Experimental evidence for the attenuating effect of SOM protection on temperature sensitivity of SOM decomposition

The ability to predict C cycle responses to temperature changes depends on the accurate representation of temperature sensitivity (Q₁₀) of soil organic matter (SOM) decomposition in C models for different C pools and soil depths. Theoretically, Q₁₀ of SOM decomposition is determined by SOM quality and availability (referred to here as SOM protection). Here, we focus on the role of SOM protection in attenuating the intrinsic, SOM quality dependent Q₁₀. To assess the separate effects of SOM quality and protection, we incubated topsoil and subsoil samples characterized by differences in SOM protection under optimum moisture conditions at 25 °C and 35 °C. Although lower SOM quality in the subsoil should lead to a higher Q₁₀ according to kinetic theory, we observed a much lower overall temperature response in subsoil compared with the topsoil. Q₁₀ values determined for respired SOM fractions of decreasing lability within the topsoil increased from 1.9 for the most labile to 3.8 for the least labile respired SOM, whereas corresponding Q₁₀ values for the subsoil did not show this trend (Q₁₀ between 1.4 and 0.9). These results indicate the existence of a limiting factor that attenuates the intrinsic effect of SOM quality on Q₁₀ in the subsoil. A parallel incubation experiment of ¹³C‐labeled plant material added to top‐ and subsoil showed that decomposition of an unprotected C substrate of equal quality responds similarly to temperature changes in top‐ and subsoil. This further confirms that the attenuating effect on Q₁₀ in the subsoil originates from SOM protection rather than from microbial properties or other nutrient limitations. In conclusion, we found experimental evidence that SOM protection can attenuate the intrinsic Q₁₀ of SOM decomposition.     

Diurnal Habitat Use by Lower Keys Marsh Rabbits

Abstract: We used radiotelemetry to locate daytime forms of endangered Lower Keys marsh rabbits (LKMRs; Sylvilagus palustris hefneri) throughout their range so we could determine habitat characteristics of diurnal cover. We typically found forms (n = 1,298) of 36 rabbits in brackish wetlands in patches of saltmarsh or buttonwoods. In freshwater wetlands, forms (n = 54) were located most often in patches of freshwater hardwoods embedded in or adjacent to freshwater marshes. Forms (n = 942) in brackish wetlands were characterized by thick groundcover (>75%), whereas those (n = 42) in freshwater wetlands had both thick groundcover and canopy vegetation. The mean minimum convex polygon around forms of 15 rabbits was 1.4 ha (SD = 1.7), with smaller ranges characterized by thick bunchgrasses or clump-forming sedges. To increase the amount of annual space usable by LKMRs, managers should provide more saltmarsh habitat interspersed with buttonwoods and enhance ground cover in existing habitat.     

Texas Latino College Student Attitudes Toward Natural Resources and the Environment

Abstract: Latinos in the United States are an increasing segment of the population and are becoming important stakeholders in the management of natural resources. Although Latinos have been included in attitudinal research on environmental concerns, few studies have focused exclusively on Latino attitudes toward natural resources and the environment. We surveyed Texas college and university students of Mexican descent (n = 635) to determine their environmental concerns. Using the New Ecological Paradigm (NEP), we determined an environmental concern score for each respondent and compared this index to several demographic variables. We found that gender, a political candidate's environmental position, mother's education, combined parental income, and, to a lesser degree, the number of grandparents born in the United States and religiosity (church attendance), were important model variables. We hypothesized that acculturation would be an important factor in predicting NEP scores; however, acculturation level was not an important predictor in our study, which we attribute to both the nature of our sample (i.e., highly acculturated college students) and small sample sizes of less-acculturated college students. We recommend that future research consider determining the importance of acculturation in Latino attitudes toward natural resources and the environment.     

