Showing papers in "Annual Review of Ecology, Evolution, and Systematics in 1984"
TL;DR: The body size is one of the most important attributes of an organism from an ecological and evolutionary point of view as mentioned in this paper, and it has a predominant influence on an animal's energetic requirements, its potential for resource exploitation, and its susceptibility to natural enemies.
Abstract: Body size is manifestly one of the most important attributes of an organism from an ecological and evolutionary point of view. Size has a predominant influence on an animal's energetic requirements, its potential for resource exploitation, and its susceptibility to natural enemies. A large literature now exists on how physiological, life history, and population parameters scale with body dimensions (24, 131). The ecological literature on species interactions and the structure of animal communities also stresses the importance of body size. Differences in body size are a major means by which species avoid direct overlap in resource use (153), and size-selective predation can be a primary organizing force in some communities (20, 70). Size thus imposes important constraints on the manner in which an organism interacts with its environment and influences the strength, type, and symmetry of interactions with other species (152, 207). Paradoxically, ecologists have virtually ignored the implications of these observations for interactions among species that exhibit size-distributed populations. For instance, it has been often suggested that competing species
3,129 citations
TL;DR: For many communities, a self-reproducing climax state may only exist as an average condition on a relatively large spatial scale, and even that has yet to be rigorously demonstrated.
Abstract: Two features characterize all natural communities. First, they are dynamic systems. The densities and age-structures of populations change with time, as do the relative abundances of species; local extinctions are commonplace (37). For many communities, a self-reproducing climax state may only exist as an average condition on a relatively large spatial scale, and even that has yet to be rigorously demonstrated (36). The idea that equilibrium is rarely achieved on the local scale was expressed decades ago by a number of forest ecologists (e.g. 10 1, 168). One might even argue that continued application of the concept of climax to natural systems is simply an exercise in metaphysics (41). While this view may seem extreme, major climatic shifts often recur at time intervals shorter than that required for a community to reach competitive equilibrium or alter the geographical distributions of species (6, 21, 43, 76, 92). Climatic variation of this kind influences ecological patterns over large areas, sometimes encompassing entire continents. Other agents of temporal change in natural communities operate over a wide range of smaller spatial scales (47, 242). Second, natural communities are spatially heterogeneous. This statement is true at any scale of resolution (242), but it is especially apparent on what is commonly referred to as the regional scale. (By region I mean an area that potentially encompasses more than one colonizable patch.) Across any land or seascape, one observes a mosaic of patches identified by spatial discontinuities in the distributions of populations (153, 159, 161, 231, 239, 240). Closer examination often reveals a smaller-scale patchwork of same-aged individuals (e.g. 85-87, 101, 146, 199,204,217-220,235,246). Discrete patch boundaries sometimes reflect species-specific responses to
2,312 citations
TL;DR: This work limits the definition of genetic structure to the nonrandom distribution of alleles or genotypes in space or time and disregard genome organization and meiotic processes that can also affect allele and genotype frequencies.
Abstract: Plant populations are not randomly arranged assemblages of genotypes but are structured in space and time (2, 29, 49, 58, 84, 112). This structure may be manifested among geographically distinct populations, within a local group of plants, or even in the progeny of individuals. Genetic structure results from the joint action of mutation, migration, selection, and drift, which in tum must operate within the historical and biological context of each plant species. Ecological factors affecting reproduction and dispersal are likely to be particularly important in determining genetic structure (2, 31, 58). Reproduction is the process that translates the current genotypic array into that of subsequent generations, while the dispersal of pollen and seeds determines the postreproductive pattems of gene dispersion within and among populations. Although the concept of genetic structure has been used in various ways (58, 130, 154), we limit our definition to the nonrandom distribution of alleles or genotypes in space or time and disregard genome organization and meiotic processes that can also affect allele and genotype frequencies. Because of the limited mobility of plants, their genetic structure implies spatial structure, or the actual physical distribution of individuals. While spatial pattems often have genetic implications, nonrandom genetic pattems can exist without a nonrandom distribution of individuals. Conversely, a population may have a nonrandom spatial distribution without any accompanying genetic structure. Spatial and genetic patterns are often assumed to result from environmental heterogeneity and differential selection pressures (22, 53, 131, 132). Selection is a ubiquitous feature of natural populations; it alters gene and
2,057 citations
TL;DR: It follows that the proportion of individuals in a population foraging in ways that enhance their fitness will tend to increase over time, and the average foraging behavior will increasingly come to be characterized by those characteristics that enhance individual fitness.
