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Invasions and extinctions reshape coastal marine food webs.

Byrnes JE, Reynolds PL, Stachowicz JJ - PLoS ONE (2007)

Bottom Line: This is because most extinctions ( approximately 70%) occur at high trophic levels (top predators and other carnivores), while most invasions are by species from lower trophic levels (70% macroplanktivores, deposit feeders, and detritivores).The consequences of the simultaneous loss of diversity at top trophic levels and gain at lower trophic levels is largely unknown.However, current research suggests that a better understanding of how such simultaneous changes in diversity can impact ecosystem function will be required to manage coastal ecosystems and forecast future changes.

View Article: PubMed Central - PubMed

Affiliation: Center for Population Biology, University of California, Davis, California, United States of America. jebyrnes@ucdavis.edu

ABSTRACT
The biodiversity of ecosystems worldwide is changing because of species loss due to human-caused extinctions and species gain through intentional and accidental introductions. Here we show that the combined effect of these two processes is altering the trophic structure of food webs in coastal marine systems. This is because most extinctions ( approximately 70%) occur at high trophic levels (top predators and other carnivores), while most invasions are by species from lower trophic levels (70% macroplanktivores, deposit feeders, and detritivores). These opposing changes thus alter the shape of marine food webs from a trophic pyramid capped by a diverse array of predators and consumers to a shorter, squatter configuration dominated by filter feeders and scavengers. The consequences of the simultaneous loss of diversity at top trophic levels and gain at lower trophic levels is largely unknown. However, current research suggests that a better understanding of how such simultaneous changes in diversity can impact ecosystem function will be required to manage coastal ecosystems and forecast future changes.

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Related in: MedlinePlus

Food web showing the connections between all trophic functional groups.Arrows represent one group consuming the group to which the arrow points. Shading indicates trophic level (none = 1, light = 2, moderate = 3, dark = 4).
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pone-0000295-g001: Food web showing the connections between all trophic functional groups.Arrows represent one group consuming the group to which the arrow points. Shading indicates trophic level (none = 1, light = 2, moderate = 3, dark = 4).

Mentions: Here we consider how modern invasions and extinctions have together changed the architecture of marine food webs by comparing the trophic distribution of invasions and extinctions. In a recent analysis for a single region, the Wadden Sea, the taxonomic distribution of extinctions and invasions differed even though overall richness was relatively unchanged [12]. However, the generality of this trend is not clear, and this study only categorized species by coarse taxonomic group, which often does not correlate with ecological function. In this paper, we classified all species in lists of global and regional marine species extinctions [13] and invasions from lists for San Francisco Bay [14], Australia [15], The Gulf of the Farallones, and the Wadden Sea [16], [17] by trophic level and feeding mode (Fig. 1, see Methods for details). We then compared the distribution of species among trophic groups in each exotic species list with that of global and regional extinctions to assess whether the trophic distribution of species additions matched that of species deletions and to estimate the net change in species richness of each trophic level and functional feeding group. Our results suggest that invasions are biased towards lower trophic levels whereas extinctions occur higher in the food web. We discuss the potential implications of these changes in trophic skew [9] for marine ecosystems.


Invasions and extinctions reshape coastal marine food webs.

Byrnes JE, Reynolds PL, Stachowicz JJ - PLoS ONE (2007)

Food web showing the connections between all trophic functional groups.Arrows represent one group consuming the group to which the arrow points. Shading indicates trophic level (none = 1, light = 2, moderate = 3, dark = 4).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1808429&req=5

pone-0000295-g001: Food web showing the connections between all trophic functional groups.Arrows represent one group consuming the group to which the arrow points. Shading indicates trophic level (none = 1, light = 2, moderate = 3, dark = 4).
Mentions: Here we consider how modern invasions and extinctions have together changed the architecture of marine food webs by comparing the trophic distribution of invasions and extinctions. In a recent analysis for a single region, the Wadden Sea, the taxonomic distribution of extinctions and invasions differed even though overall richness was relatively unchanged [12]. However, the generality of this trend is not clear, and this study only categorized species by coarse taxonomic group, which often does not correlate with ecological function. In this paper, we classified all species in lists of global and regional marine species extinctions [13] and invasions from lists for San Francisco Bay [14], Australia [15], The Gulf of the Farallones, and the Wadden Sea [16], [17] by trophic level and feeding mode (Fig. 1, see Methods for details). We then compared the distribution of species among trophic groups in each exotic species list with that of global and regional extinctions to assess whether the trophic distribution of species additions matched that of species deletions and to estimate the net change in species richness of each trophic level and functional feeding group. Our results suggest that invasions are biased towards lower trophic levels whereas extinctions occur higher in the food web. We discuss the potential implications of these changes in trophic skew [9] for marine ecosystems.

Bottom Line: This is because most extinctions ( approximately 70%) occur at high trophic levels (top predators and other carnivores), while most invasions are by species from lower trophic levels (70% macroplanktivores, deposit feeders, and detritivores).The consequences of the simultaneous loss of diversity at top trophic levels and gain at lower trophic levels is largely unknown.However, current research suggests that a better understanding of how such simultaneous changes in diversity can impact ecosystem function will be required to manage coastal ecosystems and forecast future changes.

View Article: PubMed Central - PubMed

Affiliation: Center for Population Biology, University of California, Davis, California, United States of America. jebyrnes@ucdavis.edu

ABSTRACT
The biodiversity of ecosystems worldwide is changing because of species loss due to human-caused extinctions and species gain through intentional and accidental introductions. Here we show that the combined effect of these two processes is altering the trophic structure of food webs in coastal marine systems. This is because most extinctions ( approximately 70%) occur at high trophic levels (top predators and other carnivores), while most invasions are by species from lower trophic levels (70% macroplanktivores, deposit feeders, and detritivores). These opposing changes thus alter the shape of marine food webs from a trophic pyramid capped by a diverse array of predators and consumers to a shorter, squatter configuration dominated by filter feeders and scavengers. The consequences of the simultaneous loss of diversity at top trophic levels and gain at lower trophic levels is largely unknown. However, current research suggests that a better understanding of how such simultaneous changes in diversity can impact ecosystem function will be required to manage coastal ecosystems and forecast future changes.

Show MeSH
Related in: MedlinePlus