1 - 111 ratio Predator/Prey relationship

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The rule of the game
Every kilogram of predator needs a fixed amount of prey.


25 March 2002
JOHN WHITFIELD




Every kilogram of meat-eating mammal needs 111 kilograms of prey to sustain it, say two ecologists. The rule holds from weasels to bears.

With many species of carnivore endangered, the discovery could help conservationists work out how to maintain a species' resource base.

Chris Carbone, of the Institute of Zoology, London, and John Gittleman, of the University of Virginia, found the rule when they compared the population densities of 25 species of carnivore with the population densities of their prey.

The relationship between the mass of predator and prey holds regardless of the animals' diet or habitat. It covers European badgers, which eat mainly worms, and big cats, for example. The smallest carnivore analysed was the 140-gram least weasel, the biggest the 310-kilogram polar bear.

"To see this rule emerging across a wide range of carnivores was a real surprise to me, and I think it'll surprise a lot of ecologists," says Carbone. He expects similar rules to hold for other predatory groups, such as reptiles.

"Most models [of carnivore populations] have assumed that resources aren't limiting, but that the rate of their acquisition is," says ecologist Pablo Marquet of the Catholic University of Chile, Santiago. "This shows that what really matters is the resources you have."

The result means that global biological patterns may only become apparent by looking at detailed local information, such as diet and population number, Marquet adds. "Some researchers ignore local knowledge in the hope that it will average out and you'll keep the big picture," he says.

Rule tool

The rule will be "a very useful ballpark figure" for conservationists, says Carbone. They could use it to predict the population densities of species not included in the analysis.

Carbone intends to apply it to the conservation of the Sumatran tiger. These tigers live around oil-palm plantations, and eat mainly wild pigs. Estimating the weight of the pig population will give an idea of how many tigers an area can sustain.

And where a carnivore-to-prey ratio falls much below 1/111, it could be a clue that something else, such as inbreeding, is keeping its numbers down.

The new rule is one of several general patterns to emerge recently from studies of how organisms' biology varies with their size. Last month, for example, researchers announced that the ratio of above- to below-ground tissue is constant across a wide range of plants2.


References
Carbone, C. & Gittleman, J.L. A common rule for the scaling of carnivore density. Science, 295, 2273 - 2276, (2002).
Enquist, B.J. & Niklas, K.J. Global allocation rules for patterns of biomass partitioning in seed plants. Science, 295, 1517 - 1520, (2002).
 
I think its referring to "Prey available" rather than direct consumption.

Which raises an interesting point RedFrog...

Obviously there are seasonal variations in the Prey population (but then there is also seasonal variation in the predator population, Mainly High in Spring, Low right before Spring) would also depend on the animal (individuals health ) how long an less than 1/111 ratio could be sustained

What about omnivores such as the Coyote and Black Bear ? (that study limits itself to carnivores)
 
So, my interpretation of this is that in a given habitat/range of a predator, each predator needs to have approximately 111X's its weight in prey living in that same habitat?

A 100lb mountain lion, for instance, would need to have about 11,000lbs of deer, pigs, rabbits, etc. in his habitat to choose from.
Let's see... 11K lbs of deer is only about 50-70 deer...
 
If that ratio is meant on a yearly basis, then it seems about perfect with your figures. I think lions are pretty much master deer killers and will only eat an occasional pig or rabbit. (Atleast in Colorado - no pigs here) I think the average they consume is a deer every 6 -8 days.

edit: Come to thnk of it, maybe they don't consume a deer every 6 - 8 days. They just kill that many and save the rest for the worms, coyotes, carnivorous bunnies, and Redfrog's snow snakes.
 
Yeah, but i don't see any mention of a time span there. It doesn't say that in a year, a carnivore eats 111X's its own body weight. It says it needs 111X's its weight in prey, and again, my interpretation is that it needs that in its habitat. The focus of the article seems to be that you can use counting of prey to get a rough idea how many carnivores there are in an area. ??????

But you're right, CrazyBean, i've heard the same from both good sources AND bad sources, that a cougar eats about a deer a week.
 
Encore,
That is the problem with the above study and a whole lot of other studies as well. They don't make theirself clear enough. I think that the author of this study is saying that there has to be X amount of available prey living in a particular area in order to maintain X amount of predators. This would include ALL prey animals living in that area. I only scanned the study briefly because these studies can be pretty boring to me, but that is what I think the author meant. A predator would eat himself to death if he tried to eat THAT much food every single day alright. LOL /ubbthreads/images/graemlins/smile.gif .
 
So if a lion needs say roughly 60 deer in its home range to sustain itself, in a year’s time it would kill and eat almost that number. So unless the deer population was constantly being replenished, the cat would eat itself out of house and home in short order!
 
What you have above is basically an ABSTRACT... designed for lay-people to digest easily, and its
not the entire study in detail.

Within the entire study you would find all the assumptions, constraints and mathematical equations in detail. Getting published in "Nature" (or any respectable Journal) is no easy task, the numbers and methods are reviewed heavily several times before being published, and there is a lot of competition for space.

The study in its entirety is available... for a fee.
 
Bob Mc,
That would be true IF deer were the only available prey. I think the author meant ALL prey. Deer, rabbits, gamebirds plus vaious farm animals as well.
 
Here's the abstract from Science (typos and all...). Full-text articles aren't released to online libraries by Science for 12 months, but any decent research library will have the paper version.

Population density in plants and animals is thought to scale with size as a result of mess-related energy requirements. Variation in resources,
however, naturally limits population density and may alter expected scaling patterns. We develop and test a general model for variation within and
between species in population density across the order Carnivora. We find that 10,000 kilograms of prey supports about 90 kilograms of a given
species of carnivore, irrespective of body mass, and that the ratio of carnivore number to prey biomass scales to the reciprocal of carnivore mass.
Using mess-specific equations of prey productivity, we show that carnivore number per unit prey productivity scabs to carnivore mass near -0.75, and
that the scaling rule can predict population density across more than three orders of magnitude. The relationship provides a basis for identifying
declining carnivore species that require conservation measures.[ABSTRACT FROM AUTHOR]
 
The way I read this, it states that it takes that much prey to sustain each critter. It doesn't seem to state that the critter needs to actually eat that much prey.
 
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