Abstract: Proponents of optimal foraging theory attempt to predict the behavior of animals while they are foraging; this theory is based on a number of assump tions ( 133 , 155 , 2 10, 23 1 ) . First, an individual's contribution to the next generation (i.e. its "fitness") depends on its behavior while foraging. This contribution may be measured genetically or culturally as the proportion of an individual's genes or "ideas", respectively, in the next generation. In the former case, the theory is simply an extension of Darwin's theory of evolution. Second, it is assumed that there should be a heritable component of foraging behavior, i.e. an animal that forages in a particular manner should be likely to have offspring that tend to forage in the same manner. This heritable compo nent can be either the actual foraging responses made by an animal or the rules by which an animal learns to make such responses. In other words, optimal foraging theory may apply regardless of whether the foraging behavior is learned or innate. Given these first two assumptions, it follows that the proportion of individuals in a population foraging in ways that enhance their fitness will tend to increase over time. Unless countervailed by sufficiently strong group selection (see 287, 242), foraging behavior will therefore evolve, and the average foraging behavior will increasingly come to be characterized by those characteristics that enhance individual fitness. The third assumption is that the relationship between foraging behavior and fitness is known. This relationship is usually referred to as the currency of fitness (23 1 ) . In general, any such currency will include a time scale, although in some cases it may be assumed that fitness is a function of some rate.
1,917 citations
TL;DR: The mechanism underlying the phenomenon of heterosis has received a great deal of attention from empiricists and theoreticians, and has been viewed as the consequence of either increased homozygosity at a large or inbreeding depression.
Abstract: In 1954 I Michael Lerner published Genetic Homeostasis, a compendium of observations on the relationships among heterozygosity, growth rate and other measures of performance, and developmental homeostasis These observations were primarily made on cultivated plants and domesticated animals, and the experiments usually contrasted inbred, predominantly homozygous lines with the highly heterozygous progeny of crosses between inbred lines Highly heterozygous individuals and lines generally exhibited the traits that breeders strive to fix in their strains In comparison with inbred, homozygous lines, they usually had superior growth rates; often attained greater size; and generally had more buffered developmental processes, resulting in lower morphological variation (eg 8) Contrary results, however, are known (eg 10, 89) These results-and similar studies (20, 21, 88)-have influenced the thinking of plant and animal breeders, but the impact of these studies on population biology and population genetics has, as yet, been slight The mechanism underlying the phenomenon of heterosis has received a great deal of attention from empiricists and theoreticians (see 1 11 for a review) Summarizing briefly, the antithesis of heterosis-inbreeding depression-has been viewed as the consequence of either increased homozygosity at a large
745 citations
TL;DR: It is argued that, although founder effects may cause speciation under sufficiently stringent conditions, they are only one extreme of a continuous range of possibilities, and divergence may be driven in a variety of ways, without the need for drastic external changes.
