Long-term population dynamics
of individually mapped Sonoran Desert winter annuals from the Desert Laboratory,
Tucson AZ
D. L. Venable
INTRODUCTION
Desert annual plants have played an important role as model organisms in the
development of understanding of how organisms adapt to variable and unpredictable
environments. They have also been used to exemplify ideas about non-equilibrium
community dynamics in variable environments. Yet their dynamics are not well
known empirically, especially the behavior of seeds. This data set on the population
and community dynamics of desert annuals, provides the best available long-term
data to test these ideas. There has been considerable
theoretical and experimental work carried out on the evolutionary ecology,
population ecology and community ecology of this system. Such combinations
of theoretical and experimental work with long-term observations are proving
to be a powerful approach to yield new insights and syntheses in plant ecology.
The main goal of this research was to determine how these plants adapt to
and coexist in variable and unpredictable environments. The resulting long
term population and community dynamic data has formed the backbone of a synthetic
research program on desert annuals combining evolutionary, physiological, population
and community ecological approaches to answer questions uniting functional
biology, life history evolution and community dynamics.
This data set consists of a continuous record of population and community
dynamics of desert winter annual plants on permanent plots at a Sonoran Desert
site at the Desert Laboratory near Tucson, AZ, USA. It was collected to clarify
and extend the understanding of demographic variation and covariation and its
role
in
population and community processes. Data on germination, survival and reproduction
of desert annual plants has been continuously monitored on long-term plots
established in 1982 at locations both under shrub canopies
and in the open
at this field station. Delayed germination and between year seed carry over
are thought to be important for the persistence of desert annuals, so the magnitude
of the soil seed reserves has been monitored to determine what fraction of
the seeds germinate in each year for each species under shrubs and in the open.
Seeds have been separated
from standardized soil samples and tested for viability.
METADATA CLASS I. DATA SET DESCRIPTORS
A. Data set identity:
Title: Long-term population
dynamics of individually mapped Sonoran Desert winter annuals from the Desert
Laboratory, Tucson
AZ
B. Data set identification code
C. Data set description
Principal Investigator:
D. Lawrence Venable, Department of Ecology and Evolutionary Biology, University
of Arizona, Tucson, AZ 85721 USA
Abstract:
Desert annual plants have played an important role as model organisms in
the development of understanding of how organisms adapt to variable and unpredictable
environments. They have also been used to exemplify ideas about non-equilibrium
community dynamics. The goal of
this data set is to provide a comprehensive long-term data set on demographic
variation and covariation for a guild of desert winter annual plants. Germination,
survival fecundity and seed bank dynamics have been assessed on a set of permanent
plots since 1982 at the Desert Laboratory in Tucson, Arizona. Data is provided
for individual plant including germination date, death date, fecundity, viable
seed bank and in some years, Cartesian coordinates within plots. Viable seed
densities for replicated soil samples are provided for all species since 1990.
A species by year summary of vital rates is also provided.
D. Key
words: long-term population dynamics; demography; Sonoran Desert;
annual plants, seed bank.
CLASS II. RESEARCH ORIGIN DESCRIPTORS
A. Overall project description
Identity: Long-term population
dynamics of individually mapped Sonoran Desert winter annuals from the
Desert Laboratory, Tucson AZ
Originator: Dr. D. Lawrence
Venable
Period of Study: 1982–2013
Objectives:To monitor
the germination, survival, fecundity and seed bank dynamics of desert winter
annuals
Abstract: same as above.
Source(s) of funding: National
Science Foundation grants DEB 9419905 (LTREB), DEB 0212782
(LTREB), DEB 0717466 (LTREB), and DEB 0310400 (LTREB).
B. Specific subproject description
1. Site description: Permanent
quadrats were established in 1982 at the northwest base of
Tumamoc Hill at the Desert Laboratory of the University
of Arizona in Tucson, Arizona.
Site type: The
site (725 m elevation) is a gently sloped creosote
flat dominated by Larrea divaricata (creosote bush),
which has 50% cover. The site is located in the Arizona Upland subdivision
of the Sonoran Desert.
Geography: The study
site is located at the northwest base of Tumamoc Hill 1 mile west of downtown
Tucson, AZ
(32'13" N,
111'01" W).
