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...

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Mechanisms of Maintenance of Species Diversity

We develop a theory of competition based on two mechanisms that we call the cost of rarity (Mechanism R) and the cost of commonness (Mechanism C). These reduce the rate of population increase only at high densities (asexual organisms) or both at high and low densities (sexual species). The theory predicts that, in certain circumstances, the number of coexisting species in any assemblage will be finite and that these species will differ in their utilization of resources (and in associated morphological traits) more than expected by chance. Specifically, it predicts such nonrandom assortment in assemblages of three or more (i.e. multispecies) sexual species, especially in those communities where a few species are numerically dominant, but not in two-species associations and not in asexual forms. Unlike other theories, however, ours does not predict any specific value of morphological ratio or limiting similarity.

Competition theory and the structure of ecological communities

We tested the hypothesis that species loss at one trophic level will reduce the temporal stability of populations at other trophic levels. We examined the temporal stability of annual plant populations on plots that experimentally manipulated the functional diversity of seed-eating rodent consumers. Experimental reduction of rodent functional diversity destabilized populations of small-seeded plants but had less consistent effects on larger-seeded species. Small-seeded species also exhibited a greater number of years of zero abundance. Thus, experimental reduction of rodent functional diversity resulted in lower plant diversity. The decline in the temporal stability of small-seeded plants likely resulted from increased interspecific competition by large-seeded plants. These results demonstrate that the loss of species at one trophic level can lead to reduced richness at lower trophic levels via competition and reduced temporal stability.

Reduced rodent biodiversity destabilizes plant populations.

Several species of avian and mammalian social foragers vocalize after locating food. Empirical work has shown that such food-associated calls can be detrimental to the caller because other group members are often attracted to the discovered food. Individuals can obtain anti-predator benefits from emitting food calls if group size increases in response to the vocalization but empirical work has shown that food calls also are emitted by individuals in groups of fixed size ; in such groups, the benefit of emitting food calls is less obvious. Here, I extend earlier work and propose that food-associated calls may represent auditory public information about food patch quality. Food calls thus function to provide patch quality information to other group members. Such information benefits individuals because it allows social foragers in groups of fixed size to exploit resource patches more efficiently by preventing early departures from rich resource patches. The hypothesis that food-associated calls represent auditory patch quality information makes several predictions about the likelihood that foragers will emit a food call in response to food discovery. In particular, this hypothesis predicts that foragers who : 1) are not in visual contact with other group members, 2) do not initiate group movements, or 3) are hungry, should be most likely to give food-associated calls. Empirical evidence to test these predictions is sparse but generally supports these predictions.

Food-associated calls as public information about patch quality

Falconer, D. S. 1989. Introduction to quantitative genetics. Third edition. Longman, New York, New York, USA. Gasser, C. S., and R. T. Fraley. 1989. Genetically engineering plants for crop protection. Science 244: 1293-1 299. Gould, F. 1988. Evolutionary biology and genetically engineered crops. BioScience 38:26-33. Haughn, G. W., and C. R. Somerville. 1986. Sulfonylurearesistant mutants of Arabldopsis thaliana Molecular and General Genetics 170:827-842. Hilder, V. A,, and A. M. R. Gatehouse. 1990. Transforming plants as a means ofcrop protection against insects. Outlook on Agriculture 19: 179-183. Keeler, K. H. 1988. Can we guarantee the safety of genetically engineered organisms in the environment? CRC Critical Reviews in Biotechnology 8:85-97. OTA [Office of Technology Assessment, United States Congress]. 1988. New developments in biotechnology. (3) Field testing engineered organisms: genetic and ecological issues. United States Government Printing Office. Washington, D.C.. USA.

Interactions between rodents and ants in the Chihuahuan Desert: An update

Theoretical discussions concerning how animals might best sample and select mates have suggested that individuals could base decisions either on a sample of mates (sampled-based decisions) or on a threshold of comparison (threshold-based decisions). Recent theoretical work demonstrates that threshold-based mating decisions generate higher expected fitness than sample-based mating decisions when search costs exist. Empirical results from most unmanipulated systems, however, either conclude that females make sample-based decisions or are inconclusive. A few experimental studies designed to detect mating thresholds purport to demonstrate threshold-based choice but an examination of these studies indicates such conclusions were premature. We believe that few examples of threshold-based choice exist because protocols designed to identify mating thresholds were often inconsistent with models of threshold choice. We suggest that future empirical work strive not to document mating thresholdsper se. Rather, future work might best reveal decision rules by manipulating the distribution of quality among potential mates; such manipulations predict uniquely how females using sample-based and threshold-based decision rules should behave.

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Thomas J. Valone

Papers

Competition theory and the structure of ecological communities

Reduced rodent biodiversity destabilizes plant populations.

Food-associated calls as public information about patch quality

Interactions between rodents and ants in the Chihuahuan Desert: An update

The empirical question of thresholds and mechanisms of mate choice.