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Species richness and trophic diversity increase decomposition in a co-evolved food web.

Baiser B, Ardeshiri RS, Ellison AM - PLoS ONE (2011)

Bottom Line: Knowledge of how this biodiversity relates to ecosystem functioning is important for understanding the maintenance of diversity and the potential effects of species losses and gains on ecosystems.We show that species richness and trophic diversity underlie strong linkages between food web structure and dynamics that influence ecosystem functioning.The importance of trophic diversity and species interactions in determining how biodiversity relates to ecosystem functioning suggests that simply focusing on species richness does not give a complete picture as to how ecosystems may change with the loss or gain of species.

View Article: PubMed Central - PubMed

Affiliation: Harvard Forest, Harvard University, Petersham, Massachusetts, United States of America. bbaiser@fas.harvard.edu

ABSTRACT
Ecological communities show great variation in species richness, composition and food web structure across similar and diverse ecosystems. Knowledge of how this biodiversity relates to ecosystem functioning is important for understanding the maintenance of diversity and the potential effects of species losses and gains on ecosystems. While research often focuses on how variation in species richness influences ecosystem processes, assessing species richness in a food web context can provide further insight into the relationship between diversity and ecosystem functioning and elucidate potential mechanisms underpinning this relationship. Here, we assessed how species richness and trophic diversity affect decomposition rates in a complete aquatic food web: the five trophic level web that occurs within water-filled leaves of the northern pitcher plant, Sarracenia purpurea. We identified a trophic cascade in which top-predators--larvae of the pitcher-plant mosquito--indirectly increased bacterial decomposition by preying on bactivorous protozoa. Our data also revealed a facultative relationship in which larvae of the pitcher-plant midge increased bacterial decomposition by shredding detritus. These important interactions occur only in food webs with high trophic diversity, which in turn only occur in food webs with high species richness. We show that species richness and trophic diversity underlie strong linkages between food web structure and dynamics that influence ecosystem functioning. The importance of trophic diversity and species interactions in determining how biodiversity relates to ecosystem functioning suggests that simply focusing on species richness does not give a complete picture as to how ecosystems may change with the loss or gain of species.

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Path models ( =  a priori hypotheses) describing decomposition dynamics in the Sarracenia food web.(A) The sampling effect model tests if high species richness increases the probability that an ‘important’ decomposer will be present. This model was run for each species to determine if any one species contributes disproportionately to decomposition. (B) The indirect top-down cascade model tests if mosquitoes, copepods, and rotifers indirectly facilitate bacterial decomposition by releasing bacteria from predation by protozoa (dashed lines). (C) The combined top-down cascade model tests if the indirect effects (dashed lines) from mosquitoes, copepods, and rotifers along with direct predation (solid lines) on bacteria alter decomposition. The indirect (D) and combined (E) full food web models include paths for predation by the mite (Sarraceniopus gibsoni) on bacteria and the direct decomposition by the midge (Metriocnemus knabi) as pathways that influence decomposition in addition to the pathways in models (B) and (C) respectively.
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pone-0020672-g001: Path models ( =  a priori hypotheses) describing decomposition dynamics in the Sarracenia food web.(A) The sampling effect model tests if high species richness increases the probability that an ‘important’ decomposer will be present. This model was run for each species to determine if any one species contributes disproportionately to decomposition. (B) The indirect top-down cascade model tests if mosquitoes, copepods, and rotifers indirectly facilitate bacterial decomposition by releasing bacteria from predation by protozoa (dashed lines). (C) The combined top-down cascade model tests if the indirect effects (dashed lines) from mosquitoes, copepods, and rotifers along with direct predation (solid lines) on bacteria alter decomposition. The indirect (D) and combined (E) full food web models include paths for predation by the mite (Sarraceniopus gibsoni) on bacteria and the direct decomposition by the midge (Metriocnemus knabi) as pathways that influence decomposition in addition to the pathways in models (B) and (C) respectively.

Mentions: We first used linear regression to test the relationship between species richness, TD, and decomposition and further investigated these relationships by using path analysis to test directly the two mechanisms that have been proposed to explain the relationship between biodiversity and ecosystem functioning: the sampling effect [28], [29] and niche complementarity [8], [38]. We constructed path models for each hypothesis and assessed the fit of each path model to the experimental data. Sampling effect path models simply identify relationships between species richness and specific species that contribute disproportionately to decomposition (Fig. 1a). We constructed one sampling effect path model for each species in the experiment to determine if any one species was responsible for the majority of the decomposition.


