Natural selection and the evolution of reproductive effort.

Abstract

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.

Avian Life History Evolution in Relation to Nest Sites, Nest Predation, and Food

“…The relationship between fecundity and adult survival could be driven by either trait (Williams 1966a, b, Charnov and Krebs 1974, Hirshfield and Tinkle 1975, Law 1979, Michod 1979, Bell and Koufopanou 1986. Mortality is often emphasized as the driving force (e.g., Law 1979, Michod 1979, Curio 1989, Crowl and Covich 1990, Reznick eta!.…”

Senescent birds redouble reproductive effort when ill: confirmation of the terminal investment hypothesis

“…Although this long-standing hypothesis is a key idea in evolutionary theory (e.g. Hirschfield & Tinkle 1975;Morrow et al 2003;Fessler et al 2005), only fragmentary evidence supports it.…”

Fat Is Sexy for Females but Not Males: The Influence of Body Reserves on Reproduction in Snakes (Vipera aspis)

“…The energetics of reproduction has been a central theme in the ecological study of life history variation (Hirshfield and Tinkle, 1975;Morris, 1987Morris, , 1992Winkler and Wallin, 1987;Stearns, 1992;Monaghan and Nager, 1997), and more recently this topic has become an important focus in behavioral endocrinology (Cherel, Mauget, Lacroix, and Gilles, 1994;Bronson, 1998). It is obvious that organisms cannot reproduce in the total absence of energy reserves (Frish, 1978;Frish and McArthur, 1974), but the relationship between the amount of energy reserves and reproductive output (or effort) is complex and varies among species.…”