Why Study Continental Aquatic Systems

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Unusual or Extreme Habitats

• Adaptations to Extremes
• Saline Lakes
• Hot Springs
• Cold Habitats
• Temporary Waters and Small Pools
• Ultra-Oligotrophic Habitats
• Deep Subsurface Habitats
• Neuston

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Molecular Adaptations to Extremes

• DNA- stabilized against high temperature by more
  binding proteins, more CG pairs
• RNA- more extensive regions of base pairing in
  areas that need to hold conformation
• Membranes- higher temperatures increase
  saturation, branching and length. In Archaea,
  ether lipids

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Molecular Adaptations to Extremes, continued

• Proteins- thermal stability, more ? sheets and ?
  helix, hydrophobic core, high external charge
• Salt- water is limiting. Need ways to stabilize
  proteins from too many ionic interactions.
  Complex animals pump out salt, halophilic
  bacteria and Archaea are isotonic with water.
  Some organisms use glycerol to remain isotonic
• Lack of water- similar to salt. Organisms in
  temporary habitats must be able to withstand
  desiccation

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Saline Lakes

• Closed basins, evaporation balances with inputs.
  Many lakes on earth are saline
• Chemistry dependent upon watershed
• Limitation by O2 may be important because
  solubility decreases with increased salinity
• Brine shrimp can be important consumers, will not
  coexist with fish
• Aral Sea in Russia was the fourth largest lake in
  the world but irrigation has decreased the lake
  area by half. Dust storms from dried lake basin
  now cause health problems

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Brine shrimp Artemia franciscana (ASLO image
gallery)
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Salinity Tolerance
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Hot Springs

• Thermophilic- heat loving organisms
• Bacteria and Archaea only inhabit highest
  temperatures
• Chemistry variable from very acidic to basic
• Acid springs dominated by sulfide sulfur
  oxidizing bacteria common

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Upper Temperature Tolerances
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Emerald pool- Yellowstone (waymark.com)
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Adaptation to Hot Temperatures
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Community Dynamics in Hunters Hot Spring
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Cold Habitats

• Arctic habitats
• Organisms inhabit ice and snow
• Snow algae color snow pink
• Arctic lakes can be ice-free for only a month or
  two
• Antarctic lakes always have an ice cover

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Watermelon snow (www.estes-park.com)
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Temporary Waters and Small Pools

• Can be categorized by permanency
• Generally lack fish, larger pools can be
  important for large crustacea and amphibian
  breeding
• Prairie potholes important for waterfowl
• Small pools in plants etc. form unique habitat.
  Important for mosquito larvae
• Some vernal pools (e.g. California) have high
  numbers of endemic species

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Ultra-Oligotrophic Habitats

• Very low nutrients can be stressful
• If carbonate low enough, mollusks cannot survive
• Organisms grow slowly

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ultra-oligotrophic Waldo Lake(www.waldocats.org
/ )
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Deep Subsurface Habitats

• All inhabited by microbes as long as liquid water
  exists
• Found at depths to 940 m
• Fungi rare, Bacteria and Archaea most common,
  protozoa top predators
• Active microbes found in waters isolated for 1200
  years
• Some may run off methanogenesis, H2 and CO2 come
  from rocks. Only ecosystem on earth not
  ultimately dependent upon photosynthesis

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Water Surface Layer

• Neuston- microbes at surface, Pleuston-
  macrorgansims at surface
• Unique chemical and biological habitat
• Extreme, high light and UV
• Velia capria use chemical that lowers water
  tension to move up to 10 cm/s

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Organisms of the Water Surface
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Nutrient Use and Remineralization

• Use of nutrients
• Nutrient limitation and relative availability
• Resource ratios and stoichiometry of primary
  producers
• Stoichiometry of heterotrophs, their food, and
  nutrient remineralization

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Use of Nutrients

• Uptake into cell, Michaelis-Menten V uptake,
  S substrate conc. Ks half saturation
  constant
• Monod equation, growth µ is growth rate
• Droop equation links concentration in cell (Q)
  and minimum concentration in cell for growth (Q0)
  to growth

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Nutrient Limitation and Relative Availability

• Relative availability of nutrients
• Nutrient limitation
• The Paradox of the Plankton and nutrient
  limitation

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Relative Availability of Nutrients
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Concept of Nutrient Limitation

• Leibigs Law of the Minimum
• The case for multiple nutrient limitations

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Hutchinsons Paradox of the Plankton

• Competitive exclusion principle- only one
  organism is a best competitor for a limiting
  resource and will dominate
• Leibigs Law- only one nutrient limits
• Observation- most phytoplankton cells have
  similar composition
• The Paradox- why are there commonly 100s of
  species of phytoplankton in a lake?

