Transcript Slide 1

IT DEPENDS
If S is small:
E
S+ P
X
>
E(2)
P(2)
Keep searching for preferred prey,
do not consume non-preferred prey
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
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., no resource competition
Caracal
Serval
Cheetah
5 coexisting cats in the Serengeti:
Species
mass
preferred prey
prey mass
Lion
190 kg
wildebeest, zebra
270-690 kg
Leopard
65 kg
Cheetah
50 kg
Caracal
Serval
Impala
behavior
coop. hunting
60 kg
stealth
Thompson gazelles
25 kg
speed
20 kg
Hyrax, steenbok
5 kg
???
13 kg
birds
100’s g
leaping
Meet the Handlers….
Obvious differences in morphology,
particularly of feeding appendages,
between species
IT DEPENDS
If S is large:
E
S+ P
<
E(2)
P(2)
Eat what you find - preferred or not
Do not pass up an encountered item
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
Four species
of
coexisting
warblers
1 item = 10 sec
1 item = 31 sec
- There is a preferred habitat
62s
- At low density the population is
on the preferred habitat
- At higher densities the population is
a generalist using both habitats
20s
40s
60s
2
2
2
2
3
3
3
3
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
(-) Density
dependence
Fitness
i.e., growth rate,
reproduction,
survivorship
1
2
3
4
N (density)
2 habitats
Fitness
And individuals are
free to choose
N (density)
2 habitats
Fitness
And individuals are
free to choose
N (density)
Fitness
N (density)
Fitness
N*
selective
N (density)
generalist
Let’s add a second species
and assume it prefers
habitat B:
F2
N*2
F1
N*1
N1
N2
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
Selective
on A
N1
Both A & B
N2
Become
SWITCH LINES
Both A & B
N*2
Selective
on B
N*1
Selective
on A
N1
Both A & B
If species have density
dependent effects on
one another the switching
lines will bend away
N2
Both A & B
N*2
Selective
on B
N*1
Selective
on A
N1
Both A & B
Sp 1 sel. on A;
Sp 2 generalist
Each spp is
selective on a
unique habitat
N2
Both A & B
N*2
NO
COMPETITION
Sp 2 sel. on B;
Sp 1 generalist
Selective
on B
N*1
Selective
on A
N1
Both A & B
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.
Habitat selection among
5 spp of Parulid warblers
in a Maine spruce forest
And now for the slippery slope.....
Is it habitat
or diet that
separates
competitors??
5 cm
10 cm
15 cm
Niche separation in the Seabirds