B. Disturbance and preda7on in fish Example. Meffe 1984 studied how floods allow na:ve prey to survive preda:on by exo:c species 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 immediately in response to velocity increase (lab experiments) Exo:c 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) Poeciliopsis occidentalis downstream Gambusia ffinis Na&ve Non- Na&ve displaced far downstream by flood In springs that have been (by small dams), mosquito fish introduc:on leads to rapid of topminnows. In springs, topminnow high popula:ons. Poeciliopsis occidentalis Gambusia affinis Naturally flashy spring % na:ve fish What is role of disturbance in species co- existence in this system? 1
C. Disturbance & species establishment and invasion Example. Fausch et al. (2001) looked at invasion success of rainbow trout in five regions around the world. Par:cular are vulnerable to disturbance: Emerging fry of rainbow trout can be washed downstream. of flood disturbance rela:ve to in introduced rainbow trout rainbow dictates establishment Na:ve Range Invasion Success Invasion Success D. Disturbance and Invertebrate Abundance last disturbance event Example. Flecker and Feiferek (1983) - Flashy tropical stream (Fig. 10-7 in text) - Interpret? - Why important? Shows general pa^ern seen in streams Why do the numbers of species change with :me since disturbance? Where do they come from? 2
Example. Palmer et al. (1992) studied a sandy- bo^omed stream in coastal plain of Virginia Dominant fauna in channel is meiofauna (small metazoans living within the sand ( hyporheic zone ). Depth to bedrock = 50 cm. What is response of different taxa to spates (i.e., small floods)? How can recovery be so quick? Reproduc:on? (Calculated to be fast enough to explain recovery!) Recoloniza&on: from where???? Woody debris patches serve as hydaulic!! Example. Ma^haei et al. (2000) studied a flashy New Zealand stream and the effect of disturbance on insect abundance and species richness. TREATMENTS Stable vs. unstable (based on actual movement during flood) SAMPLING TIMES Before disturbance Same on both 3- d ajer peak Q Stable increases - Why? Unstable declines - Why? unstable stable 19- d ajer peak Q Same again - Why? Similar for Richness CONCLUSION Stable stone refuge! [refugium, refugia] 3
E. Disturbance and stream food webs Power et al. (1996) found that the magnitude and :ming of floods in northern California rivers (South Fork Eel River) determine tje of food chain during period. Flood magnitude and :ming vary from year to year. 1 Key player: Dicosmoecus gilvipes a dominant caddisfly species is vulnerable to early winter floods but is invulnerable to invert and fish predators. 2 3 macroinvertebrates 4 algae Dicosmoecus gilvipes a dominant grazing caddisfly species is to early winter floods when it is in stage but is to invert and fish predators. In years with big winter floods, Dicosmoecus has small popula:on size. In years with big small (less scour) floods, Dicosmoecus has large popula:on size. Dams on these rivers can capture winter peak flows and cause downstream reaches to not experience scouring floods on a regular basis. 4
In absence of early season floods (natural dry years in unregulated rivers or dams on regulated rivers), Dicosmoecus and usurps energy flow, trunca:ng food chain to 2 lengths. This has the poten:al to reduce growth rates of top predators juvenile steelhead trout. 4- level food chain 2- level food chain Companion study (Woo^on et al. (1996) - Food webs in unregulated rivers versus dammed rivers in northern California: What would you expect? algae vulnerable grazers (after Wootton et al. 1996) invulnerable grazers Predators (small steelhead) 5
Food chain length varies among streams with different disturbance regimes? Recent disturbance FCL Disturbance is a measure. (Note intermi^ent streams in red circles)? Stream drying FCL! Food chain length measured with. Long food chains mean top predators (fish, amphibians) Sabo et al. (Science 2010) Food chain length varies among streams with different disturbance regimes (a) Resources with disturbance (d) FCL with disturbance McHugh (Ecol. Le^ers 2010) 6
3 Models of Disturbance and Community Structure (1) Intermediate Disturbance Hypothesis - Based on species iden::es (taxonomy) (2) Habitat Template Model - Based on species traits (3) Patch Dynamics Model - Combina:on of 1 and 2 But first some examples of how disturbance mediates outcomes of species interac:ons Theory 1: The Intermediate Disturbance Hypothesis - species diversity (or richness) varies with disturbance (or habitat stability) Predic:on? Maximum species diversity at level of natural disturbance. Mechanism? (What explains pa^ern?) What kinds of species will occur at either end of the disturbance gradient? Evidence for IDH in streams? 7
Test of IDH Townsend et al. (1997) Sampled invertebrate communi:es in many throughout a river catchment in New Zealand. Sites differed in intensity of bed movement (What would cause this?) Theory 2: The Habitat Template Concept Species should vary along environmental gradients Traits that environmental condi:ons allow species to occur in that habitat. Townsend & Hildrew (1994) Southwood (1977) 8
Test #2 - Inverts: [Richards et al. 1997] Streams in Great Lakes drainage that differ geologically and thus in how fast runoff is generated during precipita:on. A measure of stream flashiness Test #2 - Inverts: [Richards et al. 1997] Sampled many stream reaches and calculated probability of moderate and high representa:on of different species traits: Long- lived (merovol:ne) species rare in flashy flashier stream sites. Obligate deposi:onal taxa increase with pool habitats. Clinger species (e.g., mayflies) decline with fine sediment. merovol:ne taxa Index of flood intensity Obligate deposi:onal taxa Clinger taxa 9