IT DEPENDS
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IT DEPENDS. E. E(2). Keep searching for preferred prey, do not consume non-preferred prey. >. If is small:. S. S +. X. P. P(2). Selective Diet. Pursuers or Handlers – Put their time into pursuit/handling prey. Small

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S

IT DEPENDS

E

E(2)

Keep searching for preferred prey,

do not consume non-preferred prey

>

If is small:

S

S +

X

P

P(2)

Selective Diet

Pursuers or Handlers – Put their time into pursuit/handling prey. Small

changes in, e.g., beak size/shape results in large tradeoffs between

P1 and P2 (cannot be simultaneously efficient at handling foods 1 and 2)

B/c they have selective diets – diet choice provides a means of reducing

or eliminating competition thereby allowing species to coexist

Those species coexisting through diet choice often have highly variable

feeding appendages from species to species that most efficiently extract

and/or handle preferred food


S

How does diet selection provide a mechanism of coexistence??

Tradeoffs between E’s, S’s or P’s such that

2 (or more) species have distinct prey

preferences and therefore do not share resources

i.e., noresource competition


S

Caracal

Serval

Cheetah


S

5 coexisting cats in the Serengeti:

Species mass preferred prey prey mass behavior

Lion 190 kg wildebeest, zebra 270-690 kg coop. hunting

Leopard 65 kg Impala 60 kg stealth

Cheetah 50 kg Thompson gazelles 25 kg speed

Caracal 20 kg Hyrax, steenbok 5 kg ???

Serval 13 kg birds 100’s g leaping


S

Meet the Handlers….

Obvious differences in morphology,

particularly of feeding appendages,

between species


S

IT DEPENDS

E

E(2)

Eat what you find - preferred or not

Do not pass up an encountered item

<

If is large:

S

S +

P

P(2)

Generalist Diet

Searchers – Put their time into searching for prey

B/c they have general diets they MUST rely on alternative means to

reduce/eliminate competition

Species converge onto a similar body plan


S

Four species

of

coexisting

warblers


S

1 item = 10 sec

1 item = 31 sec

- There is a preferred habitat

62s

- At low density the population is

on the preferred habitat

20s

- At higher densities the population is

a generalist using both habitats

40s

60s

2

2

2

2

3

3

3

3


S

FISH

FOOD

FISH

FOOD

FISH

FOOD

FISH

FOOD


S

The Ideal Free Distribution – individuals settle into habitats such that

the benefit (i.e., fitness) of each individual is equalized between habitats

and no individual can do better by switching to an alternative habitat.

It is a NO REGRETS (optimal) strategy

e.g. grocery line, line at passport control, cars on a 3-lane highway

AND RATS!!

http://www.youtube.com/watch?v=sB4dBRI-qBY


S

(-) Density

dependence

Fitness

i.e., growth rate,

reproduction,

survivorship

1

2

3

4

N (density)


S

2 habitats

Fitness

And individuals are

free to choose

N (density)


S

2 habitats

Fitness

And individuals are

free to choose

N (density)


S

Fitness

N (density)


S

Fitness

N*

N (density)

selective

generalist


S

Let’s add a second species

and assume it prefers

habitat B:

F2

N*2

N2

F1

N*1

N1


S

Combine the two figures into one

N2

We know these two

points from the last

two figures: the

SWITCH POINTS

Both A & B

N*2

Selective

on B

N*1

N1

Selective

on A

Both A & B


S

N2

Become

SWITCH LINES

Both A & B

N*2

Selective

on B

N*1

N1

Selective

on A

Both A & B


S

N2

If species have density

dependent effects on

one another the switching

lines will bend away

Both A & B

N*2

Selective

on B

N*1

N1

Selective

on A

Both A & B


S

Sp 1 sel. on A;

Sp 2 generalist

Each spp is

selective on a

unique habitat

N2

Both A & B

Sp 2 sel. on B;

Sp 1 generalist

NO

COMPETITION

N*2

Selective

on B

N*1

N1

Selective

on A

Both A & B


S

CONCLUSION:

Habitat Selection, as is the case for Diet Choice, can result in

2 species having distinct preferences – that is, each species

prefers a unique habitat type, thus eliminating competition.

As such, habitat selection provides a powerful mechanism

of coexistence - one that is widespread throughout nature.


S

Habitat selection among

5 spp of Parulid warblers

in a Maine spruce forest


S

5 cm

10 cm

15 cm

And now for the slippery slope.....

Is it habitat

or diet that

separates

competitors??


S

Niche separation in the Seabirds


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