Response of littoral invertebrates to reduction of fish density: simultaneous experiments in ponds with different fish assemblages

1. We experimentally reduced densities of predatory fish in replicated 2 m² areas of the littoral zone in two ponds to test whether density and biomass of invertebrates would respond to release from fish predation. The ponds are of similar size and in close proximity, but support different fish assemblages: bluegills ( Lepomis macrochirus Rafinesque) and largemouth bass ( Micropterus salmoides (Lacepede)) in one pond, and bluespotted sunfish ( Enneacanthus gloriosus (Holbrook)) and chain pickerel ( Esox niger Lesueur) in the other. Fish densities were reduced to less than 15% of ambient levels in both experiments.
2. In the bluegill–bass pond, density and biomass of most invertebrate taxa and size classes were unaffected by the fish manipulation. Total invertebrate densities did not differ significantly between fish treatments, but total invertebrate biomass was significantly greater where fish density was reduced, averaging 30% higher over the course of the study. Likewise, manipulation of fish in the bluespotted sunfish–pickerel pond had few significant effects on individual taxa and size classes. There were no significant effects on total invertebrate abundance in the bluespotted sunfish–pickerel pond.
3. Our results provide direct experimental evidence consistent with the collective evidence from previous work, suggesting that the impact of fish predation on density and biomass of invertebrate prey in littoral habitats is variable, but generally weak. Invertebrates that coexist successfully with fish in littoral systems probably are adept at taking advantage of refugia offered by the structurally complex physical environment.     

Estimating the Breeding Population of Long-Billed Curlew in the United States

ABSTRACT Determining population size and long-term trends in population size for species of high concern is a priority of international, national, and regional conservation plans. Long-billed curlews (Numenius americanus) are a species of special concern in North America due to apparent declines in their population. Because long-billed curlews are not adequately monitored by existing programs, we undertook a 2-year study with the goals of 1) determining present long-billed curlew distribution and breeding population size in the United States and 2) providing recommendations for a long-term long-billed curlew monitoring protocol. We selected a stratified random sample of survey routes in 16 western states for sampling in 2004 and 2005, and we analyzed count data from these routes to estimate detection probabilities and abundance. In addition, we evaluated habitat along roadsides to determine how well roadsides represented habitat throughout the sampling units. We estimated there were 164,515 (SE=42,047) breeding long-billed curlews in 2004, and 109,533 (SE=31,060) breeding individuals in 2005. These estimates far exceed currently accepted estimates based on expert opinion. We found that habitat along roadsides was representative of long-billed curlew habitat in general. We make recommendations for improving sampling methodology, and we present power curves to provide guidance on minimum sample sizes required to detect trends in abundance.     

Multiscale Habitat Selection by Burrowing Owls in Black-Tailed Prairie Dog Colonies

ABSTRACT Some populations of western burrowing owls (Athene cunicularia hypugaea) have declined in recent decades. To design and implement effective recovery efforts, we need a better understanding of how distribution and demographic traits are influenced by habitat quality. To this end, we measured spatial patterns of burrowing owl breeding habitat selection within black-tailed prairie dog (Cynomys ludovicianus) colonies in northeastern Wyoming, USA. We compared burrow-, site-, colony-, and landscape-scale habitat parameters between burrowing owl nest burrows (n = 105) and unoccupied burrows (n = 85). We sampled 4 types of prairie dog colonies: 1) owl-occupied, active with prairie dogs (n = 16); 2) owl-occupied, inactive (n = 13); 3) owl-unoccupied, active (n = 14); and 4) owl-unoccupied, inactive (n = 14). We used an information-theoretic approach to examine a set of candidate models of burrowing owl nest-site selection. The model with the most support included variables at all 4 spatial scales, and results were consistent among the 4 types of prairie dog colonies. Nest burrows had longer tunnels, more available burrows within 30 m, and less shrub cover within 30 m, more prairie dog activity within 100 m, and were closer to water than unoccupied burrows. The model correctly classified 76% of cases, all model coefficients were stable, and the model had high predictive ability. Based on our results, we recommend actions to ensure persistence of the remaining prairie dog colonies as an important management strategy for burrowing owl conservation in the Great Plains of North America.     

The relationship between the Rubisco reaction mechanism and models of photosynthesis*

Abstract. A new model of photosynthesis published recently in this journal (H. Farazdaghi & G. E. Edwards, Plant, Cell and Environment (1988) 11 , 789–798; 799–809) clams to have a more complete mechanistic basis than currently used models based on the paper of G. D. Farquhar, S. von Caemmerer & J. A. Berry (Planta (1980) 149 , 78–90). In this paper, we examine the validity of the new kinetic expression for the rate of CO₂ fixation by Rubisco, and the derivation of an equation for photosynthetic CO₂ assimilation as a function of light intensity and CO₂ concentration presented in the new model. In addition, we compare measured response curve of photosynthesis to CO₂ and light with simulated curves using alternative models. We conclude that the new model is mechanistically misleading and, empirically, overestimates the extent to which light and CO₂ co-limit the rate of photosynthesis under most physiological conditions.     

Polynucleotide Polymorphism in Solution

X-ray scattering experiments in solution show that poly dI.poly dC, poly (d(I-C). d(I-C)) and poly dG.poly dC have structures dissimilar to the A, B and C forms of DNA, while poly rI.poly rC is like the A′-RNA form.     

Isolation of Catenated Forms of R Factor DNA from Minicells

STUDIES^1–6 of the molecular nature of antibiotic resistance (R) factors in Escherichia coli have shown that several of them consist of covalently closed molecules of circular DNA. Use was made of this property in the separation of the R factor from chromosomal DNA of E. coli, which has a similar nucleotide-base composition. In selecting for covalently circular R factor DNA molecules, however, the procedures used in these earlier experiments-caesium chloride-ethidium bromide centrifuga-tion⁷ and bulk nitrocellulose adsorption²—necessarily selected against isolation of other (non-circular) forms of R factor DNA that might have been present.     

An Explanation of Color Nomenclature Universale

Specific physiological perception mechanisms account for some of the regularities associated with the lexical encoding of basic color terms described by Berlin and Kay (1969). This paper, however, focuses upon those regularities explained through reference to certain general principles of naming-behavior which are also pertinent to domains other than color . [cognitive anthropology, folk classification, language change, language universale, naming-behavior]