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James R. Ehleringer - One of the best experts on this subject based on the ideXlab platform.
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Summer and winter drought in a cold desert ecosystem (Colorado Plateau) part II: effects on plant carbon assimilation and growth
Journal of Arid Environments, 2005Co-Authors: Susanne Schwinning, Benjamin I. Starr, James R. EhleringerAbstract:We investigated the effects of winter and summer drought on a shrub/grass community of the Colorado Plateau in western North America, a winter-cold, summer-hot desert that receives both winter and summer precipitation. Summer, winter and yearlong drought treatments were imposed for 2 consecutive years using rainout shelters. We chose three perennial species for this study, representing different rooting patterns and responsiveness to precipitation pulses: Oryzopsis hymenoides, a perennial bunch grass with shallow roots; Gutierrezia sarothrae, a subshrub with dimorphic roots; and Ceratoides lanata, a predominantly deep-rooted woody shrub. Growth for all three species was far more sensitive to winter than to summer drought. The primary reason was that plants did not grow in summer and also did not appear to use summer-assimilated carbon to support growth in the following spring. We hypothesize that the relative scarcity and uncertainty of summer rain on the Colorado Plateau prevents most species from evolving adaptations that would improve their use of summer rain. Together with the results of the companion paper, which focused on plant water relations, we conclude that variation in fall to spring precipitation would have strong effects on primary productivity, and could cause reversible fluctuations in community composition, while increased variation in summer precipitation, through causing high rates of mortality among shallow-rooted species in dry years, has the potential to cause lasting and perhaps irreversible community change, especially if coinciding with the invasion of western landscapes by cheatgrass, tumble weed and other grazing tolerant exotics.
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Summer and winter drought in a cold desert ecosystem (Colorado Plateau) part I: effects on soil water and plant water uptake
Journal of Arid Environments, 2005Co-Authors: Susanne Schwinning, Benjamin I. Starr, James R. EhleringerAbstract:We investigated the effects of winter and summer drought on plants of the Colorado Plateau in western North America. This winter-cold, summer-hot desert region receives both winter and summer precipitation. Droughts were imposed for two consecutive years using rainout shelters. Here, we examine drought effects on the hydrologic interactions between plants and soil. We chose three perennial species for this study, representing different rooting patterns and responsiveness to precipitation pulses: Oryzopsis hymenoides, a perennial bunch grass with shallow roots; Gutierrezia sarothrae, a subshrub with dimorphic roots; and Ceratoides lanata, a predominantly deep-rooted woody shrub. Drought effects on plant water status were qualitatively similar among species, despite morphological differences. Summer drought affected the water status of all species more negatively than winter drought. Isotopic analysis of stem water revealed that all three species took up deeper soil water under drought conditions and shallow soil water after a large rainfall event in summer. Thus all three species appeared to use the same water sources most of the time. However, after a particularly dry summer, only the deepest-rooted species continued to take up soil water, while the more shallow-rooted species were either dead or dormant. Our study suggests therefore that increased occurrence of summer drought could favor the most deep-rooted species in ecosystem.
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Dominant cold desert plants do not partition warm season precipitation by event size
Oecologia, 2003Co-Authors: Susanne Schwinning, Benjamin I. Starr, James R. EhleringerAbstract:We conducted experiments to examine the quantitative relationships between rainfall event size and rainwater uptake and use by four common native plant species of the Colorado Plateau, including two perennial grasses, Hilaria jamesii (C_4) and Oryzopsis hymenoides (C_3), and two shrubs, Ceratoides lanata (C_3), and Gutierrezia sarothrae (C_3). Specifically, we tested the hypothesis that grasses use small rainfall events more efficiently than shrubs and lose this advantage when events are large. Rainfall events between 2 and 20 mm were simulated in spring and summer by applying pulses of deuterium-labeled irrigation water. Afterwards, pulse water fractions in stems and the rates of leaf gas exchange were monitored for 9 days. Cumulative pulse water uptake over this interval (estimated by integrating the product of pulse fraction in stem water and daytime transpiration rate over time) was approximately linearly related to the amount of pulse water added to the ground in all four species. Across species, consistently more pulse water was taken up in summer than in spring. Relative to their leaf areas, the two grass species took up more pulse water than the two shrub species, across all event sizes and in both seasons, thus refuting the initial hypothesis. In spring, pulse water uptake did not significantly increase photosynthetic rates and in summer, pulse water uptake had similar, but relatively small effects on the photosynthetic rates of the three C_3 plants, and a larger effect on the C_4 plant H. jamesii. Based on these data, we introduce an alternative hypothesis for the responses of plant functional types to rainfall events of different sizes, building on cost-benefit considerations for active physiological responses to sudden, unpredictable changes in water availability.
