Dammed rivers: impoundments facilitate fish invasions

Abstract

1. River damming and other anthropogenic disturbances of natural habitats are among the main drivers of species loss through a range of direct and indirect effects. While the effects of river damming on aquatic species are relatively well studied, particularly with regard to their impacts on diadromous species and stenotopic riverine specialists, there is a paucity of studies quantifying the effects of dam construction on whole communities. 2. We conducted a global meta-analysis focussed on fish communities, comparing species richness, abundance and proportion of alien species between dammed and undammed rivers. Both longitudinal and cross-sectional studies were examined. 3. We found that construction of dams did not have a noticeable effect on fish richness and abundance, but the increase in proportion of alien species was significant (mean effect size of 0.62). 4. Our findings suggest that the conversion of lotic waterbodies into lentic habitats result in the extirpation of species unable to withstand a drastic change in environmental conditions, but the loss is compensated by colonising lacustrine or eurytopic species taking advantage of reduced competition and the availability of new niches specific to lentic habitats. However, when eurytopic natives are absent from waterbodies connected to the newly constructed reservoirs, vacant niches are instead exploited by alien species, resulting in impoverishment of native species richness although overall species richness may be maintained.

Dams have varying impacts on fish communities across latitudes: a quantitative synthesis

“…The impacts of dams on fish biodiversity followed a clear gradient across latitudes, from a general lack of diversity changes in boreal regions to substantial ones in the tropics. A previous meta‐analysis by Liew et al () suggested that dams have similar effect across regions, but their analyses did not consider the boreal region. In addition, our analyses are based on a substantially larger pool of information, representing a 60% increase in number of references considered by Liew et al ().…”

“…A previous meta‐analysis by Liew et al () suggested that dams have similar effect across regions, but their analyses did not consider the boreal region. In addition, our analyses are based on a substantially larger pool of information, representing a 60% increase in number of references considered by Liew et al (). As such, the gradient of effects we report on here clearly underscores the need for an understanding of regional fish assemblages, and the context of stressors when evaluating the impacts of damming rivers on fish biodiversity.…”

Bottom‐up influences on tropical freshwater food web structure support the “environmental filtering” hypothesis

“…In this article, we demonstrated the probable mechanisms of food web assembly. Our study sites were well‐suited in addressing this critical question in ecology because reservoirs represent a novel habitat type often associated with fluxes in community assemblages driven by species turnovers (Liew et al b ). The sites also shared a common pool of potential colonizers of roughly equal propagule pressure/dispersal probabilities because of Singapore's unique geography (i.e., small island with high levels of accessibility).…”

Fish and mussels: Importance of fish for freshwater mussel conservation

“…The buffering of extreme flows due to flow management favours fish and mussel species that have preference for stable ecosystem conditions (McManamay & Frimpong, ). The presence of reservoirs and flow regulation may also be responsible for changes on fish communities by promoting invasive species (Clavero, Hermoso, Aparicio, & Godinho, ; Liew, Tan, & Yeo, ), which can displace natives (Hermoso, Clavero, Blanco‐Garrido, & Prenda, ; Marchetti, Light, Moyle, & Viers, ; Marchetti & Moyle, ), a situation that will likely affect the fish–mussel relationship (Brainwood et al., ; Watters, ) with possible implications for mussel conservation (see below).…”