Collapse and reorganization of a food web of Mwanza Gulf, Lake Victoria

A.S. Downing, E.H. van Nes, J. Janse, F. Witte, I.J.M. Cornelissen, M. Scheffer, W.M. Mooij

Research output: Contribution to journalArticleAcademicpeer-review

31 Citations (Scopus)

Abstract

Lake Victoria (in East Africa) is the world's second largest fresh-water system. Over the past century the ecosystem has undergone drastic changes. Some 30 years after the introduction of Nile perch and tilapia in the 1950s, the highly diverse community of native haplochromines collapsed, leaving a system dominated by only four species: the native cyprinid dagaa and shrimp Caridina nilotica, as well as the introduced Nile perch and Nile tilapia. More recently, an unexpected resurgence of haplochromines has been reported. To better grasp these changes in terms of ecosystem functioning and of changes in growth of trophic groups, we created mass-balances of the food web near Mwanza (Tanzania) before, during and after the Nile perch boom (1977, 1987 and 2005), using the application ECOPATH. We connected these mass-balances with a dynamic model assuming linear trends in net growth rates of the trophic groups. Our analysis suggests that the Nile perch boom initially altered the biomass distribution over trophic levels. Also, results indicate that not only fishing but also changes at the detritivores' trophic level might have played an important role in driving changes in the system. Both the mass-balances and the dynamic model connecting them reveal that after a major distortion during the Nile perch boom, the biomass distribution over the main trophic levels had largely recovered to its original state by 2005. However, no such return appeared in terms of community structure. Biodiversity in the new state is dramatically lower, consisting of introduced species and a few native surviving species. We conclude that at an aggregate level Lake Victoria's ecosystem has proved to be resilient in the sense that its overall trophic structure has apparently recovered after a major perturbation. By contrast, its intricate functional structure and associated biodiversity have proven to be fragile and seem unlikely to recover
LanguageEnglish
Pages229-239
JournalEcological Applications
Volume22
Issue number1
DOIs
Publication statusPublished - 2012

Fingerprint

trophic level
food web
mass balance
lake
biodiversity
trophic structure
lake ecosystem
ecosystem
cyprinid
biomass
introduced species
native species
fishing
community structure
perturbation
gulf
water
distribution
trend
analysis

Keywords

  • african great-lakes
  • nile perch
  • morphological-changes
  • lates-niloticus
  • east-africa
  • fish
  • biodiversity
  • challenges
  • fisheries
  • predator

Cite this

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title = "Collapse and reorganization of a food web of Mwanza Gulf, Lake Victoria",
abstract = "Lake Victoria (in East Africa) is the world's second largest fresh-water system. Over the past century the ecosystem has undergone drastic changes. Some 30 years after the introduction of Nile perch and tilapia in the 1950s, the highly diverse community of native haplochromines collapsed, leaving a system dominated by only four species: the native cyprinid dagaa and shrimp Caridina nilotica, as well as the introduced Nile perch and Nile tilapia. More recently, an unexpected resurgence of haplochromines has been reported. To better grasp these changes in terms of ecosystem functioning and of changes in growth of trophic groups, we created mass-balances of the food web near Mwanza (Tanzania) before, during and after the Nile perch boom (1977, 1987 and 2005), using the application ECOPATH. We connected these mass-balances with a dynamic model assuming linear trends in net growth rates of the trophic groups. Our analysis suggests that the Nile perch boom initially altered the biomass distribution over trophic levels. Also, results indicate that not only fishing but also changes at the detritivores' trophic level might have played an important role in driving changes in the system. Both the mass-balances and the dynamic model connecting them reveal that after a major distortion during the Nile perch boom, the biomass distribution over the main trophic levels had largely recovered to its original state by 2005. However, no such return appeared in terms of community structure. Biodiversity in the new state is dramatically lower, consisting of introduced species and a few native surviving species. We conclude that at an aggregate level Lake Victoria's ecosystem has proved to be resilient in the sense that its overall trophic structure has apparently recovered after a major perturbation. By contrast, its intricate functional structure and associated biodiversity have proven to be fragile and seem unlikely to recover",
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Collapse and reorganization of a food web of Mwanza Gulf, Lake Victoria. / Downing, A.S.; van Nes, E.H.; Janse, J.; Witte, F.; Cornelissen, I.J.M.; Scheffer, M.; Mooij, W.M.

