Download Chapter 1: Introduction - Green Resistance

Welcome to BIOL 207 – General Ecology
Fall 2010/2011
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www.greenresistance.wordpress.com
Know that site.
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Extra Credit
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Index cards for chapter 1?
Remember: we’re using a new book this semester
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Chapter 1: Introduction
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“Where we humans fit in a less than perfect world is a
judgment each of you must make, guided by your
own sense of values and moral beliefs. Regardless of
your own stand, it will be more useful to you and to
human kind in general if your judgment is informed
by a scientific understanding of how natural systems
work and the ways in which humans are a part of
the natural world.”
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other important questions
 what is ecology
 what do ecologists do
 what are ecologists interested in
 where did ecology emerge from in the first place
 ... what is its relationship to my life?
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What is Ecology? …. Oikos = home
“By ecology, we mean the body of knowledge concerning
the economy of nature -- the investigation of the total
relations of the animal both to its organic and to its
inorganic environment; including above all, its friendly
and inimical relation with those animals and plants
with which it comes directly or indirectly into contact -in a word, ecology is the study of all the complex
interrelationships referred to by Darwin as the
conditions of the struggle for existence.”
Ernst Haeckel, 1870.
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So, what is ecology?
 Ecology is the science by which we study how organisms
(animals, plants, and microbes) interact in and with the natural
world.
 in that case - ecology is the oldest science!
 early ecologists were applied ecologists. how so?
 ecology is also a ‘pure’ science - understanding for the sake of
understanding
 ecologists strive to develop an understanding of very basic and
apparent problems in a way that recognizes the uniqueness and
complexity of all aspects of nature but seeks patterns and
predictions within the complexity
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Ecology - A Science for Today
 We have a great need for ecological understanding:
 what are the best policies for managing our environmental
support systems -- our watersheds, agricultural lands,
wetlands?
 we must apply ecological principles to:
 solve or prevent environmental problems
 inform our economic, political, and social thought and practice
Example?
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So what do ecologists do?
 They try to explain and understand
 Two different classes of explanation in biology: proximate and
ultimate
 Proximate explanation: what is going on ‘here and now’
 The present distribution and abundance of a particular species of bird
may be ‘explained’ in terms of the physical environment that the bird
tolerates, the food it eats, and the parasites and predators that attack
it
 Ultimate explanation: answer in evolutionary terms
 How did this bird come to have these properties that now govern its
life…
 Ecologists must describe before they explain…
 Ecologists also try to predict what will happen to x under y
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Scales, diversity, and rigor
 Ecological phenomena occur at a variety of scales
 Ecological evidence comes in a variety of different sources
 Ecology relies on truly scientific evidence and application of
statistics
Questions of Scale: Ecological Systems
Large and Small
 Individual Organism (“No smaller unit in biology ... has a
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separate life in the environment...”)
Population (many organisms of the same species living
together)
Guild (a group of populations that utilizes resources in
essentially the same way)
Community (many populations of different kinds living in
the same place)
Ecosystem (assemblages of organisms together with their
physical environment; community + physical environment)
Biosphere (the global ecosystem, all organisms and
environments on earth)
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ecological
systems
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Ecological systems… human view
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Perspectives of Ecologists: Organism
Approach
 How do form, physiology, and behavior lead to survival?
 Focus is on adaptations, modifications of structure and
function, that suit the organism for life in its environment:
 adaptations result from evolutionary change by natural
selection, a natural link to population approach…
? - Why are trees the dominant plants in warm, moist
environments – and shrubs the dominant plants in regions
with cool, wet winters and hot, dry summers?
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Perspectives of Ecologists: Population
Approach
 What determines the numbers of individuals and their
variations in time and space?
 Focus is on processes of birth and death, immigration and
emigration, influenced by:
 the physical environment
 evolutionary processes
 interactions with other populations, a natural link to
community approach…
? – Why have mosquitoes increased in number and in extent?
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Perspectives of Ecologists: Community
Approach
 How are communities structured from their component
populations?
 Focus is on the diversity and relative abundance of different
kinds of organisms living together, affected by:
 population interactions, promoting and limiting coexistence
 feeding relationships, responsible for fluxes of energy and
materials, a natural link to ecosystem approach...
? – what is the relationship between birds, crops, and insects?
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Perspectives of Ecologists: Ecosystem
Approach
 How can we account for the activities of populations in the
common “currencies” of energy and materials?
 Focus is on movements of energy and materials and
influences of:
 organisms large and small
 climate and other physical factors, including those acting on a
global scale, a natural link to biosphere approach...
? – movement of Nitrogen… ?
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Perspectives of Ecologists: Biosphere
Approach
 How can we understand the global movements of air and
water, and the energy and chemical elements they contain?
