Page 1. CHAPTER 13 YL ¡«ЕР Simulating Large-Scale Population Dynamics Using Small-Scale Data Grah... more Page 1. CHAPTER 13 YL ¡«ЕР Simulating Large-Scale Population Dynamics Using Small-Scale Data Graham E. Forrester Department of Biological Sciences University of Rhode Island Kingston, Rhode Island 02881 Mark A ...
Although field experiments allow rigorous tests of ecological hypotheses, they are usually limite... more Although field experiments allow rigorous tests of ecological hypotheses, they are usually limited to small spatial scales. We often want to know if their findings extrapolate to larger scales, especially when seeking to apply their results to conservation and management. Experiments on small coral reef fishes (bridled gobies) occupying small habitat patches reveal that locally density-dependent mortality is inflicted by predators. As prey become crowded, they suffer a progressively increasing shortage of structural refuges. Consequently, goby mortality at small-scales is well described by a model in which vulnerability is proportional to the ratio of gobies to refuges. A manipulation of refuge abundance on entire reefs, which are the size of small marine reserves and approach the scale at which some reef fisheries operate, suggests that a similar interaction occurs at this much larger spatial scale. This result is in accord with a scaling model which indicates that the effects of r...
Proceedings of the National Academy of Sciences, 2005
Field experiments provide rigorous tests of ecological hypotheses but are usually limited to smal... more Field experiments provide rigorous tests of ecological hypotheses but are usually limited to small spatial scales. It is thus unclear whether these findings extrapolate to larger scales relevant to conservation and management. We show that the results of experiments detecting density-dependent mortality of reef fish on small habitat patches scale up to have similar effects on much larger entire reefs that are the size of small marine reserves and approach the scale at which some reef fisheries operate. We suggest that accurate scaling is due to the type of species interaction causing local density dependence and the fact that localized events can be aggregated to describe larger-scale interactions with minimal distortion. Careful extrapolation from small-scale experiments identifying species interactions and their effects should improve our ability to predict the outcomes of alternative management strategies for coral reef fishes and their habitats.
Proceedings of the National Academy of Sciences, 2005
Field experiments provide rigorous tests of ecological hypotheses but are usually limited to smal... more Field experiments provide rigorous tests of ecological hypotheses but are usually limited to small spatial scales. It is thus unclear whether these findings extrapolate to larger scales relevant to conservation and management. We show that the results of experiments detecting density-dependent mortality of reef fish on small habitat patches scale up to have similar effects on much larger entire reefs that are the size of small marine reserves and approach the scale at which some reef fisheries operate. We suggest that accurate scaling is due to the type of species interaction causing local density dependence and the fact that localized events can be aggregated to describe larger-scale interactions with minimal distortion. Careful extrapolation from small-scale experiments identifying species interactions and their effects should improve our ability to predict the outcomes of alternative management strategies for coral reef fishes and their habitats.
IN THEIR REPORT “STRONG TOP-DOWN CONtrol in southern California kelp forest ecosystems” (26 May, ... more IN THEIR REPORT “STRONG TOP-DOWN CONtrol in southern California kelp forest ecosystems” (26 May, p. 1230), B. S. Halpern et al. conclude that these forests show strong top-down (consumer-driven) control and that bottom-up (resource-driven) control in such systems may often be overestimated. These conclusions run counter to most of the extensive literature (1–4) on the ecology and natural history of kelp forests in southern California. There are numerous examples of the importance of storms and low nutrients over large spatial and temporal scales, especially during El Niños (3, 5–7) but also from decadal climate shifts (8). Halpern et al. used a short-term data set that did not include El Niño–Southern Oscillation or decadal climate shifts. Moreover, they used satellite-derived offshore chlorophyll a concentration data as a measure of “resources” without establishing that these data were a good proxy for nutrients or primary production in nearshore kelp forests and despite evidence t...
The extent to which artificial reefs may be useful for mitigation of environmental impacts, fishe... more The extent to which artificial reefs may be useful for mitigation of environmental impacts, fisheries management, and conservation depends in part upon how well the organisms that live on them fare. We tested whether fish living on artificial reefs were in similar condition (weight-at-length), grew, foraged, reproduced, and produced tissue at rates similar to those on natural reefs. We studied five artificial–natural reef pairs spread over >200 km in the Southern California Bight. Underwater visual transects were used to quantify density and size structure of four target species (Paralabrax clathratus, Paralabrax nebulifer, Semicossyphus pulcher, and Embiotoca jacksoni), which were also collected to measure foraging success, condition, growth, reproductive output, and tissue production. Generally, fish living on artificial reefs fared as well or better than those on natural reefs, with some exceptions. Semicossyphus pulcher fared better on artificial reefs, having higher foraging...
