Trophic Ecology

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Trophic Ecology

• What are the trophic interactions in streams
• Microbial Loop
• Invertebrate consumers
• Consumers of CPOM
• Consumers of FPOM
• Herbivores consumers of autotrophs
• Predators consumers of other animals
• Fish consumers functional feeding groups
• Herbivores
• Predators
• Other vertebrate predators
• How to track the flow of energy through the system

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• the microbial food web is a sink for C transfer,
  although still important in remineralizing C and
  nutrients
• bacterial production has been shown to reach
  virtually all consumers including fish
• invertebrates and fishes, the concepts of FFG and
  guild greatly aid our assessment of feeding roles
  by adding the where and the how to the
  what of re- source consumption

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• FFGs of macroinvertebrates, categorized according
  to food sources and mechanism of food
  acquisition, reflect the four most important food
  resources found in streams periphyton, CPOM,
  FPOM, and animal prey.
• FFGs provide insight into the relative importance
  of various basal resources.
• Further feeding specialization is seen to varying
  degrees within each of these feeding groups
• Most suitable for late instars

4

• guilds of fishes categorize feeding roles through
  a combination of what is eaten and where it is
  consumed, such as midwater versus benthic
  invertivores
• Relatively few fishes are herbivorous in the
  temperate zone
• most members of an assemblage fall into various
  categories of invertivores or piscivores
• Extensive functional specialization can be
  observed in fish mouthparts, digestive
  capabilities, and sensory modalities for
  detecting prey
• Other vertebrate predators
• Salamanders
• Crocodiles
• Otters
• Herons
• Diving Ducks/Predatory Ducks
• Mink

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Trophic Ecology
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Trophic Ecology
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Trophic Ecology
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Invertivore, Piscivore, Herbivore
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http//pond.dnr.cornell.edu/nyfish/Petromyzontidae
/sealamprey.html
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fe.html
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• How to we assess the flow of energy through a
  food web?
• What sort of components do we need to examine
• Think of Primary Production

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Terminology

• Standing crop vs. secondary production
• Standing stock
• biomass or energy per unit area at one point in
  time units are g/m2
• Production
• Biomass or energy produced per unit area per unit
  time g/m2/day
• Primary production vs. secondary production
• Net Primary Production Gross primary production
  - respiration
• Net primary production secondary production
• Numbers of studies
• secondary production lags far behind primary
  production

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Invertebrate Ecology -

• Important for understanding Population and
  community processes
• Secondary production
• living organic matter, or biomass, produced by an
  animal population during an Interval of time
• Net production of consumers above respiration and
  excretion
• The flow rate of biomass produced
• Units biomass or energy per unit area per unit
  time
• combines in one measurement
• Individual growth
• Population survivorship
• Secondary Production - most appropriate response
  to consider when trying to understand mechanisms
  of population or community regulation

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Secondary Production Methods

• Basic methods for secondary production
• Cohort Method
• Voltinism and Lifespan are the two key parameters
• Actual Cohort Methods
• Bugs tend to lay eggs at same time
• Grow at similar rates
• Emerge synchronously
• Calculation of productivity is easy from field
  samples
• Frequent quantitative sampling of the population
  over life cycle
• Data is used to construct true growth and
  survivorship curves
• Four Kinds of Cohort Methods
• Allen Curve
• Removal Summation Method
• Increment Summation Method
• Instantaneous Growth

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Secondary Production Cohort Method

• Points represent
• loss of individuals
• increase in individual size
• Standing stock at any time is
• Standing Stock Nt x Wt
• Production for the cohort Total area under
  curve
• Four methods are different ways of estimating
  this area
• Note if there is no mortality production No x
  Wf
• Standing Stock at end Nf x Wf Portion reaching
  final instar emerge

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Secondary Production Cohort Methods

• Allen Curve Method
• Graphical
• non-algebraic representation
• Sample frequently enough to decipher growth
  pattern between dates
• Area under the curve total cohort production
• Can use either an exponential curve or a smoothed
  curve connecting individual data points
• Can determine production between 2 dates
• Increment-summation (Pechen and Shushkina 1964)
• Sum of the growth increments over the lifespan of
  the cohort
• ? (mean WN)
• Can determine production between 2 dates, i.e. as
  it's added
• Rather than drawing a continuous curve
  successive N and W values can be used to
  calculate production between date
• The area of the rectangle defined by Y and Z can
  be calculated as N?W
• this equals production over ?t
• Total cohort production can be calculated by
  doing this over the whole time

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Secondary Production Cohort Methods

• Removal-summation (Boysen-Jensen 1919) -
  estimated mortality sum losses
• Basis - what Is produced eventually dies or is
  removed
• Production Is not accounted for until it is lost
  Equals trapezoid of X Y
• Calculated as ? (mean WN)
• Total Production is added by summing these areas
• Production Is not accounted for until it is lost

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Secondary Production Cohort Methods

• ?B the increase or decrease in standing stock
  during ?t is equal to the area Z X
• Actual production (YZ) during ?t is equal to the
  production lost (XY) plus ?B ( Z-X)
• Thus the increment Summation and Removal
  Summation Methods are just different ways of
  adding up the areas under the curves should
  give the same result

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Secondary Production Cohort Methods

