Two-phase species-time relationships in North American land birds

The species-time relationship (STR) is a macroecological pattern describing the increase in the observed species richness with the length of time censused. Understanding STRs is important for understanding the ecological processes underlying temporal turnover and species richness. However, accurate characterization of the STR has been hampered by the influence of sampling. I analyzed species-time relationships for 521 breeding bird survey communities. I used a model of sampling effects to demonstrate that the increase in richness was not due exclusively to sampling. I estimated the time scale at which ecological processes became dominant over sampling effects using a two-phase model combining a sampling phase and either a power function or logarithmic ecological phase. These two-phase models performed significantly better than sampling alone and better than simple power and logarithmic functions. Most communities’ dynamics were dominated by ecological processes over scales less than 5 years. This technique provides an example of a rigorous, quantitative approach to separating sampling from ecological processes

An empirical evaluation of four variants of a universal species-area relationship

The Maximum Entropy Theory of Ecology (METE) predicts a universal species-area relationship (SAR) that can be fully characterized using only the total abundance (N) and species richness (S) at a single spatial scale. This theory has shown promise for characterizing scale dependence in the SAR. However, there are currently four different approaches to applying METE to predict the SAR and it is unclear which approach should be used due to a lack of empirical evaluation. Specifically, METE can be applied recursively or a non-recursively and can use either a theoretical or observed species-abundance distribution (SAD). We compared the four different combinations of approaches using empirical data from 16 datasets containing over 1000 species and 300,000 individual trees and herbs. In general, METE accurately downscaled the SAR (R^2> 0.94), but the recursive approach consistently under-predicted richness, and METEs accuracy did not depend strongly on using the observed or predicted SAD. This suggests that best approach to scaling diversity using METE is to use a combination of non-recursive scaling and the theoretical abundance distribution, which allows predictions to be made across a broad range of spatial scales with only knowledge of the species richness and total abundance at a single scale.Comment: main text: 20 pages, 2 tables, 3 figure

Effects of recording media on echolocation data from broadband bat detectors

Bat detectors are an important tool for ecological studies of bats. However, the quality and quantity of data may be affected by the recording devices used to record the output from the detector. We compared recordings of bat activity from audiocassette recorders and computers. Numbers of calls/hour, passes/hour, identifiable passes/hour, and feeding buzzes/hour were similar (all P’s \u3e 0.1) between recording devices. All call characteristics, except for the minimum frequency and characteristic frequency, differed (P \u3c 0.05) between tapes and computers. Species identification with discriminate function analysis was less reliable with tape data than with computer data, particularly when the model built with computer-recorded reference calls was tested with tape-recorded calls. Therefore, we suggest when tape recorders are used for field recording that they also are used to record reference calls

The combined influence of the local environment andregional enrichment on bird species richness

It is generally accepted that local species richness at a site reflects the combined influence of local and regional processes. However, most empirical studies evaluate the influence of either local environmental variables or regional enrichment but not both simultaneously. Here we demonstrate the importance of combining these processes to understand continental scale richness patterns in breeding birds. We show that neither regional enrichment nor the local environment in isolation is sufficient to characterize observed patterns of species richness. Combining both sets of variables into a single model results in improved model fit and the removal of residual spatial autocorrelation. At short time scales local processes are most important for determining local richness, but as the time scale of analysis increases regional enrichment becomes increasingly important. These results emphasize the need for increased integration of multiple scales of processes into models of species richness

Simple Structural Differences between Coding and Noncoding DNA

Background The study of large-scale genome structure has revealed patterns suggesting the influence of evolutionary constraints on genome evolution. However, the results of these studies can be difficult to interpret due to the conceptual complexity of the analyses. This makes it difficult to understand how observed statistical patterns relate to the physical distribution of genomic elements. We use a simpler and more intuitive approach to evaluate patterns of genome structure. Methodology/Principal Findings We used randomization tests based on Morisita\u27s Index of aggregation to examine average differences in the distribution of purines and pyrimidines among coding and noncoding regions of 261 chromosomes from 223 microbial genomes representing 21 phylum level groups. Purines and pyrimidines were aggregated in the noncoding DNA of 86% of genomes, but were only aggregated in the coding regions of 52% of genomes. Coding and noncoding DNA differed in aggregation in 94% of genomes. Noncoding regions were more aggregated than coding regions in 91% of these genomes. Genome length appears to limit aggregation, but chromosome length does not. Chromosomes from the same species are similarly aggregated despite substantial differences in length. Aggregation differed among taxonomic groups, revealing support for a previously reported pattern relating genome structure to environmental conditions. Conclusions/Significance Our approach revealed several patterns of genome structure among different types of DNA, different chromosomes of the same genome, and among different taxonomic groups. Similarity in aggregation among chromosomes of varying length from the same genome suggests that individual chromosome structure has not evolved independently of the general constraints on genome structure as a whole. These patterns were detected using simple and readily interpretable methods commonly used in other areas of biology

Ecological Correlates of Geographic Range Occupancy in North American Birds

The degree to which a species is predictably encountered within its range varies 36 tremendously across species. Understanding why some species occur less frequently within their 37 range than others has important consequences for conservation and for range map based analyses 38 of ecological patterns. We examined whether patterns in geographical range occupancy can be 39 explained by species level traits

On the directions determined by a Cartesian product in an affine Galois plane

We prove that the number of directions contained in a set of the form $A \times B \subset AG(2,p)$, where $p$ is prime, is at least $|A||B| - \min\{|A|,|B|\} + 2$. Here $A$ and $B$ are subsets of $GF(p)$ each with at least two elements and $|A||B| <p$. This bound is tight for an infinite class of examples. Our main tool is the use of the R\'edei polynomial with Sz\H{o}nyi's extension. As an application of our main result, we obtain an upper bound on the clique number of a Paley graph, matching the current best bound obtained recently by Hanson and Petridis.Comment: 8 page