44 research outputs found
Selection of bee species for environmental risk assessment of GM cotton in the Brazilian Cerrado
Efeito de espĂ©cies vegetais em bordadura em cebola sobre a densidade populacional de tripes e sirfĂdeos predadores.
Analisou-se a relação entre o efeito do plantio de diferentes espĂ©cies vegetais, em bordadura, na cultura da cebola, Allium cepa L, na incidĂŞncia de Thrips tabaci Lind. e sirfĂdeos predadores, Toxomerus spp. O experimento foi conduzido na Epagri, EE de Ituporanga, de agosto a dezembro de 1998. Os tratamentos foram cebola em monocultivo; cebola + trigo mourisco (Fagopyrum esculentum Moench); cebola + nabo forrageiro (Raphanus sativus L. var. oleiferus Metzg.); cebola + cenoura (Daucus carota L., cv. Nantes e cv. BrasĂlia); cebola + milho (Zea mays L.); cebola + rĂşcula
(Eruca sativa L.) + vegetação espontânea. O plantio de diferentes espĂ©cies vegetais em bordadura nĂŁo provocou diferenças significativas na incidĂŞncia de tripes e sirfĂdeos predadores. A produtividade comercial de bulbos de cebola foi similar em sistema de monocultivo e diversificado, sugerindo ser possĂvel adotar tais sistemas sem perdas em rendimento
Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models
Both community ecology and conservation biology seek further understanding of
factors governing the advance of an invasive species. We model biological
invasion as an individual-based, stochastic process on a two-dimensional
landscape. An ecologically superior invader and a resident species compete for
space preemptively. Our general model includes the basic contact process and a
variant of the Eden model as special cases. We employ the concept of a
"roughened" front to quantify effects of discreteness and stochasticity on
invasion; we emphasize the probability distribution of the front-runner's
relative position. That is, we analyze the location of the most advanced
invader as the extreme deviation about the front's mean position. We find that
a class of models with different assumptions about neighborhood interactions
exhibit universal characteristics. That is, key features of the invasion
dynamics span a class of models, independently of locally detailed demographic
rules. Our results integrate theories of invasive spatial growth and generate
novel hypotheses linking habitat or landscape size (length of the invading
front) to invasion velocity, and to the relative position of the most advanced
invader.Comment: The original publication is available at
www.springerlink.com/content/8528v8563r7u2742