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

/pdf/experimental-design-and-data-analysis-for-biologists-8ybva8d53x.pdf

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.

/pdf/ecological-responses-to-recent-climate-change-5dddm9xeiv.pdf

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

Some exotic plants are able to invade habitats and attain higher fitness than native species, even when the native species are closely related. One explanation for successful plant invasion is that exotic invasive plant species receive less herbivory or other enemy damage than native species, and this allows them to achieve rapid population growth. Despite many studies comparing herbivory and fitness of native and invasive congeners, none have quantified population growth rates. Here, we examined the contribution of herbivory to the population dynamics of the invasive species, Lespedeza cuneata, and its native congener, L. virginica, using an herbivory reduction experiment. We found that invasive L. cuneata experienced less herbivory than L. virginica. Further, in ambient conditions, the population growth rate of L. cuneata (λ = 20.4) was dramatically larger than L. virginica (λ = 1.7). Reducing herbivory significantly increased fitness of only the largest L. virginica plants, and this resulted in a small but significant increase in its population growth rate. Elasticity analysis showed that the growth rate of these species is most sensitive to changes in the seed production of small plants, a vital rate that is relatively unaffected by herbivory. In all, these species show dramatic differences in their population growth rates, and only 2% of that difference can be explained by their differences in herbivory incidence. Our results demonstrate that to understand the importance of consumers in explaining the relative success of invasive and native species, studies must determine how consumer effects on fitness components translate into population-level consequences.

Herbivory and population dynamics of invasive and native Lespedeza.

We assess the impact of release from cattle grazing on the abundance and diversity of both winter and summer annual plant communities at an upper Chihuahuan Desert scrub site in south-eastern Arizona. In contrast to previous studies, we found that removal of herbivores (cattle) had little impact on ephemeral plant assemblages at our site. The total number of summer annual individuals per quadrat did not differ significantly, but there were significantly more winter annual plants on ungrazed quadrats. The number of species per quadrat, however, did not differ significantly between sites exposed to, or protected from, grazing in either season. Of 79 annual species recorded (34 in winter, 45 in summer), only 2 species, 1 in each season, responded significantly to the removal of cattle: Stephanomeria exigua and Polygala tweedyi were more abundant on ungrazed plots. Three additional species, Eriastrum diffusum and Cryptantha micrantha in winter, and Mollugo cerviana (summer), approached statistical significance. Differences in the effect of cattle grazing on annual plants between our results and those at other sites in the arid southwest most likely reflect differences in the speed of response by annuals in different areas. Comparisons of this with other studies underscores recent calls for studies at broader spatial and greater temporal scales.

Effects of grazing on the abundance and diversity of annual plants in Chihuahuan desert scrub habitat.

We examined short-term responses of grasses, shrubs, and rodents on experimental plots to determine how manipulations of livestock grazing and prescribed fire affect individual species and community structure in a shrub-invaded arid grassland. Two grasses and Gutierrezia sarothrae were found in lower abundance on burned plots in the growing season after plots burned; all Prosopis glandulosa survived the fire. Total rodent captures and the number of Dipodomys spectabilis did not differ among treatments. No significant interaction between burning and grazing was observed. Fire seems to have few short-term negative effects on species in this system.

Effects of fire and grazing in an arid grasslandecosystem

The abundance of ectotherms should ultimately be limited by both plant productivity and the radiant energy that makes that productivity accessible. We analyzed a 21-yr data set on ant colony abundance from a North American arid grassland site. We tested the hypothesis that seed production and temperature co-limit granivorous ant abundance. We contrasted the responses of the four most common granivorous species and two omnivorous species to rainfall (summer vs. winter) and to an 8-yr seed addition experiment (summer vs. year-round seed additions). The abundance of granivorous ants was positively correlated with summer rainfall, but not winter rainfall, and was 30% higher on plots with summer vs. year-round seed additions. In contrast, the abundance of omnivorous ants was unaffected by either rainfall or the timing of seed additions. These data suggest that both the sign and size of the covariance between monthly temperature and precipitation may affect bottom-up regulation in ectotherms.

On ectotherm abundance in a seasonal environment- studies of a desert ant assemblage

The shape of the relationship between local and regional richness has been used to infer the relative strength of local vs. regional processes in structuring communities. While most empirical work has demonstrated linear relationships, recent reviews suggest that prior work has contained biases by selecting communities from different biological provinces and by defining large-scale local communities. We evaluate the utility of inferring interaction strength from local–regional relationships by examining 11 years of data from small-scale, annual plant communities at one site with strong local interactions. Both winter and summer annual plant assemblages exhibited linear rather than saturating relationships over a wide range of regional pool sizes. Our empirical work supports recent theory suggesting that local–regional relationships cannot be used to infer the strength of interactions in communities.

Thomas J. Valone

Papers

Herbivory and population dynamics of invasive and native Lespedeza.

Effects of grazing on the abundance and diversity of annual plants in Chihuahuan desert scrub habitat.

Effects of fire and grazing in an arid grasslandecosystem

On ectotherm abundance in a seasonal environment- studies of a desert ant assemblage

Effects of regional pool size on local diversity in small-scale annual plant communities