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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

581: Madagascar Eastern Highlands

Major Habitat Type:

montane freshwaters

Author:

John S. Sparks, Department of Ichthyology, Division of Vertebrate Zoology, American Museum of Natural History, New York, NY, USA

Reviewers:

The Madagascar Eastern Highlands ecoregion encompasses a relatively narrow strip of land extending from north to south, essentially the entire length of Madagascar, and covers the upper and middle

Countries:

Madagascar

Boundaries:

The Madagascar Eastern Highlands ecoregion encompasses a relatively narrow strip of land extending from north to south, essentially the entire length of Madagascar, and covers the upper and middle reaches of the eastern coastal rivers. The ecoregion covers about 20% of the island, or about 80% of the eastern slope region (Aldegheri 1972). 

Drainages flowing into:

Indian Ocean

Main rivers or other water bodies:

From north to south, the major rivers of this region are the Bemarivo, Lokoho, Maningory, Rianila, Mangoro, Mananjary, and Mananara (Aldegheri 1972). Lake Alaotra, the largest lake on the island in surface area, is located in this ecoregion and empties into the Maningory River.

Topography:

Terrain in the region is steep, with the summits of many eastern mountains located as little as 50 km from the coast (Aldegheri 1972). 

Freshwater habitats:

Rivers in this ecoregion are generally small to moderate in size, rocky in substrate, and swift in current. Drainages are steep in their upper reaches, with numerous sections of rapids and cascades interspersed with flatter stretches of more moderate flows. These coastal rivers are short and terminate on a narrow coastal plain over a contracted continental shelf. In undisturbed areas, the water is clear and well oxygenated. Compared to rivers in western Madagascar, eastern rivers have lower pH (slightly acidic vs. neutral), higher conductivity, and much lower dissolved carbonate levels (Riseng 1997). Rainfall is high in the Eastern Highlands, 2,500-3,000 mm annually according to Aldegheri (1972), and water levels vary considerably with the occurrence of seasonal storms. In contrast to many river systems in western Madagascar, rivers in the east flow year round.

Terrestrial Habitats:

Dense evergreen forest is the principal vegetation type throughout this ecoregion, except at elevations above 1,800 m where a shift to thicket and shrubland occurs (Lowry et al. 1997). 

Fish Fauna:

Over fifty species (some awaiting description) of freshwater fish, about half of which are endemic, are known to inhabit the rivers and streams of the Madagascar Eastern Highlands. Intact native fish communities can still be found in the middle reaches of many eastern rivers, including the Nosivolo, Ankavanana, and Mananara. Exotic species become more abundant as one moves downstream into the lower reaches of many eastern basins. 

Description of endemic fishes:

Two fish families, Bedotiidae (rainbowfish) and Anchariidae (catfish), are endemic to Madagascar and are represented in this ecoregion (Sparks & Stiassny 2003). Endemic fish faunas are associated especially with Pandanus and palm swamps, such as are found in the upper Mangoro and Mananara drainages. Due to land conversion, these habitats are now quite rare in Madagascar.

Both the Mangoro-Nosivolo and Mananara Rivers harbor endemic cichlids, bedotiids, and anchariids, as well as a diversity of other native species (Reinthal & Stiassny 1991; Sparks & Reinthal 2001). The upper sections of these two rivers are regions of noteworthy diversity within the ecoregion. A small stretch of rapids in the Nosivolo River near Marolambo is the only known habitat of the endemic cichlid Oxylapia polli (Reinthal & Stiassny 1991), and an area of only a few square kilometers in the Mananara drainage encompasses the distribution of the cichlid Ptychochromoides vondrozo (Sparks & Reinthal 2001). 

In contrast, the headwaters of many other eastern rivers support markedly depauperate fish assemblages, and native fish species are frequently absent from the uppermost reaches. An example is the upper reaches of the Namarona River, with only two species of goby having been collected there (Sparks, pers. obs.). If native fishes occur at all in many of these headwaters, communities are comprised of at most a few gobioids (gobies and eleotrids), such as rock-climbing gobies of the genus Sicyopterus. Provided there are no significant barriers to upstream dispersal, eels (Anguilla spp.) also frequently migrate into these areas. Fish communities in the middle reaches of these rivers are more diverse, and are characterized by communities including endemic cichlids, bedotiids, gobioids, and anchariid catfish. 

Rivers of the Madagascar Eastern Highlands (and Madagascar Eastern Lowlands [823]) are home to number of closely related species of endemic rainbowfish of the genus Bedotia. The results of preliminary studies of this group suggest that each major eastern basin may contain a unique species (Loiselle & Stiassny 2003; Sparks & Stiassny 2003; Sparks & Smith 2004). Bedotiids of the genus Rheocles are also relatively diverse in the middle and upper reaches of eastern rivers, although nearly all species (particularly R. sikorae, R. wrightae, and R. pellegrini) are now quite rare and restricted in distribution.

