Human-induced environmental change has affected ecosystems on a global scale, altering the ecology and evolutionary trajectories of various species. Animal behavior is highly vulnerable to shifting with human impact and shifts and individual variation in animal behavior can influence functioning of the ecosystems they inhabit. Harvest of predators, for example, can have cascading effects on the behavior of their prey as they experience reduced predation pressure. Alternatively, depletion of food sources can cause wildlife to shift their behavior to access alternative food sources. Here, I explore anthropogenic impact to animal behavior and the knock-on consequences any such changes may have on ecosystems in two different systems: shoaling fish on coral reefs and seabirds that nest on oceanic islands. On coral reefs, I explored differences in shoaling behavior of coral reef fishes on two islands whose predator populations face differing fishing intensities and shed light on the ecological role of shoaling behavior to coral reefs. Fishing of marine predators and cascading effects on marine ecosystems is of critical concern. Predators are thought to be an important reason for why fish shoal, thus, reducing predator populations could alter shoaling behavior for prey fish. I also specifically characterized movement and foraging-associated behaviors of one of these fishes in this same comparative context. My work suggests that in areas with reduced predator abundance the tendency of some, but not all, fish species to form shoals is reduced. Additionally, I found differences in movement, grazing, and interactions with heterospecific fish between shoaling and solitary fish. These observations shed some empirical light on how overfishing could affect shoaling behavior and suggests that social behavior of individual may play an important role in mediating their ecological function. On oceanic islands, I examined the effects of large nesting colonies of Western Gulls (Larus occidentalis), which are known to forage on human refuse, on the Channel Islands of California. Specifically, I explored how their foraging on anthropogenic food sources may change nutrient deposition patterns at their relatively remote and protected breeding islands. Mobile animals that traverse ecosystem boundaries can fundamentally reshape environments by providing critical nutrient and energy inputs to the ecosystems they inhabit. In particular, aggregations of seabirds often transform coastal and island ecosystems through large amounts of nutrient-rich guano deposition. Anthropogenically-driven losses of these subsidies can occur through changes in abundance of mobile species, including seabirds, and have been shown to drive whole scale ecosystem state change on islands. However, even though many species that forage on anthropogenic food sources are highly mobile and may thus play important roles in moving nutrients from urban systems to otherwise conserved ecosystems, the impacts of anthropogenic supplements to spatial subsidies have been largely ignored. I found high (up to 40%) but site-specific rates of urban foraging, resulting in between 66 and 93 kg of guano per hectare (ha) on these two sites during the breeding season, driving marked seasonal increases in soil nitrogen and phosphorus content comparable to nutrient deposition in industrial agriculture. By exploring similar facets of animal behavior in two separate systems, my research highlights the footprint that human activity can cast on even remote ecosystems through impacts to animal behavior