Ed L. Frederickson

Characterising the Spatial and Temporal Activities of Free-Ranging Cows from GPS Data

Dean M. Anderson et al. — Tue, 05 Mar 2013 06:25:54 PST

Electronic tracking provides a unique way to document behaviour by cows on a continuous basis. Over 2 years 17 beef cows with calves were fitted with global positioning system (GPS) devices programmed to record uncorrected GPS locations at 1-s intervals in a semi-desert rangeland. Each cow was periodically observed during daylight hours and foraging, walking and stationary (standing/lying) activity times were recorded across days and individual cows to calculate a mean travel rate for each activity. Data without observers present were collected immediately preceding and following the abrupt weaning of calves at between 223 and 234 days of age to evaluate the potential of classifying various travel rates into foraging, walking and stationary activity. The three activities were further characterised within a 24-h period based on the sun’s angle with respect to the horizon. Only data from cows whose equipment acquired ≥ 90% of the potential GPS positional data among consecutive days were analysed. Due to problems with the equipment, data from two cows in 2009 and two cows in 2011 met these criteria. The interval evaluated consisted of four 24-h periods before abrupt weaning and seven 24-h periods following weaning. Results suggested that uncorrected 1-s positional GPS data are satisfactory to classify the behaviour by free-ranging beef cows into foraging, walking and stationary activities. Furthermore, abrupt weaning caused cows to change their spatial and temporal behaviour across and within days. Overall, travel by cows increased post-weaning with subtle within-day behavioural changes. Further research will be required to fully understand the biological importance of spatio-temporal behaviour to optimise cattle and landscape management goals.

DOI: http://dx.doi.org/10.1071/RJ11062

An Assessment of Behavioural Syndromes in Rangeland-Raised Beef Cattle

Robert L. Wesley et al. — Mon, 04 Mar 2013 11:46:05 PST

Individuals in most animal groups exhibit consistent behavioural differences across situations or over time known as behavioural syndromes. We conducted a study with a herd of young rangeland-raised cows to determine whether animals exhibited consistent differences in foraging behaviours across contexts (confinement vs. rangeland pasture) and could be clustered into behavioural type groups on the basis of a suite of correlated behaviours. We also investigated whether cows with different behavioural types performed differently in this environment. Supplement consumption rate (SCR) in confinement was used to select two groups of cows (fast eaters vs. slow eaters). This classification was validated by measuring the persistence of SCR differences through time, conducting cluster analysis to classify individuals into two behavioural types (BT1 and BT2) on the basis of a suite of 14 behavioural, physiological, and performance predictors, and comparing serum cortisol concentrations of cows in either group. Discriminant and linear correlation analyses were used to assess the influence of behavioural and performance responses on the classification of cows, and to study the relationships between behaviour and animal performance. Thirty-three young cows were tracked with GPS collars for approximately 45 days during the calving seasons of 2006 and 2007 and several performance responses were measured on each individual. Cows classified as exhibiting BT1 had significantly higher (P ≤ 0.05) SCR (mean ± SE 2006: 1.90 ± 0.1; 2007: 2.54 ± 0.1 g/s) and serum cortisol (SC) concentrations (8.8 ± 0.88 ng/mL) than BT2 counterparts (SCR 2006: 0.32 ± 0.03 g/s; SCR 2007: 1.59 ± 0.1 g/s; SC: 5.5 ± 0.5 ng/mL). Compared to BT2 cows, BT1 individuals tended to spend less time at water (BT1: 73 ± 10; BT2: 172 ± 16 min/day), cover larger areas (BT1: 21 ± 0.3; BT2: 17 ± 2 ha/day), and exhibit less concentrated search patterns (BT1: 264 ± 8.9; BT2: 314 ± 2 6 m travelled/(ha covered/day)). BT1 individuals tended to be heavier (BT1: 434 ± 7; BT2: 394 ± 10 kg) and began gaining weight sooner after calving (BT1: 44 ± 3; BT2: 69 ± 6 days). Cows exhibiting BT1 were more abundant in the herd and appeared to perform better in the rangeland environment where we conducted the study. Further research is needed to determine the constraints imposed by this behavioural syndrome on animal performance in other feeding environments.