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Resource Ratios and Stoichiometry of Primary
Producers

• Nutrient remineralization
• What short-term processes control the levels of
  dissolved inorganic nutrients such as ammonium
  and phosphate?
• Processes leading to remineralization
• Remineralization as a source of nutrient pulses
  in lentic systems

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Redfield Ratio

• 106161 CNP by moles
• Algal cells have approximately this composition
  under balanced growth
• When N is limiting, may have 10651
• When P is limiting, may have 206321
• When N and P are limiting, may have 500161
• Can serve as an index of nutrient limitation

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Nutrient Remineralization

• Usually uptake is high enough that nutrients
  would be completely exhausted without
  remineralization (regeneration)
• The concentration of dissolved nutrients is an
  amount, the flux through that pool is a rate.
  These two should not be confused
• Phosphate and ammonium concentrations can be very
  low in a eutrophic lake

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Short-Term Processes can lead to an Equilibrium
Value of Nutrient Concentration

• Change in nutrient conc uptake - regeneration

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Processes that lead to Nutrient Remineralization

• Leakage from healthy cells, excretion from
  animals
• Heterotrophic activities of bacteria
• Viral infections cause lysis of cells
• Nutrient remineralization often dominated by
  microbial processes
• In some cases, moving animals assist nutrient
  import (salmon, hippos, migrating zooplankton)

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Nutrient Pulses

• Large algal cells are poor competitors for
  nutrients at low concentrations (low surface area
  to volume ratio)
• Pulses of nutrients may last long enough to give
  large cells an advantage if they run into the
  patches, but are they stable?
• Lehman and Scavia experiment

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Stoichiometry of Heterotrophs, their Food, and
Nutrient Remineralization

• Heterotrophs remineralize nutrients in excess of
  need
• Assume 9 C of energy needed for each C used for
  growth, and growth is at Redfield ratio
• A heterotroph needs food at 1000161. If it
  eats food at 106161, it will excrete N and P

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Bacterial Remineralization Depends on Food Source
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Zooplankton Differ in Stoichiometry so vary in
Food Requirements and Remineralization
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Trophic State and Eutrophication

• Definition of trophic state
• Why does nutrient pollution resulting in algal
  blooms matter in lakes?
• Natural and cultural processes of eutrophication
  
• Relationships among nutrients, water clarity, and
  phytoplankton
• Mitigating lake eutrophication
• Managing eutrophication in streams and wetlands
• Case studies of eutrophication
• Eutrophication and wetlands

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Definition of Trophic State

• Based on nutrients or producer biomass
• A way to describe a continuum of possible trophic
  states
• Useful in comparing systems across large areas
  (e.g. an oligotrophic lake in Iowa may be
  eutrophic in Idaho)
• To be more accurate we should refer to
  heterotrophic state and autotrophic state

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Two Trophic Classification Systems for Lakes
(autotrophic state)
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Why Does Nutrient Pollution Resulting in Algal
Blooms Matter in Lakes?

• Taste and odor problems
• Blooms of toxic algae
• Aesthetics (people less willing to pay to live
  near, or recreate on, eutrophic lakes)
• Fish kills

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Natural and Cultural Processes of Eutrophication

• Classical view that lakes slowly become more
  eutrophic as they fill and become shallow,
  eventually succession leads to a marsh, then a
  meadow
• Many large lakes may be oligotrophic for much of
  their history
• Natural eutrophication can occur, but
  eutrophication caused by humans (cultural
  eutrophication) is a world-wide problem

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Relationships among Nutrients, Water Clarity and
Phytoplankton

• Managing eutrophication in lakes requires
  understanding of correlations between nutrients
  and algal biomass
• Management of fish populations can also include
  consideration of trophic state

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Nutrient-Biomass Relationships
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Linking Lake Clarity to Nutrients
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Mitigating Lake Eutrophication

