Restricted movement of prairie fishes in fragmented riverscapes risks ecosystem structure being ratcheted downstream

Abstract

1. Prairie streams are dynamic systems in which habitat patches are sporadically created and lost during extreme hydrological events. The persistence of fish species depends on life-history traits that facilitate their widespread dispersal to recolonize habitats after stochastic extirpation. Artificial barriers are thought to reduce recolonization opportunities and to ultimately displace populations downstream, but the ecological consequences of lost diversity above the barriers are largely unknown.2. The susceptibility of four prairie fishes to fragmentation and the consequent risk to stream ecosystem processes are described. The selected species exhibit wide tolerances to environmental stressors, represent unique functional feeding guilds, and have different habitat affinities.3. The ability of each species to access (jumping ability) and successfully traverse (swimming endurance) simulated instream barriers was quantified in the laboratory.Experimental stream complexes were used to isolate the effects of these species on ecosystem structure and function. These replicated single-species experiments were compared with 'no fish' controls to identify the ecological role of each. Small vertical barriers blocked most passage, and with open access all species wereunable to traverse relatively short distances against modest water velocities.Stream fragmentation will alter headwater fish assemblage structure and promote the most mobile species. Each species had slightly different effects on the stream ecosystem structure resulting from their different habitat preferences and diets. 5. Without colonization opportunities from neighbouring populations, disturbance events will alter headwater fish assemblages and may degrade the ecosystem structure above barriers.6. Fragmented riverscapes interact with harsh disturbance regimes to form an ecological ratchet. Systematic species loss above barriers outweighs the opportunity for improvement, suggesting that ecosystem structure may be moving downstream.

Selective effects of small barriers on river‐resident fish

“…Nevertheless, the results of our simulation model suggest that net downstream movement is a strong possibility where multiple barriers are present and upstream passage is challenging. This may have important conservation implications as net downstream movement could be a mechanism by which some fishes with poor jumping ability can become locally extinct above small barriers (Utzinger et al, 1998;Nislow et al, 2011;Schumann et al, 2019). As barriers can be densely distributed in rivers (e.g.…”

The local responses of aquatic ecosystems to adjacent grassland conservation: Can streams of dreams exist in a degraded riverscape?

“…Fish and aquatic macroinvertebrate populations are vulnerable to localized extirpation events as a result of the dynamic hydrological regimes (Fritz & Dodds, 2005; Lohr & Fausch, 1997; Poff & Ward, 1989). However, these species have life history characteristics that allow rapid recovery following stochastic disturbances when suitable habitats are available (Dodds et al, 2004; Lohr & Fausch, 1997; Schumann, Haag, Ellensohn, Redmond, & Graeb, 2019).…”

Extreme drought causes fish recruitment failure in a fragmented Great Plains riverscape

“…These works highlight loss of pelagicbroadcast spawning fishes from highly fragmented habitats during periods of extreme drought. Increases in the application of the ERH (Kerezsy, Gido, Magalhães, & Skelton, 2017;Perkin, Gido, Costigan, et al, 2015;Schumann, Haag, Ellensohn, Redmond, & Graeb, 2018) suggest that additional research on the mechanisms causing population extirpation during drought events is necessary for understanding ecological consequences of extreme low flow events in highly fragmented riverscapes. The ERH is contingent on disturbances causing either adult mortality prior to reproduction (e.g., Durham, Wilde, & Pope, 2006) or failed recruitment after reproduction (e.g., Rodger, Mayes, & Winemiller, 2016) at a pace more rapid than the duration of the disturbance.…”

“…The ERH is contingent on disturbances causing either adult mortality prior to reproduction (e.g., Durham, Wilde, & Pope, 2006) or failed recruitment after reproduction (e.g., Rodger, Mayes, & Winemiller, 2016) at a pace more rapid than the duration of the disturbance. Increases in the application of the ERH (Kerezsy, Gido, Magalhães, & Skelton, 2017;Perkin, Gido, Costigan, et al, 2015;Schumann, Haag, Ellensohn, Redmond, & Graeb, 2018) suggest that additional research on the mechanisms causing population extirpation during drought events is necessary for understanding ecological consequences of extreme low flow events in highly fragmented riverscapes.…”