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David D. Breshears - One of the best experts on this subject based on the ideXlab platform.
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precipitation thresholds and drought induced tree die off insights from patterns of Pinus edulis mortality along an environmental stress gradient
New Phytologist, 2013Co-Authors: Michael J Clifford, David D. Breshears, Neil S. Cobb, Patrick D Royer, Paulette L FordAbstract:Summary � Recent regional tree die-off events appear to have been triggered by a combination of drought and heat – referred to as ‘global-change-type drought’. To complement experiments focused on resolving mechanisms of drought-induced tree mortality, an evaluation of how patterns of tree die-off relate to highly spatially variable precipitation is needed. � Here, we explore precipitation relationships with a die-off event of pinyon pine (Pinus edulis Engelm.) in southwestern North America during the 2002–2003 global-change-type drought. Pinyon die-off and its relationship with precipitation was quantified spatially along a precipitation gradient in north-central New Mexico with standard field plot measurements of die-off combined with canopy cover derived from normalized burn ratio (NBR) from Landsat imagery. � Pinyon die-off patterns revealed threshold responses to precipitation (cumulative 2002– 2003) and vapor pressure deficit (VPD), with little to no mortality (< 10%) above 600 mm and below warm season VPD of c. 1.7 kPa. [Correction added after online publication 17 June 2013; in the preceding sentence, the word ’below’ has been inserted.] � Our results refine how precipitation patterns within a region influence pinyon die-off, revealing a precipitation and VPD threshold for tree mortality and its uncertainty band where other factors probably come into play – a response type that influences stand demography and landscape heterogeneity and is of general interest, yet has not been documented.
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Precipitation thresholds and drought‐induced tree die‐off: insights from patterns of Pinus edulis mortality along an environmental stress gradient
The New phytologist, 2013Co-Authors: Michael J Clifford, David D. Breshears, Neil S. Cobb, Patrick D Royer, Paulette L FordAbstract:Summary � Recent regional tree die-off events appear to have been triggered by a combination of drought and heat – referred to as ‘global-change-type drought’. To complement experiments focused on resolving mechanisms of drought-induced tree mortality, an evaluation of how patterns of tree die-off relate to highly spatially variable precipitation is needed. � Here, we explore precipitation relationships with a die-off event of pinyon pine (Pinus edulis Engelm.) in southwestern North America during the 2002–2003 global-change-type drought. Pinyon die-off and its relationship with precipitation was quantified spatially along a precipitation gradient in north-central New Mexico with standard field plot measurements of die-off combined with canopy cover derived from normalized burn ratio (NBR) from Landsat imagery. � Pinyon die-off patterns revealed threshold responses to precipitation (cumulative 2002– 2003) and vapor pressure deficit (VPD), with little to no mortality (< 10%) above 600 mm and below warm season VPD of c. 1.7 kPa. [Correction added after online publication 17 June 2013; in the preceding sentence, the word ’below’ has been inserted.] � Our results refine how precipitation patterns within a region influence pinyon die-off, revealing a precipitation and VPD threshold for tree mortality and its uncertainty band where other factors probably come into play – a response type that influences stand demography and landscape heterogeneity and is of general interest, yet has not been documented.
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nonstructural leaf carbohydrate dynamics of Pinus edulis during drought induced tree mortality reveal role for carbon metabolism in mortality mechanism
New Phytologist, 2013Co-Authors: David D. Breshears, Henry D. Adams, Matthew J Germino, Greg A Barrongafford, Maite Guardiolaclaramonte, Chris B Zou, Travis E HuxmanAbstract:Summary Vegetation change is expected with global climate change, potentially altering ecosystem function and climate feedbacks. However, causes of plant mortality, which are central to vegetation change, are understudied, and physiological mechanisms remain unclear, particularly the roles of carbon metabolism and xylem function. We report analysis of foliar nonstructural carbohydrates (NSCs) and associated physiology from a previous experiment where earlier drought-induced mortality of Pinus edulis at elevated temperatures was associated with greater cumulative respiration. Here, we predicted faster NSC decline for warmed trees than for ambient-temperature trees. Foliar NSC in droughted trees declined by 30% through mortality and was lower than in watered controls. NSC decline resulted primarily from decreased sugar concentrations. Starch initially declined, and then increased above pre-drought concentrations before mortality. Although temperature did not affect NSC and sugar, starch concentrations ceased declining and increased earlier with higher temperatures. Reduced foliar NSC during lethal drought indicates a carbon metabolism role in mortality mechanism. Although carbohydrates were not completely exhausted at mortality, temperature differences in starch accumulation timing suggest that carbon metabolism changes are associated with time to death. Drought mortality appears to be related to temperature-dependent carbon dynamics concurrent with increasing hydraulic stress in P. edulis and potentially other similar species.