• Control of nutrient sources
• internal versus external loading
• Treatment in the lake
• Macrophyte removal

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Steps to Mitigate External Loading
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Why Eutrophication should be Controlled before
the Hypolimnion goes Anoxic

• FePO4 dissociates in anoxic conditions
• If hypolimnion goes anoxic then PO43- is
  continuously recycled from sediments into the
  water column, and mixed into the epilimnion
• Can take many years to recover from
  eutrophication even if point sources and
  non-point sources are controlled

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Methods for Controlling Macrophytes
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Managing Eutrophication in Streams and Wetlands

• Methods not as clearly defined for streams and
  wetlands, methods for streams more developed than
  for wetlands
• In general, principles are the same, control of
  nutrient sources is better than treating the
  symptoms

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Relationship Between Algal Biomass and Nutrients
in Streams
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Case Studies of Eutrophication

• Lake Washington
• Lake Trummen
• Lake Tahoe
• Lake Okeechobee
• The Clark Fork River

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Lake Washington

• Noticed shift to eutrophic algal species
• Sewage diverted from Lake Washington in 1960s
• Cyanobacteria dropped out
• Were able to control trophic state before
  hypolimnion went anoxic

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Effect of Nutrient Control in Lake Washington
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Lake Trummen

• In Sweden, 1 m deep, poor water quality, frequent
  fish kills
• Controlled point and non point sources to lake in
  1960s but problems continued
• Calculated that it would take hundreds of years
  for nutrients in sediments to wash back out
• Top half meter of sediments dredged and sold as
  topsoil. Improved water quality to allow fish
  survival and human recreation

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Lake Tahoe

• Ultra-oligotrophic lake on Nevada, California
  border
• Water retention time 700 years
• Septic systems were polluting lake, N limitation
  (detergent inputs)
• After sewage pumped out of basin, P limitation
  (watershed disturbance increased N inputs)
• Secchi depths are now 20 m rather than 40 m
  historically
• Future of lake uncertain

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Everglades/ Okeechobee

• Ag fertilizer runoff caused algal blooms in
  Okeechobee and loss of native plant and algal
  communities in Everglades (cattail replacing
  sawgrass)
• Canals and locks decreasing natural flushing
• Trying to restore natural hydrology
• Experimenting with using wetland areas to scrub P
  from incoming waters
• Agricultural lobby very powerful, and huge tax
  base in Southern Florida, so this is a charged
  issue
• Not clear if the problems will be solved

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Eutrophication and Wetlands

• Wetlands serve as nutrient sinks
• Better at N than P removal because there is no
  equivalent process to denitrification in the P
  cycle
• May work to remove plant biomass and allow
  re-growth (bulk removal of P)
• Many natural wetlands are oligotrophic, and
  nutrient pollution destroys natural system

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Behavior and Interactions among Microorganisms
and Invertebrates

• Behavior of microorganisms
• Interaction types in microbial communities
• Predation and parasitism
• Competition
• Mutualism facilitation and syntrophy
• Chemical mediation of microbial interactions

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Behavior of Microorganisms

• Motility
• Taxis
• moving toward or away from stimulus
• phototaxis, light
• geotaxis, gravity
• chemotaxis, chemicals
• magnetotaxis, magnetic fields

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Relative Rates of Movement of Organisms
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Random Walk Model of Chemotaxis
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Interaction Types in Microbial Communities

• Density-mediated versus trait-mediated
  interactions
• Direct verses indirect interactions

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Predation and Parasitism

• Viruses
• Consumption of small cells
• Scrapers and shredders
• Filter feeders
• Selectivity of particle feeders
• Microbial adaptations to avoid predation
• Parasitism
• Other exploitative interactions

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Viruses

• All organisms have them
• May control algal blooms and bacterial
  populations at times
• Can be a problem in fish aquaculture
• Some small protozoa can engulf viruses
• Human disease viruses can survive in water
• Inactivated in natural environment over time
• May move genetic material across taxonomic lines

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Consumption of Small Cells and Particles

• Function of particle size
• too small, the solution is too viscous, or
  collection apparatus is too small
• too large and wont fit in mouth
• Function of particle concentration
• Function of particle quality
• Greatest rates when entire assemblage is consumed

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Consumption and Particle Size
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Consumption and Concentration Energetic
Considerations
Protozoa increase consumption then level off
Daphnia slows down when particles are dense
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Consumption by Taxonomic Group
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Avoiding Predation

