Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

Hybrid zones are, roughly speaking, narrow regions in which genetically distinct populations meet, mate, and produce hybrids. They are often only a few hundred meters wide and yet may be several hundred kilometers long. They are found in a wide variety of organisms: Tables 1 and 2 list about 150 reasonably clear examples, in which there is a spatial transition between two hybridizing forms. Such a widespread and striking phenomenon requires explanation; more importantly, it offers us several ways of understanding the nature and origin of species. First, hybrid zones pose interesting questions for the taxonomist, for they contrast two views of the species: as a set of populations delimited by genetic barriers to gene exchange; and as a set of populations maintained in a particular stable equilibrium by selection. Second, the wide range of genotypes found in a hybrid zone can be used to analyze the genetic differences and selective forces that separate the taxa involved. This may allow some inferences about the way these differences evolved and, by extrapolation, about the way fully isolated species diverge from each other. Finally, models of parapatric speciation, and of Wright's "shifting balance," involve the formation, move­ ment, and modification of hybrid zones. Hybrid zones must be understood before the plausibility of these models can be judged. After clarifying our terminology, we will summarize the relevant theory and then see how this can be used to make inferences from field data. A notable increase in the number of detailed genetic studies of hybrid zones occurred over

Analysis of Hybrid Zones

One of the strengths of scientific inquiry is that it can progress with any mixture of empiricism, intuition, and formal theory that suits the convenience of the investigator. Many sciences develop for a time as exercises in description and empirical generalization. Only later do they acquire reasoned connections within themselves and with other branches of knowledge. Many things were scientifically known of human anatomy and the motions of the planets before they were scientifically explained.

The psychological foundations of culture.

A formula for diference between amino acids combines properties that correlate best with protein residue substitution frequencies: composition, polarity, and molecular volume. Substitution frequencies agree much better with overall chemical difference between exchanging residues than with minimum base changes between their codons. Correlation coefficients show that fixation of mutations between dissimilar amino acids is generally rare.

https://science.sciencemag.org/content/sci/185/4154/862.full.pdf

Amino Acid Difference Formula to Help Explain Protein Evolution

Although ecologists commonly talk about the impacts of nonindigenous species, little formal attention has been given to defining what we mean by impact, or connecting ecological theory with particular measures of impact. The resulting lack of generalizations regarding invasion impacts is more than an academic problem; we need to be able to distinguish invaders with minor effects from those with large effects in order to prioritize management efforts. This paper focuses on defining, evaluating, and comparing a variety of measures of impact drawn from empirical examples and theoretical reasoning. We begin by arguing that the total impact of an invader includes three fundamental dimensions: range, abundance, and the per-capita or per-biomass effect of the invader. Then we summarize previous approaches to measuring impact at different organizational levels, and suggest some new approaches. Reviewing mathematical models of impact, we argue that theoretical studies using community assembly models could act as a basis for better empirical studies and monitoring programs, as well as provide a clearer understanding of the relationship among different types of impact. We then discuss some of the particular challenges that come from the need to prioritize invasive species in a management or policy context. We end with recommendations about how the field of invasion biology might proceed in order to build a general framework for understanding and predicting impacts. In particular, we advocate studies designed to explore the correlations among different measures: Are the results of complex multivariate methods adequately captured by simple composite metrics such as species richness? How well are impacts on native populations correlated with impacts on ecosystem functions? Are there useful bioindicators for invasion impacts? To what extent does the impact of an invasive species depend on the system in which it is measured? Three approaches would provide new insights in this line of inquiry: (1) studies that measure impacts at multiple scales and multiple levels of organization, (2) studies that synthesize currently available data on different response variables, and (3) models designed to guide empirical work and explore generalities.

Impact: Toward a Framework for Understanding the Ecological Effects of Invaders

The existence within natural populations of large amounts of genetic variation in molecules and morphology presents an evolutionary problem. The ‘neutralist’ solution to this problem, that the variation is usually unimportant to the organisms displaying it, has now lost much of its strength. Interpretations that assume widespread heterozygous advantage also face serious difficulties. A resolution is possible in terms of frequency-dependent selection by predators, parasites and competitors. The evidence for pervasive frequency-dependent selection is now very strong. It appears to follow naturally from the behaviour of predators, from the evolutionary lability of parasites, from the ecology of competition and, at the molecular level, from the phenomena of enzyme kinetics. Such selection can explain the maintenance not only of conventional polymorphism but also of continuous variation in both molecular and morphological characters. It can account for the occurrence of diversity within groups of haploid and self-fertilizing organisms, and for the evolution of differences between individuals in their systems of genetic control.

http://max2.ese.u-psud.fr/epc/conservation/PDFs/HIPE/Clarke1979.pdf

The Evolution of Genetic Diversity

FREQUENCY-DEPENDENT selection is capable of maintaining a balanced genetic polymorphism (Wright, 1948; Teissier, 1954; Li, 1962, Clarke and O'Donald, 1964). Under this system the selective values of genotypes are negatively related to their frequencies. It has been suggested that predators can exert frequency-dependent selection on their prey, even in the absence of mimetic resemblances between prey species. Cain and Sheppard (1954) first drew attention to this possibility, although the idea was adumbrated by Poulton (1890). It was not until 1962, however, that evidence came to light suggesting that the process does indeed occur (Clarke, 1 962a). Predators apparently concentrate on one or a few common varieties of prey, and tend to overlook rarer forms even if they are obvious. By a process of learning the predators develop specific \"searching images\" for the varieties most frequently encountered (as suggested, in another context, by Tinbergen, 1960). Selection of this type has been described as apostatic because it involves the advantage of rare phenotypes that stand out from the norm. I have argued that it is an important factor in the evolution of diversity within and between species (Clarke, l962a). A study of the land snails (Gepaea nemoralis (L.) and Gepaea hortensis (Mull.) led me to suggest that their polymorphisms are maintained, at least in part, by apostatic selection (Clarke, 1 962b). Carter (1967) has recently criticised some of my conclusions. In the present paper, I will bring up to date the evidence for apostatic selection, discuss its application to Cepaea, and reply to Carter's criticisms.

/pdf/the-evidence-for-apostatic-selection-54ayhdlohs.pdf

The evidence for apostatic selection

/pdf/the-extinction-of-partula-on-moorea-28ikl9750k.pdf

The extinction of Partula on Moorea.

/pdf/natural-selection-in-mixed-populations-of-two-polymorphic-ixlrbjkp4f.pdf

Natural selection in mixed populations of two polymorphic snails

https://www.genetics.org/content/genetics/54/5/1261.full.pdf

Bryan Clarke

Papers

The Evolution of Genetic Diversity

The evidence for apostatic selection

The extinction of Partula on Moorea.

Natural selection in mixed populations of two polymorphic snails

The inheritance of polymorphic shell characters in partula (gastropoda).