159about invasiveness in Bromus grasses. We evaluated the data in the database to
identify factors for which information for many species could be found. We then
developed hypotheses about associations between these factors and invasiveness
based on the literature (Table 6.2 ).
6.2 Methods
6.2.1 Creation and Population of the Database
We created the database of information about Bromus species using Microsoft
Access 2007 and populated it with information from many sources including
regional fl oras and manuals, online databases, papers in peer-reviewed journals,
government documents, dissertations, and theses. Over three hundred references are
cited in the database, and these are associated with species. The bibliography sec-
tion includes many more references. Basic searches by scientifi c name and country
are available. Advanced search option allows users to fi nd and compare species with
specifi c traits or other properties and to search for references.
For analyses, we used the data available in the Bromus database. We used the
species listed in the Kew Gardens GrassBase database of global grass species
(Clayton et al. 2006+ ) and the Integrated Taxonomic Information System ( ITIS )
database as valid species for data analyses. In some cases, valid species differed
among these two databases and the USDA PLANTS database.
6.2.2 Statistical Analysis
For the statistical analyses, we defi ned four dependent variables : wide introduction,
crop weed, ruderal weed, and environmental weed. To defi ne these variables, we
separated commonly used defi nitions of invasiveness into two parts: (1) wide intro-
duction and (2) negative impact. To defi ne wide introduction , we developed a 1–5
scale based on the number of biogeographic realms occupied by each species—
Palearctic, Nearctic, Afrotropic, Neotropic, Indo-Malay, Australasia, Oceania, and
Antarctic (Udvardy 1975 ; Olson and Dinerstein 2002 ). These biogeographic realms ,
which “represent the unique fl ora and fauna of the earth’s continents and ocean
basins” (World Wildlife Fund 2014 http://worldwildlife.org/biomes ) differ slightly
from continents. North Africa is included in the Palearctic realm along with Europe
and northern Asia. This puts all of the Mediterranean region into a single realm
which maps better to typical Bromus native ranges. Species were assigned a distri-
bution score of 1–3 ( not widely introduced ) if they are confi ned to their native range
or to a single biogeographic realm outside of their native range and 4 or 5 ( widely
introduced ) if they are found in two (4) or more (5) biogeographic realms outside of
their native range. To identify species that are considered to have a negative impact ,
6 Attributes That Confer Invasiveness and Impacts Across the Large Genus Bromus...