Habitat: See "Site
type" above. The quadrats extend along a transect from a flat alluvial
area and up the southeast side of a gently sloping (9°) hill,.
Geology: Plots are
located along a gently sloping bajada (fluvial piedmont) of consistent
parent material, where a strong transition occurs in the age of the soil
surface with elevation. The soil
on the slope is composed of basaltic andesite
(Phillips 1976) with a coarse sandy-loam texture (67%
sand, 20% silt, 13% clay) and with fragments ofbasaltic
rocks embedded in the surface. The surrounding lower
areas have recently derived alluvial soil, including
sandy-clay soil at the base of the hill (54% sand, 22%
silt, 24% clay) and loamy-sand soil in a series of shallow (<0.5 m deep)
and
narrow (2-3 m wide) dry drainage channels (79%
sand, 10°/o silt, 10% clay). The slope is rockier (50%
gravel) than the base of the hill (20% gravel) or rivulets (25% gravel) (Pantastico-Caldas
and Venable 1993).
Watersheds/hydrology: N/A
Site history: The
850 acre Desert laboratory site was fences in 1906 to protect it from cattle
grazing and it has been an ecological preserve subsequently.
Climate: The site
receives ~300 mm
of annual precipitation on average, about half of which
falls during the summer monsoons (July–September),
with the rest occurring sporadically through the remainder
of the year (Bowers and Turner 1985).
2. Experimental design: There
are seventy two permanent plots randomly placed along two parallel
transects. At each of thirty six random positions along the transects there
is one plot under a creosote bush shrub canopy and a matching open plot
at least 1m from the nearest shrub.
Design characteristics: N/A
Permanent Plots: 0.1
m2 permanent plots.
Data Collection Period, Frequency: In
1982 I began censusing 15 permanent plots along a 250 m transect at the
study site. In 1989, 48 additional long-term study plots were established
and in 1991
the total number was increased to 72, one
half being located under shrubs and one half in the open. The
plots have been visited following each rainfall during the germination
season to check for germination. When there is more than trace germination
(> 1%
of expected total year germination) a germination census is conducted.
Following a germination census, subsequent censuses are conducted at intervals
sufficiently short to recognize individual plants and distinguish survival
from mortality followed by new germination (i.e., every 30-45 days). Frequently,
more than one cohort per year emerges from precipitation associated with
different storm systems. Each cohort is scored separately. Fecundity has
been scored on a random subsample of five surviving plants from each species
in each cohort in each plot at the end of the growing season. In early
years 1982- 199? it was recorded for every surviving plant. Systematic annual
collection of soil cores for seed bank analysis began in 1990. The cores
are collected after the germination season, but prior to seed set from
the
following season, i.e., in February of each year.
3. Research Methods
Field/Laboratory: Each
seedling is mapped with exact location and species identity with colored
markers on acetate sheets placed with fixed coordinates over plexiglass
mapping tables. The mapping tables are set over the plots in the field. At
the end of the season, maps are scored to record germination and death dates,
and fecundity for individual plants. This sampling and data recording scheme
has been used consistently for the whole period of data collection. From this
data we have calculated mean survival from germination to reproduction and
mean fecundity of survivors for each cohort of each species in shrub and open
habitats each year. From this we calculated the average seed set per seedling
(per capita reproductive success) for each cohort of each species in the open
and shrub habitats each year (proportion surviving times mean fecundity of
survivors).
We
collect 180 soil cores (5.4 cm diameter x 2.5 cm deep) annually
using stratified random sampling (Benoit et al. 1989) along a
transect connecting the 2 demographic transects for the 24- and
17-year old plots. Half of the samples are obtained from under
creosote shrubs and half from open sites. The cores are collected
after the germination season, but prior to seed set from the
following season. Thus the viable seeds in these samples have
forgone germination in at least one season. Viable seeds rarely
occur below 2.5 cm in the study area. Samples are placed in paper
bags to insure evaporation
of any soil moisture, and if the soil is moist at the time of
collection, the paper bags are opened and placed beneath fans
to insure rapid drying with no further rot or germination. Seeds
and organic material are separated from soil particles using
a repetitive frothing, flotation, and filtering technique which
has been shown to retrieve >95% of seeds in blind tests. Individual
soil samples are mixed with tap water and stirred vigorously.
