Habitat use by seed-eating birds: a scale-dependent approach

The seedbank in arable farmland represents an important foraging resource for birds, particularly in grassland landscapes where alternative foraging opportunities may be scarce. We used a stepwise approach to examine the importance of seed food resources for farmland birds in winter. First, results from a large-scale experiment in which seed resources were manipulated to test the notion that birds aggregate at food resources, subject to a minimum threshold level. Secondly, a multiscale approach was used to characterize habitat use at a landscape scale and how this may inform agri-environment implementation. Overall seed resources declined sharply over the winter and were relatively low in most arable fields. Large-scale declines in the arable seedbank mean that much habitat may not be of sufficient quality to support foraging bird populations through a winter. At a landscape scale, extensive analyses of breeding season abundance show that bird abundance is most influenced by arable (i.e. seed-rich) habitat in grassland landscapes. The scale at which birds respond to habitat differs between species, and is related to the extent of between-season movements. Implementation of agri-environment schemes will need to consider both the quality of habitat and the context in which it is provided if recent declines in farmland bird populations are to be reversed.     

Developmental Gene Expression in Amphioxus: New Insights into the Evolutionary Origin of Vertebrate Brain Regions, Neural Crest, and Rostrocaudal Segmentation

SYNOPSIS. Amphioxus is widely held to be the closest invertebraterelative of the vertebrates and the best available stand-infor the proximate ancestor of the vertebrates. The spatiotemporalexpression patterns of developmental genes can help suggestbody part homologies between vertebrates and amphioxus. Thisapproach is illustrated using five homeobox genes (AmphiHoxl,AmphiHox2, AmphiOtx, AmphiDll, and AmphiEri) to provide insightsinto the evolutionary origins of three important vertebratefeatures: the major brain regions, the neural crest, and rostrocaudalsegmentation. During amphioxus development, the neural expressionpatterns of these genes are consistent with the presence ofa forebrain (detailed neuroanatomy indicates that the forebrainis all diencephalon without any telencephalon) and an extensivehindbrain; the possible presence of a midbrain requires additionalstudy. Further, during neurulation, the expression pattern ofAmphiDll as well as migratory cell behavior suggest that theepidermal cells bordering the neural plate may represent a phylogeneticprecursor of the vertebrate neural crest. Finally, when theparaxial mesoderm begins to segment, the earliest expressionof AmphiEn is detected in the posterior part of each nascentand newly formed somite. This pattern recalls the expressionof the segment-polarity gene engrailed during establishmentof the segments of metameric protostomes. Thus, during animalevolution, the role of engrailed in establishing and maintainingmetameric body plans may have arisen in a common segmented ancestorof both the protostomes and deuterostomes.     

Phosphonoacetic Acid: Effect on and Disposition by Tetrahymena1

The antiviral agent phosphonoacetic acid inhibits growth of Tetrahymena thermophila at concentrations comparable to those inhibiting growth of other eukaryotic cells, with 50% inhibition at 0.5 mM phosphonoacetic acid. The compound is cytotoxk to Tetrahymena at concentrations greater than 2.0 mM. When a culture of Tetrahymena the growth of which was totally inhibited by 2.0 mM phosphonoacetic acid was diluted with fresh medium, growth resumed in an exponential, rather than synchronous, fashion. [2–¹⁴C]phosphonoacetic acid is not metabolized by Tetrahymena.     

Lack of geographic variation in anonymous nuclear polymorphisms in the American oyster, Crassostrea virginica

Comparing geographic variation of noncoding nuclear DNA polymorphisms, which presumably are neutral to natural selection, with geographic variation of allozymes is potentially a good way to detect the effects of selection on allozyme polymorphisms. A previous study of four anonymous nuclear markers in the American oyster, Crassostrea virginica, found dramatic differences in allele frequency between the Gulf of Mexico and the Atlantic Ocean. In contrast, 14 allozyme polymorphisms were fairly uniform in frequency between the two areas. This led to the conclusion that all of the allozyme polymorphisms were kept uniform in frequency by balancing selection. To test the robustness of this pattern, six additional anonymous nuclear DNA polymorphisms were surveyed in oysters from Panacea, Fla, and Charleston, S.C. on the Gulf and Atlantic coasts, respectively. Unlike the previously studied DNA markers, the six DNA polymorphisms examined here show geographic variation that is not significantly greater than that of allozymes. The reason for the discrepancy between the two sets of DNA polymorphisms is unclear.      

