This book is designed to help the reader understand the concepts and methods of spatial pattern analysis. The book is divided into three sections of three Chapters each. The first three Chapters lay the foundations of the material by discussing the basic concepts, considerations for the acquisition of data, and the basic methods for a single species in one dimension, concentrating on data from strings of contiguous quadrats. The middle third of the book describes extensions of the basic methods to the analysis of two species, of multiple species and of data used to investigate two-dimensional patterns. The last three Chapters describe different aspects of spatial pattern analysis: point pattern data, pattern on environmental gradients and future extensions of pattern analysis.

The book is written in the first person plural throughout, not as an affectation, but because the material presented here is not the work of just one person, but of a whole group of people who have contributed to the overall research program. That group includes students and associates whose names will be obvious from the citations: Dan MacIsaac, Dave Blundon, Elizabeth John, Maria Zbigniewicz, Rob Powell, Colin Young, and so on. Other students and researchers have allowed us to use their data for illustrative purposes and these include John Stadt and Michael Hunt Jones.

The book does not present the material with a thoroughly consistent notation. This was a deliberate decision, based on the reasoning that a book-wide notation would be forced to be elaborate and thus eventually clumsy.

Introduction

The natural world is a patchy place. The patchiness manifests itself in many ways and over a wide range of scales, from the arrangement of continents and oceans to the alternation of the solid grains of beach sand and the spaces between them. Plants in the natural world also are patchy at a great range of scales from the global distributions of biomes to the arrangements of trichomes and stomata on the surface of a leaf. When the patchiness has a certain amount of predictability so that it can be described quantitatively, we call it spatial pattern. Although the concept of pattern is often associated with nonrandomness, in some cases we will want to allow the possibility of random pattern, because true randomness does permit a certain amount of prediction. As an illustration of spatial pattern, Figure 1.1 presents an example from the literature, a map of the patches of Calluna vulgaris (heather) in a 10m × 20m plot in central Sweden (redrawn from Diggle 1981). A transect through the vegetation, such as the one illustrated in the lower part of the figure, reveals a fairly regular alternation of patches of high density and gaps between them.

Pattern and process

The impetus to study spatial pattern in plant communities comes from the view that in order to understand plant communities, we should describe and quantify their characteristics, both spatial and temporal, and then relate these observed characteristics to underlying processes such as establishment, growth, competition, reproduction, senescence, and mortality.

Introduction

In Chapter 1, one of the first topics introduced was the distinction between treating the information on the spatial arrangement of plants as dimensionless points in a plane or as a mosaic of patches filling the plane. In this chapter, we will examine a number of methods that evaluate certain properties related to spatial pattern using the positions of individual plants in a plane. Several reviews of the analysis of spatial point patterns are available (Diggle 1983; Upton & Fingleton 1985; Cressie 1991), and it is not the intention to repeat a great deal of the material covered in those books. Instead, those methods that parallel the approaches described elsewhere in this book, but using points rather than density or presence, will be emphasized. In general, the kind of data that will be used here is mapped plant positions within a defined study area or plot. Considerations of the shape of the study plot to be used are discussed in Chapter 2.

There are several considerations to be included in our examination and evaluation of methods based on the positions of individual plants. The first is that for an investigation of spatial pattern, techniques that merely distinguish among the three possibilities of clumped, more-or-less random, and overdispersed are not really of interest for the purposes of this book. We want to get more out the analysis; for example, if the plants are overdispersed, what is their spacing, how uniform is the spacing, is the spacing the same between plants of different kinds?

Abstract

All but one or two indigenous species of Compositae on the Hawaiian Islands are endemic to the archipelago, the descendants of ten founder species. Five of the ten endemic lineages (the silversword alliance, Bidens, Lipochaeta sect. Aphanopappus, Lipochaeta sect. Lipochaeta and Tetramolopium) comprise 77 of the 90 endemic species of Hawaiian Compositae and have been regarded as examples of adaptive radiation. The great breadth of morphological and ecological variation in the silversword alliance and Hawaiian Bidens, the two largest groups, is exceptional for insular floras worldwide. Biosystematic and molecular evolutionary data have revealed high genetic similarity between species and lack of effective sterility barriers in each of the five major groups of endemic Hawaiian Compositae, consistent with the young age of the lineages and the long-persistent, woody life-forms of most species. Most species of Hawaiian Compositae are self-compatible, but exceptional breeding system diversity exists, in part associated with selection for outcrossing, with self-incompatibility in the silversword alliance, gynodioecy in Hawaiian Bidens, and gynomonoecy and monoecy in Hawaiian Tetramolopium. Phylogenetic comparisons between the silversword alliance and Hawaiian Tetramolopium show contrasting patterns of adaptive shifts, with recurrent transformations in life-form and habitat preferences in different lineages of the silversword alliance, and a minimal number and narrower range of such transformations in the younger Hawaiian Tetramolopium group. The extent to which lineage size and numbers of major evolutionary shifts in Hawaiian Compositae are attributable to lineage age, origin of key innovations or ‘preadaptations’ is uncertain.