http://dx.doi.org/10.1016/j.applanim.2012.04.005

Within-Plant Distribution of Volatile Compounds on the Leaf Surface of Flourensia Cernua

Rick E. Estell et al. — Mon, 04 Mar 2013 11:36:54 PST

We are using Flourensia cernua as a shrub model to study how terpenes affect livestock herbivory. Two experiments were conducted to examine distribution of volatile chemicals within a plant in an effort to minimize sample variability. In Experiment 1, leaves (current year's growth) were collected from 20 tarbush plants. Two leaders were sampled from each of three positions (outer canopy, subcanopy, and basal) in all four quadrants (based on ordinal direction). In Experiment 2, 10 leaders of current year's growth were removed from another 20 plants. Leaders were collected from the outer canopy of each quadrant and separated into thirds before removing leaves, thereby creating three leaf age categories. Volatile compounds were extracted with ethanol and analyzed with gas chromatography/mass spectrometry. Ninety-four chemicals (including 15 unknowns) were present on the leaf surface of F. cernua. Although 14 and 21 compounds differed (P < 0.05) among quadrants in Experiments 1 and 2, respectively, no consistent quadrant effect was detected in either study. Leaf position differed (P < 0.05) for 52 chemicals in Experiment 1 but outer canopy and subcanopy leaves differed for only 10 compounds. In Experiment 2, 63 compounds differed among leaf age categories. Immature leaves contained greater concentrations of 46 chemicals (P < 0.05) than intermediate or mature age categories, but intermediate and mature leaves differed for only seven compounds. Estimated total concentration (i.e., cumulative concentration of all compounds) was not affected by leaf position but varied among leaf age categories (P < 0.05; immature > intermediate > mature). Differences in leaf position were attributed about equally to mono- and sesquiterpenes, whereas leaf age differences were primarily due to sesquiterpenes. Leaf position and age both affect terpene concentration and sampling variability for tarbush. However, little difference was detected between subcanopy and canopy positions. Thus, by avoiding basal sprouts and sampling from the mid-point of current year's growth, sampling variation should be minimal.

DOI: http://dx.doi.org/10.1016/j.bse.2012.11.020

A Holistic View of an Arid Ecosys tem: A Synthesis of Research and Its Applications

Brandon T. Bestelmeyer et al. — Mon, 04 Mar 2013 11:22:46 PST

A primary objective of the Jornad a Basin research program has been to provide a broad view of desert grassland ecology. Architects of the program, especially scientists with the Jornada Basin Long-Term Ecological Research (LTER) program, felt that existing ecological data sets were usually of too short a duration and represented too few ecosystem components to provide a foundation for predicting dynamics in response to disturbances (NSF 1979). This recognition gave rise to the LTER approach—using long-term and multidisciplinary research at particular places to advance a holistic and broad-scale but also mechanistic view of ecological dynamics.

Managing Livestock Using Animal Behavior: Mixed Species Stocking and Flerds

D. M. Anderson et al. — Thu, 16 Feb 2012 12:23:06 PST

Mixed-species stocking can foster sound landscape management while offering economic and ecological advantages compared with mono-species stocking. Producers contemplating a mixed-species enterprise should reflect on several considerations before implementing this animal management strategy. Factors applicable to a particular producer's landscape must be considered together with goals and economic constraints before implementing mixed-species stocking. A major consideration when using mixed-species stocking is how to deal with predation losses, especially among small ruminants. An approach being adopted in some commercial operations capitalizes on using innate animal behaviors to form cohesive groups of two or more livestock species that consistently remain together under free-ranging conditions. These groups are referred to as flerds. The mixing of a flock of sheep and/or goats with a herd of cattle into a flerd has been shown to protect sheep and goats from coyote predation, as well as offering other husbandry advantages. Some of the added advantages include more efficient conversion of forage into animal protein. Creation of flerds, their maintenance and advantages are discussed.

