Loss of forb diversity in relation to nitrogen deposition in the UK: regional trends and potential controls

In this study we investigate the impact of nitrogen (N) deposition on the diversity of three different vegetation functional groups – forbs, grasses and mosses – using a field survey of acid grasslands across Great Britain. Our aim is to identify the vegetation types that are most vulnerable to enhanced N deposition, and to shed light on the mechanisms that may be driving N‐initiated species changes in the UK. Sixty‐eight randomly selected grasslands belonging to the UK National Vegetation Classification group U4 (Festuca ovina–Agrostis capillaris–Galium saxatile grassland) were studied along a gradient of atmospheric N deposition ranging from 6 to 36 kg N ha^?1 yr^?1. At each site, vegetation was surveyed and samples were taken from the topsoil and subsoil. Aboveground plant material was collected from three species: a forb, grass and moss. Both the species richness and cover of forbs declined strongly with increasing N deposition, from greater than eight species/20% cover per m² quadrat at low levels of N to fewer than two species/5% cover at the highest N deposition levels. Grasses showed a weak but significant decline in species richness, and a trend toward increasing cover with increasing N input. Mosses showed no trends in either species richness or cover. Most of the decline in plant species richness could be accounted for by the level of ammonium deposition. Soil KCl‐extractable ammonium concentration showed a significant positive correlation with N input, but there was no relationship between N deposition and extractable nitrate. In the soil O/A horizon, there was no relationship between N deposition and %N, and only a very weak positive relationship between the level of N deposition and the C : N ratio. Finally, in the vegetation, there was no relationship between N deposition and either shoot tissue N concentration or N : P ratio for any of the three reference species. Combining our regional survey with the results of published N‐addition experiments provides compelling evidence that there has been a significant decline in the species richness and cover of forbs across Great Britain, and that the primary cause is competition due to an increase in the cover of grasses in response to enhanced deposition of reactive N, primarily NH₄⁺.     

Modulation of respiratory metabolism in response to nutrient changes along a soil chronosequence

Laboratory studies indicate that plant respiratory efficiency may decrease in response to low nutrient availability due to increased partitioning of electrons to the energy‐wasteful alternative oxidase (AOX); however, field confirmation of this hypothesis is lacking. We therefore investigated plant respiratory changes associated with succession and retrogression in soils aged from 10 to 120 000 years along the Franz Josef soil chronosequence, New Zealand. Respiration rates and electron partitioning were determined based on oxygen isotopic fractionation. Leaf structural traits, foliar nutrient status, carbohydrates and species composition were measured as explanatory variables. Although soil nutrient levels and species composition varied by site along the chronosequence, foliar respiration across all sites and species corresponded strongly with leaf nitrogen concentration (r² = 0.8). In contrast, electron partitioning declined with increasing nitrogen/phosphorus (r² = 0.23) and AOX activity correlated with phosphorus (r² = 0.64). Independently, total respiration was further associated with foliar Cu, possibly linked to its effect on AOX. Independent control of AOX and cytochrome pathway activities is also discussed. These responses of plant terminal respiratory oxidases – and therefore respiratory carbon efficiency – to multiple nutrient deficiencies demonstrate that modulation of respiratory metabolism may play an important role in plant responses to nutrient gradients.     

Hunting and Gathering in Tropical Rain Forest: Is It Possible?

Hunters and gatherers living in tropical forests represent an important part of the total range of variation among contemporary hunting and gathering societies. Studies of tropical forest hunting and gathering peoples have contributed to our perceptions of the foraging way of life. Yet no peoples have ever been directly observed living independently of agriculture in tropical rain forest. This article tests the hypothesis that humans do not exist nor have ever existed independently of agriculture in tropical rain forest. We find no convincing ethnographic evidence and, with the possible exception of Malaysia, no archeological evidence for pure foragers in undisturbed tropical rain forests. Negative evidence cannot be conclusive, but it suggests that we need to carefully reexamine common assumptions concerning the recent history of tropical forest dwellers, the adaptability of preagricultural humans, the geographic and environmental range of hominids, and the form and consequences of selection pressures acting on humans in warm, humid environments. The overriding purpose of this article is to stimulate further ecological and archeological research in the neglected tropical forest areas of the world.     

