Density Patterns of Piper Ant-Plants and Associated Arthropods: Top-Predator Trophic Cascades in a Terrestrial System?1

Top-predator (fourth-trophic-level) controlled trophic cascades are thought to be uncommon in terrestrial systems, but actual quantitative tests and comparisons of bottom-up and top-down forces in systems with more than three linear trophic levels are rare. Here, we describe the density patterns of the arthropod community associated with Piper ant-plants in Costa Rican wet forests. Consumers in this community comprise a complex, interacting web of herbivores, predaceous ants, and predators of ants. Although the hollow stems and petioles of the Piper plants provide some protection to resident ants from predation, specialized Dipoena spiders and Phyllobaenus beetles exploit Pheidole ants inhabiting Piper plants. We report abundance patterns of plants, ants and predators in four forests. These patterns of abundance are consistent with predictions of top-down cascades across four trophic levels when the top predators are effective (beetles). We discuss how top-down and bottom-up forces may interact in systems with less effective top predators (spiders).     

Seedling and Sprout Response to Slash-and-Burn Agriculture in a Tropical Deciduous Forest1

Survival and growth of seedlings and sprouts were assessed in three plots for 16 mo following the slashing and burning of a tropical deciduous forest in Jalisco, Mexico. We encountered a total of 47 species: 21 seedling species and 35 sprout species. Calliandra formosa and Piptadenia flava were the most common seedling species; Bursera arborea, Cordia alliodora, and Piptadenia constricta were the most common sprouts. Colubrina triflora, Diphysa occidentalis, and Cnidoscolus spinosus had limited sprouting ability. Twenty-six species were represented by one seedling or one sprout. Thirty-eight percent of the seedlings were tree species, 59 percent were shrub species, and 2 percent were vines species. In contrast, 86 percent of the sprouts were from trees and 13 percent from shrubs. One year after the initial measurements, 29 percent of the seedlings and 13 percent of the sprouts were dead. Each of the seedling means (number of stems/individual, height and diameter of the tallest stem, and elliptical crown area) was significantly smaller (P < 0.05) than that of sprouts at all three measurement periods, but relative growth rates were similar. Total canopy area of seedlings had a larger relative increase than did the canopy area of sprouts. The presence of seedlings increased species diversity compared to calculated diversity excluding seedlings. Timing of fruit dispersal in relation to the date of burning and the high number of Leguminosae species in the forest appeared to favor seedling establishment for some species.     

Litter in a first–order stream of a temperate deciduous forest (Margaraça Forest, central Portugal)

To evaluate the importance and fate of organic matter inputs in forested streams, we determined the litterfall inputs and the benthic coarse particulate organic matter (CPOM) in one headwater stream flowing through a mixed deciduous forest, during one year. Both vertical traps and the stream bottom were sampled monthly. The material collected was sorted into four main categories: leaves, fruits and flowers, twigs and debris. Litter production was 715 g m−2 y−1 and seasonal, with 73% of the annual total during October–December (autumn). Leaves comprised the largest litter component. Benthic organic matter was 1880 g m−2 y−1, and was also seasonal. Highest accumulation was attained in spring, and twigs and branches comprised the major component. This revised version was published online in July 2006 with corrections to the Cover Date.     

Long-term change in an unmanaged population of wych elm subjected to Dutch elm disease

1 Changes in a population of Ulmus glabra in Lady Park Wood (UK), a mixed deciduous native woodland, were studied by means of permanent transects. All individuals reaching 1.3 m height were recorded at irregular intervals from 1945 to 1993.
2 Dutch elm disease struck this population in about 1972. Most of the canopy and subcanopy stems were killed, but a few, slow-growing, subcanopy individuals survived unscathed.
3 Subsequent seedling regeneration and growth of sprouts from rootstocks of infected trees was substantial and vigorous. Twenty-three years after the outbreak of disease the number of elm individuals had increased by about 40%. Disease has, however, continued to afflict vigorous, exposed individuals.
4 The large-scale distribution of elm has been unaffected, but the small-scale pattern has changed due to the concentration of seedling regeneration in gaps.
5 The elm population appears to be differentiating into (i) a large high-turnover subpopulation of fast-growing, but repeatedly diseased maiden individuals and sprouts, and (ii) a small, low-turnover subpopulation of slow-growing individuals rooted in suboptimally dry, secluded sites.     

Phosphorus compartmentation in Pinus serotina Michx. (pond pine); observations from in vivo nuclear magnetic resonance spectroscopy

³¹P nuclear magnetic resonance (NMR) spectroscopy was used to estimate the amount of inorganic phosphate (Pi) present in the cytoplasm and vacuole of root tips and subapical root segments of pond pine ( Pinus serotina Michx.). In root tips of seedlings grown with 100 mmol m^–3P (HP) the cytoplasmic Pi content, on a root volume basis, was ≈ 1·5 μ mol cm^–3 and the vacuolar Pi content, on a root volume basis, was ≈ 3·4 μ mol cm^–3. In root tips from Pi starved seedlings the cytoplasmic Pi content, on a root volume basis, was ≈ 0·75 μ mol cm^–3; vacuolar Pi was too low to be reliably estimated. Similar results were obtained with subapical root segments; the Pi concentration in the cytoplasm was maintained at around 2 mol m^–3 while that in the vacuole varied with Pi supply. This work demonstrates for the first time that quantitative measurements of the subcellular compartmentation of Pi can be made in young tissues of a woody species. The results indicate that cytoplasmic Pi levels are maintained across a range of external Pi supplies probably by withdrawing Pi stored in the vacuole.     

