STREAM ECOLOGY

River Continuum Concept Model Model for understanding and predicting changes within biotic communities of riverine ecosystems based upon geomorphic changes within those ecosystems Specifically: Energy flow / dynamics Diversity / community assemblages

What is a model? Predictive tool based on knowing something about the natural state If we know something about an ecosystems natural state we should be able to predict the response of biological communities to changes in that natural state

Diversity

Diversity Streams are dynamic systems whose biotic communities change with changes in the physical (geomorphological) stream channel e.g. width, depth, gradient Chemical water quality Riparian community e.g. open, partially closed, closed

Stream Dynamics The River Continuum Concept - Provides a framework within which we can understand and predict the responses of these dynamic biotic communities to their abiotic environments

River Continuum Concept Model

Diversity: headwater streams orders 1 to 3 Narrow with canopy cover nearly complete Water temperature range (∆ T max) is small, only a few degrees Diversity is low due to three primary factors: A narrower/smaller range of optimum metabolic temperatures for organisms living there Stream is largely homogeneous morphologically with few different habitats. (lateral vs main channel vs stream bank undercut Energy sources are primarily allochthonous

River Continuum Concept Model

Diversity: middle stream orders 4 to 6 Have Maximum diversity due to three primary factors: Increased range of optimum metabolic temperatures for organisms Streams tend to be wider with more lateral habitats. More heterogeneous stream morphology Increased trophic pathways provided by a combination riparian cover and open stream canopy

River Continuum Concept Model

Diversity: higher stream orders 7 + Typically low diversity (lower than orders 4 - 6) for three primary reasons: Light penetration is impeded by increased turbidity and increased depth of water decreasing primary productivity Increased habitat homogeneity due to depth and width of river and sediment loads Due to the reason above rivers tend to be reliant on FPOM coming from upstream

River Continuum Concept Model

Energy Flow

Energy Flow: stream orders 1 to 3 Riparian community is primary source of energy Riparian cover provides energy input-CPOM Typically nutrient poor: Watershed energy comes from Allochtonous (out of stream) sources Conditioned by fungi Colonized by bacteria Eaten by insects to get bacteria

Leaf litter enters stream Colonized by hyphomycete fungi- Fungi break though outside of leaf and open it up. Bacteria colonize inside of leaf, feeding on the sugars inside “Conditioning” Shredders eat the conditioned leaf to get to the bacteria Leaf pieces, bacteria, and feces sent downstream- FPOM available to collectors http://www.mayang.com/textures/Nature/images/Water/raindrops_on_water_050595.JPG

Energy Flow: 1-3 order streams P/R < 1 Benthic community composed primarily of shredders and collectors

Shredders Grazers Collectors - organisms that take CPOM (Coarse, Particulate Organic Matter) and breaks it down into FPOM (Fine, Particulate Organic Matter) Example: aquatic potato bug, freshwater shrimp/scuds Grazers -Feed on plants Example: algae/periphyton Scrapers Scrape rocks- ex: snails Collectors Organisms that typically catch FPOM and feet on it. Ex: Midges http://www.bugsurvey.nsw.gov.au http://www.superiortrips.com/IMAGES/periphyton.jpg

Energy Flow: Stream orders 4-6 Stream widens, light penetration is good due to low turbidity Stream shifts from allochthonous (from outside) to autochthonous (from within) enegry sources. (i.e.- primary production) 1. P/R > 1= more productivity 2. Benthic community shifts from one dominated by shredders and collectors to one dominated by collectors and grazers (scrapers)

Energy Flow: stream orders 7 + Stream gets deeper and wider, greater turbidity and decreased light  community shifts again P/R < 1 Almost exclusively collectors and predators Stream ecosystem downstream relies on FPOM from upstream sources to fuel downstream ecosystem By destabilizing upstream through deforestation, we impact downstream Entire lower stream reliant on organisms that feed on FPOM **What we do here has an impact further along Ex: Delaware river