31 research outputs found
Flooded forests: Death by drowning, not herbivory
Trees on small islands formed when a new hydroelectric dam was filled are said to have been killed by leaf-cutter ants that were no longer regulated by their armadillo predators. This top-down hypothesis is questioned and an alternative bottom-up hypothesis is proposed: the trees died because their roots were flooded.White, T.C.R
Response of grazing snails to phosphorus enrichment of modern stromatolitic microbial communities
Impacto da adubação orgĂąnica sobre a incidĂȘncia de tripes em cebola.
Analisou-se a relação entre adubação orgĂąnica e a incidĂȘncia de Thrips tabaci Lind. em cebola (Allium cepa L), na EE de Ituporanga,entre agosto e dezembro de 1998. Os tratamentos foram determinados de acordo com a necessidade de N para a cultura pela anĂĄlise de solo. Empregou-se como fonte orgĂąnica diversos adubos fornecendo 75 Kg/ha de N (esterco suĂno; adubo Barriga Verde proveniente de esterco de aves; composto orgĂąnico; esterco de peru; hĂșmus); 37,5 Kg/ha de N (metade da dose normal com esterco de suĂno); as testemunhas foram adubação mineral fornecendo 30-120-60 kg/ha de N-P2O5-K2O e o dobro da dose (60-240-120 kg/ha de N-P2O5-K2O); e testemunha sem adubação. Nenhum tratamento apresentou incidĂȘncia de T. tabaci superior Ă testemunha sem adubo. A adubação mineral em relação Ă orgĂąnica nĂŁo favoreceu significativamente a incidĂȘncia de T. tabaci . O processo de conversĂŁo do manejo do solo da ĂĄrea experimental de convencional para orgĂąnico pode ter
favorecido a infestação similar do inseto entre tratamentos. No perĂodo de maior incidĂȘncia de T. tabaci, a relação com nutrientes foi descrita por um modelo envolvendo K/Zn, B e N de maneira positiva. A correlação entre nutrientes e T. tabaci nĂŁo foi linear na maioria
das avaliaçÔes. A adubação orgĂąnica pode substituir a adubação mineral na cultura da cebola, pois foi possĂvel atingir nĂveis de produtividade similares para ambos tratamentos
Press-in-piling: the installation of instrumented steel tubular piles with and without driving shoes
RNA responses to N- and P-limitation; reciprocal regulation of stoichiometry and growth rate in Brachionus
Does a vascular fungus of tomato induce a defence response or a change in host plant quality that also affects the oviposition of spider mites?
What has stopped the cycles of sub-Arctic animal populations? Predators or food?
The populations of many species of sub-Arctic animals have recently ceased to fluctuate cyclically. The ultimate cause of this would seem to be changes in the weather, and the proximate cause has been credited to less winter snow allowing predators better access to their prey, thus enabling them to prevent surges in the prey's abundance. But there is evidence that this is not so; that, rather, the numbers of predators are limited by the abundance of their prey. Furthermore, there is alternative evidence that suggests that changes in the cyclical availability of food, brought about by changing weather conditions, may be dampening fluctuations in the abundance of these populations. On the wider ecological front, the evidence presented here further supports the commonality of how a shortage of food of a quality that can support breeding, not the action of predators, generally limits the abundance of populations of both prey and predator. © 2011 Gesellschaft fĂŒr Ăkologie.T.C.R. Whit
How should toxic secondary metabolites be distributed between the leaves of a fast-growing plant to minimize the impact of herbivory?
1. This paper considers the possibility that the key determinant of leaf age feeding preferences in foliovores is not the concentration of either nutrients or secondary metabolites, but is the ratio of the two. 2. In some fast-growing plants, nitrogen is most heavily defended by defensive toxins in the young leaves. This empowers the use of a simple model of leaf-age preference, based on the conflict between maximizing nutrient intake and minimizing toxicosis. 3. Young leaves are particularly valuable, not only because they lock up nitrogen, but also because their assimilative value is high. We calculate the loss of value due to herbivory and find that, if the herbivore is moderately intolerant of toxicity and feeds selectively on its predicted optimal leaf age, the costs of damage are greatly reduced. However, efficient toxin distribution protects the plant only if it grows rapidly, so that the well protected young foliage retains a high value. 4. The trends are reconcilable with observed leaf-age preferences of both polyphagous and oligophagous species. There is, as yet, little empirical evidence to substantiate the model, but it may be useful for future studies to focus on the toxin:nutrient ratio as a potentially important determinant of feeding preferences