1. Brooke Penaluna USFS PNW Research Station Oregon State University
The importance of location: Responsiveness of stream-living fish populations
Brooke Penaluna
USFS PNW Research Station
Oregon State University
Co-authors: S. Railsback, J. Dunham, S. Johnson, A. Skaugset, and R. Bilby

2. Trask Watershed Fish component: multiple lines of inquiry

3. Location within landscape matters
The evolution of concepts in stream ecology has culminated in a collective recognition that location within a landscape matters to aquatic biota (Hynes 1975; Vannote et al. 1980; Wiens 2002). At present, the dominance of these ideas in the literature has given rise to a landscape-based perspective whereby streams are viewed as patchy and heterogeneous environments (Minshall et al. 1985; Perry and Schaeffer 1987; Townsend 1989) that vary across various spatio-temporal dimensions (Ward 1989; Ward and Stanford 1995) within a stream network (Benda et al. 2004). Specific processes driving this heterogeneity include influences of stream flow (Poff et al. 1997), interactions of rivers with their floodplains (Junk et al. 1989) and riparian zones (Gregory et al. 1991), upslope processes (Montgomery 1999), surface- and groundwater interactions (Boulton et al. 1989), and how these processes interact in the form of high magnitude and low-frequency events that are often regarded in the context of disturbance (Resh et al. 1988; Swanson et al. 1988, Reeves et al. 1995). Collectively, these longitudinal, lateral, and vertical processes influence location-specific conditions within a landscape through time (Ward 1989; Poole 2002). Although it is well-known that these location-related processes strongly affect streams and their biota (see Resh et al. 2003), quantifying the relative influences of different processes among locations and through time can be extremely challenging.
Specific processes driving this heterogeneity include influences of stream flow (Poff et al. 1997), interactions of rivers with their floodplains (Junk et al. 1989) and riparian zones (Gregory et al. 1991), upslope processes (Montgomery 1999), surface- and groundwater interactions (Boulton et al. 1989), and how these processes interact in the form of high magnitude and low-frequency events that are often regarded in the context of disturbance (Resh et al. 1988; Swanson et al. 1988, Reeves et al. 1995). Collectively, these longitudinal, lateral, and vertical processes influence location-specific conditions within a landscape through time (Ward 1989; Poole 2002). Although it is well-known that these location-related processes strongly affect streams and their biota (see Resh et al. 2003), quantifying the relative influences of different processes among locations and through time can be extremely challenging.

4. Headwater streams are ideal to study location-related processes
Habitat template
Stream gradient
Stream shape
Habitat units
Velocity shelter
Hiding cover
Spawn gravel
Headwater streams provide an ideal setting because they are tightly coupled with terrestrial ecosystems and may be more responsive to their location, they can be highly dynamic (Moore and Richardson 2003), and it is possible to observe tremendous differences within and among streams in the space of just a few hundred meters (e.g., Benda et al. 2004). Accordingly, fish living in these settings are affected by the juxtaposition of dynamic environmental regimes and relatively fixed physical features of streams also described as the physical habitat template (Southwood 1977; Southwood 1988; Poff and Ward 1990). The habitat template is mostly determined by a hierarchical arrangement of geologic and topographic features, which are ultimately formed by forces such as glaciation and plate tectonics (Frissel et al. 1986; Montgomery 1999; Beechie et al. 2010). Given enough time, virtually any physical characteristic of a habitat template may exhibit variability although they are generally more fixed over shorter temporal extents (Frissell et al. 1986; Benda et al. 2004). The habitat template for a headwater stream location (e.g., slope, elevation, stream size, channel geomorphology, instream habitat) interacts with local climate to produce environmental regimes, such as stream flow, temperature, and turbidity. The dynamics of these environmental regimes are particularly marked on a daily, seasonal, and annual extent and when compared to the habitat template are much more variable (Arthington 2012). Although there is a general understanding that location-related influences are important to fish, there is still considerable uncertainty remaining about the role of environmental regimes and the habitat template in headwater streams and how exactly they influence population dynamics of fish.
Environmental regimes
Stream flow
Stream temperature
Turbidity
Nutrients

5. Headwater streams can be quite different
Trask River Watershed
Pothole
Gus
Upper Mainstem (UM)
Rock

6. Trout demography is unique to each site

7. What is the spatial variability of fish population biomass across
headwater streams?
2) What is the role of environmental regimes and the habitat template to
fish population biomass?
Habitat template
Environmental regimes

8. Using an Individual-based Model to understand complex interactions
individuals
population
community
Individuals grow and change
Variability among individuals of same age
3) Resources used by individuals reflect availability
4) Population abundance is based on field data
Goal: to compare fish biomass to observed patterns from field
A simulation model that includes multiple biological levels of hierarchy, spatial scales, time scales, and stochastic events
Grimm and Railsback 2005

9. inSTREAM model Habitat template Environmental Regimes
Channel shape, velocity shelter, hiding refuge, and spawn gravel
Environmental Regimes
Stream temperature, flow, and turbidity
individual
behavior
population responses

10. What is the spatial variability in fish population biomass across
headwater streams?

11. Headwater streams from same watershed can have very different population biomass densities

12. Headwater streams have significantly distinct fish responses
Higher biomass
Lower biomass
4 years x 2 seasons = 8 points per site
All pairwise comparisons significant P<0.05
Biomass data using 5 age classes
Transform: square root
Resemblance: Euclidean distance

13. Fish populations differ even within a few hundred meters within the same watershed
But, what are these differences due to? Fixed habitat template or dynamic environmental regimes?

14. fish population biomass?
2) What is the role of environmental regimes and the habitat template to
fish population biomass?
Habitat template
Environmental regimes
Gus
Rock
Pothole
Upper Mainstem
Gus
Rock
Pothole
Upper Mainstem

15. Even with differing environmental regimes fish populations maintain similar responses

16. Habitat template controls fish response
Higher biomass
Lower biomass
4 years x 2 seasons x 4 sites = 32 points per site
All pairwise comparisons significant P<0.05

17. Next step: examine alternative scenarios
Stream flow
Stream temperature
Turbidity
Nutrients
Stream gradient
Stream shape
Habitat units
Velocity shelter
Hiding cover
Spawn gravel
Habitat template
Environmental regimes
Forest harvest
Climate change

18. Conclusions
Fish populations among headwater streams respond differently to same factors because the habitat template controls fish responses
Headwater streams with higher heterogeneity in their habitat template also had higher fish biomass
This may suggest that certain headwater streams may be more sensitive than others to changes in environmental regimes from climate change or forest harvest

19. Acknowledgements
Funding sources: EPA STAR grant, USGS FRESC, Trask Watershed Study OSU graduate school and FW departmental scholarships, AFS scholarships, USFS PNW PhD committee: Jason Dunham, Steve Railsback, Sherri Johnson, Lisa Ganio, Matt Betts, Jim Hall Field help: Boyd Carroll, Ben Ramirez Graphics help: Kathryn Ronnenberg, Ivan Arismendi