Chapter 1: Introduction to the Science of...

Chapter 1: Introduction to the

Science of Ecology

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Just what is ecology, anyway?

• Root from Greek “oikos”

• First used as a word by Henry David

Thoreau in 1858

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• Definitions according to

– Ernst Haekel: “total relations of an animal to

both it organic and inorganic environment”

– Charles Elton: “scientific

natural history”

– H.G. Andrewartha: “scientific study of the

distribution and abundance of organisms”

– Eugene Odum: “structure and function of

nature”

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• Definitions according to

– Charles Krebs: “scientific study of the

interactions that determine the distribution

and abundance of organisms”

• where organisms are found

• how many occur there

• why they live there

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History of ecology

• Hunter-gatherers

• Agricultural age

• Egyptians through Aristotle

– fear of plagues

– explanations relating to ecology

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History of ecology

• Advances beginning in the 17th century

– John Graunt (c. 1662)

• father of demography

• described human populations in

quantitative terms

– Antony van Leewenhoek (c. 1687)

• reproductive rates of grain beetles, carrion flies

(1 pair >740,000 in 3 months), human lice

• first attempts to calculate theoretical rates of

increase for animal species

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History of ecology

• Advances after the 17th century

– Buffon (c. 1756)

• Georges-Louis Leclerc, Comte de Buffon

• author of Natural History

• humans, plants and animals all regulated by the

same processes

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History of ecology


– Thomas Malthus (c. 1798)

• author of Essay on Population

• numbers of organisms increase geometrically, but

their relative food supply may never increase more

than arithmetically

Generation

_0 1 2 3 4__

Population: 2 4 8 16 32

Food supply: 2 4 6 8 10

• concluded that food supply limits population size

9

History of ecology


– Adolphe Quetelet (c. 1835)

• potential ability of a population to

grow geometrically is balanced by a

resistance to growth

– Pierre-François Verhulst (c. 1838)

• derived equation describing growth of a

single population over time: logistic

• his work was overlooked for 100 years

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History of ecology

• Advances in the 18th and 19th centuries

– balance of nature versus natural selection

– recognition of interrelations of organisms

within communities

• Edward Forbes (c. 1844)

– communities in British coastal waters and Mediterranean

– zones of different depths with different communities

• Stephen Forbes (c. 1887)

– author of The Lake as a Microcosm

– affecting one species in a community can influence the

whole community

Fig. 1.1 (p. 5): The four biological disciplines closely

related to ecology.

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Ecology versus environmental science

• Ecology: focuses on the natural world of

interactions of plants and animals

(including humans) with their natural

environments

• Environmental science: focuses on

human impacts on the Earth’s

environments (physical, chemical,

biological)

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Approaches to studying ecology

Descriptive ecology (what?)

Functional ecology (how?)

Evolutionary ecology (why?)

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• Evolutionary ecology

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• Functional ecology

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• Descriptive ecology

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Fig. 1.4 (p. 10): Relationship between distribution and

abundance.

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Fig. 1.5 (p. 11): Abundance of the horned lark in North

America, 1994-2003.

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Fig. 1.6 (p. 12): Distribution and abundance of the

red kangaroo in Australia, 1980-1982.

Fig. 1.7 (p. 13): Levels of integration studied in biology.

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• Species

– organism level of integration

– fundamental unit in ecology

– three-part definition

• group of actually or potentially interbreeding

organisms,

• that are reproductively isolated from other kinds

of organisms, and

• that produce viable offspring

Levels of integration in biology

24

• Population

– group of organisms of the same species

occupying a given area at a given time

– unique property = density

– examples:

• humans

• bluebirds

• fox squirrels


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• Community

– group of interacting populations occupying a

given area

– unique property = species diversity

– examples:

• bottomland hardwood plant community

• coastal prairie plant community

• bay bottom benthic community


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• Ecosystem

– group of interacting communities, linked by

lines of energy transfer

– abiotic features

– biotic features

– examples:

• Galveston Bay

• East Texas piney woods

• pond


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Methods used to study ecology

• Theoretical (mathematical)

• Laboratory

• Field

• Plant ecology versus animal ecology

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Th

e s

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nti

fic m

eth

od

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Chapter 2: Evolution and Ecology

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Ecology and evolution

• Evolution (in ecological terms)

– change in traits of a population over time

– involves changes in the frequency of

individual genes in a population from one

generation to the next

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What mechanism drives evolution?

