Taborsky Barbara, Dieckmann Ulf, Heino Mikko
Department of Behavioural Ecology, University of Bern, Wohlenstrasse 50A, CH-3032 Hinterkappelen, Switzerland.
Proc Biol Sci. 2003 Apr 7;270(1516):713-21. doi: 10.1098/rspb.2002.2255.
In many organisms survival depends on body size. We investigate the implications of size-selective mortality on life-history evolution by introducing and analysing a new and particularly flexible life-history model with the following key features: the lengths of growth and reproductive periods in successive reproductive cycles can vary evolutionarily, the model does not constrain evolution to patterns of either determinate or indeterminate growth, and lifetime number and sizes of broods are the outcomes of evolutionarily optimal life-history decisions. We find that small changes in environmental conditions can lead to abrupt transitions in optimal life histories when size-dependent mortality is sufficiently strong. Such discontinuous switching results from antagonistic selection pressures and occurs between strategies of early maturation with short reproductive periods and late maturation with long reproductive cycles. When mortality is size-selective and the size-independent component is not too high, selection favours prolonged juvenile growth, thereby allowing individuals to reach a mortality refuge at large body size before the onset of reproduction. When either component of mortality is then increased, the mortality refuge first becomes unattractive and eventually closes up altogether, resulting in short juvenile growth and frequent reproduction. Our results suggest a new mechanism for the evolution of life-history dimorphisms.
在许多生物体中，生存取决于体型大小。我们通过引入并分析一个具有以下关键特征的新型且特别灵活的生活史模型，来研究体型选择性死亡率对生活史进化的影响：连续繁殖周期中生长和繁殖期的长度可以在进化上发生变化，该模型并不将进化限制于确定性或不确定性生长模式，并且终生繁殖窝数和大小是进化上最优生活史决策的结果。我们发现，当体型依赖性死亡率足够强时，环境条件的微小变化会导致最优生活史的突然转变。这种不连续的转变源于拮抗选择压力，发生在繁殖期短的早熟策略和繁殖周期长的晚熟策略之间。当死亡率是体型选择性的且与体型无关的部分不太高时，选择有利于延长幼体生长，从而使个体在繁殖开始前达到较大体型的死亡避难所。当死亡率的任何一个组成部分增加时，死亡避难所首先变得不再有吸引力，最终完全关闭，导致幼体生长缩短和频繁繁殖。我们的结果为生活史二态性的进化提出了一种新机制。
