behind the big cat's and bear's, who is the top predator?

[Balam]

Here's a better picture showing the size difference between an adult guanaco and a female cougar:

*This image is copyright of its original author

*This image is copyright of its original author

Cougars are opportunistic killers like all cats are, they will kill whatever prey they have the easiest access to at all times. That being said, they are very much capable of feeding on larger ungulates so long as they're abundant in the areas in which they live.

In Patagonia cougars overwhelmingly favor the guanaco as their main prey, the sizes of guanacos in Tierra del Fuego, deep in the Patagonia, varies between 100 and 150 kg. From the study: Lama Guanicoe (Müller, 1776) body size in continental Patagonia and Tierra del Fuego:

*This image is copyright of its original author

From the study: Diet of puma (Puma concolor) in sheep ranches of central Patagonia (Argentina):

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

The study highlights that very large domestic prey like cattle and horses will be targeted selected when guanaco numbers were low, and yet when guanaco and sheep numbers are high, cougars will choose for guanaco rather than sheep, despite guanacos being substantially larger.

Predation on adult guanaco in the Patagonia is performed by both sexes, therefore if we take the baseline average of 120 kg for guanacos in Tierra del Fuego and compare it to the average sizes of cougars in the region:

*This image is copyright of its original author

We get the following aspect ratio: if we assume female cougars to weigh on average 40 kg 1:0.34, or roughly 3 times the cougar's size.
For male cougars with an average weight of around 70 kg, the aspect ratio is 1:0.59, so slightly less than half.
If we use the average female weight of around 40 kg and compare it to a very large guanaco or around 150 kg, the aspect ratio would the most extreme at 1:0.27 or nearly five times the size difference.

Females targeting huge guanacos, exemplifying the drastic size difference:

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

A similar ratio could be expected following the size difference between introduced red deer in the Patagonia and cougars. With elk, the size difference would be even greater, and while females will tend to avoid hunting full-grown elk and select for smaller ungulates, the large males do focus on predation on these very large ungulates. 

The article: Ferocious appetites: Study finds mountain lions may be eating more than previously believed, cougars here too focused on juveniles, but the large males went after the larger game:

Knopff basis his conclusions on data collected from more than 1,500 kill sites while tracking 54 cougars with GPS collars. The collars allowed the University of Alberta researchers, including his wife Aliah, to move in quickly after a kill to identify what was taken and by which lion.

.....
The use of GPS collars enabled Knopff and his colleagues to collect more data. As a result, he found that mountain lions killed more deer, elk and moose during the summer by focusing on juveniles and actually killed fewer animals in winter. The information contradicts previous studies conducted in Idaho.
....The mountain lions' prey included deer, elk, bighorn sheep, coyotes, feral horses, beaver and porcupines.
....Adult male cougars can weigh 140 to 165 pounds. One male cougar in Knopff's study tipped the scales at 180 pounds and primarily fed on moose and feral horses. Females typically weigh around 100 pounds. From nose to tail the big cats can measure 6.5 to 10 feet long. The average lifespan for a male is 8 to 10 years, 12 to 14 for females.
.....
“Our kill rate estimates indicate that adult cougars are highly effective predators, killing at rates at the upper end of those recorded for wolves in both frequency and biomass,” Knopff wrote.
.... “We had one male cougar kill 18 moose in less than a year,” Knopff said.

The Albertan moose mentioned in that study is larger than the shiras moose some say cougars exclusively predate on, which is not true.
With Knopff supplementary data from Ongoing Cougar Research in Alberta, Canada, we get further information on the ages of horses killed by cougars specialized on predating the which were mentioned in the article above, and the kills include adult wild horses, who are more difficult to bring down than their domestic counterparts and substantially larger than other free-roaming equids like wild asses:

*This image is copyright of its original author

*This image is copyright of its original author

Someone tried to overlook the feats of cougars killing Shiras moose as the moose being "small" (despite the moose surpassing 300 kg in weight), they forgot to mention that the kills performed on those moose were done by females and not just males, and female cougars very rarely weight more than 45 kg.

"People wonder if the cats get beat up during the capture process. F47 went and killed this adult moose just a few days after we recollared her. Its the first time we’ve documented a female cougar killing an adult moose on this project. I guess she is feeling ok!"

The most dramatic kills performed by cougars is that of a female of less than 50 kg recorded bringing down bull elk, she was also reported to have killed a yearling wolf, credits to faess for saving excerpt:

"Here is your Monday morning video. In this one F109 visits a kill site from F61. The main feature of this clip is near the end when F109 performs a scrape with her hind feet. Cougars scrape to communicate their presence, breeding status, fitness/dominance and more. It is a fascinating behavior that deserves further study. F109 by the way is an impressive cat - she only weighs 88 pounds and hunts ~600 pound bull elk. She is also the only cat in our study to ever kill a wolf."

I posted this recently on the predation thread, a cougar of unknown sex killed an adult cow according to the hunter:

"Thanks to my man Steve and his dogs for getting me my first lion. It killed a full grown cow a week ago and we finally caught up with it today. Craziest hunt I have ever been on!"

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

Lastly, cougars have been recorded killing adult bears, not just sub-adult ones, from the article Mountain Lions Versus Black Bears, and once again it was a female cougar and not a male making the kill:

"So…why don’t mountain lions defend their kills from bears? On occasion, they do. In one case in California, a large female mountain lion was displaced by an average-sized female black bear from a deer kill. The lion abandoned the site for 24 hours, but then looped back to confront the bear. What we found when we visited the kill a week later were the remains of the deer and bear, side by side. But our research has shown that this is the rare encounter. Typically mountain lions hear the approach of the bear, and don’t even stick around to spit and hiss. They just leave. Perhaps the risks of injury in a fight outweigh the loss of a meal."

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I'm convinced that for their size, cougars take the largest prey in proportion and with the most regularity, followed closely by the ounce (P. uncia). Reply