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CREAM-SKIMMER VERSUS CRUMB-PICKERS ( Coexistence based on patch use ). Habitat. Patch. Food item. Its not necessarily how quickly you eat, but what you leave behind. Cream-skimmer are poor exploiters – leave much food behind

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slide1

CREAM-SKIMMER VERSUS CRUMB-PICKERS

(Coexistence based on patch use)

Habitat

Patch

Food item

Its not necessarily how quickly you eat, but what you leave behind

slide2

Cream-skimmer are poor exploiters – leave much food behind

Crumb-pickers are good exploiters that leave very little food behind

slide3

Golden-winged Sunbird

Variable Sunbird

Malachite Sunbird

slide4

Variable

Golden-winged

Malachite

mint

flower

62% nectar

removal

82%

90%

Bill: 20mm 33mm 30mm

Time: 2.8 sec 1.8 sec 1.3 sec

Rate: 1.1 l/s 2.4l/s 3.6l/s

(Gill and Wolf 1978)

slide5

Variable

Malachite

Can the Malachite Sunbird invade a world of Variable Sunbirds?

slide6

Variable

Malachite

Can the Malachite Sunbird invade a world of Variable Sunbirds?

slide7

Variable

Malachite

Can the Variable Sunbird invade a world of Malachite Sunbirds?

slide8

Variable

Malachite

Can the Variable Sunbird invade a world of Malachite Sunbirds?

slide9

So, Crumb-pickers always beat out Cream-skimmers (all else equal).

How can we get CS and CP to coexist??

slide10

So, Crumb-pickers always beat out Cream-skimmers (all else equal).

How can we get CS and CP to coexist??

First, recognize that patches can come in 2 forms…

Rich Patches and Poor Patches

(and rich patches become poor patches as food is depleted)

Because Cream-skimmers always lose at the poor patch,

to have an advantage, they must be the first (on average)

to reach a rich patch.

HOW??

slide11

So, Crumb-pickers always beat out Cream-skimmers (all else equal).

How can we get CS and CP to coexist??

First, recognize that patches can come in 2 forms…

Rich Patches and Poor Patches

(and rich patches become poor patches as food is depleted)

Because Cream-skimmers always lose at the poor patch,

to have an advantage, they must be the first (on average)

to reach a rich patch.

  • Be fast!!!
  • Be DESPOTIC – and just beat the snot out of CPs
slide12

Coexisting gerbils in the Negev Desert, Israel

Gerbillus allenbyii

Allenby’s Gerbil

~20 g

Gerbillus pyramidum

Egyptian Gerbil

Both eat seeds of desert annuals

Both are nocturnal

~40 g

slide13

Coexisting gerbils in the Negev Desert, Israel

Gerbillus allenbyii

No matter where or when you put a

food patch (composed of seed and sand)

out Gaalways forages it down to a lower

resource abundance than Gp

Gp = cream skimmer

Ga = crumb picker

Gerbillus pyramidum

slide14

Coexisting gerbils in the Negev Desert, Israel

Gerbillus allenbyii

Gp

Gerbillus pyramidum

Ga

Grams of seeds

left behind

open

under bush

slide15

But gerbils partition the night. G. pyramidum forages

early in the night (rich patches), whereas G. allenbyii

forages later (poor patches).

Control

Gp removed

Percentage of

trays visited by

G. allenbyii

Time (hrs after sunset)

But this activity pattern disappears when

G. pyramidum is removed

(Kotler et al. 1996)

slide16

Gp come

out

Gp back

to burrow

Ga come

out

Let’s kick some

Allenbyii butt

ARE THEY GONE YET??

Food patch

slide17

The Cream-skimmer, G. pyramidum, monopolizes access

to high quality patches by interference competition, and

pushes the smaller G. allenbyii aside.

Ultimately, the whole system works b/c much of

the inner Negev Desert experiences strong nightly

winds that redistribute seeds on a nightly basis.

On the coast, where winds are not strong,

G. pyramidum does not occur.