In this part of the book we turn our attention toward general patterns and processes of evolution, although these issues have been dealt with to some extent in other chapters. In Chapter 11, Bruce Bohm provides the first review of distributions of plant secondary products in island ecosystems. Some workers have suggested (e.g., Carlquist, 1980) that in view of their probable defensive functions from fungi and insects, many compounds have, in the more open (and certainly different) habitats of oceanic islands, possibly undergone loss of diversity. That is, relaxation of predation pressure would surely lead to loss of defensive chemicals over many generations. Bohm's survey suggests the contrary. No obvious loss of compounds is seen when comparing chemical arsenals in island plants with continental relatives.

In Chapter 12, the theme of chromosomal stability in endemic plants of oceanic islands is continued by Stuessy & Crawford, that was initiated in Chapter 1 by Gerald Carr for the Hawaiian Islands. This new chapter extends Carr's observations for the Hawaiian Islands into the endemic angiosperm floras of the Juan Fernandez, Bonin and Galapagos Islands, as well as comparisons with the Canary Islands and the Queen Charlotte Islands. The Canaries have a complex geological history, are older relative to the other archipelagos and are very close to the source area in continental Africa. Much more cytological variation in certain genera is seen. On the Queen Charlotte Islands, which are essentially part of the Canadian continent separated only by vagaries of sea level, typical continental levels of chromosomal variation are revealed.

Abstract

Ullung Island is located 150 km east of Korea in the East Sea at 37° N latitude. The island is of volcanic origin, 73km2 in area and approximately 1.8 million years old. Ullung Island contains 700 species of vascular plants of which 37 angiosperms are endemic. Closest phytogeographic ties of the island flora are with South Korea and Central Japan. This chapter offers preliminary observations on relationships of Ullung Island endemics with presumptive source-area relatives. Initial assessments of morphological changes suggest a tendency towards increased stature in island taxa as well as a loss of pubescence and prickles (e.g., in Rubus takesimana). Detailed morphological comparisons using principal components analysis of the endemic Hepatica maxima and close congeners in northeastern Asia support further the observed trends. New chromosome counts are presented for 48 taxa of Ullung Island, including first reports for eight species, representing 40% of the native and endemic angiosperms. These data, in consort with previously published cytological information regarding presumptive relatives, suggest that few aneuploid or euploid changes have occurred during speciation of the angiosperm flora on this island. The endemic angiosperms of Ullung Island appear mostly to have evolved by simple anagenesis, there being little evidence of intra-island cladogenetic speciation events.

Ullung Island is a small island 150 km east of mainland Korea and 300 km west from Japan (Fig. 9.1), extending from 37°27′ to 37°33′ N and from 130°47′ to 130°56′ E.

Abstract

Chromosome numbers available for about 38% of the 956 native species of Hawaiian plants indicate that more than 80% are polyploid. However, support for the occurrence of autochthonous polyploidy is very limited, with fairly clear examples in Peperomia, Portulaca, and Wikstromia; less certain instances in Bobea, Lepidium, Plantago and Psychotria; and dubious examples in Labordia and Polygonum. Likewise, evidence of chromosome evolution in the form of gross structural changes or dysploidy is sparse and clearly demonstrated only in the silversword alliance of Argyroxiphium, Dubautia and Wilkesia. Luzula and Peperomia may provide additional examples of dysploidy. In contrast, a large number of groups, most notably Bidens, Cyrtandra, Hibiscadelphus, Lipochaeta, Pipturus, Scaevola, Tetramolopium, Vaccinium and the lobelioid genera Brighamia, Clermontia, Cyanea, Delissea, Lobelia, Rollandia and Trematolobelia, are seemingly characterized by complete chromosome stasis, at least with respect to gross structural alterations, dysploidy and polyploidy. There appears to be little or no indication that chromosome evolution on the Hawaiian Islands has proceeded in a manner particularly different from continental areas. Rather, the examples of insular chromosome evolution appear to reflect the tendencies inherent in their continental ancestors. In light of the evidence accumulating from molecular studies, it is concluded that the overall patterns of chromosome structural evolution and chromosome stasis observed in plants are most readily explained on the basis of structural variants having different selective values that are determined by the relative positions of critical genes in the genome.

Abstract

Evolution of higher plants on oceanic islands is now understood to be different in certain respects from that in plant groups of continental regions. This volume re-emphasizes the long-held view that island plants often undergo rapid speciation under directional selection through adaptive radiation. Such dramatic morphological change is usually not accompanied by changes in chromosome number (nor structural rearrangements) nor in genetic composition as evidenced by isozyme and RAPD loci. Geographic isolation, especially between islands, is fundamental as a stimulus for speciation. Change in island size and habitat spectra over geological time causes rapid ecological shifts and concomitant extinctions. Modern sources of data and methods of analysis have provided us with some of these newer perspectives and suggest continued research protocols involving: (1) basic floristic inventories using consistent species concepts; (2) preliminary evolutionary hypotheses; (3) geological data and history (especially of vulcanism); (4) explicit phylogenetic hypotheses; (5) estimates of character evolution, including co-evolution and adaptive complexes; (6) postulates of modes of speciation; (7) rigorous biogeographic analyses; and (8) communication of conservation priorities to appropriate officials and agencies.