The suspension containing floating organic matter and small soil
particles are then immediately decanted through an organza-cloth
filter placed in a Buchner funnel attached to suction. This filter
has been shown to capture all seeds of the smallest-seeded species
in this guild of annual plants (Evax multicaulis, mean seed size,
0.025 mg). This process is repeated multiple times until the
decanted liquid is clear. Then the organza filter and debris
are placed in a labeled petri dish and oven dried for >24
hrs at 40C. The organic matter with seeds is then sifted with
standard testing sieves and all fractions that potentially contain
seeds from the annual plant guild are spread out a spoonful at
a time and examined under a dissecting microscope. All seeds
are separated, counted, and identified to species by comparison
to voucher seeds. The seeds are cut or poked through the seed
coat to determine viability. Seeds with juicy, oily, or fleshy
embryos or endosperm are scored as viable. Tetrazolium
chloride testing gives inferior results due to the difficulty
of manipulating our smallest seeds and because some deeply dormant
viable seeds show only minimal staining. Under the field conditions
from which these soil samples are collected seeds usually undergo
easily recognizable changes upon death (dessication or decay
of endosperm or embryo). Counting of viable seeds is superior
for our system to the germination-based procedures sometimes
used in other seed bank studies because viable seeds of our
species often do not germinate completely (Adondakis and Venable
2004).
Instrumentation: N/A
Taxonomy and systematics: Plant
names are per Bowers and Turner (1985).
Permit history: N/A
Legal/organizational requirements: None.
4. Project personnel: Sandy
Adondakis, Amy Angert, Greg Barron-Gafford, Ursula Basinger, Amy Bell, Tony Caprio, Maria
Clauss, Ben Collins, Jonathan Cox, Michelle Davis, Norm Douglas, Jonathan
Duke, Carrie Enquist, Gordon Fox, Kathy Gerst, Kevan Gilliam, Christine
Golightly, Jenny Gremer, Alice Halloran, Amelia Hazard, Jonathan Horst, Tani Hubbard,
Travis Huxman, Renee Janaway, Amanda Jaksha, Bruce Kendall, Greg Ketner,
Oxana Kougot, Holly Lawson, Kristen McCoy, Chris McDonald, Ken Moriuchi,
Cathie Pake, Marissa Pantastico, Catherine Pearson, Jim Pearson, Stephanie
Roberts, Pilar Sanchez, Marcelo Schneider, Sabrina Stebens, Michelle Stubbs,
Michael Wagenheim and Brian Weeks.
CLASS III. DATA SET STATUS AND ACCESSIBILITY
A.Status
Latest Update: Feb. 2013
Latest Archive date: June 2012
Metadata status: The metadata are complete and up to date.
Data verification: See
V. A. 3.
B.Accessibility
Storage location and medium: Data
is available at http://www.eebweb.arizona.edu/faculty/venable/LTREB.htm.
It is also on the several personal computers and DVDs at the Venable lab
in Excel files and an Access database.
Contact person: D.
Lawrence Venable, Department of Ecology and Evolutionary Biology, University
of Arizona, Tucson, AZ 95721 USA, E-mail: venable@email.arizona.edu.
Copyright restrictions: None.
Proprietary restrictions: None.
Costs: None.
CLASS IV. DATA STRUCTURAL
DESCRIPTORS
SPECIES BY YEAR MEANS
A. Data Set File
Identity: species_x_year.csv
Size: 18,014 bytes.
Format and storage mode: ASCII
text, comma separated. No compression scheme was used.
Header information: The first row of the file contains the variable
names below.
Alphanumeric attributes: Mixed.