Bird–mammal associations in forest openings of northern Congo (Brazzaville)

Resident and migrant birds and several mammal species utilize natural forest openings to exploit foraging opportunities that are otherwise rare or absent in the dense forest of equatorial Africa. Certain bird species exhibit protocooperative and commensal relationships with these mammals. In a large marshy opening, five species of birds exploited the actions of large terrestrial mammals to flush prey, two species of birds used two species of aquatic mammals to expose prey, and another bird species fed directly on mammalian ectoparasites. African jacanas had a higher foraging rate when associated with gorillas and elephants than when alone, and great egrets had a higher capture efficiency when elephants were present. In a second opening, covered by a shallow, algae-laden pond, African jacanas, finfeet, and Hartlaub's ducks competed to remove arthropod ectoparasites from forest buffalo and bongo antelope, both of which consistently reacted to the alarm calls of jacanas and Hartlaub's ducks. At least ten species of birds directly benefit from associations with mammals. Indirect benefits were also noted as African jacanas, black crakes, and palm-nut vultures selected food items from elephant and buffalo dung.     

Synthetic Peptide Fragments as Probes for Structure Determination of Potassium Ion-Channel Proteins

Potassium channels are a diverse class of transmembrane proteins that are responsible for diffusion of potassium ion across cell membranes. The lack of large quantities of these proteins from natural sources, is a major hindrance in their structural characterization using biophysical techniques. Synthetic peptide fragments corresponding to functionally important domains of these proteins provide an attractive approach towards characterizing the structural organization of these ion-channels. Conformational properties of peptides from three different potassium channels (Shaker, ROMK1 and minK) have been characterized in aqueous media, organic solvents and in phospholipid membranes. Techniques used for these studies include FTIR, CD and 2D-NMR spectroscopy. FTIR spectroscopy has been a particularly valuable tool for characterizing the folding of the ion-channel peptides in phospholipid membranes; the three different types of potassium channels all share a common transmembrane folding pattern that is composed of a predominantly -helical structure. There is no evidence to suggest the presence of any significant -sheet structure. These results are in excellent agreement with the crystal structure of a bacterial potassium channel (Doyle, D. A. et al. (1998) Science 280:69–77), and suggest that all potassium channel proteins may share a common folding motif where the ion-channel structure is constructed entirely from -helices.     

Ecophysiological responses of Japanese forest tree species to ozone, simulated acid rain and soil acidification

In this review, I summarized the results obtained from experimental studies on the ecophysiological responses of Japanese forest tree species to O₃, simulated acid rain and soil acidification. Based on the studies conducted in Japan, exposure to ambient levels of O₃ below 100 nl·l⁻¹ (ppb) for several months is sufficient to inhibit dry matter production and net photosynthesis of sensitive Japanese forest tree species such as Siebold's beech and Japanese zelkova. On the other hand, exposure to simulated acid rain with a pH of 4.0 or above for several months cannot induce any adverse effects on dry matter production and physiological functions of Japanese forest tree species. However, when the pH of simulated rain or fog is lowered below 4.0, negative effects appear on dry matter production and physiological functions such as transpiration in several sensitive Japanese forest tree species such as Japanese fir and Nikko fir. Based on limited information, it may be concluded that (1) Al dissolved into soil solution is the most important limiting factor for dry matter production, physiological functions and nutrient status of Japanese forest tree species grown in acidic soil, (2) the (Ca+Mg+K)/Al molar ratio in soil solution is a useful indicator to evaluate and predict the effects of soil acidification due to acid deposition on whole-plant dry matter production of Japanese forest tree species at the present time and in the future, and (3) Japanese coniferous tree species such as Japanese cedar and red pine are relatively sensitive to a reduction in (Ca+Mg+K)/Al molar ratio in soil solution compared with European forest tree species such as Norway spruce.     

Sequence-specific 1H assignment and secondary structure of the bacteriocin AS-48 cyclic peptide

The bacteriocin AS-48 is a cationic peptide (7149 Da) having a broad antimicrobial spectrum, encoded by the 68 kb conjugative plasmid pMB2 from Enterococcus faecalis S-48. It is a unique peptide since it has a cyclic structure, which is achieved by the formation of a tail–head peptide bond after ribosomal synthesis (Gálvez et al., 1989; Martínez-Bueno et al., 1994; Samyn et al., 1994). Preliminary CD and calorimetric studies (data not shown) pointed towards a highly helical and very stable three dimensional structure.All the information gathered until now indicates that the target of AS-48 is the cytoplasmic membrane in which it opens channels or pores, leading to dissipation of the proton motive force and cell death, which in some cases is also followed by bacterial lysis (Gálvez et al., 1991). This peptide is a suitable tool for studying protein–membrane interactions, and it also offers promising perspectives for biotechnological applications.Knowledge of the 3D structure of AS-48 is a first step in the conduct of further structure–function studies. Here we report the complete¹ H NMR assignment of its proton resonances together with the resulting secondary structure pattern as prerequisites for the determination of a high-resolution 3D solution structure.