This volume illustrates the breadth of plant island biological studies from the morphological to the molecular and from the phylogenetic to the biogeographic. The chapters contained herein reflect the dynamic nature of studies of oceanic islands, which in large measure parallel existing ideas and approaches now prevalent in modern plant systematics and evolutionary biology (e.g., Hoch & Stephenson, 1995).

Abstract

Examination of flower morphology and function of three species of genus Callicarpa (Verbenaceae) endemic to the Bonin Islands, C. glabra, C. nishimurae and C. subpubescens, reveals all three species to be dioecious. Male plants have short-styled flowers with sterile ovaries, whereas female plants have long-styled flowers with non-germinating pollen grains. Although the non-germinating pollen grains of female flowers are inaperturate, their size and content are almost the same as the normal 3-colpate pollen grains of male flowers. On the Bonin Islands, the insect fauna for the pollination of Callicarpa plants is sparse and the flowers of the three species produce little nectar. The non-germinating pollen grains of the female flowers may have been maintained as a reward for insect pollinators. Such an unusual dioecism has never been reported from Verbenaceae. The sexual system of Callicarpa on the Bonin Islands might have evolved under biological conditions unique to small oceanic islands.

The evolution of dioecy in flowering plants has been discussed as one of the interesting phenomena in evolutionary biology (e.g., Darwin, 1877; Lewis, 1942; Ross & Weir, 1976; Charlesworth & Charlesworth, 1978; Bawa, 1980; Ross, 1980; Lloyd, 1980; Charnov, 1982; Willson, 1983). Furthermore, the existence of dioecy in island plants has received considerable attention by several workers (Baker, 1955, 1967; Carlquist, 1974; Bawa & Opler, 1975; Ehrendorfer, 1979; Bawa, 1980, 1982; Baker & Cox, 1984; Cox, 1985).

Concerning the colonization of dioecious plants on islands, Bawa (1980, 1982) examined various ecological attributes of dioecy and suggested that dioecious taxa may have been disproportionately more successful in colonizing islands than hermaphroditic taxa.

Abstract

Studies of plants, endemic or otherwise, on islands have disclosed the presence of a wide variety of natural products, acetylenes, alkaloids, cyanogenic glycosides, flavonoids, terpenoids and others. In the vast majority of instances, the chemistry of the island species parallels the chemistry of related continental species with regard to the class or classes of natural product under consideration. In some cases, compound profiles are very similar to those of continental species; in some, simpler profiles are seen, while in others, enriched arrays of compounds occur. In a only a few well-documented cases, notably cyanogenic species on the Galapagos Islands, has loss of the compounds in question apparently occurred.

Many classes of naturally occurring compounds have been implicated as herbivore feeding deterrents and that they exert that activity because of their toxicity. I offer the alternative suggestion that their effectiveness arises from simply tasting bad. It has been suggested that deterrent compounds would be lost if the predator were removed. However, in the absence of herbivore pressure most island species appear to maintain their capacity to manufacture these putative defensive compounds. Therefore, I suggest that the compounds may serve other functions in the plant.

The aims of this chapter are to review the literature concerning secondary compounds reported from island species with emphasis on endemics and to comment on: (1) the use of these data to evaluate evolutionary relationships with mainland species and with each other; and (2) the operation of these compounds in defensive roles in the island environment.

Abstract

The Bonin Islands, consisting of about 20 small islands, are located in the western Pacific Ocean about 1000 km south of the Japanese mainland. The flora of the Bonin Islands is characterized by a high proportion of endemism: 30.4% of indigenous angiosperms, or c. 43% of trees and shrubs. Although humans have inhabited the Bonin Islands for less than 200 years, their impact on the flora has been substantial. Because each island is so small and the diversity of available habitats low, plant species have few options for survival. In addition to the negative effects of human impact, climatic disasters such as droughts or typhoons have exerted considerable damage on certain species. After World War II, the Bonin Islands were left almost uninhabited during more than 20 years of military occupation. During this period many crops and cultivated species escaped and outcompeted original vegetation. Feral goats also contributed to the damage. Of the approximately 460 taxa of flowering plants now found native to the Bonin Islands (including c. 140 endemic taxa), about 80 taxa are considered endangered. Recent efforts toward conservation of selected endangered endemic taxa are discussed.

The Bonin Islands are located in the western Pacific Ocean about 1000 km south of the Japanese mainland. They consist of about 20 small islands scattered in the area of 26°30′ to 27°40′ N, and 142°00′ to 142°15′ E. These islands are aggregated into three groups from north to south; Mukojima, Chichijima and Hahajima.