Michael R. Willig

Leptospirosis: a zoonotic disease of global importance

In the past decade, leptospirosis has emerged as a globally important infectious disease. It occurs in urban environments of industrialised and developing countries, as well as in rural regions worldwide. Mortality remains significant, related both to delays in diagnosis due to lack of infrastructure and adequate clinical suspicion, and to other poorly understood reasons that may include inherent pathogenicity of some leptospiral strains or genetically determined host immunopathological responses. Pulmonary haemorrhage is recognised increasingly as a major, often lethal, manifestation of leptospirosis, the pathogenesis of which remains unclear. The completion of the genome sequence of Leptospira interrogans serovar lai, and other continuing leptospiral genome sequencing projects, promise to guide future work on the disease. Mainstays of treatment are still tetracyclines and beta-lactam/cephalosporins. No vaccine is available. Prevention is largely dependent on sanitation measures that may be difficult to implement, especially in developing countries.

What is the observed relationship between species richness and productivity

Understanding the relationship between species richness and productivity is fundamental to the management and preservation of biodiversity. Yet despite years of study and intense theoretical interest, this relationship remains controversial. Here, we present the results of a literature survey in which we examined the relationship between species richness and productivity in 171 published studies. We extracted the raw data from published tables and graphs and subjected these data to a standardized analysis, using ordinary least-squares (OLS) regression and generalized linear-model (GLIM) regression to test for significant positive, negative, or curvilinear relationships between productivity and species diversity. If the relationship was curvilinear, we tested whether the maximum (or minimum) of the curve occurred within the range of productivity values observed (i.e., was there evidence of a hump?). A meta-analysis conducted on the distribution of standardized quadratic regression coefficients showed that ...

Functional diversity of microbial communities: A quantitative approach

Abstract Evaluating the biodiversity of microbial communities remains an elusive task because of taxonomic and methodological difficulties. An alternative approach is to examine components of biodiversity for which there exists a reasonable chance of detecting patterns that are biologically meaningful. One such alternative is functional diversity. We propose a procedure based on the Biolog identification system to quickly, effectively, and inexpensively assess aspects of the functional diversity of microbial communities. The numbers and types of substrates utilized by bacterial communities, as well as the levels of activities on various substrates and patterns of temporal development, constitute an information-rich data set from which to assess functional diversity. Data from six plant communities (black grama grassland. Sporobolus grassland, creosotebush bajada, herbaceous bajada, mesquite-playa fringe, and playa grassland) located along an elevational and moisture gradient at the Jornada Long-Term Ecological Research site in the northern Chihuahuan Desert, are analyzed to illustrate the procedure and its relevance to biodiversity. Our analyses demonstrate that the Biolog system can detect considerable variation in the ability of microbial communities to metabolize different carbon compounds. Variation in substrate use was compartmentalized differently along the moisture gradient. Differences in functional diversity were dependent upon the class of carbon sources (guild-specific results). A multifaceted approach to biodiversity that comprises both functional and taxonomic perspectives represents fertile ground for future research endeavors.

Impacts of Extreme Weather and Climate on Terrestrial Biota

Climate is a driver of biotic systems. It affects individual fitness, population dynamics, distribution and abundance of species, and ecosystem structure and function. Regional variation in climatic regimes creates selective pressures for the evolution of locally adapted physiologies, morphological adaptations (e.g., color patterns, surface textures, body shapes and sizes), and behavioral adaptations (e.g., foraging strategies and breeding systems). In the absence of humans, broad-scale, long-term consequences of climatic warming on wild organisms are generally predictable. Evidence from Pleistocene glaciations indicates that most species responded ecologically by shifting their ranges poleward and upward in elevation, rather than evolutionary through local adaptation (e.g., morphological changes). But these broad patterns tell us little about the relative importance of gradual climatic trends as compared to extreme weather events in shaping these processes. Here, evidence is brought forward that extreme ...