Susanne Schwinning - One of the best experts on this subject based on the ideXlab platform.
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Effects of Nitrogen Deposition on an Arid Grassland in the Colorado Plateau Cold Desert
Rangeland Ecology & Management, 2005Co-Authors: Susanne Schwinning, Benjamin I. Starr, Nathan J. Wojcik, Mark E. Miller, James E. Ehleringer, Robert L. SanfordAbstract:Abstract Historically, ecosystems in the southwestern United States derived much of their nitrogen (N) from N-fixation in biological soil crusts. Today, these regions have highly reduced crust cover, and atmospheric deposition may be the dominant source of N. This study investigates the effects of increased nitrogen deposition on nitrogen uptake, photosynthesis, and growth of the two main forage grasses on the Colorado Plateau, galleta ( Hilaria jamesii [Torr.] Benth.) and Indian ricegrass ( Oryzopsis hymenoides , [Roemer & J.S. Schultes] Ricker ex Piper). Plots were fertilized for 2 years with 0, 10, 20, and 40 kg nitrogen ha −1 annually, up to 4× the estimated current annual deposition rate, in 2 applications per year (spring and summer). Half-plots were fertilized with either (NH 4 ) 2 SO 4 in KCl solution or with KNO 3 solution to determine possible differences in the effects of NH 4 + and NO 3 − in this system. Neither grass increased leaf photosynthesis or tiller size due to supplemental N. Galleta also did not increase tiller density, while estimated live tiller density in Indian ricegrass increased up to 50% in the second year. Nitrogen applications accelerated the onset of water stress in both species presumably through stimulating ecosystem transpiration. Nitrogen form did not significantly affect any aspect of grass physiological performance or growth. However, leaf nitrogen in NH 4 + -fertilized plants was significantly more isotopically enriched than in NO 3 − -fertilized plants, suggesting that both species incorporated NH 4 -N only after it had been enriched by soil turnover. Seedlings of Russian Thistle ( Salsola iberica , Sennen & Pau), a noxious annual invasive weed on western rangelands, grew rapidly in the first summer on plots with 40 kg nitrogen ha −1 per annum, and more so on plots fertilized with NO 3 − than with NH 4 + . The study suggests that changes in the timing and amount of nitrogen input may alter community composition through facilitating the invasions of summer-active noxious weeds.
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Summer and winter drought in a cold desert ecosystem (Colorado Plateau) part II: effects on plant carbon assimilation and growth
Journal of Arid Environments, 2005Co-Authors: Susanne Schwinning, Benjamin I. Starr, James R. EhleringerAbstract:We investigated the effects of winter and summer drought on a shrub/grass community of the Colorado Plateau in western North America, a winter-cold, summer-hot desert that receives both winter and summer precipitation. Summer, winter and yearlong drought treatments were imposed for 2 consecutive years using rainout shelters. We chose three perennial species for this study, representing different rooting patterns and responsiveness to precipitation pulses: Oryzopsis hymenoides, a perennial bunch grass with shallow roots; Gutierrezia sarothrae, a subshrub with dimorphic roots; and Ceratoides lanata, a predominantly deep-rooted woody shrub. Growth for all three species was far more sensitive to winter than to summer drought. The primary reason was that plants did not grow in summer and also did not appear to use summer-assimilated carbon to support growth in the following spring. We hypothesize that the relative scarcity and uncertainty of summer rain on the Colorado Plateau prevents most species from evolving adaptations that would improve their use of summer rain. Together with the results of the companion paper, which focused on plant water relations, we conclude that variation in fall to spring precipitation would have strong effects on primary productivity, and could cause reversible fluctuations in community composition, while increased variation in summer precipitation, through causing high rates of mortality among shallow-rooted species in dry years, has the potential to cause lasting and perhaps irreversible community change, especially if coinciding with the invasion of western landscapes by cheatgrass, tumble weed and other grazing tolerant exotics.
