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

A high number of tree species, low density of adults of each species, and long distances between conspecific adults are characteristic of many low-land tropical forest habitats. I propose that these three traits, in large part, are the result of the action of predators on seeds and seedlings. A model is presented that allows detailed examination of the effect of different predators, dispersal agents, seed-crop sizes, etc. on these three traits. In short, any event that increases the efficiency of the predators at eating seeds and seedlings of a given tree species may lead to a reduction in population density of the adults of that species and/or to increased distance between new adults and their parents. Either event will lead to more space in the habitat for other species of trees, and therefore higher total number of tree species, provided seed sources are available over evolutionary time. As one moves from the wet lowland tropics to the dry tropics or temperate zones, the seed and seedling predators in ...

Herbivores and the Number of Tree Species in Tropical Forests

To investigate the time course of speciation, we gathered literature data on 119 pairs of closely related Drosophila species with known genetic distances, mating discrimination, strength of hybrid sterility and inviability, and geographic ranges. Because genetic distance is correlated with divergence time, these data provide a cross-section of taxa at different stages of speciation. Mating discrimination and the sterility or inviability of hybrids increase gradually with time. Hybrid sterility and inviability evolve at similar rates. Among allopatric species, mating discrim- ination and postzygotic isolation evolve at comparable rates, but among sympatric species strong mating discrimination appears well before severe sterility or inviability. This suggests that pre- zygotic reproductive isolation may be reinforced when allopatric taxa become sympatric. Analysis of the evolution of postzygotic isolation shows that recently diverged taxa usually produce sterile or inviable male but not female hybrids. Moreover, there is a large temporal gap between the evolution of male-limited and female hybrid sterility or inviability. This gap, which is predicted by recent theories about the genetics of speciation, explains the overwhelming pre- ponderance of hybridizations yielding male-limited hybrid sterility or inviability (Haldane's rule).

http://max2.ese.u-psud.fr/epc/conservation/PDFs/HIPE/Coyne1989.pdf

Patterns of speciation in drosophila.

In six bird species convenient for study, niches are known to be broader on some islands than on the mainland. In every case there is also greater variation in a bill measurement on the islands, except for one species in which the niche on the Canary Islands is narrower than that on the mainland. The adjusted variances average about twice as great in the broader niche. These and other results suggest that continuous variation within local populations is often adaptive in itself and is not part of the genetic or phenotypic load.

Morphological variation and width of ecological niche

The literature on the response of insect species to the changing environments experienced along altitudinal gradients is diverse and widely dispersed. There is a growing awareness that such responses may serve as analogues for climate warming effects occurring at a particular fixed altitude or latitude over time. This review seeks, therefore, to synthesise information on the responses of insects and allied groups to increasing altitude and provide a platform for future research. It focuses on those functional aspects of insect biology that show positive or negative reaction to altitudinal changes but avoids emphasising adaptation to high altitude per se. Reactions can be direct, with insect characteristics or performance responding to changing environmental parameters, or they can be indirect and mediated through the insect's interaction with other organisms. These organisms include the host plant in the case of herbivorous insects, and also competitor species, specific parasitoids, predators and pathogens. The manner in which these various factors individually and collectively influence the morphology, behaviour, ecophysiology, growth and development, survival, reproduction, and spatial distribution of insect species is considered in detail. Resultant patterns in the abundance of individual species populations and of community species richness are examined. Attempts are made throughout to provide mechanistic explanations of trends and to place each topic, where appropriate, into the broader theoretical context by appropriate reference to key literature. The paper concludes by considering how montane insect species will respond to climate warming.

Terrestrial insects along elevation gradients: species and community responses to altitude

The flavopilosa group of species of Drosophila, subgenus Drosophila, was established for D. flavopilosa Frey and 13 other species from the Neotropical region (Wheeler et al., 1962). In Chile, the exclusive natural breeding and feeding sites of D. flavopilosa are the flowers of the solanaceous plant, Cestrum parqui L'Her. Recently, Dr. A. Hunter from the Los Andes University (Colombia) and the present author, found inside the flowers of another species of Cestrum (C. tomentosum Sandwith) near Bogota, larvae of two other species of the group (D. acroria and another form not yet determined). These observations suggest that the members of the group are mainly pollen feeders, and probably are associated with different species of Cestrun. Although up to now it has not been possible to breed D. flavopilosa under laboratory conditions, the analysis of larval samples collected directly in their natural breeding sites, has allowed the author to study the chromosomal structure of some Chilean populations of the fly (Brncic, 1962). These studies have demonstrated that the populations of D. flavopilosa are polymorphic for the gene arrangements in their chromosomes, and that the frequencies of certain heterokaryotypes vary according to the geographic regions. These studies have also shown that there is an altitudinal gradient in the distribution of some of these gene arrangements. Such an analysis was interesting for many reasons.

Ecological and cytogenetic studies of drosophila flavopilosa, a neotropical species living in cestrum flowers.