RANDOMNESS, AREA, AND SPECIES RICHNESS'

Thorough censuses have been made of breeding birds on islands in Pymatuning Lake, a reservoir at the Pennsylvania-Ohio border. Analysis of the censuses yields the conclusion that for these islands the variation of the number of resident avian species with island size is that which one would expect if the birds were distributed randomly, with the probability of a breeding pair residing on an island proportional to the area of the island and independent of the presence of other pairs. This type of random placement of individuals can yield species-area relations which differ from those commonly employed for analysis of biogeographic data.

RELATIONSHIPS AMONG INDICES SUGGEST THAT RICHNESS IS AN INCOMPLETE SURROGATE FOR GRASSLAND BIODIVERSITY

Although many indices estimate diversity, species richness recently has been used as a surrogate for diversity in many studies in ecology, biogeography, and conservation. Underlying assumptions of this approach are that all diversity indices, including those that weight species importance by their relative abundance (e.g., evenness), are correlated pos- itively, and that richness accounts for a large proportion of the variance in diversity. We addressed these assumptions with data from six grassland sites using univariate and mul- tivariate analyses of a variety of indices (species evenness, richness, rarity, dominance, and Simpsons diversity index). Univariate correlations between plant species evenness and richness were weak and negative at each site. Principal-component analyses consistently revealed two significant components of variation in diversity. Richness and evenness were largely orthogonal, with Simpsons diversity loading between them. Thus, measures of species diversity based on relative abundance, as well as richness, may be necessary to capture the full complexity of diversity in conservation studies and in experiments of biodiversity and ecosystem functioning. At these and perhaps other sites, species richness was an incomplete surrogate for diversity.

LANDSCAPE RESPONSES OF BATS TO HABITAT FRAGMENTATION IN ATLANTIC FOREST OF PARAGUAY

Abstract Understanding effects of habitat loss and fragmentation on populations or communities is critical to effective conservation and restoration. This is particularly important for bats because they provide vital services to ecosystems via pollination and seed dispersal, especially in tropical and subtropical habitats. Based on more than 1,000 h of survey during a 15-month period, we quantified species abundances and community structure of phyllostomid bats at 14 sites in a 3,000-km2 region of eastern Paraguay. Abundance was highest for Artibeus lituratus in deforested landscapes and for Chrotopterus auritus in forested habitats. In contrast, Artibeus fimbriatus, Carollia perspicillata, Glossophaga soricina, Platyrrhinus lineatus, Pygoderma bilabiatum, and Sturnira lilium attained highest abundance in moderately fragmented forest landscapes. Forest cover, patch size, and patch density frequently were associated with abundance of species. At the community level, species richness was highest in partly deforested landscapes, whereas evenness was greatest in forested habitat. In general, the highest diversity of bats occurred in landscapes comprising moderately fragmented forest habitat. This underscores the importance of remnant habitat patches to conservation strategies.

Similarity of Mammalian Body Size across the Taxonomic Hierarchy and across Space and Time

Although it is commonly assumed that closely related animals are similar in body size, the degree of similarity has not been examined across the taxonomic hierarchy. Moreover, little is known about the variation or consistency of body size patterns across geographic space or evolutionary time. Here, we draw from a data set of terrestrial, nonvolant mammals to quantify and compare patterns across the body size spectrum, the taxonomic hierarchy, continental space, and evolutionary time. We employ a variety of statistical techniques including “sib‐sib” regression, phylogenetic autocorrelation, and nested ANOVA. We find an extremely high resemblance (heritability) of size among congeneric species for mammals over ∼18 g; the result is consistent across the size spectrum. However, there is no significant relationship among the body sizes of congeneric species for mammals under ∼18 g. We suspect that life‐history and ecological parameters are so tightly constrained by allometry at diminutive size that animals can only adapt to novel ecological conditions by modifying body size. The overall distributions of size for each continental fauna and for the most diverse orders are quantitatively similar for North America, South America, and Africa, despite virtually no overlap in species composition. Differences in ordinal composition appear to account for quantitative differences between continents. For most mammalian orders, body size is highly conserved, although there is extensive overlap at all levels of the taxonomic hierarchy. The body size distribution for terrestrial mammals apparently was established early in the Tertiary, and it has remained remarkably constant over the past 50 Ma and across the major continents. Lineages have diversified in size to exploit environmental opportunities but only within limits set by allometric, ecological, and evolutionary constraints.

