Over the past decades animals living in the rainforest unwittingly changed their diet, from healthy to "junk food". That's not because Burger King opened a new restaurant in the rainforest of Uganda, but because climate change has made leaves less nutritious than they used to be.
Latest research shows that in some tree species whose young leaves are most often eaten by red colobus monkeys, the ratio of protein to fiber had decreased by more than 30%. This reduction took place over the last 15-30 years as a result to global warming, however researchers are unsure which factors in the environment are causing the change in leaf chemistry. What is sure is that this new nature is not what we wished for, and neither the animals having to deal with those changes.
Local monkeys are managing the changes compensating their lack of nutritions eating double portion of leaves. For now this might still work for the monkeys, but as the trees are part of a big ecosystem the future effects are hard to predict.