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12321. [Article] Maximizing urban property values through open space conservation
This study investigates the share of open space that maximizes total private property values in urban areas. Open space poses a number of trade-offs to city managers. On the one hand, previous studies ...Citation Citation
- Title:
- Maximizing urban property values through open space conservation
- Author:
- Oakley, Winston
This study investigates the share of open space that maximizes total private property values in urban areas. Open space poses a number of trade-offs to city managers. On the one hand, previous studies have shown that certain kinds of open space can increase property values, which tends to increase tax revenues. On the other hand, open space typically requires substantial capital to establish and perpetual maintenance costs to maintain. This means that in order to keep the city budget balanced, financing open space requires either taking money away from other municipal services, which may be of greater value to residents than open space, or increasing the property tax rate. Both these courses of actions tend to reduce property values, and therefore, lower tax revenues. Open space also incurs an opportunity cost, in that land used for open space could be developed and taxed. While previous research has modeled these trade-offs, there is still more to be learned by empirically estimating the share of open space that maximizes property values in urban areas. According to the theoretical underpinnings of this study, one of the primary determinants of a city's value-maximizing, or "optimal", share of open space is the price elasticity of housing supply. Therefore, in order to estimate the optimal share of open space, this study estimates the price elasticity of housing supply for 349 U.S. Metropolitan Statistical Areas (MSAs). According to theory, the other factors that determine the optimal share of open space are the price elasticity of housing demand, the economies of scale in the provision of municipal services, the elasticity of property values with respect to municipal services, and the elasticity of housing demand with respect to open space. For these factors, an example value is establish based on prior research and used commonly among all MSAs to estimate the optimal share. Once the estimated and example values are determined, they are inserted into the equation that determines the optimal share of open space. The result provides an estimate of this optimal share of open space for 349 MSAs. On average, the model, combined with the estimated and assumed values, produces very low estimates for the optimal share of open space. The mean optimal share was 1.5%, and 95% of the estimates were 5% or less. For shares based on statistically significant supply elasticity estimates, optimal shares ranged from 0.2% to 27%. In order to gauge how far cities were from their estimated optimal share of open space, this study compared the estimated optimal share to observed shares of open space in 72 MSAs. When compared to observed shares of open space, the model (along with the estimated and assumed values) showed that 89% of the observed MSAs displayed "excesses" of open space, or, an observed share of open space that exceeded their optimal share. The other 11% demonstrated a "shortage" of open space. The average deviation between optimal and actual share was an excess of 6.3 percentage points. Further analysis was conducted in order to account for the error inherent in the supply elasticity estimates (and subsequently inherent to the estimates of optimal share). Once this error was accounted for, only two cities still showed evidence of having open space shortages: Stockton, CA and Miami, FL. However, both cities were within a percentage point of their optimal share's confidence interval, making it possible these cities are not experiencing meaningful shortages of open space. In contrast, 92% of the cities in the sample set showed statistically significant excesses of open space. Of these, five MSAs exceeded their confidence intervals by 15 or more percentage points: Austin, TX; Albuquerque, NM; Akron, OH; New Orleans, LA; and Anchorage, AK. Because these cities' actual share of open space lies so far above their optimal share, it is very likely that decreasing open space area would increase property values. Two cities in the sample fell within their optimal share's confidence interval: Washington, DC and Virginia Beach, VA. Of all the cities in the sample set, these two are the most likely to be at their optimal share of open space, and therefore, are the most likely to decrease property values by making any changes to their share of open space. After this primary analysis, a sensitivity analysis was conducted in order to determine how assumptions regarding the variables impacted the estimated optimal share of open space. A reasonable range for each variable was established based on the literature, and this range was used to test each variable’s effect on the optimal share of open space. These tests revealed that the optimal share is not especially sensitive to the assumed values for the price elasticity of housing demand, nor to the economy of scale in the provision of municipal services. However, the elasticity of property values with respect to municipal services and the elasticity of housing demand with respect to open space both have large influences on the optimal share. The impact of all the other variables increased as supply elasticity decreased, and as the elasticity of housing demand with respect to open space increased. Because the elasticity of housing demand with respect to open space has such a disproportionate influence on the optimal share of open space, and because there is very little empirical evidence surrounding its value, further analysis was done to investigate this variable. By assuming that the 72 MSAs for which there is an observed share of open space are at their optimal share, in conjunction with the estimated and assumed values for the other variables, one can estimate the implied value for the elasticity of housing demand with respect to open space. Using this method, this study found that the average implied elasticity was 0.57. While this result could indicate that open space has a higher-than-assumed effect on housing demand, evidence from the literature suggests this value is too high. It is more likely that this result provides further evidence that the model is indicating actual shares of open space are higher than optimal. In the final portion of the sensitivity analysis, cities' observed shares of open space were again assumed to be at the optimal level, however, the other variables assume the limits of their reasonable range so as to make the implied elasticity as high or as low as possible. This analysis provided further evidence of discrepancies between actual and optimal shares of open space. While the evidence for open space shortages was fairly slim, the analysis reinforced evidence that some cities have excess open space. Those that presented the highest implied elasticities (and therefore show the strongest evidence of open space excess) are Austin, TX; Akron, OH; and Greensboro, NC. By comparing optimal shares of open space to observed shares of open space, the results show that the majority of cities could likely increase property values by decreasing their share of open space. This study also sheds new light on the relationship between housing demand and open space. By defining a reasonable value and range for the elasticity of housing demand with respect to open space, this study adds to the scarce information on this variable. While the results of this study indicate that many urban areas in the U.S. have larger shares of open space than would maximize property values, it is important to emphasize that the value-maximizing share of open space is not the socially optimal share. Open space provides a number of other social benefits that are not capitalized into property values, and are therefore not considered in this study. Environmental benefits are one important example. Further research is needed to determine the socially optimal amount of open space that maximizes social welfare. The appendices of this study list both the estimates of housing supply elasticity and the estimates of value-maximizing share for the 349 MSAs in the sample set. For the managers of cities that were included in the study, these figures can provide valuable information to help them better understand the implications of open space provision. The housing supply elasticities serve to better illuminate housing markets in their area. The optimal share estimates allow managers to better understand the relationship between property values and open space. For the managers of cities not included in this study, the methods presented here offer a relatively simple way to calculate their own housing supply elasticity and optimal share. With data on housing prices, housing construction, and population, interested parties can estimate the supply elasticity in their cities. Using this estimate in combination with the values this study assumed for the other variables, they can estimate their own value-maximizing share of open space. By comparing this figure to their present share of open space, city managers can gain a better understanding of the effect open space has on the property values within their city.
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Phytophthora cinnamomi is a soilborne pathogen that causes root rot disease of highbush blueberry (Vaccinium corymbosum L.). When new installations of susceptible blueberry cultivars are infected with ...
Citation Citation
- Title:
- Cultural controls for suppressing Phytophthora cinnamomi root rot of blueberry
- Author:
- Yeo, John R.
