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Completed
Inter-guild differences in the recovery of cichlid species in Lake Victoria (Tanzania): causes and possible consequences of lost predominance by detritivores
FunderNetherlands Organisation for Scientific Research (NWO)
Duration01 Jul 2005 - 06 Jul 2010
Project codeWB 84-587
Open Access mandatePublications: NoResearch data: No
Identifiers
Project timeline100%
Description
Lake Victoria had a fish fauna, dominated by 500+ species of cichlids. In the 1950s the Nile perch, a huge predator, was introduced into the lake. When its population rapidly increased in the 1980s, about 200 cichlid species vanished. At the same time a marked increase in algal blooms ensuing decreases in oxygen concentration and water transparency has been observed. Over-exploitation during the 1990s reduced the Nile perch population, and a concomitant increase of a few cichlid species was observed. Year-round sampling in 2001-2002 revealed the recovery of about 25 species. However, only one trophic group (the zooplanktivores) reached its previous level of abundance. Originally the detritivores formed the most important guild, with more than 13 species making up 31% of the cichlid biomass, followed by the zooplanktivores with 27%. Though about 4 detritivorous species were regularly caught again during the past few years, preliminary data analysis suggests they contributed only 5-10% to the cichlid biomass, while the zooplanktivores currently make up more than 80%. Potential causes for the differences in recovery of detritivores and zooplanktivores include: (1) differences in predation pressure by Nile perch on the two groups; (2) differences in their plasticity and evolvability; (3) changes in the nutrient content of detritus; (4) differences in the impact of environmental contamination with heavy metals on the two groups. In the present project these aspects are studied. Additionally, the inter-guild differences in recovery offer the opportunity to test the explanations suggested for the intra-guild differences observed in the zooplanktivores. Linking ecological and morphological adaptations and their constraints seems a fruitful, generally applicable approach in extinction studies and may provide new insights into the mechanisms of extinction and survival in tropical fish. The study will also contribute to the knowledge of the plasticity and evolvability of the evolutionary successful haplochromine cichlid fishes. As a spin off, the study may give insight in the possible consequences for the lake&8217;s ecosystem of the reversed dominance of detritivores and zooplanktivores and in the effects of diversity changes on ecosystems.
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Lake Victoria had a fish fauna, dominated by 500+ species of cichlids. In the 1950s the Nile perch, a huge predator, was introduced into the lake. When its population rapidly increased in the 1980s, about 200 cichlid species vanished. At the same time a marked increase in algal blooms ensuing decreases in oxygen concentration and water transparency has been observed. Over-exploitation during the 1990s reduced the Nile perch population, and a concomitant increase of a few cichlid species was observed. Year-round sampling in 2001-2002 revealed the recovery of about 25 species. However, only one trophic group (the zooplanktivores) reached its previous level of abundance. Originally the detritivores formed the most important guild, with more than 13 species making up 31% of the cichlid biomass, followed by the zooplanktivores with 27%. Though about 4 detritivorous species were regularly caught again during the past few years, preliminary data analysis suggests they contributed only 5-10% to the cichlid biomass, while the zooplanktivores currently make up more than 80%. Potential causes for the differences in recovery of detritivores and zooplanktivores include: (1) differences in predation pressure by Nile perch on the two groups; (2) differences in their plasticity and evolvability; (3) changes in the nutrient content of detritus; (4) differences in the impact of environmental contamination with heavy metals on the two groups. In the present project these aspects are studied. Additionally, the inter-guild differences in recovery offer the opportunity to test the explanations suggested for the intra-guild differences observed in the zooplanktivores. Linking ecological and morphological adaptations and their constraints seems a fruitful, generally applicable approach in extinction studies and may provide new insights into the mechanisms of extinction and survival in tropical fish. The study will also contribute to the knowledge of the plasticity and evolvability of the evolutionary successful haplochromine cichlid fishes. As a spin off, the study may give insight in the possible consequences for the lake&8217;s ecosystem of the reversed dominance of detritivores and zooplanktivores and in the effects of diversity changes on ecosystems.
