Great Basin Naturalist Memoirs
Volume 2 Intermountain Biogeography: A Symposium
Article 6
3-1-1978
The flora of Great Basin mountain ranges: diversity,
sources, and dispersal ecology
K. T. Harper
Department of Botany and Range Science, Brigham Young University, Provo, Utah 84602
D. Carl Freeman
Department of Botany and Range Science, Brigham Young University, Provo, Utah 84602
W. Kent Ostler
Department of Botany and Range Science, Brigham Young University, Provo, Utah 84602
Lionel G. Klikoff
Department of Biology, Allegheny College, Meadville, Pennsylvania 16335
Follow this and additional works at: http://scholarsarchive.byu.edu/gbnm
Recommended Citation
Harper, K. T.; Freeman, D. Carl; Ostler, W. Kent; and Klikoff, Lionel G. (1978) "The flora of Great Basin mountain ranges: diversity,
sources, and dispersal ecology," Great Basin Naturalist Memoirs: Vol. 2, Article 6.
Available at: http://scholarsarchive.byu.edu/gbnm/vol2/iss1/6
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THE FLORA OF GREAT BASIN MOUNTAIN RANGES:
DIVERSITY, SOURCES, AND DISPERSAL ECOLOGY
K. T. Harper', D. Carl
Abstract.— The high elevation
floras of
Freeman
1
,
W. Kent
Ostler
and Lionel G. Klikoff2
1
,
9 mountainous "mainlands"
(3 in
the Sierra-Cascade system and 6 in
the High Plateau-Wasatch-Teton system) and 15 isolated mountain "islands" in the Intermountain Region have
been analyzed. Mainland
area
floras
support more species per unit area and show a smaller increase in diversity as
increased than islands. In this respect, the isolated mountains behave as true islands.
is
demics
is
low on the islands (never exceeding 5 percent of any
whelmingly dominated by species with no apparent modifications
flora),
The number
however; and the island
of en-
floras are over-
Furthermore, the east-
for long-range dispersal.
ern mainland has exerted a far greater influence on the flora and the vegetation of the islands than has the
western mainland, despite the fact that the former
dispersal ecology,
by long-range
they were less
and sources
We
dispersal.
is
downwind
of the islands. Thus, evidence from endemics,
mountains have not acquired their
of the floras suggests that the isolated
conclude that although the
floras of the islands
isolated in the relatively recent past than at the present.
The
full floras
have many insular characteristics,
island floras
do not appear
to
be
in
equilibrium in the sense that immigrations equal extinctions.
The biogeography
and Wilson 1970, Brown 1971a, Heatwole
and Levins 1972, and MacArthur, Diamond,
and Karr 1972).
In this paper we consider the vascular
of disjunct segments of
similar habitat has intrigued biologists since
the days of Charles
Darwin (1859) and A.
Wallace (1880). Their pioneering observations were based primarily on oceanic islands, but others have analyzed the biology
R.
plant floras of islandlike enclaves of mesic
environment on high mountains
in
the
of such habitats as caves (Culver, Holsinger,
deserts of the Great Basin. In the strictest
and Baroody 1973), woodlots (Curtis 1956),
fresh water lakes (Barbour and Brown
1974), and isolated patches of herb land in
sense, these high
high-elevation forests (Vuilleumier 1970).
desert
agules
carriers
their
may
rest
in
the
fact
of the unfavorable environments that sepa-
is
of islandlike environments to
partially explained
by the
rate the islands (Billings 1977). Furthermore,
can be prepared for several disjunct points
reasonably short time. Furthermore,
evidence suggests that at varying times in
is-
land systems are ideally suited for the analysis of
the
such dynamic processes as dispersal,
community
structure
ics also
appear
strated
and more
to
confined
studied
in
(Lindeman
1942,
the
of
islands
to
the
slopes
of
the
to that
were
now
mountains
Berger 1967). Nevertheless, the tops of the
high
island
systems than in larger, more heterogeneous
environments
many
(Wells and Jorgensen 1964 and Wells and
and trophic dynam-
have been better demoneasily
Pleistocene
connected by vegetation similar
competition, and evolution. Basic principles
of
or
complete inventories of selected taxa
The appeal
in a
less isolated
and survive to move on again. Also,
species of the mountain islands could evolve
(and apparently often have) from the floras
biologists
that
mountains are
than oceanic islands, since dispersing prop-
mountains of the arid West provide
patches of habitat that may have
disjunct
much
Simberloff
in
'Department of Botany and Range Science, Brigham Young University, Provo, Utah H4WI2
'Department of Biology, Allegheny College, Meadville, Pennsylvania 16335.
81
common
with real
islands.
GREAT BASIN NATURALIST MEMOIRS
82
Methods
and the Teton-Wasatch-High
in Wyoming, Idaho, and
Utah) have long had relatively free access
California
Plateau
This paper
or
floras
is
based entirely on published
of
checklists
collected extensively
ranges.
We
utilize
workers
No. 2
who have
on specific mountain
9 floras from the more-
system
to large floras
adapted for
life
at
high ele-
vations and thus qualify as mainland floras
in the
parlance of island biogeographers.
The mountain
have been assigned
mountain systems that
flank the Great Basin on the west and east
and floras or checklists for 15 mountain
discrete
ranges in or near the Great Basin (Fig.
1,
elevation of these islands and their distance
floras
from the mainlands were taken from topo-
or-less
Table
continuous
1).
We
have assumed that the
of the relatively continuous flanking
tain
Fig.
moun-
systems (the Cascade-Sierra system in
1.
Location of the floras considered.
the
islands
boundaries which are defined by
7500 foot contour
graphic
maps.
line.
The
size
and
Island-to-mainland distances
were computed by summing the distances
1
1
INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM
1978
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83
GREAT BASIN NATURALIST MEMOIRS
84
across inter-island barriers of desert
(areas
ranges than
below 7500 feet) along the
possible from a particular
route
we have
shortest
island
the
to
tion
No. 2
now
is
Accordingly,
available.
used only area, elevation, and loca-
our analysis of factors controlling
in
nearest edge of each mainland.
plant diversity.
It should be noted that our island areas
and distances to mainlands do not always
agree with those reported by Brown
(1971a), Johnson (1975), and Behle (1977),
who have used some of the same islands
that we have. Those discrepancies arise
from the manner in which the mainland
and island borders are defined by the sever-
The component species of each checklist
have been individually considered for in-
authors.
al
Brown
(1971a),
for
example,
combined the White and Inyo ranges, but
the flora used in our work (Lloyd and Mitchell 1973) covers only the White MounJohnson (1975)
tains.
let
the lower edge of
woodland serve as the edge of his
islands, while we have followed Brown
(1971a) and used the 7500 foot contour as
species from
known
We
our study.
clusion in
the
have eliminated
which are not
checklists
occur above 7500
to
Species
feet.
and reproduce in desert environments have also
been excluded. This latter criterion was
used to improve the likelihood that the isthat are potentially able to survive
lands considered are at least currently functioning as islands.
in
We
experienced difficulty
rigidly applying this last criterion, since
some
species
which occur above 7500
feet
forest or
along the eastern edge of the Great Basin
the island edge.
do not extend above that elevation in the
Sierras. We have included all species which
occur above 7500 feet on the eastern edge
In Johnson's (1975) work,
the Pine Valley Mountains
to
were considered
be part of the mainland, but our
dictate that those mountains
an
criteria
be considered
of
Great Basin
the
deserts) but
do not tolerate
(that
normally occur below that
ele-
vation on the western mainland.
