Eco-tourism is a major industry in Madagascar. It places economic value on their natural resources that would otherwise be exploited for income. If you're considering ecotourism, make sure to do some background on the companies before traveling to make sure that they are taking care of the land and area that you're going to see. It is important for tourism companies to have sustainable practices because they are acting as stewards of the land. Their goal should be to protect the land, not extensive capitalistic gains.
Around 50% of visitors to Madagascar visit protected areas1. This assigns a direct value to the natural wonders of Madagascar for the people. In addition, half of the park fees go to the local community not to mention the money that is put into local economies and infrastructure through the purveyance of local handiworks, and through jobs provided at the parks, restaurants, hotels, and as guides.
If you're looking for some trips, here are a few cites to check out.