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

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what is ecologywhat do ecologists dowhat are ecologists interested inwhere 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 14

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Ecology - A Science for TodayWe 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 problemsinform our economic, political, and social thought

and practice

Example?

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So what do ecologists do?

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They try to explain and understandTwo different classes of explanation in biology:

proximate and ultimateProximate 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 termsHow 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

Scales, diversity, and rigorEcological phenomena occur at a variety of

scalesEcological evidence comes in a variety of

different sourcesEcology relies on truly scientific evidence

and application of statistics

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Questions of Scale: Ecological Systems Large and Small

Individual Organism (“No smaller unit in biology ... has a 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 ApproachWhat 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 environmentevolutionary processesinteractions 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 ApproachHow 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 ApproachHow 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 smallclimate 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:

distributions of organismschanges in populationscomposition of communitiesproductivity of ecosystems

? – climate change ?!

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Questions of scale: time scalesEcologists also work on a variety of time

scalesEcological Succession – the successive and

continuous colonization of a site by certain species populations, accompanied by the extinction of othersCan 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)

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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 hoursocean temperature varies over weeks or

months

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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 VariationSpatial 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 variationthe faster an individual moves:

the smaller the scale of spatial variationthe more quickly it encounters new environmentsthe shorter the temporal scale of variation

spatial and temporal scales are correlatedfrequency is inversely related to extent/severity

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Diversity of ecological evidenceObservations and field experimentsControlled Laboratory experimentsSimple laboratory systemsAnd mathematical models

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Ecology Employs the Scientific Method

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observationobservation

predictionprediction

experimentexperimenthypothesishypothesis oror modelmodel

inductioninductioninductioninduction

deductiondeductiondeductiondeduction

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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 PitfallsA 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 periodsthe 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 equationsmodel is an hypothesis and yields predictions

that can be tested; examples include:models of disease spreadmodels 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 rigorTrue of false: you can prove anything with

statisticsYou cannot prove anything with statisticsStatistical 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) ScienceBased 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 practiceLet’s examine some more real research

programs3 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 vision to capture prey

Galaxias rely on mechanical cues

Thus: invertebrates in a trout stream more at risk of predation during daylight hours

Conclusions derived from both readily controlled conditions of a lab experiment and from the more realistic and more variable circumstances of a field experiment

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Brown trout: population levelHow does brown trout impact the distribution of native fish?

198 sites selected.

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

At each site, a variety of physical variables were measured

Using statistics, ?: which physical variables (if any) distinguished one type of site from another ?

A: Galaxias restricted to sites upstream of waterfalls [cannot be climbed by trout]. Why? Direct predation by trout on native fish below waterfall

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Brown trout: community level? Do these changes have community consequences that impact other species ?

Do trout affect the stream food web differently from the displaced Galaxias?

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

Trout -> lower invertebrates -> higher algae

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Brown trout: ecosystem and energy flow

? Will the rate at which radiation energy is captured through photosynthesis by the algae be greater in the trout stream?

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

? In the trout stream, will the higher primary production be associated with a faster rate of uptake by algae of plant nutrients (nitrate, ammonium, phosphate) from the flowing stream water?

Also yes.

Conclusion: a trophic cascade is responsible for the patterns observed at the ecosystem level

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Succession…

Ecological succession – what is it?

Excellent place to study: old agricultural fields in the eastern US, abandoned by farmers

What have the studies at Cedar Creek illustrated?

What is the natural successional sequence of plants?

From this understanding: an artificial manipulation can be planned; historical records can be examined

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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

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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 anti-inflammatory drug (NSAID) and when given to working animals it can reduce joint pain and so keep them working for longer. )

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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 1Ecological 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 2Ecological 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 balancedsteady states apply to fluxes of materials

and energy at all levels of ecological organization

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Physical and Biological Principles 3The maintenance of living systems requires

the expenditure of energy:life forms exist out of equilibrium with their

physical environmentlosses must be replaced by energy or

materials procured by the organismthe 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 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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