Phytophthora cinnamomi is a soilborne pathogen that causes root rot disease of highbush blueberry (Vaccinium corymbosum L.). When new installations of susceptible blueberry cultivars are infected with P. cinnamomi, plants often fail to grow significant new tissue, greatly reducing yields over the life of the planting. Chemical fungicides are available for disease suppression including mefenoxam and phosphonate compounds. However these tools are not available for organically certified growers. Initially, this research focused on non-chemical control strategies for blueberry root rot disease, including cultivar selection, soil amendments (gypsum and a variety of organic materials) via a series of trials in the greenhouse. Based on the findings of the greenhouse experiments, a field trial was conducted to evaluate a combination of cultural factors in a two year field experiment. Pre-plant gypsum incorporation into soil was evaluated as a control strategy in the field experiment in combination with other cultural practices that were hypothesized to affect disease including mulch type (geotextile weedmat or sawdust), and drip irrigation line placement. Eighteen highbush blueberry cultivars and advanced breeding selections were evaluated for susceptibility or resistance in three greenhouse experiments. Cultivars varied widely in susceptibility, with 'Duke,' 'Draper,' 'Bluetta,' 'Blue Ribbon,' 'Cargo,' 'Last Call,' 'Top Shelf,' and 'Ventura' exhibiting high levels of susceptibility to the disease. More resistant cultivars included 'Legacy,' 'Liberty,' 'Aurora,' 'Overtime,' 'Reka,' and 'Clockwork'. By selecting cultivars with superior resistance, growers may avoid yield losses associated with the disease, enhancing production profitability. Although choosing a disease resistant cultivar is likely the most effective control strategy for blueberry, other cultural disease control practices are needed when susceptible cultivars are grown to fill market demands. Fungicides can control disease in conventional plantings, but cannot be applied within certified organic production systems. Gypsum and organic amendments sometimes provide suppression of Phytophthora root rot in crops other than blueberry. Three greenhouse trials were conducted to evaluate organic soil amendments (peat, sawdust, dairy solids compost, yard debris compost, and composted municipal biosolids blended with douglas-fir bark) incorporated at 20% v/v into soil, and gypsum (CaSO₄) incorporated at 5% (v/v) for disease suppression in factorial combination. Trials were conducted with a disease susceptible cultivar ('Draper'), and soil moisture was maintained near saturation, favoring disease development. Organic amendments did not suppress disease in any of the experiments. Gypsum was effective in disease suppression in one of the three experiments. Gypsum provides a source of soluble calcium, and previous reported studies have demonstrated a mechanism for calcium-mediated suppression of P. cinnamomi. An additional greenhouse study was conducted to determine the relationship between gypsum application rate, soluble calcium in soil solution, and disease suppression. Soluble Ca in soil solution reached a plateau concentration of ~454 mg Ca L⁻¹ soil solution at gypsum application rates equal to or above 16 meq gypsum 100g⁻¹ soil. Higher gypsum application rates did not increase soil solution Ca, or provide additional disease suppression. Rates of gypsum required for disease suppression increase soil electrical conductivity (EC) beyond current recommended salinity guidelines for blueberries (> 2.0 mS/cm). The effects of salinity on plant growth were evaluated in a six month greenhouse experiment, using gypsum (CaSO₄) or potassium sulfate (K₂SO₄) salts to increase EC. Treatment EC levels ranged from 0.3 to 2.6 mS/cm, in ten increments. The maximum EC value chosen for this experiment approximates the maximum value for gypsum solubility in soil solution. Aboveground plant biomass declined more rapidly when EC was supplied by potassium sulfate than it did with gypsum. Root biomass declined when EC was supplied by potassium sulfate, but it was not affected by gypsum rate. Leaf cation concentrations responded strongly to increasing rates of potassium sulfate application. Leaf K increased dramatically, accompanied by declines in leaf Ca and Mg concentration. In contrast, leaf cation concentrations were much more stable when EC was adjusted by gypsum addition. Under the conditions of this greenhouse experiment, the increase in EC accompanying gypsum application had only minor effects on plant growth and nutrient uptake, suggesting that gypsum application is a viable option for trial in the field. A two year field trial was conducted to evaluate cultural practices for efficacy in suppressing P. cinnamomi root rot disease. Pre-plant gypsum incorporation into soil was evaluated as a control strategy in combination with other cultural practices that were hypothesized to affect disease: mulch type (geotextile weed mat vs. sawdust), and drip irrigation line placement. Disease suppression over two growing seasons was evaluated with the highly susceptible cultivar 'Draper' grown on a site with clay loam soil. P. cinnamomi inoculum was mixed into soil before planting. Experimental design was a 2x2x2 factorial with 2 mulch types (geotextile weed mat or douglas-fir sawdust), 2 drip line placements (narrow or wide placement relative to plant row), and 2 gypsum rates (0 and + gypsum). Gypsum was incorporated into planting beds in a 30-cm band at an application rate of 22,420 kg ha⁻¹ in-band equivalent to 2,242 kg ha⁻¹ on a whole-field basis. Drip irrigation treatments consisted of two drip lines placed either adjacent to the plant crown or 20-cm on either side of the crown (wide placement). A fungicide treatment was included to provide an assessment of the efficacy of cultural disease control vs. a chemical alternative. The fungicide treatment was mulched with sawdust and irrigated with drip lines adjacent to plants, and did not receive gypsum application. Mulch type had no significant effect on plant biomass after two years, but plants grown under sawdust had slightly higher biomass and less root infection. Soluble Ca, as measured by mini-lysimeters placed in the rootzone, was increased by gypsum application, especially with wide placement of drip irrigation lines. The disease suppressive effect of gypsum amendment depended on irrigation line placement. Soluble Ca movement in soil was associated with water movement away from drip emitters. When drip irrigation lines were placed adjacent to the plant crown, soluble Ca was moved away from the plant with the wetting front. With wide drip line placement , soluble Ca was moved toward the roots. Plants grown with wide drip line placement and gypsum addition had the lowest root infection incidence and highest plant biomass, likely as the result of more soluble Ca in the rootzone. Despite significant increases in plant biomass with gypsum and widely-placed irrigation lines, plants treated with conventional fungicide had approximately twice as much biomass after two growing seasons. An integrated control program is required for cultural suppression of blueberry root rot disease. Organic production using highly susceptible cultivars in the presence of P. cinnamomi is difficult, and may not produce equivalent yields to conventional production. Improved plant performance in the presence of P. cinnamomi was observed in these trials using cultivar resistance, gypsum, and widely-spaced drip irrigation lines. Other cultural practices, such as careful irrigation scheduling, and appropriate rate and timing of N fertilizer application are also important for disease suppression. In the future, greater P. cinnamomi disease suppression should be possible by using the disease suppressive cultural practices identified in this research in combination with a disease-resistant cultivar.
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Range, areas of concentrated activity, and dispersal characteristics for juvenile Steller sea lions Eumetopias jubatus in the endangered western population (west of 144° W in the Gulf of Alaska) are poorly ...
Citation Citation
- Title:
- Range-use estimation and encounter probability for juvenile Steller sea lions (Eumetopias jubatus) in the Prince William Sound-Kenai Fjords region of Alaska
- Author:
- Meck, Stephen R.
