Differential responses of UK upland plants to nitrogen deposition

Native upland species, Nardus stricta , Eriophorum vaginatum , Erica cinerea and Vaccinium vitis-idaea were given 3 or 60 kg N ha⁻¹ yr⁻¹, over 2 yr, applied as a mist (NH₄NO₃). The high N treatment increased above-ground biomass in all four species, but only significantly in E. cinerea , E. vaginatum and N. stricta . Biomass increases in E. vaginatum and N. stricta resulted from enhanced tiller production rather than shoot elongation. Root growth increased in N. stricta , so that root:shoot ratio in this species was unchanged by N. Root growth in E. vaginatum , E. cinerea and V. vitis-idaea did not respond to N and their root:shoot ratios decreased. Tissue N concentrations increased in both shoots and roots of all species in response to N. The accumulated foliar N did not increase the proportion of N allocated to Rubisco and the photosynthetic capacities of N. stricta , E. vaginatum and V. vitis-idaea were unchanged. Thus growth responses to N were due to altered allocation rather than increased rate of photosynthesis per unit leaf area. The high N treatment increased flower production significantly in E. cinerea but not in the other species. Although in this experiment dwarf shrubs were more responsive than graminoids to N, in the field at current N inputs the enhanced tillering of the graminoids may be more competitively advantageous, especially where gaps develop in the canopy. Thus increasing N deposition may lead to increased grassiness of upland heath, and in particular, a spread of N. stricta .     

A revision of the western Palaearctic species of Urophora Robineau-Desvoidy (Diptera: Tephritidae)

Abstract A key is provided to twenty-four western Palaearctic species of Urophora Robineau-Desvoidy. The hosts of twenty-three species which attack Asteraceae are listed, including those being used or investigated as possible weed biocontrol agents. The species are divided into four species groups and the differing host relationships and types of galls induced by these groups are discussed. U.lopholomae sp.n. and U.affinis ssp. calcitrapae ssp.n., associated with Centaurea (Lopholoma) spp. and C. (Calcitrapa) spp. respectively, are described. U. algerica (Hering) and U.sjumorum (Rohdendorf) are both treated as subspecies of U. quadrifasciata (Meigen). U.pontica is given full specific status and U.hispanica is removed from synonymy. The following new synonymies are made (junior synonyms in parentheses): U. angustifascia (Hering) (= Euribia phaeocera Hering); U. cardui (Linnaeus) (= U. reaumurii Robineau-Desvoidy, lectotype designated); U. jaceana (Hering) (= E.conyzae Hering); U.maura (Frauenfeld) (= E. tecta Hering); U. mauritanica Macquart (= U. lejura Rondani, Trypeta macrura Loew); U.solstitialis (Linnaeus) (= E.sonderupi Hering, U. veruata Rondani ); U.stylata (Fabricius) (= E.pia Hering, U. vulcaanica Rondani); U. terebrans (Loew) (= E. approximata Hering, T. eriolepidis Loew, E. manni Hendel). The possibility that U. quadrifasciata is a species complex is discussed; it is also suggested that U.affinis and U.jaceana represent the morphological extremes of a complex. The misuse of the name Musca stylata Fabricius in the genus Myopites Blot is noted.     

Herbivory-induced signalling in plants: perception and action

Plants and herbivores have been interacting for millions of years. Over time, plants have evolved mechanisms to defend against herbivore attacks. Herbivore-challenged plants reconfigure their metabolism to produce compounds that are toxic, repellant or anti-digestive for the herbivores. Some compounds are volatile signals that attract the predators of herbivores. All these responses are tightly regulated by a signalling network triggered by the plant's perception machinery. Several compounds that specifically elicit herbivory-induced responses in plants have been isolated from herbivore oral secretions and oviposition fluids. Elicitor perception is rapidly followed by cell membrane depolarization, calcium influx and mitogen-activated protein kinase (MAPK) activation; plants also elevate the concentrations of reactive oxygen and nitrogen species, and modulate phytohormone levels accordingly. In addition to these reactions in the herbivore-attacked regions of a leaf, defence responses are also mounted in unattacked parts of the attacked leaf and as well in unattacked leaves. In this review, we summarize recent progress in understanding how plants recognize herbivory, the involvement of several important signalling pathways that mediate the responses to herbivore attack and the signals that transduce local into systemic responses.     

Sensory feedback in the control of mouthpart movements in the desert locust Schistocerca gregaria

ABSTRACT. When imposed movements were applied to one or both mandibles of the desert locust, Schistocerca gregaria , the other mouthparts moved in synchrony with the mandibles. This occurred in the presence or absence of food, and when the mandibles were driven at a higher or lower frequency than that seen during normal feeding. Electromyogram recordings from the mandibular closer muscles revealed bursts of activity at the same frequency as the imposed movement. This activity occurred during mandibular closing. Burst length was a function of driving wavelength. At low driving frequencies (less than 0.5 Hz), smaller bursts were seen prior to the longer closing burst; a series of similar small bursts was seen when the mandibles were held in the open position. When one mandible was driven, closer muscle activity was largely confined to that side. In the presence of food, however, activity was seen in both closer muscles. A possible mechanism for this is described. After destruction of the campaniform sensilla on the ventral surface of the mandibles, the bursts of activity in the mandibular closers, seen when the mandibles were held open, were replaced by continuous activity. This suggests that the function of these sensilla is to inhibit motor output to the closer muscles when the tension becomes high. When feeding on relatively incompressible food the closer muscle burst length increased, although chewing frequency did not alter. This effect was also produced by loading the mandibles artificially. A model for the feedback control of this behaviour is proposed.     

Comparisons of habitat structure and plant,arthropod and bird diversity between mainland and island sites near Perth,Western Australia

Detailed estimations of habitat structure, plant species diversity and diversity of arthropods were made at six 4.0 ha sites, two on mainland Western Australia near Perth and four on adjacent islands. The number of resident passerine bird species was also recorded at each site. Plant species diversity, and horizontal foliage diversity (=patchiness) varied only slightly between sites. There were significant positive correlations between arthropod Order diversity and bird diversity, and between vertical foliage diversity and bird diversity. In both Acacia and dune scrub, the Rottnest Island sites had more individuals of arthropods than the mainland sites but these belonged to fewer Orders. Numerical imbalance between arthropod Orders on Rottnest Island probably results from diminution of predators (passerine birds) there. As the actual number of arthropods is higher on the islands, the absence of so many species of passerine birds may result from other factors (ecological and historical).     

Reintroduction as a tool for population recovery of farmland birds

Conservation efforts in the United Kingdom have increasingly sought to restore the populations and ranges of birds affected by changes to their habitat or by direct human persecution. One approach is reintroduction, although this is likely to be appropriate in only a limited set of circumstances, involving a small number of species. This paper reviews the use of reintroduction as a tool for conserving birds associated with lowland farmland, highlighting the benefits of this approach to conservation, as well as the potential dangers. Two case studies are presented to illustrate how different reintroduction techniques are required, depending on the species involved and the donor stock available. The internationally agreed, though not legally binding, IUCN guidelines for reintroduction projects are summarized, together with the requirements of The Wildlife & Countryside Act (1981) in relation to the release of birds into the wild in Britain. Potential changes to current legislation are suggested, to prevent inappropriate and potentially damaging reintroduction projects from being carried out in the future.