Can increased niche opportunities and release from enemies explain the success of introduced Yellowhammer populations in New Zealand?

Some introduced species succeed spectacularly, becoming far more abundant in their introduced than in their native range. 'Increased niche opportunities' and 'release from enemy regulation' are two hypotheses that have been advanced to explain the enhanced performance of introduced species in their new environments. Using an introduced bird species, the Yellowhammer Emberiza citrinella , which was first released in New Zealand in 1862, as a model, we tested some predictions based on these hypotheses. By quantifying habitat availability and quality, and measuring nest predation rates, we investigated whether increased niche opportunities or release from nest predation could explain the higher density of the Yellowhammer in New Zealand farmland, compared to farmland in their native Britain. Yellowhammer territory densities were over three times higher in New Zealand (0.40 territories per ha) than in comparable British farmland (0.12 territories per ha), and Yellowhammer densities remained significantly higher in New Zealand, after accounting for differences in habitat availability. The density and diversity of invertebrates, a key food resource for nestling Yellowhammers, was significantly lower in New Zealand than in Britain. Hence, these aspects of niche availability and quality cannot explain the higher density of Yellowhammers in New Zealand. Nest predation rates in New Zealand were similar to those in Britain, suggesting that release from nest predation also could not account for the higher density of Yellowhammers in New Zealand. Differences in winter survival, due to differences in winter food supply or the severity of the winter climate, along with release from other types of 'enemy' regulation are possible alternative explanations.     

The abundance,distribution and structural characteristics of tree‐holes in Nothofagus forest,New Zealand

Tree‐holes provide an important microhabitat that is used for feeding, roosting and breeding by numerous species around the world. Yet despite their ecological importance for many of New Zealand's endangered species, few studies have investigated the abundance or distribution of tree‐holes in native forests. We used complementary ground and climbed tree surveys to determine the abundance, distribution and characteristics of tree‐holes in undisturbed Nothofagus forest in the Lewis Pass, New Zealand. We found that hole‐bearing trees were surprisingly abundant compared with many other studies, including Australian Eucalyptus species and American beech. In fact, we estimated as many as 3906 tree‐holes per hectare, of which 963 holes per hectare were potentially large enough to provide roost sites for hole‐nesting bats in New Zealand, while only eight holes per hectare were potentially suitable for specialist hole‐nesting birds. This was of great interest as primary cavity‐excavating animals are absent from New Zealand forests, compared with North America and Australia. Moreover, tree‐hole formation in New Zealand is likely to be dominated by abiotic processes, such as branch breakage from windstorms and snow damage. As has been found in many other studies, tree‐holes were not uniformly distributed throughout the forest. Tree‐holes were significantly more abundant on the least abundant tree species, Nothofagus fusca, than on either N. menziesii or N. solandri. In addition to tree species, tree size was also an important factor influencing the structural characteristics of tree‐holes and their abundance in this forest. Moreover, these trends were not fully evident without climbed tree surveys. Our results revealed that ground‐based surveys consistently underestimated the number of tree‐holes present on Nothofagus trees, and illustrate the importance of using climbed inspections where possible in tree‐hole surveys. We compare our results with other studies overseas and discuss how these are linked to the biotic and abiotic processes involved in tree‐hole formation. We consider the potential implications of our findings for New Zealand's hole‐dwelling fauna and how stand dynamics and past and future forest management practices will influence the structural characteristics of tree‐holes and their abundance in remnant forest throughout New Zealand.     

Some new Darwin vascular plant specimens from the Beagle voyage

This paper reports 24 newly discovered specimens of 21 species made by Charles Darwin in Argentina, Australia, Brazil, Chile, Ecuador and Uruguay while on the 1831–1836 voyage of HMS Beagle. They have been found in Cambridge University Herbarium and the herbaria of the Missouri Botanical Garden, Natural History Museum, London, New York Botanical Garden and the Royal Botanic Gardens, Kew, since the earlier publications of Porter. Included are type specimens of Calceolaria darwinii (isotype; = C. uniflora), Cuscuta gymnocarpa (holotype and isotypes), C. sandwichiana var. mimosae (isolectotypes = C. gymnocarpa), Ephedra frustillata (lectotype and isolectotypes), Ourisia breviflora (isolectotype), Polypodium paleaceum (syntype?; = Ctenitis sloanei) and Urera gaudichaudiana (holotype; = Laportea aestuans). © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 12–18.     

