S. K. Morgan Ernest, Thomas J. Valone, and James H. Brown. 2009. Long-term monitoring and experimental manipulation of a Chihuahuan Desert ecosystem near Portal, Arizona, USA. Ecology 90:1708.

INTRODUCTION

Many pressing questions in both applied and basic science deal with predicting how ecosystems, communities, and populations will change through time in response to climate change, extinctions, invasions, and land use change. Long-term data is critical for studying the temporal dynamics of ecological systems and understanding how ecological systems adjust to changes. Long-term monitoring allows scientists to address many otherwise hard to study issues, such as: (1) the differences between long-term and short-term responses to perturbations, (2) the impacts of rare events, which by their nature are difficult to predict and study with short-term monitoring, and (3) the aspects of ecosystem structure and function that are resilient to perturbations.

Although long-term data is critical to our ability to understand and predict long-term responses of ecosystems to environmental change, experimental manipulations often play an important role in understanding ecosystems. By manipulating components of an ecosystem, we gain greater insight into the role they play in determining the structure and function of a particular system. The combination of long-term monitoring and experimental manipulation has the potential to provide important and novel insights into how the role of species, functional groups, or even entire guilds, can change in response to changes in the environment.

Here we present a database that combines both long-term monitoring and experimental manipulation of a Chihuahuan Desert ecosystem near Portal, AZ. For over 30 years this site – from here on referred to as the Portal Project - has been studying the interactions within and between the rodent and ant communities, their effects on the structure of the annual plant community, and the response of all three groups (plants, ants, and rodents) to changes in climate. Research at the Portal Project was initiated in 1977 by Drs. James H. Brown, Diane W. Davidson, and O. James Reichman. This data set spans 1977–2002 for these three core taxonomic groups and from 1980–2002 for precipitation, which has been recorded at the site since 1980. Additional information about the site can be found in Brown (1998).

Since the database consists of four distinct data sets (rodent, plant, ant, precipitation), each of which has distinct methodology and data set structure, there is a separate metadata file for each data set. This metadata file contains the metadata for the site and an overall description of the structure of this data paper.

METADATA AND DATA STRUCTURE

A. Database identity: This database contains four data sets - rodent, plant, ant, precipitation – and the metadata for each file.

Overall Title: Long-term monitoring and manipulation of a Chihuahuan Desert ecosystem near Portal, Arizona.

Rodent Data set Title: Long-term monitoring and experimental manipulation of a rodent community in the Chihuahuan Desert near Portal, Arizona.

Plant Data set Title: Long-term monitoring and experimental manipulation of a Chihuahuan Desert plant community near Portal, Arizona.

Ant Data set Title: Long-term monitoring and manipulation of an ant community in the Chihuahuan Desert near Portal, Arizona.

Precipitation Data set Title: Long-term monitoring of precipitation at a long-term site in the Chihuahuan Desert near Portal, Arizona.

B. Data set and metadata identification codes: Each data set has its own file and its own metadata documenting the data collection details and data set structure.

Current Principal Investigators:

James H. Brown, Department of Biology, University of New Mexico, Albuquerque NM 87131

Thomas J. Valone, Department of Biology, Saint Louis University, Saint Louis MO 63103

S. K. Morgan Ernest, Department of Biology, Utah State University, Logan UT 84322

Abstract: Desert ecosystems have long served as model systems in the study of ecological concepts (e.g., competition, resource pulses, top-down/bottom-up dynamics). However, the inherent variability of resource availability in deserts, and hence consumer dynamics, can also make them challenging ecosystems to understand. Study of a Chihuahuan desert ecosystem near Portal, Arizona, began in 1977. At this site, 24 experimental plots were established in 1977 and divided among controls and experimental manipulations. Experimental manipulations over the years include removal of all or some rodent species, all or some ants, seed additions, and various alterations of the annual plant community. While some of these manipulations were discontinued early on, others (i.e., ant and rodent manipulations) have been maintained throughout the study. Monitoring of the composition and abundances of ants, plants, and rodents has occurred continuously on all 24 plots. From 1977–2002, individual-level data on rodents (i.e., species, sex, size, reproductive condition) was collected monthly for each plot. From 1983–2002, the species-level abundances of plants were sampled on permanent quadrats. From 1977–2002, the species-level abundance of ant colonies was recorded for each plot and from 1988–2002 additional information on ant abundances were recorded. Finally, from 1980–2002 we recorded precipitation at the study site.

