Increasing drought favors nonnative fishes in a dryland river: evidence from a multispecies demographic model

Abstract

Understanding how novel biological assemblages are structured in relation to dynamic environmental regimes remains a central challenge in ecology. Demographic approaches to modeling species assemblages show promise because they seek to represent fundamental relationships between population dynamics and environmental conditions. In dryland rivers, rapidly changing climate conditions have shifted drought and flooding regimes with implications for fish communities. Our goals were to (1) develop a mechanistic multispecies demographic model that links native and nonnative species with river flow regimes, and (2) evaluate demographic responses in population and community structure to changing flow regimes. Each fish species was represented by a stage‐structured matrix, and species were coupled together into a multispecies framework through density‐dependent relationships in reproduction. Then, community dynamics were simulated through time using annual flow events classified from gaged streamflow data. We parameterized the model with vital rates and flow–response relationships for a community of native and nonnative fishes using literature‐derived values. We applied the simulation model to the Verde River (Arizona, USA), a major tributary within the Colorado River Basin, for the past half century (1964–2017). Model validation revealed a match between model projections and relative abundance trends observed in a long‐term fish monitoring dataset (1994–2008). At the beginning of the validation period (1994), model and survey observations showed that native species comprised approximately 80% of total abundance. Model projections beyond the survey data (2008–2017) predicted a shift from a native dominant to a nonnative dominant assemblage, coinciding with increasing drought frequency. Trade‐offs between native and nonnative species dominance emerged from differences in mortality in response to the changing sequence of major flow events including spring floods, summer high flows, and droughts. In conclusion, the demographic approach presented here provides a flexible modeling framework that is readily applied to other stream systems and species by adjusting or transferring, when appropriate, species vital rates and flow‐event thresholds.

Dynamic contributions of intermittent and perennial streams to fish beta diversity in dryland rivers

“…High flow events are known to induce dispersal of native fishes elsewhere in the Colorado River Basin for increased foraging, spawning, or exploring activities (Booth, Flecker, & Hairston, ; Cathcart, Gido, & McKinstry, ; Cross et al, ), leading to decreased probability of local extinction (Budy, Conner, Salant, & Macfarlane, ). Years with the highest flow anomalies are also times when extreme spring floods or summer monsoons have occurred, and may have been detrimental to non‐native species populations (Bestgen, Wilcox, Hill, & Fausch, ; Gido, Propst, Olden, & Bestgen, ; Rogosch et al, ). These flow conditions, which are more favourable for native species compared to non‐native species, additionally benefit native species by providing some release from negative biotic interactions (Propst, Gido, & Stefferud, ; Stefferud, Gido, & Propst, ).…”

“…High flow events are known to induce dispersal of native fishes elsewhere in the Colorado River Basin for increased foraging, spawning, or exploring activities (Booth, Flecker, & Hairston, 2014;Cathcart, Gido, & McKinstry, 2015;Cross et al, 2013), leading to decreased probability of local extinction (Budy, Conner, Salant, & Macfarlane, 2015). Years with the highest flow anomalies are also times when extreme spring floods or summer monsoons have occurred, and may have been detrimental to non-native species populations (Bestgen, Wilcox, Hill, & Fausch, 2017;Gido, Propst, Olden, & Bestgen, 2013;Rogosch et al, 2019).…”

Designing flow regimes to support entire river ecosystems

“…Native fishes prosper under flow regimes with more frequent and reliable (i.e. annual) spawning floods and no drought (Rogosch et al, 2019). Thus, bigger floods are beneficial for vegetation and fishes, but the timescale of response differs.…”

“…Floods and droughts interact with vital rates, affecting population sizes, which opens vacant space (vegetation) or biomass (fish) for recruitment during the next year if conditions are met. Both models have demonstrated a strong ability to recover known patterns on the landscape via tests against empirical data (Lytle et al, 2017; Rogosch et al, 2019).…”

Flow regimes control the establishment of invasive crayfish and alter their effects on lotic macroinvertebrate communities

“…Despite increasing research considering the role of hydrology as a control on the establishment and subsequent population dynamics of INNS/native species (e.g. Lynch, Leasure, & Magoulick, 2018;Rogosch et al, 2019), we are unaware of any studies quantifying the interactive effect of INNS and hydrologic variability upon the composition of the receiving community (with the exception of a mesocosm study; Magoulick, 2014). Understanding the interaction between hydrological variability and invasive species is thus vital, particularly in the face of climate change (Chen & Olden, 2017;Poff, 2018;Rahel & Olden, 2008).…”