Aquatic and terrestrial ecosystems are linked by flows of materials known as resource subsidies. Habitat alterations in one ecosystem can alter the magnitude, timing, or form of these subsidies and cause cascading effects in recipient systems. Beaver populations are recovering in North America and recolonization of these ecosystem engineers can alter channel geomorphology by converting stream channels into complexes of ponds and wetlands. These changes in the physical characteristics of the aquatic habitat can cause shifts in aquatic insect communities from lotic to lentic communities. Changes in aquatic insect community structure can lead to changes in aquatic insect emergence and potentially influence riparian bird communities. We examined how beaver recolonization influenced stream habitat type (pool vs riffle), aquatic insect emergence, and riparian bird communities in Kimball Creek, CO from 2012-2015. Kimball Creek represents a degraded western stream severly impacted by historically heavy cattle grazing and the extirpation of beavers. We quantified aquatic insect emergence using floating emergence traps and assessed riparian bird communities using bird point counts. We predicted sites with beaver ponds would have higher aquatic insect emergence biomass and abundance, and consequently higher riparian bird species richness.
Results/Conclusions
Preliminary analyzes indicates that beaver recolonization has caused a shift in habitat type among study reaches with many reaches exhibiting an increase in the proportion of pool habitat. For example, from 2012-2015 pool habitat increased from 57% to 94% for reach 2, and from 53% to 100% for reach 8. Thirty-three bird species were reported across all study reaches. Species richness among reaches ranged from 11-17. Previous investigations of bird communities around Kimball Creek have indicated a declining trend in species richness and diversity from upstream to downstream reaches corresponding to a gradient of increasing degradation at downstream reaches. This study elucidates how beaver recolonization may reconnect aquatic and terrestrial food webs previously severed by beaver extirpation.