DOI 10.1017/S175173111200016X

Ecological Services To and From Rangelands of the United States

Ed L. Frederickson et al. — Tue, 15 Nov 2011 11:12:00 PST

The over 300 million ha of public and private rangelands in the United States are characterized by low and variable precipitation, nutrient-poor soils, and high spatial and temporal variability in plant production. This land type has provided a variety of goods and services, with the provisioning of food and fiber dominating through much of the 20th century. More recently, food production from a rangeland-based livestock industry is often pressured for a variety of reasons, including poor economic returns, increased regulations, an aging rural population, and increasingly diverse interests of land owners. A shift to other provisioning, regulating, cultural, and supporting services is occurring with important implications for carbon sequestration, biodiversity, and conservation incentives. There are numerous goods and services possible from rangelands that can supply societal demands such as clean water and a safe food supply. The use of ecologically-based principles of land management remains at the core of the ability of private land owners and public land managers to provide these existing and emerging services. We suggest that expectations need to be based on a thorough understanding of the diverse potentials of these lands and their inherent limits. A critical provisioning service to rangelands will be management practices that either maintain ecological functions or that restore functions to systems that have been substantially degraded over past decades. With proper incentives and economic benefits, rangelands, in the U.S. or globally, can be expected to provide these historical and more unique goods and services in a sustainable fashion, albeit in different proportions than in the past.

Effects of Eugenol, α-terpineol, Terpin-4-ol, and Methyl Eugenol on Consumption of Alfalfa Pellets by Sheep

Ed L. Frederickson — Tue, 15 Nov 2011 09:53:52 PST

Many secondary compounds are typically present in unpalatable shrubs on arid and semi-arid rangelands. However, the relationship between intake by livestock and concentration of individual chemicals has been examined for very few of these compounds. Four experiments were conducted to examine effects of individual volatile compounds on intake of alfalfa pellets by lambs. Forty-five lambs (9 lambs/treatment) were individually fed alfalfa pellets with eugenol, α-terpineol, terpin-4-ol, or methyl eugenol applied at one of five concentrations. Treatments were multiples (0, 0.5, 1, 2, and 10×) of the concentration (×) of each compound on the leaf surface of Flourensia cernua. Treatment solutions were sprayed on alfalfa pellets (0.64 kg/lamb/d, dry matter basis), and intake was measured during a 20-min interval for five days. A day effect (P < 0.001 for both linear and quadratic contrasts) was detected in all four experiments, but no day × treatment interactions were observed (P > 0.05). No treatment effects were observed (P > 0.05) for any of the chemicals tested; thus, eugenol, α-terpineol, terpin-4-ol, and methyl eugenol were not related to intake of alfalfa pellets by lambs under the conditions of this study.

Volatile Compounds on the Leaf Surface of Intact and Regrowth Tarbush (Flourensia cernua DC) Canopies