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Nonstructural leaf carbohydrate dynamics of Pinus edulis during drought‐induced tree mortality reveal role for carbon metabolism in mortality mechanism
The New phytologist, 2013Co-Authors: Henry D. Adams, David D. Breshears, Matthew J Germino, Chris B Zou, Greg A. Barron-gafford, Maite Guardiola-claramonte, Travis E HuxmanAbstract:Summary Vegetation change is expected with global climate change, potentially altering ecosystem function and climate feedbacks. However, causes of plant mortality, which are central to vegetation change, are understudied, and physiological mechanisms remain unclear, particularly the roles of carbon metabolism and xylem function. We report analysis of foliar nonstructural carbohydrates (NSCs) and associated physiology from a previous experiment where earlier drought-induced mortality of Pinus edulis at elevated temperatures was associated with greater cumulative respiration. Here, we predicted faster NSC decline for warmed trees than for ambient-temperature trees. Foliar NSC in droughted trees declined by 30% through mortality and was lower than in watered controls. NSC decline resulted primarily from decreased sugar concentrations. Starch initially declined, and then increased above pre-drought concentrations before mortality. Although temperature did not affect NSC and sugar, starch concentrations ceased declining and increased earlier with higher temperatures. Reduced foliar NSC during lethal drought indicates a carbon metabolism role in mortality mechanism. Although carbohydrates were not completely exhausted at mortality, temperature differences in starch accumulation timing suggest that carbon metabolism changes are associated with time to death. Drought mortality appears to be related to temperature-dependent carbon dynamics concurrent with increasing hydraulic stress in P. edulis and potentially other similar species.
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Comparing response of Pinus edulis tree-ring growth to five alternate moisture indices using historic meteorological data
Journal of Arid Environments, 2008Co-Authors: C.p. Kempes, David D. Breshears, Orrin Myers, James J. EbersoleAbstract:Abstract Annual growth of semiarid tree species is generally limited by a period of water deficit and this relationship can be reflected in interannual variation in tree-ring width of semiarid species such as Pinus edulis , a pinon pine that is widely distributed across the southwestern United States. Tree-ring width of P. edulis and other semiarid tree species is most frequently related to annual precipitation amount alone or to the Palmer drought severity index (PDSI). But water deficit and associated variation in moisture can also be described using numerous other indices such as the standardized precipitation index (SPI), and a comparison of the performance of several indices that relate historical climate data to tree-ring variation in P. edulis is lacking. We compared abilities to predict radial tree-ring growth of P. edulis using five metrics of water availability: PDSI, two indices based on precipitation alone (total precipitation and SPI), and two indices that factor in temperature to determine water deficit (based on Walter climate diagrams that use monthly precipitation and temperature). Each metric was evaluated over three commonly used time periods (water year, calendar year, and June–August) using the limited available data from P. edulis sites in the southwestern USA where co-located tree-ring and weather data were available. Our results indicate that PDSI was the best predictor of P. edulis ring widths, regardless of time period, and provide a first comparative test of PDSI with SPI and Walter indices that can be further tested as larger data sets become available.
Catherine A. Gehring - One of the best experts on this subject based on the ideXlab platform.
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An elusive ectomycorrhizal fungus reveals itself: a new species of Geopora (Pyronemataceae) associated with Pinus edulis.