Abstract: Are new species formed in rare catastrophes, distinct from the normal processes of phyletic evolution? Or does reproductive isolation evolve gradually, as a by-product of the divergence of gene pools? Mayr (120-124) has argued the former, holding that speciation usually results from genetic revolutions triggered by founder effects: An isolated population, small in numbers and in geographic extent, colonizes a new area. Both changes in selection pressures and genetic drift result in the rapid shift of many genes to a new, coadapted combination, which is reproductively isolated from the ancestral population. Carson (27, 29, 3 1) and Templeton (I175-180), among others, have put forward similar models. This cluster of theories is woven from many strands; we will try to tease these apart in order to find out precisely which processes may be involved in speciation by founder effect. By placing them in the context of other models, we will argue that, although founder effects may cause speciation under sufficiently stringent conditions, they are only one extreme of a continuous range of possibilities. Complete geographic isolation is unnecessary; absolute coadaptation between "closed" systems of alleles is unlikely; and divergence may be driven in a variety of ways, without the need for drastic external changes. Reproductive isolation is most likely to be built up gradually, in a
643 citations
TL;DR: Data is reviewed suggesting that at least in certain cases, architectural constraints affect the range of morphological plasticity that can be expressed and it is postulate that when these constraints are present, plants consist not only of morphology subunits but, as Adams (4) first suggested, of physiological subunits as well.
Abstract: Phenotypic plasticity is an important element in the response repertoire of plants (25). It may be manifested as changes in organ (e.g. leaf) morphology as well as in patterns of biomass distribution. Morphological plasticity throughout growth is possible because plant development is modular in form (77, 184, 185). Growth results from the reiteration of basic morphological subunits produced by meristems. Because meristems may develop into either reproductive or vegetative structures, patterns of biomass distribution reflect developmental decisions (121, 172, 180). In this essay, we review data suggesting that at least in certain cases, architectural constraints affect the range of morphological plasticity that can be expressed. Because carbon is frequently viewed as a critical currency of allocation (76, 165), we focus on how these constraints influence assimilate (i.e. carbon) production and utilization. We postulate that when these constraints are present, plants consist not only of morphological subunits (185) but, as Adams (4) first suggested, of physiological subunits as well. We call these integrated physiological units (IPUs) and propose that they are made up of identifiable arrays of morphological subunits that together function as relatively autonomous structures with respect to the assimilation, distribution, and utilization of carbon. If such units of physiological integration exist,
631 citations
TL;DR: As a dynamic process of genetic change, evolution manifests itself in two ways: it produces adaptive characters, and it produces species as mentioned in this paper. But to recognize that evolution has occurred by studying these products does not satisfy interested population geneticists.
Abstract: As a dynamic process of genetic change, evolution manifests itself in two ways: It produces adaptive characters, and it produces species. To recognize that evolution has occurred by studying these products does not satisfy interested population geneticists. They see their science as providing an opportunity to contribute information that permits us to describe how the process of descent with genetic change occurs in populations of sexually reproducing, crossfertilizing organisms.
615 citations
509 citations
TL;DR: Many flowers produce rewards, usually nectar or pollen or both, but flowers do not always reward pollinators; his observations were on the genus Orchis.
Abstract: Many flowers produce rewards, usually nectar or pollen or both. C. K. Sprengel (165), the founder of modern floral biology, was the first to report that flowers do not always reward pollinators; his observations were on the genus Orchis. Subsequent authors (7; 51; 66; 97; 99; 105; 186, p. 21; 195) have discussed various aspects of deceitful flowers that attract pollinators by resembling rewarding flowers or other objects.
469 citations
TL;DR: A corollary of provisioning offspring with food is a stable, relatively high metabolic rate, which ensures that parents can maintain a steady flow of food to the relatively few, "expensive" offspring.
Abstract: We limit our discussion of food storage, or caching, to the movement of potential food items from one location to another for eating at some later time. This activity occurs exclusively in those animals that bring food to their offspring, and not in those that bring their offspring to food (i.e. that lay their eggs near food in a favorable microhabitat). Provisioning offspring is limited taxonomically to mammals, most birds, and some Hymenoptera. Moving food to a favorable microhabitat was apparently the first transitional step in the evolution of more complex systems of provisioning offspring in hymenopterans (72). Although all species that cache food provision their offspring, the converse is not true. Relatively few of the animals that provision their young with food also cache food, and caching food has no obvious connection to the glandular secretion of milk, which probably initiated offspring provisioning in the evolutionary history of mammals. Repeated traveling from a foraging area to dependent young seems to precondition animals for caching food. One of the goals of our review will be to determine what other conditions among species of birds and mammals and their food favor the evolution of caching. We limit our discussion to birds and nonhuman mammals because of our own backgrounds and because experimental studies have recently been done on these vertebrates (4, 14, 20, 48a, 62, 10la, 103-105, 116, 117, 128), although earlier investigations started with wasps (121). A corollary of provisioning offspring with food is a stable, relatively high metabolic rate (even in the Hymenoptera), which ensures that parents can maintain a steady flow of food to the relatively few, "expensive" offspring
TL;DR: The unnecessary limitations that have been imposed on the application of electrophoretic data in systematic studies are assessed and the issues and problems that fuel the controversy over analytical procedures are identified.
