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

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Modern Applied Statistics With S

Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

Aim In a selected literature survey we reviewed studies on the habitat heterogeneity–animal species diversity relationship and evaluated whether there are uncertainties and biases in its empirical support.

Location  World-wide.

Methods  We reviewed 85 publications for the period 1960–2003. We screened each publication for terms that were used to define habitat heterogeneity, the animal species group and ecosystem studied, the definition of the structural variable, the measurement of vegetation structure and the temporal and spatial scale of the study.

Main conclusions  The majority of studies found a positive correlation between habitat heterogeneity/diversity and animal species diversity. However, empirical support for this relationship is drastically biased towards studies of vertebrates and habitats under anthropogenic influence. In this paper, we show that ecological effects of habitat heterogeneity may vary considerably between species groups depending on whether structural attributes are perceived as heterogeneity or fragmentation. Possible effects may also vary relative to the structural variable measured. Based upon this, we introduce a classification framework that may be used for across-studies comparisons. Moreover, the effect of habitat heterogeneity for one species group may differ in relation to the spatial scale. In several studies, however, different species groups are closely linked to ‘keystone structures’ that determine animal species diversity by their presence. Detecting crucial keystone structures of the vegetation has profound implications for nature conservation and biodiversity management.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.0305-0270.2003.00994.x

Animal species diversity driven by habitat heterogeneity/diversity: the importance of keystone structures

New studies are documenting trophic cascades in theoretically unlikely systems such as tropical forests and the open ocean. Together with increasing evidence of cascades, there is a deepening understanding of the conditions that promote and inhibit the transmission of predatory effects. These conditions include the relative productivity of ecosystems, presence of refuges and the potential for compensation. However, trophic cascades are also altered by humans. Analyses of the extirpation of large animals reveal loss of cascades, and the potential of conservation to restore not only predator populations but also the ecosystem-level effects that ramify from their presence.

Trophic cascades revealed in diverse ecosystems.

The density and diversity of the spider community has been closely tied to the structural complexity of the local environment For instance, soil dwelling spiders increase dramatically when the litter layer is enhanced because there are more retreats and hiding places and because temperature and humidity extremes are moderated Web-building spiders are directly linked to the configuration of the vegetation because of specific web attachment requirements Both correlative and experimental data sup- port a tight relationship between spider density and habitat structure Most of the available data show that agricultural practices which enhance the structural complexity of the environment (such as intercropping, mulching, and conservation tillage practices) enhance the density and diversity of the spider community The key question regarding spiders in agroecosystems is, of course, whether they are in any way sup- pressing the activity of herbivores Some studies uncovered a strong link between habitat complexity, spider abundance and plant productivity; but others have not, and the mechanisms by which spiders could exert a top-down effect are not clear More investigation into the specifics of how habitat structure influ- ences the predator-prey interactions in agroecosystems is needed in order to truly understand and manage agricultural production in a responsible manner

Architectural features of agricultural habitats and their impact on the spider inhabitants

http://biology.fullerton.edu/swalker/pdfpubs/personsetal2001abs.pdf

Wolf spider predator avoidance tactics and survival in the presence of diet-associated predator cues (Araneae: Lycosidae).

Summary

1. The distribution of the large orb-weaving spider Argiope trifasciata in old field habitats of North America and the habitat selection process this species used was studied for 2 years.



2. Because web spiders have limited dispersal abilities and an energetically costly prey capture device, they do not have the ability to sample potential foraging sites. Structural complexity of the vegetation to which the web must be attached is relatively easy to assess. The hypothesis that the structural complexity is a primary factor in determining initial web site selection was tested both by relating the natural distribution of the spiders across habitats to vegetational complexity and by manipulating the complexity of the habitats in a series of experiments.



3. Argiope trifasciata was not distributed evenly among three old field vegetation types. Habitat complexity was related to spider density in both years although no measure of insect activity, prey capture, or prey consumption was correlated with spider distribution.



4. Three experimental manipulations were conducted to test the impact of habitat structure on spider establishment: (1) the amount of natural vegetation was reduced, (2) structures were added to a simple habitat, and (3) the complexity of the structures added was varied. In each case, spiders were introduced and establishment of webs was monitored. In all manipulations, spider establishment was related to the complexity of the substrate available.



5. These results are important for understanding the cues that influence foraging site selection and therefore provide insight into the distribution of species with limited dispersal abilities and high site investment requirements.

Habitat selection in a large orb-weaving spider: vegetational complexity determines site selection and distribution.

Spiders are abundant predators in many agricultural systems. The goal of this study was to determine if the influence of spiders as predators could cascade through the food web and affect primary producers. We examined the effects of spider augmentation and removal in soybean monocultures to assess their impact on the damage experienced by the plants. In two of three years (1990 and 1992), leaf damage was reduced in areas where spiders were added, and in one of two years (1992), there was increased damage in areas where spiders were removed. The biomass of insects killed by the spiders was positively correlated with spider mass and the leaf damage near augmentation sites was negatively correlated with the mass of insects killed by the spiders. In this study, small changes in spider density had a significant localized effect on the plants, especially in years when damage due to pest insects was high. These data also verified that trophic cascades and top-down control are in operation at measurable levels in soybean food webs

Top-Down Effects in Soybean Agroecosystems: Spider Density Affects Herbivore Damage

The wolf spider, Pardosa milvina, displays effective antipredator behavior (reduced activity) in the presence of silk and excreta cues from adults of another cooccurring wolf spider, Hogna helluo. However, Pardosa and Hogna engage in size-structured intraguild predation, where Pardosa may be either the prey or predator of Hogna. We tested the ability of adult female Pardosa to vary antipredator responses toward kairomones produced by Hogna that vary in size. Hogna were maintained on filter paper for 24 hr. We then presented the paper to adult female Pardosa simultaneously paired with a blank sheet of paper. One treatment had two sheets of blank paper to serve as a control. The Hogna stimulus treatments were as follows (N = 15/treatment): (1) 1 Hogna half the mass of Pardosa; (2) 1 Hogna of equal mass of a Pardosa; (3) 1 adult Hogna, 30 times the mass of Pardosa; and (4) 8 Hogna each 0.25 the mass of Pardosa. Pardosa decreased activity in the presence of kairomones from Hogna of equal or larger size, but showed no change in activity in the presence of a blank control or from a single Hogna smaller than itself. Pardosa showed a reduction in activity in the presence of cues from eight small Hogna. Pardosa avoided substrates with adult Hogna cues, but showed no avoidance response to any other treatment. These results suggest that Pardosa is showing graded antipredator behavior relative to the quantity of predator kairomones present rather than directly discriminating among the different sizes of the predator.

/pdf/wolf-spiders-show-graded-antipredator-behavior-in-the-4oa1vtk4j7.pdf

Ann L. Rypstra

Papers

Architectural features of agricultural habitats and their impact on the spider inhabitants

Wolf spider predator avoidance tactics and survival in the presence of diet-associated predator cues (Araneae: Lycosidae).

Habitat selection in a large orb-weaving spider: vegetational complexity determines site selection and distribution.

Top-Down Effects in Soybean Agroecosystems: Spider Density Affects Herbivore Damage

Wolf spiders show graded antipredator behavior in the presence of chemical cues from different sized predators