An analytical model of latitudinal gradients of species richness with an empirical test for marsupials and bats in the New World

Although latitudinal gradients in species richness are well-documented for a plethora of taxa in terrestrial, freshwater, and marine environments, little consensus exists concerning the predominant biological factor that is responsible for the pattern. We produced an analytical null model to assess the degree to which gradients in species richness could be a consequence of the random determination of the limits of species ranges. The model predicts a parabolic increase in species richness toward the middle of a latitudinal domain in the absence of underlying environmental gradients. Our stochastic model accounted for a significant portion of variation in marsupial and bat species richness for each of three different latitudinal domains in the New World: continental limits, the latitudinal extent of each higher taxon, and the smallest latitudinal extent which comprises 95% of the species in the higher taxon. A unique prediction of the stochastic model, which distinguishes it from all other hypotheses, is that parabolic latitudinal gradients in richness should exist for species wholly contained within random latitudinal subsets. Observed gradients for New World marsupials and bats document that this is true. Regardless of taxon or domain, differences between observed and expected species richness (residuals) were not related appreciably to latitudinal band area (r2 i 0.15). The ubiquity and similarity of latitudinal gradients in species richness for different taxa could be a consequence of pervasive stochastic mechanisms rather than a product of a dominant underlying environmental gradient to which all species respond. Application of our null model to other gradients (e.g., depth, productivity, disturbance) may provide insight into mechanisms affecting patterns of species richness in other ecological or biogeographic settings.

GEOGRAPHICAL ECOLOGY AT THE COMMUNITY LEVEL: PERSPECTIVES ON THE DIVERSITY OF NEW WORLD BATS

The ubiquity of the latitudinal gradient of species richness is well documented at coarse scales of resolution, but the extent to which the pattern is recapitulated at the level of local communities for any aspect of biodiversity (i.e., richness, evenness, or di- versity) is unclear. We examined how attributes of New World bat diversity vary with each other and with latitude at two scales of resolution: local communities and regional species pools. We calculated 14 indices of diversity (species richness (three), evenness (four), dominance (three), and diversity (four)) from species abundance distributions for 32 in- tensively sampled local sites between 42.258 N and 24.128 S latitude. The species richness of each corresponding regional pool was estimated from published range maps. In general, the gradient of local species richness was less steep than the corresponding gradient of regional species richness; beta diversity in the tropics is greater than that for temperate communities. All aspects of diversity at the local scale did not vary with latitude in the same manner. The latitudinal gradient in species diversity of local communities was pri- marily a consequence of the corresponding gradient in species richness. Local richness increased and became more variable with decreasing latitude. In contrast, species evenness did not vary in a systematic fashion with latitude. Although the absolute number of rare species in communities increased faster with latitude than did that of common species, both abundance classes proportionately increased with latitude in equivalent ways throughout the New World. In general, latitudinal variation at the community level was detected in diversity indices that were insensitive to the abundance of species. The dramatic increase in species richness at broad scales of resolution toward the tropics (gamma diversity) was as much a consequence of increased richness at the local level (alpha diversity) as it was a consequence of the latitudinal increase in species turnover among communities (beta diversity). Future theoretical research should examine the correlates of latitude that enhance differentiation among communities at low latitudes (i.e., those which enjoy high produc- tivities). Conservation strategies based on assessments of diversity at coarse levels of resolution (gamma diversity) should be implemented with caution because beta diversity inflates regional estimates of diversity.