| quality or quantity: the direct and indirect effects of host plants on herbivores and their natural enemies. | resource quality (plant nitrogen) and resource quantity (plant density) have often been argued to be among the most important factors influencing herbivore densities. a difficulty inherent in the studies that manipulate resource quality, by changing nutrient levels, is that resource quantity can be influenced simultaneously, i.e. fertilized plants grow more. in this study we disentangled the potentially confounding effects of plant quality and quantity on herbivore trophic dynamics by separately ... | 2005 | 15517407 |
| bottom-up and top-down effects on insect herbivores do not vary among sites of different salinity. | it has been suggested, but rarely tested, that the relative strength of top-down and bottom-up factors in communities varies along an environmental stress gradient. we compared the strength of bottom-up and top-down effects on the densities of insect herbivores along a range of sites of different salinities in west-central florida. we used a 2 x 2 factorial design with plots divided into four treatments: (1) bottom-up manipulation, where fertilizer was applied to increase plant quality; (2) top- ... | 2006 | 17089675 |
| the influence of species identity and herbivore feeding mode on top-down and bottom-up effects in a salt marsh system. | in this study we investigated the potential importance of species identity and herbivore feeding mode in determining the strengths of top-down and bottom-up effects on phytophagous insect densities. in 1998, we conducted two factorial field experiments in which we manipulated host plant quality and intensity of parasitoid attack on three salt marsh herbivores, the planthoppers prokelisia marginata and pissonotus quadripustulatus (homoptera: delphacidae), which feed only on spartina alterniflora ... | 2002 | 28547312 |
| the gall midge asphondylia borrichiae (diptera: cecidomyiidae): an indigenous example of host-associated genetic divergence in sympatry. | speciation usually is conceptualized as occurring via three biogeographic modes: allopatry, parapatry, and sympatry. sympatric speciation has been the most controversial because of the difficulty of developing plausible theoretical models in which the homogenizing effects of gene flow are sufficiently overcome to permit genetic divergence to occur in the absence of geographic barriers restricting gene flow. recently, a number of hypothetical models for sympatric speciation have been advanced and ... | 2012 | 23068183 |