The ecological impact of climate change has been well-documented in tropical cloud forests, where weather patterns and topography conspire to create a persistent cloud settling into a mountain saddle and an insular ecosystem characterized by high endemism and steep climatic and biological gradients. The long-term studies of Costa Rica's Monteverde Cloud Forest by herpetologist J. Alan Pounds and others have chronicled a drying trend since the mid-seventies, and a corresponding loss of frog and lizard species, along with an invasion of submontane bird species into cloud forest habitat. As the lower elevations begin to desiccate, birds like the Emerald Toucanet (Aulacorhynchus prasinus) can follow the cloud as it slips over time up the mountainside, as long as their preferred habitat persists in the area. Less mobile species, like the Spiny-headed Treefrog (Anotheca spinosa), find greater difficulty adapting to the change. Pounds has also postulated that dissolved toxins from air pollution may become concentrated in the sparser mist, and that climate change may assist the spread of lethal amphibian chytridiomycosis in montane habitats.