Beavers cut, but do not prefer, an invasive shrub, Amur honeysuckle ( Lonicera maackii )
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ORIGINAL PAPER
Beavers cut, but do not prefer, an invasive shrub, Amur honeysuckle (Lonicera maackii) Janet L. Deardorff
. David L. Gorchov
Received: 18 October 2019 / Accepted: 19 September 2020 Ó Springer Nature Switzerland AG 2020
Abstract The North American beaver is a keystone riparian obligate which creates and maintains riparian areas by building dams. Invasive shrubs are common in riparian zones in the eastern U.S., but it is not known if beavers promote or inhibit these invasions. In southwest Ohio, we investigated beaver preference for Amur honeysuckle (Lonicera maackii), a prevalent riparian invader, compared to other woody species. At each of eight sites, we identified woody stems greater than 2.5 cm diameter on two 120 9 2 m transects parallel to the water’s edge and six, 25 m secondary transects perpendicular to these, recording diameter, distance to the water’s edge, and whether cut by beaver. The roles of plant genus, diameter, and distance to water in determining which stems were cut by beaver were determined by binomial generalized regression. Beaver preference for each genus and each site was quantified with an electivity index, which utilizes the proportion of stems cut compared to available stems. Probability of stem cutting depended
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10530-020-02365-8) contains supplementary material, which is available to authorized users. J. L. Deardorff (&) D. L. Gorchov Department of Biology, Miami University, Oxford, OH 45056, USA e-mail: [email protected]
on genus, diameter, and distance; stems closer to water and with smaller diameter had a higher probability of being cut. Although L. maackii comprised 41% of cut stems, it was low preference for beaver at six of eight sites. Beaver electivity for L. maackii was negatively associated with the density of small diameter stems of preferred taxa (Salix, Ligustrum, Pyrus, Carya and Acer negundo). These findings indicate that beaver do not hinder L. maackii. Another non-native shrub, Elaeagnus umbellata, had high electivities, suggesting beavers may impede its invasion. Keywords Castor canadensis Electivity Exotic species Riparian areas
Introduction Through heavy grazing or browsing, herbivores can change the composition of palatable and unpalatable plant species in an area (Tierson et al. 1966; Marquis 1981). Selective feeding on a non-native plant species could prevent invasion, consistent with the biotic resistance hypothesis (BRH), which states that ecosystems with higher biodiversity are more resistant to invasion than those with lower biodiversity (Elton 1958). In contrast, if the herbivore avoids or has low preference for the non-native species, that could
D. L. Gorchov e-mail: [email protected]
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J. L. Deardorff, D. L. Gorchov
promote invasion, as predicted by the enemy release hypothesis (ERH) (Maron and Vila 2001). North American Beavers, Castor canadensis, have been observed consumin
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