Animal Population Sampling Methods

Recap

• Last week's lecture focused on plant population sampling methods
• The quadrat, line intercept, belt transect and point-frequency intercept methods were discussed

Animal Population Sampling Methods

• Animal populations are sampled through trapping and collecting, marking, aging, sex determination, home range and territory determination, and estimating numbers.

Trapping and Collecting

• Several methods are used for trapping and collecting insects, aquatic organisms, soil organisms, small animals in vegetation, and birds and mammals.
• Diurnal insects: Aerial nets, heavy duty sweep nets, and ultraviolet light traps are used.
• Nocturnal insects: Mercury-vapor light traps, Malaise traps and quadrats or transects.
• Aquatic Organisms: Dip nets, bottom nets, wire-basket scraper nets, plankton towing nets, trawl nets, and seine nets.
• Soil Organisms: Varying funnel methods like Berlese or Tullgren funnels.
• Small Animals in Vegetation: Sweep nets with frames, beating vegetation with sticks and canvas collecting trays, and drag nets.
• Birds and Mammals: Cannon nets, mist nets, live traps (wood or wire), snap traps, Sherman traps, and traps with sticky surfaces, pitfall traps.

Marking Animals

• Marking animals allows researchers to track individuals over time
• This information is used to estimate population sizes, track movements, and study behavior

Marking Methods

• Arthropods and Snails: Quick-drying cellulose paint
• Fish: Strap tags, stream or pennant tags, plastic tags, acoustic tags, and clipping fins.
• Frogs, Toads, Salamanders: Toe clipping.
• Birds: Serially numbered aluminum bands, cellulose or aluminum colored bands, toe clipping, fur clipping, ear notching, tattooing, and dying plumage.
• Small Mammals: Toe clipping, fur clipping, tattooing.
• Larger Animals: Fur clipping, tattooing, dyes, GPS collars, strap tags, plastic discs attached to ears, and radio or GPS collars.
• Note: Some methods are invasive, unethical, and have largely been phased out.

Sampling

• Most commonly used census technique
• Two basic approaches: Area-based and non-area-based

Area-based Sampling

• Usually involves sampling during a single time period
• Involves plots and plotless sampling
• Basic equation: P = D x A
  • P = Population number
  • D = Density (number of animals per unit area)
  • A = Surface area (i.e.total area occupied by animals)

Plot Sampling

• Density calculated using D = y/a
  • D = number of animals per unit area
  • y = number of animals in a sample plot
  • a = area of the sampling plot
• Follows the sampling methods of Quadrats and Standard Strip Sampling

Standard Strip Sampling

• Narrow, long plots with a fixed width
• Equation used to calculate density: D = y/LW
  • D = number of animals per unit area
  • y = number of animals in a sample plot
  • L = length of strip
  • W = width of strip
• y in the equation is the mean calculated from each transect or plot

Non-Area-based Sampling

• Usually involves sampling at more than one time period
• Involves Change in ratio and Regression sampling methods
• Plotless sampling

Non-Area-based: Selective Removal

• Involves removing individuals from the population — often influencing ratios of age, sex, or types of animals
• Considers changes in ratios over two sampling periods
• Assumptions:
  • Population is stationary
  • Probability of capture is equal for each animal
  • Probability of capture remains constant between sampling periods
• Challenging to meet these assumptions

Non-Area-based: Selective Removal Equation

• Used to estimate the population at the time of the first survey (N1)
• N1 = (Tx - V2 x T) / (V2 - V1)
  • N1 = Population estimate at the first survey time
  • V1 = Ratio of one variable during the first survey
  • V2 = Ratio of the same variable at the second survey
  • Tx = Number of animals of variable x that were added or removed between surveys
  • T = Tx + Ty, where Ty = number of animals of variable y (second gender or age etc.) that were added or removed between surveys