The missing link: do impacts of beavers traverse aquatic-terrestrial boundaries?

Project Description

Reintroduction of keystone species such as beavers is considered part of the solution to the freshwater biodiversity crisis. A primary motivation for reintroducing beavers is to create heterogeneous habitats that support novel communities of animals and plants compared to the surrounding landscape. Beavers alter the structure and chemistry of their habitat, resulting in reduced flow rates and increased organic matter from inundated vegetation and input of falling leaves, which decomposes and releases nutrients that support the base of a food web consisting of shredders and detritivores (Nummi et al., 2011; Law et al., 2016). Case studies on beaver impacts have previously focused on few key taxa and demonstrated that many, but not all species benefit from beaver activity. For example, previous studies indicate that the impacts of beavers on freshwater insects – which play key roles in ecosystem functioning and are important indicators of ecological quality of freshwaters - are complex. Studies have reported reduced species richness in beaver-modified habitats at the local scale (Law et al., 2016; Washko et al. 2020), but important differences between sites (Law et al. 2016; Robinson et al. 2020) and increased richness and gamma diversity at the landscape scale due to the mosaic of habitats created in a beaver-inhabited landscape (Law et al. 2016). Insects that have aquatic and terrestrial life stages (e.g. mayflies, stoneflies, caddisflies, dragonflies, damselflies, mosquitoes, midges and others) are an important link between these two habitats, transferring material, nutrients and energy from water to land, and potentially impacting the trophic structure and dynamics of food webs. Many of these species are important food sources for terrestrial predators including spiders, predatory insects, and vertebrates such as amphibians, bats and birds. Previous research has demonstrated that bats benefit from the presence of beavers, presumably because of the increased number of emergent insects associated with beaver ponds (Nummi et al. 2011). However, the diversity and abundance of terrestrial insects associated with beaver habitats has not yet been investigated, and the flow of energy up the food chain from aquatic to terrestrial habitats has been overlooked when investigating impacts of beavers. The aims of this project are therefore to:
1. Determine how beaver activity traverses the aquatic-terrestrial boundary by impacting the diversity and abundance of insects with aquatic and terrestrial life stages.
2. Investigate whether the impact of beaver activity can be seen higher up the terrestrial food chain, by investigating the diversity and abundance of terrestrial invertebrate consumers.

We hypothesize that aquatic insect community composition will be different in beaver habitat compared to the surrounding area, with a shift towards species that favour slow-flow or no flow conditions, and that abundance of emergent insects and their terrestrial predators will be higher in beaver-modified habitats, but depend on the spatial scale of investigation (Law et al. 2016).

The student will carry out rigorous spatio-temporal surveys of both aquatic and terrestrial insects along a transect from upstream to downstream of the reintroduction site at the Cropton Beaver Trial, North Yorkshire. Other UK beaver reintroduction sites will potentially also be sampled. We are currently seeking larger scale funding to continue this work, beyond the MSc, but conventional surveys may be complemented with eDNA surveys if funds permit. The project is in partnership with Forestry England, Natural England and BugLife.

Law, A., McLean, F. and Willby, N. J. (2016) ‘Habitat engineering by beaver benefits aquatic biodiversity and ecosystem processes in agricultural streams’, Freshwater biology, 61(4), pp. 486–499.
Nummi, P. et al. (2011) ‘Bats benefit from beavers: a facilitative link between aquatic and terrestrial food webs’, Biodiversity and conservation, 20(4), pp. 851–859.
Robinson, C. T. et al. (2020) ‘Beaver effects on macroinvertebrate assemblages in two streams with contrasting morphology’, The Science of the total environment, 722, p. 137899.
Washko, S., Roper, B. and Atwood, T. B. (2020) ‘Beavers alter stream macroinvertebrate communities in north‐eastern Utah’, Freshwater biology. Available at: https://onlinelibrary.wiley.com/doi/abs/10.1111/fwb.13455.