coincident with reduced growth. The overall effect of increased energy stores is presumably for use during offshore migration and/or for overwinter survival.

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Musical chairs mortality functions: density-dependent deaths caused by competition for unguarded refuges

Cited by 19 publications

References 54 publications

Diversity and stability of herbivorous fishes on coral reefs

Diversity and stability of herbivorous fishes on coral reefs

Identifying Thresholds for Ecosystem-Based Management

Energy allocation in juveniles of a warm-temperate reef fish

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