KNOWLEDGE BASE

This paper reported on an analysis of beavers and fish biodiversity across a 780 km2 area in the USA. The researchers found a complex relationship, where beaver pond age, the order of the stream, and other environmental conditions, all influenced fish biodiversity. However, one clear conlusion was that beaver ponds promoted fish species diversity, especially in smaller streams. The text also considers how beavers' historic extinction in the local area may have influenced fish populations.

By the early 20th century, only about 1,200 Eurasian beavers remained in eight distinct populations, due to over-hunting. This paper reported how conservation efforts had increased their numbers to around 430,000 by the end of the 20th century, although three of the relict populations remained endangered. Habitat destruction and competition with North American beavers were ongoing threats, and growing beaver populations were increasing human-beaver conflict. The paper recommended preservation and restoration of riparian woodlands with natural water regimes.

This study quantified the survival rates of juvenile Atlantic salmon in a Canadian stream using seven years of data. The paper discussed different factors influencing the variation in survival rates. Beaver dams were noted as a factor which can limit the migration and influence the density of fish at different stages of their lifecycle.

In Alaska, scientists tested some theories predicting the relationship between ecosystem disturbances (such as flooding) and species richness (as a measure of biodiversity). Their study sites included some beaver ponds, as well as other streams and wetlands. This text reported on their findings, which supported the idea that occasional flooding supported a high number of species.

In this remarkable study, researchers showed how beavers indirectly benefit a (very cute!) species of leaf beetle in the USA. Beavers had cut cottonwood trees, which regrew but containing twice the level of defensive chemicals in their new shoots. This 'resprout' growth empowered beetle populations, with the beetles benefitting from more nitrogen and energy in the shoots. The beetles even processed the plant's defense chemicals to make their own, making them better defended against their predators. Overall, this process was shown to support biodiversity and regeneration of a now-rare habitat in the USA.