For each species included
island.
we have noted
in
the study,
means of disand geographic range. The lifeform
As noted elsewhere in this symposium
(West et al. 1977), distance to the nearest
mainland is a weak ecological variable in
categories recognized are:
the Great Basin, since each mountain range
ennial
has probably received migrant species from
shrub, or 5) tree. Categories of dispersal in-
We
measured the width of
valley barrier between each mountain system and both mainlands in an effort to obboth mainlands.
tain
better
a
understanding
of
the
bio-
geographic consequences of distance.
(1976)
demonstrated that habitat diversity
exerts
a
strong
and vascular
influence
on diversity
of
plants, respectively. John-
son (1975) used plant criteria to quantify
habitat
diversity
for
birds on
clude:
Great Basin
forb,
3)
mega wind,
1)
2)
annual, 2) per-
1)
perennial
graminoid, 4)
miniwind,
3) stick-
no apparent modification.
Species were placed in the
following groups with respect to geographic
tight, 4) fleshy fruit, or 5)
range:
Johnson (1975) and Harner and Harper
birds
persal,
lifeform, likely
occurring on both mainlands, 2)
1)
confined to
the
western mainlands and a
few isolated mountains, 3) confined to the
eastern mainlands and a few isolated mountains, or 4) known only from one or a few
mountains
of
the
in this study.
several
Because the authors
checklists
were uneven
in
mountains, but his criteria for habitat diver-
their treatment of taxa of subspecific rank,
would lead to circular logic if they
were used to help explain plant diversity.
Conceivably, one could devise a habitat diversity measure based on physical characteristics of the sample areas, but a useful mearequire
more
sure
would
probably
information about individual mountain
we have
sity
It
will
ignored such taxa.
be recognized that many arbitrary
decisions are required to classify
all
of the
species in respect to the foregoing characteristics.
We
classification
have
given
mgren and Reveal
followed
in
the
(1966),
the
index
lifeform
of
except that
Hol-
we
85
INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM
1978
have separated annual plants from perennial
We
herbs.
consider
be dust-like seeds
megawind propagules
(as
in orchids)
with large plumose appendages
to
and seeds
(as in
milk-
geographic range
ciencies of the
have used them
certain
for
we
lists,
analyses
that
would have been otherwise impossible
to
make.
We
weeds) that can be expected to be regularly
have used Holmgren and Reveal
transported over a mile by wind. Miniwind
(1966) as our nomenclatural authority for
propagules are considered to include such
species occurring
fruits as
winged
some chenopods,
utricles of
samaras of maples, grass caryopses that have
surface-to-volume ratios, and winged
large
the Great Basin.
in
menclature of species that occur
nia but
do not occur
in the
Munz and Keck
lows
all
No-
in Califor-
Great Basin
(1959).
fol-
Species
Normal dispersal distance
miniwind propagules is probably no more
than a few yards. The sticktight category
according to Kearney and Peebles (1951) or
includes "hitchhiker" fruits such as those of
Clokey
Xanthium, Arctium, Circaea, and Bidens
which are presumably adapted for dispersal
largely resolved with the
seeds of conifers.
mentioned that occur
of
study area but not in California are
(1951).
the south of the
to
named
Problems of synonymy were
Holmgren and Re-
veal (1966) checklist.
on the fur or feathers of vertebrates. Under
the heading of fleshy fruits, we include
drupes,
pomes,
and
berries,
sume
Results
cones
fleshy
such as those borne by Juniperus.
We
as-
The Study Areas
such propagules appeal to and
that
are often dispersed
by
birds.
Our
Propagules des-
ignated as having no modifications for dis-
produced by a great variety of
which seeds are relalarge, have a small surface-to-volume
and are without wings or plumose ap-
samples are drawn from 6
and from areas ranging in size from 1
3,630 square miles. The mainland floras
floristic
states
persal are
to
dry-fruited species in
are distributed across a north-south gradient
tively
450 miles in the west (3 floras) and
600 miles in the east (6 floras). The 15 islands are geographically centered on the
Great Basin and are spread across more
than 400 miles of distance in both northsouth and east-west directions (Fig. 1). Maximum elevation varies from 14,495 to 9105
ft above sea level among mainland areas
and from 14,246 to 8235 ft among islands
ratio,
pendages.
The categorization
individual
of
species
according to geographic range also present-
ed
difficult
recorded
problems.
on
were separated
previously
lists
Once
computer
the floras
cards,
the
were
species
into the four floristic groups
mentioned.
Examination of the
thus compiled demonstrated that
some
of about
(Table
1).
of the species that supposedly occurred only
Unfortunately, few climatological stations
on western mainlands did in fact also occur
infrequently on the eastern mainlands, even
though they were not encountered on any
of the checklists. In like manner, some species on the list of taxa found only on checklists from the eastern mainlands are known
are maintained at high elevations in the re-
to occur (usually sparingly)
on the western
mainland. Finally, species that occur on
land checklists but not on mainland
lists
is-
are
rarely local endemics, but are instead north-
ern or southern species or
uncommon main-
land species that have reached some of the
isolated
mountains.
Despite
these
defi-
gion.
The few data
that are available sug-
and westmainlands are somewhat similar in
respect to annual precipitation and potential evaporation at comparable elevations,
gest that the climates of eastern
ern
while the island areas tend to receive
precipitation
and
less
to experience greater po-
tential evaporation than either mainland.
Conditions conducive to aridity appear to
be maximal on the more southerly of the
mountain islands considered (United States
Department of Interior 1970).
GREAT BASIN NATURALIST MEMOIRS
The Flora
A
above 7500
ft
considered in
percent
Species confined to the western mainland or
of 2,225 different
total
elevation
in
species occur
the
24
floras
paper. Approximately 27
this
occur
species
those
of
No. 2
on
both
that occur
on the mainland and a few
Agropywn
&
pringlei (Scribn.
Allium obtusurn
mainlands and on occasional mountain
ranges between the mainlands. Some 29
percent of the species appear on the western but not the eastern mainland, and
roughly 30 percent of the species are represented on the eastern but not the western
mainland. The remaining species (about 14
Libocedrus decurrens Torr.
were recorded only on island
checklists (Table
2).
Bromus
breviaristatus Buckl.
Carex amplifolia Boott
Carex tahoensis Smiley
Cheilanthes gracillima D.C. Eaton
Cryptantha mohavensis (Greene) Greene
Hulsea brevifolia Gray
Mimulus
torreyi A.
Gray
Oryzopsis kingii (Bol.) Beal
Pinus jefferyi Grev.
Species representative of those occurring
Sm.) Hitchc.
Lemmon
Artemisia douglasiana Bess.
percent)
iso-
lated mountains include the following:
&
Balf.
&
Populus trichocarpa Torr.
Gray
on both mainlands include the following:
Prunus emarginata (Dougl.) Walp.
Aconitum columbianum Nutt.
Stipa californica
Sequoiadendron giganteum (Lindl.)