Species richness and trophic diversity increase decomposition in a co-evolved food web.

Baiser B, Ardeshiri RS, Ellison AM - PLoS ONE (2011)

Path models ( =  a priori hypotheses) describing decomposition dynamics in the Sarracenia food web.(A) The sampling effect model tests if high species richness increases the probability that an ‘important’ decomposer will be present. This model was run for each species to determine if any one species contributes disproportionately to decomposition. (B) The indirect top-down cascade model tests if mosquitoes, copepods, and rotifers indirectly facilitate bacterial decomposition by releasing bacteria from predation by protozoa (dashed lines). (C) The combined top-down cascade model tests if the indirect effects (dashed lines) from mosquitoes, copepods, and rotifers along with direct predation (solid lines) on bacteria alter decomposition. The indirect (D) and combined (E) full food web models include paths for predation by the mite (Sarraceniopus gibsoni) on bacteria and the direct decomposition by the midge (Metriocnemus knabi) as pathways that influence decomposition in addition to the pathways in models (B) and (C) respectively.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3108618&req=5

pone-0020672-g001: Path models ( =  a priori hypotheses) describing decomposition dynamics in the Sarracenia food web.(A) The sampling effect model tests if high species richness increases the probability that an ‘important’ decomposer will be present. This model was run for each species to determine if any one species contributes disproportionately to decomposition. (B) The indirect top-down cascade model tests if mosquitoes, copepods, and rotifers indirectly facilitate bacterial decomposition by releasing bacteria from predation by protozoa (dashed lines). (C) The combined top-down cascade model tests if the indirect effects (dashed lines) from mosquitoes, copepods, and rotifers along with direct predation (solid lines) on bacteria alter decomposition. The indirect (D) and combined (E) full food web models include paths for predation by the mite (Sarraceniopus gibsoni) on bacteria and the direct decomposition by the midge (Metriocnemus knabi) as pathways that influence decomposition in addition to the pathways in models (B) and (C) respectively.
Mentions: We first used linear regression to test the relationship between species richness, TD, and decomposition and further investigated these relationships by using path analysis to test directly the two mechanisms that have been proposed to explain the relationship between biodiversity and ecosystem functioning: the sampling effect [28], [29] and niche complementarity [8], [38]. We constructed path models for each hypothesis and assessed the fit of each path model to the experimental data. Sampling effect path models simply identify relationships between species richness and specific species that contribute disproportionately to decomposition (Fig. 1a). We constructed one sampling effect path model for each species in the experiment to determine if any one species was responsible for the majority of the decomposition.

Bottom Line: Knowledge of how this biodiversity relates to ecosystem functioning is important for understanding the maintenance of diversity and the potential effects of species losses and gains on ecosystems.We show that species richness and trophic diversity underlie strong linkages between food web structure and dynamics that influence ecosystem functioning.The importance of trophic diversity and species interactions in determining how biodiversity relates to ecosystem functioning suggests that simply focusing on species richness does not give a complete picture as to how ecosystems may change with the loss or gain of species.

View Article: PubMed Central - PubMed

Affiliation: Harvard Forest, Harvard University, Petersham, Massachusetts, United States of America. bbaiser@fas.harvard.edu

ABSTRACT
Ecological communities show great variation in species richness, composition and food web structure across similar and diverse ecosystems. Knowledge of how this biodiversity relates to ecosystem functioning is important for understanding the maintenance of diversity and the potential effects of species losses and gains on ecosystems. While research often focuses on how variation in species richness influences ecosystem processes, assessing species richness in a food web context can provide further insight into the relationship between diversity and ecosystem functioning and elucidate potential mechanisms underpinning this relationship. Here, we assessed how species richness and trophic diversity affect decomposition rates in a complete aquatic food web: the five trophic level web that occurs within water-filled leaves of the northern pitcher plant, Sarracenia purpurea. We identified a trophic cascade in which top-predators--larvae of the pitcher-plant mosquito--indirectly increased bacterial decomposition by preying on bactivorous protozoa. Our data also revealed a facultative relationship in which larvae of the pitcher-plant midge increased bacterial decomposition by shredding detritus. These important interactions occur only in food webs with high trophic diversity, which in turn only occur in food webs with high species richness. We show that species richness and trophic diversity underlie strong linkages between food web structure and dynamics that influence ecosystem functioning. The importance of trophic diversity and species interactions in determining how biodiversity relates to ecosystem functioning suggests that simply focusing on species richness does not give a complete picture as to how ecosystems may change with the loss or gain of species.

Show MeSH
Related in: MedlinePlus