 Focus is on the global circulation of matter and energy,
affecting:
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distributions of organisms
changes in populations
composition of communities
productivity of ecosystems
? – climate change ?!
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Questions of scale: time scales
 Ecologists also work on a variety of time scales
 Ecological Succession – the successive and continuous
colonization of a site by certain species populations,
accompanied by the extinction of others
 Can be studied from weeks (decomposition?) … to thousands
of years (ice age to present)
 Migration
 Can be studied in butterflies (days…) or in forest trees
(thousands of years … or decades)
Systems and Processes:
Dimensions in Time and Space
 Nothing in nature is static: anything we can measure
(conditions, number of organisms) exhibits variation.
 Variation has temporal and spatial components.
 Variation in each measurement has a characteristic scale; for
the same degree of change:
 air temperature varies over hours
 ocean temperature varies over weeks or months
(weather vs climate?)
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Temporal Variation
 Consider two kinds of temporal variation:
 predictable, cyclic variations (daily, seasonal)
 unpredictable, irregular variations
 A temporal “rule of thumb”:
 the more extreme the condition, the less frequent (compare cold
fronts and hurricanes) … but…
 but frequency and severity are relative terms that depend on the
organism!
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Spatial Variation
 Spatial variation occurs at very small (forest sunflecks)
and very large (latitudinal variation in solar flux) scales.
 Scale of variation importance is a function of the organism:
 the two sides of a leaf are different to an aphid
 a moose eats the whole leaf, aphid and all
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Time and Space
 A few generalizations:
 moving organisms experience spatial variation as temporal variation
 the faster an individual moves:
 the smaller the scale of spatial variation
 the more quickly it encounters new environments
 the shorter the temporal scale of variation
 spatial and temporal scales are correlated
 frequency is inversely related to extent/severity
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Diversity of ecological evidence
 Observations and field experiments
 Controlled Laboratory experiments
 Simple laboratory systems
 And mathematical models
Ecology Employs the Scientific Method
induction
observation
hypothesis
or model
experiment
prediction
deduction
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What is an hypothesis?
An hypothesis is an idea about how the
world works:
 e.g., “Frogs sing on warm nights
after periods of rain.”
We often wish to understand two
components of such a phenomenon:
 how? (encompasses physiological
processes) [how does a frog
respond to temperature and
rainfall?]
 why? (encompasses costs and
benefits of the behavior to the
individual) (how to answer..)
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Experiments test predictions.
 Hypotheses generate predictions:
 if observations confirm the prediction, the hypothesis is
strengthened (not proven)
 if observations fail to confirm the prediction, the hypothesis is
weakened (or rejected)
 Best tests of hypotheses are experiments:
 independently manipulate one/few variables (or trick frogs
into singing on a ‘wrong’ night)
 establish appropriate controls
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Some Potential Pitfalls
 A correlation between variables does not establish causation.
 Many hypotheses cannot be tested by experimental methods
because:
 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
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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 laboratory
or field setting
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Microcosms…
communities of freshwater invertebrates
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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.
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Yes: insects increased 70% -> leaf area %
lost increased 22% to 35%
 So?
 Leads to important question:
Will the decreases in bird populations caused by fragmentation
of forests in the eastern US and elsewhere result in increased
insect damage to forests?
Other questions?
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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 to
conclusions that can be drawn
 In ecology –as in all sciences – we search for confident
conclusions, not provable truths
Rigorous (accurate, exhaustive) Science
 Based on conclusions that are the results of investigations
carried out with the express purpose of deriving those
conclusions
 Based on conclusions to which a level of confidence can be
attached, measured on an agreed scale
 -- note Boxes 1.2 and 1.3 and 1.4
Ecology in practice
 Let’s 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 of
statistics
Brown trout
in NZ
 Effects on individuals,
populations, communities
and ecosystems
 Understanding enhanced
(naturally) when links
between all these levels are
made clear(er)
 Brown trout (Salmo trutta)
– introduced to NZ in 1967
from Europe
 Much can be learned by
comparing ecology of
streams containing trout
with those occupied by
non-migratory native fish in
the genus Galaxias
 Question: is the native
Galaxias (on the right)
hiding from the introduced
predator?
Brown Trout: examining the individual level
What are the consequences
for invertebrate feeding
behavior?
 Mayfly nymphs of various
species: are there
differences in their activity
rhythms depending on
whether they are in
Galaxias or trout steams?
 In a Galaxias stream: active
both day and night
 In a trout stream: daytime
activity most reduced
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Brown Trout:
examining the individual level
 Trout rely primarily on
 Conclusions derived from
vision to capture prey
both readily controlled
conditions of a lab
experiment and from the
more realistic and more
variable circumstances of a
field experiment
 Galaxias rely on mechanical
cues
 Thus: invertebrates in a
trout stream more at risk of
predation during daylight
hours
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Brown trout: population level
How does brown trout impact the distribution of native fish?
