B. Disturbance and preda7on in fish

Transcription

1 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 Low density at spring source before flood Non- na&ve Gambusia displaced far downstream by flood

2 In springs that have been stabilized (by small dams), mosquito fish introduc:on leads to rapid decline of topminnows. In naturally heavily flooded springs, topminnow maintains high popula:ons. Poeciliopsis occidentalis Gambusia affinis Figure 6 % na:ve fish Naturally flashy spring What is role of disturbance in species co- existence in this system?

3 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 life stages are vulnerable to disturbance: Emerging fry of rainbow trout can be washed downstream. Timing of flood disturbance rela:ve to fry emergence in introduced rainbow trout rainbow dictates establishment success Time of emergence Na:ve Range Moderat Invasion Success Low Invasion Success

4 D. Disturbance and Invertebrate Abundance Time since last disturbance event Example. Flecker and Feiferek (1983) - Flashy tropical stream (Fig 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?

5 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)? All groups decline How can recovery be so quick? Reproduc:on? (Calculated to not be fast enough to explain recovery!) Recoloniza&on: from where???? Woody debris patches serve as hydaulic REFUGE!!

6 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 aier peak Q Stable increases - Why? Unstable declines - Why? unstable stable 19- d aier peak Q Same again - Why? Similar for Richness CONCLUSION Stable stone refuge! [refugium, refugia]

7 E. Disturbance and stream food webs Power et al. (1996) found that the magnitude and :ming of winter- spring floods in northern California rivers (South Fork Eel River) determine tje length of food chain during summer low flow period. Flood magnitude and :ming vary from year to year. 1 Key player: Dicosmoecus gilvipes a dominant grazing caddisfly species is vulnerable to early winter floods but is invulnerable to invert and fish predators. 2 3 macroinvertebrates 4 algae

8 Dicosmoecus gilvipes a dominant grazing caddisfly species is vulnerable to early winter floods when it is in early instar stage but is invulnerable to invert and fish predators. In years with big winter floods, Dicosmoecus has small popula:on size. Dammed rivers have reduced peak flows 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. What happens to Dicosmoecus popula:on abundance in dammed rivers?

9 In absence of early season floods (natural dry years in unregulated rivers or dams on regulated rivers), Dicosmoecus dominates and usurps energy flow, trunca:ng food chain to 2 lengths. This has the poten:al to reduce growth rates of predaceous juvenile steelhead trout. algae vulnerable grazers invulnerable grazers 4- level food chain 2- level food chain Predators (small steelhead) ( Wootton, Power et al. 1996)

10 Food chain length varies among streams with different disturbance regimes? Recent disturbance shortens FCL Disturbance is a measure of flow variability. (Note intermi_ent streams in red circles) Food chain length measured with 15 N. Long food chains mean top predators (fish, amphibians)? Stream drying shortens FCL! Sabo et al. (Science 2010)

11 Food chain length varies among streams with different disturbance regimes (a) Resources decline with disturbance index (d) FCL declines with disturbance index McHugh et al. (Ecol. Le_ers 2010)

12 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

13 Theory 1: The Intermediate Disturbance Hypothesis - species diversity (or richness) varies with disturbance (or habitat stability) Predic:on? Maximum species diversity at intermediate level of natural disturbance. Diversity or Richness Mechanism? (What explains pa_ern?) What kinds of species will occur at either end of the disturbance gradient? Differences in compe::ve ability, tolerance, etc. r- selected and K- selected species Evidence for IDH in streams? disturbance

14 Townsend et al. (1997) Test of IDH Sampled invertebrate communi:es in many stream reaches throughout a river catchment in New Zealand. Sites differed in intensity of bed movement (What would cause this?)

15 Theory 2: The Habitat Template Concept Species traits should vary along environmental gradients Traits that match environmental condi:ons allow species to occur in that habitat. Townsend & Hildrew (1994) Southwood (1977)

16 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 Stream 1 Stream 2 Sediment Fine to coarse Fine gravel/sand Hydrologic regime (disturb. Freq.) stable (L) flashy (H) Insect species richness Proportion sedentary taxa in stream Dominance by mobile mayfly species CPOM/FPOM Maximum size of mobile mayfly

17 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 Stream 1 Stream 2 Sediment Fine to coarse Fine gravel/sand Hydrologic regime (disturb. Freq.) stable (L) flashy (H) Insect species richness H L Proportion sedentary taxa in stream L H Dominance by mobile mayfly species L H CPOM/FPOM H L Maximum size of mobile mayfly H L

18 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

19 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