Special characters/fields: N/A
Authentication procedures: MD5 Checksum for the file:
6f80aa9b810796934b12dd759fd18069
B. Variable information
Variable
name |
Variable
definition |
Units |
Storage
type |
Range numeric
value codes |
Variable
codes and definitions |
species |
Species |
N/A |
Character |
N/A |
Species acronym consists of the first
two letters of the genus and species, e.g. Evax multicaulis is
coded as "evmu" |
year |
Year |
N/A |
Integer |
N/A |
Year
is coded as the Spring
year, e.g., Fall 1982-Spring 1983 is coded "1983". |
germ |
Number of seedlings
that emerged |
seedlings |
Integer |
0-4638 |
N/A |
survive |
Number of the
plants surviving to the reproductive census |
plants |
Integer |
0-2380 |
This number was obtained by following the individual seedlings
counted in "germ". |
seedlings per m2 |
seedlings per
meter squared |
seedlings/m2 |
Floating
Point |
0-2497.14 |
This is converted from "germ" |
lx |
Survival |
plants/seedling |
Floating
Point |
0.00-1.00 |
proportion
of seedlings surviving to reproduction (=survive/germ). "." means undefined,
which occurs when germ = 0. |
bx |
per capita
seed production |
seeds/plant |
Floating
Point |
0.00-1098.53 |
Average
number of seeds per plant surviving to the reproductive census. "."
means undefined (no seedlings surviving to reproduce) or rarely, missing
data. |
lxbx |
reproductive
success |
seeds/seedling |
Floating
Point |
0.00-917.80 |
Probability of surviving from emergence to reproduction x
mean seed set of reproductive plants (lx times bx). ("." means undefined,
i.e., germ = 0). |
seeds per m2 |
Number of viable
seeds per m2 in the soil seed bank |
seeds |
Floating Point |
0-24,137.56 |
N/A |
germ fraction |
proportion
of seeds in the seed bank that germinated |
seedlings/seed |
Floating
Point |
0.00-1.00 |
seedlings per m2/(seedlings per m2+seeds/m2). "." means undefined,
i.e., no seeds or seedlings in samples monitored. |
INDIVIDUAL PLANT CENSUS DATA
A. Data Set File
Identity: census_data.csv
Size: 5,512,180 bytes.
Format and storage mode:ASCII text, comma separated. No compression scheme was used.
Header information: The
first row of the file contains the variable names below.
Alphanumeric attributes:
Mixed.
Special characters/fields:
N/A
Authentication procedures:
MD5 Checksum for the file: 6f80aa9b810796934b12dd759fd18069
B. Variable information
Variable
name |
Variable
definition |
Units |
Storage
type |
Range numeric
value codes |
Variable
codes and definitions |
year |
Year |
N/A |
Integer |
N/A |
Year
is coded as the Spring
year, e.g., Fall 1982-Spring 1983 is coded "1983". |
plot-habitat-replicate |
Quadrat identifier
|
N/A |
Character |
N/A |
plot
number, habitat type ("shrub" or "open"), and replicate |
species |
Species |
N/A |
Character |
N/A |
Species acronym consists of the first two letters of
the genus and species, e.g. Evax multicaulis is coded
as "evmu" |
| germ date |
Germination
census date |
mm/dd/yyyy |
Date |
N/A |
Census
at which seedling was first recorded. |
death
date |
Death
census date |
mm/dd/yyyy |
Date |
N/A |
First
census at which plant was no longer alive or date of reproductive
census if plant survived to the final census. |
seeds |
lifetime
seed production |
seeds |
floating
point |
0.00-8000 |
"-99" means this plant reproduced
but was not in the sub sample for which reproduction was counted. |
plot
group |
plot
group identifier |
N/A |
Character |
N/A |
"ltp"
are plots that were first censused in 1982-1983. "gfp" are plots that
were first censused in 1989-1990. |
x |
horizontal plant
position coordinate |
mm |
integer |
0-545 |
horizontal distance
of the plant from the "lower left" corner of the quadrat |
y |
vertical plant
position coordinate |
mm |
integer |
0-248 |
vertical distance
of the plant from the "lower left" corner of the quadrat |
SEED BANK DATA
A. Data Set File
Identity: seed_bank.csv
Size: 4,216,923 bytes.
Format and storage mode: ASCII
text, comma separated. No compression scheme was used.
Header information: The first row of the file contains the variable
names below.
Alphanumeric attributes: Mixed.