Ed L. Frederickson et al. — Tue, 15 Nov 2011 09:41:04 PST

Shrub expansion into desert grasslands is a serious problem resulting in loss of forage and rangeland productivity. Flourensia cernua DC (tarbush) is one such shrub contributing to the decline of Chihuahuan Desert grasslands. Our previous research has shown tarbush consumption by sheep and goats to be negatively related to leaf surface concentration of individual terpenes and epicuticular wax. Concentrations of compounds such as terpenes often change with plant age and phenology. Our objective was to examine the effect of altering the vegetative state of tarbush on volatile chemicals. Ninety tarbush plants were randomly selected, and all biomass within 10 cm of the soil surface was removed from 45 plants during winter dormancy. Leaves were collected the following summer during active growth from the canopy of intact controls and resprouts. Leaf surface volatiles were analyzed by gas chromatography-mass spectroscopy and subjected to univariate analysis of variance and stepwise discriminate analysis. Of the 87 compounds present on tarbush leaves, 35 were greater in canopy samples and 16 were greater in regrowth samples based on univariate analysis (P<0.05). Mean concentration of total volatiles on canopy leaves tended to be less (P=0.062) than that of regrowth (3,642 vs. 4,684 μg/g DM). Nine compounds in the discriminant analysis (α-muurolene, iso-borneol, unknown#6, p-cymen-8-ol, unknown#7, sabinene, β-caryophyllene, δ-cadinene, and α- copaene) explained 95% of the variation between canopy and regrowth samples. Lower cumulative concentration of volatile compounds in canopy than regrowth samples suggests repsrouts may be less vulnerable to herbivory than intact tarbush.

Effects of Cis-ß-Ocimene, Cis-Sabinene Hydrate, and Monoterpene and Sesquiterpene Mixtures on Alfalfa Pellet Intake by Lambs

Ed L. Frederickson et al. — Tue, 15 Nov 2011 09:28:43 PST

Interpretive Summary: The conversion of grasslands to shrublands in the western United States and in arid regions throughout the world is a serious concern to livestock producers and ecologists. This process of desertification not only reduces available forage for livestock and wildlife, but also leads to increased soil erosion and reduced biodiversity. These shrubs often contain chemicals that make them unpalatable to browsing animals. We have been conducting a long-term study on the impact of volatile plant chemicals such as terpenes on shrub consumption by livestock. Our previous work showed that for a common shrub in the northern Chihuahuan Desert (tarbush), animals exhibited a variable preference for different plants that was partly explained by the concentration of volatile leaf surface chemicals. In this study, we applied two chemicals and two chemical mixtures to alfalfa pellets and fed them to lambs to determine if they affected intake when applied at concentrations approximating those found in tarbush. The two individual chemicals (cis-ß-ocimene and cis-sabinene hydrate and the monoterpene mixture (borneol, camphene, camphor, 1,8-cineole, limonene, myrcene, and a-pinene) did not affect intake of alfalfa pellets by lambs, and therefore do not appear to be related to low preference for tarbush. However, the sesquiterpene mixture (ß-caryophyllene, caryophyllene oxide, a-copaene, and a-humulene) tended to decrease intake by lambs. This trend for decreased intake as concentration of the sesquiterpene mixture increased suggests sesquiterpenes may be partly involved in the avoidance of shrubs by livestock. Information about chemicals that control intake will help us identify mechanisms to alter how much of a particular plant species is eaten by livestock.

Technical Abstract: The transition of grasslands to shrub-dominated scrubland reduces livestock productivity and contributes to impoverished human conditions in arid and semiarid regions worldwide. Many shrubs increasing in dominance contain secondary compounds that deter herbivores. Knowledge concerning the effects of specific compounds on herbivore diets is limited but may provide useful insights into desertification. Flourensia cernua is a dominant shrub in the northern Chihuahuan Desert that contains an abundance of terpenes. Four experiments were conducted to determine the effects of individual terpenes (cis-ß-ocimene and cis-sabinene hydrate; Exp. 1 and 2) or mixtures of monoterpenes (borneol, camphene, camphor, 1,8-cineole, limonene, myrcene, and a-pinene; Exp. 3) or sesquiterpenes (ß-caryophyllene, caryophyllene oxide, a-copaene, and a-humulene; Exp. 4) on intake of alfalfa pellets by lambs. Forty-five lambs (9 lambs/treatment) were individually fed treated alfalfa pellets for 20 min each morning for 5 days. Five treatments (0X, .5X, 1X, 2X, and 10X; multiples of the concentrations of the same terpenes in Flourensia cernua) were applied to alfalfa pellets (637 g, DM basis) in an ethanol carrier. Experiments were preceded by a 10-d adaptation period to untreated pellets. Except during the 20-min test, lambs were maintained outdoors and fed untreated alfalfa pellets (total mean intake = 4.7% of BW, DM basis). Day × treatment interactions were detected (P < 0.04) in Exp. 1 and 4, due to greater intake for 0X than other treatments on day 1 (Exp. 1) and lower intake for the 10X treatment on day 1 and 2 (Exp. 4). A trend for decreased intake (g/kg BW) as concentration of the sesquiterpene mixture increased was observed in Exp. 3 (P = 0.093 for the linear contrast). Although there was a tendency for the sesquiterpene mixture to decrease intake, cis-ß-ocimene, cis-sabinene hydrate, and the monoterpene mixture did not appear to affect intake by lambs. Thus, sesquiterpenes may exert antiherbivory properties under certain conditions that may contribute to shrub dominance with extended periods of livestock foraging.