Balsamorhiza
sagittate. (Pursh)
&
Merr
Davy
Taxus brevifolia Nutt.
Nutt.
Trifolium andersonii A. Gray
Carex aurea Nutt.
Tsuga mertensiana (Bong.) Carr.
Carex lanuginosa Michx.
Elymus glaucus Buckl.
Epilobium angustifolium
Species confined to the eastern mainland or
L.
to that
Equisetum arvense L.
Fritillaria
Geum macrophyllum
mainland and a few
islands are rep-
resented by the species listed below.
atropurpurea Nutt.
Willd.
Glyceria eUita(Na.sh) A.
S.
Abies lasiocarpa (Hook.) Nutt.
Hitchc.
Hackelia floribunda (Lehm.)
Lonicera involucrata (Rich.)
M.
Bank
I.
Acer grandidentatum Nutt.
Johnst.
Balsamorhiza macrophyllum Nutt.
Besseya wyomingensis
& Am.
Qsmorhiza chilensis Hook.
(A. Nels.)
Rydb.
Populus tremuloides Michx.
Calamagrostis scopulorum M. E. Jones
Pinus ponderosa Laws.
Ceanothus martini M. E. Jones
Purshia tridentata (Pursh)
Chlorocrambe hastata
DC.
Sitanion hystrix (Nutt.)
J.
adunca
J.
Wats.) Rydb.
&
Gray
Erigeron ursinus D.C. Eaton
G. Smith
Geum
Thalictrum fendleri Engelm.
Viola
(S.
Clematis columbiana (Nutt.) Torr.
Ribes cereum Dougl.
rossii (R. Br.) Ser.
Hierochloe odorata
G. Smith
(L.)
Beauv.
Mertensia arizonica Greene
Moldavica parviflora (Nutt.) Britton
Orthocarpus tolmiei Hook.
&
Arn.
Pinus edulis Engelm.
Table
istics
General distributional character-
2.
of the flora considered.
Primula parryi A. Gray
2.225
Total species
Quercus gambelii Nutt.
Ribes wolfii Rothrock
Species occurring on checklists
613
from both mainlands
Picea pungens Engelm.
Thermcypsis
montana Nutt.
Species confined to western mainland
or occurring on western
and some
Species occurring on the checklists of some
mainland
the isolated mountains but on neither
mainland include local endemics as well as
more widespread species that penetrate our
of
islands but not on
eastern mainland
Species confined to eastern mainland
or occurring on eastern mainland
and some
area
islands but not on
western mainland
Species recorded only on islands
from
primarily
northern
Representatives
678
floras.
288
groups are
listed
below.
of
or
each
southern
of
these
87
INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM
1978
Endemics Listed by Location
Castilleja linoides
Eriogonum
and well removed from the maindo not differ significantly (Table 3).
had anticipated that since perennial
close to
lands)
Ruby Mountain Area
We
Gray
kingii Torr.
&
Gray
Primula capillaris Holmgren
Spring Range
Angelica scabrida Clokey
&
&
show
forbs
Holmgren
preference
a
more
land habitats appear to be
Mathias
more mesic
for
(Harner and Harper 1973) and the
sites
is-
xeric than
Antennaria soliceps Blake
the mainlands, such species might be under-
Castilleja clokeyi Pennell
represented on the isolated mountains.
Cirsium clokeyi Blake
data lend no support to that idea.
Opuntia charlestonensis Clokey
Penstemon keckii Clokey
species
Clokey
Potentilla beanii
Silene clokeyi C. L. Hitchc.
&
among
ported in Table
Maguire
The number
Synthyris ranunculina Pennell
Tanacetum compactum Hall
the
also uniformly
floristic
groups
re-
3.
of annual species
is
consid-
erably higher on the western as opposed to
Toiyabe Mountains
Draba arida C.
and graminoides are
distributed
The
Woody
the eastern mainland (Table
L. Hitchc.
3).
In fact,
if
only herbaceous species are considered, Chi-
Mertensia toyabensis Macbr.
num-
square analysis demonstrates that the
Wheeler Peak
Eriogenum Holmgrenii Reveal
ber of annual species on the two mainlands
Species Entering from North
departs significantly from
Castilleja viscidula A.
Gray
Cymopterus
Wats
nivalis S.
cies
Erigeron watsoni (A. Gray) Cronq.
significantly
Also,
tions.
occur
in the
combined
island flora does not differ
Species Entering from South
Agastache pallidiflora (Heller) Rydb.
eastern
Antennaria marginata Greene
and
mainland
are
species
Arenaria confusa Rydb.
&
Schult.
flora
of
floras of
Festuca arizonica Vasey
in
Billings (1972)
Aqailegia triternata Payson
Roem.
flora of the
is-
lands than on the western mainland, but the
Selaginella selaginoides (L.) Link
Eleocharis montana (H.B.K.)
random expecta-
fewer annual spe-
this
from that of the
more common
the
Chabot
respect.
have noted that annual
Sierras
than
the
alpine
other
alpine
in
in
North America.
Muhlenbergia wrightii Vasey
Floristic Diversity Considerations
In respect to lifeform characteristics, the
floras
the
of
Table
lands
3.
mainlands and islands (both
Species-area
flora
Lifeform relationships of the floras considered.
was a barrier width
"far islands" category:
The
for
criterion for separation of near
of less than or greater than 100 miles.
Deep Creek,
relationships
the
The following
among
floras)
is
and
far
numbers
of species in
enclosed by parentheses.
Lifeform Class
Group
W. mainlands
Perennial Herbs
Shrubs
Forbs
Graminoides
is-
four islands constitute the
Jarbidge, Santa Rosa, and Spring. Expected
each category (assuming random distribution of lifeform classes
Floristic
total
and various lifeform subsamples there-
Annuals
Total
GREAT BASIN NATURALIST MEMOIRS
88
of are
shown
Figure
in
2.
both mainlands and islands
Three generalizations can be
for
under
No. 2
do exhibit strong
study
similarities
with true islands.
The
may be
drawn from that figure: 1) there are consistently more species per unit area on the
attributable to the classification of a single
mainlands than on the
flora.
We
flora
as
islands, 2) floristic di-
third
strates that
accounts for more of the variation in spe-
consistently
on mainlands
line
correlation coefficients for species-area
line
cies diversity
(i.e.,
relationships
on
are
islands than
larger
usually
for
islands
1 and 2
numerous island
(MacArthur and Wil-
for
flora
fall
but Figure 2 demonand lifeform subsamples
on the species-area trend
and well below the trend
for
mainlands. Correlation coefficients
both mainlands and islands would have
improved had we classified
as an island. The area lies
been
Canyon
Bryce
at
commented on here only
tinuous system of highlands extending south
from northern Utah and along the western
AREA ISO MILES)
Fig. 2. Species-area relationships for
mainland and island
floras.