Drosophila pavani of the mesophragmatica group of the subgenus Drosophila is a typically endemic species found abundantly in the central zone of Chile and in a restricted region close to the Andean range in Argentina (Brucie and Koref-Santibaiiez, 1957). There is evidence that this species is able to coexist in nature with certain cosmopolitan species of the subgenus Sophophora such as D. simulans apparently sharing the same basic food resources (Brncic, 1970). On the contrary, D. pavani very seldom has been found coexisting in the same breeding sites with other sympatric species such as D. melanogaster. Budnik and Brncic (1974) studied under laboratory conditions the effects of preadult competition for food between D. pavani and D. simulans, D. melanogaster, or D. willistoni, a third member of the subgenus Sophophora that does not occur in Chile. These experiments revealed that egg-toadult viability of D. pavani decreases significantly in the presence of D. melanogaster larvae but not in the presence of the other two species. D. simulans and D. melanogaster do not suffer appreciable changes in survival when competing with D. pavani, but the viability of D. willistoni is drastically inhibited. Studies carried out by Weisbrot (1966), and Dawood and Strickberger (1969) among others indicated that the metabolic waste products of the \"ebony\" mutant of D. melanogaster affect the viability of D. melanogaster wild type, and the wastes of D. melanogasier interfere with the growth of D. pseudoobscura preadults. According to these authors the explanation of this phenomenon is that each genotype releases biotic wastes that alter the food medium in which the larvae grow, thus affecting differentially the survival and development of the larvae under competitive conditions (see Parsons, 1973, for review).

Effects of larval biotic residues on viability in four species of drosophila.

In their monograph published in 1952, Patterson and Stone knew of 613 described species of Drosophila. The number of known species has beeen growing rapidly in recent years. This growth is due to two causes. First, the Drosophila fauna of somlle previously unexplored regions is being investigated. Secondly, some of the old "species" are being ana. lyzed with the aid of genetic, cytological, and ecological techniques. fn several instances, such arnalysis has disclosed the existence of extremely interesting groups of very closely related, and yet biologically quite clearly independent, sibling species which were previously confused under one species name. The obscura species group (Dobzhansky and Epling, 1944; Dobzhansky, 1951; Buzzati-Traverso and Scossirolli, 1952), the virilis group (Patterson and Stone, 1952), and the willistoni group (Burla et al., 1949) are examples. The neotropical faunal region contains apparently the greatest diversity of species of Drosophila. The study of Drosophila of this region is still in an early exploration stage. Many territories have never been studied for Drosophila, and the nature of most of the described species is inadequately understood. The present article reports the results of a study of the evolutionary status of a cluster of related species, which may be called the 1esophragmatica species group from the oldest described species Drosophila mnesophragrnatica Duda. Some species of this group are quite common in parts of Peru,

The mesophragmatica group of species of drosophila

Chile is situated in the southwestern part of South America, between parallels 17°32′ S. and 56° S., and between meridians 75°40′ W. and 66°33′ W. The country is isolated from the rest of the neotropical zone by strong geographic and bioclimatic barriers: in the north, the Peruvian-Chilean desert, one of the most arid expanses in the world; in the east it is separated from Argentina and Bolivia by the Andes mountains, which prevent the migration of many living organisms. Only south of the lake region (39° S.) is there a zone that allows some species to pass from one side of the Andes to the other. Even so, the climate of this part of the country is unfavorable for the survival of many insects, among them those of the genus Drosophila to which this paper refers. The Andean areas of Chile and Argentina, south of the lake region down to the southern tip of the Hemisphere, constitute a Zoogeographic region which is separated from the rest of South America by the cold and arid barrier of the Patagonian “pampa.”

Studies on the Evolutionary Biology of Chilean Species of Drosophila

When the Chilean endemic species Drosophila pavani compete during the pre- adult stage on a limited amount of food with D. melanogaster, D. simulans, and D. willistoni, developmental periods were significantly retarded, but egg-to-adult viability decreased only in the presence of D. melanogaster. In the same experiments, two of the other three species suffered no modifications in survival and developmental time, but in D. willistoni viability was reduced in the presence of D. pavani larvae. The lengthening of the developmental period of D. pavani may result in utilization of different resources, thus avoiding the direct effects of exploitation competition. The decrease in egg-to-adult viability of D. willistoni in the presence of D. pavani does not seem to be exclusively dependent on food competition. In experiments in which the culture medium was previously "conditioned" by D. pavani larvae, but with an excess of food, the viability of D. willistoni also decreased, indicating that the metabolic waste products of the first species probably interferes with the development of the second.

Danko Brncic

Papers

Ecological and cytogenetic studies of drosophila flavopilosa, a neotropical species living in cestrum flowers.

Effects of larval biotic residues on viability in four species of drosophila.

The mesophragmatica group of species of drosophila

Studies on the Evolutionary Biology of Chilean Species of Drosophila

Preadult Competition between Drosophila Pavani and Drosophila Melanogaster, Drosophila Simulans, and Drosophila Willistoni