Dust Emissions from Undisturbed and Disturbed, Crusted Playa Surfaces: Cattle Trampling Effect

Ed L. Frederickson et al. — Tue, 15 Nov 2011 08:08:47 PST

Dry playa lake beds can be a significant source of fine dust emissions during high wind events in arid and semiarid landscapes. The physical and chemical properties of the playa surface control the amount and properties of the dust emitted. In this study, we use a field wind tunnel to quantify the dust emissions from a bare, fine-textured playa surface located in the Chihuahua Desert at the Jornada Experimental Range, near Las Cruces, New Mexico, USA. We tested natural, undisturbed crusted surfaces and surfaces that had been subjected to two levels of domestic animal disturbance.

The animal disturbance was provided by trampling produced from one and ten passes along the length of the wind tunnel by a 630 kg Angus-Hereford cross cow (Fig. 1). The trampling broke the durable crust and created loose erodible material. Each treatment (natural crust, one pass, and ten passes) was replicated three times. A push-type wind tunnel with a 6 m long, 0.5 m wide, and 1 m high test section was used to generate dust emissions under controlled conditions (Fig. 2). Clean medium sand was dropped onto the tunnel floor to act as an abrader material.

The tunnel wind speed was equivalent to 15 m/s at a height of 2 m over a smooth soil surface. The tunnel was initially run for ten minutes, with no abrader added. A second 30 minute run was subsequently sampled as abrader was added to the wind stream. Dust and saltating material were collected using an isokinetic slot sampler at the end of the tunnel. Total airborne dust was collected on two 25 cm x 20 cm glass fiber filters (GFF) and measured using a GRIMM particle monitor every 6 sec throughout each test run.

Disturbance by trampling generated increased saltating material and airborne dust. The amount of saltating material measured during the initial (no abrader added) run was approximately 70% greater and 5.8 times the amount of saltating material measured on the one pass and ten pass plots, respectively, compared with that observed on the undisturbed plots. The total amount of dust measured during the initial (no abrader added) run on GFF on the one pass and ten pass plots was almost twice and three times, respectively, that observed on the undisturbed plots. The ten pass treatment generated about 75% more PM10 dust than the undisturbed plots during the 30 minute abrader run.

Mesquite: A Long View

Ed L. Frederickson et al. — Tue, 15 Nov 2011 07:59:38 PST

Mesquite (Prosopis glandulosa) is among the most successful plants in Northern México and America"s arid Southwest. Mesquite optimizes pollinator services and reproductive effort, resulting in seeds that persist in herbivore digestive tracts and soil seed banks for extended periods. An extensive root system fully occupies the soil profile long distances from its base, allowing it to harvest water and nutrients with extraordinary efficiency. Root nodules harbor nitrogen-fixing bacteria allowing mesquite to overcome usual nitrogen limitations. Mesquite survival is determined early, but once established, it is long-lived, often benefiting from hardships killing most plants. So with mesquite"s superior adaptations and competitive advantage, why has it only recently dominated desert landscapes? An answer may reside in the literature housing the knowledge of anthropologists and archaeologists studying the Jornada Mogollon, and prehistoric peoples of North America"s warm deserts. Extensive use of mesquite by prehistoric peoples maybe a mechanism for dispersal of desert shrubs during the Holocene and controlling its distribution prior to European influence. A long-view of mesquite demography appears essential for reinterpreting our relationship with mesquite. A relationship that now cost millions of dollars annually to control its abundance and provide for lost ecosystem services.

