Abstract
Reflecting a global trend, freshwater wetlands in Madagascar have received little conservation or research attention. Madagascar is a global conservation priority due to its high level of species endemism but most work has focused on protecting forests. For the first time, we investigated the state of wetlands across the country to determine the effects of human disturbance. We conducted a rapid survey of 37 wetlands, using waterbirds and benthic invertebrates as ecological indicators. We recorded nine variables relating to human disturbance, revealing widespread wetland destruction. Principal Components Analysis reduced the nine variables to a single Principal Component (PC) that explained 50% of the dataset variance, demonstrating that different forms of human disturbance are ubiquitous and inseparable. The disturbance PC provides an index of how pristine a lake is and in Generalized Linear Models (GLMs) was significantly inversely related to the number of waterbird species present and the density of Chironomidae. The disturbance PC was estimated for every wetland in a GIS-derived dataset of wetland locations in Madagascar, giving a country-wide frequency distribution of disturbance. To validate the estimated PC values, we used the GLMs to predict the number of endemic bird species at an independent sample of 22 lakes. The predicted values correlated with the observed number of species, demonstrating that our procedure can identify lakes with high biodiversity value. The disturbance PC provides a convenient method for ranking sites, and a country-wide ranking demonstrates that the only near-pristine lakes in Madagascar are small sites that have been preserved by remoteness from human activity and not conservation management. The strategy of conserving high biodiversity remnants is insufficient because existing remnants suffer some degree of degradation and only support small populations of threatened species. Large-scale restoration of degraded wetlands is required for the long-term conservation of Madagascar’s freshwater biodiversity.
Highlights
Freshwater ecosystems are the most threatened major habitat type globally [1], with freshwater vertebrate species declining faster than those in either terrestrial or marine realms [2]
Given the imbalance in protection between forests and wetlands, we aimed to investigate for the first time the status of wetlands across the country and use this information to assess whether the existing extremely low level of conservation protection is sufficient to protect remaining freshwater biodiversity
There were significant associations between PC1 and the number of invertebrate and bird taxa (Table 2, Fig 3), but other principal component axes were not significantly associated with biodiversity
Summary
Freshwater ecosystems are the most threatened major habitat type globally [1], with freshwater vertebrate species declining faster than those in either terrestrial or marine realms [2]. The main threats to wetlands globally are overexploitation of wetland resources including fish, pollution from agricultural and industrial processes, flow modification to provide water for cities and especially crops, habitat destruction or degradation, invasive species and climate change [5,6,7]. All of these problems are exacerbated by rising human populations, and tropical areas are seeing the highest rates of population growth and agricultural growth [7]. Since 1960, the highland regions have lost 60% of wetlands, compared to 20% of forests [9]
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