Abstract
The abundance, diversity and community composition of ground-dwelling arthropods present in three different types of Cantabrian heathland grazed by small ruminants were studied. A factorial design of three vegetation types (heather-, gorse- or grass- dominated) and two grazer species (sheep or goats) with two replicates was established in twelve 0.6 ha paddocks. Ground-dwelling arthropods (Araneae, Opiliones, Isopoda, Julida, Microcoryphia, Hemiptera, Coleoptera and Hymenoptera) were recorded using pit- fall traps and plant cover and canopy height assessed in each paddock in 2005, 2006 and 2007. Higher abundances and more families of ground dwelling arthropods were recorded in areas dominated by heather, although certain species were more numerous in areas dominated by grass. The direct effects of the grazer species on arthropods were subtle compared to their great effect on the vegeta- tion. Significant interactions between grazer species and vegetation were observed for some taxa and the overall arthropod commu- nity composition. Gradient analyses indicate that arthropod assemblages that include Lycosidae, Opiliones and Carabidae differed between vegetation types and years, but are not affected by the grazer species. Our study shows that areas dominated by shrubby and diverse heather had the highest diversity and abundance of arthropods. Species composition varied along a gradient in the structure of the vegetation, which in turn was modified by the grazer species.
Highlights
Heathland is a semi-natural shrubland habitat that occupied large areas in the humid regions of Western Europe in the past (Gimingham, 1992), and currently the high rates of loss and degradation of this habitat are of special concern in many countries (Farrel, 1989; Piessens & Hermy, 2006) and their conservation the aim of various agro-environmental programs (Brown, 1990; Thompson et al, 1995)
Plant dynamics differed between vegetation types, and grazing effects were more pronounced in grass dominated than in heather dominated shrublands (Jáuregui et al, 2009)
Shrub cover and height decreased while herbaceous cover increased more in paddocks grazed by goats than by sheep
Summary
Heathland is a semi-natural shrubland habitat that occupied large areas in the humid regions of Western Europe in the past (Gimingham, 1992), and currently the high rates of loss and degradation of this habitat are of special concern in many countries (Farrel, 1989; Piessens & Hermy, 2006) and their conservation the aim of various agro-environmental programs (Brown, 1990; Thompson et al, 1995). While certain Coleoptera might be more affected by changes in the floristic composition than in the structural features, other groups such as Araneae, Opiliones, Hemiptera or Orthoptera respond mainly to the structural characteristics of the plant canopy (Gardner, 1991; Gibson et al, 1992a; Dennis et al, 1998; Wettstein & Schmid, 1999; Rosa Garcia et al, 2009) They are widely distributed, diverse and relatively well-known taxonomically, making them potential bioindicators. The current study aimed to test the following hypotheses: (a) the abundance and diversity of arthropods in shrubby and structurally more complex vegetation is greater than in simpler grass dominated vegetation; (b) sheep and goat grazing affect the arthropod fauna differently through their different effect on vegetation; and (c) grazing effects depend on the type of vegetation, i.e., is there is an interaction between both factors
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