Relationships for the total flora and
various lifeform subsets thereof are shown. Mainland data are represented
with triangles. The individual
respond to specific
A
floras are identified in the
floras identified in
regression equations; subscript
and
the
southern extremity of the more-or-less con-
emphasize that the isolated mountains
son 1967) and are
to
its
islands
than for mainlands). Observations
biogeographic studies
mainland,
for
have been duplicated
in
partially
have treated the Bryce Canyon
on islands than mainlands as area increases, and 3) area usually
versity increases faster
observation
represents area.
i
Table
1.
diagram
by
dots; insular floras are
for total species
shown
combined: numbers cor-
Subscript c indicates mainland correlation coefficients or
indicates island coefficients
and equations. S represents number
of species
INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM
1978
edge of the Colorado Plateau. We initially
considered the habitat breaks along the
highland
corridor
be
to
and
short
in-
consequential as migration barriers and thus
on the mainland classification for the
In retrospect, it seems likely that the
settled
area.
decreasing likelihood of an island being col-
onized by dispersing taxa as size decreases
and
increased likelihood of local extinc-
2)
Brown
mals on
pected
set
has
corridor
in the area.
species-area
Slopes (Z-values) for the
shown
regression lines of Figure 2 are
as
the exponents of area (A) in the equations
The Z-value
associated with the figure.
0.11
for
on the
flora
total
mainlands
commonly
of
is
and 0.326
mam-
has previously reported a Z-value
mammals, using a more
of 0.428 for boreal
group of species and a different
restricted
mountains (Brown
of
for boreal
Great Basin moun-
sites of isolated
He
tains.
little islands.
Z-values of 0.165
reports
(1977)
for boreal birds
combined
with general climatic differences and unusual soils to effectively filter out numerous
northern taxa that would otherwise be exnarrowness of the
on
tion of small populations
Our Z-
1971a).
value for vascular plants on isolated mounthose for boreal
lies between
which seem definitely to be in equilibrium on the moimtains (i.e., neither inthus
tains
birds,
creasing or decreasing in respect to
number
re-
of species per unit area over long time peri-
ported (e.g., 0.12-0.17 by MacArthur and
Wilson 1967). The average Z-value of .19
believed to be losing species by local ex-
smaller than
slightly
reported
values
quadrats
nested
for
juniper ecosystems of Utah and
in
pinyon-
New
Mexi-
co (Harner and Harper 1976) should probably not be
compared
to
the Z-values ob-
tained for mainlands in this study, since
seems
rats
likely that Z-values for nested
where the
few acres
largest
sample area
it
quadonly a
is
always be larger than values
will
for regional floras
from areas ranging
in size
from a few to several hundred square miles.
The Z-value
of 0.31 for the total flora of
islands (Fig. 2)
is
well within the range of
ods),
and small boreal mammals, which are
new
tinction faster than
Plants
mammals than
like
taxa can colonize.
general appear to behave
in
like birds
more
on the moun-
and perennial herbs yield
tains considered,
Z-values that are especially steep and ap-
proach the values reported for mammals.
Both area and maximum elevation of the
mountain ranges were strongly positively
correlated with total vascular species on
those ranges in this study (Table 4). There
was a weak negative correlation between
number
and distance
of species
to the near-
values (0.20-0.35) reported for a variety of
est
mainland. In multiple correlation analy-
kinds of biota on true islands and close to
sis,
only area makes a large contribution to
value
of
expected
(MacArthur and Wilson 1967).
the
the
theoretically
0.26-0.27
We
call attention in passing to the fact that
woody
plants have
flatter
species-area
gression lines than perennial herbs
mainlands and
The
lines
on both
of
species-area
regression
mainlands has been attributed to
the fact that small sample areas there carry
individuals of
adapted
to the
many
of
multiple
related with area
little
new
species that are poorly
sample area but nevertheless
determination
relation
(r
=
0.66) that
it
brings
information into the multiple cor-
analysis.
Distance also
multivariate equation; but
islands.
flatness
for
re-
coefficient
(R 2 ). Elevation appears to be so closely cor-
contributes only
slightly
it,
enters
over 0.01 to the
Revalue (Table 4).
The overwhelming dominance of area
the
multiple
correlation
probability, an illusion.
and
Harper
the
like elevation,
analysis
is,
in
in
all
Wyckoff (1973) and
have demon-
occur there because vigorous populations of
Harner
each such taxon
suitable
strated that both environmental favorability
(MacArthur and Wilson 1967). The
(annual precipitation and/ or soil texture)
and environmental heterogeneity (variation
in soil characteristics, elevation, and/or ex-
habitats
exist
in
nearby,
steepness of species-area trend lines for
lands
is
related to at least
two
factors:
is-
1)
(1976)
No. 2
GREAT BASIN NATURALIST MEMOIRS
90
posure)
strong
a
exert
on
influence
the
number of vascular plant species per unit
area. However, since area subsumes all of
these
variables,
alone
it
consistently
ac-
counts for a highly significant amount of
variation
the
in
diversity
floral
almost
in
number
of
species
analyses, but
it
multiple
the
tion
in
The
dissimilar
simple
in
makes a
correlation
analysis.
species
number-
for
results
correlation
sizeable contribu-
distance relationships for species of western
may be
or eastern mainland origin
related
any suite of samples. Unfortunately, data on
environmental favorability and hetero-
to
geneity are not available for the sample of
western mainland (149 miles) than from the
mountains considered here.
We
have thus
the
Table 5 seem
in
single
We
commented
plicating effect of
earlier
two
on
the
com-
close mainlands in
evaluate
between
the
island
influence
of
distance
and mainland on floristic diwe have measured the
more
considered
distant
from the
to
suggest that use of a
(distance
may
nearest
to
We
main-
obscure the impor-
tance of distance in studies of island
is-
land biogeography studies. In order to better
distance
land) as in Table 4
distance.
islands
eastern (117 miles). In any event, the results
nevertheless useful variables of area, eleva-
and
the
are on the average
resorted to the use of the less definitive but
tion,
that
fact
floras.
recognize also that a decrease in spe-
any given checklist is to be expected
one moves away from the center of the
cies of
as
geographical area sampled for the checklist.
every island from each mainland. Then, by
Such a decrease with distance would be expected even in large continental areas of
relatively uniform climate, topography, geo-
using only species that appear to be con-
logical
versity of the islands,
width
unfavorable
of
habitat
separating
fined to one mainland or to one mainland
and a few
islands
(i.e.,
species
common
to
both mainlands or unique to islands were
excluded),
we
used simple and multiple cor-
substratum, and geological history
and may have nothing to do with dispersal
habits of the species.
flect
The decrease may
rienced by locally evolved taxa as they at-
expand
relation to analyze the relative influence of
tempt
and distance from mainland
on the number of species from either eastern or western mainlands on the 15 islands.
The results (Table 5) show that distance
now becomes the major factor influencing
the number of western mainland species on
the islands. For eastern mainland species,
established vegetations.
area, elevation,
distance
Table
is
is
not significantly correlated with
4.
Factors influencing the
measured
to the nearest
Factor
Area of island
Elevation of highest peak
Distance to mainland
number
re-
nothing more than the difficulty expe-
to
their
range
through
Sources of the Flora
In this section
we
consider the question
of source of the floras of the isolated
tains.
cal
How
endemics make to the
lated ranges?
ft.
mountain
lo-
floras of the iso-
Are the island
of vascular plant species on the 15
mainland area having an elevation over 7500
moun-
important a contribution do
floras
islands.
derived
Distance
INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM
1978
In order to evaluate the relative contribu-
equally from eastern and western mainlands,
or
one source more important than the
is
and eastern mainland floras
we have separated out
species unique to western as opposed to
eastern mainlands (see Table 2). The relation of western
to individual islands,
other?