Range, areas of concentrated activity, and dispersal characteristics for juvenile Steller sea lions Eumetopias jubatus in the endangered western population (west of 144° W in the Gulf of Alaska) are poorly understood. This study quantified space use by analyzing post-release telemetric tracking data from satellite transmitters externally attached to n = 65 juvenile (12-25 months; 72.5 to 197.6 kg) Steller sea lions (SSLs) captured in Prince William Sound (60°38'N -147°8'W) or Resurrection Bay (60°2'N -149°22'W), Alaska, from 2003-2011. The analysis divided the sample population into 3 separate groups to quantify differences in distribution and movement. These groups included sex, the season when collected, and the release type (free ranging animals which were released immediately at the site of capture, and transient juveniles which were kept in captivity for up to 12 weeks as part of a larger ongoing research program). Range-use was first estimated by using the minimum convex polygon (MCP) approach, and then followed with a probabilistic kernel density estimation (KDE) to evaluate both individual and group utilization distributions (UDs). The LCV method was chosen as the smoothing algorithm for the KDE analysis as it provided biologically meaningful results pertaining to areas of concentrated activity (generally, haulout locations). The average distance traveled by study juveniles was 2,131 ± 424 km. The animals mass at release (F[subscript 1, 63] = 1.17, p = 0.28) and age (F[subscript 1, 63] = 0.033, p = 0.86) were not significant predictors of travel distance. Initial MCP results indicated the total area encompassed by all study SSLs was 92,017 km², excluding land mass. This area was heavily influenced by the only individual that crossed over the 144°W Meridian, the dividing line between the two distinct population segments. Without this individual, the remainder of the population (n = 64) fell into an area of 58,898 km². The MCP area was highly variable, with a geometric average of 1,623.6 km². Only the groups differentiated by season displayed any significant difference in area size, with the Spring/Summer (SS) groups MCP area (Mdn = 869.7 km²) being significantly less than that of the Fall/Winter (FW) group (Mdn = 3,202.2 km²), U = 330, p = 0.012, r = -0.31. This result was not related to the length of time the tag transmitted (H(2) = 49.65, p = 0.527), nor to the number of location fixes (H(2) = 62.77, p = 0.449). The KDE UD was less variable, with 50% of the population within a range of 324-1,387 km2 (mean=690.6 km²). There were no significant differences in area use associated with sex or release type (seasonally adjusted U = 124, p = 0.205, r = -0.16 and U = 87, p = 0.285, r = -0.13, respectively). However, there were significant differences in seasonal area use: U = 328, p = 0.011, r = -0.31. There was no relationship between the UD area and the amount of time the tag remained deployed (H(2) = 45.30, p = 0.698). The kernel home range (defined as 95% of space use) represented about 52.1% of the MCP range use, with areas designated as "core" (areas where the sea lions spent fully 50% of their time) making up only about 6.27% of the entire MCP range and about 11.8% of the entire kernel home range. Area use was relatively limited – at the population level, there were a total of 6 core areas which comprised 479 km². Core areas spanned a distance of less than 200 km from the most western point at the Chiswell Islands (59°35'N -149°36'W) to the most eastern point at Glacier Island (60°54'N -147°6'W). The observed differences in area use between seasons suggest a disparity in how juvenile SSLs utilize space and distribute themselves over the course of the year. Due to their age, this variation is less likely due to reproductive considerations and may reflect localized depletion of prey near preferred haul-out sites and/or changes in predation risk. Currently, management of the endangered western and threatened eastern population segments of the Steller sea lion are largely based on population trends derived from aerial survey counts and terrestrial-based count data. The likelihood of individuals to be detected during aerial surveys, and resulting correction factors to calculate overall population size from counts of hauled-out animals remain unknown. A kernel density estimation (KDE) analysis was performed to delineate boundaries around surveyed haulout locations within Prince William Sound-Kenai Fjords (PWS-KF). To closely approximate the time in which population abundance counts are conducted, only sea lions tracked during the spring/summer (SS) months (May 10-August 10) were chosen (n = 35). A multiple state model was constructed treating the satellite location data, if it fell within a specified spatiotemporal context, as a re-encounter within a mark-recapture framework. Information to determine a dry state was obtained from the tags time-at-depth (TAD) histograms. To generate an overall terrestrial detection probability 1) The animal must have been within a KDE derived core-area that coincided with a surveyed haulout site 2) it must have been dry and 3) it must have provided at least one position during the summer months, from roughly 11:00 AM-5:00 PM AKDT. A total of 10 transition states were selected from the data. Nine states corresponded to specific surveyed land locations, with the 10th, an "at-sea" location (> 3 km from land) included as a proxy for foraging behavior. A MLogit constraint was used to aid interpretation of the multi-modal likelihood surface, and a systematic model selection process employed as outlined by Lebreton & Pradel (2002). At the individual level, the juveniles released in the spring/summer months (n = 35) had 85.3% of the surveyed haulouts within PWS-KF encompass KDE-derived core areas (defined as 50% of space use). There was no difference in the number of surveyed haulouts encompassed by core areas between sexes (F[subscript 1, 33] << 0.001, p = 0.98). For animals held captive for up to 12 weeks, 33.3% returned to the original capture site. The majority of encounter probabilities (p) fell between 0.42 and 0.78 for the selected haulouts within PWS, with the exceptions being Grotto Island and Aialik Cape, which were lower (between 0.00-0.17). The at-sea (foraging) encounter probability was 0.66 (± 1 S.E. range 0.55-0.77). Most dry state probabilities fell between 0.08-0.38, with Glacier Island higher at 0.52, ± 1 S.E. range 0.49-0.55. The combined detection probability for hauled-out animals (the product of at haul-out and dry state probabilities), fell mostly between 0.08-0.28, with a distinct group (which included Grotto Island, Aialik Cape, and Procession Rocks) having values that averaged 0.01, with a cumulative range of ≈ 0.00-0.02 (± 1 S.E.). Due to gaps present within the mark-recapture data, it was not possible to run a goodness-of-fit test to validate model fit. Therefore, actual errors probably slightly exceed the reported standard errors and provide an approximation of uncertainties. Overall, the combined detection probabilities represent an effort to combine satellite location and wet-dry state telemetry and a kernel density analysis to quantify the terrestrial detection probability of a marine mammal within a multistate modeling framework, with the ultimate goal of developing a correction factor to account for haulout behavior at each of the surveyed locations included in the study.
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In the first set of studies, 2 experiments evaluated the influence of supplement composition on ruminal forage disappearance, performance, and physiological responses of Angus × Hereford cattle consuming ...
Citation Citation
- Title:
- Nutritional strategies to improve the reproductive performance of beef females
- Author:
- Cappellozza, Bruno Ieda
