If CO2 was in very small amounts then it would be the limiting factor of photosynthesis, this means the process will take place at a much slower rate because it is lacking one of the raw materials it needs for the process to occur. To find the optimum light intensity you really need all other factors to be at optimum levels or in abundance.
The correct answer is sex linkage.
Sex linkage refers to the phenotypic expression of an allele, which relies upon the gender of an individual and is directly associated with the sex chromosomes. These genes are regarded sex-linked as their expression and patterns of inheritance vary between the males and females. The sex linkage cannot be the same as genetic linkage, the sex-linked genes can be associated genetically.
The answer your looking for is adaptation. I would know, for I just recently finished a chapter on it.
Because the small area of that desert provides the provisions the organism needs. They adapt to their climate, so as long as the desert keeps its supply, the organism will stay