In isolated land areas or in islands why reptiles grow larger and mammals shrink?

Question

For eg,in indonesia the lizards grown to maximum ,the komodo dragons and the fossil bones of pygmy elephants in the same area

Answer 1

Some reasons why reptiles are large:

* reptiles are often the top predator on small islands that lack mammals or marsupials, and the komodo dragon is probably the top predator in its environment
* carnivores are generally larger than their prey, and secondary predators are generally larger than primary predators
* larger body size makes a larger number of prey species available
* larger body and predatory capabilities size gives komodo dragons the ability to out-compete scavengers, and dominate yet another food source
* Cold-blooded species have relatively low energetic requirements, compared to a mammal, so large body size is less likely to become an energetic constraint in reptiles
* Larger reptiles generally produce a larger number of eggs and a higher percentage of eggs that hatch than small individuals, so selection favors larger reptiles.

Some reasons why mammals are small:

* A large mammalian herbivore requires a large amount of area to obtain enough food, and area is limited on islands
* With a finite amount of forage available, there is a finite amount of animal biomass that can be supported. The animal biomass can either consist of a few large individuals or many small individuals
* Populations with few individuals are much more likely to go extinct than populations with a large number of individuals
* given these factors, selection would tend to favor small mammals.

Answer 2

It will not necessarily go that way; it will occur iff there are survival advantages to lizards to be large, and to mammals to be small. One would have to examine the ecosystem in detail to discern what such advantages might be.

Answer 3

http://eduscapes.com/nature/lizard/index1.htm
arjournals.annualreviews.org/doi/abs/10.1146/annurev.ea