In the first set of studies, 2 experiments evaluated the influence of supplement composition on ruminal forage disappearance, performance, and physiological responses of Angus × Hereford cattle consuming a low-quality, cool-season forage (8.7 % CP and 57 % TDN). In Exp. 1, 6 rumen-fistulated steers housed in individual pens were assigned to an incomplete 3 x 2 Latin square design containing 2 periods of 11 d each and the following treatments: 1) supplementation with soybean meal (PROT), 2) supplementation with a mixture of cracked corn, soybean meal, and urea (68:22:10 ratio, DM basis; ENER), or 3) no supplementation (CON). Steers were offered meadow foxtail (Alopecurus pratensis L.) hay for ad libitum consumption. Treatments were provided daily at 0.50 and 0.54 % of shrunk BW/steer for PROT and ENER, respectively, to ensure that PROT and ENER intakes were isocaloric and isonitrogenous. No treatment effects were detected on rumen disappearance parameters of forage DM (P ≥ 0.33) and NDF (P ≥ 0.66). In Exp. 2, 35 pregnant heifers were ranked by initial BW on d -7 of the study, allocated into 12 feedlot pens (4 pens/treatment), and assigned to the same treatments and forage intake regimen as in Exp. 1 for 19 d. Treatments were fed once daily at 1.77 and 1.92 kg of DM/heifer for PROT and ENER, respectively, to achieve the same treatment intake as % of initial BW used in Exp. 1 (0.50 and 0.54 % for PROT and ENER, respectively). No treatment effects (P = 0.17) were detected on forage DMI. Total DMI was greater (P < 0.01) for PROT and ENER compared with CON, and similar between PROT and ENER (P = 0.36). Accordingly, ADG was greater (P = 0.01) for PROT compared with CON, tended to be greater for ENER compared with CON (P = 0.08), and was similar between ENER and PROT (P = 0.28). Heifers receiving PROT and ENER had greater mean concentrations of plasma glucose (P = 0.03), insulin (P ≤ 0.09), IGF-I (P ≤ 0.04), and progesterone (P₄; P = 0.01) compared to CON, whereas ENER and PROT had similar concentrations of these variables (P ≥ 0.15). A treatment × hour interaction was detected (P < 0.01) for plasma urea N (PUN), given that PUN concentrations increased after supplementation for ENER and PROT (time effect, P < 0.01), but did not change for CON (time effect; P = 0.62). In conclusion, beef cattle consuming low-quality cool-season forages had similar ruminal forage disappearance and intake, performance, and physiological status if offered supplements based on soybean meal or corn at approximately 0.5 % of BW (DM basis). The following experiment evaluated the influence of supplement composition on performance, reproductive, and metabolic responses of Angus × Hereford heifers consuming a low-quality cool-season forage (8.7 % CP and 57 % TDN). Sixty heifers (initial age = 226 ± 3 d) were allocated into 15 drylot pens (4 heifers/pen; 5 pens/treatment), and assigned to the same treatments as reported above. Heifers were offered meadow foxtail (Alopecurus pratensis L.) hay for ad libitum consumption during the experiment (d -10 to 160). Beginning on d 0, PROT and ENER were provided daily at a rate of 1.30 and 1.40 kg of DM/heifer to ensure that PROT and ENER intakes were isocaloric and isonitrogenous. Hay and total DMI were recorded for 5 consecutive days during each month of the experiment. Blood was collected every 10 d for analysis of plasma P₄ to evaluate puberty attainment. Blood samples collected on d -10, 60, 120, and 150 were also analyzed for PUN, glucose, insulin, IGF-I, NEFA, and leptin. Liver samples were collected on d 100 from 2 heifers/pen, and analyzed for mRNA expression of genes associated with nutritional metabolism. No treatment effect was detected (P = 0.33) on forage DMI. Total DMI, ADG, mean concentrations of glucose, insulin, and IGF-I, as well as hepatic mRNA expression of IGF-I and IGFBP-3 were greater (P ≤ 0.02) for PROT and ENER compared with CON, and similar between PROT and ENER (P ≥ 0.13). Mean PUN concentrations were also greater (P < 0.01) for PROT and ENER compared with CON, whereas PROT heifers had greater (P < 0.01) PUN compared with ENER. Plasma leptin concentrations were similar between ENER and PROT (P ≥ 0.19), and greater (P ≤ 0.03) for ENER and PROT compared with CON on d 120 and 150 (treatment × day interaction; P = 0.03). Hepatic mRNA expression of mitochondrial phosphoenolpyruvate carboxykinase was greater (P = 0.05) in PROT compared with CON and ENER, and similar between CON and ENER (P = 0.98). The proportion of heifers pubertal on d 160 was greater (P < 0.01) in ENER compared with PROT and CON, and similar between PROT and CON (P = 0.38). In conclusion, beef heifers consuming a low-quality cool-season forage had a similar increase in DMI, growth, and overall metabolic status if offered supplements based on soybean meal or corn at 0.5 % of BW. The last experiment was designed to determine if frequency of protein supplementation impacts physiological responses associated with reproduction in beef cows. Fourteen non-pregnant, non-lactating beef cows were ranked by age and BW, and allocated to 3 groups. Groups were assigned to a 3 × 3 Latin square design, containing 3 periods of 21 d and the following treatments: 1) soybean meal (SB) supplementation daily (D), 2) SB supplementation 3 times/wk (3WK), and 3) SB supplementation once/wk (1WK). Within each period, cows were assigned to an estrus synchronization protocol; 100 μg of GnRH + controlled internal drug release (CIDR) containing 1.38 g of P4 on d 1, 25 mg of PGF₂α on d 8, and CIDR removal + 100 μg of GnRH on d 11. Grassseed straw was offered for ad libitum consumption. Soybean meal was individually supplemented at a daily rate of 1 kg/cow (as-fed basis). Moreover, 3WK were supplemented on d 0, 2, 4, 7, 9, 11, 14, 16, and 18, whereas 1WK were supplemented on d 4, 11, and 18. Blood samples were collected from 0 (prior to) to 72 h after supplementation on d 11 and 18, and analyzed for PUN. Samples collected from 0 to 12 h were also analyzed for plasma glucose, insulin, and P4 (d 18 only). Uterine flushing fluid was collected concurrently with blood sampling at 28 h for pH evaluation. Liver biopsies were performed concurrently with blood sampling at 0, 4, and 28 h, and analyzed for mRNA expression of carbamoylphosphate synthetase I (CPS-I; h 28), and CYP2C19 and CYP3A4 (h 0 and 4 on d 18). Plasma urea-N concentrations were greater (P < 0.01) for 1WK vs. 3WK from 20 to 72 h, and greater (P < 0.01) for 1WK vs. D from 16 to 48 h and at 72 h after supplementation (treatment × hour interaction; P < 0.01). Moreover, PUN concentrations peaked at 28 h after supplementation for 3WK and 1WK (P < 0.01), and were greater (P < 0.01) at this time for 1WK vs. 3WK and D and for 3WK vs. D. Expression of CPS-I was greater (P < 0.01) for 1WK vs. D and 3WK. Uterine flushing pH tended (P ≤ 0.10) to be greater for 1WK vs. 3WK and D. No treatment effects were detected (P ≥ 0.15) on expression of CYP2C19 and CYP3A4, plasma glucose and P4 concentrations, whereas plasma insulin concentrations were greater (P ≤ 0.03) in D and 3WK vs. 1WK. Hence, decreasing frequency of protein supplementation did not reduce uterine flushing pH or plasma P₄ concentrations, which are known to impact reproduction in beef cows. In summary for all the experiments presented herein: (1) pregnant and developing replacement beef heifers consuming a low-quality, cool-season forage equally utilize and benefit, in terms of growth and metabolic parameters, from supplements based on protein or energy ingredients provided at approximately 0.5 % of heifer BW/d, (2) energetic supplementation at approximately 0.5 % BW/d did not impair forage disappearance parameters in rumen-fistulated steers, and (3) decreasing soybean meal supplementation frequency to once a week did not increase uterine pH, plasma P₄, and expression of hepatic enzymes associated with steroid catabolism in ruminants.
