Planning An Exological Study Flashcards
What are the general steps to planning an ecological study
Identify research question
Define hypothesis and identify assumptions
Design survey/experiments
Collect data/samples, carefully record results
Analyse & interpret data to test hyp
Present results
What are two approaches to collecting data
Surveys (correlational study)
Record what occurs in natural system
Experiments
Allows to standardize certain aspects that we are not interested in / remove variability
Counts/measurements taken from samples are estimates - different from true populations because of
Natural heterogeneity/ variability
Sampling/ measurement error
Sampling design is critical why do we need to consider what we need to measure
Changes in relative density may occur
Temporal change
Comparions (before/after pollution)
Spatial variation
What prior info do you need on a species before sampling
Where are they (planktonic/benthic what depth)
What size are they - mesh size
Behavior- can they escape capture
Abundance
- how many sampling units
- how big sampling units
- informed by pilot survey or literature
What are different placement types of sampling units
Random sampling
Systematic sampling
Stratified random sampling
What’s random sampling
Every possible combination of sampling units has an equal and independent chance of being selected.
Problems with random sampling
Most organisms aren’t randomly dispersed
Distribution is patchy or related to environmental gradients
Random sampling inefficient, large variation between samples, poor precision.
What’s systematic sampling
The initial sampling unit is randomly selected
All other sample units spaces at uniform intervals.
Are representative of the area
Examples
- transect sampling
- temporal systematic sampling (sample taken every 2 weeks)
What’s stratified random sampling
Population is subdivided into subpopulations of known sizes.
A simple random sample of at least two units is drawn from each sub population
What needs to be considered for the timing and frequency of sampling
Influences of tide/ weather
Day/night differences
Differences between life stages adults/juveniles/larvae
Behavior- immigration, reproduction
What are the two plotless techniques
Line transect method
Distance method
How does the line transect method work
Distance at which organisms are sighted from the transect line are used to estimate density.
Transects can be made on foot, land vehicle, boat, plane.
How does distance method work
Two approaches
1. Distance between a randomly selected organism and it’s nearest neighbor is measured
2. Distance between a random point and the nearest organism is measured
The greater the density the smaller the summed distance