 198 sites selected.
 At each site, a variety of
physical variables were
measured
 Streams of similar
dimensions chosen at
random in each of 3
tributaries from each of 8
subcatchments of the river
 Sites: (1) no fish; (2)
Galaxias only; (3) trout only;
(4) both Galaxias and trout
 Using statistics,  ?: which
physical variables (if any)
distinguished one type of site
from another ?
 A: Galaxias restricted to sites
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upstream of waterfalls [cannot
be climbed by trout]. Why?
Direct predation by trout on
native fish below waterfall
Brown trout: community level
? Do these changes have community consequences that
impact other species ?
 Do trout affect the stream
 Trout -> lower
food web differently from
the displaced Galaxias?
invertebrates -> higher
algae
 3 treatments established (no fish;
Galaxias; trout) at naturally
occurring densities in several
randomized blocks in a stretch of
stream. Algae and invertebrates
– and then fish introduced and
then algae and invertebrates
sampled
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Brown trout: ecosystem and energy
flow
 ? Will the rate at which
 ? In the trout stream, will the
radiation energy is captured
through photosynthesis by
the algae be greater in the
trout stream?
higher primary production
be associated with a faster
rate of uptake by algae of
plant nutrients (nitrate,
ammonium, phosphate)
from the flowing stream
water?
 Annual net primary
production (rate of production
of plant – i.e. algal – biomass)
six times greater in the trout
stream than in the Galaxias
stream
 Also yes.
 Conclusion: a trophic cascade
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is responsible for the patterns
observed at the ecosystem
level
Succession…
 What is the natural
 Ecological succession –
successional sequence of
plants?
what is it?
 Excellent place to study:
 From this understanding:
old agricultural fields in
the eastern US,
abandoned by farmers
an artificial manipulation
can be planned; historical
records can be examined
 What have the studies at
Cedar Creek illustrated?
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 22 fields at different
stages in an old-field
succession
(abandoned
between 1927 and
1982) were surveyed
in 1983; 22
‘snapshots’
 Correlations!
 ?: are the
correlations in (a) –
(d) the result of an
effect of field age –
or is the causal
agent nitrogen with
which age is
correlated?
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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 become
less similar in species composition over time?
 Yes. But 10 years later, plots receiving different amounts of N had
diverged in species composition. The greater the difference in N input,
the greater the divergence
 (2) do patches receiving similar supply rates of nitrogen become
more similar in species composition over time?
 At the start, different. After 10 years, plots within the two fields
subjected to similar rates of N had
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Artificial experiments: search for
causation
 Time itself is not the only cause of successional changes in
species composition
 Differences in available nitrogen cause successions to diverge;
similarities cause them to converge much more quickly than
they would otherwise do
 Time (= opportunity to colonize) and nitrogen are clearly
intimately intertwined. More unanswered ecological questions.
 Know the Hubbard Brook study
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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 from
visceral gout (uric acid accumulation) followed by
kidney failure. Why? Carcasses of domestic
animals treated with diclofenac were lethal to
captive vultures (diclofenac is a non-steroidal antiinflammatory drug (NSAID) and when given to
working animals it can reduce joint pain and so
keep them working for longer. )
 Other elements?
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A modeling study: what proportion of carcasses (C) would have to
contain lethal doses of diclofena to cause the observed population
declines?
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Physical and Biological Principles 1
 Ecological systems are physical entities:
 life builds on physical properties and chemical reactions of
matter
 all processes obey the physical laws of thermodynamics (?)
 but life still pursues many varied options
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Physical and Biological Principles 2
 Ecological systems exist in dynamic steady states:
 despite substantial fluxes of energy and matter, ecological
systems remain more or less unchanged
 gains and losses are more or less balanced
 steady states apply to fluxes of materials and energy at all
levels of ecological organization
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Physical and Biological Principles 3
 The maintenance of living systems requires the
expenditure of energy:
 life forms exist out of equilibrium with their physical
environment
 losses must be replaced by energy or materials procured by
the organism
 the price of maintaining a dynamic steady state is energy
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Physical and Biological Principles 4
 Ecological systems undergo evolutionary change
through time:
 physical and chemical properties, and physical laws, are immutable,
but life exhibits remarkable diversity
 structures and functions of organisms (adaptations) are
evolutionary products of natural selection, recognized by Charles
Darwin
 complexity builds upon complexity
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Costa Rican mantid’s cryptic coloration
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Summary
 Ecology is the scientific study of the natural environment and the relationships of
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organisms to one another and to their surroundings.
Ecologists study a variety of organisms and processes, spanning a wide range of spatial
and temporal scales.
Individual organisms live in habitats and have unique niches reflecting conditions
tolerated 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 environmental
problems. Solving these problems will require application of ecological principles.
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