In: Ecological Applications, Vol. 22, No. 1, 2012, p. 229-239.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Collapse and reorganization of a food web of Mwanza Gulf, Lake Victoria

AU - Downing, A.S.

AU - van Nes, E.H.

AU - Janse, J.

AU - Witte, F.

AU - Cornelissen, I.J.M.

AU - Scheffer, M.

AU - Mooij, W.M.

PY - 2012

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N2 - Lake Victoria (in East Africa) is the world's second largest fresh-water system. Over the past century the ecosystem has undergone drastic changes. Some 30 years after the introduction of Nile perch and tilapia in the 1950s, the highly diverse community of native haplochromines collapsed, leaving a system dominated by only four species: the native cyprinid dagaa and shrimp Caridina nilotica, as well as the introduced Nile perch and Nile tilapia. More recently, an unexpected resurgence of haplochromines has been reported. To better grasp these changes in terms of ecosystem functioning and of changes in growth of trophic groups, we created mass-balances of the food web near Mwanza (Tanzania) before, during and after the Nile perch boom (1977, 1987 and 2005), using the application ECOPATH. We connected these mass-balances with a dynamic model assuming linear trends in net growth rates of the trophic groups. Our analysis suggests that the Nile perch boom initially altered the biomass distribution over trophic levels. Also, results indicate that not only fishing but also changes at the detritivores' trophic level might have played an important role in driving changes in the system. Both the mass-balances and the dynamic model connecting them reveal that after a major distortion during the Nile perch boom, the biomass distribution over the main trophic levels had largely recovered to its original state by 2005. However, no such return appeared in terms of community structure. Biodiversity in the new state is dramatically lower, consisting of introduced species and a few native surviving species. We conclude that at an aggregate level Lake Victoria's ecosystem has proved to be resilient in the sense that its overall trophic structure has apparently recovered after a major perturbation. By contrast, its intricate functional structure and associated biodiversity have proven to be fragile and seem unlikely to recover

AB - Lake Victoria (in East Africa) is the world's second largest fresh-water system. Over the past century the ecosystem has undergone drastic changes. Some 30 years after the introduction of Nile perch and tilapia in the 1950s, the highly diverse community of native haplochromines collapsed, leaving a system dominated by only four species: the native cyprinid dagaa and shrimp Caridina nilotica, as well as the introduced Nile perch and Nile tilapia. More recently, an unexpected resurgence of haplochromines has been reported. To better grasp these changes in terms of ecosystem functioning and of changes in growth of trophic groups, we created mass-balances of the food web near Mwanza (Tanzania) before, during and after the Nile perch boom (1977, 1987 and 2005), using the application ECOPATH. We connected these mass-balances with a dynamic model assuming linear trends in net growth rates of the trophic groups. Our analysis suggests that the Nile perch boom initially altered the biomass distribution over trophic levels. Also, results indicate that not only fishing but also changes at the detritivores' trophic level might have played an important role in driving changes in the system. Both the mass-balances and the dynamic model connecting them reveal that after a major distortion during the Nile perch boom, the biomass distribution over the main trophic levels had largely recovered to its original state by 2005. However, no such return appeared in terms of community structure. Biodiversity in the new state is dramatically lower, consisting of introduced species and a few native surviving species. We conclude that at an aggregate level Lake Victoria's ecosystem has proved to be resilient in the sense that its overall trophic structure has apparently recovered after a major perturbation. By contrast, its intricate functional structure and associated biodiversity have proven to be fragile and seem unlikely to recover

KW - african great-lakes

KW - nile perch

KW - morphological-changes

KW - lates-niloticus

KW - east-africa

KW - fish

KW - biodiversity

KW - challenges

KW - fisheries

KW - predator

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DO - 10.1890/11-0941.1

M3 - Article

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