摘要:

Summary1. Dominance/subordinance is a relationship between two individuals in which one defers to the other in contest situations. Each such relationship represents an adaptive compromise for each individual in which the benefits and costs of giving in or not giving in are compared. Familiar associates in groups or neighbours on nearby territories may develop relatively stable dominant‐subordinate relationships based on individual recognition. Although the aggressive aspects of dominance are usually emphasized, the less conspicuous actions of the subordinate individual are actually more important in maintaining a stable relationship.2. In evolutionary terms, dominance essentially equals priority of access to resources in short supply. Usually the subordinate, who would probably lose in combat anyway, is better off to bide its time until better able to compete at another time or another place. Both individuals save time, energy, and the risk of injury by recognizing and abiding by an established dominant‐subordinate relationship.3. Dominance can be either absolute or predictably reversible in different locations or at different times. Of the various forms of dominance behaviour, rank hierarchies and territoriality represent the two extremes of absolute and relative dominance, respectively. A dominance hierarchy is the sum total of the adaptive compromises made between individuals in an aggregation or organized group. Many animals seem to be capable of both absolute and relative dominance, and within species‐specific limits the balance may shift toward one or the other. High density, or a decrease in available resources, favours a shift from relative to absolute dominance. Some species may exhibit both simultaneously. Social mammals may have intra‐group hierarchies and reciprocal territoriality between groups, while the males of lek species may exhibit ‘polarized territoriality’ by defending small individual territories, with the most dominant males holding the central territories where most of the mating takes place.4. Territoriality is a form of space‐related dominance. Most biologists agree that its most important function is to provide the territory holder with an assured supply of critical resources. Territoriality is selected for only when the individual's genetic fitness is increased because its increased access to resources outweighs the time, energy, and injury costs of territorial behaviour.5. Territoriality was first defined narrowly as an area from which conspecifics are excluded by overt defence or advertisement. The definition has been variously expanded to include all more or less exclusive areas without regard to possible defence, and finally to include all areas in which the owner is dominant. I define territory as a fixed portion of an individual's or group's range in which it has priority of access to one or more critical resources over others who have priority elsewhere or at another time. This priority of access must be achieved through social interaction.6. My definition excludes dominance over individual space and moving resources, and includes areas of exclusive use maintained by mutual avoidance. It differs from most other definitions in its explicit recognition of time as a territorial parameter and its rejection of exclusivity and overt defence as necessary components of territorial behaviour. There is an indivisible continuum of degrees of trespass onto territories, and functionally it is priority of access to resources that is important rather than exclusive occupancy.7. There is a similarly indivisible continuum in the intensity of behaviour needed to achieve priority of access to resources. Deciding whether or not an exclusive area is defended leads to the pointless exercise of trying to decide which cues indicating the owner's presence are conspicuous enough to merit being called defence. Concentrating on overt defence emphasizes the aggressive aspects of territorial behaviour rather than the equally or more important submissive aspects such as pass

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00379.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Summary1. Modes of larval development play important roles in the ecology, biogeography, and evolution of marine benthic organisms. Studies of the larval ecology of fossil organisms can contribute greatly to our understanding of such roles by allowing us to race effects on evolutionary time scales.2. Modes of development can be inferred for well preserved molluscan fossils because the size of the initial larval shell (Protoconch I in gastropods, Prodissoconch I in bivalves) reflects egg size. Other morphological criteria are also available, and a comparative approach based on related taxa with known development may be the most reliable method. By combining larval and adult traits, it is possible to recognize modes of larval development in at least some fossil bryozoans, brachiopods, and echinoderms as well.(a) Planktotrophic larvaearise from small eggs, are released in enormous numbers with little parental investment per offspring, and suffer tremendous mortality during and shortly after a planktic existence. These larvae feed on the plankton during development, and are commonly capable of a prolonged free‐swimming existence, and thus wide dispersal.(b) Nonplanktotrophic larvae(which include both planktic lecithotrophic forms and ‘direct developers’) generally arise from large eggs, with relatively few young produced per parent. Relative to planktotrophic larvae, nonplanktotrophic larvae generally receive greater parental investment per larva, and larval mortality is generally lower. These larvae rely on yolk for nutrition during development, and planktic durations are generally much briefer than for species with planktotrophic larvae, so that dispersal capability is considerably less. Energetic investment per egg is generally higher than in planktotrophs, but as there are lower fecundities as well it is difficult to generalize about the total energetic cost of one mode of reproduction against the other.3. Owing to the high dispersal capability of planktotrophic larvae, it has been suggested that species with such larvae will be geographically widespread, geologically long‐ranging, and exhibit low speciation and extinction rates. Species with nonplanktotrophic larvae will tend to be geographically more restricted, geologically short‐ranging, and exhibit high speciation and extinction rates (again, as a consequence of their characteristically low larval dispersal capabilities).4. Recognition of differential dispersal capabilities can play a role in paleobiogeo‐graphic analyses. Concurrent study of the distribution of groups with contrasting modes of development will permit testing of hypotheses concerning timing, magnitudes and frequencies of migration and vicariance events.5. Larval types are not randomly distributed in the oceans, but relationships with other aspects of the organisms' biology and habitats are very complex. Mode of development varies with:(a) Ecology.A simple r–––K model of adaptive strategies is clearly insufficient to explain the observed relationships: while many ‘equilibrium’ species have nonplanktotrophic larvae, and organisms living in less prdictable environments often have planktotrophic larvae, some of the most opportunistic marine species have nonplanktotrophic larvae. Nonetheless, planktotrophic development seems most suited for exploitation of patchy but widespread habitats.(b) Latitude.At shelf depths, planktotrophy is predominant in the tropics, and decreases sharply at high latitudes.(c) Depth.Incidence of planktotrophy decreases with depth across the continental shelf, at least in some taxa. Beyond the shelf, many deep‐sea organisms are nonplanktotrophic (e.g. most bivalves, peracarid crustaceans), but planktotrophic development appears to be present in other groups (prosobranch gastropods, ophiuroids, and bivalves inhabiting transient habitats such as sunken wood and hydrothermal vents).These trends in developmental types will be accompanied by trends in evolutionary rates and patterns as outlined above. The study of larval ecology by paleobiologists will yield insights into the processes that gave rise to ancient evolutionary and biogeographic patterns, and will permit the development and testing of hypotheses on the origins of the patterns

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00380.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00381.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00382.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Summary1. Bacterial blight of cotton is potentially one of the most damaging diseases of cotton.2. Its symptoms and adverse effect on yield are described.3. Control measures include: (i) cultural techniques of crop sanitation, and the destruction of crop residues, as well as close seasons and crop rotation; (ii) chemical seed treatments and foliar sprays; (iii) the breeding of resistant varieties.4. Techniques are described for the breeding of resistant varieties, and sources of useful genetic plant resistance identified.5. The complex nature of the interactions between host genetic resistance, variation in the pathogen and environment is emphasized.6. Successful resistance‐breeding programmes in Africa and the USA are reviewed, and attention is drawn to the pressing need for resistant varieties in India and Pakistan.7. Continued success in the control of bacterial blight will require integrated programmes that include cultural methods, the use of chemicals (particularly as seed treatments) and the cultivation of resistant varieties with durable resistanc

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00383.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00384.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY