Showing papers in "Annual Review of Ecology, Evolution, and Systematics in 1992"

Biological invasions by exotic grasses, the grass/fire cycle, and global change

Abstract: Biological invasions into wholly new regions are a consequence of a far reaching but underappreciated component of global environmental change, the human-caused breakdown of biogeographic barriers to species dispersal . Human activity moves species from place to place both accidentally and deliberately-and it does so at rates that are without precedent in the last tens of millions of years. As a result , taxa that evolved in isolation from each other are being forced into contact in an instant of evolutionary time. This human-caused breakdown of barriers to dispersal sets in motion changes that may seem less important than the changing composition of the atmosphere , climate change , or tropical deforestation-but they are significant for several reasons. First , to date , biological invasions have caused more species extinctions than have resulted from human-caused climatic change or the changing composition of the atmosphere . Only land use change probably has caused more extinction, and (as we later discuss) land use change interacts strongly with biological invasions. Second, the effects of human-caused biological invasions are long-term: changes in climate, the atmosphere, and land use may be reversible in hundreds to thousands of years, but the breakdown of biogeographic barriers has resulted in self-maintaining and evolving

The nearly neutral theory of molecular evolution

Abstract: For a long time the study of evolution has been based on morphology; the long neck of a giraffe, the human brain, a bird’s wing, and so on. Morphological change in evolution is explained by Darwin’s theory of natural selection, but this theory is largely qualitative rather than quantitative. Population genetics started more than half a century ago as an attempt to understand evolutionary change quantitatively. Because evolution must take place in all individuals of a species, the change of gene frequency in the population has been analyzed. However, so long as the facts of evolution are based on morphological traits, evolutionary change is very difficult to connect with gene frequency change except in relatively few circumstances. The remarkable progress of molecular biology has made it possible to apply population genetics theory to real data. We now know that genetic information is stored in linear sequences of DNA which are stably transmitted from generation to generation, and we can compare the linear sequences of DNA and amino acids among species. It is also possible to compare secondary and tertiary structures of proteins and nucleic acids from various sources. Because of such progress, some aspects of traditional neo-Darwinism are beginning to need revision. The first step in such a revision is the neutral mutation-random drift hypothesis put forward by Kimura (47) in 1968. In the next year, King & Jukes (53a) published a similar idea, though from a more biochemical point of view than that of Kimura. This theory states that most evolutionary changes at the molecular level are caused by random genetic drift of selectively neutral or nearly neutral mutations rather than by natural selection. Because this theory was contrary to the neo-Darwinian view at that time, it provoked much controversy. A complete review of the theory is found

Human population growth and global land-use/cover change

Abstract: Contemporary interdisciplinary research on human-induced global environmental change recognizes two broad and overlapping fields of study (67). That of industrial metabolism investigates the flow of materials and energy through the chain of extraction, production, consumption, and disposal of modem industrial society. That of land-use/land-cover change, our concern here, deals with the alteration of the land surface and its biotic cover. Environmental changes of either kind become global change in one of two ways (106): by affecting a globally fluid system (the atmosphere, world climate, sea level) or by occurring in a localized or patchwork fashion in enough places to sum up to a globally significant total. Land-use change contributes to both kinds of global change: to such systemic changes as trace-gas accumulation and to such cumulative or patchwork impacts as biodiversity loss, soil degradation, and hydrological change. Land-use/land-cover change is a hybrid category. Land use denotes the human employment of the land and is studied largely by social scientists. Land cover denotes the physical and biotic character of the land surface and is studied largely by natural scientists. Connecting the two are proximate sources of change: human activities that directly alter the physical environment. These activities reflect human goals that are shaped by underlying social driving forces. Proximate sources change the land cover, with further environmental consequences that may ultimately feed back to affect land use. Contemporary global environmental change is clearly unique. The human reshaping of the earth has reached a truly global scale, is unprecedented in its magnitude and rate, and increasingly involves significant impacts on the

Natural Hybridization as an Evolutionary Process

Abstract: Studies of natural hybridization have generally addressed evolutionary questions using one of the three following frameworks: (i) taxonomy or systematics (57, 59, 73, 79, 111, 172); (ii) mechanisms of reproductive isolation and speciation (21, 23, 24, 26, 32, 34, 47, 56, 60, 82, 91, 110, 132, 134, 136, 141, 143, 157, 158, 167, 169, 173); or (iii) natural hybridization as a fundamental evolutionary process that produces consequences that are significant in their own right (1-4, 6, 31, 62, 77, 90, 100, 116, 122, 128, 130, 162, 166, 174). This review emphasizes the conceptual and empirical basis for the last of these contexts. The evolutionary significance of natural hybridization is thus addressed through two general questions: "To what extent has this process been involved in the evolutionary history of plant and animal species?" and "How does the fitness of hybrid individuals compare with that of the parental taxa?" Natural hybridization and introgression (the transfer of genetic material between the hybridizing taxa through backcrossing; 2, 3) have been ascribed varying levels of importance with regard to the genetic makeup of species and the evolutionary history of species complexes (2, 4, 6, 24, 61, 62, 72, 86, 89, 90, 97, 100, 116, 122, 124, 136, 156, 170, 172). In the extreme, introgression may lead to either the merging of the hybridizing forms (61, 178) or the reinforcement of reproductive barriers through selection for assortative (conspecific) mating (45, 76; but see 37, 136). Another potential consequence is the production of more or less fit introgressed genotypes (107; 87), allowing the expansion of the introgressed form into a novel habitat (89; but see 33, 55). Hybrid individuals may also act as a "hybrid sink" to which pest species are preferentially attracted, thus limiting the ability of pest species

Global Changes During the Last 3 Million Years: Climatic Controls and Biotic Responses

Abstract: Research during the last 20 years has led to a major expansion in knowledge about long-term climatic variability and dynamics. Two developments in particular have advanced the theoretical understanding of the major environmental changes that induce continuous changes in ecosystems. The first development was a recognition that the alternation of glacial and interglacial climates has been paced by the variations in solar radiation generated by periodic variations in the Earth's orbit. The second development involved an increased understanding of the hierarchical controls of regional climatic variations. Studies of marine plankton from deep-sea cores were critical to the first development, whereas the second development arose from regional to global syntheses of paleoclimatic data combined with analyses of paleoclimatic simulations from climate models. These two sets of information illustrate a theoretical framework for understanding temporal climatic variations at the subcontinental scale, and they lead to a recognition that elements of the biosphere such as vegetation and marine plankton have experienced large periodic variations in climate for millions of years. In this paper, we describe the major global climatic variations for the last 20 kyr (kilo years, i.e. 20,000 years), the last 175 kyr, and the last 3 Myr (million years). We combine a map view of changes from the last 20 kyr

Resampling methods for computation-intensive data analysis in ecology and evolution

Abstract: The advent of fast, relatively inexpensive (thus, widely available) microcomputers is transforming the way we analyze data in ecological and evolutionary research. Even more profound, however, are the associated changes in questions asked, empirical methods used, studies conducted, and interpretations offered. Now that an array of computation-intensive statistical methods is newly available for general use, it seems particularly important to assess their advantages and limitations, to note how they are currently being used, and then to consider implications for the future. I focus in this review on four related techniques known in the statistical and biological literature as randomization (or permutation) tests, Monte Carlo methods, bootstrapping, and the jackknife. I refer to them collectively as resampling methods, because each involves taking several-to-many samples from the original data set (randomization, bootstrap, jackknife) or from a stochastic process like the one believed to have generated the data set (Monte Carlo). Each of these methods is actually an extensive family of techniques and specific applications that cannot be thoroughly examined here; instead, I briefly characterize the focal methods and then survey the recent literature in ecology and evolution to identify the issues most frequently associated with these techniques. It emerges that resampling methods are well represented in

Behavioral Homology and Phylogeny

Abstract: The sociobiology debates of the 1970s increased interest in the biology of behavior. At the same time, the growth of cladistics increased interest in how to do systematics and phylogenetic reconstruction. Yet, there are surprisingly few recent papers dealing explicitly with behavior from a phylogenetic perspective. Lack of communication between students of behavior and students of systematics is partly to blame. If one says to a behavioral ecologist, "Isn't it curious that there are white bears in the arctic?" he may say that there is nothing curious about it because they are white like all the other arctic mammals, and the fact that they are bears is irrelevant to the broad patterns of evolution. If one asks the same of a systematist he may reply that there is nothing curious about it because they are still bears like all the others, and the fact that they are white is irrelevant to the broad patterns of evolution. Both perspectives are partly right, and both are less than the whole story. Systematists tend to look for constraints of history, while behaviorists usually prefer to work with a warm ball of clay that lies ready to take on any shape the outside forces push upon it. Some of what follows is review and some is more philosophical, but the point of the paper is simple. Determining homology among behaviors is no different than determining homology among morphological structures. Behavior is not special, it is only more difficult to characterize. Ethology (the study of behavior) is a relatively young science and does not yet have the benefit of centuries of debate and consensus, but that provides more reason for us to take up the challenge now. Ethology has made almost no advance with respect to a phylogenetic understanding of behavior since the late 1950s, and most

Artificial Selection Experiments

Abstract: A knowledge of the magnitude of genetic variability and covariability of quantitative traits in natural populations and an understanding of the action of forces that maintain variation and those that lead to change are fundamental to the study of evolutionary biology. Artificial selection experiments, in which known strong forces are applied to laboratory or field populations over a greatly curtailed evolutionary timescale, have been and continue to be an important source of information on the genetics of quantitative characters and their effects on fitness.

GLOBAL ENVIRONMENTAL CHANGE: An Introduction

Abstract: This issue of the Annual Review of Ecology and Systematics includes a set of papers on the ecological causes and consequences of global environmental change, and on the methods by which these can be studied. Global studies are likely to be among the most important concerns of ecological research and teaching for some decades. While the Annual Review of Ecology and Systematics has published a number of papers in this area (cf 4, 7, 22, 41, 44), the Editorial Committee believed that it would be useful to bring together a set of reviews selected to illustrate the breadth of ecologists' contributions to research on global environmental change. This collection is designed to demonstrate that a very wide array of ecological research is crucial to the analysis of global change-and that both our basic work as ecologists and our contribution to the understanding of Earth as a system will be enhanced if we keep that relevance in mind. Earth is a dynamic system; global environmental change has always been a part of its functioning. A recent and prominent example is the glacial/interglacial cycles of the past 2 million years (12, 13, 16). The current interest in global change arises from the fact that some components of human-caused global change have reached a magnitude at least equal to that of natural changes-and the human-caused changes are often more rapid than and beyond the bounds of natural change, at least for the past millions of years.

On Comparing Comparative Methods

Abstract: Virtually every field in the biological sciences uses comparative, cross-taxonomic analysis. Unlike experimental study, comparative analyses have historically relied on simple correlation of traits across species. In the past ten years, especially since publication of a few landmark papers (e.g. 13, 24), this straightforward comparative methodology has become obsolete. Three simultaneous developments produced this change. First, accumulation of basic data on many phenotypic traits allows for more taxonomically complete and quantitative study; this is particularly evident in relatively modem fields of behavior and ecology (6, 7, 34, 48, 49, 96). Second, the essential framework of comparative study is more solid than ever: systematic biology has delivered a proliferation of classifications for most animal and plant taxa, including detail of a variety of systematic characters, topology of evolutionary radiations, and statistical boundaries on specific taxonomic schemes. Third, comparative studies now are unavoidably statistical; to paraphrase Felsenstein's (24) proclamation for bringing phylogeny into comparative study, "phylogenies [statistics] are fundamental to comparative biology; there is no doing it without taking them into account" (p. 14). Ignoring statistics in comparative study is tantamount to doing an experiment with no control; quite simply, comparative studies require careful selection of appropriate statistical techniques (66). Each of these developments has revitalized an old methodology which is entering a new phase of application in behavior, ecology, and evolution. Although quite exciting, this also brings considerable confusion to the practitioner who simply wants to search for general trends across species or to test a favorite evolutionary hypothesis against independently derived taxa, both reminiscent of classic comparative biology. Therefore, the aim of this paper is to present some of the active and controversial issues that must now be confronted in any comparative study.

