Population Ecology and Habitat Use

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Population Ecology and Habitat Use

• (Autecology)

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Announcements and Such

• Assignment 1 due today!
• Black Earth next week Come prepared to leave at
  1230 pm (Back 5-530pm)
• Readings/Lab Handout on side wall
• Other?

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What is Population Ecology?

• Ecology is the study of the interactions that
  determine the distribution and abundance of
  organisms Charles Krebs
• Population represents one level on which to
  approach ecology
• Other levels???
• Population level interactions
• Demographics

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What is a Population?

• A population is a group of fish of the same
  species that are alive in a defined area at a
  given time (Wootton 1990)
• Area can be arbitrary, physical, or genetic
• Stock population subject to fisheries
  management

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Gene Pools

• Distinct gene pools distinct biological
  populations.
• Several may be present in one area
• Gel Electrophoresis used to estimate differences
  in allele frequency
• Morphology also used to distinguish populations

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Population Density

• On rare occasions, density can be measured
  directly
• Small enclosed systems
• Migration
• Usually, density is assessed from samples
• Eggs estimated with quadrats
• Pelagic larvae sampled with modified plankton
  nets
• Juvenile and adult fish with nets, hook and line,
  or electrofishing

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Mark/Recapture
n1
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Catch per Unit Effort

• Density is reduced by fishing and natural
  mortality while it is increased by stocking and
  recruitment.
• If two samples are taken with the same fishing
  effort over a short time period, mortality,
  stocking, and recruitment are negligible

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Catch per Unit Effort
Assume probability of capture is constant
Then N n12/(n1-n2)
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Population Change
Immigration
DENSITY
Mortality
Natality
Emigration
There are a number of ways to measure growth rate
and mortality.
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Patterns of Mortality

• Eggs and larvae suffer the largest losses

2 cohorts each produce 10,000,000 eggs 90.5
survivorship/day yields 24,787 survivors at 60
days 95.1 survivorship/day yields 497,871
survivors at 60 days
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Density Dependence
Rate of Change (per capita)
Population Density
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Density Dependence
Recruitment
Stock (Parental Cohort)
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Fish Populations in Wisconsin

• Populations of fish are distributed based
  primarily on
• Type and amount of food available
• Temperature
• Oxygen demand
• Flow velocity
• Tolerance of pollution

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Food and Thermal Niches
Largemouth bass
Prey Weight (Relative)
Green Sunfish
Bluegill
Temperature (Celsius)
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Distribution in Lakes Temperature
20-30 C
4-20 C
4 C
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Distribution in Lakes Temperature

• Habitat separated and competition reduced by
  stratification
• Bass and Bluegill (eurytherms) in the epilimnion
• Pike, Perch, and walley (mesotherms) in the
  metalimnion
• Lake Trout (stenotherms) in the hypolimnion
• Competition in winter more intense

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Movement

• Fishes may move about the water column or around
  various depths for
• Foraging shallow water cooler at night plankton
  moves about at night
• Spawning nest sites often in shallows

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Oxygen Demand

• Eutrophic lakes can have anoxic hypolimnions in
  the summer
• Primarily affects coldwater species (i.e. trout)

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Lotic Systems
Here be Floodwaters
Watershed Boundry
Flowing Water
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Distribution in Rivers

• Systems zone longitudinally

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Fish Distribution in Rivers

• Headwaters are colder, faster, and have limited
  primary producers (Trout, Sculpin)
• Transitional zones are generally variable, and
  contain a smattering of species (Variable)
• Deposition zones are warm, slow, and often times
  turbid (from sediment load) and polluted (from
  proximity to agriculture and urban areas) (Carp,
  Centrachids)

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From Baltz et al. 1982
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Diversity Within A Reach

• Riffles (scuplins, stonerollers, darters
  smaller fish)
• High flow velocity
• Well oxygenated
• Rocky substrate
• Generally shallow
• Eddies/pools (trout, larger fish)
• Low flow velocity
• Also well oxygenated
• More cover, usually behind some large substrate
  or debris
• Generally deep

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Lab Identifying Fish

• Dichotomous keys
• Will always present you with two choices, e.g.
• Body noticeably covered with scales Go to 2
• Scales not covering body or too small to be seen
  Go to 12
• Follow the choices until you have reached a
  species!
• Beckers Fishes of Wisconsin tome provides our
  class with our keys

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Things to keep in mind

• Some choices are obvious (i.e. jaws vs. jawless).
• Many others require careful scrutiny
• Lateral line has 45-48 scales (Library Carp,
  Nerdus poindexterii)
• Lateral line has 50-56 scales (Northern
  Shiteater, Carpus stinkostomus)
• Finding the lateral line, counting scales,
  identifying mouth partsstruggling through the
  keys now will save you strife later

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Secondary Keys

• www.wiscfish.org
• Non-dichotomous harder to narrow down to
  species, easier to get to a few choices
• Actual photos, detailed attribute descriptions
  help identify species
• Requires a computer, not good for field IDs
• Google.com
• Theres bound to be something there

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Black Earth Creek Field Trip

• Goals
• - Illustrate aspects of fish ecology in a
  Wisconsin trout stream
• - Collect fish and stream habitat data to use in
  research paper
• - Demonstrate various field methods for fish
  collection
• - Experience the field portion of research
• Quick Question How many people have waders?

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Whats Ecology -is the study of the distribution
and abundance of living organisms and how the
distribution and abundance are affected by
interactions between the organisms and their
environment (Krebs).
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Metrics!

• Habitat
• Reach length
• Width
• Depths
• Velocity
• Substrate
• Canopy cover
• Land width
• Buffer width
• Undercut

• Fish
• Length
• Weight
• Species
• Number
• Sampling Effort
• Diet
• Method of Sampling

Two teams everyone works on both teams!
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How does habitat influence fish community?
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Defining Geomorphic Stream Units
Undercut Bank
Riffle
Pool
Run
Goal is to sample at least 6 different units!
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Notice how they are positioned
ANODE (business end)
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Use the current(s) to your advantage!!
Lead fish right to your netters
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Moving Block Nets 2 people
HOW TO SET UP
Electrofishing
5 people
Fish can be released down stream of
electrofishing crew
Workup Station
3 people
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Stream habitat measurements
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Flagging transects 2 people
Flow Velocity
1 person
Measure thalweg, depth, width 4 people
Data Recorders- MOST IMPORTANT!!!
2 people