1.5.2 The Oribatid Mite Data
Oribatid mites (Acari: Oribatida) are a very diversified group of small (0.2
to 1.2 mm) soil-dwelling, mostly microphytophagous and detritivorous arthropods.
A well-aerated soil or a complex substrate like Sphagnum mosses present in bogs
and wet forests can harbour up to several hundred thousand (10
5 ) individuals per
square metre. Local assemblages are sometimes composed of over a hundred
species, including many rare ones. This diversity makes oribatid mites an interesting
target group to study community-environment relationships at very local scales.
The example data set is composed of 70 cores of mostly Sphagnum mosses
collected in a peat moss mat bordering a small lake (Lac Geai) on the territory of
the Station de biologie des Laurentides of Université de Montréal, Québec, Canada
in June 1989. The data were collected in order to test various ecological hypotheses
about the relationships between living communities and their environment when the
latter is spatially structured, and develop statistical techniques for the analysis of the
spatial structure of living communities. It has since become a classical test data set,
used in several publications (e.g. Borcard et al. 1992; Borcard and Legendre 1994;
Borcard et al. 2004; Wagner 2004; Legendre 2005; Dray et al. 2006; Griffith and
Peres-Neto 2006). These data are available in packages vegan and ade4.
The data set ("mite.RData") comprises three files that contain the abundances of
35 morphospecies, 5 substrate and microtopographic variables, and the X-Y Cartesian coordinates of the 70 cores (in cm). The environmental variables are the
following (Table 1.3):
The cores have been sampled on a 10.0 m  2.6 m strip of various substrates
forming a transect between a mixed forest and the lake’s free water on the shore of an
acidic lake. Figure 1.1 shows the 70 soil cores and the types of substrate.
1.6 A Quick Reminder About Help Sources
The R language was designed to be a self-learning tool. So you can use and abuse of
the various ways to ask questions, display code, run examples that are imbedded in
the framework. Some important help tools are presented here (Table 1.4).
Table 1.3 Environmental variables of the oribatid mite data set used in this book and their units
Variable
Code
Units
Substrate density (dry matter)
SubsDens
gÁdm
À3
Water content
WatrCont
gÁdm
À3
Substrate
Substrate
7 unordered classes
Shrubs
Shrub
3 ordered classes
Microtopography
Topo
Blanket – Hummock
1.6 A Quick Reminder About Help Sources
7
Oribatid mites (Acari: Oribatida) are a very diversified group of small (0.2
to 1.2 mm) soil-dwelling, mostly microphytophagous and detritivorous arthropods.
A well-aerated soil or a complex substrate like Sphagnum mosses present in bogs
and wet forests can harbour up to several hundred thousand (10
5 ) individuals per
square metre. Local assemblages are sometimes composed of over a hundred
species, including many rare ones. This diversity makes oribatid mites an interesting
target group to study community-environment relationships at very local scales.
The example data set is composed of 70 cores of mostly Sphagnum mosses
collected in a peat moss mat bordering a small lake (Lac Geai) on the territory of
the Station de biologie des Laurentides of Université de Montréal, Québec, Canada
in June 1989. The data were collected in order to test various ecological hypotheses
about the relationships between living communities and their environment when the
latter is spatially structured, and develop statistical techniques for the analysis of the
spatial structure of living communities. It has since become a classical test data set,
used in several publications (e.g. Borcard et al. 1992; Borcard and Legendre 1994;
Borcard et al. 2004; Wagner 2004; Legendre 2005; Dray et al. 2006; Griffith and
Peres-Neto 2006). These data are available in packages vegan and ade4.
The data set ("mite.RData") comprises three files that contain the abundances of
35 morphospecies, 5 substrate and microtopographic variables, and the X-Y Cartesian coordinates of the 70 cores (in cm). The environmental variables are the
following (Table 1.3):
The cores have been sampled on a 10.0 m  2.6 m strip of various substrates
forming a transect between a mixed forest and the lake’s free water on the shore of an
acidic lake. Figure 1.1 shows the 70 soil cores and the types of substrate.
1.6 A Quick Reminder About Help Sources
The R language was designed to be a self-learning tool. So you can use and abuse of
the various ways to ask questions, display code, run examples that are imbedded in
the framework. Some important help tools are presented here (Table 1.4).
Table 1.3 Environmental variables of the oribatid mite data set used in this book and their units
Variable
Code
Units
Substrate density (dry matter)
SubsDens
gÁdm
À3
Water content
WatrCont
gÁdm
À3
Substrate
Substrate
7 unordered classes
Shrubs
Shrub
3 ordered classes
Microtopography
Topo
Blanket – Hummock
1.6 A Quick Reminder About Help Sources
7