Academic journal article The American Midland Naturalist

Revisiting the Role of Aquatic Plants in Beaver Habitat Selection

Academic journal article The American Midland Naturalist

Revisiting the Role of Aquatic Plants in Beaver Habitat Selection

Article excerpt

INTRODUCTION

Beaver (Castor canadensis, C. fiber) have long been a compelling research subject due to their extensive ecological impacts. In contemporary times understanding long-term beaver habitat selection remains important because beaver can promote ecological restoration and help mitigate the effects of climate change on water resources (Albert and Trimble, 2000; Emme and Jellison, 2004; Pollock et al., 2004; Maringer and Slotta-Bachmayr, 2006; FaceCollins and Johnston, 2007; Burchsted et al., 2010; Buckley et al., 2011; Carpenedo, 2011; Wild, 2011; Baldwin, 2013). In addition beaver flooding of private lands continues to be problematic, requiring management decisions that are scie_72.tifically informed (Albert and Trimble, 2000; Emme and Jellison, 2004; Pollock et al, 2004; Maringer and Slotta-Bachmayr, 2006; Face-Collins and Johnston, 2007; Burchsted et al., 2010; Buckley et al., 2011; Carpenedo, 2011; Wild, 2011; Baldwin, 2013).

Beaver habitat selection has been extensively investigated through studies that compare beaver occupancy or density with habitat characteristics, yet several limitations remain (Appendix A, Table Al). One limitation is the duration of study. Studies of beaver habitat selection over 1 to 2 y are abundant but longer-term studies are few {for exceptions, see Howard and Larson, 1985; Broschart et al., 1989; Fryxell, 2001). Another limitation is the type of aquatic habitat considered. Most related research has focused on stream habitats, whereas fewer studies have considered factors affecting beaver selection of different lake habitats {finexceptions, see Slough and Sadleir, 1977; Fryxell, 2001). Finally, empirical research demonstrates lack of consensus regarding the importance of deciduous woody vegetation to beaver habitat selection. The most broadly used beaver habitat suitability index (HSI) for North America (Allen et al., 1983) considers woody vegetation a key limiting factor, and some studies have found woody vegetation variables are important to beaver occupancy or density {e.g., Slough and Sadleir, 1977; McComb et al, 1990; Fustec et al., 2003; František et al, 2010). However, in other research, woody vegetation had a weak or negligible relationship with beaver occupancy or density {e.g., Howard and Larson, 1985; Beier and Barrett, 1987; Robel et al., 1993; Hartman, 1996; Barnes and Maliik, 1997; Suzuki and McComb, 1998; Cox and Nelson, 2009).

Some discrepancy is to be expected between beaver habitat selection in different locations or times, particularly regarding generalist herbivores such as beaver that can adjust food choices based on availability (Northcott, 1971; Histøl, 1989). Resource availability is heterogeneous over space and time such that in different locations or time periods, varying factors may limit an animal's potential to occupy a site (Hunter and Price, 1992). Nonetheless, resource managers may benefit from further clarification of factors that address unexplained variation of beaver occupancy and density given the importance of beaver habitat selection to a range of wetlands management efforts.

Aquatic plants (macrophytes) may be important to beaver habitat selection but have scarcely been assessed in previous empirical studies (Appendix A, Table Al). Exceptions include two studies that solely considered water lily species (Nuphar spp. or Nymphaea spp.). Water lilies were important to C. canadensis density in lakes and streams of Ontario over time (Fryxell, 2001) but not to C. fiber occupancy of Swedish streams in a single year (Hartman, 1996). Macrophytes can be consumed with minimal predation risk (Fryxell and Doucet, 1993) and may offer some nutritional benefits to beaver over terrestrial plants, including better digestibility, higher crude protein, and higher sodium and iron (Fraser et al, 1984; Tischler, 2004). One modeling effort found that energetics did not explain beavers' observed preference for white water lily {Nymphaea odorata) over terrestrial species, but authors only considered lily leaves and stems without accounting for beaver consumption of water lily rhizomes (Doucet and Fryxell, 1993). …

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