Evaluating monitoring methods to guide adaptive management of a threatened amphibian (Litoria aurea)

Prompt detection of declines in abundance or distribution of populations is critical when managing threatened species that have high population turnover. Population monitoring programs provide the tools necessary to identify and detect decreases in abundance that will threaten the persistence of key populations and should occur in an adaptive management framework which designs monitoring to maximize detection and minimize effort. We monitored a population of Litoria aurea at Sydney Olympic Park over 5 years using mark–recapture, capture encounter, noncapture encounter, auditory, tadpole trapping, and dip‐net surveys. The methods differed in the cost, time, and ability to detect changes in the population. Only capture encounter surveys were able to simultaneously detect a decline in the occupancy, relative abundance, and recruitment of frogs during the surveys. The relative abundance of L. aurea during encounter surveys correlated with the population size obtained from mark–recapture surveys, and the methods were therefore useful for detecting a change in the population. Tadpole trapping and auditory surveys did not predict overall abundance and were therefore not useful in detecting declines. Monitoring regimes should determine optimal survey times to identify periods where populations have the highest detectability. Once this has been achieved, capture encounter surveys provide a cost‐effective method of effectively monitoring trends in occupancy, changes in relative abundance, and detecting recruitment in populations.     

Structure of theory in vegetation science

In order to help evaluate progress in vegetation science, we present an outline of the components of theory. Theory has both empirically and conceptually based components, and is tied together by a hierarchical framework. Theory is related to observable phenomena to further the most general goal of science, understanding. More specific tactics to advance understanding include explanation, generalization, and testing. Different components of theory permit the operation of specific tactics. Most components of theory are exemplified by one or more aspects of vegetation science. However, there are some conceptual and empirical components in need of further development. We conclude that vegetation science does in fact conform to the contemporary view of a developing theory, and that this theory can serve as a fruitful guide to research and application of concepts to the field.     

Effects of egg yolk and glycerol levels in lactose-EDTA-egg yolk extender and of freezing rate on the motility of frozen-thawed stallion spermatozoa

Two experiments were designed to evaluate the effects of egg yolk and glycerol concentrations, freezing rate, and clarification of a lactose-EDTA-egg yolk extender on the post-thaw motility of stallion spermatozoa. In both experiments there was no influence of freezing rate (vapor vs controlled) on the percentage of progressively motile spermatozoa after thawing. Furthermore, no significant interaction among treatments was detected. In Experiment 1, clarified (centrifuged at 34,400 × g for 30 min) lactose-EDTA-egg yolk extenders containing 16 or 20% egg yolk and 3 or 4% glycerol were superior to those containing 12% egg yolk or 2% glycerol, based on the percentage of progressively motile stallion spermatozoa at 0, 30, 60, and 90 min after thawing. However, in Experiment 2, clarification of the lactose-EDTA-egg yolk extender was detrimental to the ability of the stallion spermatozoa to survive after thawing; 4% glycerol was superior to 2% glycerol. The best extender based on the percentage of progressively motile spermatozoa after thawing was nonclarified lactose-EDTA-egg yolk extender containing 20% egg yolk and 4% glycerol.     

Measuring the host preference of parasites: An aid in evaluating biotypes ofAnagrus epos [Hym.: Mymaridae]

Populations ofAnagrus epos Girault are being imported and evaluated for the biological control of variegated grape leafhopper,Erythroneura variabilis Beamer, a newly introduced pest of grapes in central California. To distinguish different biotypes, a field test was developed that quantifies host preference.E. epos collected from geographically isolated regions of western United States and northern Mexico showed different levels of preference towards the variegated leafhopper and its close relative the grape leafhopper,Erythroneura elegantula Osborn, a native to central California. Host preference values may aid in the identification of relased biotypes using leafhopper eggs on leaves sampled from release sites.      

Growth and composition of Escherichia coli subjected to square-wave perturbations in nutrient supply: Effect of varying amplitudes

The effect of regular variations in the input limiting nutrient concentration at different cycle amplitudes on the growth and composition (elemental and macromolecular) of Escherichia coli ML30 in chemostat culture is described. The cycle time was maintained constant at 2.0 hr. The basal level of nutrient fed to cultures was also maintained constant but the concentration amplitude was varied over a range from 0.2 to 5.0 g/liter. A lag between the stimulus and organisms response was observed and found to be independent of cycle amplitude over most of the range examined. Increasing the cycle amplitude did not effect the cell yield from glucose or the elemental composition of the organisms. However, large variations in the macromolecular composition of the cells (on a dry weight basis) were found; at 4.0 g/liter amplitude the cells contained some 82% protein. The relevance of this type of reactor operation in large-scale fermentations is discussed.     

Plant litter: Its dynamics and effects on plant community structure

We discuss the dynamics of plant litter, the effects of litter on the chemical and physical environment, the direct and indirect effects of plant litter on plant populations and communities, and different adaptative traits that may be related to litter accumulation. The production of litter depends primarily on the site productivity, but other properties of the environment, as well as chance, may introduce important variation. The existence of time lags between the production of plant organs and their transformation into litter appears as a relevant character of litter dynamics seldom included in models. Herbivory, and other processes that destroy biomass or reduce productivity, may reduce the amount of litter produced. The destruction of litter encompasses a complex of interactions. The main processes, including physical and chemical degradation, consumption by invertebrates and decomposition, are differentially affected by the environment and by the physical and chemical characteristics of the litter itself. The relative importance of those processes varies among systems. Litter alters the physical and chemical environment directly and indirectly. The decomposition of litter may release both nutrients and phytotoxic substances into the soil. The physical changes produced by litter also alter the activity of decomposers, resulting in an indirect effect on the chemical environment. The accumulated litter intercepts light, shading seeds and seedlings, and reduces the thermal amplitude in the soil. By reducing maximum soil temperatures, and creating a barrier to water vapor diffusion, litter reduces evaporation from the soil. However, litter may also diminish water availability when it retains a large proportion of rainfall. Litter creates a physical barrier for seedling and sprout emergence and to seeds reaching the soil.     

Suppression of iron uptake deficiency in Escherichia coli K-12 by loss of two major outer membrane proteins.

A novel iron uptake system was observed in pseudorevertants of $\text{Escherichia}$,$\text{coli}$ strains defective in ferrienterochelin transport. The new system is unique in that it is an active transport system that does not utilize any known siderophore. Acquisition of the new uptake system occurs concomitantly with the loss of two major outer membrane proteins (b and c) believed to function as structural components of transmembrane pores.