Nucleotides and related compounds in bracken

The role of sugar nucleotides in polysaccharide synthesis is discussed. The presence of acid soluble nucleotides in bracken rhizomes was demonstrated (20 μmol/kg fresh weight) and the uridine series was shown to predominate accounting for some 80% of the total. The following were identified, UDP-glucose (60%), UDP-galactose (15%), UDP-xylose (9%), UDP-arabinose (3%), UDP-glucuronic acid (4%), GDP-mannose (6%) and GDP-fucose (3%). It is probable that these sugar nucleotides supply the full complement of sugars identified in the carbohydrate fractions of bracken.     

A new rhizomatous Oryza species (Poaceae) from Sri Lanka

VAUGHAN, D. A., 1990. A new rhizomatous Oryza species (Poaceae) from Sri Lanka. The confusing taxonomy of the Sri Lankan Oryza officinalis complex is clarified with the recognition of a new rhizomatous species, Oryza rhizomatis Vaughan. This species has been found across the dry zone. The other species of the complex in Sri Lanka, O. eichingeri , occurs in moist habitats and is smaller and less common than 0. rhizomatis. The new species is described.     

Ontogeny of intersexual head shape and prey selection in the pitviper Agkistrodon piscivorus

Different animal intraspecific classes commonly differ in their prey selection. Such differences in feeding ecology are thought to reduce resource competition between classes, but other factors (i.e. behavioural, morphological, and physiological differences) also contribute to this widespread phenomenon. Although several studies have correlated the size of the feeding apparatus with prey selection in many animals, few studies have examined how the shape of the feeding apparatus is related to prey selection. Furthermore, even though the dietary regimen of many animals changes during ontogeny, few studies have examined how shape changes in the feeding apparatus may be related to these ontogenetic dietary shifts. Here we address these issues by examining how head shape, head size and prey selection change over ontogeny in adult males, adult females and juveniles of the cottonmouth snake Agkistrodon piscivorus . Our scaling data for head characteristics showed that all head measurements in adult male and female A. piscivorus scaled with significant negative allometry, whereas juvenile head measurements typically scaled isometrically, except for head volume (positive) and head length (negative). Thus, juveniles have relatively broad and high, but short, heads. Large adult male and female A. piscivorus have relatively small head dimensions overall. Thus, juveniles appear to undergo a rapid change in head volume, which subsequently slows considerably as sexual maturity is achieved. However, our multivariate analysis of size-adjusted head dimensions showed that juveniles differed only slightly in their head shape compared with adult male and female A. piscivorus . In general, prey size increased with snake size across all age and sex groups, but an ontogenetic shift in prey type was not detected in either males or females.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 151–159.     

THE EFFECT, ON OYSTER SPATFALL, OF CONTROLLING BARNACLE SETTLEMENT WITH DDT

During the summer of 1955 experiments were made with DDT to control barnacle fouling of oyster spat collectors. Results showed that effective control of barnacles on artificial collectors doubled the yield of oyster spat. Shell cultch treated in the same way gave less conclusive results, partly because of the poor spatfall experienced.
Oyster spat on treated artificial collectors were approximately 40% bigger, at the end of 2 1/2 months, than those on controls. Evidence from shells, however, indicated that DDT initially inhibited the growth of oyster spat. Apparently spat become stunted in natural conditions, because they are unable to compete effectively for food with the dense barnacle populations. Competition amongst barnacles themselves also causes stunting.
The dense population of Elminius modestus on the east coast oyster grounds may have a long-term effect on both the yield and growth of oysters.     

Frequency-dependent selection on aposematic prey: some experiments

Experiments to measure the strength of frequency-dependent selection on dimorphic populations of distasteful, brightly coloured prey were carried out, using pastry cylinders as prey and wild birds as predators. When the two forms were haphazardly intermingled, the birds took a relative excess of whichever form happened to be the rarer if all prey in the population were distasteful but selected the forms independently of frequency if they were all neutral in flavour. They did not take an excess of the rarer form from populations of distasteful prey when that form was distributed in a single clump rather than evenly dispersed among the commoner form. This confirms the expectation that rarer forms of aposematic animals are at a frequency-dependent disadvantage when they are intermingled with commoner forms but not when they occur in clusters.