Seasonal Patterns of Abundance of Tundra Arthropods near Barrow

Arthropods active on the surface of the tundra near Barrow, Alaska, were trapped throughout four summer seasons (1966-1969), using "sticky-board" traps. More than 95% of the arthropods (excluding Acarina and Collembola) captured were of the order Diptera. Adults of most species of Diptera emerged in the middle two weeks of July; the abundance of arthropods on the tundra surface was maximal at that time. Year-to-year variations in abundance of various arthropod taxa are related to prevailing weather conditions and to the cycle of tundra disturbance and recovery associated with the abundance of brown lemmings.Modalités de l’abondance des arthropodes de la toundra selon les saisons, près de Barrow.  Près de Barrow, Alaska, on a, ou cours des quatre étés (1966-1969), capturé au moyen de pièges à glu les arthropodes actifs à la surface de la toundra.  Plus de 95 pour cent des arthropodes capturés (à l’exclusion des Acariens et des Collemboles) appartenaient à l’ordre des Diptères.  Les adultes de la plupart des espèces de Diptères apparaissaient au cours des deux semaines du milieu de juillet : c’est à ce moment que les arthropodes étaient les plus nombreux à la surface de la toundra.  Les variations annuelles d’abondance des divers taxa d’arthropodes sont liées aux conditions du temps et au cycle de déprédation et de reprise de la toundra selon l’abondance des lemmings

Clonal integration beyond resource sharing: implications for defence signalling and disease transmission in clonal plant networks

Item does not contain fulltextResource sharing between ramets of clonal plants is a well-known phenomenon, which allows stoloniferous and rhizomatous species to internally translocate water, mineral nutrients and carbohydrates from sites of high supply to sites of high demand. The mechanisms and implications of resource integration in clonal plants have extensively been studied in the past. Vascular ramet connections are likely to provide an excellent means to share substances other than resources, such as systemic defence signals and pathogens. The aim of this paper is to propose the idea that physical ramet connections of clonal plants can be used (1) to transmit signals, which enable members of clonal plant networks to share information about their biotic and abiotic environments, and (2) to facilitate the internal distribution of systemic pathogens in clonal plant networks and populations. We will focus on possible mechanisms as well as on potential ecological and evolutionary implications of clonal integration beyond resource sharing. More specifically, we will explore the role of physiological integration in clonal plant networks for the systemic transmission of direct and indirect defence signals after localized herbivore attack. We propose that sharing defence induction signals among ramets may be the basis for an efficient early warning system, and it may allow for effective indirect defence signalling to herbivore enemies through a systemic release of volatiles from entire clonal fragments. In addition, we will examine the role of clonal integration for the internal spread of systemic pathogens and pathogen defence signals within clonal plants. Clonal plants may use developmental mechanisms such as increased flowering and clone fragmentation, but also specific biochemical defence strategies to fight pathogens. We propose that clonal plant networks can act as stores and vectors of diseases in plant populations and communities and that clonal life histories favour the evolution of pathogens with a low virulence