Abstract
BackgroundThe allocation of resources between offspring size and number is a central question of life-history theory. Although several studies have tested the existence of this trade-off, few studies have investigated how environmental variation influences the allocation of resources to offspring size and offspring number. Additionally, the relationship between population dynamics and the offspring size and number allocation is far less understood.MethodsWe investigate whether resource allocation between egg size and clutch size is influenced by the ambient temperature and whether it may be related to apparent nest survival rate. We measured 1548 eggs from 541 nests of two closely related shorebird species, the Kentish Plover (Charadrius alexandrinus) and the White-faced Plover (C. dealbatus) in China, in four populations that exhibit contrasting ambient environments. We weighed females, monitored nest survival, and calculated the variance of ambient temperature.ResultsAlthough we found that egg size and clutch size were all different between the four breeding populations, the reproductive investment (i.e. total clutch volume) was similar between populations. We also found that populations with a high survival rate had relatively larger eggs and a smaller clutch than populations with a low nest survival rate. The latter result is in line with a conservative/diversified bet-hedging strategy.ConclusionsOur findings suggest that plovers may increasing fitness by investing fewer, larger or many, small according local nest survival rate to make a similar investment in reproduction, and thereby may have an impact on population demography.
Highlights
The allocation of resources between offspring size and number is a central question of life-history theory
Breeding performance and ambient environment between populations Egg size and clutch size was significantly different among the four populations
The egg size was not statistically correlated with any environmental factors, such as ambient temperature, daily temperature difference and temperature variance, egg size increased with female body mass (Table 1)
Summary
The allocation of resources between offspring size and number is a central question of life-history theory. Understanding the relationship between the size and number of progeny is a central question of life-history theory (Clutton-Brock 1991; Stearns 1992). The existence of the number-size trade-off should be tested (Lessells et al 1989; Hein et al 2018), but should be explored under the impacts of different environment and/or maternal conditions, and their consequences on resource allocation strategy. In any given reproduction attempt, life-history theory suggests that parents should make a fundamental decision about how to allocate resources between egg size and clutch size (Stearns 1992). There has been no attempt to explain the relationship between the offspring size-number trade-off and population dynamics, such as nest survival rate
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