• Instantaneous Growth Method
• Assumes and exponential increase in individual
  biomass
• Production is calculated at
• Production g ?t ?
• g ?t ln(Wt?t / Wt)
• ? (mean B) (Bt Bt?t)/2
• Bt NtWt

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Secondary Production Cohort Method

• Problems with the methods
• These are often viewed as the ideal method
  against which others are compared
• Assume that
• samples are collected from a population growing
  synchronously
• All hatch at an instant in time
• Growth is at the same rate
• Following the true survivorship curve and true
  growth curve
• We are following an apparent and not true
  survivorship and growth curve
• Some individuals are dying and some are growing
  into next instar even before all are hatched

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Concept of Production to Biomass Ratio P/ B

• Production (P) and mean standing stock biomass
  provides critical information about the
  production dynamics
• Cohort P/B and annual P/B provide different
  information
• Cohort P/B is the production of a real cohort
  divided by mean biomass for the length of time it
  takes a cohort to complete development
• This development time is called cohort production
  interval or CPI
• The Examples
• Cohort P/B is calculated by taking any estimate
  of P and dividing it by CPI or 5.6 and equals
  roughly 5
• The cohort P/B is related to the shapes of the
  growth and survivorship curves than to individual
  growth and is independent of time for a cohort to
  grow for hatching to emergence
• Usually varies from 2 8
• Annual P/B annual production divided by mean
  biomass over entire year
• Directly related to individual growth rate
• Annual mean B 50.4 / sampling dates (9) 4.58
• P/B 29.69/4.58 6.48 for removal summation and
  Units of P/B is /year
• TURNOVER TIME - THE AMOUNT OF TIME IT TAKES TO
  REPLACE THE BIOMASS OF THE POPULATION and is the
  inverse of Annual P/B

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Secondary Production Size-Frequency Method

• Most species are not a neat synchronous cohort
• An average size frequency distribution
  calculated from samples taken over a year will
  approximate the average survivorship of a
  hypothetical average cohort
• Analogous to the removal-summation method except
  that W?N values are based on changes between size
  groups rather than between sampling dates
• Assumes that larval development takes a year
• Benke Adjusted by 365/CPI multiplied by the size
  frequency calculation

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Secondary Production Quick Methods

• Several methods have been developed but require
  major assumptions
• Production estimated from mean standing stock
  biomass
• Since cohort P/B ratios are constant 5 one can
  assume an annual P/B of 5 for univoltine spp.
• Production estimated from emergence data
• In some situations this may be the only way what
  are they? And why?
• Production is estimated from maximum standing
  stock biomass
• Ratio of production to max biomass is often close
  to 1.5 but will need to add in CPI
• P/B ratio is estimated as Temp2/10 where temp is
  in oC
• This stinks and is very limited

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Magnitude of Production and Turnover

• Magnitude of production depends on
• The standing stock biomass
• The rate of biomass turnover or annual P/B ratio
• Since cohort P/B is 5
• The length of aquatic life or CPI is the primary
  determinant of annual P/B
• Production might be high because of
• High biomass alone
• High turnover (Short CPI) or a combination of
  these two
• Lentic Systems studied mostly Chironimids
• Midge 162 g dry wt/m2
• 10 50 g dry wt/m2 is normal and due to high
  biomass rather than turnover
• some estimates of annual P/B ratios ranged from
  2.9 36
• Due to short development times
• Some tropical midges develop in 5 days in warm
  water
• Assume high cohort P/B of 8
• Annual P/B 8 x 365/5 584 biomass turnover
  rate is less than a day
• Never reported but seems likely
• Lotic Estimates
• Total of 200 g dry wt/m2/year

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Applications of secondary production studies

• Allen paradox (Allen 1951)
• "Allen's Paradox" - Horokiwi Stream, NZ fishes
  require more invertebrate food than stream
  apparently can produce
• Horokiwi stream, New Zealand
• Benthos production Insufficient to support
  observed fish production based on ecotrophic
  coefficients and gross production efficiency
• Possible explanations

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The Allen Paradox Predator consumption

• Allen 1951 calculated that fishes in the Horkiwi
  Stream of New Zealand required 100 time more
  benthic prey biomass in a year than was available
• He calculated that benthic animals must have an
  annual P/B100
• Allens P/B was higher than obtained in estimates
  of secondary production of similar streams
• Estimates of weekly P/B needed to be 1 to meet
  predator removal and an annual P/B of 30 to meet
  dragon fly predation

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Explanations

• Part of the answer was the presence of multiple
  generations per year
• Most estimates for species that had life cycles
  lasting one year thus annual P/B were low
• When you account for CPI and chironomids you come
  out on top
• Import
• Drift from upstream areas
• Terrestrial sources
• Overlooked habitat
• Snags
• Hyporheos
• Meiofauna

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Applications of secondary production studies

• Determining the contribution of various food
  sources to secondary production rates
• Trophic basis of production studies (e.g. Benke
  and Wallace 1980)
• Proportion in diet ? contribution to production
  - must account for assimilation and production
  efficiencies
• NPE P/A
• AE A/I
• GPE AE NPIE
• Can determine major driving force from an
  energetics viewpoint
• Can determine minimum estimates of production of
  other food sources
• Can gain insights into changes in food quality
  and abundance available to organisms downstream