Long term effects of altered aquatic-terrestrial subsidies (NERC funded)
Summary
Streams and rivers are linked to the terrestrial habitats around them by the exchange of nutrients, detritus and organisms. Most investigations of these exchanges have focused on how aquatic systems are influenced by inputs from the terrestrial environment, but more recent work has identified the potential importance of flows of material from the aquatic habitat to the adjacent terrestrial habitat. A substantial part of aquatic animal production is insects, which as they emerge, move into the riparian habitat where they become prey for terrestrial predators (e.g. spiders and beetles). Short-term manipulations of aquatic subsidies have demonstrated that the availability of aquatic subsidies can result in a distributional response of riparian predators along the stream edge. However, to understand the ecosystem and community consequences, we need to know whether such findings can be "scaled-up" in space and time: are the density and community structure of riparian consumers along streams really determined by differences in the productivity and composition of aquatic insects? This study will address this gap in our understanding and the findings could have important management and conservation implications. If aquatic subsidy is important, protection of terrestrial species may depend as much on the management of aquatic habitats as it does on the management of the riparian habitats themselves.
Aims
The aim of this research is to understand the effects that aquatic subsidy has on riparian food web function. Specifically, we will test whether:
- predators respond to increased subsidy by changing their diet, moving into riparian habitats, or having increased population growth.
- input of energy to terrestrial predators changes the impact they have on other terrestrial species (herbivores), and the processes (herbivory) these species drive.
Approach
We will use distributional and movement studies, experimental field exclosures, and a combination of stable isotope analyses and dietary sampling to disentangle the complex effects of aquatic subsidies on terrestrial ecosystems.