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Resource Productivity (resource + productivity)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

THE ROLE OF SIZE-SPECIFIC PREDATION IN THE EVOLUTION AND DIVERSIFICATION OF PREY LIFE HISTORIES

EVOLUTION, Issue 5 2002
Troy Day
Abstract Some of the best empirical examples of life-history evolution involve responses to predation. Nevertheless, most life-history theory dealing with responses to predation has not been formulated within an explicit dynamic food-web context. In particular, most previous theory does not explicitly consider the coupled population dynamics of the focal species and its predators and resources. Here we present a model of life-history evolution that explores the evolutionary consequences of size-specific predation on small individuals when there is a trade-off between growth and reproduction. The model explicitly describes the population dynamics of a predator, the prey of interest, and its resource. The selective forces that cause life-history evolution in the prey species emerge from the ecological interactions embodied by this model and can involve important elements of frequency dependence. Our results demonstrate that the strength of the coupling between predator and prey in the community determines many aspects of life-history evolution. If the coupling is weak (as is implicitly assumed in many previous models), differences in resource productivity have no effect on the nature of life-history evolution. A single life-history strategy is favored that minimizes the equilibrium resource density (if possible). If the coupling is strong, then higher resource productivities select for faster growth into the predation size refuge. Moreover, under strong coupling it is also possible for natural selection to favor an evolutionary diversification of life histories, possibly resulting in two coexisting species with divergent life-history strategies. [source]

A new role for MSY in single-species and ecosystem approaches to fisheries stock assessment and management

FISH AND FISHERIES, Issue 1 2001

In 1977, Peter Larkin published his now-famous paper, ,An epitaph for the concept of maximum sustained yield'. Larkin criticized the concept of single-species maximum sustained yield (MSY) for many reasons, including the possibility that it may not guard against recruitment failure, and the impossibility of maximising sustainable yields for all species simultaneously. However, in recent years, there has been a fundamental change in the perception of the fishing mortality associated with MSY (FMSY) as a limit to be avoided rather than a target that can routinely be exceeded. The concept of FMSY as a limit is embodied in several United Nations Food and Agriculture Organization (FAO) agreements and guidelines, and has now been incorporated into the US Magnuson,Stevens Fishery Conservation and Management Act. As a result, the United States now requires the development of overfishing definitions based on biological reference points that treat the FMSY as a limit reference point and must also define a lower limit on biomass below which rebuilding plans with strict time horizons must be developed. This represents a major paradigm shift from the previously mandated (but often unachieved) objective to simply maintain fishing mortalities at levels below those associated with recruitment overfishing. In many cases, it requires substantial reductions in current fishing mortality levels. Therefore, the necessity of the new paradigm is continually questioned. This paper draws on examples from several fisheries, but specifically focuses on the recent US experience illustrating the practical difficulties of reducing fishing mortality to levels below those corresponding to MSY. However, several studies suggest that even more substantial reductions in fishing mortality may be necessary if ecosystem considerations, such as multispecies interactions, maintenance of biodiversity and genetic diversity, and reduction of bycatch and waste, are taken into account. The pros and cons of moving beyond single-species assessment and management are discussed. A US plan for improving stock assessments indicates that even a ,basic' objective such as ,adequate baseline monitoring of all managed species' may be extremely costly. Thus, the suggestion of Larkin (1983, 1997) that the costs of research and management should not exceed 10,20% of the landed value of the catch may preclude comprehensive ecosystem management. More importantly, neither single-species nor ecosystem-based fisheries management is likely to improve appreciably unless levels of fishing capacity are aligned with resource productivity, as is currently being promoted by FAO and several individual nations. [source]

Endocrine mechanisms of primate life history trade-offs: Growth and reproductive maturation in vervet monkeys

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 6 2009
Patricia L. Whitten
Life history theory predicts that the timing of maturation will result from a trade-off between growth and the age of first reproduction. This trade-off and its mechanisms of action are still poorly understood in many species and have not been well studied at the individual level. This study examined hypothesized trade-offs between growth and reproductive maturation in wild populations of vervet monkeys (Cercopithecus aethiops) from Kenya, East Africa. Individuals were sampled from four populations in widely separated sites differing in temperature, altitude, and rainfall. Biological samples and morphometric measures were collected from 50 adult males, 83 adult females, and 225 juveniles. Gonadal steroids and leptin levels were analyzed by radioimmunoassay of sera from 136 juvenile males and 90 juvenile females. Cross-sectional profiles of morphometric and endocrine data were used to assess the onset and cessation of growth in relation to sexual maturation. Gonadal steroids were used to assess sexual maturation and breeding onset. Leptin was used as an index of nutritional state. Estimates of mortality were derived from population age-structure. Across populations, higher resource productivity and nutrient status were associated with more rapid growth. Shorter growth duration was associated with earlier reproductive onset. These findings provide support for models of trade-offs between the timing of growth completion and reproductive onset, but they are contradicted by the evidence that reproduction precedes the cessation of growth in these populations. The biphasic actions of estradiol provide an alternative model and mechanism for the growth-reproduction trade-off. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source]