Abstract
Conservation attention on charismatic large vertebrates such as dolphins is often supported by the suggestion that these species represent surrogates for wider biodiversity, or act as indicators of ecosystem health. However, their capacity to act as indicators of patterns or trends in regional biodiversity has rarely been tested. An extensive new dataset of >300 last-sighting records for the Yangtze River dolphin or baiji and two formerly economically important fishes, the Yangtze paddlefish and Reeves’ shad, all of which are probably now extinct in the Yangtze, was collected during an interview survey of fishing communities across the middle-lower Yangtze drainage. Untransformed last-sighting date frequency distributions for these species show similar decline curves over time, and the linear gradients of transformed last-sighting date series are not significantly different from each other, demonstrating that these species experienced correlated population declines in both timing and rate of decline. Whereas species may be expected to respond differently at the population level even in highly degraded ecosystems, highly vulnerable (e.g. migratory) species can therefore display very similar responses to extrinsic threats, even if they represent otherwise very different taxonomic, biological and ecological groupings. Monitoring the status of river dolphins or other megafauna therefore has the potential to provide wider information on the status of other threatened components of sympatric freshwater biotas, and so represents a potentially important monitoring tool for conservation management. We also show that interview surveys can provide robust quantitative data on relative population dynamics of different species.
Highlights
Charismatic large vertebrates represent a very small component of global biodiversity, but have always received a disproportionate amount of conservation attention and funding due to high public and scientific interest in such species [1]
Previous studies have not investigated temporal changes in the population status of large vertebrates and other sympatric species as environments become progressively modified through human agency, to assess whether population trends are correlated between species and whether large vertebrates can act as ‘‘population trend indicators’’ rather than ‘‘classic’’ indicator species
Population trends are typically analysed using longitudinal studies that collect progressive data on the status of target taxa over time, a technique that can permit reconstruction of relative or absolute population status depending on data quality [41]
Summary
Charismatic large vertebrates represent a very small component of global biodiversity, but have always received a disproportionate amount of conservation attention and funding due to high public and scientific interest in such species [1]. The conservation focus on large vertebrates may be partly justified because these species are vulnerable to extinction in comparison to many other taxa [2], the limited resources available for conservation mean that this bias is often defended by suggestions that it will provide benefits to wider levels of biodiversity Because they usually require relatively extensive geographical areas to support viable populations, large vertebrates (typically large mammals and birds) are regularly used as focal ‘umbrella’ species in protected area development and management, on the assumption that appropriate protection will be conferred to sympatric co-occurring species assemblages [3,4]. Further studies are required to clarify the potential for charismatic large vertebrates such as river dolphins to monitor status and trends of freshwater biodiversity in threatened aquatic systems
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