These data have been used in a variety of publications documenting the effects of the experimental manipulations as well as the response of populations and communities to long-term changes in climate and habitat. Sampling is ongoing and this database will be periodically updated.

D. Key words: ants; Chihuahuan Desert; LTREB data; plants; rodents.

CLASS II. RESEARCH ORIGIN DESCRIPTORS

A. Overall project description

Identity: Long-term data for the four core data collection efforts for the Portal Project LTREB  - rodents, plants, ants, precipitation.

Originators: Drs. James H. Brown, Diane W. Davidson, James Reichman.

Period of Study: 1977–2002

Objectives:To monitor the long-term community dynamics of the rodent, ant and plant communities of a Chihuahuan Desert ecosystem in response to natural variation in climate and experimental manipulation of various plant and animal groups.

Sources of funding: National Science Foundation grants: DEB 76-83858, BSR 80-21535, BSR 85-06729, BSR 87-18139, DEB 92-21238, DEB 97-07406, DEB-0129298/0211069, DEB-0348896/0348255, and a grant from the Department of Energy.

FIG. 1. Top: Schematic of the Portal Project study area showing the 24 experimental plots (numbered) within the 20 ha study area (gray outline). Bottom: A detailed view of a plot showing the permanent sampling grids. Numbers along the edges of the plot denote the coordinate system that results in the stake/quadrat numbers in the data sets. Solid circles represent that rodent/ant grid, open squares the plant grid. Note: map is not to scale.

Site type:The site occurs in an upper-elevation Chihuahuan Desert habitat (1330 m), dominated by a mixture of shrubs (e.g. Flourensia cernua, Acacia sp., Prosopis sp.) and grasses (e.g. Aristida sp. Bouteloua sp., Muhlenbergia porteri.). Dominance of grasses vs. shrubs has shifted over the 30 years of the study, shifting from what was mainly a desertified open grassland to a mixed shrubland (Brown et al 1997). The site itself sits on a bajada at the base of the Chiricahua Mountains and consists of mainly sandy soils.

1.Site description:The entire study area is approximately 20 ha and within this area there are 24 experimental plots (Fig 1). Each plot is 0.25 ha (50 m × 50 m) and fenced with hardware cloth topped with aluminum flashing. Access to these plots by rodents is regulated by gates cut into fencing. On each plot there are permanent census grids: one for rodents and ants and another for plants. For the rodent/ant grid, 49 permanent trapping stations are marked by rebar stakes forming a 7 × 7 grid, with 6.25 m between stakes. Every stake on a plot has a unique identifying number denoting the coordinate of that stake on that plot. For example, stake 11 is the first stake on the first row. Rows are numbered 1 through 7 going from the most northern row to the most southern. Columns are numbered 1 through 7 going from the most western column to the most eastern (Fig 1). The plant grid contains fewer rows and columns (4 rows, 4 columns). Numbering of the plant stakes follows similar rules to the rodent/ant grid, except that even numbered rows and columns are skipped (censuses use rows 1,3,5,7 and columns 1,3,5,7). Each plant quadrat is 1 m south of the rodent/ant stake of the corresponding number. Details for how these grids are used for data collection can be found in the metadata for the specific data set files.

Geography:The study site is located approximately 6.5 km north and 2 km east of the town of Portal, AZ (31°56'20.29"N 109° 4'47.44"W).

Site history : The site occurs on lands managed by the U.S. Bureau of Land Management. This region has been grazed by cattle since at least the late 19th century. In 1977, a cattle fence was erected around the study area to exclude cattle and no grazing has occurred on the 20 ha since that time.

Climate: There are two rainy seasons at the site, occurring roughly from Oct–April and July–Sept. Typically 60% of the annual rainfall occurs in the summer (Brown and Ernest 2002). The two rainy seasons result in generally two distinct annual plant communities, with a few bi-seasonal annual species.

2. Experimental design:The study consists of 24 experimental plots, assigned to various ant, rodent, and plant manipulations. Although a subset of the plots has maintained a consistent manipulation since 1977, other plots have been reassigned over the course of the study.

