No abstract

Costs of sexual traits are of central importance to the theory of sexual selection. To qualify as a cost in line with theoretical models, empirical studies must demonstrate that sexual traits cause negative effects on one component of fitness of the trait bearer. Moreover, it must be demonstrated that the costs are differential such that negative effects on fitness are more severe for individuals in poor condition than for individuals in good condition. However, in the current literature, there is confusion over what qualifies as a cost, and costs are often anticipated based on findings of increased expenditure. Consequently, it seems that the generally accepted notion that sexual traits are costly is in fact based almost exclusively on indirect evidence and that direct empirical evidence is very scarce.

Understanding the ultimate causes of population declines and extinction is vital in our quest to stop the currently rampant biodiversity loss. Comparison of ecological characteristics between threatened and nonthreatened species may reveal these ultimate causes. Here, we report an analysis of ecological characteristics of 23 threatened and 72 nonthreatened butterfly species. Our analysis reveals that threatened butterflies are characterized by narrow niche breadth, restricted resource distribution, poor dispersal ability, and short flight period. Based on the characteristics, we constructed an ecological extinction risk rank and predicted which of the currently nonthreatened species are at the highest risk of extinction. Our analysis reveals that two species currently classified as nonthreatened are, in fact, at high risk of extinction, and that the status of a further five species should be reconsidered.conservation biology ͉ threatened species ͉ biodiversity ͉ Lepidoptera ͉ World Conservation Union Red List