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Summer and winter drought in a cold desert ecosystem (Colorado Plateau) part I: effects on soil water and plant water uptake
Journal of Arid Environments, 2005Co-Authors: Susanne Schwinning, Benjamin I. Starr, James R. EhleringerAbstract:We investigated the effects of winter and summer drought on plants of the Colorado Plateau in western North America. This winter-cold, summer-hot desert region receives both winter and summer precipitation. Droughts were imposed for two consecutive years using rainout shelters. Here, we examine drought effects on the hydrologic interactions between plants and soil. We chose three perennial species for this study, representing different rooting patterns and responsiveness to precipitation pulses: Oryzopsis hymenoides, a perennial bunch grass with shallow roots; Gutierrezia sarothrae, a subshrub with dimorphic roots; and Ceratoides lanata, a predominantly deep-rooted woody shrub. Drought effects on plant water status were qualitatively similar among species, despite morphological differences. Summer drought affected the water status of all species more negatively than winter drought. Isotopic analysis of stem water revealed that all three species took up deeper soil water under drought conditions and shallow soil water after a large rainfall event in summer. Thus all three species appeared to use the same water sources most of the time. However, after a particularly dry summer, only the deepest-rooted species continued to take up soil water, while the more shallow-rooted species were either dead or dormant. Our study suggests therefore that increased occurrence of summer drought could favor the most deep-rooted species in ecosystem.
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Dominant cold desert plants do not partition warm season precipitation by event size
Oecologia, 2003Co-Authors: Susanne Schwinning, Benjamin I. Starr, James R. EhleringerAbstract:We conducted experiments to examine the quantitative relationships between rainfall event size and rainwater uptake and use by four common native plant species of the Colorado Plateau, including two perennial grasses, Hilaria jamesii (C_4) and Oryzopsis hymenoides (C_3), and two shrubs, Ceratoides lanata (C_3), and Gutierrezia sarothrae (C_3). Specifically, we tested the hypothesis that grasses use small rainfall events more efficiently than shrubs and lose this advantage when events are large. Rainfall events between 2 and 20 mm were simulated in spring and summer by applying pulses of deuterium-labeled irrigation water. Afterwards, pulse water fractions in stems and the rates of leaf gas exchange were monitored for 9 days. Cumulative pulse water uptake over this interval (estimated by integrating the product of pulse fraction in stem water and daytime transpiration rate over time) was approximately linearly related to the amount of pulse water added to the ground in all four species. Across species, consistently more pulse water was taken up in summer than in spring. Relative to their leaf areas, the two grass species took up more pulse water than the two shrub species, across all event sizes and in both seasons, thus refuting the initial hypothesis. In spring, pulse water uptake did not significantly increase photosynthetic rates and in summer, pulse water uptake had similar, but relatively small effects on the photosynthetic rates of the three C_3 plants, and a larger effect on the C_4 plant H. jamesii. Based on these data, we introduce an alternative hypothesis for the responses of plant functional types to rainfall events of different sizes, building on cost-benefit considerations for active physiological responses to sudden, unpredictable changes in water availability.
William S Longland - One of the best experts on this subject based on the ideXlab platform.
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seedling recruitment in Oryzopsis hymenoides are desert granivores mutualists or predators
Ecology, 2001Co-Authors: William S Longland, Stephen H Jenkins, Stephen Vander B Wall, Joseph A Veech, Sanjay PyareAbstract:Granivorous animals that cache as well as consume seeds may actually serve as mutualists to their plant resources. Seeds of Indian ricegrass (Oryzopsis hymenoides), a perennial bunchgrass in North American deserts, are consumed by various desert granivores and dispersed by seed-caching heteromyid rodents. We used a three-way factorial design at a western Nevada site to selectively exclude or allow access to experimental plots by granivorous rodents and seed harvester ants, and to subsequently follow the fate of radio- labeled Indian ricegrass seeds introduced to the plots. In addition to the presence or absence of rodents or ants, the third experimental treatment factor was to allow "initial caching" of the radiolabeled seeds by single Merriam's kangaroo rats (Dipodomys merriami), which were confined to certain plots for one night. Both rodents and ants larder-hoarded seeds in their burrows, but seedlings rarely established from larders. Only rodents also placed seeds in scatterhoards: shallowly buried surface caches distributed about an animal's home range. Following initial caching by a kangaroo rat, the number of seedlings established from scatterhoards was significantly greater (usually by more than an order of magnitude) than those from seeds unharvested by either type of granivore. With no initial caching, rodents reduced seedling recruitment from unharvested seeds but facilitated compensatory seedling recruitment from scatterhoards. Seeds harvested by ants seldom established seedlings. We used a seed fate model to estimate that, on average, rodents and ants harvested 96% and 7%, respectively, of seeds to which they had exclusive access, and that the probability of seedling establishment for a seed harvested by a rodent was an order of magnitude greater than from a seed harvested by an ant and slightly greater than for an unharvested seed. The predicted rank order of seedling recruitment among nine experimental treatments based on expected effects of rodent seed caching closely matched the observed ranking pattern, indicating that rodents determined seedling recruitment patterns of Indian ricegrass. Because rodents harvested such a large majority of seeds and their caches enhanced seedling es- tablishment, they played a central role in the population dynamics of Indian ricegrass.