Treatments: Experimental manipulations have been altered for some plots over the course of the study. Changes in treatment assignment occurred in 1985 and 1987. Changes in treatment were initiated when the manipulation did not cause significant changes in the rodent community (see Brown 1998 for details). Because responses were either non-existent or minor, plots that were plant manipulations or seed additions from 1977–1987 and were assigned as controls in 1987 are often treated as “long-term controls” for research focusing on the long-term dynamics at the site.

Rodent treatments: Rodent manipulations are effected through the use of gates in the fencing of each plot. Rodent removals contain no gates and any rodents captured on those plots are promptly removed. All other plots contain 16 gates (4 per plot side); gates consist of holes cut through the hardware cloth of the fencing. Gate size is manipulated to exclude subsets of the rodent community. Dimensions for gates on kangaroo rat removal plots are 1.9 cm × 1.9 cm, D. spectabilis removals were 2.6 cm × 3.0 cm, and control plots are 3.7 cm × 5.7 cm. Species caught on plots from which they are supposed to be excluded are removed from the site and the access point to the plot is located and eliminated. Plots affected by these treatments are listed in Table 1, columns 2–4.

Plant treatments: Since 1988 there have been no direct manipulations of the plant community. Before 1988, annuals were “removed” by applying an herbicide (brand: Roundup), but this removal was not considered successful and was discontinued (Brown 1998). Plots affected by these treatments are listed in Table 1, column 3.

Seed additions: Since 1985 there have been no seed additions to any plot. Before 1985, seed additions were conducted by applying 96 kg milo (Sorghum vulgare) and/or millet (Panicum miliaceum) seeds to designated plots (Davidson et al 1985). Plots affected by these treatments are listed in Table 1, column 2.

Ant treatments: Since 1977, ant manipulations have been conducted by applying a commercial poison (Mirex [Allied Chemical Corporation] through 1980 and AMDRO [American Cyanamide Company] afterwards) to designated plots (Davidson et al 1985). Removal of all ants was conducted by widespread application of the baited poison across the designated plot. Selected removal of Pogonomyrmex rugosus was conducted by application of the baited poison at conspicuous mounds of that species (Brown 1998). Plots affected by these treatments are listed in Table 1, columns 2–4.

TABLE 1. Changes in treatment assignments to the 24 experimental plots through time. To help highlight which plots were modified, only changes in treatment after 1985 are recorded below. Blank cells denote no changes in treatment from the previous time period. Pogonomyrmex rugosus was a dominant granivorous ant species that declined at the site. Banner-tailed kangaroo rats (Dipodomys spectabilis) were a dominant rodent granivore that also declined during the 1980s. (Table modified from Brown 1998).

Plot	1977–1985	1985–1987	1988–2002
1	· Mixed-size seeds added in pulse	· All annuals removed	· Banner-tailed kangaroo rat removed
2	· Small seeds added	· Summer annuals removed	· Unmanipulated control
3	· Kangaroo rats removed · Pogonomyrmex rugosus removed		· Kangaroo rats removed · All ants removed
4	· All ants removed
5	· Banner-tailed kangaroo rats removed		· All rodents removed
6	· Large seeds added	· Winter annuals removed	· Kangaroo rats removed
7	· All rodents removed
8	· Pogonomyrmex rugosus removed		· All ants removed
9	· Mixed-size seeds added	· Bi-seasonal annuals removed	· Banner-tailed kangaroo rats removed
10	· All rodents removed · All ants removed
11	· Unmanipulated control
12	· Pogonomyrmex rugosus removed		· All ants removed
13	· Large seeds added	· Winter annuals removed	· Kangaroo rats removed · All ants removed
14	· Unmanipulated control
15	· Kangaroo rats removed
16	· All rodents removed
17	· All ants removed
18	· Mixed-sized seeds added in pulse	· All annuals removed	· Kangaroo rats removed
19	· Kangaroo rats removed · Pogonomyrmex rugosus removed		· Kangaroo rats removed · All ants removed
20	· Mixed-sized seeds added	· Biseasonal annuals removed	· Kangaroo rats removed · All ants removed
21	· Kangaroo rats removed
22	· Small seeds added	· Summer annuals removed	· Unmanipulated control
23	· All rodents removed · All ants removed
24*	· Banner-tailed kangaroo rats removed		· All rodents removed

* plot 24 was not initiated until 1979 (Samson et al. 1992)

F. Publications using the data sets, study site, or other resources:

Publications listed here either used data collected by the Portal Project, used the research site for their own data collection, or significantly used other Portal Project resources to accomplish the research.

