Reproductive effort is defined as that proportion of the total energy budget of an organism that is. devoted to reproductive processes. Reproductive effort at a given age within a species will be selected to maximize reproductive value at that age. Reproductive effort is not directly affected by changes in juvenile survivorship, nor necessarily reduced by an increase in adult survivorship. Selection for high levels of reproductive effort should occur when extrinsic adult mortality is high, in environments with constant juvenile survivorship, and in good years for juvenile survivorship in a variable environment, provided that the quality of the year is predictable by adults. Data necessary to measure reproductive effort and to understand how selection results in different levels of effort between individuals and species are discussed. We make several predictions about the effect of increased resource availability on reproductive effort. The empirical bases for testing these predictions are presently inadequate, and we consider data on energy budgets of organisms in nature to be essential for such tests. We also conclude that variance in life table parameters must be known in detail to understand the selective bases of levels of reproductive effort.Reproductive effort has become a central concept in theories of life history evolution. Fisher (1) evidently first called attention to the significance of determining how natural selection adjusts the partitioning of the energy budgets of organisms among reproduction, growth, and maintenance. Theories of how selection effects this adjustment have been developed by Williams (2, 3), Gadgil and Bossert (4), Schaffer (5), and others. Empirical evidence has been variously in accord with, or contradictory to, theoretical predictions (e.g., refs. 6-8).The difficulties in understanding the evolution of reproductive effort stem from the fact that predictions from theory are, in many cases, results of assumptions in the models which require careful examination before the predictions may be considered relevant to organisms in nature. Difficulties also arise because it is not clear what data constitute adequate measures of reproductive effort. It is impossible at present to decide whether failure of the data to be consistent with theory is due to inappropriate estimators or to inadequate theory.The purposes of this paper are: (i) to reexamine the theory of the evolution of reproductive effort, cost, and fitness; (ii) to predict those environmental conditions that result in selection for high and low levels of effort; and (iii) to suggest a methodological framework for the study of reproductive effort that will allow unequivocal tests of theoretical predictions.
New technologies could revolutionize ocean observation
Experiments measured the effects of differences in controlled temperature and food intake on reproduction, growth, and survival of female Japanese medaka, Oryzias latipes, a daily spawning killifish. Maintenance of isolated breeding females at nine different food—temperature treatments allowed the construction of individual energy budgets and hence the measurement of reproductive effort (the proportion of an individual's total energy intake devoted to reproduction). Increased temperature was associated with increased total reproduction and decreased growth at all food levels, although total production (sum of reproduction + growth) was essentially the same at all temperatures. Increased food intake led to higher fecundity at two of the three temperatures, while reproductive effort actually declined with increased food intake at two temperatures. Growth (change in female length, total mass, ovary size, and total energy content) increased with greater food intake at all temperatures. There was no evidence of an increase in reproductive effort with size or age; fecundity declined during the experiments although food intake was constant. Costs of reproduction included reduction in energy content of fish tissue and substantial loss of mass in many fish that nevertheless continued to reproduce at high levels. Reproduction and growth were in general negatively correlated, suggesting that individuals reproducing the most were not able to grow as rapidly as individuals reproducing less. Mortality varied substantially (0—30%) among the treatments and was highest at high temperatures and high levels of reproductive effort.
Two‐thirds of all known coral species live in waters that are deep, dark, and cold. Yet due to the difficulty of researching them in their natural environment, their biology and ecology are poorly understood. Deep‐sea coral communities provide habitat for many vertebrate and invertebrate species, including some commercially important fish and crustacean populations. Some have levels of biological diversity comparable to shallow‐water reefs. They are also highly susceptible to disturbance from many of our deep‐sea activities. Bottom trawling in particular has caused considerable destruction of these communities around the world. Due to their extreme longevity and slow growth, recovery is likely to be in the order of decades or even centuries. We provide an overview of deepwater coral biology and ecology, identify the more manageable threats, and suggest recommendations to mitigate further loss.
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