Field Experiment

Doing Fieldwork

  • major part of ecology

  • collect samples from nature, bring back to lab, analyze them

Lab vs Field Studies

  • lab studies are controlled and very useful once you have identified variable so of interest

    • may miss out on identifying important interacting variables

  • field studies have more realism than lab studies, and they are better for examining how the environment affects variables of interest

    • harder to control, and unsuitable conditions for parts of the year

    • can’t change water levels from precipitation

    • must be ready at certain times

tips for successful fieldwork

  • practice your data-collection before you go into the field

    • make sure that you do not forget any equipment, and you are efficient with your time

  • take random samples

    • can sample randomly, haphazardly (may miss out on certain individuals that are hard to find)

    • divide up into grid and then use a random number general for which square

    • made effort to choose those with good variation (more representative) - typical to population

  • be consistent in how you measure variables

    • same person measure every individual or 2 people measure some from each sample

    • measure from same location in plant

    • angle light sensor in same way

    • agree on what represents a species — treat it the same

    • knock of dirt from roots

  • make notes on what you are seeing — take photos of your activities

    • can explain why measurements are different (record to help explain unexpected variations)

    • good for explaining methods — good for posters

  • use controls for your experiments

    • controls become another “treatment group”

    • manipulate individuals — know it’s because of our changes not something else

  • have a backup plan, just in case your original plan cannot be done

    • weather, equipment

dress rehearsals: make sure you are ready

  • sometimes, what you are measuring on an individual may be affected by something other than the variable of interest

    • if you notice something that could affect the measurement on that individual, make note of it as an irregularity (Tim’s word — fine for this class)

    • this could be grounds for excluding it from the analysis later

  • example: you are measuring growth of a plant at different temperatures and you see that the plant has a parasite

    • that plant is probably shorter than you’d predict based on its temperature

    • good reason to exclude from analysis

    • can remove it from analysis

set an internal deadline that is at least 2 days before the due date so that you can look over each others’ work

elect a group leader who will initiate communication, put things together, and talk to Tim if the group dynamics are a problem

organism → populations → communities (potential for interaction; overlap in space and time)→ ecosystem (abiotic too) → biosphere (all components of Earth)


This project:

  • develop your own research question on how the environment of a soil affects its microbial community

  • will be looking at how environmental differences affect species richness (the number of different species) of microbes (e.g. yeast or bacteria) that form colonies that can be seen with a naked eye after they have been allowed to grow in culture for a few days

  • you will collect your own soils from 2 different locations of your choice that you think will have differences in microbial diversity

    • those soils have their own growth history

    • in the previous season, they were used to grow different types of crop

    • be sure to note where the soil came from!

    • you will also have a “control” soil, which came from a gardening centre

  • meet group, decide on research question, think about where you should go to collect your soil

    • why do you think they would have a difference?

    • develop a hypothesis for your experiment

    • TA’s will show you how to collect soil samples and make notes about the environmental conditions your soil experienced during collection

  • second session: will isolate the microbes from the soils you had decided to compare (remember to bring your soil samples to the lab!)

    • will use gravity-fed sedimentation to isolate microbes from the soil, and then you will spread your inocula on Petri dish

    • during the time that gravity is separating the microbes from the soil, read up on what sort of microbial colonies you can expect to find next week


different species (even different microbial species) have different environmental needs to grow successfully

  • some species require certain nutrients that could be in low supply

  • in many soils, nitrogen is often one of those nutrients that is in low supply

  • some plants are able to “fix” nitrogen, making it available for the soil community

  • you might find that microbes are more abundant in areas with nitrogen — you might find that some species dominate habitats where there is a good supply of nutrients (e.g. decomposing material)

    • there may be a lot of microbes, but not very high species richness

    • consider moisture levels, distance to foot traffic, how hard-packed the soil is


Lab 1

why are you picking those locations?

  • temperature, salinity, or moisture levels

  • diversity of samples you see on plant

  • is there decomposing material nearby?

  • think about what was grown there

NA: nutrient agar

NA + P + A: nutrient agar plus penicillina dn streptomyocin (only eukaryote)


choose a larger volume than what you need

  • put in selectino process

  • random, haphazard, targeted (centre, this one is under a dead raccoon)


familiarize yourself with the available equipment

decide on a research question: hypothesis, what will you measure

  • trowel and bag (mostly)


2 soils of your choice + potting soil + water

3 soils of your choice + water

  • soil moisture (near river and field) — a lot of other variables that are inconsistent

    • think about something close and then 5 from river