BIO120H1 Lecture Notes - Trematode Life Cycle Stages, Pesticide, Observational Study

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3 Feb 2013
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Obs studies no clear hyp or methodologies, easy to return noisy info
Experiments how a predator affects a prey
Controlled Experiments in lab under diff conditions ctrl all variables
Modeling approach complex math rep of nature pop growth as we see in future can
be modeled in diff ways
Carry cap eg :
Most would think ecology operating on bigger scale but inc work with cellular scale
Experimental Design:
Replicate: T absent or T absent higher mortality associated with present T
Is that significant or random chance? (only pick 2 ppl as a sample size?)
Need a bigger sample size
Replicating cedar creek minesota 5.5 m (100x)
Why replicate?
Not only do we need to replicate but also randomize (accounting for soil composition)
We can then assume all subject to soil variation
Dec in growth from fertilizer
Can’t make conclusions w/out control
Ctrl = none added
Fish study effect of hormone on fish what is the ctrl?
1. Act of putting hormone into it (need to inject also with saline water ctrl)
2. Stabbing of the syringe (catching and handling)
other ctrl is just to handle it (no stabbing syringe)
multiple controls for effect of hormone and the syringe
expctrls used to account for anything that may affect results
3 attributes to exp = generality, realism, and precision
can’t capture all 3
Triangle (generality, realism at the top and precision)
Lab exp precise control all envi variables can do it again and get exact results but
it’s not very realistic (not all org naturally live in this envi) , and not subject to all
processes low generality
Realism field experiments not precise if go to another pond and do same exp
need to account for pond differences, but we know it’s realistic field, also not general
take place at 1 place at one time may not apply to all of world (human large scale
studies adding nutrients to grasslands)
Exp usually try to maximize one of these
Amphibian populations want to know why as an ecologists for these deformities and
decreasing populations
Geography Australia 18 species of amphibs are extinct, and 23 threatened
Need for ctrl insects and maintaining ecosystems
Several hyp to explain why:
Pathogens? (parasites) spreading in amphib populations = ribeiroia inside gut of
waterbirds they defecate eggs into water
Miracidia effect snails effecting cercariae…
Ctrl’d experiment but not realistic (they live in ponds subject to all kinds of things
pollution, atm changes etc)
2 frogs exposed to parasites as you inc parasite exp more deformities (almost
80%) as well as dying increases (experimental evidence parasite affects amphib
Field Exp (to account for pollution?)
Frogs can absorb chemicals easily
Pesticide concentrations differed
Mesh enclosure keep parasites but diff ponds with concentration
Small mesh that kept parasites out (big mesh allows them in)
Left diagram parasites cause? no effect of parasite regardless of environment
Right envi cause? interaction effect effect of parasite
Hyp pesticides dec the ability of frogs to resist inf by parasite
What is it about pesticides that allow for greater deformities?
Lab exp 2 controls
1 is nothing added
2 is added solvent that pesticides are dissolved in
low and high pesticides
# of immune cells dec w/ pesticides (therefore they decrease immune resp)
now showing at a mechanistic lvl - that pesticides causing more susceptibility of
can’t use any single factor as explanation bad for policy
caused by complex factors
Observational study Amphib pop UV light had effect
ponds around farms releasing nitrates or not at diff elevations
farms higher elevations exposed to more UV light
interaction effect
no nitrate in pond doesn’t matter what elevation pond is at
w/ nitrate if high elevation(uv) survive at lower rate vs those w/out
UV effects in only in certain circumstances
So what is causing the declines?
Its complex
Interaction of what is happening at landscape lvl, use of fertilizers, pesticides, solar
Parasites that infecting frogs and also food web
Parasite moving thru bunch of hosts
If you’re coming up with solns it will be complex to regulate