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Why are ecological interactions important?. Interactions can affect distribution and abundance. Interactions can influence evolution. Competition – two species share a requirement for a limited resource  reduces fitness of one or both species. Ecological effects of competition.

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Presentation Transcript
slide1

Why are ecological interactions important?

Interactions can affect distribution and abundance.

Interactions can influence evolution.

slide2

Competition – two species share a requirement for a

limited resource  reduces fitness of one or both species

slide3

Ecological effects of competition

Intraspecific competition – between individuals of the

SAME species

contributes to K (carrying capacity)

Interspecific competition – between individuals of

DIFFERENT species

How does interspecific competition affect N?

slide4

k rats excluded

control

0 .2 .4 .6 .8 1

# deer mice captured

1978-801988-90

(Heske, E. J., J. H. Brown, and S. Mistry 1994)

What is the effect of kangaroo rat competition on deer mice?

slide5

competitive exclusion principle

If two species have the same niche, the stronger

competitor will eliminate the other competitor.

“Complete competitors cannot coexist.”

slide6

Why do kangaroo rats exclude deer mice?

What if you put more seeds in the environment?

What if you added another resource to the environment?

slide7

Complete competitors cannot coexist.

Competitive exclusion is reached more slowly with

higher resource abundances.

Stable coexistence requires niche differentiation,

such that members of each species compete

more strongly among themselves than with

members of the other species.

 (intraspecific > interspecific)

slide8

α12 – effect of an

indv of species 2 on

an indv of species 1

α21 – effect of an

indv of species 1 on

an indv of species 2

α21 & α21 = competition coefficients

How does interspecific competition affect N?

dN1

dt

r1N1 K1-N1

K1

species 1

=

dN2

dt

r2N2 K2-N2

K2

species 2

=

slide9

intraspecific

competition

interspecific

competition

How does interspecific competition affect N?

Lotka-Volterra equations

dN1

dt

r1N1 K1-N1 - α12N2

K1

species 1

=

dN2

dt

r2N2 K2-N2- α21N1

K2

species 2

=

What does it mean ifα12= 1? What ifα12= 0.5?

slide10

Competitors can coexist:

if intraspecific competition is stronger than

interspecific competition, for both species

Translate this intoα12andα21.

for coexistence, α12< 1 andα21< 1

Predict α12andα21for k rats and mice.

slide11

Lotka-Volterra competition equations = including

interspecific competition in the logistic model.

Competition coefficients (’s) show per capita

competitive effect of each species on the other.

When ’s are less than 1, stable coexistence is possible.

 implies that niches don’t completely overlap

slide12

A classic interspecific competition experiment

two species of Paramecium

predict the outcome of

interspecific competition

P. aurelia

P. caudata

ac = 0.8

ca = 1.1

Gause (1934)

what is the niche
What is the niche?

set of conditions

within which an organism

can maintain a viable

population

multi-dimensional

with as many

dimensions as their

are limiting conditions

ecological

niche

light intensity

okay

temperature

salinity

slide14

Fundamental niche depends on physical (abiotic) conditions.

Realized niche depends on biotic as well as abiotic conditions.

What is the realized niche of each barnacle?

What is the fundamental niche of each?

slide15

How can we determine the realized niche of each barnacle?

Where do they grow when allowed to compete?

Balanus

and

Chthamalus

growth

rate

Balanus

realized

niche

Chthamalus realized niche

low

middle

high

Location in intertidal zone

slide16

How can we determine the fundamental niche of each barnacle?

Removal experiments – remove each species and see

where the other grows

Balanus alone

Balanus

fundamental

niche

growth

rate

Chthamalus alone

Chthamalus fundamental niche

low

middle

high

Location in intertidal zone

slide17

The niche of a species may contract in the presence of a

competitor species.

This phenomenon leads to resource (niche) partitioning

and coexistence among functionally similar species.

The narrower niche resulting from competition is called

the realized niche.

What happens if the competitor is removed?

slide18

competitive release – niche of the competitively-inferior species

expands in the absence of the

competitively-superior species

competitive

release

growth

rate

Chthamalus with

Balanus

Chthamalus

alone

realized niche

fundamental niche

low

middle

high

Location in intertidal zone

slide19

Streams with only

Planaria species A

Streams with only

Planaria species B

Streams with both

Planaria species

What are the fundamental

and realized niches for

each species?

slide20

The niche of a species may contract in the presence of a

competitor species.

This phenomenon leads to resource (niche) partitioning

and coexistence among functionally similar species.

The narrower niche resulting from competition is called

the realized niche.

When the dominant competitor is removed, the niche of

the inferior competitor can expand by competitive release.