Registered users receive a variety of benefits including the ability to customize email alerts, create favorite journals list, and save searches.
Please note that a BioOne web account does not automatically grant access to full-text content. An institutional or society member subscription is required to view non-Open Access content.
Contact firstname.lastname@example.org with any questions.
This paper evaluates the Trophic Cascade hypothesis and its predictive effects of food web structure regulation on primary productivity in lake ecosytems. The hypothesis prognosticates that the top of the aquatic food web, either with or without piscivorous fishes, should have cascading interactions through the trophic levels ultimately impacting algal biomass. Extensive experiments have shown validity to the hypothesis, while critics of the idea, through their own research, claim that it is too simplistic of a mechanism lost in the complexities of food web dynamics and nutrient loading models. I discuss the development of the Trophic Cascade hypothesis, its strengths and weaknesses, and conclude with the recognized and current synthesis. Many researchers now recognize the interactions of both top-down foraging mechanisms and bottom-up nutrient loading dynamics on lake primary production when assessing lacustrine systems.
The discrete nature of vernal pools provides opportunities for experiments revealing information applicable to numerous habitats otherwise more difficult to examine in their entirety. This study examines vernal pool diversity in relation to pool thermal regime, morphology, and inter-pool distribution. Using Island Biogeography theory, we predicted that (1) the number of species in a community should be positively correlated with habitat size, and (2) inter-pool distance should be negatively correlated with biological similarity. We developed two alternative hypotheses, based on the expectation that larger pools should be more thermally stable. These hypotheses ask whether thermally stable or variable pools facilitate invertebrate diversity. We studied eight vernal pools on Kennedy Table in Madera County, California. We took measurements of surface-area, mean depth, and volume of each pool, temperature was logged for four weeks, and invertebrates were systematically sampled. All data was analyzed with Pearson correlation or stepwise multiple regression. The results indicated strong negative correlations between average depth with temperature maximum and temperature standard deviation. Pool proximity and invertebrate assemblage similarity were positively related. There was no significant correlation between temperature variation and species richness. Species diversity was not significantly correlated with pool morphology. Our study suggests that vernal pools do not follow standard theories about species diversity. As vernal pools diminish, it is increasingly important for similar studies to continue and expand in order to better understand the driving forces behind their unique faunal assemblages.
Of the cadherin-type Bacillus thuringiensis biopesticide receptors cloned to date, BT-R1 remains the best characterized regarding toxin binding affinity and specificity. While at least four related clones have been identified in different Lepidopterans, little is known about the tissue distribution or natural function of any of these receptors in insect larvae. The goal of this study was to better evaluate the distribution of processed BT-R1 mRNAs in Manduca sexta larvae and to search for alternative mRNA processing products which may lead to receptor proteins of differing function or ligand specificities/affinities. Our results in fact indicate that the BT-R1 mRNA is present only within tissues of the midgut, and that expression is relatively uniform throughout the length of the organ. Due to the lack of related transcripts and alternative splicing products, it is now clear that studies of BT-R1 isolated from M. sexta midguts indeed involve only a single high-affinity receptor protein.
The Ketogenic Diet (KD), which combines initial food deprivation with a diet high in fat, was first used to treat childhood epilepsy in the 1920s. The KD induces ketosis, producing β-hydroxybutyrate (BHB), which appears to be a factor that reduces the frequency of seizures. The purpose of this study was to develop an animal model in which the direct administration of BHB produced the same effect as the KD. Techniques were developed for administering BHB by gastric gavage and measuring its levels in blood; levels were measured after periods of food given ad libitum and food deprivation. Rats fed ad libitum had average blood BHB levels of 0.06 mmol/L, while rats deprived of food for 12 hr had average levels of 0.69 mmol/L. The seizure protection range in rats begins at 0.7 mmol/L (Likhodii et al., 2000). The time necessary for the body to remove BHB from the blood was determined to be less than 1 hr. Repeated doses were given at short intervals to increase BHB levels from baseline. Repeated doses of BHB at 15 min intervals caused a continual increase in blood BHB levels, with seizure protection levels being reached. Blood BHB levels elevated by initial food deprivation were maintained above baseline with repeated administration of BHB. Current research is focusing on comparing blood BHB levels achieved by orally administered BHB, the KD, and a combination of orally administered BHB and the KD. Additionally, blood BHB levels resulting from more concentrated doses of BHB are being measured.