1. Brown, J. H., and D. W. Davidson. 1977. Competition between seed-eating ants and rodents in desert ecosystems. Science 196:880–882.
2. Brown, J. H., O. J. Reichman, and D. W. Davidson. 1979. Granivory in desert ecosystems. Annual Review of Ecology and Systematics 10:201–227.
3. Davidson, D.W., J. H. Brown, and R. S. Inouye. 1980. Competition and the structure of granivore communities. Bioscience 30:233–238.
4. Inouye, R. S., G. S. Byers, and J. H. Brown. 1980. Effects of predation and competition on survivorship, fecundity, and community structure of desert annuals. Ecology 61:1344–1351.
5. Inouye, R. S. 1981. Interactions among unrelated species: granivorous rodents, a parasitic fungus, and a shared prey species. Oecologia 49:425–427.
6. Munger, J. C., and J. H. Brown. 1981. Competition in desert rodents: an experiment with semipermeable exclosures. Science 211:510–512.
7. Bowers, M. A., and J. H. Brown. 1982. Body size and coexistence in desert rodents: chance or community structure. Ecology 63:391–400.
8. Price, M. V., and J. H. Brown. 1983. Patterns of morphology and resource use in North American desert rodent communities. Great Basin Naturalist Memoirs 7:117–134.
9. Brown, J. H. 1984. Desert rodents: a model system. Acta Zoologica Fennica 172:45–49.
10. Brown, J. H., and M. A. Bowers. 1984. Patterns and processes in three guilds of terrestrial vertebrates. Pages 282–296 in D.R. Strong, et al. editors. Ecological Communities. Princeton University Press, Princeton, New Jersey, USA .
11. Brown, J. H., and J. C. Munger. 1985. Experimental manipulation of a desert rodent community: food addition and species removal. Ecology 66:1545–1563.
12. Brown, J. H. 1985. Organization of North American desert rodent associations: insights from geographic comparisons and perturbation experiments. Australian Mammalogy 8:131–136.
13. Davidson, D. W. 1985. An experimental study of diffuse competition in harvester ants. American Naturalist 125:500–506.
14. Davidson, D. W., D. A. Samson, and R .S. Inouye. 1985. Granivory in theChihuahuan Desert : Interactions within and between trophic levels. Ecology 66:486–502.
15. Brown, J. H., and D. W. Davidson. 1986. Do desert rodent populations increase when ants are removed: reply. Ecology 67:1423–1425.
16. Brown, J. H., D. W. Davidson, J. C. Munger, and R. S. Inouye. 1986. Experimental community ecology: the desert granivore system. Pages 41–61 in J. M. Diamond and T. J. Case, editors. Community ecology. Harper and Row, New York, New York, USA.
17. Hopf, F. A., and J. H. Brown. 1986. The bulls-eye method for testing randomness in ecological communities. Ecology 67:1139–1155.
18. Bowers, M. A., D. B. Thompson, and J. H. Brown. 1987. Spatial organization of a desert rodent community: food addition and species removal. Oecologia 72:77–82.
19. Brown, J. H., and M. A. Kurzius. 1987. Composition of desert rodent faunas: combinations of coexisting species. Annales Zoologici Fennici 24:227–237.
20. Brown, J. H., and R. A. Ojeda. 1987. Granivory: patterns, processes, and consequences of seed consumption on 2 continents. Revista Chilena De Historia Natural 60:337–349.
21. Zeng, Z. Y., and J. H. Brown. 1987. Population ecology of a desert rodent: Dipodomys merriami in theChihuahuan Desert . Ecology 68:1328–1340.
22. Zeng, Z. Y., and J. H. Brown. 1987. A method for distinguishing dispersal from death in mark-recapture studies. Journal of Mammalogy 68:656–665.
23.  Morton, S. R., and D. W. Davidson. 1988. Comparative structure of harvester ant communities in arid Australia andNorth America . Ecological Monographs 58:19–38.
24. Brown, J. H., and Z. Y. Zeng. 1989. Comparative population ecology of 11 species of rodents in theChihuahuan Desert . Ecology 70:1507–1525.
25. Brown, J. H. and B. A. Maurer. 1989. Macroecology: The division of food and space among species on continents. Science 243:1145–1150.