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EFFECTS OF SEED DENSITY ON GERMINATION AND ESTABLISHMENT OF A NATIVE AND AN INTRODUCED GRASS SPECIES DISPERSED BY GRANIVOROUS RODENTS
American Midland Naturalist, 1997Co-Authors: Michael H. Mcmurray, Stephen H Jenkins, William S LonglandAbstract:-Dense aggregations of Oryzopsis hymenoides (Indian ricegrass) and Bromus tectorum (cheatgrass) seeds occur in rodent caches in the Great Basin. Rodent caching behavior may influence establishment and persistence of these two desert grasses. Seed caches of rodents clearly introduce exaggerated seedling competition in these species. Greenhouse experiments were used to determine if establishment and persistence of these species were affected differently by densities of seeds in caches. Germination and establishment of Indian ricegrass, a native perennial grass, were less affected by high seed densities than germination and establishment of cheatgrass, an introduced annual weed. The different natural histories of these species, as well as data presented here, suggest that the high seed densities introduced by caching behavior of desert rodents may be beneficial to Indian ricegrass and harmful to cheatgrass.
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Seeding Indian ricegrass in an arid environment in the Great Basin
Journal of Range Management, 1994Co-Authors: James A. Young, William S Longland, Robert R. Blank, Debra E. PalmquistAbstract:Indian ricegrass [Oryzopsis hymenoides (R. & S.) Rickerl is a valuable forage species adapted to arid rangelands in temperate deserts. The purpose of this study was to test the influence of seeding date, depth, and rate on Indian ricegrass emergence and seedling establishment of acid scarified and intact caryopses (seeds). The seeding experiments were conducted on a wind eroding sand sheet of Lahontan age in western Nevada. During the initial year of planting, seeds of the cultivars Nezpar and Paloma Indian ricegrass were successfully established without pretreatment by acid scarification. Acid scarified seeds did not result in the established seedling stands in the field. Initial seedings were done in a season with prolonged moisture events with total precipitation about twice the average. Seedling stands of crested wheatgrass [Agropyron desertorum (Fisch.) ex Link Schult] as well as other exotic and native herbaceous and woody species were established during the first year. During the next 4 years crested wheatgrass seedlings were never again established. Indian ricegrass seedlings were established in 3 of the 4 subsequent years of seeding trials using a seeding rate of 0.8 seeds/cm of row and a seeding depth of 1 cm. Indian ricegrass seedling emergence was increased by either increasing the planting depth to 5 cm or by reducing the seeding rate to 0.03 seeds/cm of row. The ultra-low seeding rate resulted in a significant saving in seed cost.
Benjamin I. Starr - One of the best experts on this subject based on the ideXlab platform.
