Resource subsidy flows across freshwater-terrestrial boundaries and influence on processes linking adjacent ecosystems

Freshwaters receive more than water from their catchments, including a large amount of materials and biologically available energy, referred to as cross-ecosystem resource subsidies. The passive flows of energy such as leaf litter and terrestrial invertebrate inputs, as well as dissolved organic carbon, are donor-controlled, whereas other flows, such as between fish and fish-eating birds, have more directly coupled feedbacks. There are also flows upstream or to the terrestrial environment in the form of adult aquatic insects, salmon carcasses and particulate carbon through overbank flooding, as well as directed foraging activities. Hypotheses about the effects of flux rates, timing, quality and physical structure of such resource subsidies on the responses of consumers have been experimentally tested at many trophic levels. Many freshwater and terrestrial consumers depend on these subsidies for at least part of their life cycle, and timing of inputs can affect growth. Developing more quantitative relations between the population and community responses across gradients of cross-ecosystem resource subsidy input rates will require exploring the shape of the relations, as well as the effects of quality and timing on responses. The stage is now set to consider how resource subsidies might affect the stability of communities and processes such as the strength of trophic cascades. The high degree of connectivity between the land and water are essential to biodiversity conservation and to ensuring that critical aquatic ecosystem services are sustained. The management of riparian areas is a key to the security of these values. Copyright (c) 2014 John Wiley & Sons, Ltd.