• Neutralists

– evolution occurs by chance (genetic drift)

– genetic mutations occur 1/1,000,000 DNA

replications

– some get fixed in the population change

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What mechanism drives evolution?

• Selectionists

– evolution is driven by adaptation and natural

selection (e.g., Darwin, Wallace in the 1850s)

– parameters

• genetic variation

• excess offspring

• competition

• fitness

• heritability of traits

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How natural selection works

Theory Example

The reproductive potential of

populations is great, but

Rabbits should be able to cover

the whole earth, but

populations tend to remain

constant in size, because

they don’t, because

populations suffer high mortality. many are caught by predators.

Individuals vary within

populations, leading to

Some rabbits run faster than

others

differential survival of individuals. and escape from predators.

Traits of individuals are inherited

by their offspring.

So do their offspring.

The composition of the population

changes by the elimination of unfit

individuals.

Populations of rabbits, as a

whole, tend to run raster than

their predecessors.

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Why natural selection occurs

• Genetic variability in individuals

• Heritability of genetic traits

• Influence of the environment on survival

and reproduction

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Processes of evolution

• Adaptation

– natural selection acts on phenotypes to cause

change in the genetic make-up of a

population over time

• Speciation

– members of a population become

reproductively isolated from each other,

leading in time to separate species

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Natural selection by adaptation

• Natural selection operates on phenotypes

• Changes in gene frequencies occur only

when there is a correlation between

phenotype (fitness) and genotype

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Fig. 2.2 (p. 21): Three types of selection on phenotypic

characters.

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Fig. 2.3 (p. 21): Directional selection for beak size in the

Galapagos ground finch, Geospiza forza.

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Fig. 2.4 (p. 22): Stabilizing selection for birth weight

in humans.

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Fig. 2.1 (p. 20):

Stabilizing

selection for

hatching

synchrony in

lesser snow

geese.

Fig. 2.6 (p. 23):

Disruptive selection

in the three-spine

stickleback in British

Columbia, (a)

smaller, limnetic

form, (b) larger,

benthic form.

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• Determination of clutch size in birds

– David Lack (1947)

– balance between

• proximate factors (physiology of the birds that

control ovulation and egg-laying)

• ultimate factors (how many young can

successfully fledge, determined by genetic,

population and environmental factors)

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Fig. 2.7 (p. 24): Cost-benefit model for evolution of

clutch size in birds.

Fig. 2.8, p. 25):

Production of

young blue tits

in relation to

clutch size,

Wytham Woods,

Oxford, England

– survival of

young birds in

manipulated

nests is poor.

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Fig. 2.9 (p. 25): Number of house wren chicks fledged

from manipulated broods – disagreement with Lack’s

hypothesis.

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• Industrial melanism in the common

peppered moth (Biston betularia)


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• Early 1800s: mostly light form, few melanics (carbonaria) in England

• Over next 100 years, melanics increased in abundance

• In some industrialized areas, found only melanics

• Light or dark forms follow simple Mendelian genetics

• 1950s: HBD Kettlewell’s mark-recapture and ecology studies

Natural selection in B. betularia

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Distribution

of light and

dark forms of

B. betularia

in Great

Britain, 1950s

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B. betularia mark-recapture study

Number of

moths

Industrial site Non-industrial

site

Light

form

Dark

form

Light

form

Dark

form

Marked and

released201 601 496 473

Recaptured 34 205 62 30

Percent

recaptured16 34 12 6

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• What is the specific agent of selection for fitness in the dark form moths?– industrial site: tree trunks

darker from soot, dark form camouflaged

– non-industrial site: dark forms stand out on lighter trunks

Natural selection in B. betularia

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Number of B. betularia taken by birds

Light

form

Dark

form

From trees at non-

industrial site 26 164

From trees at

industrial site 43 15

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Fig. 2.1 (p. 18):

Evolution in the

common peppered

moth in England

since 1950.

