Ecology Employs the Scientific Method
induction observation hypothesis or model experiment prediction
deduction 60 1 What is an hypothesis? An hypothesis is an idea
about how theworld works: e.g., Frogs sing on warm nightsafter
periods of rain. We often wish to understand twocomponents of such
a phenomenon: how? (encompasses physiologicalprocesses) [how does a
frogrespond to temperature andrainfall?] why? (encompasses costs
andbenefits of the behavior to theindividual) (how to answer..) 61
2 Experiments test predictions.
Hypotheses generate predictions: if observations confirm the
prediction, the hypothesis isstrengthened (not proven) if
observations fail to confirm the prediction, the hypothesis
isweakened (or rejected) Best tests of hypotheses are experiments:
independently manipulate one/few variables (or trick frogsinto
singing on a wrong night) establish appropriate controls 62 3 Some
Potential Pitfalls
A correlation between variables does not establish causation. Many
hypotheses cannot be tested by experimental methodsbecause: the
scale is too large: patterns may have evolved over long periods the
spatial extent is too large for manipulation causal factors cannot
be independently tested 63 4 Some Approaches to Difficult
Problems
Mathematical models are powerful tools: researcher portrays system
as set of equations model is an hypothesis and yields predictions
that can be tested;examples include: models of disease spread
models of global carbon Microcosms are sometimes useful: microcosms
replicate essential features of the system in a laboratoryor field
setting 64 5 Microcosms communities of freshwater
invertebrates
6 Hypothesis: bird predation on insect herbivores reduces the
amount of leaf area consumed. Field Study: construct bird-proof
cages to allow insects freedom of movement. 7 Yes: insects
increased 70% -> leaf area % lost increased 22% to 35%
So? Leads to important question: Will the decreases in bird
populations caused by fragmentationof forests in the eastern US and
elsewhere result in increasedinsect damage to forests? Other
questions? 67 8 Statistics and scientific rigor
True of false: you can prove anything with statistics You cannot
prove anything with statistics Statistical analysis attaches a
level of confidence toconclusions that can be drawn In ecology as
in all sciences we search for confidentconclusions, not provable
truths Rigorous (accurate, exhaustive) Science
Based on conclusions that are the results of investigationscarried
out with the express purpose of deriving thoseconclusions Based on
conclusions to which a level of confidence can beattached, measured
on an agreed scale -- note Boxes 1.2 and 1.3 and 1.4 Ecology in
practice Lets examine some more real research programs
3 main points Ecological phenomena occur at a variety of scales
Ecological evidence comes from a variety of different sources
Ecology relies on truly scientific evidence and the application
ofstatistics Brown troutin NZ Effects on individuals,populations,
communitiesand ecosystems Understanding enhanced(naturally) when
linksbetween all these levels aremade clear(er) Brown trout (Salmo
trutta) introduced to NZ in from Europe Much can be learned
bycomparing ecology ofstreams containing troutwith those occupied
bynon-migratory native fish inthe genus Galaxias Question: is the
nativeGalaxias (on the right)hiding from the introducedpredator?
Start here Brown Trout: examining the individual level
What are the consequencesfor invertebrate feedingbehavior? Mayfly
nymphs of variousspecies: are theredifferences in their
activityrhythms depending onwhether they are inGalaxias or trout
steams? In a Galaxias stream: activeboth day and night In a trout
stream: daytimeactivity most reduced Brown Trout: examining the
individual level
Trout rely primarily onvision to capture prey Galaxias rely on
mechanicalcues Thus: invertebrates in atrout stream more at risk
ofpredation during daylighthours Conclusions derived fromboth
readily controlledconditions of a labexperiment and from themore
realistic and morevariable circumstances of afield experiment Brown
trout: population level
How does brown trout impact the distribution of native fish? At
each site, a variety ofphysical variables weremeasured Using
statistics, ?: whichphysical variables (if any)distinguished one
type of sitefrom another ? A: Galaxias restricted to sitesupstream
of waterfalls [cannotbe climbed by trout]. Why?Direct predation by
trout onnative fish below waterfall 198 sites selected. Streams of
similardimensions chosen atrandom in each of 3tributaries from each
of 8subcatchments of the river Sites: (1) no fish; (2)Galaxias
only; (3) trout only;(4) both Galaxias and trout Brown trout:
community level
? Do these changes have community consequences thatimpact other
species ? Do trout affect the streamfood web differently fromthe
displaced Galaxias? 3 treatments established (no fish;Galaxias;
trout) at naturallyoccurring densities in severalrandomized blocks
in a stretch ofstream. Algae and invertebrates and then fish
introduced andthen algae and invertebratessampled Trout ->
lowerinvertebrates -> higheralgae Brown trout: ecosystem and
energy flow
? Will the rate at whichradiation energy is capturedthrough
photosynthesis bythe algae be greater in thetrout stream? Annual
net primaryproduction (rate of productionof plant i.e. algal
biomass)six times greater in the troutstream than in the
Galaxiasstream ? In the trout stream, will thehigher primary
productionbe associated with a fasterrate of uptake by algae
ofplant nutrients (nitrate,ammonium, phosphate)from the flowing
streamwater? Also yes. Conclusion: a trophic cascadeis responsible
for the patternsobserved at the ecosystemlevel Succession What is
the natural successional sequence of plants?
