Substrate-Organism Relationships. Substrate Type & Size

Transcription

1 Substrate-Organism Relationships Substrate = Substratum (Substrata) Fundamental Roles 1) Habitat 2) Food 3) Protection Substrate Type & Size Inorganic mineral particle Exposed Bedrock Particles (from weathered bedrock) Wentworth Scale: B > C > G > Sa > Si (> C) Organic Fine Particulate OM (FPOM, < 1mm) Course Particulate OM (e.g., whole leaves) (CPOM, > 1mm) Wood Living plant surfaces / Macrophytes (angiosperms, bryophytes) 1

2 Relationships between aquatic insect richness and abundance with particle size and texture? - In the graph below, label the 3 lines with the numbers = Species richness (total number of species) - 2 = Total organism abundance (total number of individuals) - 3 = Organism density (abundance/surface area of particle) max 0 Gravel Pebble Cobble Particle type This figure from the Allan & Castillo shows results of total number of aquatic insects colonizing substrates of different surface features that were put in the stream for 14 and 28 days. From the figure and the legend, you should identify what the experimental treatments were, and what the results of the experiment show about insect preferences for stone substrates in this stream. 73 C O 6 (a) r Rough Smooth Algae intact D Day 14 H Day 28 Rough Smooth Algae removed [You should start by explaining the patterns in the graphs as completely as you can.] (b) 300 With Without Crevices FIGURE 5.9 Mean number of species (±1 SE) colonizing rough and smooth stones from which microalgae were either (a) removed or left intact and (b) with or without crevices. Values are adjusted for area of stone. (Reproduced from Downes et al ) 2

3 Mineral Particle Mixtures Density and biomass of invertebrates Sand supports low abundance and biomass Gravel/pebble support more. WHY? Sand Gvl Pbl Cob Boul Interstitial spaces between substrate particles influence many aspects of habitat quality LIST SOME! Habitat space Detritus accumulation Flow (Fig.8-12, Ward) Oxygen Stability during high flows What would current distribution in sand look like? Sand Gravel-Cobble Cobble-Boulder 3

4 Fish spawning Salmonids can create redds in gravel having median size up to 10% of their body length Particles < 1 mm reduce gravel permeability and impair egg development (reduced flow and oxygen) Particles 1-10 mm block intergravel pores and impede swim-up of newly-hatched fish. Organic substrates Table classic study of a forested stream with range of substrate sizes sand supports fewest numbers and species organic substrates support diversity similar to gravel, with greater abundance (but they are seasonal) Wood 2 major roles (1) Steep channels: creates habitat (pools) and increases CPOM retention. (2) Low gradient channels with silt/sand bottoms: creates productive habitat that is stable during floods Table 3.5 (Allan & Castillo) Satilla River, GA 4

5 Stability Particle resistance to movement by high flows Critical erosion velocity Fig Moss on stones (This pattern will hold for invertebrates as well!)?? A rolling stone gathers no moss the proof! Example. MaVhaei et al. (2000) studied a flashy New Zealand stream and the effect of disturbance on insect abundance and species richness. TREATMENTS Stable vs. unstable cobbles on streambed (based on actual movement during flood) SAMPLING TIMES Before disturbance Same on both 3- d aher peak Q # on Stable increases - Why? # on Unstable declines - Why? 19- d aher peak Q No difference - Why? Similar for Richness unstable stable CONCLUSION Stable stones are a refuge! [refugium, refugia] 5

6 Organism-substrate relationships? General patterns -- interacting factors, due to correlations among important variables: (name 4) Current Oxygen Food Stability Riffles: coarse substrate mixtures with high interstitial flows, high O 2, trapped CPOM, and relatively high stability Pools: fine substrates, low interstitial flows, low O 2 in sediments; lots of organic matter (much buried in sand), low stability during high flows 6