Distribution Mapping and Niche Characterization of the Endemic African Storks
Date
2021-05
Authors
Gula, Jonah
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Abstract
The endemic African storks–African Openbill Anastomus lamelligerus, Abdim’s Stork Ciconia abdimii, African Woollyneck Ciconia microscelis, Saddlebill Stork Ephippiorhynchus senegalensis, Marabou Stork Leptoptilos crumeniferus, and Yellowbilled Stork Mycteria ibis–generally are poorly studied and their conservation status assessments have been created using mixed methods that are neither transparent nor replicable. Besides standardized population surveys, empirical distributions and environmental requirements are two of the most fundamental knowledge gaps that can contribute to the development of a data-driven status assessment for each species. Distribution mapping is a valuable proxy for determining population trends and range changes over time, albeit with caveats, that can provide some baseline information for assessing status. Environmental niche modeling (ENM) further contributes by estimating species-environment relationships that can be used to infer ecological needs (e.g. preferred habitats) and susceptibility to threats (e.g. climate change, land use change). Therefore, I employed both mapping and ENM to evaluate current distribution and environmental associations of African storks at two spatial scales, range-wide and regionally.
The six stork species were widespread from East to Southern Africa and varied in their degree of change in distribution in these regions between the historic (pre-1990) and recent (1990–2020) time periods. The African Openbill, African Woollyneck, Saddlebill Stork, Marabou Stork, and Yellow-billed Stork each exhibited a highly fragmented range in West Africa and all species but the African Woollyneck declined regionally from the historic to the recent period. Environmental niche models had high predictive capacity and stork species had scale-dependent responses to environmental variation. Annual and seasonal precipitation variables as well as land cover were the most important inputs across most models. All species had an optimum range of annual precipitation between c. 500–1000 mm regardless of scale. The African Openbill stood apart from the other species in its contrasting responses to several seasonal precipitation variables at several model scales, indicating important differences in ecology. All species had strong positive associations with flooded land cover types at all scales, and all but the African Openbill had the weakest association with croplands in West Africa. Niche similarity among species was high in all models, regardless of scale, suggesting similar environmental requirements and susceptibility to environmental changes.
The findings of this study represent a significant improvement to the understanding of the ecological needs and primary threats to African storks. Particularly, results highlight regional declines of potential metapopulations in West Africa, which, among other anthropogenic impacts such as overfishing and dam construction, can be
attributed to multi-year drought beginning in the 1970s. Recovery of depleted West African populations is threatened by near-future climate change and habitat degradation. While populations in other regions certainly face similar threats, storks in West Africa appear most at risk of extinction and require immediate conservation attention.
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Keywords
Distribution, Storks, Africa, Waterbirds, Niche, Climate, Mapping, range, Population
Citation
Gula, J. (2021). <i>Distribution mapping and niche characterization of the endemic African storks</i> (Unpublished thesis). Texas State University, San Marcos, Texas.