My 2cents. To tell you the truth, I do like the picture as it is. The dark empty space above does give me a feeling by itself. Though the rule of third does apply to many composition, it does not have to apply in all photos. I think a tighter shot may seems too focus on the subject but as it is, it gives me the overall ambience feeling of its environment. The lighting, texture of the branch and position of the iguana gives a very strong aethestic feeling to it.