So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

An essential textbook for any student or researcher in biology needing to design experiments, sample programs or analyse the resulting data The text begins with a revision of estimation and hypothesis testing methods, covering both classical and Bayesian philosophies, before advancing to the analysis of linear and generalized linear models Topics covered include linear and logistic regression, simple and complex ANOVA models (for factorial, nested, block, split-plot and repeated measures and covariance designs), and log-linear models Multivariate techniques, including classification and ordination, are then introduced Special emphasis is placed on checking assumptions, exploratory data analysis and presentation of results The main analyses are illustrated with many examples from published papers and there is an extensive reference list to both the statistical and biological literature The book is supported by a website that provides all data sets, questions for each chapter and links to software

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Experimental Design and Data Analysis for Biologists

There is now ample evidence of the ecological impacts of recent climate change, from polar terrestrial to tropical marine environments. The responses of both flora and fauna span an array of ecosystems and organizational hierarchies, from the species to the community levels. Despite continued uncertainty as to community and ecosystem trajectories under global change, our review exposes a coherent pattern of ecological change across systems. Although we are only at an early stage in the projected trends of global warming, ecological responses to recent climate change are already clearly visible.

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Ecological responses to recent climate change.

Predation has long been implicated as a major selective force in the evolution of several morphological and behavioral characteristics of animals. The importance of predation during evolutionary ti...

Behavioral decisions made under the risk of predation: a review and prospectus

▪ Abstract The focus of most ideas on diversity maintenance is species coexistence, which may be stable or unstable. Stable coexistence can be quantified by the long-term rates at which community members recover from low density. Quantification shows that coexistence mechanisms function in two major ways: They may be (a) equalizing because they tend to minimize average fitness differences between species, or (b) stabilizing because they tend to increase negative intraspecific interactions relative to negative interspecific interactions. Stabilizing mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations in population densities and environmental factors in space and time. Equalizing mechanisms contribute to stable coexistence because they reduce large average fitness inequalities which might negate the effects of stabilizing mechanisms. Models of unstable coexitence...

/pdf/mechanisms-of-maintenance-of-species-diversity-340h1nopps.pdf

Mechanisms of Maintenance of Species Diversity

An important stabilizing mechanism in most diversity-stability models is the insurance hypothesis, which involves correlation/covariance relationships among species. These models require that species do not fluctuate synchronously over time: that is, the correlation between pairs of species does not equal 1.0. However, the strength of this stabilizing mechanism increases as correlations decline away from 1.0, especially as they become more negative and also as the summed covariance across all species pairs becomes more negative. We evaluated the importance of the insurance hypothesis as a stabilizing mechanism by examining a variety of terrestrial assemblages using long-term data from the Global Population Dynamics Database, the Breeding Bird Survey, and a long-term site in southeastern Arizona, USA. We identified co-occurring assemblages of species and calculated the Spearman rank correlations of all pairs of species and the summed covariance of the entire assemblage. We found that, in most assemblages, positive correlations were two to three times more common than negative and that the magnitude of the positive correlations tended to be stronger than the negative correlations. For all but three assemblages, the summed covariance was positive. Data from larger spatial scales tended to exhibit more positive correlations, but even at the smallest spatial scales, positive correlations outnumbered negative. We suggest that species often covary positively because coexisting species respond similarly to fluctuations in their resource base driven by climatic fluctuations. As such, our review suggests that the insurance hypothesis may not be a strong mechanism stabilizing fluctuations in natural terrestrial communities.

An empirical evaluation of the insurance hypothesis in diversity–stability models

Summary

1  Spatial distribution–abundance relationships have been intensively studied. Workers have now begun to study temporal relationships but little is known about how these are related to spatial patterns. We examined these relationships both over space and time using 15 years of data from permanent quadrats in the Chihuahuan Desert.



2  Winter and summer annual communities were analysed. Within single years, the species in each community exhibited a positive relationship between distribution and abundance at two spatial scales, 0.25-ha plots and 0.25-m2 quadrats. Over 15 years, the species in each community also exhibited a positive relationship between abundance and the number of years in which they were present. Species frequency distributions, both in space and over time, were scale-dependent.



3  Over space, the frequency distribution was bimodal at large (plot) scales, but unimodal at small (quadrat) scales in both communities. Over time, the frequency distribution was bimodal for winter annuals but unimodal for summer annuals, a difference we attribute to the marked difference between the two communities in the temporal consistency of rank abundance of species. We conclude that both niche and metapopulation models can be used in explaining the distribution patterns of species but at different scales. The factors and processes in these models are not mutually exclusive in determining the overall abundance and distributions of these species in space and over time.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2745.2000.00466.x

Abundance and distribution of desert annuals: are spatial and temporal patterns related?

We evaluated the ability of path analysis to characterize direct and indirect interactions in a natural ecological system. Based on previous experimental work, we constructed a path diagram reflecting presumed relationships between kangaroo rats (Dipodomys spp.) and two other small rodent species. The technique was applied to examine the direct effects of competition and indirect effects mediated through vegetation. Path analysis gave varying and sometimes uninterpretable results when applied to data collected from unmanipulated and manipulated systems. The variation most likely can be attributed to some combination of inadequate specification of the path diagram, differences between unmanipulated and manipulated systems, varying responses to experiments of different duration, and natural temporal variation. Because these issues are applicable to many kinds of complex systems, we suggest caution before applying and when interpreting the results of path analysis.

Path Analysis: A Critical Evaluation Using Long-Term Experimental Data

Effects of livestock removal and perennial grass recovery on the lizards of a desertified arid grassland

When a group of individuals exploits a single patch, each forager acquires just a fraction of the patch sample information generated by the group. Because of this, individuals in groups may generate less precise patch estimates than solitary foragers. In addition, in cohesive groups, individuals may be forced to abandon a patch they estimate to be of high quality simply because all other group members abandon the patch. I quantify the associated foraging costs of less precise patch estimates and group cohesion by performing a series of Monte Carlo simulations. I compare the performance of a solitary forager with that of three possible patch estimation and departure strategies for group foragers. The three group strategies differ in the amount or kind of patch sample information used to estimate patch quality

Thomas J. Valone

Papers

An empirical evaluation of the insurance hypothesis in diversity–stability models

Abundance and distribution of desert annuals: are spatial and temporal patterns related?

Path Analysis: A Critical Evaluation Using Long-Term Experimental Data

Effects of livestock removal and perennial grass recovery on the lizards of a desertified arid grassland

Patch Information and Estimation: A Cost of Group Foraging