26. Brown, J. H., and E. J. Heske. 1990. Control of a desert grassland transition by a keystone rodent guild. Science 250:1705–1707.
27. Brown, J. H., and E. J. Heske. 1990. Temporal changes in aChihuahuan Desert rodent community. Oikos 59:290–302.
28. Heske, E. J.  1990. Why do horse lubbers roost in the bushes? Southwestern Naturalist 35:455–458.
29. Brown, J. H. and P. F. Nicoletto. 1991. Spatial scaling of species composition: body masses of North-American land mammals. American Naturalist 138:1478–1512.
30. Heske, E. J., and M. Campbell. 1991. Effects of an 11-Year Livestock exclosure on rodent and ant numbers in the Chihuahuan Desert ,Southeastern Arizona . Southwestern Naturalist 36:89–93.
31. Inouye, R. S. 1991. Population biology of desert annual plants. Pages 27–54 in G. A. Polis, editor. Ecology of Desert Communities. University of Arizona Press, Tucson, Arizona, USA.
32. Patterson, B. D. and J. H. Brown. 1991. Regionally nested patterns of species composition in granivorous rodent assemblages. Journal of Biogeography 18:395–402.
33. Thompson, D. B., J. H. Brown, and W. D. Spencer. 1991. Indirect facilitation of granivorous birds by desert rodents: experimental evidence from foraging patterns. Ecology 72:852–863.
34. Bowers, M. A., and J. H. Brown. 1992. Structure in a desert rodent community: use of space around Dipodomys spectabilis mounds. Oecologia 92:242–249.
35. Frank, D. H., and E. J. Heske. 1992. Seasonal changes in space use patterns in the Southern Grasshopper Mouse, Onychomys torridus torridus. Journal of Mammalogy 73:292–298.
36. Samson, D. A., T. E. Philippi, and D. W. Davidson. 1992. Granivory and competition as determinants of annual plant diversity in theChihuahuan Desert. Oikos 65:61–80.
37. Fox, B. J., and J. H. Brown. 1993. Assembly rules for functional groups in North American desert rodent communities. Oikos 67:358–370.
38. Heske, E. J., J. H. Brown, and Q. F. Guo. 1993. Effects of kangaroo rat exclusion on vegetation structure and plant species diversity in theChihuahuan Desert. Oecologia 95:520–524.
39. Hopf, F. A., T. J. Valone, and J. H. Brown. 1993. Competition theory and the structure of ecological communities. Evolutionary Ecology 7:142–154.
40 Philippi , T. 1993. Bet-hedging germination of desert annuals - beyond the 1st year. American Naturalist 142:474–487.
41.Philippi , T. 1993. Bet-hedging germination of desert annuals: variation among populations and maternal effects in Lapidium lasiocarpum. American Naturalist 142:488–507.
41. Heske, E. J., J. H. Brown, and S. Mistry. 1994. Long-Term experimental study of aChihuahuan Desert rodent community: 13 years of competition. Ecology 75:438–445.
42. Morton, S. R., J. H. Brown, D. A. Kelt, and J. R. W. Reid. Comparisons of community structure among small mammals of North American andAustralian Deserts. Australian Journal of Zoology 42:501–525.
43. Shenbrot, G. I., K. A. Rogovin, and E. J. Heske. 1994. Comparison of niche-packing and community organization in desert rodents inAsia and North-America. Australian Journal of Zoology 42:479–499.
44. Valone, T. J., J. H. Brown, and E. J. Heske. 1994. Interactions between rodents and ants in theChihuahuan Desert : An update. Ecology 75:252–255.
45. Guo, Q. F., D. B. Thompson, T. J. Valone, and J. H. Brown. 1995. The effects of vertebrate granivores and folivores on plant community structure in theChihuahuan Desert. Oikos 73:251–259.
47. Kelt, D. A., and T. J. Valone. 1995.  Effects of grazing on the abundance and diversity of annual plants inChihuahuan Desert scrub habitat. Oecologia 103:191–195.
48. Skupski, M. P. 1995.  Population ecology of the Western Harvest Mouse, Reithrodontomys megalotis - a long-term perspective. Journal of Mammalogy 76:358–367.
49. Valone, T. J., and J. H. Brown. 1995. Effects of competition, colonization, and extinction on rodent species diversity. Science 267:880–883.