Vermetid gastropods have the potential to reduce foraging by herbivorous fishes on algae on coral... more Vermetid gastropods have the potential to reduce foraging by herbivorous fishes on algae on coral reefs because they produce mucous nets that cover the surfaces of coral skeletons, potentially inhibiting foraging by fishes. We assessed this possibility using both observational and experimental approaches in Moorea, French Polynesia. Foraging rates of herbivorous fishes (total number of bites by all species per minute) were recorded in plots that varied naturally in the cover of vermetid mucous nets. This study, done at six sites, revealed that foraging on algal turf declined with increasing cover of vermetid mucous nets, ranging from ~2 to 22 bites m−2 min−1 at 0 % coverage to 0–5 bites m−2 min−1 at 100 % coverage. The magnitude of this effect of vermetid nets varied among microhabitats (high, mid, and low bommies) and sites, presumably due to variation in the intensity of herbivory. Experimental removal of vermetid mucous nets from plots more than doubled the foraging intensity on turf algae relative to when vermetid nets were present at high (≥70 %) cover. Our results indicate that algal turf on coral reefs may benefit from associational refuge from grazing provided by vermetid gastropods, which might in turn harm corals via increased competition with algal turf.
A negative relationship between population growth and population density (direct density dependen... more A negative relationship between population growth and population density (direct density dependence) is necessary for population regulation and is assumed in most models of harvested populations. Experimental tests for density dependence are lacking for large-bodied, harvested fish because of the difficulty of manipulating population density over large areas. We studied a harvested coral reef fish, Lutjanus apodus (schoolmaster snapper), using eight large, isolated natural reefs (0.4-1.6 ha) in the Bahamas as replicates. An initial observational test for density dependence was followed by a manipulation of population density. The manipulation weakened an association between density and shelter-providing habitat features and revealed a positive effect of population density on recruitment and survival (inverse density dependence), but no effect of density on somatic growth. The snappers on an individual reef were organized into a few shoals, and we hypothesize that large shoals on high-density reefs were less vulnerable to large piscivores (groupers and barracudas) than the small shoals on low-density reefs. Reductions in predation risk for individuals in large social groups are well documented, but because snapper shoals occupied reefs the size of small marine reserves, these ecological interactions may influence the outcome of management actions.
Page 1. CHAPTER 13 YL ¡«ЕР Simulating Large-Scale Population Dynamics Using Small-Scale Data Grah... more Page 1. CHAPTER 13 YL ¡«ЕР Simulating Large-Scale Population Dynamics Using Small-Scale Data Graham E. Forrester Department of Biological Sciences University of Rhode Island Kingston, Rhode Island 02881 Mark A ...
Although field experiments allow rigorous tests of ecological hypotheses, they are usually limite... more Although field experiments allow rigorous tests of ecological hypotheses, they are usually limited to small spatial scales. We often want to know if their findings extrapolate to larger scales, especially when seeking to apply their results to conservation and management. Experiments on small coral reef fishes (bridled gobies) occupying small habitat patches reveal that locally density-dependent mortality is inflicted by predators. As prey become crowded, they suffer a progressively increasing shortage of structural refuges. Consequently, goby mortality at small-scales is well described by a model in which vulnerability is proportional to the ratio of gobies to refuges. A manipulation of refuge abundance on entire reefs, which are the size of small marine reserves and approach the scale at which some reef fisheries operate, suggests that a similar interaction occurs at this much larger spatial scale. This result is in accord with a scaling model which indicates that the effects of r...
Proceedings of the National Academy of Sciences, 2005
Field experiments provide rigorous tests of ecological hypotheses but are usually limited to smal... more Field experiments provide rigorous tests of ecological hypotheses but are usually limited to small spatial scales. It is thus unclear whether these findings extrapolate to larger scales relevant to conservation and management. We show that the results of experiments detecting density-dependent mortality of reef fish on small habitat patches scale up to have similar effects on much larger entire reefs that are the size of small marine reserves and approach the scale at which some reef fisheries operate. We suggest that accurate scaling is due to the type of species interaction causing local density dependence and the fact that localized events can be aggregated to describe larger-scale interactions with minimal distortion. Careful extrapolation from small-scale experiments identifying species interactions and their effects should improve our ability to predict the outcomes of alternative management strategies for coral reef fishes and their habitats.
