1. Fish #1. Meffe 1984 - predator-prey and invasion –Endangered Sonoran topminnow (Poeciliopsis occidentalis) lives in small spring creeks subject to violent flash floods. –Topminnow adapted to avoid flash floods Move rapidly to streamside during increase in velocity (lab experiments show) –Exotic mosquito fish (Gambusia) introduced and the eat topminnow. Not so smart about floods! Mosquito fish displaced downstream during floods and don’t maintain high density in upstream pools (Fig. 12.6, Meffe) downstream Non-Native Native Poeciliopsis occidentalis Gambusi affinis Hydrologic Disturbance Low density at spring source before flood Downstream displacement by flood

2. Poeciliopsis occidentalis Gambusi a affinis In springs that have been “stabilized” (by small dams), mosquito fish introduction leads to rapid decline of topminnows. In naturally heavily flooded springs, topminnow maintains high populations. Figure 6 % native fish

3. Timing of flood disturbance relative to fry emergence in introduced rainbow trout rainbow dictates establishment success of exotic Native Range Low Invasion Success Moderate Invasion Success Hydrologic Disturbance #2. Fausch et al. (2001) - invasion success emergence

4. Food Webs ( Power et al. 1996 ) -In northern California rivers, interannual variation in magnitude and timing of winter-spring floods, which determine length of food chain during summer low flow period. -Dicosmoecus gilvipes a dominant grazing caddisfly species is vulnerable to early winter floods but is invulnerable to invert and fish predators -In absence of early season floods, Dicosmoecus dominates and usurps energy flow (2-chain food web) and significantly reduces growth rates of juvenile steelhead trout. 4-level food chain 2-level food chain Hydrologic Disturbance

5. Companion study (Wootton et al. (1996) -Food webs in unregulated rivers versus dammed rivers in northern California: What would you expect? algae vulnerable grazers invulnerable grazers Predators (small steelhead) What do dams do to flood timing? (after Wootton et al. 1996)

6. Some issues about disturbance Disturbance is an event that causes mortality(or alters resources) Mortality depends on : –Habitat characteristics (Refugia) Channel morphology / Substrate (mobility) –Taxonomic group: Algae / Inverts / Fish / Riparian vegetation –Magnitude of event -"little" vs. "lots" of mortality so … Disturbance is –  scale-dependent ! –  context-dependent! (different in different settings)

7. Important distinction: –An individual disturbance is event; –temporal pattern of events is regime Event vs. Regime (ecological response) (evolutionary adjustment) [some mortality]["adaptation"]

8. Some Questions: Question #1: If disturbance causes mortality, and streams highly disturbed, how do species persist??!! –"Weedy" traits (Fig. 5) High mobility (colonizing) Fast (or asynchronous) life cycles High fecundity –Specific behavior / life history adaptations to avoid disturbance Spatial refuge: –Move to spatial refugia (e.g., Matthaei et al. 2000) –Abetus (water bug) and flash floods Temporal refuge: –Fast development in flashy system (e.g., Gray 1981, Fig. 4) –Time emergence prior to predictable floods (Lytle 2002) Low chance for 50 day development 10 days

9. Question #2 : If disturbance causes mortality, but species avoid disturbance, then is the event really a disturbance? Or are species well “adapted” ? Example: annual predictable disturbances in Rocky Mountain streams. Adaptation or Disturbance? –Under what conditions can "adaptation" occur? Signal is frequent (relative to life span) Signal not TOO extreme (survivors needed!) Signal-to-noise ratio is high (periodic, predictable) –What if disturbance is frequent, yet unpredictable? –Fast development –Asynchronous, multivoltinism (bet hedging)

10. Natural Flow Regime and Evolution Extreme events (floods and droughts) exert primary selective pressure for adaptation, because they often represent sources of mortality. Lytle & Poff. 2004. Adaptations to natural flow regimes. Trends in Ecology & Evolution. Types of adaptations: Life History, Behavior, Morphology

11. A second approach to predicting communtiy composition -- Functional Trait Composition –IDEA: Characterize the traits of species in the community, rather than the taxonomic identity. Not just the life history traits (as done by Crowl for snails) –ADVANTAGES: Traits related directly to environmental forces that vary from site to site –Disturbance, temperature, pollution, siltation, etc. Traits can be applied across biogeographic boundaries –DISADVANTAGES: Being able to describe species in terms of traits that are “sensitive” or directly responsive to environmental factors –Some specific studies coming shortly!

12. Habitat Template Model Species traits vary along environmental gradients Southwood (1977) Schlosser (1987) Townsend & Hildrew (1994)

13. Stream #1 Stream #2 SedimentFine to coarseFine gravel/sand Hydrol. Regime"stable""flashy" Disturbance Freq.LH RichnessHL Dominance by mobile mayfly (similar to Baetis)LH Drift rateLH Sedentary taxaHL CPOM/FPOMHL Max. size of mayflyHL Test of Habitat Template Test #1 - Inverts: [Scarsbrook and Townsend 1993] 2 streams in New Zealand #1 stable, high habitat heterogeneity #2 flashy, low habitat heterogeneity ?

14. Stream #1 Stream #2 SedimentFine to coarseFine gravel/sand Hydrol. Regime"stable""flashy" Disturbance Freq.LH RichnessHL Dominance by mobile mayfly (similar to Baetis)LH Drift rateLH Sedentary taxaHL CPOM/FPOMHL Max. size of mayflyHL Test of Habitat Template Test #1 - Inverts: [Scarsbrook and Townsend 1993] 2 streams in New Zealand #1 stable, high habitat heterogeneity #2 flashy, low habitat heterogeneity

15. Test #2 - Inverts: [Richards et al. 1997] Streams in Great Lakes drainage that differ geologically and thus in “flashiness” Long-lived (mero-voltine) species rare in flashy watersheds and in flashier stream reaches. “Clinger” species (e.g., mayflies) decline with fine sediment.

16. Test #3 - Fish: [Poff & Allan 1995] Streams in Wisconsin and Minnesota that differ in terms of hydrologic variability Ho: Fish communities will vary in functional composition depending on stream hydrology. 1) Define 2 different community “types” based solely on species traits 2) Define a “gradient” of hydrologic variability among the 34 streams 3) Test Ho. (Community types fall out along gradient of stream stability.) Flashier stream types have fish traits: generalist foragers, generalist habitat, slow water, tolerant of silt