50. Valone, T. J., J. H. Brown, and C. L. Jacobi. 1995. Catastrophic decline of a desert rodent, Dipodomys spectabilis:  Insights from a long-term study. Journal of Mammalogy 76:428–436.
51. Brown, J. H., and A. Kodric-Brown. 1996. Discovery: Biodiversity on the borderlands. Natural History 105:58–61.
52. Guo, Q. F., and J. H. Brown. 1996. Temporal fluctuations and experimental effects in desert plant communities. Oecologia 107:568–577.
53. Guo, Q. F. 1996. Effects of bannertail kangaroo rat mounds on small-scale plant community structure. Oecologia 106:247–256.
54. Kelt, D. A., J. H. Brown, E. J. Heske, P. A. Marquet, S. R. Morton, J. R. W. Reid, K. A. Rogovin, and G. Shenbrot. 1996. Community structure of desert small mammals: Comparisons across four continents. Ecology 77:746–761.
55. Valone, T. J., and J. H. Brown. 1996. Desert rodents: long-term responses to natural changes and experimental manipulations. Pages 555–583 in M. L. Cody and J. A. Smallwood, editors. Long-term Studies of Vertebrate Communities. Academic Press, Orlando, Florida, USA.
56. Brown, J. H., T. J. Valone, and C. G. Curtin. 1997. Reorganization of an arid ecosystem in response to recent climate change. Proceedings of the National Academy of Sciences, USA 94:9729–9733.
57. Guo, Q. F., and J. H. Brown. 1997. Interactions between winter and summer annuals in the Chihuahuan Desert. Oecologia 111:123–128.
58. Smith, F. A., J. H. Brown, and T .J. Valone. 1997. Path analysis: A critical evaluation using long-term experimental data. American Naturalist 149:29–42.
59. Brown, J. H. 1998. The desert granivory experiments at Portal. Pages 71-95 in W.L. Resetarits, Jr and J. Bernardo, editors. Issues and Perspectives in Experimental Ecology. Oxford University Press, Oxford, UK.
60. Guo, Q. F. 1998. Microhabitat differentiation inChihuahuan Desert plant communities. Plant Ecology 139:71–80.
61. Guo, Q. F., and W. L. Berry. 1998. Species richness and biomass: Dissection of the hump-shaped relationships. Ecology 79:2555–2559.
62. Guo, Q. F., J. H. Brown, and B. J. Enquist. 1998. Using constraint lines to characterize plant performance. Oikos 83:237–245.
63. Schlesinger, W. H., and A. M. Pilmanis. 1998. Plant-soil interactions in deserts. Biogeochemistry 42:169–187.
64. Curtin, C. G., D. A. Kelt, T. C. Frey, and J. H. Brown. 1999. On the role of small mammals in mediating climatically driven vegetation change. Ecology Letters 3:309–317.
65. Kelt, D. A., K. Rogovin, G. Shenbrot, and J. H. Brown. 1999. Patterns in the structure of Asian and North American desert small mammal communities. Journal of Biogeography 26:825–841.
66. Kelt, D. A. 1999. On the relative importance of history and ecology in structuring communities of desert small animals. Ecography 22:123–137.
67. Maurer, B. A. 1999. Untangling ecological complexity.University of Chicago Press, Chicago, Illinois, USA.
68. Meyer, M. D., and T. J. Valone. 1999. Foraging under multiple costs: the importance of predation, energetic, and assessment error costs to a desert forager. Oikos 87:571–579.
69. Valone, T. J., and D. A. Kelt. 1999. Fire and grazing in a shrub-invaded arid grassland community: independent or interactive ecological effects? Journal of Arid Environments 42:15–28.
70. Brown, J. H., B. J. Fox, and D. A. Kelt. 2000. Assembly rules: Desert rodent communities are structured at scales from local to continental. American Naturalist 156:314–321.
71. Ernest, S. K. M., J. H. Brown, and R. R. Parmenter. 2000. Rodents, plants, and precipitation: spatial and temporal dynamics of consumers and resources. Oikos 88:470–482.
72. Guo, Q. F., J. H. Brown, T. J. Valone, and S. D. Kachman. 2000. Constraints of seed size on plant distribution and abundance. Ecology 81:2149–2155.
