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

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

Variable Sunbird

Golden-winged Sunbird

Malachite Sunbird

VariableMalachiteGolden-winged

62% nectar removal

90%82%

Bill: 20mm 33mm 30mmTime: 2.8 sec 1.8 sec 1.3 secRate: 1.1 l/s 2.4 l/s 3.6 l/s

(Gill and Wolf 1978)

mintflower

VariableMalachite

Can the Malachite Sunbird invade a world of Variable Sunbirds?

VariableMalachite

Can the Malachite Sunbird invade a world of Variable Sunbirds?

VariableMalachite

Can the Variable Sunbird invade a world of Malachite Sunbirds?

VariableMalachite

Can the Variable Sunbird invade a world of Malachite Sunbirds?

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

How can we get CS and CP to coexist??

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??

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.

(1) Be fast!!!

(2) Be DESPOTIC – and just beat the snot out of CPs

Coexisting gerbils in the Negev Desert, Israel

Gerbillus pyramidumEgyptian Gerbil

Gerbillus allenbyiiAllenby’s Gerbil

~40 g

~20 g

Both eat seeds of desert annualsBoth are nocturnal

Coexisting gerbils in the Negev Desert, Israel

Gerbillus pyramidum

Gerbillus allenbyii

No matter where or when you put a food patch (composed of seed and sand) out Ga always forages it down to a lowerresource abundance than Gp

Gp = cream skimmerGa = crumb picker

Coexisting gerbils in the Negev Desert, Israel

Gerbillus pyramidum

Gerbillus allenbyii

Grams of seedsleft behind

Gp

Ga

open under bush

Percentage oftrays visited by

G. allenbyii

Time (hrs after sunset)

Control

Gp removed

(Kotler et al. 1996)

But gerbils partition the night. G. pyramidum foragesearly in the night (rich patches), whereas G. allenbyii forages later (poor patches).

But this activity pattern disappears when G. pyramidum is removed

Food patch

Gp come out

Gp backto burrow

Ga come out

Let’s kick someAllenbyii butt ARE THEY GONE YET??

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 ofthe 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.