In respect to endemics, the data suggest
that their contribution to the floras of the
isolated
91
mountains
comparatively minor.
is
contribution
tive
of
eastern
high elevations appears to be considerably
plotted
on the Spring Range (the Charleston
Mountains which Clokey [1951] studied are
part of this range) than on any other range
mainlands in Figure
of
larger
even on the Spring
Yet
considered here.
is
respective
the
to
or
The data demonsource
area
many more
con-
species to
western
source
only one island (the White
Moun-
than
islands
On
3.
eastern
the
contributes
sistently
the
distance
against
that
strate
western
uniquely
on individual islands
species
endemics of moderate-to-
The number
does the
Range, which Clokey (1951) considered to
be about five million years old, endemics
area.
account for only about 5 percent of the
flora above 7500 ft. Endemics account for
a larger percentage of the total flora than
than 2 percent of the White Mountain
the preeminence of the eastern source area
less
flora
(Lloyd and Mitchell 1973). In contrast,
plant endemics on
many remote
oceanic
is-
the eastern. As will be
to
Such data force one
1974).
conclude that the mountain ranges con-
sidered
are
far
less
isolated
oceanic islands such as
waiian
Islands,
or
New
the majority of the flora
Table
5.
St.
than
remote
Helena, the Ha-
Caledonia,
is
endemic.
Factors influencing the
number
where
shown
later (Fig. 4),
can be demonstrated for
in island floras
To
further illustrate the relative contribu-
tion of the respective mainlands to the
we have compiled
land floras,
matrix for
24
the
Table
in
7.
of vascular plant species
and on islands only are excluded. Width
from each mainland has been determined for all islands.
(Table
among
At
first
6).
floras
glance,
the low sim-
on the islands when species occur-
Western Mainland Species
Contribution to
Coefficient
Number
(r)
Coefficient of
Determination (R 2
of Species
Elevation of highest peak
.644
W. mainland
.646
Distance to
Multiple
with
)
.502
Area of island
.092
.417
Total
.509
R =
.714
Eastern Mainland Species
Contribution to
Coefficient of
Simple Correlation
Coefficient
Factor
Number
(r)
Multiple
with
Determination (R 2 )
of Species
Area of island
.590
Elevation of highest peak
.306
Distance to E. mainland
.137
among
Various interare summarized
of barrier (distance) separating an island
Simple Correlation
is-
a similarity
possible combinations
all
floras
relationships
ring on both mainlands
Factor
all
dispersal types.
lands account for over 50 percent of the
flora (Carlquist
does the western mainland contribute
tains)
.348
.156
Total
.504
R =
.710
No. 2
GREAT BASIN NATURALIST MEMOIRS
92
ilarity
values seem
to
indicate
little
com-
The second
the western, mainland.
of the
values
foregoing items indicates, as one might ex-
must be evaluated in light of the way in
which they are computed: for example, the
37 percent similarity value between the
to those ranges. Read-
mountain
be a more random assemblage of species than is found in individual
floras on either mainland. Items 3 and 4 indicate that the island floras have been more
referred to the similarity equation
influenced by the eastern than the western
among
monality
floras,
but
those
Ruby and Deep Creek Mountains
223 species
ers are
common
represents
pect, that the flora of individual
islands tends to
given in the legend for Table 7 for details
mainland,
of computation.
"downwind"
Several relationships reported in Table 7
merit attention:
1)
internal similarity of the
from the western mainland
identical to the comparable figure
floras
ern mainland
less
similar
floras, 2)
to
is
almost
for east-
the island floras are
each other than are floras
from either mainland,
3)
island floras are,
on the average, more similar to eastern
mainland floras than to western mainland
floras, and 4) even islands closest to the
western mainland have slightly closer floristic
affinities
40,—
W
30
m
Q
LU
20
with the eastern, rather than
despite
(in
the
this
fact
case,
they
that
the
lie
prevailing
westerly winds) from the western mainland.
This
last fact
is
visually conspicuous in the
many
of the dominant plants of
most of the isolated mountain ranges have
eastern affinities. Examples of such domi-
field since
nant,
or at least abundant,
plants
the following:
Agropijron spicatum (Pursh) Scribn.
Amelanchier
alnifolia (Nutt.) Nutt.
Amelanchier atahensis Koehne
Artemisia arbuscula Nutt.
Artemisia tridentata Nutt.
&
Smith
include
INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM
1978
Bromus anomalus Rupr.
Caltha leptosepala
DC.
Ceanothus martini M. E. Jones
Delphinium occidentale
(S.
Wats.)
S.
Wats.
Geranium fremontii Torr.
Holodiscus dumosus (Hook.) Heller
Juniperus osteosperma (Torr.) Little
Lathyrus pauciflorus Fern.
Lewisia rediviva Pursh
Oenothera eaespitosa Nutt.
Pachistima myrsinites(Puish) Raf.
Phlox longifolia Nutt.
Primula pamji A. Gray
Ranunculus
jovis A. Nels.
Valeriana occidentalis Heller
Since others (McMillan 1948 and Major
and Bamberg 1967) have speculated about
the relative effectiveness of northern and
southern migration lanes from the western
Rocky Mountains
outliers of the
in provid-
ing species for interior Great Basin
tains,
we have
ing the similarity matrix of Table
we have summarized
interior
Ruby,
three
moun-
investigated that problem us6.
Below
the relations of four
ranges in the Basin (Deep Creek,
Toiyabe,
and Wheeler Peak) with
northern sources (northern Wasatch,
Mount Timpanogos, and Red Butte Canyon)
and two southern sources (Bryce Canyon
National Park and Pine Valley Mountains).
Average
Mountain Range
Deep Creek
Percent
with
Similarity
Three
Two
Northern
Southern
Sources
Sources
93
GREAT BASIN NATURALIST MEMOIRS
94
Kalmia
polifolia
ered in Table
Wang.
Ledum glandulosum
Nutt.
propagules
Finns albicaulis Engelm.
Rubus
8.
Species having miniwind
between
contribute
and
28.8
33.5 percent of the species. Together, these
parviflorus Nutt.
two
Southern Route
types account for almost 85
dispersal
On
percent of the species considered.
Creene
ArctosUiphtjlos patula
No. 2
the
average, species having propagules modified
Nieotiinui attenuata Torr.
Pivaphullum ramosissimum (Nutt.) Rydb.
by wind (megawind
for long-range dispersal
Pinus aristata Engelm.
dispersal
Pinus ponderosa Laws.
cent
type)
of
all
contribute
species
in
almost
our
7.5
floras.
per-
Fleshy
fruited species contribute slightly fewer spe-
Dispersal Ecology
Plant
dispersal
habits
in
cies (average 6.1 percent of all species),
both mainland
and island floras are dominated by types
which have no apparent modifications for
dispersal and types with weak modifications
for dispersal by wind (Table 8). For convenience,
we
refer to the latter category as the
"miniwind"
modification.
Species
whose
propagnles have no apparent modifications
for dispersal
account for from 50.4 to 53.7
percent of the species in the floras consid-
Table
6.
Similarity
among
ed are percent similarity
area in Table
1.
species
dispersed
the few
by
sticktights
and
contribute
remaining species (about 2.5 per-
cent).