The potential for application of individual-based simulation models for assessing the effects of global change

Abstract: The environmental changes that could result from human activities are sufficiently large to be characterized as an "uncontrolled global experiment" (7). The obvious lack of experimental control when complex changes are global in scale, along with a myriad of other logistic difficulties, confound the evaluation of global consequences. This has created a need for reasoned extrapolations from experimental and observational data and the application of computer models to predict the ecological response of the terrestrial surface to changes in the environment. The first model-based evaluations of global changes for terrestrial vegetation focused on identifying which phenomena need to be considered and at what temporal and spatial scales (88, 33). Then the emphasis on plant physiology and biophysics (22, 27, 41, 71, 72, 118) versus the emphasis on individualplant natural history and demography (34, 43, 44, 55, 56, 76, 121) formed

Spatial Scales and Global Change: Bridging the Gap from Plots to GCM Grid Cells

Abstract: The complexity of earth system processes results from interactions among the physical, chemical, and biological subsystems that vary in both time and space. Gaining an understanding of these dynamics has taken on great importance in the context of current environmental change and the portent of even larger scale global change. Appreciation for the concept of "scaling" is increasing as we are challenged to integrate data and models from different disciplines and different time and space scales. In particular, biophysical and ecological information, intrinsically derived at the scale of the individual organism, must be extrapolated to the regional and global scales of climate models. Unfortunately, this may not always be a simple process due to complex spatial variations and nonlinearities in dynamics across landscapes. Bridging the gap between our site-level ecological understanding and global scale phenomena challenges our current disciplinary approach and requires new strategies for acquiring and interpreting information on large-scale earth system dynamics. Research tools such as remote sensing and simulation modeling hold the potential for clarifying general ecological principles by expanding limitations inherent in site-level studies (81, 125). In combination, technologies of remote sensing, geographic information systems, and simulation modeling permit quantitative assessment of the consequences of heterogeneity in earth systems over a broad range of spatial and temporal scales. Remote sensing techniques extend measurements to scales over which biospheric processes operate and

Gastropod phylogeny and systematics

Abstract: Gastropod phylogenetic systematics has seen a recent boost, prompted by the discovery of new taxonomic groups (especially in the hydrothermal-vent faunas) , the development of new and refined morphological and molecular techniques, and the application of new analytical methods of phylogenetic systematics . The class Gastropoda ("snails and slugs") is the largest group of mollusks in terms of species and one of the few animal groups successfully to inhabit marine, freshwater, and terrestrial biotopes . The enormous morpho­ logical and trophic diversity as well as other aspects of gastropod biology has been reviewed elsewhere (e.g. 7 , 1 8 , 78, 80, 90, 95, 99 , 103, 154 , 172 , and numerous articles in 190) . For a general overview see Cox (24) and Solem (152); comprehensive systematic references include the works of Thiele ( 164) , Wenz ( 1 88), Zilch ( 194), Knight et al (94) , Franc (34) , and Boss (17). I report and comment on the status of phylogenetic investigations in the Gastropoda and give a review of attempted classifications. 1 Estimates for extant gastropod species range from 40,000 ( 16) to over 100,000 (51) , comprising about 80% of all extant molluscan taxa . In the traditional division of subclasses, an estimated 53% of the recognized species are prosobranchs (largely marine but with terrestrial and freshwater represen­ tatives) , 4% opisthobranchs (marine), and 43% pulmonates (terrestrial and

Definition and Evaluation of the Fitness of Behavioral and Developmental Programs

Abstract: Whereas population genetics underrates the organism, life history theory underrates the gene. These fields are limited, in part because they ignore each other and in part because they ignore development. Thus the perspective of life history motivates a new look at development because developmental mechanisms could connect population genetics with life history theory to form a predictive theory of evolution more powerful than either of the first two attempted. (Bonner 1982, p. 238)

Trace Fossils and Bioturbation: The Other Fossil Record

Abstract: organisms is best known from body fossils. The activity of both shelly and soft-bodied organisms in sediment can be understood by studying the burrows, tracks, and trails which they create. When preserved in the fossil record these features are called trace fossils. Because preservation of soft-bodied organisms is rare, evidence of behavior is particularly important for understanding the history of soft-bodied marine life. Thus, while the fossil record is generally viewed as consisting of body fossils, the record of trace fossils offers an alternative and independent data source. In the many environmental settings where body fossils are poorly preserved, trace fossils may provide the only evidence of past life. The study of trace fossils and the record of bioturbation (the process by which animals rework the sediment) is a subdiscipline of paleontology called ichnology. Ichnological data is being used as critical evidence for such questions as the timing of the evolution of the Metazoa, changes of life habits, and the invasion of new habitats. This review of trace fossils concentrates on several aspects of the nature of the marine ichnological record. Specifically, after introducing several concepts of ichnology, we discuss three broad areas within ichnology where trace fossils and the record of bioturbation are providing paleobiological data 339