Mycologia, 2014Co-Authors: Lluvia Flores-rentería, Matthew K. Lau, Louis J. Lamit, Catherine A. GehringAbstract:Species of the genus Geopora are important ectomycorrhizal associates that can dominate the communities of some plant taxa, such as pinyon pine (Pinus edulis), a widespread tree of the western United States. Several members of the genus Geopora are known only from ectomycorrhizal root tips and thus have not been described formally. The sporocarps of some Geopora species occur infrequently because they depend on wet years for sporulation. In addition, Geopora sporocarps can be small and may be hypogeous at some developmental stage, limiting the opportunities for describing their morphology. Using molecular and morphological data, we have described a new species of fungus, Geopora pinyonensis, which produced ascocarps after unusually high precipitation at a northern Arizona site in summer 2012. Based on analysis of the ITS and nuLSU regions of the rDNA, G pinyonensis is a new species of Geopora. It has small sporocarps and ascospores relative to other members of the genus; however, these morphological features overlap with other species. Using rDNA data from sporocarps and ectomycorrhizal root tips, we show that the sporocarps correspond to an abundant species of ectomycorrhizal fungus associated with pinyon pines that is increasing in abundance in drought-affected landscapes and may promote drought tolerance.
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Microsatellite primers in the foundation tree species Pinus edulis and P. monophylla (Pinaceae).
Applications in plant sciences, 2013Co-Authors: Andrew L. Krohn, Lluvia Flores-rentería, Catherine A. GehringAbstract:Premise of the study: Microsatellite primers were developed in the foundational tree species Pinus edulis to investigate population differentiation of P. edulis and hybridization among closely related species. Methods and Results: Using a hybridization protocol, primer sets for 11 microsatellite loci were developed using megagametophyte tissue from P. edulis and scored for polymorphism in three populations of P. edulis and a single P. monophylla population. The primers amplified simple and compound di-, tri-, and pentanucleotide repeats with two to 18 alleles per locus. Conclusions: These results demonstrate the utility of the described primers for studies of population differentiation within and among P. edulis populations as well as across putative hybrid zones where P. edulis may coexist with sister species.
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Three-way interactions among ectomycorrhizal mutualists, scale insects, and resistant and susceptible pinyon pines.
The American naturalist, 1997Co-Authors: Catherine A. Gehring, Neil S. Cobb, Thomas G. WhithamAbstract:Abstract Herbivores and mycorrhizal fungi are important associates of most plants, but little is known about how these organisms interact. In a 9‐yr experiment, we examined how the pinyon needle scale (Matsucoccus acalyptus) affects and is affected by the ectomycorrhizal mutualists found on the roots of scale‐resistant and ‐susceptible pinyon pines (Pinus edulis). Three major results emerged. First, removal experiments demonstrated that scales negatively affected ectomycorrhiza. Second, although ectomycorrhiza could either positively or negatively influence scale performance by improving plant vigor or increasing plant investment in antiherbivore defenses, we found no ectomycorrhizal effect on scale mortality when we experimentally enhanced levels of ectomycorrhiza. This represented the first test of whether ectomycorrhiza promote plant resistance and contrasted with studies showing that arbuscular mycorrhiza negatively affected herbivores. Third, pinyon resistance to scales mediated the asymmetrical inte...