• Mechanical
• size (too small or too large)
• spines (chemical cues may induce protection)
• Chemical
• toxins (must be a majority in community, e.g.
  algal bloom)
• poor quality
• Behavioral
• escape

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Competition

• Exploitation versus interference competition
• Resource ratio theory
• Allelochemicals

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Resource Ratio Theory
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increasing
Species 2 wins, (low Si, high P)
Species 2, zero survival line
coexistence
PO43-
Species 1 wins, (high Si, low P)
Species 1, zero survival line
increasing
SiO42-
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Mutualism Facilitation and Syntrophy

• Highly co-evolved mutualisms rare in freshwaters
  relative to marine
• N-fixing symbionts occur
• Syntrophy
• Nostoc-midge example

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Chemical Mediation of Microbial Interactions

• Most microbial interactions mediated by chemicals
• All organisms use chemical cues
• Need to consider hydrodynamics (e.g. Reynolds
  number)
• unidirectional interactions in unidirectional flow

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Predation and Food Webs

• Detritivory and omnivory
• Adaptation to predation pressure
• Adaptations of predators
• Non-lethal effects of predation
• Trophic levels, food webs, and food chains
• The trophic cascade
• Theoretical community ecology and aquatic food
  webs

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Detritivory and Omnivory Many Organisms are
Omnivorous
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Using Stable Isotopes to Document Food Webs

• Several isotopes can be used to document food
  webs. The most common ratios used are 15N/14N
  and 13C/12C, expressed in parts per thousand
• Nitrogen is heavier as you move up the food web.
  Organisms track the C ratio in their food

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Examples of Isotopes in Food Webs
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Adaptation to Predation Pressure

• Mechanical
• size (too small or too large)
• spines (chemical cues may induce protection)
• Chemical
• toxins (must be large food item relative to
  predator)
• poor quality
• Behavioral
• escape (chemical, hydrodynamic, visual cues)

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Diel Vertical Migration in Daphnia
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Additional Behavioral Response of Daphnia

• May dive or swarm in response to chemicals
  released when conspecifics are crushed
• May produce diapausing eggs in response to
  chemical cues
• May reproduce more quickly at a smaller size

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Adaptations of Predators

• Hide and wait versus active foraging
• Sensory adaptations (sight, visual, hydrodynamic,
  electrical, chemical)
• Functional response versus numerical response
  (Hollings functional response curves)
• Predation only when predator pressure is lower
  (e.g. many predators need to worry about being
  prey)

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Functional Response Curves
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Foraging can be Modified by Food Density
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Non-lethal Effects of Predation

• Many predators dont kill prey, but can alter
  their survival
• Another prey species may be your savior if a
  predator switches to that prey instead of you
  when your population numbers are low
• Macrophytes are not eaten entirely, but can be
  grazed to some degree

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Trophic Levels, Food Webs, and Food Chains

• Food chains
• producers, primary consumers, secondary
  consumers, decomposers
• simple linear viewpoint
• Food webs
• allow for more complexity such as feeding at
  different trophic level
• more difficult to work with

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The Trophic Cascade

• Postulated since 1880 that predators can control
  herbivores and increase biomass of producers
• Top-down versus bottom-up control
• May use biomanipulation to control trophic state

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Conceptual Diagram of Trophic Cascade
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Biomanipulation in Netherland Lakes
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Trophic Cascade in a River
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Theoretical Community Ecology and Aquatic Food
Webs

• Are more diverse systems more stable?
• Is biodiversity related to ecosystem function?
• What controls lengths of food chains?

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Nonpredatory Interspecific Interactions among
Plants and Animals in Freshwater Communities

• Competition
• Mutualism and facilitation
• Other species interactions
• Complex community interactions

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Competition

• Difficult to establish in the field
• Primary producers compete for nutrients and
  light, benthic for space
• Can structure wetland plant communities
• Leads to evolutionary specialization (niche
  partitioning) over time

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Niche Partitioning in Two Rotifers
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Mutualism and Facilitation

• Mutualism usually approached on a case-by-case
  basis
• Cichlid fish will brood in multi-species groups
  to protect eggs from predators
• Groups of wetland plants may facilitate each
  other in harsh environments
• Invertebrates may facilitate others in feeding
  relationships