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Effects of Nitrogen Deposition on an Arid Grassland in the Colorado Plateau Cold Desert
Rangeland Ecology & Management, 2005Co-Authors: Susanne Schwinning, Benjamin I. Starr, Nathan J. Wojcik, Mark E. Miller, James E. Ehleringer, Robert L. SanfordAbstract:Abstract Historically, ecosystems in the southwestern United States derived much of their nitrogen (N) from N-fixation in biological soil crusts. Today, these regions have highly reduced crust cover, and atmospheric deposition may be the dominant source of N. This study investigates the effects of increased nitrogen deposition on nitrogen uptake, photosynthesis, and growth of the two main forage grasses on the Colorado Plateau, galleta ( Hilaria jamesii [Torr.] Benth.) and Indian ricegrass ( Oryzopsis hymenoides , [Roemer & J.S. Schultes] Ricker ex Piper). Plots were fertilized for 2 years with 0, 10, 20, and 40 kg nitrogen ha −1 annually, up to 4× the estimated current annual deposition rate, in 2 applications per year (spring and summer). Half-plots were fertilized with either (NH 4 ) 2 SO 4 in KCl solution or with KNO 3 solution to determine possible differences in the effects of NH 4 + and NO 3 − in this system. Neither grass increased leaf photosynthesis or tiller size due to supplemental N. Galleta also did not increase tiller density, while estimated live tiller density in Indian ricegrass increased up to 50% in the second year. Nitrogen applications accelerated the onset of water stress in both species presumably through stimulating ecosystem transpiration. Nitrogen form did not significantly affect any aspect of grass physiological performance or growth. However, leaf nitrogen in NH 4 + -fertilized plants was significantly more isotopically enriched than in NO 3 − -fertilized plants, suggesting that both species incorporated NH 4 -N only after it had been enriched by soil turnover. Seedlings of Russian Thistle ( Salsola iberica , Sennen & Pau), a noxious annual invasive weed on western rangelands, grew rapidly in the first summer on plots with 40 kg nitrogen ha −1 per annum, and more so on plots fertilized with NO 3 − than with NH 4 + . The study suggests that changes in the timing and amount of nitrogen input may alter community composition through facilitating the invasions of summer-active noxious weeds.
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Summer and winter drought in a cold desert ecosystem (Colorado Plateau) part II: effects on plant carbon assimilation and growth
Journal of Arid Environments, 2005Co-Authors: Susanne Schwinning, Benjamin I. Starr, James R. EhleringerAbstract:We investigated the effects of winter and summer drought on a shrub/grass community of the Colorado Plateau in western North America, a winter-cold, summer-hot desert that receives both winter and summer precipitation. Summer, winter and yearlong drought treatments were imposed for 2 consecutive years using rainout shelters. We chose three perennial species for this study, representing different rooting patterns and responsiveness to precipitation pulses: Oryzopsis hymenoides, a perennial bunch grass with shallow roots; Gutierrezia sarothrae, a subshrub with dimorphic roots; and Ceratoides lanata, a predominantly deep-rooted woody shrub. Growth for all three species was far more sensitive to winter than to summer drought. The primary reason was that plants did not grow in summer and also did not appear to use summer-assimilated carbon to support growth in the following spring. We hypothesize that the relative scarcity and uncertainty of summer rain on the Colorado Plateau prevents most species from evolving adaptations that would improve their use of summer rain. Together with the results of the companion paper, which focused on plant water relations, we conclude that variation in fall to spring precipitation would have strong effects on primary productivity, and could cause reversible fluctuations in community composition, while increased variation in summer precipitation, through causing high rates of mortality among shallow-rooted species in dry years, has the potential to cause lasting and perhaps irreversible community change, especially if coinciding with the invasion of western landscapes by cheatgrass, tumble weed and other grazing tolerant exotics.
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Summer and winter drought in a cold desert ecosystem (Colorado Plateau) part I: effects on soil water and plant water uptake
Journal of Arid Environments, 2005Co-Authors: Susanne Schwinning, Benjamin I. Starr, James R. EhleringerAbstract:We investigated the effects of winter and summer drought on plants of the Colorado Plateau in western North America. This winter-cold, summer-hot desert region receives both winter and summer precipitation. Droughts were imposed for two consecutive years using rainout shelters. Here, we examine drought effects on the hydrologic interactions between plants and soil. We chose three perennial species for this study, representing different rooting patterns and responsiveness to precipitation pulses: Oryzopsis hymenoides, a perennial bunch grass with shallow roots; Gutierrezia sarothrae, a subshrub with dimorphic roots; and Ceratoides lanata, a predominantly deep-rooted woody shrub. Drought effects on plant water status were qualitatively similar among species, despite morphological differences. Summer drought affected the water status of all species more negatively than winter drought. Isotopic analysis of stem water revealed that all three species took up deeper soil water under drought conditions and shallow soil water after a large rainfall event in summer. Thus all three species appeared to use the same water sources most of the time. However, after a particularly dry summer, only the deepest-rooted species continued to take up soil water, while the more shallow-rooted species were either dead or dormant. Our study suggests therefore that increased occurrence of summer drought could favor the most deep-rooted species in ecosystem.