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Comparisons of ectomycorrhizae on pinyon pines (Pinus edulis; Pinaceae) across extremes of soil type and herbivory
American Journal of Botany, 1994Co-Authors: Catherine A. Gehring, Thomas G. WhithamAbstract:Using field and greenhouse studies, we examined the relationships among pinyon pines (Pinus edulis), their ectomycorrhizal mutualists, and their moth herbivores as a function of soil fertility. We studied two soil types-the ash and cinder soils of the San Francisco volcanic field and nearby sandy loam soils. In the field, pinyons growing in cinders suffered from reduced moisture, negative nitrogen mineralization rates, low phosphate levels, reduced growth, and high moth herbivory relative to pinyons growing in sandy loam. Pinyons growing in cinders also had twofold higher levels of ectomycorrhizal colonization than their noncinder counterparts. Similarly, in the greenhouse, seedlings grown in cinders had higher levels ofectomycorrhizal colonization and greater numbers of ectomycorrhizae than seedlings grown in sandy loam. Seedling shoot growth was significantly enhanced by ectomycorrhizae in both soils. These patterns support three conclusions. First, field and greenhouse studies demonstrated that trees growing in nutrient-poor soils had higher levels of ectomycorrhizal colonization than trees growing in better soils. Second, across soil types, variation in ectomycorrhizal colonization was better predicted by soil fertility than by herbivory. However, herbivory negatively affected ectomycorrhizae in the stressful cinder environment. Third, although mycorrhizae can be parasitic under some conditions, ectomycorrhizae had mutualistic impacts on pinyon seedlings across the environmental extremes we studied.
Neil S. Cobb - One of the best experts on this subject based on the ideXlab platform.
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precipitation thresholds and drought induced tree die off insights from patterns of Pinus edulis mortality along an environmental stress gradient
New Phytologist, 2013Co-Authors: Michael J Clifford, David D. Breshears, Neil S. Cobb, Patrick D Royer, Paulette L FordAbstract:Summary � Recent regional tree die-off events appear to have been triggered by a combination of drought and heat – referred to as ‘global-change-type drought’. To complement experiments focused on resolving mechanisms of drought-induced tree mortality, an evaluation of how patterns of tree die-off relate to highly spatially variable precipitation is needed. � Here, we explore precipitation relationships with a die-off event of pinyon pine (Pinus edulis Engelm.) in southwestern North America during the 2002–2003 global-change-type drought. Pinyon die-off and its relationship with precipitation was quantified spatially along a precipitation gradient in north-central New Mexico with standard field plot measurements of die-off combined with canopy cover derived from normalized burn ratio (NBR) from Landsat imagery. � Pinyon die-off patterns revealed threshold responses to precipitation (cumulative 2002– 2003) and vapor pressure deficit (VPD), with little to no mortality (< 10%) above 600 mm and below warm season VPD of c. 1.7 kPa. [Correction added after online publication 17 June 2013; in the preceding sentence, the word ’below’ has been inserted.] � Our results refine how precipitation patterns within a region influence pinyon die-off, revealing a precipitation and VPD threshold for tree mortality and its uncertainty band where other factors probably come into play – a response type that influences stand demography and landscape heterogeneity and is of general interest, yet has not been documented.
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Precipitation thresholds and drought‐induced tree die‐off: insights from patterns of Pinus edulis mortality along an environmental stress gradient
The New phytologist, 2013Co-Authors: Michael J Clifford, David D. Breshears, Neil S. Cobb, Patrick D Royer, Paulette L FordAbstract:Summary � Recent regional tree die-off events appear to have been triggered by a combination of drought and heat – referred to as ‘global-change-type drought’. To complement experiments focused on resolving mechanisms of drought-induced tree mortality, an evaluation of how patterns of tree die-off relate to highly spatially variable precipitation is needed. � Here, we explore precipitation relationships with a die-off event of pinyon pine (Pinus edulis Engelm.) in southwestern North America during the 2002–2003 global-change-type drought. Pinyon die-off and its relationship with precipitation was quantified spatially along a precipitation gradient in north-central New Mexico with standard field plot measurements of die-off combined with canopy cover derived from normalized burn ratio (NBR) from Landsat imagery. � Pinyon die-off patterns revealed threshold responses to precipitation (cumulative 2002– 2003) and vapor pressure deficit (VPD), with little to no mortality (< 10%) above 600 mm and below warm season VPD of c. 1.7 kPa. [Correction added after online publication 17 June 2013; in the preceding sentence, the word ’below’ has been inserted.] � Our results refine how precipitation patterns within a region influence pinyon die-off, revealing a precipitation and VPD threshold for tree mortality and its uncertainty band where other factors probably come into play – a response type that influences stand demography and landscape heterogeneity and is of general interest, yet has not been documented.