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Natural selection within a species

• Favors those individuals who can produce the most offspring

– number of offspring per mating• at 2 per mating: 24 8 16 32

• at 3 per mating: 3 9 27 81 243

– number of times individual can reproduce over its lifetime

• 1 time @ 2 young = 2

• 3 times @ 2 young = 6

• 10 times @ 2 young = 20

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Natural selection within a species

• Favors those who survive the given

environmental conditions (fitness)

• Offset by parental investment: parental

care decreases as number of offspring

increases

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Coevolution

• Specific trait of

Species A evolves in

response to a specific

trait of Species B,

which in turn evolves

in response to the trait

of Species A

SPECIES A

SPECIES B

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Coevolution

• Ehrlich and Raven from

studies on plants and

insects that eat them

• Specific and reciprocal

• Diffuse coevolution: >2

species involved

SPECIES A

SPECIES B

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Examples of coevolution

• Oryctolagus rabbits and Myxoma virus

• Tropical ant-plant relationships: melastomes and

Inga

• Cecropia trees and Azteca ants

• Oropendulas and wasps

• Amazon water lily (Victoria amazonica) and

scarab beetles (Cyclocephala sp)

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Myxoma virus and Oryctolagus

rabbits in Australia

• Rabbits introduced to Australia in late 1800s

• Rapidly increased in abundance severe problem, destroyed rangelands used for sheep

• Myxoma common parasite of new world rabbits

– causes smallpox

– in balance in S. American rabbit populations

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• Myxoma introduced as a potent killer of Australian

rabbits

– initially killed 99.8% of the rabbit population

– within three generations, virus 40-60% effective

– rabbit populations increased and reached an

equilibrium with the virus



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Fig. 13.16a (p. 248): Population crash of European

rabbits in Australia following introduction of Myxoma

virus in 1951.

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Fig. 13.16b (p. 248): Decline in mortality rates of

European rabbits in Australia as a function of time after

introduction of Myxoma virus.

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Fig. 13.16c (p. 248): Effect of vaccination on numbers of

adult rabbits in fenced areas in SE Australia.

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• Apparent coevolution between rabbits and Myxoma virus

– rabbits that were fit (survived and reproduced) were resistant to lethal effects of virus and passed that trait to young

– simultaneously, Myxoma virus increased its fitness by becoming less virulent

• virus transmission requires mosquito vector

• best strategy is intermediate virulence: not kill host before mosquito can transmit



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• Primary domatia

Melastomataceae

Tropical ant-plant relationships

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• Primary domatia

IngaMelastomataceae

Tropical ant-plant relationships

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Cecropia trees and Azteca ants

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prostoma

septum


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Bead

bodies

supply

glucose


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Mullerian

bodies

supply

glycogen


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Oropendulas and wasps

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Amazon water lily and scarab beetles

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Day 1 Day 2


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Fig. 2.11 (p. 27): Evolution and “arms race” between

parasitic cowbird and parasitized species that try to

defend their nests by ejecting cowbird chicks.

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Fig. 2.12 (p. 28): Evolution and “arms races” between

rough-skinned newt (Taricha granulosa) from western

N. America and garter snake (Thamnophis sirtalis) that

preys on these newts.

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Evolution by speciation

• Basic requirement: reproductive isolation

between populations

• Reproductive isolation

– prevention of mating

– production of nonviable offspring

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Reproductive isolation

• Prezygotic (prevention of mating)

– environmental

– behavioral

– mechanical

– physiological

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Reproductive isolation

• Postzygotic (production of nonviable

offspring)

– offspring weak, do not survive to maturity

– developmental problems

• sterility

• abnormal gonads

– segregational

– F2 breakdown

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Three hypotheses for speciation

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• Allopatric (geographic) speciation

– physical or geographical separation

– each population undergoes independent evolution,

adaptation to separate environment

• Parapatric speciation

– part of population enters new habitat

– no physical barrier

• Sympatric speciation

– occurs within population before any differences can

be seen

Three hypotheses for speciation

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Units of natural selection

• Individual

• Gametic: selection at level of sperm and

ova

• Kin: social organization, altruistic behavior

• Group: population broken into groups with

different genetic, adaptive attributes

• Sexual: dominance in males or females

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