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Mutualism in 3 Tubificid Oligochaetes
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Other Species Interactions

• Many examples where one species has a strong
  effect on another and the second little effect on
  the first
• Humans are the ultimate example, we harm many
  species that have little influence on us. We
  also help some species (e.g. sportsfish) that
  have little effect on our survival

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Complex Community Interactions

• Disturbance
• Succession
• Indirect interactions
• Strong interactors

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Disturbance

• Response to disturbance dependent upon
  characteristics of disturbance and organisms
• Disturbance
• intensity
• areal extent
• frequency
• Organisms
• colonization ability
• resistance (e.g. diapause)
• distance to refugia
• growth rate
• What are some potential examples of disturbance
  in wetlands, lakes, and streams?

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An Example of Harshness
Characterized by time since flood,
intensity of flood, time since dried,
length of dry period, and distance from source of
permanent water
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Succession

• Often represented as a predictable sequence of
  community development after a disturbance or
  change in environment
• Seasonal succession in lakes
• Succession after reservoir construction
• Colonization after flooding in rivers
• Wetland restoration

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Seasonal Succession in Lakes
Concentration
Si
Total P
Large grazer resistant phytoplankton
Cyanobacteria
Diatoms
per L
Small body rapid growing zooplankton
per L
Large zooplankton
Biomass per m2
Macrophytes
Total young of the year fish
per m2
Larvae of individual fish species
Total Fish Biomass per m2
All fish
Stratification
Autumn mixing
Winter Spring Summer Autumn Winter
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Seasonal Succession in Fish Reproduction
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Seasonal Succession in Streams
Leaves in stream
Light at stream surface
Amount
Discharge
Discharge or temperature
Temperature
Biomass
Periphyton
Fast seasonal, insect larvae with summer
reproduction
Biomass
Biomass
Slow seasonal, insect larvae with winter growth
Long-lived species and quick reproducers (fish,
predators, mosses , FBOM feeders)
Biomass
Winter Spring Summer Autumn Winter
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Succession Following Reservoir Construction

• Macrophytes become established, community becomes
  more diverse over decade or so
• Productivity initially high because of nutrients
  released from flooded vegetation
• Fish and invertebrate communities shift from
  riverine to lacustrine and pelagic lake species

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Succession and Wetland Restoration

• Two approaches
• let natural processes restore natural community
  (e.g. from seed bank or come in on waterfowl
  etc.)
• re-introduce native species
• Often difficult to introduce species and get them
  all to take
• Some species will take a long time to come back,
  if ever, so reintroduction needs to occur
• A blend of the approaches should be taken

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Indirect Interactions

• How long are interaction chains in natural
  communities?
• Trophic cascade good example of indirect
  interaction chains
• Cladophora can benefit epiphytes (place to live)
  and indirectly grazers. The grazers may help
  Cladophora by lowering the amount of epiphytes
  that compete for nutrients

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Indirect Interactions between Fish and Ducks
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Fish Ecology and Fisheries

• Biogeographical determinants of fish assemblage
  diversity
• Physiological aspects influencing growth,
  survival, and reproduction
• Population dynamics of fishes
• Regulating exploitation of fish stocks
• Stocking fish for fisheries
• Aquaculture

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Biogeographical Determinants of Fish Assemblage
Diversity

• More diverse on large continents than small
• More diverse in old lakes and watersheds
• More diverse in tropics than temperate
• More diverse with more within-habitat diversity
• More diverse in larger rivers than small

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Fish Diversity with Distance Downstream
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Physiological Aspects Influencing Growth,
Survival, and Reproduction

• Energetics control growth, survival and
  reproduction
• Osmoregulation can be important, particularly for
  andromedous species
• Temperature, oxygen, food quantity and quality,
  predator avoidance all important

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Energetics across a Gradient
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Temperature Interacts with Trophic State
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Effect of a Predator on Food Consumption
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Population Dynamics of Fishes

• Stock- population size
• Production- population growth
• Recruitment- number entering an age class
• Numerous indices to quantify stock, production,
  age structure,and recruitment

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Regulating Exploitation of Fish Stocks

• Maximum sustainable yield- calculated when number
  of adults and young known
• Regulations used include size allowed, closed
  seasons, gear, and number of fish removed
• Closed seasons particularly useful for times when
  fish are susceptible to harvesting (e.g. spawning
  times)