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INSECT HERBIVORY INCREASES LITTER QUALITY AND DECOMPOSITION: AN EXTENSION OF THE ACCELERATION HYPOTHESIS
Ecology, 2003Co-Authors: Samantha K. Chapman, Thomas G. Whitham, Neil S. Cobb, Stephen C. Hart, George W. KochAbstract:Herbivore alteration of litter inputs may change litter decomposition rates and influence ecosystem nutrient cycling. In a semiarid woodland at Sunset Crater National Monument, Arizona, long-term insect herbivore removal experiments and the presence of herbivore resistant and susceptible pinyon pines (Pinus edulis) have allowed characterization of the population- and community-level effects of herbivory. Here we report how these same two herbivores, the mesophyll-feeding scale insect Matsucoccus acalyptus and the stem-boring moth Dioryctria albovittella alter litter quality, dynamics, and decomposition in this ecosystem. We measured aboveground litterfall, litter chemical composition, and first-year litter decomposition rates for trees resistant and susceptible to both herbivores and for susceptible trees from which herbivores had been experimentally removed for 16–18 years. Both herbivores significantly increased nitrogen concentration and decreased lignin:nitrogen and carbon:nitrogen ratios of abovegrou...
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Long-term sexual allocation in herbivore resistant and susceptible pinyon pine ( Pinus edulis )
Oecologia, 2002Co-Authors: Neil S. Cobb, Robert T. Trotter, Thomas G. WhithamAbstract:Chronic herbivory by the stem-boring moth (Dioryctria albovittella) alters the sexual expression of a monoecious tree, pinyon pine (Pinus edulis) by reducing female function and increasing male function. Observations and long-term moth removal experiments show that 55% of susceptible trees can lose all female function. Moth herbivory has little effect on male function in young trees, but has an important effect on older trees, where moth-susceptible trees produced 1.5 times more pollen than moth-resistant trees. Susceptible trees were 6.5 times more likely to exhibit male-only function than either resistant trees or susceptible trees that have had their moths experimentally removed. This herbivore-induced sex change is caused primarily by differential moth attack and the resulting mortality of the shoots that bear female reproductive structures. Moth attack rates were positively correlated with individual stem biomass (female stems >non-reproductive stems >male stems). Moth attack also increased conelet abortion on unattacked shoots, indicating that moths indirectly reduce female function. Moth-induced altering of sexual function is also expressed at the population level. Male function is relatively greater in stands with high moth densities on stressful soils than in stands with few moths. Under certain conditions, sexual selection theory suggests that the negative effects on female function could be overcome with greater investment in male function. Because susceptible trees produce large amounts of pollen and are more abundant than moth-resistant trees, frequency-dependent selection may counteract selection against susceptible genotypes. Plant-herbivore interaction studies typically examine negative impacts of herbivory on female function, but not positive effects on male function. Here we demonstrate that herbivory may have important effects on the evolutionary ecology of pinyon by both promoting male function and depressing female function.
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Three-way interactions among ectomycorrhizal mutualists, scale insects, and resistant and susceptible pinyon pines.
The American naturalist, 1997Co-Authors: Catherine A. Gehring, Neil S. Cobb, Thomas G. WhithamAbstract:Abstract Herbivores and mycorrhizal fungi are important associates of most plants, but little is known about how these organisms interact. In a 9‐yr experiment, we examined how the pinyon needle scale (Matsucoccus acalyptus) affects and is affected by the ectomycorrhizal mutualists found on the roots of scale‐resistant and ‐susceptible pinyon pines (Pinus edulis). Three major results emerged. First, removal experiments demonstrated that scales negatively affected ectomycorrhiza. Second, although ectomycorrhiza could either positively or negatively influence scale performance by improving plant vigor or increasing plant investment in antiherbivore defenses, we found no ectomycorrhizal effect on scale mortality when we experimentally enhanced levels of ectomycorrhiza. This represented the first test of whether ectomycorrhiza promote plant resistance and contrasted with studies showing that arbuscular mycorrhiza negatively affected herbivores. Third, pinyon resistance to scales mediated the asymmetrical inte...