From this understanding:an artificial manipulationcan be planned;
historicalrecords can be examined Ecological succession what is it?
Excellent place to study:old agricultural fields inthe eastern
US,abandoned by farmers What have the studies atCedar Creek
illustrated? 22 fields at differentstages in an
old-fieldsuccession(abandonedbetween 1927 and1982) were surveyedin
1983; 22snapshots Correlations! ?: are thecorrelations in (a) (d)
the result of aneffect of field age or is the causalagent nitrogen
withwhich age iscorrelated? Artificial experiments: search for
causation
6 replications. Two fields (one abandoned for 46 yrs; one for 14
yrs);nitrogen manipulations Questions: (1) do patches receiving
different supply rates of nitrogen becomeless similar in species
composition over time? Yes. But 10 years later, plots receiving
different amounts of N haddiverged in species composition. The
greater the difference in N input,the greater the divergence (2) do
patches receiving similar supply rates of nitrogen becomemore
similar in species composition over time? At the start, different.
After 10 years, plots within the two fieldssubjected to similar
rates of N had become remarkably similar Artificial experiments:
search for causation
Time itself is not the only cause of successional changes inspecies
composition Differences in available nitrogen cause successions to
diverge;similarities cause them to converge much more quickly
thanthey would otherwise do Time (= opportunity to colonize) and
nitrogen are clearlyintimately intertwined. More unanswered
ecological questions. Know the Hubbard Brook study A modeling
study: why Asian vultures were heading for extinction?
Vulture populations were declining by 22 to 50 %each year Loss of
vultures ? And ? Common element: each had suffered fromvisceral
gout (uric acid accumulation) followed bykidney failure. Why?
Carcasses of domesticanimals treated with diclofenac were lethal
tocaptive vultures (diclofenac is a non-steroidal anti-
inflammatory drug (NSAID) and when given toworking animals it can
reduce joint pain and sokeep them working for longer. ) Other
elements? A modeling study: what proportion of carcasses (C) would
have to contain lethal doses of diclofena to cause the observed
population declines? Physical and Biological Principles 1
Ecological systems are physical entities: life builds on physical
properties and chemical reactions ofmatter all processes obey the
physical laws of thermodynamics (?) but life still pursues many
varied options 54 25 Physical and Biological Principles 2
Ecological systems exist in dynamic steady states: despite
substantial fluxes of energy and matter, ecologicalsystems remain
more or less unchanged gains and losses are more or less balanced
steady states apply to fluxes of materials and energy at alllevels
of ecological organization 55 26 Physical and Biological Principles
3
The maintenance of living systems requires theexpenditure of
energy: life forms exist out of equilibrium with their
physicalenvironment losses must be replaced by energy or materials
procured bythe organism the price of maintaining a dynamic steady
state is energy 56 27 Physical and Biological Principles 4
Ecological systems undergo evolutionary changethrough time:
physical and chemical properties, and physical laws, are
immutable,but life exhibits remarkable diversity structures and
functions of organisms (adaptations) areevolutionary products of
natural selection, recognized by CharlesDarwin complexity builds
upon complexity 57 28 Costa Rican mantids cryptic coloration
58 29 Summary Ecology is the scientific study of the natural
environment and the relationships oforganisms to one another and to
their surroundings. Ecologists study a variety of organisms and
processes, spanning a wide range of spatialand temporal scales.
Individual organisms live in habitats and have unique niches
reflecting conditionstolerated and functional role. All ecological
systems obey natural laws and are subject to evolutionary change.
Ecologists employ the scientific method. Humans are part of the
global ecosystem and have created numerous
environmentalproblems.Solving these problems will require
application of ecological principles. 71 30
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