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Stocking Fish for Fisheries

• Many fisheries managers stock fish
• Useful to boost native stocks
• Can introduce new species (e.g. lake species when
  a reservoir or pond is made)
• Some major problems with introductions include
  disease, outcompeting native fishes,
  hybridization with native fishes, lack of genetic
  diversity in populations

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Aquaculture

• World fish production dominated by carp, an
  important source of protein in many developing
  countries
• Management of aquaculture requires understanding
  of ecology including trophic state, transmission
  of disease, ecology of food organisms

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Global Production of some Freshwater Organisms
in 1989
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Zooplankton predators
Benthic predators
Foragers
0.7
2
0.5
Zooplankton
Benthic consumers
2
12
Phytoplankton
Periphyton
71
41
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Freshwater Ecosystems

• General approaches to ecosystems
• Groundwater ecosystems
• Streams
• Lakes and reservoirs
• Wetlands
• Comparison of freshwater ecosystems

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General Approaches to Ecosystems

• Trophic levels
• Energy flux budgets
• Efficiency of trophic levels not 100
• Nutrient budgets

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Trophic Pyramids and Energy Flux
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A Nutrient Flux Budget
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Biodiversity and Ecosystem Function

• Controversial
• Usually enough microbial diversity is present for
  an ecosystem to function at same rate regardless
  of diversity
• Important in low diversity systems (e.g. if only
  one species of shredder, then its absence will
  substantially alter the ecosystem)
• Benthic invertebrate diversity may alter nutrient
  flux across sediment/water interface

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Groundwater Ecosystems

• Often rely on organic material washed in from
  surface
• Can be ultraoligotrophic
• Permeability and water flow very important,
  animals common when large channels exist in
  groundwater

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Relative Rates of Ecosystem Respiration
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Streams

• Flood pulse concept
• Autochthonous versus allochthonous production
• Nutrient spiraling
• River continuum concept

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Flood Pulse Concept

• The traditional idea was that floods were
  disturbances
• More recent realization that flooding is an
  integral part of ecosystems
• Moves materials to and from riparian flood zone
• Increases connectivity between oxbows and
  wetlands in riparian areas and river
• Resets communities
• Encourages reproduction of some species

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Autochthonous versus Allochthonous Production

• When light reaches system, more primary
  production
• Forested areas have large amounts of leaf input
• Metabolic measurements suggest almost all streams
  are net heterotrophic, some just more so than
  others

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Nutrient Spiraling
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River Continuum Concept
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Lakes and Reservoirs

• View of lake ecosystems has expanded to include
  watershed
• Global surveys suggest that shallow lakes are
  more common than deep (littoral zone important
  part of ecosystem)
• Surveys of CO2 shows supersaturation in most
  lakes, indicating that heterotrophy is more
  important that autotrophy

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Generalized Ecosystem Characteristics of
Temperate Lakes
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Wetlands

• Most productive ecosystems on earth
• Herbivory not very important in most systems
• Hydrology drives function, including flow
  thorough and nutrient sources

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Pantanal, the Worlds Largest Wetland Ecosystem
Complex

• Brazil, Bolivia, Paraguay
• During wet season, floods connect pools
• During dry season, pools isolated and concentrate
  fish and their predators
• Home to many endangered species
• Plans underway to channelize river and decrease
  the upper part of the wetland by half

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Comparison of Freshwater Ecosystems across
Gradients
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Comparison of Trophic Webs
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Experimental Design in Aquatic Ecology

• Natural Experiments
• Simulation Modeling
• Manipulative Experiments

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Natural Experiments

• Things happen naturally to whole systems that can
  be used to test ideas about those systems (Mt.
  St. Helens)
• Natural patterns can be determined via
  correlation
• Not causation, but does increase understanding of
  systems

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Simulation Modeling

• Models can indicate where we lack knowledge
• Models can test scenarios where experimentation
  is impossible (e.g., global warming)
• Sensitivity analysis can be used to find the
  variables that control the parameter of interest

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Manipulative Experiments

• To formally test a hypothesis, a manipulative
  experiment is necessary
• Need controls and replication
• When experiments are properly designed,
  statistics can be used to test probability that a
  specific result supports the hypothesis