Our data
modified
for
indicate
that
long-range
dispersal
movement
types
(i.e.,
and megawind categories) show
no tendency to be overrepresented on the
remote islands (Table 8). In contrast,
Carlquist (1967) has shown that as many as
58 percent of the plant species that reach
fleshy fruit
the 24 floras as determined with the Jaccard (1912) similarity index. Values report-
for all possible pairs of floras. Checklist
numbers correspond
to those assigned to
each
INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM
1978
remote oceanic islands are dispersed
inter-
by birds (mostly fleshy fruits). Propagules borne externally on birds by virtue of
nally
being held
quently
place by barbs or
in
account
also
(sticktights)
20
over
percent)
of
He found windborne
troductions.
be poorly represented (usually
percent of the flora) on
Table
all
less
the
in-
seeds to
than 10
of Jaccard (1912). Jaccard's index
is
among
computed
in flora A,
and B
represents the number of species
is the number in flora B.
Areas Considered
Western mainland
(internal similarity)
Eastern mainland (internal similarity)
Mountain
islands (internal similarity)
W. mainland compared
E.
with islands
mainland compared with islands
W. mainland compared with E. mainland
Four closest islands to W. mainland
compared to W. mainland
Four closest islands to W. mainland
compared
Four
to E.
mainland
closest islands to E.
compared
Four closest
compared
to
mainland
W. mainland
islands to E.
to E.
mainland
mainland
considered ecolog-
island
to
be strong
determinants of the dispersal types that succeeded.
In
contrast
to
Carlquist's findings,
Hed-
berg (1970) found wind-dispersed plants to
represent almost 30 percent of the flora
above about 7900
on the mountains of
ft
east Africa. In Hedberg's study, plants dis-
the floras considered.
C
C
He
the
The index
of similarity used
is
that
as follows:
SI
In the equation,
islands.
conditions on
ical
(fre-
save the closest
Floristic similarity relations
7.
prickles
many
for
remote
of the
95
X
100.
common
to the
two
floras,
A
is
the
number
of species
Average
No. of
No. of
Floras
Comparisons
Percent
Involved
Averaged
Similarity
3
GREAT BASIN NATURALIST MEMOIRS
96
by birds accounted
internally
to 2 percent of the alpine flora of
1
The
is
relationship
presented
between
various
dis-
and island-to-mainland distance
in
Figure
4.
There,
we
regress
percent saturation of species of various
persal habits
coefficients
(i.e.,
the
number
dis-
of species of
a given dispersal habit on each island
pressed as a percentage of the
is
ex-
number of
would be
is
between correlation
disparity
for
saturation-distance
and western species
for eastern
east Africa.
persal types
The great
for
persed
only
No. 2
noteworthy. In five of the
much
r-values are
cies.
It
six
analyses
Figure 4
in
analyses the
larger for western spe-
seems possible that those values
age of the two
flect a differential in
on
elements
most
of
the
re-
floristic
islands.
If
the
Rocky Mountains are much older than the
Sierras, as Billings (1977) reports,
it
pos-
is
that the eastern floristic element has
species of that dispersal habit that
sible
expected in an area of comparable size on
dispersed essentially to
the appropriate mainland) against distance.
poorly related to distance, while the west-
As expected, the regression lines all have
negative slopes, and there is a slight (but
statistically nonsignificant) tendency for dis-
ern element
persal types that are easily dispersed over
of
long distances (megawind and fleshy fruit
demonstrate
types) to have regression lines with gentler
ennial
slopes than are obtained for species that are
represented
be dispersed far from the parAverage slope values for western
less likely to
ent plant.
and eastern mainlands and each
type are shown below.
dispersal
Type
Slope Value
Megawind
.03
Fleshy Fruits
.05
Miniwind
.08
Sticktight
.(MS
No
.07
in
Figure 4 also support our
earlier conclusion that the eastern
has exerted a
greater
influence
now
is
actively dispersing.
call
and
species
(i.e.,
attention
con-
a
to
plant
that
graminoid
the
in
Our data
lifeform.
woody
plants
species
and
are
broad-range
per-
over-
category
occurring on both mainlands) and un-
derrepresented
in
the
unique to islands (Table
category
9).
of species
Perennial forbs,
mainland
on the
mountain islands than has the western mainEvery dispersal type shows greater
land.
observed
evolutionary
rather
than dispersal processes. In general,
woody
plants
The data
and
spicuous relationship between range limits
terns
Modification
limit
on the other hand, display a significant tendency toward underrepresentation in the
broad-range
category
and
overrepresentation in the island-only class. Annual species show no significant trends in
this respect. It seems possible that the pat-
Average
Dispersal
is still
we
Finally,
its
ically
to
reflect
and graminoides appear to be ecologbroad niched and to have the ability
become community dominants. In conmany perennial forb genera seem to
trast,
be narrow niched and to rarely achieve a
dominant place in their community.
saturation for eastern species than for species
from the western mainland. Since the
number
the
of species originating from each of
two mainlands
Table
2),
is
roughly
equal
Discussion
(see
the results in Figure 4 suggest that
species from the eastern mainlands have
been about four times as effective in reaching and surviving on the islands as those
from the west. On the average island, western species have a saturation value of 8 percent, but the comparable value for species
from the eastern mainland is 36 percent.
Mountains
One might
as Islands
expect an island flora to be
distinguished from that of the nearest main-
land in a variety of ways. As
study,
it
seemed
should display
1)
to
us
that
we began
insular
this
floras
an overrepresentation of
species modified in one
way
or another for
97
INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM
1978
long-distance dispersal, 2) fewer species per
and/ or extinction (See Critchfield and Al-
on the mainland, 3)
steeper species-area curves than for mainland floras, 4) uneven stocking of species
ecologically preadapted for existence on
lenbaugh
unit area than observed
available islands,
and
higher rates of en-
5)
demism than the mainland.
Our results demonstrate
satisfy
and thus
qualify as islands, but they fail to qualify on
other counts. The islands do indeed have
of our preconceived notions
fewer species per unit area than adjacent
mainlands, and species-area trend lines for
than those for mainAlthough the amount of en-
steeper
are
islands
lands (Fig.
2).
demism
low on the
is
representation of species modified for long-
range dispersal on the islands in large part
The isolated mountains are overwhelmingly dominated by species with no
obvious means for being dispersed great distances. Furthermore, there is no tendency
failed.
that the isolated
mountains of the Intermountain West
some
1969 for range details for these
and other conifers in the Great Basin.)
Our expectations relative to an over-
islands
than 5 percent), the amount
(always less
still
appears to
for species with
tance
modifications for long-dis-
dispersal
to
be overrepresented on
even the most distant islands (Table 8). Our
data do, however, show a weak tendency
percent saturation of poorly dispersed
for
species
(i.e.,
sticktight
more
no-modification, miniwind, and
categories)
to
decline faster and
reliably (larger r-values) with distance
be higher than on areas of comparable elevation and size on the mainlands. Too,
there is uneven stocking of species on the
islands. The Pine Forest Mountains of extreme northwestern Nevada, for example,
than for megawind and fleshy-fruited spe-
by Pinus albicaulis Engelm., the
Santa Rosas by Pinus flexilis James, while
the Jarbidge and Ruby Mountains to the
east and the Sierras to the west have both.