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Dominant cold desert plants do not partition warm season precipitation by event size
Oecologia, 2003Co-Authors: Susanne Schwinning, Benjamin I. Starr, James R. EhleringerAbstract:We conducted experiments to examine the quantitative relationships between rainfall event size and rainwater uptake and use by four common native plant species of the Colorado Plateau, including two perennial grasses, Hilaria jamesii (C_4) and Oryzopsis hymenoides (C_3), and two shrubs, Ceratoides lanata (C_3), and Gutierrezia sarothrae (C_3). Specifically, we tested the hypothesis that grasses use small rainfall events more efficiently than shrubs and lose this advantage when events are large. Rainfall events between 2 and 20 mm were simulated in spring and summer by applying pulses of deuterium-labeled irrigation water. Afterwards, pulse water fractions in stems and the rates of leaf gas exchange were monitored for 9 days. Cumulative pulse water uptake over this interval (estimated by integrating the product of pulse fraction in stem water and daytime transpiration rate over time) was approximately linearly related to the amount of pulse water added to the ground in all four species. Across species, consistently more pulse water was taken up in summer than in spring. Relative to their leaf areas, the two grass species took up more pulse water than the two shrub species, across all event sizes and in both seasons, thus refuting the initial hypothesis. In spring, pulse water uptake did not significantly increase photosynthetic rates and in summer, pulse water uptake had similar, but relatively small effects on the photosynthetic rates of the three C_3 plants, and a larger effect on the C_4 plant H. jamesii. Based on these data, we introduce an alternative hypothesis for the responses of plant functional types to rainfall events of different sizes, building on cost-benefit considerations for active physiological responses to sudden, unpredictable changes in water availability.
Sanjay Pyare - One of the best experts on this subject based on the ideXlab platform.
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seedling recruitment in Oryzopsis hymenoides are desert granivores mutualists or predators
Ecology, 2001Co-Authors: William S Longland, Stephen H Jenkins, Stephen Vander B Wall, Joseph A Veech, Sanjay PyareAbstract:Granivorous animals that cache as well as consume seeds may actually serve as mutualists to their plant resources. Seeds of Indian ricegrass (Oryzopsis hymenoides), a perennial bunchgrass in North American deserts, are consumed by various desert granivores and dispersed by seed-caching heteromyid rodents. We used a three-way factorial design at a western Nevada site to selectively exclude or allow access to experimental plots by granivorous rodents and seed harvester ants, and to subsequently follow the fate of radio- labeled Indian ricegrass seeds introduced to the plots. In addition to the presence or absence of rodents or ants, the third experimental treatment factor was to allow "initial caching" of the radiolabeled seeds by single Merriam's kangaroo rats (Dipodomys merriami), which were confined to certain plots for one night. Both rodents and ants larder-hoarded seeds in their burrows, but seedlings rarely established from larders. Only rodents also placed seeds in scatterhoards: shallowly buried surface caches distributed about an animal's home range. Following initial caching by a kangaroo rat, the number of seedlings established from scatterhoards was significantly greater (usually by more than an order of magnitude) than those from seeds unharvested by either type of granivore. With no initial caching, rodents reduced seedling recruitment from unharvested seeds but facilitated compensatory seedling recruitment from scatterhoards. Seeds harvested by ants seldom established seedlings. We used a seed fate model to estimate that, on average, rodents and ants harvested 96% and 7%, respectively, of seeds to which they had exclusive access, and that the probability of seedling establishment for a seed harvested by a rodent was an order of magnitude greater than from a seed harvested by an ant and slightly greater than for an unharvested seed. The predicted rank order of seedling recruitment among nine experimental treatments based on expected effects of rodent seed caching closely matched the observed ranking pattern, indicating that rodents determined seedling recruitment patterns of Indian ricegrass. Because rodents harvested such a large majority of seeds and their caches enhanced seedling es- tablishment, they played a central role in the population dynamics of Indian ricegrass.
