Abstract
Reproductive behavior cannot be understood without taking the local level of competition into account. Experimental work in great tits (Parus major) showed that (1) a survival cost of reproduction was paid in environments with high levels of competition during the winter period and (2) experimentally manipulated family size negatively affected the ability of parents to compete for preferred breeding boxes in the next spring. The fact that survival was affected in winter suggests that the competitive ability of parents in winter may also be affected by previous reproductive effort. In this study, we aim to investigate whether (1) such carryover effects of family size on the ability of parents to compete for resources in the winter period occurred and (2) this could explain the occurrence of a survival cost of reproduction under increased competition. During two study years, we manipulated the size of in total 168 great tit broods. Next, in winter, we induced competition among the parents by drastically reducing the availability of roosting boxes in their local environment for one week. Contrary to our expectation, we found no negative effect of family size manipulation on the probability of parents to obtain a roosting box. In line with previous work, we did find that a survival cost of reproduction was paid only in plots in which competition for roosting boxes was shortly increased. Our findings thus add to the scarce experimental evidence that survival cost of reproduction are paid under higher levels of local competition but this could not be linked to a reduced competitive ability of parents in winter.
Highlights
Competition within the social environment of a parent may be an important selective force on its reproductive behavior (Nicolaus et al, 2012; Svensson & Sheldon, 1998; Wilson, 2014)
The trade-off between current and future reproduction implies that if a parent increases its investment into current reproduction, this leads to physiological costs for the parent; in turn, these physiological costs are expected to lead to fitness costs of reproduction
After experimental reduction of the number of roosting boxes in winter, we found that (1) prior family size manipulation did not affect the ability of great tit parents to claim one of the scarce roosting boxes, but (2) we did find that the short period of increased competition for roosting boxes resulted in a survival cost of reproduction, strengthening the scarce experimental evidence (Nicolaus et al, 2012) that survival cost of reproduction depend on the competitive situation
Summary
Competition within the social environment of a parent may be an important selective force on its reproductive behavior (Nicolaus et al, 2012; Svensson & Sheldon, 1998; Wilson, 2014). The actual empirical evidence, especially for a survival cost of reproduction, has proved mixed; (avian: Linden & Moller, 1989; Dijkstra et al, 1990; Stearns, 1992; Golet, Irons, & Estes, 1998; Parejo & Danchin, 2006; Santos & Nakagawa, 2012; mammals: Stearns, 1992; Hamel et al, 2010), in some populations, a survival cost of reproduction has been detected, but not in others One reason for this discrepancy may be that a survival cost of reproduction may only occur when competition in the social environment is high (Nicolaus et al, 2012; Oksanen, Koivula, Koskela, & Mappes, 2007). We expected that if the availability of roosting boxes was limited, experimentally manipulated family size would negatively affect the ability of parents to claim a roosting box in the subsequent winter This in turn could result in a survival cost of reproduction for the parents involved. We quantified the effect of family size manipulation on the ability of parents to claim a roosting box and on the apparent survival of parents in relation to the increased competition for roosting boxes
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