The observed distribution pattern for these
and many other species [e.g., Abies concolor
(Gord. & Glend.) Lindl. and Picea engel-
have
mannii Parry ex Engelm.] seems explainable
only in terms of randomness of colonization
perses the seeds of several pines
are stocked
Table
cies
9.
Range
which are probably more
persed (Figure
in
each category.
easily
dis-
4).
Recent literature references demonstrate
that at least
some
classified
of the species that
we
unmodified for dispersal
as
are, in fact, highly
adapted for dispersal by
we placed all
vertebrate animals. Although
conifers with
unwinged seeds
in the
dified-for-dispersal category, a recent
unmopaper
by Vander Wall and Balda (1977) shows
that
P.
the
Clark's
albicaulis,
and
Nutcracker regularly
P. flexilis)
Plant lifeform relative to the range limits of the species considered. Expected
appears in parentheses
Category
cies,
(P.
dis-
edulis,
in a sublingual
number
of spe-
GREAT BASIN NATURALIST MEMOIRS
98
pouch and caches them in soil suitable for
and growth. In addition,
their germination
Nutcracker
the
known
is
to
and Pinus ponderosa in northern Arizona.
Vander Wall and Balda (1977) have evidence for the dispersal of seeds over 13
miles in a single flight by the Nutcracker.
In California, the Nutcracker regularly
feeds on and caches the seeds of Pinus monophylla Torr. & Frem. and Pinus jefferyi as
well as Pinus albicaulis and Pinus flexilis
(D. Tomback, personal communication).
narrowed the barriers between
cantly
Our
discussion
each
volved
clusively.
long-distance
iferous tree seed.
munication)
J.
con-
of
transport
Pederson (personal com-
reports
Band-tailed
the
that
Pigeon has been taken several miles from
the
nearest
Quercus gambelii
south-
in
eastern Utah with a crop full of unbroken
mountains as
of
islands
would not be complete without some comment on the question of equilibrium of species number on the islands. Brown (1977)
contends that birds are and small mammals
are not in equilibrium on isolated mountains
in our study area. Are the plants in equilibrium? It will be recognized that the equilibrium argument is based on two assumptions:
1) local extinctions do occur, and 2) new introductions occur as often as extinctions on
Johnson (1975) suggests that the Pinon Jay
and the Band-tailed Pigeon may also be inin
is-
lands.
occasionally
feed on the winged seeds of Pinus aristata
No. 2
if
island.
not
Both assumptions are
A
definitive
we know
that
impossible,
tactically
test
to
con-
would require
of every population of every
we mon-
species on every island, and that
itor
difficult,
test
each island regularly enough (preferably
annually) in order to
became
extinct or
know when
a species
immigrated and became
acorns. Staniforth
and Cavers (1977) demonsome seeds of two Polygonum
lapathifolium L. and P. pensyl-
established there. Obviously, such data are
that
not available for any island in our study. As
passing
status of our islands relative to the equilib-
strate
species
(P.
vanicum
L.)
retain
after
viability
through the digestive tract of the cottontail
rabbit
in
eastern
Canada.
The foregoing
data lead us to suspect that large seeds from
the dry fruits of
ally
many
species will eventu-
be shown to be dispersed by vertebrate
a
any
consequence,
about
statement
the
rium question must be based on inferences,
not facts.
With
Pinus
is
con-
aristata
and
respect to extinctions, there
evidence
clusive
flexilis
that
Pinus
coexisted with Abies concolor
animals.
and Juniperus osteospenna on Clark Moun-
The foregoing discussion is an acknowledgement that we have underestimated the
number of plant species that are modified
years ago (Mehringer and Ferguson
for
long-range
transport
Nevertheless, the
number
on
our
islands.
of species in the
no-modification and miniwind categories
we
tain in southeastern California about 25,000
Today neither
Similarly,
1969).
of these pines occurs there.
Pinus monophylla and Juniperus
osteosperma
existed
on
the
Turtle
Range
is
14,000 years ago (Wells and Berger 1967),
still
but do not occur there now. The relatively
forced to conclude that the vast majority of
steep species-area curves for herbs (Fig. 2)
the species there did not reach those sites
may
by long-range dispersal. Although the high
elevation community types may never have
been able to survive on the valley floors at
no evidence in support of that possibility.
Concerning new immigrations onto the
isolated mountains, there are abundant records of exotic species invading at lower
so
great
on the
islands
that
any time during the Pleistocene,
are
as
Wells
indicate extinctions, but
we can
offer
and Berger (1967) argue, many of the community components may have been able to
elevations (Young, Evans, and Major 1972).
migrate directly across valley floors during
cases
that period. Also, as Billings (1977)
sizes,
climatic
empha-
cooling would have signifi-
Nevertheless,
of
we know
unaided
of no
documented
immigrations
onto
mountains of species that cannot survive
at least
some microsites on the
the
in
valley floors.
INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM
1978
There
evidence
strong
is
modified for
long-range
overrepresented on the
species
that
dispersal
islands
not
are
relative
to
and
immigrations had been in equilibrium, even
since the close of the Pleistocene, one might
have expected long-range dispersal types to
be at least somewhat overrepresented on islands; but even that tendency is not observed (Table 8). As noted above, there is a
the mainlands (Table
weak tendency
8).
If
extinctions
pine
flora
1977)
(Billings
of
the
isolated
The evidence seems to imply
that three basic factors have combined to
give the Rocky Mountain element an admountains.
vantage over that from the Sierra. Those
factors
are:
material,
1)
and
time,
2)
parent
geological
3) climate.
As Billings (1977) has noted, most of the
Great Basin mountains are younger than the
Rockies and older than the present Sierra
long-distance dispersal types to decline less
Nevada and Cascade ranges. Thus, species
from the east have had longer to colonize
rapidly against distance from the mainland
the
than for supposedly
taxa from the Sierra, since that flora
These two
percent
for
less
saturation
of
well-dispersed taxa.
evidence lead us to ten-
bits of
tatively conclude that the flora of the iso-
mountains than high-elevation
isolated
have arisen much
later than the
first.
must
In ad-
propagules of species unique to the
dition,
not in equilibrium, even
western mainlands would have had great
though some species do appear to be mov-
establishing themselves on the
mountain islands even after reaching them,
since most habitats would have already
been occupied by eastern taxa.
lated mountains
is
ing about in the area.
If
the islands are not in equilibrium, the
extinction
rate
must be low
for
plant
all
difficulty
groups and especially so for the woody taxa.
We
draw
flatness
this
inference from the relative
most
of the species-area curve for
on
Plants originating at higher elevations
the western mainland could generally be ex-
pected to be adapted to acidic
plant groups (Fig. 2) in contrast to
mam-
the Sierra
mals (Brown
infer-
acidic,
Nevada
since
soils,
ence seems valid since herbaceous plants as
1967).
composed of
igneous rock (Major and Bamberg
Soils on the isolated Mountains, how-
primary producers should be able
ever,
have
1977).
Intuitively,
this
main-
to
tain larger populations than their vertebrate
consumers.
