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.