Other noteworthy aquatic biotic elements:

In addition to freshwater fishes, this ecoregion supports extremely high richness and endemism among aquatic frogs. About 130 aquatic frogs are described from the ecoregion with nearly 65 percent being endemic. Many endemic frogs of the genus Boophis, which lay their eggs directly in water, are restricted to mid-altitude forests in eastern Madagascar (Glaw & Vences 1994). The middle and upper reaches of eastern rivers are also home to the nocturnal and rarely seen semi-aquatic tenrec, Limnogale mergulus. Tenrecs comprise an endemic family of insectivores of which only Limnogale, with webbed feet, is adapted for a semi-aquatic existence (Eisenberg & Gould 1970). Benstead et al. (2000) identify three additional mammal species, all endemic viverrids (viz. Fossa fossana, Galidea elegans, and Mungotictis decemlineata), which depend at least partially upon aquatic habitats. In the wetlands, both the Alaotra little grebe (Tachybaptus rufolavatus, CR) and the Madagascar pochard (Aythya innotata, CR), have not been observed recently and may be extinct (IUCN 2002). Other bird species in this ecoregion that are limited to marshland habitats on Madagascar include the slender-billed flufftail (Sarothrura watersi, EN), Madagascar snipe (Gallinago macrodactyla), and Madagascar rail (Rallus madagascariensis) (Langrand 1990). Forested regions in the ecoregion support a number of endemic and highly threatened crayfish species belonging to the genus Astacoides (Hobbs 1987; Benstead et al. 2000). Preliminary studies indicate that diversity and endemism of aquatic insects is, likewise, high in this region (Benstead et al. 2000).

Justification for delineation:

This ecoregion is defined by the upper reaches of the eastern coastal drainages above about 200 m elevation and distinguished by an endemic aquatic fauna. 

Level of taxonomic exploration:

Fair. Of the five major aquatic ecoregions of Madagascar, ichthyologists have probably explored the Madagascar Eastern Highlands and Madagascar Eastern Lowlands [583] most thoroughly. This is largely due to the presence of a number of larger towns and a network of passable roads along the coast that permit access to the upper and middle reaches of many eastern rivers. Yet, there are still many east coast drainages that remain to be surveyed for fishes and other freshwater taxa. For example, a major gap exists in our knowledge of ichthyofaunal communities for the middle and upper reaches of rivers extending from the Masoala Peninsula south to Lake Alaotra (Sparks & Stiassny 2003). The middle and upper reaches of many of these rivers have yet to be inventoried for freshwater fishes and should be considered top research priorities.

References/sources:

Aldegheri, M. (1972)"Rivers and streams on Madagascar" In Battistini, R.;Richard-Vindard, G. (Ed.). Biogeography and ecology in Madagascar. (pp. 261-310) The Hague, The Netherlands: Dr. W. Junk.

Benstead, J. P., Stiassny, M. L. J., et al. (2000)"River conservation in Madagascar" In Boon, P.J.;Davies, B.R.;Petts, G.E. (Ed.). Global perspectives on river conservation: Science, policy and practice. (pp. 205-231) Chichester, UK: John Wiley & Sons.

Eisenberg, J. F.,Gould, E. (1970). "The tenrecs: A study in mammalian behavior and evolution" Smithsonian Contributions to Zoology 27 1-138.

Glaw, F.,Vences, M. (1994). "A field guide to the amphibians and reptiles of Madagascar" Leverkusen, Germany: Moos-Druck.

Hobbs, H. H. (1987). "A review of the crayfish genus Astacoides (Decapoda: Parastacidae)" Smithsonian Contributions to Zoology 443 1-50.

Langrand, O. (1990). "Guide to the birds of Madagascar" New Haven, Connecticut, USA: Yale University Press.

Loiselle, P. V.,Stiassny, M. L. J. S. (2003)"Bedotia" In Goodman, S.M.;Benstead, J.P. (Ed.). The natural history of Madagascar. (pp. 867-868) Chicago, IL, USA: University of Chicago Press.

Lowry, P. P., II, Schatz, G. E., et al. (1997)"The classification of natural and anthropogenic vegetation in Madagascar" In Goodman, S.M.;Patterson, B.D. (Ed.). Natural change and human impact in Madagascar. (pp. 92-123) Washington, D.C., USA: Smithsonian Institution Press.

Reinthal, P.,Stiassny, M. L. J. (1991). "The freshwater fishes of Madagascar: A study of an endangered fauna with recommendations for a conservation strategy" Conservation Biology 5 231-243.

Riseng, K. J. (1997). "The distribution of fishes and the conservation of aquatic resources in Madagascar, M.Sc. Thesis" Unpublished Thesis. University of Michigan.

Sparks, J. S.,Reinthal, P. N. (2001). "A new species of Ptychochromoides from southeastern Madagascar (Teleostei: Cichlidae), with comments on monophyly and relationships of the ptychochromine cichlids" Ichthyological Explorations of Freshwaters 12 115-132.

Sparks, J. S.,Smith, W. L. (2004). "Phylogeny and biogeography of the Malagasy and Australasian rainbowfishes (Teloste: Melanotaenioidei): Gondwanan vicariance and evolution in freshwater" Molecular Phylogenetics and Evolution 33(3)

Sparks, J. S.,Stiassny, M. L. J. (2003)"Introduction to Madagascar's freshwater fishes" In Goodman, S.M.;Benstead, J.P. (Ed.). The natural history of Madagascar. (pp. 849-863) Chicago, USA: The University of Chicago Press.

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