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12325. [Article] Polyunsaturated fatty acid metabolism in broiler chickens : effects of maternal diet
Three experiments were conducted in broiler hens to study the influence of dietary n-3 polyunsaturated fatty acids (PUFA) on egg quality, antioxidant status in progeny, and eicosanoid production in tissue. The ...Citation Citation
- Title:
- Polyunsaturated fatty acid metabolism in broiler chickens : effects of maternal diet
- Author:
- Bautista Ortega, Jaime
Three experiments were conducted in broiler hens to study the influence of dietary n-3 polyunsaturated fatty acids (PUFA) on egg quality, antioxidant status in progeny, and eicosanoid production in tissue. The objective of experiment 1 was to determine the effect of hen age and dietary n-3 PUFA on egg quality and hatchability. Two-hundred-twenty breeder chicks (males and females) (Cobb Breeders) were raised until 20 weeks of age following the company guidelines. At this age, 3 groups of birds (24 breeder hens and 3 roosters) were randomly allocated to one of the following dietary treatments: 3.5% sunflower oil (Low n-3 diet), 1.75% sunflower oil + 1.75% fish oil (Medium n-3 diet) or 3.5% fish oil (High n-3 diet). Egg quality was evaluated at 29, 37 and 45 weeks of age by determining total egg weight, its components (albumen, yolk and shell) and shell thickness. Total fat content in the yolk and its fatty acid profile was also determined. Egg production was recorded daily. Breeder hens fed the High n-3 diet laid lighter eggs with lighter yolks, albumens and shells than those fed the Medium and Low n-3 diets (p<0.05). Eggs laid by hens fed the Medium n-3 diet had thicker shells than those laid by hens fed the Low n-3 diet (p<0.05). Egg weight, yolk weight, albumen weight, shell weight and shell thickness increased significantly with hen age (p<0.05). Total fat content in the yolk was significantly higher in the eggs laid by 37-week-old and 45-week-old hens than in those laid by 29-week-old hens. Hens fed the high n-3 diet laid eggs with significantly higher n-3 PUFA and lower n-6 PUFA content than hens from the other treatments (p<0.05). Hen age did not affect the n-3 or n-6 PUFA content. Fertility and hatchability were not affected by maternal diet. Total egg weight, yolk weight, albumen weight and shell weight was decreased by feeding n-3 PUFA to breeder hens. The decreased n6:n3 ratio brought about by maternal dietary n-3 PUFA was further investigated in connection with possible effects on antioxidant and eicosanoid status in newly hatched chicks. The objective of experiment 2 was to determine the effect of maternal diet (Low, Medium and High n-3) on the antioxidant and eicosanoid status, tissue fatty acid profile and lipid peroxidation in the newly hatched chick. Two-hundred-ninety-eight eggs were collected from the 29-week-old breeder hens mentioned in experiment 1. After incubation, day-old chicks were randomly selected from a pool of eggs laid by hens fed the three experimental diets. Antioxidant status was established by measuring activity of antioxidant enzymes (glutathione peroxidase, glutathione reductase, superoxide dismutase and catalase) and the content of total glutathione. Hatchability and total fat content in the tissues were not affected by maternal diet. n-3 PUFA content increased and n-6 PUFA decreased significantly in chick’s tissue (p<0.05) hatched from hens fed the fish-oil supplemented diet compared to those hatched from hens fed the Low n-3 diet (p<0.05). Total glutathione and antioxidant enzyme activity was not affected by maternal diet, except for catalase, whose activity was significantly lower in chicks hatched from hens fed the High n-3 and the Medium n-3 diets than in those hatched from hens fed the Low n-3 diets (p<0.05). Malondialdehyde, a measure of lipid peroxidation, was significantly lower in the liver of chicks hatched from eggs laid by hens fed the High n-3 diet than in those hatched from hens fed the Medium n-3 diet. Maternal dietary n-3 PUFA was successfully transferred to the newly hatched chicks without compromising their antioxidant status. The decreased n-6/n-3 ratio observed in chicks hatched from hens fed the fish-oil supplemented diets needs was further investigated relative to its downstream modulatory effects in connection with fat metabolism. The objective of experiment 3 was to establish the effect of maternal diet on fatty acid accretion in heart tissue, and the production of eicosanoids by heart tissue homogenates and peripheral blood mononuclear cells (PBMNC) from broilers fed diet devoid of long-chain PUFA. Broilers were hatched from hens fed the Low, Medium or High n-3 diet. One-hundred-fortyfour 1-day-old chicks were weighed and randomly allocated to four pens housed in three rooms of similar dimensions. Temperature was controlled according to specifications by Cobb Breeders during the 42 days that the experiment lasted. A cardiac morphological study was conducted on a weekly basis starting at 14 days of age to assess the heart weight relative to body weight. Also, the ventricular weights index (right ventricular weight divided by the total ventricular weight) was determined weekly from 14 days onwards. Day-0 chicks hatched from hens fed the High n-3 diet were significantly lighter than those hatched from hens fed the Low n-3 diet. After accounting for age, chicks hatched from hens fed the Low n-3 diet were significantly heavier than those hatched from hens fed the High n-3 diet (p<0.05). Maternal diet did not affect heart weight, after accounting for age. The heart percentage (heart weight relative to body weight) was significantly higher in chicks hatched from hens fed the High n-3 diet than in those hatched from hens fed the Low n-3 diet (p<0.05). The ventricular weights index was not affected by maternal diet. At 7 and 14 days of age, arachidonic acid (AA) content in heart tissue was significantly lower in chicks hatched from hens fed the High n-3 diet than those hatched from hens fed the Low n-3 diet (p<0.05). At 7 days of age, AA content in the heart tissue of chicks hatched from hens fed the High n-3 diet was significantly lower than in those hatched from hens fed the Medium n-3 diet (p<0.05). At day 0, the heart tissue production of prostaglandin E2 (PGE2) was significantly higher in the chicks hatched from hens fed the Low n-3 diet than in those hatched from hens fed the Medium or High n-3 diets (p<0.05). At the same age, thromboxane A3 (TXA3) production was significantly lower in the heart tissue of chicks hatched from hens fed the Low n-3 diet than in that of chicks hatched from hens fed either the Medium or Low n-3 diets (p<0.05). At day 7, PBMNCs isolated from chickens hatched from hens fed the Low and Medium n-3 diets produced significantly higher PGE2 and TXA2 concentrations than those isolated from birds hatched from eggs laid by hens fed the High n-3 diet (p<0.05). At day 31, PBMNCs isolated from chickens hatched from hens fed the Medium and High n-3 diets produced significantly higher PGE2 and TXA2 concentrations than those isolated from chicks hatched from eggs laid by hens fed the Low n-3 diet (p<0.05). Chicks hatched from hens fed the High n-3 diet had a higher heart/body weight than those hatched from the Low n-3 diet. Thus, chicks hatched from hens fed the Low n-3 diet may be at higher risk of developing cardiovascular complications related to high AA concentrations in the heart and blood cells during the first week of age. Further research is encouraged in which the three subpopulations of broilers (i.e.hatched from hens fed the Low, Medium and High n-3 diets) are raised under commercial conditions to investigate how the economic loss, due to a reduction in body weight observed in the High n-3 chickens compares with the potential reduction in mortality during the first week of age. Finally, the mechanistic action of n-3 PUFA needs further investigation, especially molecular aspects related to modulatory effects on gene expression.
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12326. [Article] The Role of Bone Marrow Adipose Tissue in Bone Loss During Spaceflight and Simulated Spaceflight in Rodents
The reduction in mechanical load imparted on the body during spaceflight presents unique physiological challenges. One detrimental and seemingly unavoidable response to microgravity is rapid bone loss. ...Citation Citation
- Title:
- The Role of Bone Marrow Adipose Tissue in Bone Loss During Spaceflight and Simulated Spaceflight in Rodents
- Author:
- Keune, Jessica Ann