73. Guo, Q. F., J. H. Brown, and T. J. Valone. 2000. Abundance and distribution of desert annuals: are spatial and temporal patterns related? Journal of Ecology 88:551–560.
74. Kelt, D. A. and J. H. Brown. 2000. Species as units of analysis in ecology and biogeography: are the blind leading the blind? Global Ecology and Biogeography 9:213–217.
75. Brown, J. H., T. G. Whitham, S. K. M. Ernest , and C. A. Gehring. 2001. Complex species interactions and the dynamics of ecological systems: Long-term experiments. Science 293:643–650.
76. Brown, J. H., S. K. M. Ernest, J. M. Parody, and J. P. Haskell. 2001. Regulation of diversity: maintenance of species richness in changing environments. Oecologia 126:321–332.
77. Charnov, E. L., J. P. Haskell, and S. K. M. Ernest. 2001. Density-dependent invariance, dimensionless life histories and the energy-equivalence rule. Evolutionary Ecology Research 3:117–127.
78. Ernest, S. K. M., and J. H. Brown. 2001. Delayed compensation for missing keystone species by colonization. Science 292:101–104.
79. Ernest, S. K. M., and J. H. Brown. 2001. Homeostasis and compensation: The role of species and resources in ecosystem stability. Ecology 82:2118–2132.
80. Sullivan, H. L., C. G. Curtin , C. A. Reynolds, and S. G. Cardiff. 2001. The effect of topography on the foraging costs of heteromyid rodents. Journal of Arid Environments 48:255–266.
81. Valone, T. J., and D. Thornhill. 2001. Mesquite establishment in arid grasslands: an experimental investigation of the role of kangaroo rats. Journal of Arid Environments 48:281–288.
82. Brown, J. H., and S. K. M. Ernest. 2002. Rain and rodents: Complex dynamics of desert consumers. Bioscience 52:979–987.
83. Guo, Q. F., J. H. Brown, and T. J. Valone. 2002. Long-term dynamics of winter and summer annual communities in the Chihuahuan Desert. Journal of Vegetation Science 13:575–584.
84. Kaspari, M., and T. Valone. 2002. On ectotherm abundance in a seasonal environment - studies of a desert ant assemblage. Ecology 83:2991–2996.
85. Smith, K. F., Z. D. Sharp, and J. H. Brown. 2002. Isotopic composition of carbon and oxygen in desert fauna: investigations into the effects of diet, physiology, and seasonality. Journal of Arid Environments 52:419–430.
86. Valone, T. J., and C. D. Hoffman. 2002. Effects of regional pool size on local diversity in small-scale annual plant communities. Ecology Letters 5:477–480.
87. Valone, T., M. Meyer, J. H. Brown, and R. M. Chew. 2002. Timescale of perennial grass recovery in desertified arid grasslands following livestock removal. Conservation Biology 16:995–1002.
88. Valone, T. J., and C. Hoffman. 2003. Population stability is higher in more diverse annual plant communities. Ecology Letters 6:90–95.
89. Valone, T. J., and C. D. Hoffman. 2003. A mechanistic examination of diversity-stability relationships in annual plant communities. Oikos 103:519–527.
90. Valone, T. J. 2003. Examination of interaction effects of multiple disturbances on an arid plant community. Southwestern Naturalist 48:481–490.
91. Thibault, K. M., E. P. White, and S. K. M. Ernest. 2004. Temporal dynamics in the structure and composition of a desert rodent community. Ecology 85:2649–2655.
92. Valone, T. J., and M. Kaspari. 2004. Interactions between granivorous and omnivorous ants in a desert grassland: results from a long-term experiment. Ecological Entomology, 30:116–121.
93. White, E. P., S. K. M. Ernest, and K. M. Thibault. 2004. Trade-offs in community properties through time in a desert rodent community. American Naturalist 164:670–676.
94. Adler, P. B., E. P. White, W. K. Lauenroth, D. M. Kaufman, A. Rassweiler, and J. A. Rusak. 2005. Evidence for a general species-time-area relationship. Ecology 86:2032–2039.
95. Ernest, S. K. M. 2005. Body size, energy use, and community structure of small mammals. Ecology 86:1407–1413.