In Search of "Organ III" Strata-a Sedimentary Record of the Medieval Warm Period (ca. AD 900 to 1300)

Ed L. Frederickson et al. — Tue, 15 Nov 2011 07:55:49 PST

The period AD 900 to 1300, internationally referred to as the Medieval Warm Period, is a critical time for the archaeological record of the Southwestern USA. During the Medieval Warm Period both alluvial and eolian sedimentation increased, but not to the magnitude of the middle Holocene (the Altithermal) or since Historical erosion began in the middle 1850s (the end of the Little Ice Age). Locally, the term "Organ III" has been given to the Medieval Warm Period allostratigraphic unit. It is a subtle unit stratigraphically between Altithermal sediments (Organ I) and Historical sediments. Diagnostic features for identifying these three units include the following: Organ I has distinct carbonate filaments and strong pedogenic structure; Organ III has very faint carbonate filaments and weak pedogenic structure; Historical deposits have no carbonate and sedimentary layers. The Organ III stratum is most obvious in geomorphic settings with contrasting parent materials or where an occupational surface underlies the Organ III unit. In addition to its archaeological significance, the Organ III unit provides information about the relative magnitude of current climate change as compared to prehistoric climate change.

Composition of Ceanothus Gregii Oil as Determined by Steam Distillation and Solid-Phase Microextraction

Ed L. Frederickson et al. — Tue, 15 Nov 2011 07:37:01 PST

Ceanothus gregii Gray was collected from the Jornada Experimental Range in south central New Mexico. Current year’s growth was collected from ten plants found within an approximate 50 m radius of the GPS coordinates N32°40.605’ and W106°33.486’at an altitude of 1,741 m during July 2001. Composite samples of the plants were steam distilled in triplicate, and the composite oil was analyzed using both GC-FID and GC/MS. The volatile composition of the same plants was also examined using solid-phase microextraction (SPME) with a 100?m polydimethylsiloxane fiber. Mass spectra and retention indices were used to identify 41 previously described compounds. Methyl salicylate (16.8%), hexenal (11.8%) and n-decanal (7.0%) were the major identified compounds

Do Changes in Connectivity Explain Desertification

Ed L. Frederickson et al. — Thu, 03 Nov 2011 10:09:30 PDT

Arid and semiarid regions cover more than 40% of Earth's land surface. Desertification, or broadscale land degradation in drylands, is a major environmental hazard facing inhabitants of the world's deserts as well as an important component of global change. There is no unifying framework that simply and effectively explains different forms of desertification. In this article, we argue for the unifying concept that diverse forms of desertification, and its remediation, are driven by changes in the length of connected pathways for the movement of fire, water, and soil resources. Biophysical feedbacks increase the length of connected pathways, explaining the persistence of desertified landscapes around the globe. Management of connectivity in the context of environmental and socioeconomic change is essential to understanding, and potentially reversing, the harmful effects of desertification.

A Retention Index Calculator Simplifies Identification of Plant Volatile Organic Compounds

Ed L. Frederickson — Thu, 03 Nov 2011 10:01:21 PDT

Plant volatiles (PVOCs) are important targets for studies in natural products, chemotaxonomy and biochemical ecology. The complexity of PVOC profiles often limits research to studies targeting only easily identified compounds. With the availability of mass spectral libraries and recent growth of retention index (RI) libraries, PVOC identification can be achieved using only gas chromatography coupled to mass spectrometry (GCMS). However, RI library searching is not typically automated, and until recently, RI libraries were both limited in scope and costly to obtain.

