Leatherbury Kathryn N, Travis Joseph
Department of Biological Science Florida State University Tallahassee Florida.
Ecol Evol. 2018 Dec 14;9(1):100-110. doi: 10.1002/ece3.4634. eCollection 2019 Jan.
The feedbacks from population density to demographic parameters, which drive population regulation, are the accumulated results of several ecological processes. The compensatory feedback from increased population density to fertility includes at least two distinct factors, the effects of decreases in per capita food level and increases in the social density (the number of interacting individuals). Because these effects have been studied separately, their relative importance is unknown. It is also unclear whether food limitation and social density combine additively to influence fertility. We investigated these questions with two factorial experiments on reproduction in the Least Killifish, . In one experiment, we crossed two levels of density with two levels of a total food ration that was distributed to all individuals. In the other experiment, we crossed two levels of density with two levels of per capita food. Whereas the first experiment suggested that the effects of variation in food level and density were synergistic, the second experiment indicated that they were not. The apparent synergism-the statistical interaction of food and density levels-was the result of confounding per capita food with social density in that design. In the second experiment, the effects of social density on reproductive rate were stronger than the effects of food level, whereas the effects of food level were stronger on offspring size at parturition than those of social density. The results suggest that the social stresses that emerge at higher densities play an important role in the compensatory response of fertility to density, a role, that is, at least as important as that of decreased per capita food levels.
从种群密度到驱动种群调节的人口统计学参数的反馈，是几个生态过程的累积结果。种群密度增加对繁殖力的补偿性反馈至少包括两个不同的因素，即人均食物水平下降的影响和社会密度（相互作用个体的数量）增加的影响。由于这些影响是分别研究的，它们的相对重要性尚不清楚。食物限制和社会密度是否以相加的方式共同影响繁殖力也不清楚。我们用关于细纹鳉鱼繁殖的两个析因实验研究了这些问题。在一个实验中，我们将两种密度水平与分配给所有个体的两种总食物配给水平进行交叉。在另一个实验中，我们将两种密度水平与两种人均食物水平进行交叉。第一个实验表明食物水平和密度变化的影响是协同的，而第二个实验表明它们不是。明显的协同作用——食物和密度水平的统计相互作用——是该设计中人均食物与社会密度混淆的结果。在第二个实验中，社会密度对繁殖率的影响比食物水平的影响更强，而食物水平对分娩时后代大小的影响比社会密度的影响更强。结果表明，在较高密度下出现的社会压力在繁殖力对密度的补偿反应中起重要作用，也就是说，这一作用至少与人均食物水平下降的作用同样重要。
