Studies were carried out to determine species richness and abundance of rock-dwelling cichlids, Mbuna, in Lake Malawi. A total of 40 heterogeneous sites which yielded 10 genera, 136 species and a species-genus ratio o...Studies were carried out to determine species richness and abundance of rock-dwelling cichlids, Mbuna, in Lake Malawi. A total of 40 heterogeneous sites which yielded 10 genera, 136 species and a species-genus ratio of 13.6, were surveyed by scuba diving in transects laid at six depths on each site. Species diversity and abundance were generally high in the rocky bottom habitats with a general trend of the two variables decreasing with depth, except at Likoma and Chizumulu Islands where they increased with increasing depth. This was due to dominant species inhabiting water depths of 10 to 15 m. Relative abundance was generally low in all the sites where few species had relative abundance of more than 10%. The same was applied to relative site frequency; more than 60% of the species were rare with relative site frequency of less than 10%. These low estimates support the fact that most of the Mbuna species are endemic within localities in the lake. Southern part of the lake has lower abundance and richness of Mbuna with the exception of islands compared to the northern part of the lake. This is explained by high prevalence of sandy and muddy lake bottom in the south as opposed to rocky bottom in the north.展开更多
The first comprehensive study of abundance, richness and distribution of Mbuna in Lake Malawi was carried out in the 1980s. The present study examined changes of species richness and abundance of Mbuna with time. Most...The first comprehensive study of abundance, richness and distribution of Mbuna in Lake Malawi was carried out in the 1980s. The present study examined changes of species richness and abundance of Mbuna with time. Most sites demarcated during the 1980s survey were explored in order to determine changes in abundance and composition of Mbuna over a period of more than 20 years Chi-square analysis revealed significant difference （p 〈 0.05） in abundance of Mbuna between 1983 and 2005 with the exception of Chinyankhwazi and Chinyamwezi where the difference was not significant （p 〉 0.05）. Cluster analysis showed changes in species composition between 1983 and 2005 in various sites. Generally, there were more species lost in a given area than new species observed in 2005. Decline in Mbuna species richness might have been caused by siltation, harvesting of Mbuna for food and ornamental fish trade while new species were mostly introduced through translocation from one part of the lake to another.展开更多
Molecular and field studies suggest that Mbuna have limited migration range and are restricted by habitat discontinuities especially in areas where rocky habitats are separated by stretches of sand. This study estimat...Molecular and field studies suggest that Mbuna have limited migration range and are restricted by habitat discontinuities especially in areas where rocky habitats are separated by stretches of sand. This study estimated regional diversity of Mbuna in Lake Malawi. The estimated fl-diversity for all sites was 114.5 Mbuna suggesting that there was high level of allopatrism for the species complex. Sympatric index was low in the two regions of southern and northern lake and the observed high-end richness strongly correlated with minimum species richness. The sympatric index for the whole lake was 0.8, with non-monotypic species complexes showing declining values of sympatric index and the decline was dependent on the geographical scale of the area covered. The northern region sites had mean habitat ranking of 84.5% while the southern sites had habitat ranking of 56.7% supporting the observation that there are more rocky habitats in the northern part of the lake than in the southern. Implications of habitat ranking are discussed in terms of species abundance and richness.展开更多
文摘Studies were carried out to determine species richness and abundance of rock-dwelling cichlids, Mbuna, in Lake Malawi. A total of 40 heterogeneous sites which yielded 10 genera, 136 species and a species-genus ratio of 13.6, were surveyed by scuba diving in transects laid at six depths on each site. Species diversity and abundance were generally high in the rocky bottom habitats with a general trend of the two variables decreasing with depth, except at Likoma and Chizumulu Islands where they increased with increasing depth. This was due to dominant species inhabiting water depths of 10 to 15 m. Relative abundance was generally low in all the sites where few species had relative abundance of more than 10%. The same was applied to relative site frequency; more than 60% of the species were rare with relative site frequency of less than 10%. These low estimates support the fact that most of the Mbuna species are endemic within localities in the lake. Southern part of the lake has lower abundance and richness of Mbuna with the exception of islands compared to the northern part of the lake. This is explained by high prevalence of sandy and muddy lake bottom in the south as opposed to rocky bottom in the north.
文摘The first comprehensive study of abundance, richness and distribution of Mbuna in Lake Malawi was carried out in the 1980s. The present study examined changes of species richness and abundance of Mbuna with time. Most sites demarcated during the 1980s survey were explored in order to determine changes in abundance and composition of Mbuna over a period of more than 20 years Chi-square analysis revealed significant difference （p 〈 0.05） in abundance of Mbuna between 1983 and 2005 with the exception of Chinyankhwazi and Chinyamwezi where the difference was not significant （p 〉 0.05）. Cluster analysis showed changes in species composition between 1983 and 2005 in various sites. Generally, there were more species lost in a given area than new species observed in 2005. Decline in Mbuna species richness might have been caused by siltation, harvesting of Mbuna for food and ornamental fish trade while new species were mostly introduced through translocation from one part of the lake to another.
文摘Molecular and field studies suggest that Mbuna have limited migration range and are restricted by habitat discontinuities especially in areas where rocky habitats are separated by stretches of sand. This study estimated regional diversity of Mbuna in Lake Malawi. The estimated fl-diversity for all sites was 114.5 Mbuna suggesting that there was high level of allopatrism for the species complex. Sympatric index was low in the two regions of southern and northern lake and the observed high-end richness strongly correlated with minimum species richness. The sympatric index for the whole lake was 0.8, with non-monotypic species complexes showing declining values of sympatric index and the decline was dependent on the geographical scale of the area covered. The northern region sites had mean habitat ranking of 84.5% while the southern sites had habitat ranking of 56.7% supporting the observation that there are more rocky habitats in the northern part of the lake than in the southern. Implications of habitat ranking are discussed in terms of species abundance and richness.
