Ecology Study of how organisms interact with each other and with their environment

Ecology

• Study of how organisms interact with each other and with their environment

Levels of Ecological Organization• Populations

– groups of individuals of the same species living together in one area

• Communities– populations of different species living together

in one area

• Ecosystems– communities and the non-living parts of the

environment with which they interact

Population Structure

Key aspects:

• Population Size

• Population Density

• Population Dispersion

Population Size

• Affects populations ability to survive

• small populations - more likely to go extinct

Population Density

• Number of individuals per unit area

• low density can be problem too

Population Dispersion

• Spacing of individuals within the population

• Random, uniform or clumped

• Clumped dispersion is when individuals aggregate in patches.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 52.2a

• By contrast, uniform dispersion is when individuals are evenly spaced.


Fig. 52.2b

• In random dispersion, the position of each individual is independent of the others.

• Overall, dispersion depends on resource distribution.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 52.2c

Survivorship Curves

• Graphical representation of the survivorship (opposite of mortality) at each age

Survivorship Curves

• Type I– increased risk of dying when old

• Type II– equal chance of dying at all ages

• Type III– increased chance of dying when young

Fig. 56.10

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

0 25

Pro

port

ion

Sur

vivi

ng1.0

0.1

Human (type I)

Hydra (type II)

Oyster (type III)

0.01

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Percent of Maximum Life Span10075

Fig. 56.11


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0.0020.0030.0040.005

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Poa annua – most like Type II

Population Growth

• Biotic Potential– r– the rate a population would grow at with no

limits– intrinsic rate of increase

Exponential Growth

dN/dt = rN

r = (b - d) + (i - e)

Fig. 56.16-1Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

0 5 10Number of Generations (t)

Pop

ulat

ion

Siz

e (N

)

15

1250

1000

750

= 1.0 N

500

250

0

dNdt

Carrying Capacity

• populations eventually reach a limit to their growth

• K = number of individuals that the environment can support

Logistic Growth

dN/dt = rN ((K - N)/ K)

• growth rate slows as the carry capacity is approached

• sigmoid growth curve (S-shaped)

• most populations remain constant in size

Fig. 56.16Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

0 5 10Number of Generations (t)

Pop

ulat

ion

Siz

e (N

)

15

1250

1000

750

= 1.0 N

500

250

0

= 1.0 N

Carryingcapacity

1000 – N1000

dNdt

dNdt

Fig. 56.17


N = K

Below K Above K

Population Size (N)

Pop

ulat

ion

Gro

wth

Rat

e (d

N/d

t)

0

NegativeGrowthRate

PositiveGrowthRate

CarryingCapacity (K)

Fig. 56.18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1915 1925 1935 1945

a. b.

200 10 30 5040

10

8

6

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2

0 Num

ber

of C

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400

300

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Num

ber

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(th

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Time (years) Time (days)

Logistic Growth

Fig. 56.24


4000B.C.

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2000B.C.

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Significant advancesin public health

IndustrialRevolution

Bubonic plague“Black Death”

Year

Limits to Population Growth

• Resource limitation- competition

• predation

Community Ecology

• Study interactions among populations

• Niche– total of all the ways an organism uses resources

in its environment– food consumption, space utilization, temp

range, etc...

• Habitat– physical location

Competition

• struggle between organisms to utilize the same resource when the resource is limited

• niches overlap and resources are limited

Fig. 57.4Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

High tide

Low tideLow tide

C.stellatus fundamental and realized niches are identical whenS.balanoides is removed.

S.balanoides and C.stellatus competing

Chthamalus

Chthamalusrealized niche

Chthamalusfundamentalniche

Semibalanus

Semibalanusrealized niche

Semibalanusfundamentalniche

J.H. Connell’s classical study of barnacles

Competition

• “fighting” = interference competition

• consuming shared resources = exploitative competition

Competition

• Interspecific competition– between individuals from different species

• Intraspecific competition– between individuals from same species

One Possible Result of Competition

• Competitive exclusion– no species can occupy the same niche

indefinitely– one species will be outcompeted and be driven

to extinction locally

Fig. 57.5Gausse’s

Experiments


0

50

100

150

200

40 8 12 16 20 24 40 8 12 16 20 24 40 8 12 16 20 24

a.

