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Introduction
Species RichnessResults from the Northern Rocky Mountains
MUSEUM ofPALEONTOLOGY
MUSEUM ofMUSEUM ofPALEONTOLOGYPALEONTOLOGYANTHONY D. BARNOSKY MARC A. CARRASCO
Barstovian (105 locs.)
Arikareean (236 locs.)
Hemingfordian(21 locs.)
EFFECTS OF CLIMATIC AND TECTONICPERTURBATIONS ON MAMMALIAN COMMUNITIES
00.10.2
0.30.40.5
-60 -40 -20 0 20 40 60 80
Difference in Species Richness(Lower minus Higher Interval)
Su
rviv
al I
nd
ex (
SI)
B C A
65 55 45 35 25 15 5
100
200
-1.0
-2.0
0
1.0
2.0
3.0
Age in Millions of Years
Num
ber
of S
peci
es Atlantic d 18O
Faunal Turnover
Relative Abundance
Rat
ios
of N
umbe
rs o
f Spe
cim
ens
(NIS
P)
in C
ompa
red
Gro
ups
Pocket Mice / Gophers
Antelopes / Oreodonts x 10
(Oreodonts / Horses) x 10
He2&3
Ba2Ar2
Post-Warming
10
20
0
10
0
48
1216
Pre-Warming
BeginWarming
0
203040
Rat
ios
of N
umbe
rs o
f Spe
cies
in
Com
pare
d G
roup
s
Pocket Mice / Gophers
Rhinos / Horses
Antelopes / Oreodonts
Camels / Oreodonts
2
6
10
14
18
Ar1
He2&3
He1Ar4Ar3
Ba1Ba2
Ba3
Ar2
(Oreodonts+Camels+Antelopes) / Horses
Beginning of Warming Event
Studies that focus on large geographic (continental) and long temporal scales (millions of years) tend to demonstrate little correlation between climate change and mammalian species turnover rates or diversity as shown below in a graph that compares the North American mammal species richness through time to the Atlantic d18O curve (sources of data: Alroy, 2000, Geology 28:1024; and Miller et al., 1987, Paleoceanography2:3).
As the scales resolve to local sites over decades, centuries, or millennia, however, some species clearly appear and disappear. For example, faunal effects that have been attributed to Pleistocene climate changes in numerous studies include changes in: (1) species composition of communities, (2) biogeographic ranges of individual species, (3) relative abundance of species and individuals, (4) phenotype/genotype, and (5) extinction rates.
ALPHA DIVERSITY (Graphs D, E, F)Species diversity at discrete localities may have increased coincident with the Miocene Climatic Optimum. The He2&3 localities contain the most species at sample sizes of 30 to 200 specimens. However, thesepoint estimates are potentiallysubject to time and communitybiases.
Study Goals and MethodsWe suspect that studies that focus on too large a scale blur the effect of climate change on mammalian communities, because a given global change elicits differing local climatic responses. We also suspect that species richness by itself can be an ambiguous gauge of change in mammalian communities, in part because it is so difficult to reliably determine in paleontological samples.
We test these suppositions by examining effects of the late-early Miocene Climatic Optimum warming event on faunas of the northern U.S. Rocky Mountains. The warming event began 18.5 Ma, peaked around 17 Ma, and lasted until about 14 Ma. Thus it is of a temporal scale that characteristically demonstrates little correlation between global climate change and faunal turnover patterns. However, the geographic scale is small enough to prevent mixing of substantially different climatic zones as seen in the climate prediction model below.
Miocene were clearly different than these, we assume that the study area also represented a uniform climatic zone then. Our lab currently is working on ways to more accurately delineate Miocene climate patterns in the western U.S.
Under our MIOMAP Project, we are compiling all mammal records of Miocene age in the U.S. A Geographic Information System (ARC/INFO) and other statistical techniquesare used to determine how closely species turnover patterns correlate on a region-by-region basis with the timing of the mid-Miocene Climatic Optimum and with tectonic activity in the northern Rocky Mountains and Great Basin.
SUMMER SOIL MOISTURE
The survival index provides a crude estimate of faunal turnover and is computed as SI=(Survivors/Species Pool), where 'Survivors' is the number of species surviving across an interval boundary, and 'Species Pool' is the number of species found in the lower interval. Plotted as a function of the difference between species richness in adjacent stratigraphic intervals, anomalous SI values appear coincident with the onset of the warming event. A and B designate the points for the transition between He1 and He2&3 for the entire dataset and for the 'mountains only' dataset, respectively. C denotes the Ar1-Ar2 transition for the localities near the Wyoming-Nebraska border only.
The relative abundance of species within higher taxa (left graph) changes dramatically at the warming event. Pocket mice replace gophers. Antelopes, camels, and horses become more dominant over rhinos andoreodonts.
This map exemplifies output from climate models that assume continued growth of world greenhouse gas emissions (source: Climate Change Impacts on the United States, U.S. Global Change Research Program). All models predict resultant global warming will change local climatic parameters to different extents. Our study area (white line) represents a region that shows a more or less uniform climate response given modern geographic constraints. While climatic patterns in the
The maps to the right indicate areas from which fossildata have been compiled and entered in the MIOMAPdatabase. Only the northern Rocky Mountain data(Idaho, Montana, Wyoming) are analyzed in this poster.Most of the areas indicated by white dots containmultiple collecting localities. Numbers of specimens range from tens to thousands per locality. A fullexplanation of the MIOMAP project is available athttp://ib.berkeley.edu/labs/barnosky.
