Introduction The more than 5,400 mammal species are divided between 28 orders (Figure 19.1), almost all of which include species that occur in forests. Mammals occupy every substantial area of forest worldwide and play multiple ecological roles (Table 19.1). The diversity of most large orders peaks in the tropics (Rolland et al., 2014), and more than 120 species of mammals have been recorded from the richest tropical rainforest sites (e.g. Happold, 1996; Voss and Emmons, 1996; Figure 19.2). Diversity declines slowly with latitude but rapidly with isolation on oceanic islands, reflecting the poor cross-water dispersal of most taxa. Diversity has also declined since the Pleistocene origin and spread of modern humans. The majority of terrestrial ecosystems outside Africa have lost large mammals since the middle Pleistocene (Corlett, 2013) and declines in vulnerable species have accelerated in recent decades (Di Marco et al., 2014).