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Re: Carnivore Energetics: Why Are Lions Not As Big As Elephants?



--- Sim Koning <simkoning@msn.com> wrote:

> 
> I understand, but my point was about the fact that
> the article said the 
> reason giant theropods got so big was because they
> had slower metabolic 
> rates
> 
> "The authors also note that the largest terrestrial
> non-mammalian predators, 
> such as Giganotosaurus and Tyrannosaurs, may have
> achieved their massive 
> size by having a lower metabolic rate"
> 
> so my question is if that?s the only reason, why
> couldn?t mammals do the 
> same? Which is to say I think there is more to it
> than just the metabolic 
> rates of the predator, which seems to be what
> everyone else is saying.

+++++++++++++++++++++++++++++

First, I'd like to point out that the authours merely
threw that idea out as a suggestion for the size
disparity.


Secondly, there's the ecology of modern day mammals
that needs to be taken into account. Modern and
near-modern mammals (in particular, the megafaunae)
have evolved to deal with wide open grasslands. This
presents a problem to a mammalian predator (in
particular, a big cat) that "decides" to get bigger. 

Take for example, a leopard. I choose leopards because
their hunting style is more similar to most other
large cats (vs. lions and cheetahs which both evolved
unique styles of hunting). Leopards, like all cats,
are ambush hunters. They need to get as close as
possible (~1 meter, or 2) before sprinting after their
prey. If a leopard were to be born with a genetic
disposition that resulted in its doubling in size,
then the big cat (now much bigger cat) has a
concealment problem. Grasslands are big and open. Big
cats often "guerrilla crawl" to their prey in an
effort to stay hidden in the grass. If they get
spotted too soon, the chase is off. Prey will either
run away, walk away, or head toward the predator.
Regardless, the result is the same: no food this time.
Grasslands probably provide a good size constraint for
cats. I'm not entirely sure why dogs are all small. I
think it has to due with pursuit hunting. That
requirement also seems to put a limit on size. That
many dogs hunt in packs, probably also provides a good
reason for the lack of large size (bigger animals have
bigger mouths to feed).

That the largest cats today (tigers) are jungle cats,
also suggests that grasslands might be a prime factor
in size contraint. If more large prey lived in
jungles, tigers might grow bigger.

As for polar bears (a possible wrench in this
speculation), they can probably get away with being
large because their prey doesn't live in the same
place they do. A seal has to risk sticking its head
out of the water to check for a bear. That's a far cry
from a wildebeest spotting a lion from a fifty meters
away.


Jason


"I am impressed by the fact that we know less about many modern [reptile] types 
than we do of many fossil groups." - Alfred S. Romer



 
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