Habitat Use of Fox Squirrels in an Urban Environment

Abstract: Tree squirrels are one of the most familiar mammals found in urban areas and are considered both desirable around homes and, conversely, a pest. We examined fox squirrel (Sciurus niger) habitat use in inner city and suburban areas using radiotelemetry. We estimated habitat selection ratios at differing scales by season and fox squirrel activity. Telemetry data suggests that during periods of inactivity radiocollared fox squirrels (n = 82) selected 1) areas with greater tree canopy, 2) live oaks (Quercus fusiromis and Q. virginiana), and 3) trees with larger diameters and canopies. When inactive during the winter and spring, fox squirrels also preferred, within their core areas, to use the inside of buildings, and during periods of activity in the autumn and spring, fox squirrels preferred grassy areas. During periods of activity, fox squirrels avoided using pavement but did not exclude it from their core-area movements. Fox squirrels' ability to use buildings and to tolerate pavement in core-area movements make vast areas of the urban environment available to fox squirrels. In evaluating habitat variables that increased fox squirrel activity in urban areas, we found the number of large and medium trees, amount of pavement and grassy areas, canopy cover, number of oaks, and the area covered by buildings were all important factors in predicting fox squirrel activity in an urban environment. Our data suggests urban planners, animal damage control officials, wildlife managers, and landscapers who want to control urban fox squirrel populations through habitat manipulation should consider the reduction of oaks trees, a reduction of the canopy cover, and restricting the access of fox squirrels to buildings. Alternatively, home owners and squirrel enthusiasts hoping to bolster fox squirrel populations in urban areas should consider increasing the number of large mast—bearing trees and canopy cover and providing nest boxes.     

Climate‐growth analysis for a Mexican dry forest tree shows strong impact of sea surface temperatures and predicts future growth declines

Tropical forests will experience relatively large changes in temperature and rainfall towards the end of this century. Little is known about how tropical trees will respond to these changes. We used tree rings to establish climate‐growth relations of a pioneer tree, Mimosa acantholoba, occurring in tropical dry secondary forests in southern Mexico. The role of large‐scale climatic drivers in determining interannual growth variation was studied by correlating growth to sea surface temperature anomalies (SSTA) of the Atlantic and Pacific Oceans, including the El Niño‐Southern Oscillation (ENSO). Annual growth varied eightfold over 1970–2007, and was correlated with wet season rainfall (r=0.75). Temperature, cloud cover and solar variation did not affect growth, although these climate variables correlated with growth due to their relations with rainfall. Strong positive correlations between growth and SSTA occurred in the North tropical Atlantic during the first half of the year, and in the Pacific during the second half of the year. The Pacific influence corresponded closely to ENSO‐like influences with negative effects of high SSTA in the eastern Pacific Niño3.4 region on growth due to decreases in rainfall. During El Niño years growth was reduced by 37%. We estimated how growth would be affected by the predicted trend of decreasing rainfall in Central America towards the end of this century. Using rainfall predictions of two sets of climate models, we estimated that growth at the end of this century will be reduced by 12% under a medium (A1B) and 21% under a high (A2) emission scenario. These results suggest that climate change may have repercussions for the carbon sequestration capacity of tropical dry forests in the region.     

The Effect of Different Levels of N Limitation on Sugars, Amino Acids, Growth and Biomass Partitioning in Broadbean (Vicia faba L.)

Broadbean plants (Vicia faba L.) were submitted to three differentlevels of steady state N limitation. Relative addition ratesof N were 0.06, 0.1 and 0.14d^-1. Plants were harvested at fiveevenly distributed times over a 2d period. Shoot growth correspondedwell with the imposed treatment. Root growth, relative to shootgrowth, was highest at the 0.06d^-1treatment. Diurnal patternsof soluble sugars, amino acids and starch were analysed. Onaverage, soluble sugar levels were highest in the plants ofthe 0.06d^-1treatment whereas average free amino acid levelswere highest in the 0.14d^-1treatment. Shoot growth increasedas the concentration of shoot amino acids increased. No suchcorrelation however could be found between root growth and freesugar levels in the root. Broadbean; Vicia faba L.; exponential addition; N limitation; free sugar; amino acids; diurnal cycle; functional equilibrium; starch     

A novel indirect defence in Brassicaceae: Structure and function of extrafloral nectaries in Brassica juncea

While nectaries are commonly found in flowers, some plants also form extrafloral nectaries on stems or leaves. For the first time in the family Brassicaceae, here we report extrafloral nectaries in Brassica juncea. The extrafloral nectar (EFN) was secreted from previously amorphic sites on stems, flowering stalks and leaf axils from the onset of flowering until silique formation. Transverse sections at the point of nectar secretion revealed a pocket‐like structure whose opening was surrounded by modified stomatal guard cells. The EFN droplets were viscous and up to 50% of the total weight was sugars, 97% of which was sucrose in the five varieties of B. juncea examined. Threonine, glutamine, arginine and glutamate were the most abundant amino acids. EFN droplets also contained glucosinolates, mainly gluconapin and sinigrin. Nectar secretion was increased when the plants were damaged by chewing above‐ and belowground herbivores and sap‐sucking aphids. Parasitoids of each herbivore species were tested for their preference, of which three parasitoids preferred EFN and sucrose solutions over water. Moreover, the survival and fecundity of parasitoids were positively affected by feeding on EFN. We conclude that EFN production in B. juncea may contribute to the indirect defence of this plant species.     