96. Goheen, J. R., E. P. White, S. K. M. Ernest, and J. H. Brown. 2005. Intra-guild compensation regulates species richness in desert rodents. Ecology 86:567–573.
97. White, E. P., and J. H. Brown. 2005. The template: patterns and processes of spatial variation. Pages 31-47 in G. M. Lovett, et al., editors. Ecosystem function in heterogeneous landscapes.  Springer-Verlag , New York, New York, USA .
98. Yin, Z. Y., Q. F. Guo, H. Ren, and S. L. Peng. 2005. Seasonal changes in spatial patterns of two annual plants in the Chihuahuan Desert ,USA . Plant Ecology 178:189–199.
99. White, E. P., P. B. Adler, W. K. Lauenroth,  R. A. Gill, D. Greenberg, D. M. Kaufman, A. Rassweiler, J. A. Rusack, M. D. Smith, J. R. Steinbeck, R. B. Waide, and J. Yao. 2006. A comparison of the species-time relationship across ecosystems and taxonomic groups. Oikos 112:185–195.
100. Goheen, J. R., E. P. White, S. K. M. Ernest, and J. H. Brown. 2006. Intraguild compensation regulates species richness in desert rodents: reply. Ecology 87:2121–2125.
101. Schutzenhofer, M. R., and T. J. Valone. 2006. Positive and negative effects of exotic Erodium cicutarium on an arid ecosystem. Biological Conservation 132:376–381.
102. Houlahan, J. E., D. J. Currie, K. Cottenie, G. S. Cummings, S. K. M. Ernest, C. S. Findlay, S. D. Fuhlendorf, U. Gaedke, P. Legendre, J. J. Magnuson, B. H. McArdle, E. H. Muldavin, D. Noble, R. Russell, R. D. Stevens, T. J. Willis, I. P. Woiwod, and S. M. Wondzell. Compensatory dynamics are rare in natural ecological communities. Proceedings of the National Academy of Science (USA ) 104:3273–3277.
103. Valone, T. J., and M. R. Schutzenhofer. 2007. Reduced rodent biodiversity destabilizes plant populations. Ecology 88:26–31.
104. White, E.P., and M.A. Gilchrist. 2007. Effects of population-level aggregation, autocorrelation, and interspecific interaction on the species-time relationship in two desert communities. Evolutionary Ecology Research 9:1329–1347.
105.  White, E. P. 2007. Spatiotemporal scaling of species richness: patterns, processes and implications. Pages 325–346 in D. Storch, P. A. Marquet, and J. H. Brown, editors. Scaling Biodiversity. Cambridge University Press, Cambridge, UK .
106. Castellano, M. J., and T. J. Valone. 2007. Livestock, soil compaction, and water infiltration rate: evaluating a potential desertification recovery mechanism. Journal of Arid Environments 71:97–108.
107. Valone, T. J., and N. A. Barber. 2008. An empirical evaluation of the insurance hypothesis in diversity-stability models. Ecology 89:522–531.
108. Thibault, K. M., and J. H. Brown. 2008. Impact of an extreme climatic event on community assembly. Proceedings of the National Academy of Science (USA ) 105:3410–3415.

ACKNOWLEDGMENTS

We would like to thank the literally hundreds of people who have made this project possible. Without their assistance and dedication, this project would not have been possible. Untold volunteers have contributed to the data collection over the decades.

LITERATURE CITED

Brown, J. H. 1998. The desert granivory experiments at Portal. Pages 71–95 in W.L. Resetarits, Jr and J. Bernardo, editors. Issues and perspectives in experimental ecology. Oxford University Press, Oxford, UK.

Brown, J. H., and S. K. M. Ernest. 2002. Rain and rodents: Complex dynamics of desert consumers. Bioscience 52:979–987.

Brown, J. H., T. J., Valone, and C. G. Curtin. 1997. Reorganization of an arid ecosystem in response to recent climate change. Proceedings of the National Academy of Sciences (USA) 94:9729–9733.

Davidson, D. W., D. A. Samson, and R. S. Inouye. 1985. Granivory in the Chihuahuan Desert: Interactions within and between trophic levels. Ecology 66:486–502.

Samson, D. A., T. E. Philippi, and D. W. Davidson. 1992. Granivory and competition as determinants of annual plant diversity in the Chihuahuan Desert. Oikos 65:61–80.