The reduction in mechanical load imparted on the body during spaceflight presents unique physiological challenges. One detrimental and seemingly unavoidable response to microgravity is rapid bone loss. This adaptation is hazardous not only to astronaut health, but to the success of long-duration exploration-class missions. Skeletal adaptation to spaceflight in astronauts typically includes rapid site-specific bone loss from unbalanced bone turnover, primarily in the femur, hip and vertebra. Studies of rats in space and biochemical markers from astronauts typically indicate unbalanced bone turnover results from an increase in bone resorption and either no change or a decrease in bone formation. An increase in bone marrow adipose tissue (MAT) is concurrently observed with bone loss in ground-based conditions of disuse or reduced mobility, such as bed rest. While the precise role of bone marrow adiposity is unclear, it has concurrently been associated with a decrease in bone formation. The invasive nature of bone marrow analysis and high cost associated with long-term disuse studies makes human-based research difficult to accomplish. The use of rodent subjects is a valuable tool in research for desirable size, cost, lifespan and comparable physiological systems to humans, and was thus used in the studies described in this dissertation. The central hypothesis of this dissertation states skeletal disuse results in bone loss, in part, from a reduction in ability to form osteoblasts, and occurs concurrently with MAT infiltration. Furthermore, we hypothesize that increased MAT plays a causative role in bone loss. If this hypothesis is correct: 1) an inability to produce MAT is protective against disuse-induced bone loss, and 2) an ability to produce high quantities of MAT exacerbates disuse-induced bone loss. The role of bone marrow adiposity in disuse-induced bone loss was evaluated using archived bone specimens from rats flown in space for 14 days and using mice subjected to hindlimb-unloading (HU), a ground-based model for spaceflight. The effects of the 14-day spaceflight on bone mass, density and microarchitecture in weight bearing (femur and humerus) and non-weight bearing (2nd lumbar vertebra and calvarium) bones in female rats insufficient in ovarian hormones due to ovariectomy are presented in Chapter 2. In the context of established ovarian hormone deficiency, a 14-day spaceflight resulted in bone- and bone compartment-specific decrements in bone acquisition and a negative turnover balance leading to deficits in bone mass and defective microarchitecture beyond that induced by ovx. The observed changes demonstrate the importance of evaluating multiple bones and bone compartments. The effects of a 14-day spaceflight on bone mass, bone resorption, bone formation, and MAT in lumbar vertebrae of the ovx rats was subsequently evaluated and the results are described in Chapter 3. The increase in MAT observed during this short-duration spaceflight did not impair osteoblast activity, reduce the interval osteoblasts are present on bone surfaces or decrease generation of new osteoblasts. These findings argue against the hypothesis that increased MAT produces factors that suppress bone formation. Although increased MAT did not impact osteoblast kinetics or bone formation, it is important to note that bone formation did not increase during spaceflight to compensate for the increase in bone resorption. This finding is consistent with the hypothesis that, in the context of ovarian hormone deficiency, osteoblast precursors are diverted to adipocytes instead of osteoblasts during spaceflight. These studies were the first large-scale investigation into the influence of microgravity on multi-site microarchitecture and MAT in slowly growing rats. The findings also indicated the importance of location in evaluation. A 14-day spaceflight did not result in loss of cortical bone in femur, humerus or calvaria. Cancellous bone loss was observed in femur and vertebra but not in humerus. The lumbar vertebra is not a primary weight-bearing site in rodents, yet it exhibited bone loss from increased bone resorption and no change in bone formation, as well as an increase in MAT. Importantly, our findings suggest that while MAT may increase during spaceflight it does not impair ongoing bone formation. MAT-deficient Kit[superscript W/W-v] (MAT-) mice were used to determine if absence of MAT reduced bone loss in HU mice after 14 days. The results from this study are described in Chapter 4. MAT- mice had a greater reduction in bone volume fraction than WT mice. While both HU groups had greater osteoclast perimeter than controls, HU MAT- mice had greater osteoblast perimeter, mineral apposition rate and bone formation rate compared to other treatment groups. The increase in bone formation was not sufficient to balance the increase in bone resorption during disuse, ultimately resulting in reduced bone that was of a greater magnitude in MAT-deficient mice. Targeted gene profiling further suggested a differential response of WT and MAT- mice to HU. To verify that the differences were not due to kit deficiency, we reconstituted the hematopoietic system in the Kit[superscript W/W-v] mice with WT hematopoietic stem cells. Adoptive transfer of WT bone marrow-derived hematopoietic stem cells reconstituted c-kit but not MAT in KitKit[superscript W/W-v] mice. The WT→ Kit[superscript W/W-v] mice lost cancellous bone following 14 days of HU. Together, the results do not support the hypothesis that MAT potentiates disuse-induced bone loss in mice. MAT was not increased in WT mice following HU and MAT deficiency was not protective against disuse-induced cancellous bone loss. Results from this study indicate MAT may actually have a protective role in limiting disuse-induced osteopenia, perhaps by limiting the magnitude of increased bone turnover. Chapter 5 describes results using mice with high MAT due to leptin deficiency (ob/ob) to determine if excess MAT exacerbated bone loss in HU mice after 14 days. ob/ob mice were pair-fed to WT mice to prevent the development of morbid obesity, but still maintained a greater body weight and abdominal adipose tissue than the WT mice. ob/ob mice had lower femoral bone mineral content and length, but no difference in cancellous bone volume fraction in the metaphysis and epiphysis. HU resulted in cancellous bone loss in metaphysis and epiphysis. While osteoblast perimeter was increased after HU, it was not sufficient to compensate for the increase in bone resorption leading to a reduction in cancellous bone. No significant interactions between genotype and treatment were detected for any of the endpoints measured. Together, the results do not support the hypothesis that high levels of MAT exacerbate disuse-induced bone loss in mice. The findings from this study indicate that having higher levels of MAT did not influence the bone response to disuse. While the central hypothesis that inadequate formation of osteoblasts contributes to bone loss and occurs concurrently with increased MAT infiltration was partially accepted in spaceflight, it was rejected in hindlimb unloading. Although we did observe an increase in MAT following spaceflight, it was not associated with altered osteoblast turnover or decreased bone formation. During HU, MAT levels did not change but bone formation increased. Importantly, bone resorption was increased during spaceflight and HU. Therefore, bone loss resulted from inadequate coupling of bone formation to compensate for the increase in bone resorption. These studies suggest that a simple relationship between MAT and bone mass does not exist and that targeting MAT to increase bone mass may not be an effective strategy.
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12327. [Article] Distribution and movements of Chinook salmon, Oncorhynchus tshawytscha, returning to the Yukon River basin
Chinook salmon, Oncorhynchus tshawytscha, returning to the Yukon River basin and other large river systems in western Alaska have declined dramatically since the late 1990s. This continuing trend has ...Citation Citation
- Title:
- Distribution and movements of Chinook salmon, Oncorhynchus tshawytscha, returning to the Yukon River basin
- Author:
- Eiler, John H.
Chinook salmon, Oncorhynchus tshawytscha, returning to the Yukon River basin and other large river systems in western Alaska have declined dramatically since the late 1990s. This continuing trend has raised concerns over the future status of the returns, and severely impacted commercial and subsistence fisheries within the drainage. Management is further complicated by the mixed-stock composition of the run, the presence of other temporally similar salmon species, and the need to equitably allocate harvests between the numerous fisheries and user groups scattered throughout the basin. Detailed information is needed on Chinook salmon run characteristics to better understand and manage the returns, and facilitate conservation efforts. However, this goal is exacerbated by the massive size and remote nature of the basin, the large number of highly mobile fish, and the compressed timing of the run. To address these challenges, radio telemetry was used to determine the stock composition and spawning distribution of the returns, and the migratory characteristics of the fish. The migratory patterns exhibited by returning salmon provide a number of insights into the status of the run. Since the Yukon River is essentially free-flowing (i.e., not regulated), this study also presented an opportunity to document the distribution and upriver movements of large returns of wild Chinook salmon under natural conditions. During 2002-2004, returning adult Chinook salmon were captured in the lower Yukon River (approximately 300 km upriver from the river mouth), tagged with radio transmitters, and tracked upriver using remote tracking stations located on important migratory routes and major spawning tributaries. Aerial tracking surveys were used to locate fish in spawning areas and between stations. The fish responded well to the capture and handling procedures, with most (2,790, 98%) resuming upriver movements. Although the fish initially displayed a negative tagging response, with slower migration rates observed immediately after release, the duration of this response was relatively short (several days) and less severe as the fish moved upriver. Independent measures indicated that the swimming speeds and timing of the fish upriver from the tagging area were comparable to untagged fish, suggesting that the tagging methods used were relatively benign. Fish returned to spawning areas throughout the basin, ranging from several hundred to over 3,000 km from the tagging area. Distribution patterns were similar across years, suggesting that the principal components of the run were identified. Most spawning fish were clustered in a number of key tributaries, with smaller numbers of fish located in other spatially isolated areas. The fish typically returned to clear water tributaries that were relatively entrenched, had moderate gradients, and were associated with upland areas. Fish were largely absent in lowland reaches characterized