Days Days Days

Paramecium caudatum

Paramecium aureliaParamecium bursaria

Popu

latio

n D

ensi

ty(m

easu

red

by v

olum

e)


200

150

100

50

040 8 12 16 20 24

Days

Paramecium caudatum

Paramecium aurelia

Paramecium bursaria

Pop

ulat

ion

Den

sity

(mea

sure

d by

vol

ume)

b.

Competitive Exclusion


c.

0 20 24161284

Days

Paramecium caudatum


Pop

ulat

ion

Den

sity

(mea

sure

d by

vol

ume) 75

50

25

0

Coexistence…Resource Partitioning

Fig. 57.5


0

50

100

150

200

40 8 12 16 20 24 40 8 12 16 20 24 40 8 12 16 20 24

a.

c.

200

150

100

50

00 20 2416128440 8 12 16 20 24

Days Days Days

Days Days

Paramecium caudatum


Popu

latio

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ensi

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Den

sity

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Popu

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b.

75

50

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0

Other Results of Competition

• Niche overlap can lead to...– Resource partitioning– character displacement

– Resource partitioning is the differentiation of niches that enables two similar species to coexist in a community.

Fig. 53.2Fig. 53.3


• Character displacement is the tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populationsof the same two species.– Hereditary changes

evolve that bringabout resourcepartitioning.

Fig. 53.4


Predation

• Predator uses prey for food

• prey evolves defenses, predator evolves adaptations to overcome…arms race

Predation

Plant defenses against herbivores:

• morphological - thorns, spines, plant hairs

• chemicals - secondary compounds

Animal defenses against predators:• Behavioral defenses include fleeing,

hiding, self-defense, noises, and mobbing.

Predation

• Camouflage includes cryptic coloration,

Leaf mimic katydid from the Ecuadorian Amazon

• Deceptive Markings: eyespots

http://discovermagazine.com/photos/11-the-calculating-beauty-of-butterflies

http://www.flickr.com/photos/ladyoftheflowers/2386058994/

• Mechanical defenses include spines & shells.

african-safari-pictures.com

http://www.animalpictures1.com/r-sea-urchin-112-sea-urchin-1958.htm

• Chemical defenses include odors and toxins – may get them from the plants they eat (ex: monarch butterfly & milkweed)


• Aposematic coloration is indicated by warning colors, and is sometimes associated with other defenses (toxins).

Fig. 53.6


• Mimicry is when organisms resemble other species.– Batesian mimicry is where a harmless species mimics

a harmful one.


• Müllerian mimicry is where two or more unpalatable species resemble each other.


Fig. 53.8

Fig. 57.14


Heliconius melpomene

Papilio glaucusBattus philenor

a. Batesian mimicry: Pipevine swallowtail butterfly (Battus philenor) is poisonous; Tiger swallowtail (Papilio glaucus) is a palatable mimic.

Heliconius erato

Heliconius cydnoHeliconius sapho

b. Müllerian mimicry: Two pairs of mimics; all are distasteful.

Predation

• Can promote species diversity

• predator eats superior competitor

• Keystone speciesexert an importantregulating effecton other speciesin a community.

Fig. 53.14


• If they are removed, community structure is greatly affected.

Fig. 53.15


Coevolution & interspecific interactions– Coevolution refers to reciprocal evolutionary

adaptations of two interacting species.• When one species evolves, it exerts selective

pressure on the other to evolve to continue the interaction.


The Oogpister Beetle Video

http://www.snotr.com/video/4732

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Ecology Study of how organisms interact with each other and with their environment