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Re: [dinosaur] Question

R.T. Bakker pointed to seemingly low ratios of predators to prey in dinosaur faunas as evidence of endothermy in dinosaurs. (ref- Bakker, R. (1974). Dinosaur Bioenergetics-A Reply to Bennett and Dalzell, and Feduccia. Evolution, 28(3), 497-503. doi:10.2307/2407178)

There are a lot of criticisms mounted towards this, such as the obvious ones of sampling and taphonomy, as well as the fact that large ectothermic terrestrial predators are too few nowadays to provide useful comparisons for study. Bakker generally found dinosaurs to be within the range known for endothermic communities today, and found Permo-Triassic therapsid & pseudosuchian dominated faunas to be intermediate. But, there are better (or at least more explicit) ways of assessing dinosaur metabolism. The P/P ratio is fraught with a lot of uncertainties, and since dinosaurs were different in some ways than birds & mammals today (much higher reproductive rate, more ontogenic size variation; there is also evidence of higher # of herbivores per acre in dinos than in known mammal faunas) it's possible that calculating P/P is not informative. This is probably untrue, and I think the P/P ratios as calculated by Bakker are correct or correct-ish. Dinosaur faunas appear to be much closer to the mammal side of the curve than to the 'transitional' Permian communities, and it supports both the "hot-blooded" model of dinosaur metabolism as well as the intermediate 'gigantotherm' model which is invoked to explain, say, higher numbers of vegetarian dinosaurs per unit area.

Thomas Yazbeck

From: dinosaur-l-request@usc.edu <dinosaur-l-request@usc.edu> on behalf of Dann Pigdon <dannj@alphalink.com.au>
Sent: Wednesday, March 29, 2017 12:55 AM
To: dinosaur-l@usc.edu
Subject: Re: [dinosaur] Question
On Wed, Mar 29th, 2017 at 2:54 PM, "Williams, Brandon R (West Kentucky Student)"
<bwilliams0401@kctcs.edu> wrote:

> Hello, All, I have a question that I need help with. If anyone would answer
> it I would appreciate it. What is a predator: prey biomass ratio? How were
> these used in assessing dinosaur metabolism?

A predator:prey biomass ratio compares the number of predators to the number of prey in an
ecosystem (or more correctly, compares their mass rather than their numbers). If you can measure
this ratio accurately (and it's unlikely that you can for long-extinct ecosystems), then you can make
assumptions about the metabolism of that ecosystem's predators.

If an ecosystem is to remain sustainable, its predators must not kill prey faster than their prey can
reproduce, or their prey will become extinct and the predators will run out of food for themselves.
Endothermic ("warm-blooded") predators need a lot more food to survive than exothermic ("cold-
blooded") predators. An ecosystem with a lot of warm-blooded predators must have fewer predators
relative to their prey numbers than an ecosystem dominated by cold-blooded predators.

For instance, a warm-blooded mammal such as a leopard might have to kill two antelopes a week to
keep itself fed, whereas cold-blooded reptiles such as komodo dragons or large pythons (predators
with similar masses to leopards) might only have to eat one large meal a month. That means the
leopard is eating about eight times as much food. An ecosystem where pythons or komodo dragons
are the dominant predators could have eight times more predators than an ecosystem where leopards
are the dominant predator, and that ecosystem could still remain sustainable in the long term.


 Dann Pigdon
 GIS Officer
 Melbourne, Australia