Abstract: The data base generally known as electrophoretic data is widely acknowledged to be of value to systematics (1, 2, 8, 17, 24, 79, 86). Although starch-gel electrophoresis of enzymes has become the established method of generating this data base, the analysis of electrophoretic data has remained varied and at times openly contested (28, 30, 55, 65, 67, 69, 82, 83). The treatment of these data has produced interesting results that have been perceived to demonstrate severe limitations on the nature and application of this data base at various taxonomic levels. Differing opinions on data treatment often obscure the multistep nature of these treatments. Many studies purporting to compare systematic treatments of electrophoretic data actually confuse the issue by simultaneously varying procedures at several levels, e.g. data transformation, coding, and method of analysis. Several options exist for each step, and these potential differences affect the results of comparative studies in various ways. The historical perspective employed here is essential for understanding the development of issues and the refinement of procedures. This review also assesses the unnecessary limitations that have been imposed on the application of electrophoretic data in systematic studies and identifies the issues and problems that fuel the controversy over analytical procedures. Finally, recommendations for the phylogenetic treatment of electrophoretic data are presented.
TL;DR: It is argued that rand K-selection may have important ramifications for the understanding of life history evolution, but for the model to be useful, it must be interpreted strictly as it was originally formulated: as a model of density-dependent natural selection.
Abstract: Dawkins (36, p. 293) observes that "ecologists enjoy a curious love/hate relationship with the r/K concept, often pretending to disapprove of it while finding it indispensable." Others have suggested that the model of rand K-selection is inadequate and outmoded and does not further our understanding of life history phenomena (105, 120, 123). These views unfortunately result from frequent misuse and overgeneralization of the model. I contend that rand K-selection may have important ramifications for our understanding of life history evolution, but for the model to be useful, it must be interpreted strictly as it was originally formulated: as a model of density-dependent natural selection. To minimize confusion, I begin this review with an outline of rand K-selection explicitly as a model of density-dependent natural selection. I then attempt to place this model within a historical context with other life history theory. As with recent criticisms of competition theory (109), I find that rand K-selection suffers from a lack of true tests of its hypotheses. Although it may play a significant role in the evolution of life histories, there are few empirical studies that can identify density dependence that is independent of other potential selective forces.
TL;DR: The familiar central-marginal model in evolutionary biology asserts that populations near the center of a species' range usually are contiguous, are at high density, and display high levels of genetic and phenotypic variation, while populations on the margin of the range are isolated, sparse, and chromosomally monomorphic.
Abstract: The familiar central-marginal model in evolutionary biology asserts that populations near the center of a species' range usually are contiguous , are at high density, and display high levels of genetic and phenotypic variation, while populations on the margin of the range are isolated, sparse, and chromosomally monomorphic (88 , 94). Because of their supposedly unique genetic properties , marginal populations are considered very important in speciation events ( 1 1 , 94), and some researchers now assume that speciation on the edge of the range is the predominant mode of speciation in the majority of groups (e .g . 62) . Most of the earlier data on the genetic characteristics of central and marginal popUlations came from studies of chromosomal· polymorphism in various species of Drosophila. These studies often revealed a common pattern: Popula tions from the center of the range were highly polymorphic for inverted sequences, while those near the edge of the range usually showed a marked reduction or absence of this kind of variation . By 1973 such a pattern could be documented for 1 4 of the 1 5 species that had been examined extensively enough to permit such a comparison (128). Da Cunha et al (37) and da Cunha & Dobzhansky (38) proposed that this pattern could be explained by an ecological hypothesis: The amount of chromosomal polymorphism in a population is proportional to the number of ecological niches it exploits, and more niches are
TL;DR: This work will primarily review field studies focusing on the variation in behavior, body size, and life histories and emphasize data collected on identified individuals that have been observed directly (sometimes supplemented by radio-tracking) over long periods of time.