Conclusions
The available data suggest shifts in the relative abundance of individuals within species (right graph) accompanied the warming event. Numbers of identifiable specimens (NISP) overestimate actual numbers of individuals, but nevertheless provide a reliable gauge of relative abundance. Unfortunately, requisite data for the critical time intervals Ar3, Ar4, and He1 do not yet exist.
• Alpha diversity most likely increased• Beta diversity may have changed• Species compositions changed dramatically• Relative abundance of species within higher taxa shifted• Relative abundance of individuals within species shifted
Within the northern Rockies coincident with the late-early Miocene Climatic Optimum:
Tectonic uplift as well as climate change characterized the study area duringthe Miocene Climatic Optimum. As the MIOMAP database becomes morecomplete, we will test hypotheses designed to tease apart the relative effectsof climate change and tectonism on mammal faunas. Currently we are analyzing data we have just finished compiling for the northern Great Plainsand Pacific Northwest.
Future Work
Funded by
BETA DIVERSITY (Graphs G, H, I) Bootstrap analyses that accumulatespecies with successive samples suggest higher species richness in He2&3 and Ba2 (Graph G); however, these results may simply be an artifact of differing numbers of individual specimens (NISP). Bootstrap analyses that control for numbers of specimens per sample and assume either equal (Graph H) or best estimate time spans (Graph I) for each collecting area suggest a decrease in species richness across the warming event. However, these analyses may be biased if different habitats were sampled.
Because species richness correlates with the duration of the time interval spanned (shown in Graph B), analyses in which time intervals are standardized (Graph A) are frequently used. A comparison of the Atlantic d18O curve during the Miocene to a time-standardizedspecies richness curve for the northern Rocky Mountains suggests an increase in richness corresponds with the warming event (highlighted in yellow). However, as shown in Graph C, species richness also correlates with the number of localities sampled, which is a proxy for the number of individual specimens collected. Other analytical methods (Graphs D through I) attempt to account for such potential biases but provide conflicting results.
Atlantic d18OCurve
Number of Species
Time Periodof Study
http://www.gcrio.org/NationalAssessment/overpdf/overview.html
[email protected](510) 643-6275
University of CaliforniaBerkeley, CA 94720
[email protected](510) 642-5318
and
0
5
10
15
20
25
-.25 .25 .75 1.25 1.75 2.25
Mid/Upper Cabbage Patchand Peterson Creek (Ar 2)
Split Rock (He 2&3)
log NISP
Spe
cies
Ric
hnes
s
D.
Spe
cies
Ric
hnes
s
log NISP
0
4
8
12
16
20
-.25 .25 .75 1.25 1.75 2.25
Mid/Upper Cabbage Patchand Peterson Creek (Ar 2)
Barstovian 2Localities
E.
Spe
cies
Ric
hnes
s
0
5
10
15
20
25
30
35
40
-.5 0 .5 1 1.5 2 2.5 3 3.5
Barstovian 2Localities
Split Rock (He 2&3)
log NISP
F.
A.
0
10
20
30
40
50
60
1 3 5 7 9 11 13 15 17 19 21 23 25Number of Samples
Ar2 (Peterson Creek) 16.8
Ar2 (M.U. Cabbage Patch) 17.7Ar1 (L. Cabbage Patch) 23.5
Ba2 (
Colte
r) 70
.3
He2&3 (Split Rock) 94.9
Ba2 (H
epbu
rn's M
esa)
149.7
Est
imat
ed S
peci
es R
ichn
ess G.
Square Root of NISP
Est
imat
ed S
peci
es R
ichn
ess
0
10
20
30
40
50
60
Ar2 (
Peter
son C
reek
)
Ar2 (M
.U. Cab
bage P
atch)
Ar1 (L. Cabbage Patch)
He2&3 (Split Rock)
Ba2 (Hepburn's Mesa)
Ba2 (Colter)
0 10 20 30 40
H.
Square Root of NISP
Est
imat
ed S
peci
es
Ric
hnes
s/ T
ime
Inte
rval
0
10
20
30
40
50
60
0 10 20 30 40
Ar2 (Peterson Creek) 3.5 Ma
Ar2 (M
.U. Cab
bage
Patch)
2.2 M
a
Ar1 (L. C
abbag
e Patc
h) 2 M
a
He2&3 (Split Rock) 1.5 Ma
Ba2 (Hepburn's Mesa) 1 Ma
Ba2 (Colter) 2 Ma
I.
2.0 1.5 1.0
30
25
20
15
10
5
30
25
20
15
10
5
Atlantic d18O
Age
HP2/3
HP1
CL2
CL1
BA3
BA2
BA1
HE2/3
HE1
AR4
AR3
AR2
AR1
OLIGOCENE
MIOCENE
Age
HP2/3
HP1
CL2
CL1
BA3
BA2
BA1
HE2/3
HE1
AR4
AR3
AR2
AR1
Ma Ma
RICHNESS = Species / Interval Length
Species Richness
0 10 20 30 40
Northern Rockies Species Richness
Atlantic d18O Curve
1 10 1000
20
40
60
80
Sp
eci
es
Ric
hn
ess
Number of Localities Collected
Length of Time Interval (Ma)
00
1 2 3 4
20
40
60
80
Spe
cies
Ric
hnes
s
B.
C.