The importance of canopy complexity in shaping seasonal spider and beetle assemblages in saltmarsh habitats

1. Habitat structure, including vegetation structural complexity, largely determines invertebrate assemblages in semi‐natural grasslands. The importance of structural complexity to the saltmarsh invertebrate community, where the interplay between vegetation characteristics and tidal inundation is key, is less well known. 2. It was hypothesised that canopy complexity would be a more important predictor of spider and beetle assemblages than simple vegetation attributes (e.g. height, community type) and environmental variables (e.g. elevation) alone, measured in two saltmarsh regions, south‐east (Essex) and north‐west (Morecambe Bay) U.K. Canopy complexity (number of non‐vegetated ‘gaps’ in canopy ≥ 1 mm wide) was assessed using side‐on photography. Over 1500 spiders and beetles were sampled via suction sampling, winter and summer combined. 3. In summer, saltmarshes with abundant spider and beetle populations were characterised by high scores for canopy complexity often associated with tussocky grass or shrub cover. Simple vegetation attributes (plant cover, height) accounted for 26% of variation in spider abundance and 14% in spider diversity, rising to 46% and 41%, respectively, with the addition of canopy complexity score. Overwintering spider assemblages were associated with elevation and vegetation biomass. Summer beetle abundance, in particular the predatory and zoophagous group, and diversity were best explained by elevation and plant species richness. 4. Summer canopy complexity was identified as a positive habitat feature for saltmarsh spider communities (ground‐running hunters and sheet weavers) with significant ‘added value’ over more commonly measured attributes of vegetation structure.     

Effects of US 1 Project on Florida Key Deer Mortality

ABSTRACT Approximately 26% of annual mortality for the endangered Florida Key deer (Odocoileus virginianus clavium) occurs as deer-vehicle collisions (DVCs) on the 5.6-km section of United States Highway 1 (US 1) on Big Pine Key (BPK), but extensive urban development adjacent to sections of US 1 complicates efforts to reduce DVCs. Our objective was to evaluate the effectiveness of the US 1 Project (continuous 2.6-km system of 2.4-m fencing, 2 underpasses, and 4 experimental deer guards constructed on US 1 on BPK) in reducing DVCs along US 1. Deer used the underpasses all 3 postproject years (2003–2005); however, we observed higher underpass use in 2004 and 2005 compared to 2003. Exclusion fencing reduced deer intrusions onto the fenced section of US 1 during the 3-year period (2003, n = 7 deer; 2004, n = 4; 2005, n = 12). With a reduction of deer intrusions onto this section of US 1, DVCs decreased in the fenced area by 73–100%; however, US 1 DVCs within the unfenced sections of US 1 also increased (40%) as expected. In controlling for effects of increasing deer density and traffic volume, study results suggest that highway improvements have decreased the net risk of DVCs along US 1, which indicates that use of deer fencing, deer guards, and underpasses is applicable in other urban communities experiencing unacceptable levels of DVCs.     

Distribution and Abundance of Endangered Florida Key Deer on Outer Islands

ABSTRACT Status assessment of endangered Florida Key deer (Odocoileus virginianus clavium) is currently limited by a paucity of information regarding population estimates for outer islands, which collectively comprise approximately 70% of potential habitat within the Key deer range. Practical limitations and financial considerations render traditional survey techniques impractical for application on remote outer islands. Our objective was to evaluate the utility of infrared-triggered cameras to estimate Key deer abundance on outer islands. We used digital infrared-triggered cameras and mark-resight methods to estimate Key deer abundance on 20 outer islands. Abundance estimates for primary subpopulations ranged from 15 to 16 for Howe Key, 5 to 10 for Knockemdown complex, and 13 to 17 for Little Pine Key. Other island complexes such as Ramrod Key, Water Key, and Annette complex maintain only small subpopulations (i.e., ≤5 individuals) and other previously inhabited island complexes (e.g., Johnson complex and Summerland Key) no longer maintain subpopulations. Key deer abundance was well below estimated carrying capacities on all outer islands, with larger natural populations occurring closest to Big Pine Key. Our results suggest that camera-based surveys offer a practical method to monitor abundance and population trends of Key deer on outer islands. Our study is the first to estimate Key deer abundance in these areas using technically structured model-based methods and provides managers with current and baseline information regarding Key deer subpopulations.