December 2012 Number 1 - Utah Native Plant Society

Calochortiana December 2012 Number 1
Spatial Patterns of Endemic Plant Species of the Colorado Plateau
Crystal M. Krause,
Northern Arizona University, Biological Sciences, Flagstaff, AZ
Abstract. The Colorado Plateau region supports one of the highest levels of endemism in the United States. Of the
6,800 vascular plants of the region more than 300 are endemic. Endemic species may have a higher risk of extinction
due to their restricted geographic range. This risk may be increased with climate change. To better understand the risk
to endemics, ecological niche modeling can provide a better understanding of the dynamics of environmental factors
on a species range. For the endemics of the Colorado Plateau, a changing climate may modify species range. But underlying
factors such as substrate and specialized habitat will also play a role in how a species range may change. The
focus of this study is to understand spatial patterns and factors that predict endemism and then model species potential
distribution.
The Colorado Plateau ecoregion supports one of the
highest levels of endemism in North America, ranking
in the top three ecoregions on the continent for the total
number of endemics in all taxonomic groups (Ricketts
et al 1999). The Colorado Plateau also has the highest
rate of endemism in terms of actual numbers of species
(Kartesz and Farsted 1999). The harsh, dry environment
of the Colorado Plateau has historically placed intense
environmental stress on the flora. Factors such as soil,
climate, and water scarcity among others seem to limit
the geographic range of many species. More than 300
species of vascular plants on the Colorado Plateau are
endemic. Many of the endemic plant species are edaphic
endemics restricted to one soil type, but larger geographic
patterns of plant endemism can also be seen in
the Colorado Plateau’s “sky island” habitats. Other important
areas are those below 2000m; these lower elevations
have a greater number of endemics than higher
elevations (Welsh 1978).
The Colorado Plateau contains 122,805,655 acres of
land, of these 3,622,942 acres (3 percent) are protected
lands in National Parks and Monuments, another
64,748,735 acres (52 percent) are federally owned
(Figure 1). Land ownership is also unique for the Plateau
with the third most federally controlled land per
area of all other ecoregions. Protected areas of the Colorado
Plateau have a pivotal role to play in enabling species
and ecosystems to persist. Protected areas can remove
or control many of the threatening processes such
as habitat loss and fragmentation.
The distribution of endemic plants in protected areas
is not fully known and very little work has been completed
in modeling distribution shifts in response to climate
change. To better understand the complexity and
variability climate change may have on the distribution
of plants and animals, ecologists have recently developed
the concept of computationally based Ecological
Niche Models (ENMs) (Peterson, Soberon and Samcjez-
Cordero 1999; Peterson and Vieglais 2001; Stockwell
and Peters 1999). ENMs integrate a wide range of environmental
data (including point location data) to define
potential species habitats. The output of ENMs is a set
of grids of potential habitat based on the co-occurrence
of known species locations and various environmental
conditions. Each grid is assessed for accuracy by comparing
a set of reserved species locations to the predicted
habitat distributions.
The predicted ENM habitats can be projected onto
past, current, and modeled future landscapes thus providing
testable habitat conditions that can be compared
to known conditions to assess model accuracy and improve
environmental predictions (Peterson et al. 2002).
Projection onto the current landscape indicates the present
day geographic distribution of suitable conditions
for these plant species - the species potential habitat.
Comparing these projections to historical and current
location data provides information on the changes that
plants have made in their dispersal in response to disturbances
and environmental changes in the recent past.
Projecting the model onto future landscapes provides
information of how climate change may affect the species
distribution and dispersal ability.
METHODS
MaxEnt
Data collection is the first step in modeling a species
distribution; species location point records and environmental
data are needed for the model. Location point
records used in this study are from herbaria and Natural
Heritage Programs from the Four Corners region, National
Park Service and the Bureau of Land Management.
Species with occurrence points from less than 10
populations were excluded from modeling because prior
studies have demonstrated that fewer than 10 populations
is not meaningful without extensive habitat re-
63