Growth of coniferous trees exposed to SO2 and O3 using an open-air fumigation system

Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and Sitka spruce (Picea sitchensis Bong. Carr.) were planted as 2-year-old seedlings in an open-air fumigation facility at Liphook in southern England in March 1985. The soil was a humoferric podzol of pH 4. SO₂ fumigation began in May 1987 and continued until December 1990. Long-term mean SO₂ concentrations were 4,13 and 22 nmol mo^?1. Three plots, one at each SO₂ level, were also exposed to O₃ at an average of 1–3.times the ambient level. O₃ fumigation ran from March to December 1988, May to December 1989 and February to December 1990. Each species reacted differently to treatment. Scots pine showed no growth response to either pollutant, although other work on the site demonstrated a number of deleterious effects of SO₂ on this species, including increased leaf loss and foliar injury. Stem basal diameter growth of Norway spruce was depressed in SO₂-treated plots. In contrast, extension growth of shoots of Sitka spruce increased in SO₂-treated plots, in apparent response to codeposition of NH₃-N. However, diameter growth of Sitka spruce main stems did not increase. No effects of O₃ on growth were recorded for any species.     

Performance of sampling strategies in the presence of known spatial patterns

In crop protection and ecology accurate and precise estimates of insect populations are required for many purposes. The spatial pattern of the organism sampled, in relation to the sampling scheme adopted, affects the difference between the actual and estimated population density, the bias, and the variability of that estimate, the precision. Field monitoring schemes usually adopt time‐efficient sampling regimes involving contiguous units rather than the most efficient for estimation, the completely random sample. This paper uses spatially‐explicit ecological field data on aphids and beetles to compare common sampling regimes. The random sample was the most accurate method and often the most precise; of the contiguous schemes the line transect was superior to more compact arrangements such as a square block. Bias depended on the relationship between the size and shape of the group of units comprising the sample and the dominant cluster size underlying the spatial pattern. Existing knowledge of spatial pattern to inform the choice of sampling scheme may provide considerable improvements in accuracy. It is recommended to use line transects longer than the grain of the spatial pattern, where grain is defined as the average dimension of clusters over both patches and gaps, and with length at least twice the dominant cluster size.     

A note on the distribution and abundance of puku, Kobus vardoni Livingstone, in Kasanka National Park, Zambia

This study (1994) examines the distribution and abundance of puku ( Kobus vardoni Livingstone) in Kasanka National Park (area=470 km²) Zambia, following five years of anti‐poaching control. The puku is an important 'flagship' species for the park. Most puku were confined to a limited number ( n =19) of river floodplains and dambos (total area=20·29 km²) towards the centre of the park. Large areas of 'suitable' habitat contained few, if any animals. The total population was estimated to be 613 (confidence limits=414–967) with an average density of 35·93 km⁻² on occupied sites. The population sex ratio was markedly biased towards females (mean=3·4 females to 1 male), but group sizes were similar to those recorded in other African studies. Male groups were on average (2·6), smaller than those of females (7·3). Males appeared to be particularly vulnerable to poaching. The distribution of puku reflected a patchy distribution of resources and a flexible social system. Puku numbers have increased two fold since the previous (1989) survey. Other species have faired less well. Further work is required to clarify dispersal mechanisms. Taylor's power law may provide a useful model for describing population dispersion. Kasanka is an important local refuge for this increasingly threatened species in Zambia. Metapopulation theory may be applicable to puku because of their ability to move between patches, during seasonal flooding.     

Chemical Composition of Bleeding Xylem Sap from Kiwifruit Vines

A study of the chemical composition and charge balance was madeof bleeding xylem sap collected from excised one-year-old extensionshoots of healthy, Mn-deficient, Mn-toxic and Zn-deficient kiwifruitvines (Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson)immediately prior to leafburst. The exudates were analysed formacronutrient cations and anions, trace elements, amino acids,organic acids and sugars. Major charged species measured wereCa (13.3 mM), K (8.9 mM), Mg (5.6 mM), malate (12.5 mM) andphosphate (5.8 mM). Glutamine (12 mM) was the predominant Ncarrier identified, accounting for 58 per cent of the totalN followed by NO₂^–-N (4.5 per cent), NH₄⁺-N (3.5 per cent)and arginine-N (2.9 per cent). Approximately 22 per cent ofthe N was in a hydrolysable proteinaceous fraction comprisingmainly glutamine and glutamate. Eighteen free proteinaceousamino acids were idetified in sap, the most abundant being glutamine,glutamic acid, valine, isoleucine and phenylalanine. Computersimulation of the chemical composition predicted that in additionto hydrated cations, ion pairs formed between inorganic components(SO₄^2–, HPO₄^2–, H₂PO₄^–) and cations (Ca²⁺,Mg²⁺, Mn²⁺), plus metal-organic ligand complexes (Ca Malate,Zn Malate, FeCit, CuHis, CuGln) are important species involvedin translocation. The solubility product of hydroxyapatite wasexceeded in all exudates although in vitro precipitation wasnot observed. To achieve electroneutrality with the componentsmeasured, however, formation of precipitate precursors (hydroxyapatitenuclei) had to be assumed. Irregularities in Mn nutrition (butnot Zn) were clearly indicated by the elemental compositionof exudate suggesting the use of sap analysis as a possiblepre-season indicator of nutritional status for this species. Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson, kiwifruit, xylem sap composition, trace metals, amino acids, organic acids