Seen from space, the Luquillo Mountains stand out on the eastern edge of Puerto Rico like a dark-green eye in the midst of a heterogeneous matrix of fields, forests, roads and cities in the surrounding lowlands (Fig. 1). Intercepting clouds, rain, and Saharan dust as these cross the Atlantic and make landfall in the Caribbean, the peaks of the Luquillo Mountains – El Yunque, El Toro, East Peak, and West Peak – capture resources to sustain coupled human and natural systems. The Luquillo Mountains are not tall by global standards, rising only to just over 1000 m in the short distance from the coast to the peaks, but this moderate elevational relief creates gradients that are expressed in the form and functioning of the landscape. Understanding the way in which species and ecosystems respond to gradients of climate and land use intensity is vital to the sustainability of populations, water resources, and ecosystem services. In the Luquillo Mountains these patterns are expressed in the context of the rich biodiversity of the tropics and the complex interplay of land use, hurricanes, and plant and animal responses to resources and competition. The patterns expressed by the distributions of species and the ecosystem functions that they carry out are dynamic. Understanding the nature of gradients, and responses of species to them, helps to better predict responses to future conditions and ultimately to develop and sustain the kinds of landscapes that support societal interests and human wellbeing.