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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

Trophic skew in regional invasions versus combined global and regional extinctions broken down by percentage of species in each trophic group.Colors indicate trophic level (white = 1, light grey = 2, dark grey = 3, black = 4). Extinctions are skewed towards trophic levels 3 and 4 (secondary consumers and predators) while invasions are skewed towards trophic level 2 (primary consumers).
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pone-0000295-g002: Trophic skew in regional invasions versus combined global and regional extinctions broken down by percentage of species in each trophic group.Colors indicate trophic level (white = 1, light grey = 2, dark grey = 3, black = 4). Extinctions are skewed towards trophic levels 3 and 4 (secondary consumers and predators) while invasions are skewed towards trophic level 2 (primary consumers).

Mentions: The top two trophic levels (secondary consumers and predators) contained 70% of the 133 documented global and regional marine extinctions (Fig. 2). Conversely, in each invasion list, approximately 70% of exotic species belonged to trophic level two, the majority of which were suspension feeders that directly consume plankton, deposit feeders that consume sediment organic material, or detritivores that consume decaying organic matter (Fig. 2). A comparison of the trophic distribution of extinctions with each invasion data set shows that species loss is skewed toward species from higher trophic groups relative to species gain, which is skewed towards lower order consumers (San Francisco Bay χ210 = 163.03 p<0.0001, Gulf of the Farallones National Marine Sanctuary χ29 = 126.64 p<0.0001, Australia χ210 = 90.02 p<0.0001). The functional groups most responsible for this skew are top predators (24.1% of extinctions but 6.1% of invasions on average), secondary consumers (37.6% of extinctions but 2.2% of invasions), and suspension feeding macroplanktivores (10.5% of extinctions but 44.6% of invasions). Changes in primary producers from invasions roughly match those due to extinctions. The distribution of introduced species among functional groups is remarkably similar among regions.


Invasions and extinctions reshape coastal marine food webs.

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

Trophic skew in regional invasions versus combined global and regional extinctions broken down by percentage of species in each trophic group.Colors indicate trophic level (white = 1, light grey = 2, dark grey = 3, black = 4). Extinctions are skewed towards trophic levels 3 and 4 (secondary consumers and predators) while invasions are skewed towards trophic level 2 (primary consumers).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0000295-g002: Trophic skew in regional invasions versus combined global and regional extinctions broken down by percentage of species in each trophic group.Colors indicate trophic level (white = 1, light grey = 2, dark grey = 3, black = 4). Extinctions are skewed towards trophic levels 3 and 4 (secondary consumers and predators) while invasions are skewed towards trophic level 2 (primary consumers).
Mentions: The top two trophic levels (secondary consumers and predators) contained 70% of the 133 documented global and regional marine extinctions (Fig. 2). Conversely, in each invasion list, approximately 70% of exotic species belonged to trophic level two, the majority of which were suspension feeders that directly consume plankton, deposit feeders that consume sediment organic material, or detritivores that consume decaying organic matter (Fig. 2). A comparison of the trophic distribution of extinctions with each invasion data set shows that species loss is skewed toward species from higher trophic groups relative to species gain, which is skewed towards lower order consumers (San Francisco Bay χ210 = 163.03 p<0.0001, Gulf of the Farallones National Marine Sanctuary χ29 = 126.64 p<0.0001, Australia χ210 = 90.02 p<0.0001). The functional groups most responsible for this skew are top predators (24.1% of extinctions but 6.1% of invasions on average), secondary consumers (37.6% of extinctions but 2.2% of invasions), and suspension feeding macroplanktivores (10.5% of extinctions but 44.6% of invasions). Changes in primary producers from invasions roughly match those due to extinctions. The distribution of introduced species among functional groups is remarkably similar among regions.

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