by meandering, low gradient, highly alluvial channels often associated with main river floodplains. There was suggestive evidence of mainstem spawning in reaches of the Upper Yukon. The status of fish remaining in other mainstem areas was less certain, and may represent local spawning activity or fish that died while in-transit to upriver areas. Although Chinook salmon spawned throughout the basin, the run was dominated by two regional components (Tanana and Upper Yukon), which annually comprised over 70% of the return. Substantially fewer fish returned to other areas ranging from 2-9% of the return, although the collective contribution of these stocks was appreciable. Most regional returns consisted of several principal stocks and a number of small, spatially isolated populations. Regional and stock composition estimates were similar across years even though differences in run abundance were reported, suggesting that these abundance differences were not related to regional or stock-specific differences. Run timing was relatively compressed compared to rivers in the southern portion of the range, with most stocks passing through the lower river over a 6-week period, ranging from 16 to 38 d. Run timing was generally earlier for stocks traveling farther upriver, although exceptions were noted. Lower basin stocks were primarily later run fish. Pronounced differences were observed in the migration rates (km/d) exhibited by regional stocks. Substantially slower swimming speeds were observed for fish returning to terminal tributaries in the lower basin ranging from 28-40 km/d compared to 52-62 km/d for upper basin stocks. The migratory patterns (migration rates in sequential reaches) of the fish also showed distinct regional differences. Average migration rates through the lower river were remarkably similar for the different stocks, ranging from 57-62 km/d, with most stocks exhibiting a general decline as the fish moved farther upriver. Tanana River stocks displayed a pronounced reduction in swimming speed after leaving the Yukon River main stem, with migration rates declining to 24 km/d on average as the fish approached their terminal tributaries. Conversely, upper basin stocks exhibited a relatively gradual (but variable) overall decline in migration rate even though these fish were traveling substantially greater distances upriver. Average migration rates for upper basin stocks ranged from 43-61 km/d as the fish approached their terminal tributaries. There was substantial variation in the migratory patterns exhibited by individual fish, although these patterns tended to be similar to the patterns exhibited by the regional stocks, particularly as the fish moved farther upriver from the tagging area. The dominant source of variation among fish reflected the average migration rate, with individual fish traveling slower in the lower basin exhibiting consistently slower migration rates as they moved upriver compared to their faster moving counterparts. This migratory pattern was consistent across stocks, and on average explained 74% of the within-stock variation in migration rate represented by the multivariate data. The second source of variation in migration rate reflected a shift in the relative swimming speeds of the individual fish as they progressed upriver. Although movement rates declined for nearly all of the fish during the migration, differences were observed in the pattern of the decline. Fish with faster migration rates in the lower river exhibited a pronounced decline in swimming speed as they moved upriver, whereas fish moving slower in the lower river displayed a more gradual decline in migration rate. On average, this migratory pattern explained 22% of the within-stock variation in migration rate represented by the multivariate data. Most fish (98%) exhibited continuous upriver movements and strong fidelity to the rivers they entered. However a small number of fish (n = 66) deviated from this pattern. Some of these individuals initially passed their final destination and continued upriver for varying distances before reversing direction, swimming back downstream, and entering their terminal tributary. Although most of these excursions were relatively short (< 30 km), there were several instances where fish traveled hundreds of kilometers out of their way. Thirty-four fish tracked to terminal tributaries subsequently left these rivers, and traveled to other terminal tributaries within the basin (n = 31) or were harvested in upriver fisheries (n = 3). Although most of these incidents involved nearby tributaries, major diversions were also observed, with several fish traveling over 300 km to natal rivers after leaving the initial tributary. Chinook salmon returns to the Yukon River typically consisted of a series of distinct and sizable increases in the number fish entering the river over the course of the run, commonly referred to as pulses. A large number of fish (n = 251) were radio tagged over a 4-day period during a pulse in 2003 to provide information on the progression of the pulse as it moved upriver. The time taken by the pulse to move past subsequent upriver locations increased as the fish moved farther upriver from the tagging area, with the fish passing sites located 580 and 800 km upriver over a span of 14 and 21 d, respectively. Although not surprising considering the extensive variation in migration rates observed among individual fish, this finding does suggest that these pulses do not represent cohesive aggregates of fish moving upriver. Unlike the well established methods used to estimate other life history characteristics, the development of quantitative methods for analyzing and modeling fish movements has lagged noticeably behind, due in part to the complexity associated with movement data and (prior to the advent of telemetry) the difficulty of collecting this type of information on free-ranging individuals. Two fundamentally different analytical approaches, hierarchical linear regression models and multivariate ordination, were used during this study to evaluate factors thought to influence the upriver movements of the fish. In spite of the inherent differences, both methods provided strikingly similar results, indicating that the study findings were not dependent on the approach used, and suggesting that the results were plausible based on the information available and the weight of evidence. Both analytical methods had advantages, and provided complementary information. With hierarchical linear models, it was possible to simultaneously evaluate a wide range of explanatory variables (in our case, both biological and environmental), which provided standardized comparisons and simplified the interpretation of the results. Since both fixed and random effects were incorporated in the models, it was possible to account for sources of variation when insufficient information was available to identify the underlining factors – an important consideration since few field studies provide comprehensive data. With multivariate ordination, separate analyzes were needed to examine the relationships between the migration rates and the biotic and physical variables. In addition to being cumbersome, this limitation made it more difficult to compare the relative influence of the different factors and interactions between factors. However, ordination was very useful as an exploratory tool. Although compartmentalized by stock, across fish comparisons were simple and relatively straightforward. Because the explanatory variables were evaluated separately in relation to the ordination score assigned to the fish, it was possible to examine and compare highly correlated variables. Ordination was also able to identify overall patterns within the data and assess the relative importance. While this can be accomplished within the framework of linear regression using mixture models to determine whether multiple distributions exist within the data, the process is much simpler with ordination. The migratory patterns of the fish were influenced by a wide range of factors, with evidentiary support for complex, multi-faceted relationships. Physical features of the basin demonstrated stronger explanatory power, accounting for over 70% of the observed variation in migration rate compared to 18% for the biological characteristics of the fish. Parameter estimates associated with the steepness of the migratory route and remaining distance the fish had to travel to reach their natal rivers were most strongly correlated with migration rate, with consistent relationships observed across stocks. Migration rates were also noticeably slower in extensively braided reaches of the basin. The weaker relationships between migration rate and biotic factors may reflect stabilizing selection on long-distance migrants. Smaller fish exhibited minimally faster swimming speeds on average than larger individuals. This relationship was stronger in highly braided reaches. Run timing was positively related to migration rate for most stocks. Surprisingly, upper basin stocks traveling farther upriver displayed progressively negative relationships, suggesting that late-run fish were moving slower. Ancillary information suggests that this decline may relate to deteriorating fish condition later in the season.
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12328. [Article] Students as pro-social bystanders : opportunities, past behaviors, and intentions to intervene in sexual assault risk situations
Sexual assault is a major public health concern in the U.S, and college students are particularly vulnerable to victimization. A health issue that affects nearly one in four women (Fisher, Cullen, & Turner, ...Citation Citation
- Title:
- Students as pro-social bystanders : opportunities, past behaviors, and intentions to intervene in sexual assault risk situations
- Author:
- Hoxmeier, Jill C.