Behavioral and Physiological Analyses of Ultrasound Production by Female Hamsters (Mesocricetus auratus)

The results of behavioral studies suggest specific roles forhigh-frequency vocalizations (ultrasounds) in courtship andcopulatory interactions among golden hamsters. In addition,these results, and functional interpretations based on them,can help to guide studies of physiological mechanisms controllingultrasonic communication. For example, interpretations of rodentultrasounds as sexual or agonistic signals suggest that ultrasoundrates depend on gonadal hormones. This prediction has been verifiedfor several rodent species, including hamsters. Similar reasoningshould apply to the analysis of brain mechanisms for ultrasoundproduction. In particular, the consideration of hamster ultrasoundsas sexual behaviors and vocalizations, as well as hormone-dependentresponses, suggests several brain areas as especially likelyparticipants in neural circuits mediating hormonal effects onultrasonic communication. The preliminary results of a studyin which we lesioned one of these areas, the mesencephalic centralgrey, confirm this structure's involvement in the control ofhamster ultrasounds, and, more generally, support the utilityof behavioral data in physiological studies.     

Using temperature‐dependent changes in leaf scaling relationships to quantitatively account for thermal acclimation of respiration in a coupled global climate–vegetation model

The response of plant respiration (R) to temperature is an important component of the biosphere's response to climate change. At present, most global models assume that R increases exponentially with temperature and does not thermally acclimate. Although we now know that acclimation does occur, quantitative incorporation of acclimation into models has been lacking. Using a dataset for 19 species grown at four temperatures (7, 14, 21, and 28 °C), we have assessed whether sustained differences in growth temperature systematically alter the slope and/or intercepts of the generalized log–log plots of leaf R vs. leaf mass per unit leaf area (LMA) and vs. leaf nitrogen (N) concentration. The extent to which variations in growth temperature account for the scatter observed in log–log R–LMA–N scaling relationships was also assessed. We show that thermal history accounts for up to 20% of the scatter in scaling relationships used to predict R, with the impact of thermal history on R–LMA–N generalized scaling relationships being highly predictable. This finding enabled us to quantitatively incorporate acclimation of R into a coupled global climate–vegetation model. We show that accounting for acclimation of R has negligible impact on predicted annual rates of global R, net primary productivity (NPP) or future atmospheric CO₂ concentrations. However, our analysis suggests that accounting for acclimation is important when considering carbon fluxes among thermally contrasting biomes (e.g. accounting for acclimation decreases predicted rates of R by up to 20% in high‐temperature biomes). We conclude that acclimation of R needs to be accounted for when predicting potential responses of terrestrial carbon exchange to climatic change at a regional level.     

SPICULES IN SILURIAN TABULATE CORALS FROM CANADA, AND IMPLICATIONS FOR THEIR AFFINITIES

Abstract:  Specimens of Favosites from upper Llandovery strata of Anticosti Island show three types of calcite structures, herein interpreted as spicules, preserved within their calices and on top of the last tabula. This is stratigraphically younger material, some 50 m higher than fossils described two decades earlier, in which calcified polyps, each with 12 retracted tentacles, were noted. These more recently found structures show striking similarities in form and position to point, collaret and capstan spicules found in the soft tissues of modern pipe corals, i.e. the Octocorallia (Alcyonacea). Where preserved in a distinct pattern on top of the calcite tabulae, the spicular sclerites in Favosites occur in a particular sequence. Twelve individual, or sometimes six pairs of, triradiate point spicules have shrunk to a circlet near the middle of the calice (resting on the last, outermost, tabula). Surrounding the point spicules are 3–6 circlets of curved, usually perforated, lenticular collaret spicules; and surrounding these are scattered, much smaller, capstan spicules. The spicules display variability, probably ontogenetic, in their form and relative sizes; and they are more similar in form to calcareous spicules of alcyonacean corals than to those known from calcareous sponges. Structures with 12-fold radial symmetry in Heliolites, originally described by one of us as 'septal florets', consist of elements that are considered comparable with the point spicules found in Favosites . They have been recognized in ten species of Heliolites from Silurian (Wenlock–Ludlow) strata in the Canadian Arctic islands.     

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.