Abstract: The mammalian order Carnivora is characterized by a great range of behavior al, ecological, and morphological adaptations, as well as substantial intraspe cific variability ( i .e. behavioral scaling; see 324) . For example, in wolves (see Table 1 for scientific names), body size ranges from 31 to 78 kg, litter size varies from 1 to 11, home-range size differs 50--100 fold, populations are found in every vegetational zone except tropical forests and arid deserts, and indi viduals may live alone, in pairs, or in large packs (124, 204, 332). Despite such widespread variation, comparative analyses indicate that there also is remarkable consistency (86, 105) in the ways many diverse carnivores adapt to their habitats . Therefore , it is possible to highlight trends in the phylogeny of behavior and life history characteristics by drawing on data from numerous disciplines, including anatomy, physiology, taxonomy, behavior, and ecology (16,54,83,84,92,93,97,128,191,196,199,242,243,313, 331). Due to space limitations, we will primarily review field studies focusing on the variation in behavior, body size, and life histories and emphasize data collected on identified individuals that have been observed directly (sometimes supplemented by radio-tracking) over long periods of time. Such studies are
TL;DR: Individual migration and demic diffusion are discussed in the first and last major parts of the review, respectively, and exchange among populations is discussed in three sections in which other variables are also considered.
Abstract: The importance of migration as a force influencing genetic structure has long been recognized. There are a number of ways in which migration can occur, however, each with its characteristic properties, effects on genetic structure, and problems of estimation. In the following pages, we will discuss these processes and their effects on the genetic structure and makeup of populations. In our analysis of the quantitative data on this phenomenon, we will look at human populations because of the paucity of data on migration in other organisms. For purposes of discussion, it is convenient to consider three aspects of migration: (a) individual migration (natal dispersal plus breeding dispersal), (b) exchange among genetically differentiated populations, and (c) demic diffusion (the cumulative effects of migration with population expansion, where the expansion accompanies the migration). These three aspects are not mutually exclusive, and they interact with other variables (selection, geographic distance, drift, etc.) to influence genetic differentiation among populations. We will consider some of these interactions in this review; we will not consider the interaction between migration and population structure [for a review of this, see Karlin (64)]. Individual migration and demic diffusion are discussed in the first and last major parts of the review, respectively. Exchange among populations is discussed in three sections in which other variables are also considered. In the
TL;DR: Farming based wholly upon the kinds of factors of production that have been used by farmers for generations can be called traditional agriculture, and a better definition would be based on measures of efficiency or intensity.
Abstract: Agriculture presents a fertile field for the analysis of technological change for a number of reasons, including our strong concern about the future adequacy of food supplies. In our highly urbanized world, human beings are no less dependent on the land than they were in the past, but we now have only tenuous connections to it; it is natural to wonder whether things are being done properly out there. At present, as in the past, the merits of old and new directions in agriculture are actively discussed, and words such as traditional, appropriate, alternative, and sustainable are used to characterize views that contrast with contemporary (i.e. modern or conventional) agriculture. Few of these terms have precise definitions. Schultz provides something of a foundation when he writes: "Farming based wholly upon the kinds of factors of production that have been used by farmers for generations can be called traditional agriculture" (83, p. 3). He had in mind the differences between a modem agriculture with inputs and management based on scientific knowledge, and primitive, labor-oriented systems without scientific knowledge. Since many "modern" practices have survived for hundreds of generations, a better definition would be based on measures of efficiency or intensity. Some of the terms represent beliefs in the need for less demanding life styles while recognizing that science is necessary in some degree. Others represent political or religious ideologies with elements of antiscience, including the proposition