Proceedings of the National Academy of Sciences, 2005
Field experiments provide rigorous tests of ecological hypotheses but are usually limited to smal... more Field experiments provide rigorous tests of ecological hypotheses but are usually limited to small spatial scales. It is thus unclear whether these findings extrapolate to larger scales relevant to conservation and management. We show that the results of experiments detecting density-dependent mortality of reef fish on small habitat patches scale up to have similar effects on much larger entire reefs that are the size of small marine reserves and approach the scale at which some reef fisheries operate. We suggest that accurate scaling is due to the type of species interaction causing local density dependence and the fact that localized events can be aggregated to describe larger-scale interactions with minimal distortion. Careful extrapolation from small-scale experiments identifying species interactions and their effects should improve our ability to predict the outcomes of alternative management strategies for coral reef fishes and their habitats.
IN THEIR REPORT “STRONG TOP-DOWN CONtrol in southern California kelp forest ecosystems” (26 May, ... more IN THEIR REPORT “STRONG TOP-DOWN CONtrol in southern California kelp forest ecosystems” (26 May, p. 1230), B. S. Halpern et al. conclude that these forests show strong top-down (consumer-driven) control and that bottom-up (resource-driven) control in such systems may often be overestimated. These conclusions run counter to most of the extensive literature (1–4) on the ecology and natural history of kelp forests in southern California. There are numerous examples of the importance of storms and low nutrients over large spatial and temporal scales, especially during El Niños (3, 5–7) but also from decadal climate shifts (8). Halpern et al. used a short-term data set that did not include El Niño–Southern Oscillation or decadal climate shifts. Moreover, they used satellite-derived offshore chlorophyll a concentration data as a measure of “resources” without establishing that these data were a good proxy for nutrients or primary production in nearshore kelp forests and despite evidence t...
The extent to which artificial reefs may be useful for mitigation of environmental impacts, fishe... more The extent to which artificial reefs may be useful for mitigation of environmental impacts, fisheries management, and conservation depends in part upon how well the organisms that live on them fare. We tested whether fish living on artificial reefs were in similar condition (weight-at-length), grew, foraged, reproduced, and produced tissue at rates similar to those on natural reefs. We studied five artificial–natural reef pairs spread over >200 km in the Southern California Bight. Underwater visual transects were used to quantify density and size structure of four target species (Paralabrax clathratus, Paralabrax nebulifer, Semicossyphus pulcher, and Embiotoca jacksoni), which were also collected to measure foraging success, condition, growth, reproductive output, and tissue production. Generally, fish living on artificial reefs fared as well or better than those on natural reefs, with some exceptions. Semicossyphus pulcher fared better on artificial reefs, having higher foraging...
Vermetid gastropods have the potential to reduce foraging by herbivorous fishes on algae on coral... more Vermetid gastropods have the potential to reduce foraging by herbivorous fishes on algae on coral reefs because they produce mucous nets that cover the surfaces of coral skeletons, potentially inhibiting foraging by fishes. We assessed this possibility using both observational and experimental approaches in Moorea, French Polynesia. Foraging rates of herbivorous fishes (total number of bites by all species per minute) were recorded in plots that varied naturally in the cover of vermetid mucous nets. This study, done at six sites, revealed that foraging on algal turf declined with increasing cover of vermetid mucous nets, ranging from ~2 to 22 bites m−2 min−1 at 0 % coverage to 0–5 bites m−2 min−1 at 100 % coverage. The magnitude of this effect of vermetid nets varied among microhabitats (high, mid, and low bommies) and sites, presumably due to variation in the intensity of herbivory. Experimental removal of vermetid mucous nets from plots more than doubled the foraging intensity on turf algae relative to when vermetid nets were present at high (≥70 %) cover. Our results indicate that algal turf on coral reefs may benefit from associational refuge from grazing provided by vermetid gastropods, which might in turn harm corals via increased competition with algal turf.
A negative relationship between population growth and population density (direct density dependen... more A negative relationship between population growth and population density (direct density dependence) is necessary for population regulation and is assumed in most models of harvested populations. Experimental tests for density dependence are lacking for large-bodied, harvested fish because of the difficulty of manipulating population density over large areas. We studied a harvested coral reef fish, Lutjanus apodus (schoolmaster snapper), using eight large, isolated natural reefs (0.4-1.6 ha) in the Bahamas as replicates. An initial observational test for density dependence was followed by a manipulation of population density. The manipulation weakened an association between density and shelter-providing habitat features and revealed a positive effect of population density on recruitment and survival (inverse density dependence), but no effect of density on somatic growth. The snappers on an individual reef were organized into a few shoals, and we hypothesize that large shoals on high-density reefs were less vulnerable to large piscivores (groupers and barracudas) than the small shoals on low-density reefs. Reductions in predation risk for individuals in large social groups are well documented, but because snapper shoals occupied reefs the size of small marine reserves, these ecological interactions may influence the outcome of management actions.
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