Abstract
Mammalian grazing induces changes in vegetation properties in grasslands, which can affect a wide variety of other animals including many arthropods. However, the impacts may depend on the type and body size of these mammals. Furthermore, how mammals influence functional trait syndromes of arthropod communities is not well known.We progressively excluded large (e.g. red deer, chamois), medium (e.g. alpine marmot, mountain hare), and small (e.g. mice) mammals using size‐selective fences in two vegetation types (short‐ and tall‐grass vegetation) of subalpine grasslands. We then assessed how these exclusions affected the community composition and functional traits of ground beetles (Coleoptera, Carabidae), and which vegetation characteristic mediated the observed effects.Total carabid biomass, the activity densities of carabids with specific traits (i.e. small eyes, short wings), the richness of small‐eyed species and the richness of herbivorous species were significantly higher when certain mammals were excluded compared to when all mammals had access, regardless of vegetation type. Excluding large and medium mammals increased the activity density of herbivorous carabid species, but only in short‐grass vegetation. Similarly, excluding large mammals (ungulates) altered carabid species composition in the short‐, but not in the tall‐grass vegetation. All these responses were related to aboveground plant biomass, but not to plant Shannon diversity or vegetation structural heterogeneity.Our results indicate that changes in aboveground plant biomass are key drivers of mammalian grazers’ influence on carabids, suggesting that bottom–up forces are important in subalpine grassland systems. The exclusion of ungulates provoked the strongest carabid response. Our results, however, also highlight the ecological significance of smaller herbivorous mammals. Our study furthermore shows that mammalian grazing not only altered carabid community composition, but also caused community‐wide functional trait shifts, which could potentially have a wider impact on species interactions and ecosystem functioning.
Highlights
IntroductionMammalian herbivores can alter plant biomass (Fleischner 1994, Hulme 1996, Bardgett and Wardle 2003), vegetation structure (Morris 2000, Woodcock and Pywell 2010), plant species composition (Pykälä 2003, Hülber et al 2005) and plant diversity (Olff and Ritchie 1998, Joern 2005) in grassland ecosystems through (selective) grazing (Hülber et al 2005), trampling (van Klink et al 2015b), burrowing (Bangert and Slobodchikoff 2006) and dung deposition (Schütz et al 2006)
Total biomass of carabids was significantly higher in the tall-grass than in the short-grass vegetation (Table 1, Fig. 1a), and was significantly higher when both large and mediumsized mammalian herbivores were excluded (‘S/I’), or when all mammals were excluded (‘I’) than when all mammalian herbivores were present (‘L/M/S/I’)
Our result suggests that total carabid biomass is more sensitive than total carabid activity density for identifying the effects of short-term changes in mammalian grazing intensity on carabids
Summary
Mammalian herbivores can alter plant biomass (Fleischner 1994, Hulme 1996, Bardgett and Wardle 2003), vegetation structure (Morris 2000, Woodcock and Pywell 2010), plant species composition (Pykälä 2003, Hülber et al 2005) and plant diversity (Olff and Ritchie 1998, Joern 2005) in grassland ecosystems through (selective) grazing (Hülber et al 2005), trampling (van Klink et al 2015b), burrowing (Bangert and Slobodchikoff 2006) and dung deposition (Schütz et al 2006) These changes in vegetation characteristics can, in turn, have cascading effects on a wide variety of invertebrate taxa (Bardgett and Wardle 2003, van Klink et al 2015a, Vandegehuchte et al 2018), but usually depend on the intensity, timing, duration of grazing (O’Neill et al 2003) and the productivity of the habitat (Daskin and Pringle 2016, Vandegehuchte et al 2017). Invertebrates with specific functional or ecological traits (e.g. dispersal ability, feeding habits, habitat preference) can differ in their responses to grazing of different sized mammals (Carvell 2002, Dennis 2003, Karen et al 2008, Vandegehuchte et al 2018) and modulate mammalian grazing effects on invertebrate community composition and structure (Dennis et al 1997, Cole et al 2006)
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