Special characters/fields: N/A
Authentication procedures: MD5 Checksum for the file:
6f80aa9b810796934b12dd759fd18069
B. Variable information
Variable
name |
Variable
definition |
Units |
Storage
type |
Range numeric
value codes |
Variable
codes and definitions |
year |
Year |
N/A |
Integer |
N/A |
Year
is coded as the Spring
year, e.g., Fall 1982-Spring 1983 is coded "1983". |
plot |
Letter corresponding
to sequential 10 m segments along a transect |
N/A |
Character |
D-Y |
N/A |
habitat |
Under shrub
canopy or in open habitat between shrubs |
N/A |
Character |
N/A |
N/A |
replicate |
identifier
for a random seed sample nested within plot and habitat |
N/A |
Integer |
1-10 |
Number identifying the replicate. |
species |
Species |
N/A |
Character |
N/A |
Species acronym consists of the first
two letters of the genus and species, e.g. Evax multicaulis is
coded as "evmu" |
| seeds |
Number of viable
seeds in sample |
seeds |
Integer |
0.00-1073.33 |
N/A |
area |
area of seed
sample |
cm2 |
Floating
Point |
|
N/A |
seeds per m2 |
Number of viable
seeds per m2 in the soil seed bank |
seeds/m2 |
Floating Point |
0-24,137.56 |
N/A |
SPECIES LIST
A. Data Set File
Identity: species_list.csv
Size: 3,617 bytes.
Format and storage mode: ASCII
text, comma separated. No compression scheme was used.
Header information: The
first row of the file contains the variable names below.
Alphanumeric attributes: Mixed.
Special characters/fields: N/A
Authentication procedures: MD5
Checksum for the file: 6f80aa9b810796934b12dd759fd18069
B. Variable information
Variable name |
Variable
definition |
Units |
Storage type |
Range numeric
value codes |
Variable
codes and definitions |
genus |
Latin genus
name |
N/A |
Integer |
N/A |
Year
is coded as the Spring year, e.g., Fall 1982-Spring 1983 is coded "1983". |
species |
Latin species name |
N/A |
Character |
N/A |
Genus species name as current when the lab started |
acronym |
Species acronym |
N/A |
Character |
N/A |
Species acronym consists of the first two letters of
the genus and species, e.g. Evax multicaulis is coded
as "evmu" |
family |
identifier
for a random seed sample nested within plot and habitat |
N/A |
Integer |
N/A |
FAMILY (e.g. BORAGINACEAE) |
synonym |
The synonym
for the species name in the USDA PLANTS database when the species
name used here does not correspond to the primary name given in the
PLANTS database at http://plants.usda.gov |
N/A |
Character |
N/A |
N/A |
CLASS V. SUPPLEMENTAL
DESCRIPTORS
A. Data acquisition
Data forms: NA
Location of completed data forms: The
original maps and data sheets are stored in the Venable lab at the Department
of Ecology and Evolutionary Biology.
Data entry verification procedures: See
II.B.3., Research Methods.
B. Quality assurance/quality
control procedures: All plant data with Cartesian map coordinates were
entered from the acetate maps with a Summagraphics digitizing table to .txt
files.
Plant data without coordinates were collected onto standardized data forms
from the maps
prior
to transferring to Excel files. All computer data entry was double checked
visually after original data entry. Files were scanned for outliers.
Outliers were checked against data forms or original maps.
Soil seeds were identified and checked for species ID as described in II.B.3.
Seed ID's were spot checked by a supervisor before and after viability determination.
Acuracy of the people sorting seeds also was verified by blind testing involving
counted
seeds
placed
in
samples previously without seeds.
C. Related material:
D. Computer programs and data processing algorithms:
E. Archiving:
Archival Procedures:
Redundant Archival Sites:
F. Publications and results:
Venable, D.L. 1989. Modeling the evolutionary ecology of seed banks. pp. 67-87
In: Leck, M.A., V.T. Parker, and R.L. Simpson, editors, The ecology of soil
seed banks. Academic Press, San Diego.
Pantastico, M. and D.L. Venable. 1993. Competition in two species of desert
annuals along a topographic gradient. Ecology 74: 2192-2203.
Venable, D.L., C.E. Pake and A.C. Caprio. 1993. Diversity and coexistence
of Sonoran desert winter annuals. Plant Species Biology 8: 207-216.
Pake, C.
and D.L. Venable. 1995. Is coexistence in Sonoran Desert annuals mediated
by temporal variablility in reproductive success? Ecology 76:246-261.