Jeffry B. Mitton - One of the best experts on this subject based on the ideXlab platform.
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From middens to molecules: phylogeography of the piñon pine, Pinus edulis
Journal of Biogeography, 2012Co-Authors: Kristy L. Duran, Alicia Pardo, Jeffry B. MittonAbstract:Aim Data from packrat middens have established a hypothesized historical biogeography of pinon pine, Pinus edulis, including locations of glacial refugia in the south-western USA and subsequent migration out of the refugia. In this study, we used molecular techniques to test the glacial refugial hypotheses inferred from packrat (Neotoma) midden data for P. edulis. Location South-western USA. Methods Two fragments of chloroplast DNA (a portion of the matK gene and a portion of the rbcL gene) for a total of 1045 base pairs were amplified and sequenced for 100 individuals. Thirty-one populations were sampled throughout the range of P. edulis. Phylogenetic analyses included maximum parsimony and maximum likelihood. Results Very little variation existed among the individuals sampled. Four haplotypes were identified. The inferred ancestral haplotype was the most widespread; it was most common in Texas and New Mexico where, with the exception of one individual, it was the only haplotype found. Arizona and Utah populations were more diverse, with almost half of the populations containing two or more haplotypes. The most derived haplotype was most abundant in Arizona. Main conclusions The distribution of haplotypes is geographically informative. Only one haplotype exists in the south-eastern portion of the range of P. edulis whereas up to four haplotypes are found in other populations, suggesting one of two hypotheses: either all modern populations are descended from a refugial population in central Arizona, or modern populations are descended from two refugial populations, one in central Arizona and another in Texas–southern New Mexico. Interpreting these data in the light of packrat midden data gives more support for the latter hypothesis.
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Genetic variation in piñon pine, Pinus edulis, associated with summer precipitation.
Molecular ecology, 2004Co-Authors: Jeffry B. Mitton, Kristy L. DuranAbstract:Three previous reports of microgeographical variation of glycerate dehydrogenase ( Gly ) frequencies in pinon, Pinus edulis , established the hypothesis that Gly frequencies contribute to adaptation to heterogeneous environments, specifically to variation in soil moisture. In each of these studies, the frequency of the Gly-3 allele or of Gly-33 homozygotes was higher on dry sites than on nearby moist sites. Here we attempt to extend these observations by testing the hypothesis that Gly frequencies respond to soil moisture variation on a rangewide scale. Gly frequencies were surveyed in 11 natural populations, and the frequency of the Gly-3 allele varied from 0.27 to 0.65 among the sample sites. Elevation varied from 1650 to 3100 m, and summer precipitation, defined as precipitation from April to August, varied from 13.7 to 26.4 cm. The soil types at the collection sites were schist, quaternary volcanic or a mixture of shale and sandstone. Logistic regression revealed that Gly frequencies did not respond to either elevation or soil type, but were related to summer precipitation ( P < 0.01). The correlation between summer precipitation and the frequency of the Gly-3 allele was r = − − − 0.92 ( P < 0.001). Thus, the patterns of differentiation on microgeographical scales
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pinyon Pinus edulis pinaceae associated with soil moisture1
1998Co-Authors: Jeffry B. Mitton, Michael C Grant, Ayako Murayama YoshinoAbstract:found here-allele 3 higher in frequency on dry sites-was consistent with previous studies of microgeographic variation in contrasting moist and dry sites. Trees within one of the dry sites were examined to test the hypothesis that stomata sizes and densities are heterogeneous among Gly genotypes. Heterozygotes had the longest and widest stomata; the stomatal area of heterozygotes was 28% greater than the stomatal area of homozygotes. Whereas the stomatal areas of the two homozygotes were similar, their shapes did not overlap when projected on a bivariate plot of length and width. These results suggest that stomatal shape may play a role in adapting pinyon to heterogeneity in soil moisture.
