Heterogeneity in flow disturbance around river confluences influences spatial patterns in native and non-native species co-occurrence

Boddy, Nixie C.; Booker, D. J.; McIntosh, Angus R.

doi:10.1007/s10530-020-02334-1

Cited by 7 publications

(15 citation statements)

References 61 publications

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“…Invasive species abundance is often related to their impact on native species (Kumschick et al., 2015; Latzka et al., 2016). In these riverscapes, spatial variation in flow disturbance that limited large trout densities probably mediated the strength of native–invasive interactions, an idea supported by the branch‐specific abundance patterns (Boddy et al., 2020). In light of these results, it was likely that confluence heterogeneity would also influence riverscape‐scale temporal patterns in fish assemblages, and that such effects could be widespread given the branched nature of river networks.…”

Section: Discussionmentioning

confidence: 94%

“…Thus, strong interactions between native galaxiids and non‐native trout probably led to low fish densities in homogenous confluences of stable streams, whereas around homogenous confluences of disturbed streams, the environmental harshness probably produced lower fish densities. Another study indicates the higher fish densities in heterogeneous confluences were driven by increases in galaxiid abundance, predominantly high numbers of young of year (Boddy et al., 2020). This higher density of galaxiids was probably made possible by large predatory trout being less abundant in confluences with diverse habitats (Boddy et al., 2020).…”

Section: Discussionmentioning

confidence: 99%

“…Another study indicates the higher fish densities in heterogeneous confluences were driven by increases in galaxiid abundance, predominantly high numbers of young of year (Boddy et al., 2020). This higher density of galaxiids was probably made possible by large predatory trout being less abundant in confluences with diverse habitats (Boddy et al., 2020). Invasive species abundance is often related to their impact on native species (Kumschick et al., 2015; Latzka et al., 2016).…”

Section: Discussionmentioning

confidence: 99%

“…Sampling reach length was a constant multiple of the stream width, averaged over both reaches in a branch, to avoid incorporating variability due to sampling different proportions of the available habitat depending on stream size (Peterson & Ver Hoef, 2010). Moreover, effects of confluences on stream fish assemblages extend approximately two reaches upstream, so sampling two reaches in each direction from the confluence was sufficient to represent changes in fish assemblages associated with confluence‐related habitat diversity (Boddy et al., 2020). Each sampling reach was single‐pass electrofished in an upstream direction without stopnets; the results of this method correlate well with more intensive quantitative techniques in these systems, for both Galaxiidae ( r 2 = 0.99) and Salmonidae ( r 2 = 0.82) abundance (Boddy et al., 2019).…”

Section: Methodsmentioning

confidence: 99%

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Could spatial heterogeneity in flow disturbance drive temporal stability of native–invasive species co‐occurrence in riverscapes?

Boddy

McIntosh

2021

Freshwater Biology

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Spatial heterogeneity of abiotic influences like disturbance in riverscapes could play an important role in dispersal‐aided community stability. We tested if higher spatial variability in conditions around river confluences caused by different flood disturbance regimes in branches could possibly influence the stability of a fish assemblage dominated by strong negative interactions between non‐native trout and native galaxiid fishes. We used field surveys to evaluate the effects of disturbance‐driven differences between river branches on fish densities and temporal variation in the relative abundance of galaxiids. Three repeated electrofishing surveys were conducted in two reaches of all branches of eight confluences in Canterbury, New Zealand. We found the differences in flood disturbance regimes between the two stream branches joining at a confluence were associated with higher mean fish abundance and more temporal stability in the relative abundance of native fish. Conversely, when flood disturbance conditions in the two streams joining were similar, resulting in a homogeneous confluence, fish abundance was lower and temporal variability was higher. For homogeneous confluences, strong interactions between native galaxiids and invasive trout probably produced lower fish densities where rivers with low flow disturbance met, whereas when two highly flow‐disturbed rivers met, environmental harshness probably lowered fish densities. By comparison, enhanced galaxiid temporal stability at confluences containing both disturbed and stable river branches probably reflected the combined effects of refugia from trout predation in disturbed branches and refugia from flooding in stable branches. Overall, these results are likely to reflect the combined effects of population‐specific responses to physical heterogeneity and spatially variable interspecific interactions. They may mean that river network configuration, and confluences especially, could influence community stability through a habitat portfolio effect. Furthermore, it will be worth investigating further whether preservation or restoration of differences in flow disturbance conditions in riverscapes encourages higher ecosystem resilience in the face of global change.

