Later flowering is associated with a compressed flowering season and reduced reproductive output in an early season floral resource

Oikos 000: 001–008, 2015 doi: 10.1111/oik.02573 © 2015 The Authors. Oikos © 2015 Nordic Society Oikos Subject Editor: Rein Brys. Editor-in-Chief: Dries Bonte. Accepted 18 August 2015 Later flowering is associated with a compressed flowering season and reduced reproductive output in an early season floral resource Nicole E. Rafferty, C. David Bertelsen and Judith L. Bronstein­ N. E. Rafferty (nicole.rafferty@utoronto.ca) and J. L. Bronstein, Dept of Ecology and Evolutionary Biology, Univ. of Arizona, Tucson, AZ 85721, USA. Present address for NER: Dept of Ecology and Evolutionary Biology, Univ. of Toronto, Toronto, ON, M5S 3G5, Canada. – C. D. Bertelsen, School of Natural Resources and the Environment, Univ. of Arizona, Tucson, AZ 85721, USA, and: Herbarium, Univ. of Arizona, Tucson, AZ 85721, USA.­ Climate change-induced shifts in flowering phenology can expose plants to novel biotic and abiotic environments, potentially leading to decreased temporal overlap with pollinators and exposure to conditions that negatively affect fruit and seed set. We explored the relationship between flowering phenology and reproductive output in the common shrub pointleaf manzanita Arctostaphylos pungens in a lower montane habitat in southeastern Arizona, USA. Contrary to the pattern of progressively earlier flowering observed in many species, long-term records show that A. pungens flowering onset is shifting later and the flowering season is being compressed. This species can thus provide unusual insight into the effects of altered phenology. To determine the consequences of among- and within-plant variation in flowering time, we documented individual flowering schedules and followed the fates of flowers on over 50 plants throughout two seasons (2012 and 2013). We also measured visitation rates by potential pollinators in 2012, as well as both fruit mass and seeds per fruit of flowers produced at different times. Fruit set was positively related to visitation rate but declined with later dates of flower production in both years. Total fruit production per plant was positively influenced by flowering duration, which declined with later flowering onset, as did fruit mass. Individual flowering schedules were consistent between years, suggesting that plants that begin flowering late have lower reproductive output each year. These patterns suggest that if pointleaf manzanita flowering continues to shift later, its flowering season may continue to become shorter, compressing floral resource availability for pollinators and leading to reduced reproductive output. These results reveal the negative effects of delayed phenology on reproductive output in a long-lived plant. They highlight the value of using natural variation in flowering time, in combination with long-term data, to anticipate the consequences of phenological shifts. The flowering phenologies of many plant species are changing in association with changing climatic condi- tions (Bradley et al. 1999, Abu-Asab et al. 2001, Fitter and Fitter 2002, Miller-Rushing and Primack 2008). In temperate climates, a pattern reported worldwide is for flowering onset to shift earlier in concert with warmer springtime tempera- tures (Fitter and Fitter 2002, Miller-Rushing and Primack 2008, Chambers et al. 2013). The magnitude and even the direction of shifts in flowering time can, however, vary among species in the same community (Bradley et al. 1999, Miller-Rushing and Primack 2008, CaraDonna et al. 2014) and along elevational gradients (Crimmins et al. 2010). There is some evidence that the phenologies of pollinating insects are shifting with climate change, as well (Roy and Sparks 2000, Gordo and Sanz 2006, Doi et al. 2008, Burkle et al. 2013). Together, these observational data have generated concern that phenological shifts occurring at different rates could disrupt plant–pollinator interactions by causing mis- matches in the timing of flowering and pollinator availability (Memmott et al. 2007, reviewed by Hegland et al. 2009). Increasingly, research on climate change-driven pheno- logical shifts in the context of pollination has focused on the consequences of such shifts for plant reproductive success (Kudo et al. 2004, Rafferty and Ives 2012, Kudo and Ida 2013). Shifts in the timing of life history events can expose species to novel abiotic and biotic environments, and these components can interact to determine reproductive output. The flowers of plants that bloom very early can, for example, be more vulnerable to damaging frosts (Inouye 2008), as well as reduced pollinator availability (Kudo and Ida 2013), whereas plants that bloom late can be vulnerable to desic- cation (Gimenez-Benavides et al. 2007). Measures of how reproductive output varies with flowering phenology yield useful information about potential temporal mismatches in the context of both the biotic and abiotic environment. To develop a predictive understanding of the potential reproductive consequences of a long-term shift in flowering onset, we took advantage of existing variation in flowering phenology at the population level in one species. Rela- tively few studies have used natural variation in the timing EV-1 OIKO_A_002573.indd 1 9/18/2015 6:45:50 PM