Is man really at the top of the food chain?

Wondering with man eating from a grain of rice to even tiger meat why would someone even doubt if this species that has made its appearance recently on the face of earth, be the top of the food chain? This thought did not come to me out of the blue.

After a fun filled spring weekend I was watching the series "Life" on discovery. I loved it as it covered a lot of physiology of animals, their social behavior and their evolutionary adaptation techniques. At one point they showed an amphibian in a desert like mountainous terrain being the food of an Arachnid... hey wait a minute that is strange, mmm Arachnids are spiders and pre-dates Amphibians (like frogs) with respect to evolution. A komodo dragon eating a mammal - pigs, buffalo etc., bizarre again atleast to my head.

After watching more of lower evolved animals eating higher evolved ones, I was thinking what it takes to be the top of all, Say like Simba of Lion King, It should be the collective cognitive skills of Homo sapiens isn't it? It is almost impossible to overpower carnivores like Lions, Tigers etc., and even herbivores like Rhinos, wild yaks etc by a single man, I have even seen some of the documentary on how ice age men brought down mammals for food, how they stored food to last longer and how they invented farming and have enough brain power to "create" their own food! From the evolutionary perspective that is mind boggling and that’s what makes us the kings :) mmm Just a wild thought, if dinosaurs were still roaming on earth would it have been possible for us to have born and come this far? Will there be anything in futue to bring us down? Has evolution met a saturation point? Would we adapt to even global warming? Have you ever wondered on such lines?