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Section: Discussionmentioning

confidence: 94%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Could spatial heterogeneity in flow disturbance drive temporal stability of native–invasive species co‐occurrence in riverscapes?

Boddy

McIntosh

2021

Freshwater Biology

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“…Culex in this study) are likely to equally impact the two fish species investigated here. Shifts in flow regime as a result of drying through climate change or land use changes could impact pelagic or drifting prey (Boddy et al 2020). While FR experiments are constrained by laboratory simplicity, they have been proved to show high predictive impact where differences are regarded as relative rather than absolute.…”

Section: Discussionmentioning

confidence: 99%

Prey type and temperature influence functional responses of threatened endemic Cape Floristic Ecoregion fishes

2021

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between two prey types (mosquito and chironomid larvae) at different field-representative temperatures (18 °C and 25 °C) in laboratory trials, with the aim to infer response and resilience to global change. Labeobarbus seeberi consistently outperformed Sedercypris calidus across prey types and temperature treatments at high prey densities. This was driven primarily by shorter handling times in L. seeberi, despite higher attack parameters in S. calidus under certain prey/ temperature scenarios. Temperature increase had differential effects on prey consumption dependent on fish species and prey type. However, neither species showed significant intraspecific differences in functional response between temperature conditions for either prey species, indicating community resilience to thermal change in the CFE. Context-dependent experiments can be used in tandem with field data to identify conditions of potential ecological tipping points in imperilled systems.

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Isolation management to protect threatened native galaxiid fish species: Lessons from Aotearoa New Zealand

Jolly,

Warburton,

Bowie

et al. 2024

Aquatic Conservation

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The use of barriers in freshwater systems to mitigate invasions, known as isolation management, has been increasingly implemented as a protection strategy for native fish. Barriers are crucial for securing vulnerable populations, but much remains to be learnt about the drivers of success and the implications of deliberate fragmentation. In Aotearoa‐New Zealand, henceforth Aotearoa, native non‐migratory galaxiid (NMG) fishes are characterized by a disproportionate number of threatened species with introduced salmonids (trout) identified as a key driver of NMG declines. We conducted a qualitative review of barriers protecting NMG in Aotearoa, illustrating varying outcomes and current knowledge gaps with case studies. Barrier types ranged from natural bedrock waterfalls, shallow velocity chutes and drying reaches to deliberately engineered structures (known commonly as exclusion barriers). Barriers were typically located in headwater streams or spring systems. NMG species secured by fragmentation often have high conservation value and barriers are essential for their protection. Despite the critical role of these barriers, the isolated NMG populations above them are at risk of stochastic extirpation, invasion, or re‐invasion. Exclusion barriers may restrict access to habitat for native migratory fish species and can sometimes alter or remove ideal mesohabitat from protected populations. Overall, when using exclusion barriers, managers must assess extinction risk for individual populations by isolation or invasion, balancing benefits and consequences. However, these assessments are frequently based on incomplete data and hindered by lack of general understanding of the underpinning processes. Despite well‐documented benefits to NMG population survival, key knowledge gaps such as long‐term viability of isolated populations, combinations of physical barrier parameters conferring exclusion under all flow regimes and extent of habitat loss to other native species still exist.

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Heterogeneity in flow disturbance around river confluences influences spatial patterns in native and non-native species co-occurrence

Cited by 7 publications

References 61 publications

Could spatial heterogeneity in flow disturbance drive temporal stability of native–invasive species co‐occurrence in riverscapes?

Could spatial heterogeneity in flow disturbance drive temporal stability of native–invasive species co‐occurrence in riverscapes?

Prey type and temperature influence functional responses of threatened endemic Cape Floristic Ecoregion fishes

Isolation management to protect threatened native galaxiid fish species: Lessons from Aotearoa New Zealand

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