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Levels of genetic variation captured by four descendant populations of pinyon pine (Pinus edulis Engelm.)
Biodiversity & Conservation, 1994Co-Authors: Andrea C. Premoli, Steven Chischilly, Jeffry B. MittonAbstract:An isolated cluster of populations of pinyon pine, Pinus edulis Engelm., was used to study the evolutionary dynamics of the founding of new populations. A large population at Owl Creek Canyon, Colorado, is 150 to 200 km to the north from the main distribution of pinyon pine. The population at Owl Creek was established approximately 450 years ago following long-distance dispersal and it is apparently the source of four tiny descendant populations that have been established in close proximity (5.2–11.2 km) within the last century. Genetic variation was estimated with an electrophoretic survey of proteins. Eight of ten proteins were polymorphic in the analysed populations. The recently established populations showed a reduction in the levels of heterozygosity and a decrease in the mean number of alleles per locus, particularly the two smaller (n
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levels of genetic variation captured by four descendant populations of pinyon pine Pinus edulis engelm
Biodiversity and Conservation, 1994Co-Authors: Andrea C. Premoli, Steven Chischilly, Jeffry B. MittonAbstract:An isolated cluster of populations of pinyon pine, Pinus edulis Engelm., was used to study the evolutionary dynamics of the founding of new populations. A large population at Owl Creek Canyon, Colorado, is 150 to 200 km to the north from the main distribution of pinyon pine. The population at Owl Creek was established approximately 450 years ago following long-distance dispersal and it is apparently the source of four tiny descendant populations that have been established in close proximity (5.2–11.2 km) within the last century. Genetic variation was estimated with an electrophoretic survey of proteins. Eight of ten proteins were polymorphic in the analysed populations. The recently established populations showed a reduction in the levels of heterozygosity and a decrease in the mean number of alleles per locus, particularly the two smaller (n<20) and also more distant sites from Owl Creek (Windy Site and Hewlett Gulch). Measures of genetic diversity among populations were consistent with the hypothesis that the four young populations have their source in Owl Creek. In addition, the detected inbreeding might be attributable to the caching of related seeds by birds foraging at the source population. The implications of these results for the management of widespread species, such as pinyon pine, are discussed.
Thomas G. Whitham - One of the best experts on this subject based on the ideXlab platform.
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INSECT HERBIVORY INCREASES LITTER QUALITY AND DECOMPOSITION: AN EXTENSION OF THE ACCELERATION HYPOTHESIS
Ecology, 2003Co-Authors: Samantha K. Chapman, Thomas G. Whitham, Neil S. Cobb, Stephen C. Hart, George W. KochAbstract:Herbivore alteration of litter inputs may change litter decomposition rates and influence ecosystem nutrient cycling. In a semiarid woodland at Sunset Crater National Monument, Arizona, long-term insect herbivore removal experiments and the presence of herbivore resistant and susceptible pinyon pines (Pinus edulis) have allowed characterization of the population- and community-level effects of herbivory. Here we report how these same two herbivores, the mesophyll-feeding scale insect Matsucoccus acalyptus and the stem-boring moth Dioryctria albovittella alter litter quality, dynamics, and decomposition in this ecosystem. We measured aboveground litterfall, litter chemical composition, and first-year litter decomposition rates for trees resistant and susceptible to both herbivores and for susceptible trees from which herbivores had been experimentally removed for 16–18 years. Both herbivores significantly increased nitrogen concentration and decreased lignin:nitrogen and carbon:nitrogen ratios of abovegrou...