Woody
would be expected
ulations
than
plants (especially trees)
to maintain smaller
their
vertebrate
pop-
consumers,
but would have far greater longevity. Trophic
position
much
to
and
longevity
likely
have
do with the relative extinction rate
and plants. Plant groups of
of vertebrates
differing
trophic
habit
(e.g.,
vascular
sap-
rophytes and nongreen parasites such as Co-
and Orobanche, respectively, verforms) and longevity
sus photosynthetic
should show different extinction rates.
We had not expected to find the eastern
mainland (Rocky Mountains) floristic element to be so much more successful than
the western mainland (Sierra) element on
the Great Basin mountains. As others have
noted in this symposium, the Rocky Mounrallorhiza
tain
element also dominates the avian fauna
(Behle 1977 and Johnson 1977) and the
al-
neutral
is
primarily
prevailingly
soils.
basic
circum-
to
Again, taxa from the eastern
mainland would have an advantage
in colo-
nizing the islands, since the western outliers
of the Rockies are prevailing
calcareous rocks.
is
significant
In
this
tats
it
that Billings (1950) found as-
semblages of Sierra plants
Great Basin
formed from
connection,
in
the
western
be confined to acidic habion hydrothermally altered rocks.
to
western plants have evolved
Finally,
an environment that
is
more moist and thermally
in
continental
(i.e.,
less variable)
than
less
that associated with the isolated mountains
of concern
or the western outliers of the
Johnson (1977) considers the climatic variable to be highly influential in
Rockies.
western
confining
Sierras.
We
similarly
bird
to
the
believe that continentality
may
increase
the
species
difficulty
of
estab-
lishment of western plant species that are
dispersed to the mountain islands. As in the
100
GREAT BASIN NATURALIST MEMOIRS
preceding cases, species from the east
would be better preadapted for life on the
No. 2
can be seen with particular clarity in the
southwest corner of Cache Valley, Utah.
Although Chamaebatiaria millefolium
Maxim, occurs on both of the main-
islands.
(Torr.)
Niche Expansion
Brown
dinal
lands recognized in this study,
(1971b) has shown that the altitu-
range
of
normally
a
low-elevation
chipmunk (Eutamias dorsalis) expands upward on Great Basin mountains which lack
component
conspicuous
on
On
either.
of
is
it
the
rarely a
vegetation
the remote islands, however,
Chamaebatiaria
is
often
common and
a con-
spicuous part of the vegetation.
play a niche expansion in the absence of
Finally, West et al. (1977) review evidence suggesting that the anomalously high
upper elevation of the juniper-pinyon zone
on many of the isolated mountains of the
Great Basin may be attributable to the low
normal competitors. Although quantitative
diversity of the high-elevation flora
a high elevation congener
the course of our
(£.
work on
umbrinus). In
isolated
moun-
we have observed
which plant species also
tains in the Region,
sev-
eral cases in
dis-
we
data are lacking,
take this opportunity
to put such anecdotal evidence as
is
avail-
able on record.
An
apparent case of niche expansion
presented by Abies lasiocarpa
in
the
is
Jar-
bidge Mountains. There, in the absence of
common
its
Abies
competitors
coniferous
concolor,
Picea
engelmannii,
(e.g.,
Picea
pungens, and Pseudotsuga menziesii (Mirb.)
and the
paucity of well-adapted competitors. They
note also that the niche of both juniper and
pinyon appears to be severely compressed
on the west flank of the southern and
middle Wasatch Range where Quercus gambelii and Acer grandidentata combine to
form a dense woodland. Both juniper and
pinyon occur
is
in the flora there,
but neither
an important part of the vegetation.
Franco), Abies lasiocarpa plays a major role
in forest vegetation from the sagebrush-grass
and streambank communities at low elevations to timberline. We know of no other
place where this species succeeds in such a
double zone of Artemisia tridentata oc-
Nevada and west-
curs on mountainsides of
ern Utah. There the species commonly
dominates a wide belt both below and
above the juniper-pinyon zone. It appears
work would be based would be too
rospect,
we acknowledge
tions
will
tionships
is
simply
larger mesophytes such as
In the northern
moved
into
dominated by
Quercus gambelii,
elsewhere
Wasatch Mountains, the
range of Acer grandidentatum extends
miles farther north than that of
its
lists
effort
tain brush species.
that
that all of the
will add a few species to
and many to others. Nevertheless,
the lists have yielded results that seem reasonable and defensible. Furthermore, the
sample on hand is already sufficiently large
to minimize the possibility that new collec-
ditional
Pinus ponderosa, or a rich mixture of moun-
zone
in-
results. In ret-
are probably incomplete. Undoubtedly, ad-
lists
likely that Artemisia has
meaningful
to give
some
a
we were
concerned that the checklists on which our
complete
variety of habitats.
A
Adequacy of Checklists
the inception of this study,
In
seriously
or
species-area
alter
lifeform
rela-
and dispersal-type
spectra for the floras.
manv
Management Implications
common
associate in the south, Quercus gambelii. In
mixed stands of Acer and Quercus, Acer is
normally conspicuous only on slope bases
and ravine edges. North of the limits of
Quercus, however, Acer dominates both
slopes and depressions. The phenomenon
Species-area curves reveal
much
that
should be useful to natural resource man-
The curve
agers.
ure
2,
for trees
on islands
in Fig-
for example, suggests that the Santa
Rosa Mountains are drastically understocked
with
trees.
Could
trees
be successfully
in-
INTEHMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM
1978
101
Since other islands in the study support so
still in
the open pine
Water could have been piped to the
campground with minimal disturbance to
we
the natural system around the lake. Instead,
suspect that introduction of one or a few
the current plan places every visitor in a
troduced there to provide shelter for animals
construction
or
many more
materials
man?
for
tree species than that range,
carefully selected tree species into favorable
would have a high probability of
sites
suc-
cess there.
Species-area curves also have
many
from the lake but
groves.
position to disturb the several unusual plant
and animal species that perhaps occur
only that spot on the entire range.
at
useful
implications for conservation programs for
ACKOWLEDGMENTS
unusual and rare plant and animal species.
Managers
will find the basic theory relative
to rare species
and
size
capsulized
the
following short,
in
of reserves nicely
non-
technical papers: Terborgh (1974 and 1976),
Diamond
1976,
Whitcomb
et
al.
(1976),
and
Simberloff and Abele (1976).
Johnson (1975) developed a habitat diverindex that accounted for a major por-
sity
tion of the observed variation in
number
of
on isolated mountains in the
Great Basin. Behle (1977) has verified that
bird
species
the index
sity
is
is
a useful indicator of bird diver-
throughout the Basin. Since that index
based on various plant parameters and
the presence or absence of free flowing water,
it
Many
the
We
are indebted to Dr. Noel
(1972) for his exhaustive pioneer
Holmgren
work on
biogeography of the Intermountain
It has been an invaluable aid as we
have planned and pondered this paper. Dr.
William E. Evenson prepared most of the
computer programs used in our analyses.
Our research has been supported in part by
a grant from the National Science Foundation (GB-39272) and another from the Besearch Division, Brigham Young University.
A grant from the U.S. Bureau of Beclamation through the Utah State Division of
Water Besources has helped defray pubthe
West.
lication costs for this paper.
has relevance to our discussion here.
of our small, arid
mountain ranges
in
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(a
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