UC Irvine

© 2015 British Ecological Society. Mechanisms by which climatic factors drive reproductive investment and phenology in masting species are not completely understood. Climatic conditions may act as a proximate cue, stimulating the onset of reproduction and indirectly increasing fitness through benefits associated with synchronous reproduction among individuals. Alternatively, climatic conditions may directly influence individual-level allocation to reproduction and reproductive success through effects occurring independently of synchronous reproduction. We previously showed that masting in a ponderosa pine (Pinus ponderosa) population was strongly influenced by spring mean temperature 2 years before seed cone maturation (Ti-2). However, recent work shows that the difference in temperature between previous growing seasons (ΔT) is more predictive of reproductive investment in long-lived tree species. Here, we compared four candidate models that predict seed cone production in P. ponderosa based upon different climatic factors (including Ti-2 and ΔT models). After determining the best climatic predictor, we tested for a potential mechanism by which climate might directly influence seed cone production independent of benefits via synchrony, namely effects of temperature on trade-offs between current and past reproduction (determined by underlying resource availability). We found that Ti-2 (rather than ΔT) was the best predictor of seed cone production. We further show that this same climatic factor exerts a direct fitness benefit to individuals by reducing the strength of trade-offs between current and past reproductive efforts. Synthesis. We demonstrate that a single climatic factor provides fitness benefits to individuals directly, by weakening reproductive trade-offs, and indirectly through the benefits associated with synchrony and masting. This suggests a mechanism for the origin and maintenance of masting: individuals initially respond to climatic cues that directly enhance reproduction (e.g. lower reproductive costs through weakened trade-offs) and this dynamic, expressed across multiple individuals, reinforces these benefits through the economies of scale associated with synchrony and masting. We propose a new mechanism for the origin and maintenance of masting: individuals initially respond to climatic cues that directly enhance reproduction (e.g. lower reproductive costs through weakened trade-offs) and this dynamic, expressed across multiple individuals, reinforces these benefits through the economies of scale associated with synchrony and masting.