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Long-term sexual allocation in herbivore resistant and susceptible pinyon pine ( Pinus edulis )
Oecologia, 2002Co-Authors: Neil S. Cobb, Robert T. Trotter, Thomas G. WhithamAbstract:Chronic herbivory by the stem-boring moth (Dioryctria albovittella) alters the sexual expression of a monoecious tree, pinyon pine (Pinus edulis) by reducing female function and increasing male function. Observations and long-term moth removal experiments show that 55% of susceptible trees can lose all female function. Moth herbivory has little effect on male function in young trees, but has an important effect on older trees, where moth-susceptible trees produced 1.5 times more pollen than moth-resistant trees. Susceptible trees were 6.5 times more likely to exhibit male-only function than either resistant trees or susceptible trees that have had their moths experimentally removed. This herbivore-induced sex change is caused primarily by differential moth attack and the resulting mortality of the shoots that bear female reproductive structures. Moth attack rates were positively correlated with individual stem biomass (female stems >non-reproductive stems >male stems). Moth attack also increased conelet abortion on unattacked shoots, indicating that moths indirectly reduce female function. Moth-induced altering of sexual function is also expressed at the population level. Male function is relatively greater in stands with high moth densities on stressful soils than in stands with few moths. Under certain conditions, sexual selection theory suggests that the negative effects on female function could be overcome with greater investment in male function. Because susceptible trees produce large amounts of pollen and are more abundant than moth-resistant trees, frequency-dependent selection may counteract selection against susceptible genotypes. Plant-herbivore interaction studies typically examine negative impacts of herbivory on female function, but not positive effects on male function. Here we demonstrate that herbivory may have important effects on the evolutionary ecology of pinyon by both promoting male function and depressing female function.
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Three-way interactions among ectomycorrhizal mutualists, scale insects, and resistant and susceptible pinyon pines.
The American naturalist, 1997Co-Authors: Catherine A. Gehring, Neil S. Cobb, Thomas G. WhithamAbstract:Abstract Herbivores and mycorrhizal fungi are important associates of most plants, but little is known about how these organisms interact. In a 9‐yr experiment, we examined how the pinyon needle scale (Matsucoccus acalyptus) affects and is affected by the ectomycorrhizal mutualists found on the roots of scale‐resistant and ‐susceptible pinyon pines (Pinus edulis). Three major results emerged. First, removal experiments demonstrated that scales negatively affected ectomycorrhiza. Second, although ectomycorrhiza could either positively or negatively influence scale performance by improving plant vigor or increasing plant investment in antiherbivore defenses, we found no ectomycorrhizal effect on scale mortality when we experimentally enhanced levels of ectomycorrhiza. This represented the first test of whether ectomycorrhiza promote plant resistance and contrasted with studies showing that arbuscular mycorrhiza negatively affected herbivores. Third, pinyon resistance to scales mediated the asymmetrical inte...
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Comparisons of ectomycorrhizae on pinyon pines (Pinus edulis; Pinaceae) across extremes of soil type and herbivory
American Journal of Botany, 1994Co-Authors: Catherine A. Gehring, Thomas G. WhithamAbstract:Using field and greenhouse studies, we examined the relationships among pinyon pines (Pinus edulis), their ectomycorrhizal mutualists, and their moth herbivores as a function of soil fertility. We studied two soil types-the ash and cinder soils of the San Francisco volcanic field and nearby sandy loam soils. In the field, pinyons growing in cinders suffered from reduced moisture, negative nitrogen mineralization rates, low phosphate levels, reduced growth, and high moth herbivory relative to pinyons growing in sandy loam. Pinyons growing in cinders also had twofold higher levels of ectomycorrhizal colonization than their noncinder counterparts. Similarly, in the greenhouse, seedlings grown in cinders had higher levels ofectomycorrhizal colonization and greater numbers of ectomycorrhizae than seedlings grown in sandy loam. Seedling shoot growth was significantly enhanced by ectomycorrhizae in both soils. These patterns support three conclusions. First, field and greenhouse studies demonstrated that trees growing in nutrient-poor soils had higher levels of ectomycorrhizal colonization than trees growing in better soils. Second, across soil types, variation in ectomycorrhizal colonization was better predicted by soil fertility than by herbivory. However, herbivory negatively affected ectomycorrhizae in the stressful cinder environment. Third, although mycorrhizae can be parasitic under some conditions, ectomycorrhizae had mutualistic impacts on pinyon seedlings across the environmental extremes we studied.