Objective To automate RI calculation and lookup functions commonly utilised in PVOC analysis.

Methodology Formulae required for calculating retention indices from retention time data were placed in a spreadsheet along with lookup functions and a retention index library. Retention times obtained from GCMS analysis of alkane standards and Koeberlinia spinosa essential oil were entered into the spreadsheet to determine retention indices. Indices were used in combination with mass spectral analysis to identify compounds contained in Koeberlinia spinosa essential oil.

Results Eighteen compounds were positively identified. Total oil yield was low, with only 5 ppm in purple berries. The most abundant compounds were octen-3-ol and methyl salicylate. The spreadsheet accurately calculated RIs of the detected compounds.

Conclusion The downloadable spreadsheet tool developed for this study provides a calculator and RI library that works in conjuction with GCMS or other analytical techniques to identify PVOCs in plant extracts.

Grassland in the Borderlands: Understanding Coupled Natural Human Systems and Transboundary Conservation

Ed L. Frederickson et al. — Wed, 02 Nov 2011 15:23:28 PDT

As conservationists well know, political borders rarely coincide with natural ecological boundaries. International borders such as that between the United States and Mexico traverse numerous ecosystems and watersheds. Many species of animals, birds, and insects regularly migrate between habitats across international borders. Conservation of Shared Environments collects works that take on the environmental issues along the U.S.-Mexico border. Covering topics as diverse as wildlife preservation, grassland ecology, water rights, indigenous peoples, and the ecological consequences of border security, the contributors to this volume offer not only scientific analysis but also insight on how to bridge the gaps between scientists, policy makers, and the public.

Rapid Response of a Grassland Ecosystem to an Experimental Manipulation of a Keystone Rodent and Domestic Livestock

Ed L. Frederickson — Wed, 02 Nov 2011 14:58:10 PDT

Megaherbivores and small burrowing mammals commonly coexist and play important functional roles in grassland ecosystems worldwide. The interactive effects of these two functional groups of herbivores in shaping the structure and function of grassland ecosystems are poorly understood. In North America's central grasslands, domestic cattle (Bos taurus) have supplanted bison (Bison bison), and now coexist with prairie dogs (Cynomys spp.), a keystone burrowing rodent. Understanding the ecological relationships between cattle and prairie dogs and their independent and interactive effects is essential to understanding the ecology and important conservation issues affecting North American grassland ecosystems. To address these needs, we established a long-term manipulative experiment that separates the independent and interactive effects of prairie dogs and cattle using a 2 × 2 factorial design. Our study is located in the Janos-Casas Grandes region of northwestern Chihuahua, Mexico, which supports one of the largest remaining complexes of black-tailed prairie dogs (C. ludovicianus). Two years of posttreatment data show nearly twofold increases in prairie dog abundance on plots grazed by cattle compared to plots without cattle. This positive effect of cattle on prairie dogs resulted in synergistic impacts when they occurred together. Vegetation height was significantly lower on the plots where both species co-occurred compared to where either or both species was absent. The treatments also significantly affected abundance and composition of other grassland animal species, including grasshoppers and banner-tailed kangaroo rats (Dipodomys spectabilis). Our results demonstrate that two different functional groups of herbivorous mammals, burrowing mammals and domestic cattle, have distinctive and synergistic impacts in shaping the structure and function of grassland ecosystems.

Differentiating Among Plant Spectra by Combining pH Dependent Photoluminescence Spectroscopy with Multi-Way Principal Component Analysis (MPCA)