Sexual assault is a major public health concern in the U.S, and college students are particularly vulnerable to victimization. A health issue that affects nearly one in four women (Fisher, Cullen, & Turner, 2000; Karjane, Cullen, & Turner, 2005) and that is associated with severe negative health outcomes, including depression substance abuse, suicide ideation, and risky sexual behaviors (CDC, 2012), warrants effective prevention programs. Moving away from traditional prevention efforts, which target females as potential victims in risk reduction programs and males as potential perpetrators in attitudinal-shifting programs, bystander engagement programs have become increasingly more widespread. These programs aim to engage all students on the college campus as potential bystanders who can intervene to prevent a sexual assault or reduce the harm of an assault that has already occurred (Banyard, Moynihan & Plante, 2007). Burn (2009) investigated potential barriers to pro-social bystander intervention using the Situational Model of Bystander Intervention, a model based on the original research of bystander behavior of Latanè and Darley (1970). The model outlines five barriers that influence students' intent to intervene as witnesses to sexual assault: failure to notice the situation, failure to identify the situation as high risk, failure to take intervention responsibility, failure to intervene due to skills deficit, and failure to intervene due to audience inhibition (Burn, 2009). She found that students' perception of barriers negatively correlated with intervention behaviors as bystanders to sexual assault (Burn, 2009). Although bystander engagement programs have shown initial promise in increasing students' intent to intervene, more needs to be known about the opportunities students have to intervene, their past intervention actions, and their intent to intervene in the future across the wide range of situations that encompass sexual assault risk. In addition, to develop effective programs that aim to increase pro-social behavior, understanding the salient influences of students' intent is critical. This study uses the Theory of Planned Behavior (TPB; Ajzen & Fishbein, 1991) to examine the influences of students’ intent to perform 12 different pro-social bystander behaviors. The TPB asserts that individuals' behavior is most proximally influenced by their behavioral intentions, and intentions are influences by their perceived behavioral control to perform the behavior, subjective norms that support performing the behavior, and attitudes toward the behavior (Ajzen & Fishbein, 1991). The four primary aims of this study were: 1) to examine the demographic correlates of students' opportunities, past intervention actions, and reported intent to intervene; 2) to examine any differences in students' intent to intervene based on the level of intervention (pre-, mid-, and post-assault) and type of intervention (with the potential or actual victim compared to the potential or actual perpetrator); 3) to examine the influences of perceived behavioral control, subjective norms, and attitudes on students' intent to intervene as bystanders; and 4) to compare the TPB-based model to the Situational Model of Bystander Intervention (Burn, 2009) in its ability to explain students' intent to intervene as bystanders. In the Fall of 2014, a sample of 815 undergraduate students at Oregon State University completed the Sexual Assault Bystander Behavior Questionnaire (SABB-Q), a tool comprised of items to measure students' opportunities, past behaviors, and future intent, in addition to measures assessing the influences of students' intent in line with the Theory of Planned Behavior and Burn's (2009) Situational Model of Bystander Intervention. Students who participate in Greek communities (fraternities and sororities) reported significantly greater odds of having the opportunity to perform four of the 12 intervention behaviors compared to non-Greek students, while student-athletes reported significantly greater odds of having the opportunity to perform two of the 12 intervention behaviors. Females reported significantly more past pro-social intervention behaviors (x̄ = 0.87) compared to males (x̄ = 0.79; p = 0.007). Regarding intent to intervene in the future, females reported significantly greater intent to intervene compared to males (x̄ = 6.07 vs. 5.68; p = 0.007). Students with friends who have been victims of sexual assault reported greater intent to intervene compared those without friends who have been victims (x̄ = 6.04 vs. 5.89; p = 0.02). Students with a personal history of victimization reported significantly greater intent compared to those without a personal history (x̄ =6.13 vs 5.93; p = 0.03). Students reported significantly greater intent to intervene with the potential or actual victim compared to the potential or actual perpetrator (x̄ = 6.19 vs. 5.74, p < 0.001). Females reported significantly greater intent to intervene with both the potential or actual victims and perpetrators (x̄ = 6.31 and 5.84, respectively) compared to males (x̄ = 5.88 and 5.49, respectively). Both males and females reported the greatest intent to perform post-assault intervention behavior (x̄ = 6.23), followed by pre-assault (x̄ = 6.08) and mid-assault behaviors (x̄ = 5.57). Females reported significantly greater intent to perform nine of the 12 pro-social intervention behaviors compared to males. A multiple regression analysis revealed that perceived behavioral control, subjective norms, and attitudes explained a significant proportion of the variance in intent to intervene (R² = 0.55, F(3, 771) = 315.68, p < 0.000). Perceived behavioral control was highly significant (β = 0.48, p < 0.001), as were subjective norms (β = 0.15, p < 0.001) and attitudes (β = 0.30, p < 0.001). Gender differences were also observed. For females, perceived behavioral control was highly significant (β = 0.49, p < 0.001), as were subjective norms (β = 0.15, p < 0.001) and attitudes (β = 0.29, p < 0.001). For males, perceived behavioral control was highly significant (β = 0.49, p < 0.001), as were attitudes (β = 0.29, p < 0.001). However, males' subjective norms were not significantly related (β = 0.07, p = 0.199) to their intent to intervene. Further analysis revealed a significant interaction between gender and subjective norms (β = -0.28; p = 0.039). The TPB-based model including this moderation effect explained a significant proportion of the variance in students' intent to intervene (R² = 0.57, F(6, 766) = 168.46, p < 0.000). Interveners reported significantly greater perceived behavioral control than non-interveners for seven of the 12 intervention behaviors; more supportive subjective norms than non-interveners for six of the 12 intervention behaviors; more positive attitudes than non-interveners for only one of the 12 intervention behaviors; and greater intent to intervene in the future for six of the 12 intervention behaviors. However, differences in the three TPB variables between interveners and non-interveners were not consistent for the 12 intervention behaviors. Regarding Burn's (2009) Situational Model of Bystander Intervention, a multiple regression analysis revealed two of the five barriers were significantly related to students’ intent to intervene: the failure to take intervention responsibility barrier (β = -0.29, p < 0.001) and the failure to intervene due to audience inhibition barrier (β = -0.22, p < 0.001). The model in whole explained a large proportion of the variance (R2 = 0.25, F(5, 768) = 50.14, p < 0.000). Gender differences were also observed. For females, failure to take intervention responsibility (β = -0.23; p < 0.000) and failure to intervene due to audience inhibition (β = -0.23; p < 0.001) both had a significant, negative influence on their intent to intervene. For males, failure to take intervention responsibility (β = -0.21; p < 0.014) had a significant, negative influence on intent to intervene. Additional analysis revealed no significant interactions between gender and any of the five barriers. The TPB-based model explained a greater proportion of the variance (R2 = 0.55) compared to Situational Model of Bystander Intervention (R² = 0.25) in the multiple regression analysis using all 12 intervention behaviors. All three variables in the TPB-based model were significantly related to students’ intent, whereas only two of the five barriers were significantly related. A final multiple regression analysis was conducted using all three significant TPB variables and the two significant barriers to explain students' intent to intervene. The combined model explained a significant proportion of variance in students' intent (R² = 0.58 F(5, 756) = 206.19, p < 0.000) and significantly improved upon the TPB-based model (Δ R² = 0.03; p < 0.000). The results of this study have several implications for future research and public health practice. First, it is important to ask students about their opportunities to intervene in addition to their actual intervention behaviors because this information helps paint a clearer picture of bystander engagement. This assessment could also help identify high-risk groups: students who have greater opportunities to intervene as bystanders and/or report fewer intervention behaviors compared to their reported opportunities. Second, students may conceptualize intervention behaviors differently depending on the phase of the assault and with whom the intervention behavior requires intervening. Accordingly, programs aimed at encouraging students to intervene should take these differences into consideration. Third, the Theory of Planned Behavior, used to explain and change other health-related behaviors, can effectively be applied to help uncover determinants of pro-social bystander behaviors. Perceived behavioral control, subjective norms, and attitudes appear to be salient influences in students' intent to intervene. Therefore, bystander engagement programs should incorporate activities to heighten students' skills to intervene, change social norms that support bystander intervention, and shift attitudes toward the benefits of intervening. This study demonstrates the importance of using an established, evidenced-based theoretical framework to explain behavioral influences and strengthens the argument for continued use of theory to identify, and potentially change, salient influences in behavioral performance. Students as pro-social bystanders have the potential to make a positive impact on the reduction of sexual assault on the college campus. Although the responsibility for sexual assault rests on those who perpetrate such acts, and primary prevention strategies aimed at those demonstrating a risk for perpetration are imperative, sexual assault is a public health issue that warrants a multi-pronged approach to reduce its incidence and migrate its associated harms. Programs that engage students as pro-social bystanders have the potential to make a positive impact on the reduction of sexual assault incidence in the absence of effective primary prevention strategies. The findings of this study make a contribution to the literature examining influences of students' pro-social bystander intervention to sexual assault situations and provide suggestions for strategies to increase bystander engagement.