Pake,
C.E. and D.L. Venable 1996. Seed banks in desert annuals: Implications for
persistence and coexistence in a variable environment. Ecology. 77:1427-1435.
Venable, D.L., and C.E. Pake. 1999. Population ecology of Sonoran Desert annual
plants. pp. 115-142 In: R.H. Robichaux, editor. The ecology of Sonoran Desert
plants and plant communities. University of Arizona Press, Tucson.
Moriuchi, K.S. D.L. Venable, C.E. Pake and T. Lange. 2000. Direct measurement
of seed bank age structure of a Sonoran Desert annual plant. Ecology, 81:1133-1138
Clauss M.J. and D.L. Venable. 2000. Seed germination in desert annuals: an
empirical test of adaptive bet hedging. American Naturalist, 155:168-186.
Adondakis, S. and D.L. Venable. 2004. Dormancy and germination in a guild
of Sonoran desert annuals. Ecology. 85 (9): 2582-2590.
Angert, A. L., T. E. Huxman, G. A. Barron-Gafford, K. L. Gerst, and D. L.
Venable. 2007. Linking growth strategies to long-term population dynamics in
desert annuals. Journal of Ecology 95: 321-331.
Venable, D. L. 2007. Bet hedging in a guild of desert annuals. Ecology 88(5):
1086-1090.
Huxman, T. E., G. A. Barron-Gafford, K. L. Gerst, A. L. Angert, A. P. Tyler,
and D. L. Venable. In press. 2008. Photosynthetic resource-use efficiency and
demographic variability in desert annuals. Ecology. In Press.
Venable, D. L., A. Flores-Martinez, H. C. Muller-Landau, G. A. Barron-Gafford,
and J. X. Becerra. 2008. Seed dispersal of desert annuals. Ecology. In Press.
Barron-Gafford, G. A., A. L. Angert, D. L. Venable, A. P. Tyler, K. L. Gerst,
and T. E. Huxman. in review. Photosynthetic temperature responses of desert
annuals with contrasting resource-use efficiencies. Oecologia. In Review.
H. History of data set usage
Data request history: N/A
Data set update history: N/A
Review history: N/A
Questions and comments from secondary users: N/A
ACKNOWLEDGMENTS
Funding was provided by NSF grants BSR 9107324, DEB 9419905 (LTREB), DEB 0212782
(LTREB), DEB 0453781, and DEB 0717466 (LTREB). Thanks to the following
for stimulating ideas and data collection: Sandy Adondakis,
Amy Angert, Greg Barron-Gafford,
Amy Bell, Tony Caprio, Maria Clauss, Ben Collins, Jonathan Cox, Michelle
Davis, Norm Douglas, Jonathan Duke, Carrie Enquist, Gordon Fox, Kathy Gerst,
Kevan Gilliam, Christine Golightly, Alice Halloran, Amelia Hazard, Jonathan
Horst, Tani Hubbard, Travis Huxman, Renee Janaway, Amanda Jaksha, Bruce
Kendall, Greg Ketner, Oxana Kougot, Holly Lawson, Kristen McCoy, Chris
McDonald, Ken Moriuchi, Cathie Pake, Marissa Pantastico, Catherine Pearson,
Jim Pearson, Stephanie Roberts, Pilar Sanchez, Marcelo Schneider, Sabrina
Stebens, Michelle Stubbs, Michael Wagenheim and Brian Weeks.
LITERATURE CITED
Adondakis, S., and D. L. Venable. 2004. Dormancy and germination
in a guild of Sonoran Desert annuals. Ecology
85:2582–2590.
Benoit, D. L., N. C. Kenkel, and P. B. Cavers. 1989. Factors influencing
the precision of soil seed bank estimates. Canadian Journal of Botany 67:2833-2840.
Bowers, J. E., and R. M. Turner. 1985. A revised vascular
flora of Tumamoc Hill, Tucson, Arizona. Madrono 32:225–252.
Pantastico-Caldas, M. and D.L. Venable. 1993. Competition in two species
of desert annuals along a topographic gradient. Ecology 74, 2192–2203.
Phillips, M. P. 1976. Geology of Tumamoc Hill, Sentinel
Peak and vicinity. Thesis. University of Arizona, Tucson,
Arizona. USA.
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