Ed L. Frederickson et al. — Tue, 01 Nov 2011 17:28:05 PDT

Photoluminescence spectroscopic probes offer the potential for differentiation among plant species in real-time. Spectral emission signatures (excitation at 365 nm) from three different pH (2.2, 7.5 and 12.5) phosphate buffered saline (PBS) extracts from two grasses, Sporobolus flexuosus (Thurb. ex Vasey) Rydb., [mesa dropseed], and Pleuraphis mutica Buckley [tobosa], two forbs, Dimorphocarpa wislizenii (Engelm.) Rollins [spectacle pod], and Sphaeralcea incana Torrey [pale globemallow], and leaves and twigs from two shrubs Flourensia cernua DC. [tarbush], and Atriplex canescens (Pursh) Nutt., [fourwing saltbush] were examined. Since pH has been shown to be pivotal in affecting extraction effi- ciency of other plant compounds pH seemed appropriate as an additional dimension within our multi-way principal com- ponent analysis (MPCA) to differentiate among six different plant species. In particular, MPCA allowed differentiation between Sporobolus and Pleuraphis that was not possible using only principal component analysis (PCA). This research suggests MPCA may be a more appropriate tool than PCA when attempting to discriminate among plant species.

Characterizing Foraging Patterns Among Cattle and Bonded and Non-bonded Small Ruminants Using Spatial Point Process Techniques

Ed L. Frederickson et al. — Tue, 01 Nov 2011 17:15:34 PDT

Two mixed-species livestock groups were monitored while foraging on 410 ha of brush-infested Southern New Mexico rangeland during July and August 1988. The groups consisted of crossbred Bos taurus and Bos indicus beef cattle with white-faced sheep (Ovis aries) and mohair goats (Capra hircus). The bonded group consisted of small ruminants that had their behaviours modified through socialization with cattle to form a flerd in which small ruminants consistently remained near cattle. Small ruminants in the non-bonded group had not been socialized with cattle. A subset of animal location data measured during the morning over five days for both the bonded and non-bonded groups was analyzed for spatial patterns. Only data for five morning periods (0700-0800 h) are reported because morning and afternoon spatial patterns were similar. Distance measures and Monte Carlo simulations for spatial point processes were used to analyze the data. Results suggested bonded and non-bonded groups were similar in spatial patterns of intra-specific distances for both cattle and small ruminants. However, bonding changed the repulsive relationship observed between cattle and non-bonded small ruminants stocked together to one of inter-specific attraction. Bonded small ruminants remained close to and formed inter-specific clusters with cattle. In addition, the mean number of bonded small ruminants near an arbitrary cow was consistently high. Finally, the spatial pattern of cattle across the paddock did not differ between bonded and non-bonded groups, while bonded small ruminants tended to disperse slightly more uniformly across the paddock than did non-bonded small ruminants. These findings suggest paddock utilization may be positively influenced using flerds compared to flocks and herds.

Dust Emissions from Undisturbed and Disturbed, Crusted Playa Surfaces: Cattle Trampling Effects

Ed L. Frederickson et al. — Tue, 01 Nov 2011 15:45:00 PDT

Dry playa lake beds can be significant sources of fine dust emission. This study used a portable field wind tunnel to quantify the PM10 emissions from a bare, fine-textured playa surface located in the far northern Chihuahua Desert. The natural, undisturbed crust and its subjection to two levels of animal disturbance (one and ten cow passes) were tested. The wind tunnel generated dust emissions under controlled conditions for firstly an initial blow-off of the surface, followed by two longer runs with sand added to the flow as an abrader material. Dust was measured using a GRIMM particle monitor. For the study playa, no significant differences in PM10 concentration and emission flux were found between the untrampled surface and following a single animal pass. This was the case for both the initial blow-offs and tests on plots under a steady abrader rate. Significantly higher dust loading was only associated with the effect of 10 animal passes. In the blow-offs, the higer PM10 yield after 10 passes reflected the greater availability of easily entrainable fine particles. Under abrasion, the effect of the heaviest trampling increased the emission flux by a third and abrasion efficiency by around 50% more than values on the untrampled surface. This enhanced abrasion efficiency peristed for a 30 minute period under abrasion before the positive effect of the disturbance was no longer evident. The findings highlight the role of a threshold of disturbance that determines if supply-limited surfaces will exhibit enhanced wind erosion or not after undergoing perturbation.