Abstract
The Ganges–Brahmaputra–Meghna and Karnaphuli (GBMK) River Basin in Nepal, India, and Bangladesh is among the world's most biodiverse river basins. However, human‐induced habitat modification processes threaten the ecological structure of this river basin. Among the GBMK’s diverse flora and fauna of this freshwater ecosystem, the endemic Ganges River dolphin (Platanista gangetica gangetica; GRD) is one of the most charismatic species in this freshwater ecosystem. Though a >50% population size reduction has occurred since 1957, researchers and decision‐makers often overlook the persistence (or evolutionary potential) of this species in the highly fragmented GBMK. We define the evolutionary potential as the ability of species/populations to adapt in a changing environment by maintaining their genetic diversity. Here, we review how evolutionary trap mechanisms affect the dynamics and viability of the GRD (hereafter Ganges dolphin) populations after rapid declines in their population size and distribution. We detected six potential trap mechanisms that might affect the Ganges dolphin populations discretely or in combination: (a) habitat modification; (b) occurrence of finite and geographically restricted local populations; (c) ratio of effective to estimate population size; (d) increasing risk of inbreeding depression in genetically isolated groups; (e) at‐risk behavioral attributes; and (f) direct fisheries–dolphin interactions. Because evolutionary traps appear most significant during low water season, they adversely affect demographic parameters, which reduce evolutionary potential. These traps have already caused local extirpation events; therefore, we recommend translocation among populations, including restoring and preserving essential habitats as immediate conservation strategies. Integrative evolutionary potential information based on demographic, genetic, and environmental data is still lacking. Thus, we identify gaps in the knowledge and suggest integrative approaches to understand the future of Ganges dolphins in South Asian waterways.
Highlights
While many landscapes, including freshwater ecosystems, around the world are being transformed by humans at unprecedented rates, understanding the evolutionary potential of endangered species is often ignored (Moritz & Potter, 2013)
We grouped all the potential persistence-threatening processes under six potential evolutionary trap mechanisms that might drive the evolutionary potential of the Ganges dolphin in the Ganges–Brahmaputra–Meghna and Karnaphuli River Basin (GBMK) Basin: (a) habitat modification; (b) occurrence of finite and geographically restricted local populations; (c) ratio of effective to estimate population size (Ne < 500); (d) increasing risk of inbreeding depression in genetically isolated groups; (e) at-risk behavioral traits; and (f) direct fisheries–dolphin interactions (Table 1)
Because of a lack of knowledge on potential evolutionary trap mechanisms of the Ganges dolphin, we focused on identifying evolutionary trap mechanisms that represent demographic, genetic, and environmental factors and suggest future study to prioritize these mechanisms and their interactive effects
Summary
While many landscapes, including freshwater ecosystems, around the world are being transformed by humans at unprecedented rates, understanding the evolutionary potential of endangered species is often ignored (Moritz & Potter, 2013). The few previous conservation studies of the Ganges dolphin examined habitat components (Khanal et al, 2016; Smith & Reeves, 2012), feeding and foraging behaviors (Kelkar et al, 2018), and flow regimes (Choudhary et al, 2012; Khanal et al, 2016) These previous efforts did not integrate ecological, demographic, and environmental factors that might accelerate extinction risk before genetic deterioration (Lande, 1988). We highlight possible mechanisms that could affect the dynamics and viability of the Ganges dolphin populations throughout their range in Nepal, India, and Bangladesh To our knowledge, this is the first study that demonstrates the effects of genetic, demographic, and environmental factors on the evolutionary potential of small isolated subpopulations of the Ganges dolphin. We identify research gaps that hinder our understanding of the Ganges dolphin evolution and ecology
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