Nonnative species erode the stability of desert fish communities

Keith J. Fritschie and Julian D. Olden School of Aquatic and Fishery Sciences

University of Washington

The Importance and Maintenance of Stability

Ultimately, stability depends on the richness and trait composition of a community

Time

Func

tion

Examples of Stability Hypotheses:

• Dominance Effects

• Insurance Hypothesis

• Portfolio Effects

Stability of Fish Community Production

• Reliability of fishery yields

• Downstream delivery of ecosystem functions

(nutrient recycling, aquatic-riparian linkages,

top-down trophic control)

Nonnative Contributions to Stability

• Early phases of testing stability hypotheses used randomly assembled experimental communities

• Richness: Nonnative introductions often outpace local extinctions (Sax and Gaines 2003)

• Composition: Nonnative species often have unique traits (e.g. resource acquisition, response to environment)

Our challenge: Nonnative introductions alter the richness and composition of southwestern fish communities

Roundtail Chub Sonora Sucker Spikedace

Red Shiner Smallmouth BassYellow Bullhead

Do nonnative introductions influence the stability of desert fish communities?

Approach: System, Sites, and Data

• Backpack shocking, seining, or combination• 44 sites• 18 rivers• 9 - 26 years sampled (Mean = 16)• Richness:

2.8 – 10.8 Average N Species• Composition:

0 – 78% Nonnative Dominance

Approach: Measuring Stability

Community Variability = Mean Population Variability * Community Synchrony

Thibault and Connolly, Ecology Letters, 2013

Time

Func

tion

Approach: Testing Stability Maintenance and Mechanisms

Average RichnessNonnative Dominance

Population Variability

Synchrony

Community Variability

Biological Components Mathematical Components Community Stability

Results: Biological Pathways to Stability

Synchrony Population Variability Community Variability

Nonnative Dominance Average Richness

* =

Results: Biological Pathways to Stability

Average Richness Nonnative Dominance

Population Variability Synchrony

Community Variability

- 0.328

0.899 0.635

0.712

Nobs = 44Χ2 = 2.65 df = 3 p = .448RMSEa = < .0001SRMR = .019

R2 = .11 R2 = .55

R2 = .97

Potential Mechanisms: Differential Responses to Flow

Mims et al., Ecology, 2012 Modified from Gido et al., CJFAS, 2013

Behavioral/Morphological

• Quick response and orientation to discharge• Floodplain use• Body shape• Reproductive events cued to flow events

• Examples: G.K. Meffe, Ecology, 1984 Lytle and Poff, TREE, 2005

Life History Strategy

• Tradeoffs in fecundity, parental investment, and generation time • LHS occurrence related to hydrologic regime

• Examples: Olden et al., Eco. Monographs, 2006

Mims et al., Ecology, 2012

Photo Credit: Mark Fuller

Potential Mechanisms: Differential Responses to Flow

Taylor’s Power Law:• Relationship between species’ mass and variance across sites• Common measure of population stability• Lower slope indicates higher stability

• Nonnative species significantly less stable

• Life history-stability patterns not consistent across nativity• Evidence for important behavioral/morphological

differences?

Slop

e

Equil. Opp. Per.

Native Nonnative

Conclusions and Next Steps

• Nonnative dominance destabilizes desert fish communities, independent of richness

• Nonnative species’ populations are less stable than natives:• Not accounted for by life histories• Evidence of important behavioral and morphological differences?

• Nonnative dominance may also stabilize communities through asynchrony: why?• Differential responses to flow: response diversity• Increasing species interactions

• Implications for ecosystems?• Rivers and riparian areas disproportionately important for diversity in arid lands• Alterations to ecosystem processes in rivers may impact the riparian corridor• Thus, understanding the mechanisms underlying population and community stability

are important for conservation, management, and ecosystem functioning goals

Acknowledgements

Jeff Cole, Navajo Nation Dept. Fish and Wildlife

Lisa Eby, University of Montana

Bill Fagan, University of Maryland

Keith Gido, Kansas State University

Eliza Gilbert, New Mexico Dept. Fish and Game

Thomas Hardy, Texas State University

The late W.L. Minckley, Arizona State University

David Propst, New Mexico Dept. Game and Fish

Peter Reinthal, University of Arizona

John Rinne, USFS Rocky Mtn Research Station

Zach Shattuck, Bio-West

Jerry Stefferud, USFS Retired

Sally Stefferud

James Whitney, Kansas State University

Funding

National Science Foundation

Western Division AFS -

Sustainable Fisheries Foundation

Background Image

Mike Reyfman Photography

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