Abstract
Climate can affect plant populations through direct effects on physiology and fitness, and through indirect effects on their relationships with pollinating mutualists. We therefore expect that geographic variation in climate might lead to variation in plant mating systems. Biogeographic processes, such as range expansion, can also contribute to geographic patterns in mating system traits. We manipulated pollinator access to plants in eight sites spanning the geographic range of Clarkia pulchella to investigate geographic and climatic drivers of fruit production and seed set in the absence of pollinators (reproductive assurance). We examined how reproductive assurance and fruit production varied with the position of sites within the range of the species and with temperature and precipitation. We found that reproductive assurance in C. pulchella was greatest in populations in the northern part of the species' range and was not well explained by any of the climate variables that we considered. In the absence of pollinators, some populations of C. pulchella have the capacity to increase fruit production, perhaps through resource reallocation, but this response is climate dependent. Pollinators are important for reproduction in this species, and recruitment is sensitive to seed input. The degree of autonomous self-pollination that is possible in populations of this mixed-mating species may be shaped by historic biogeographic processes or variation in plant and pollinator community composition rather than variation in climate.
Highlights
The reproductive success of primarily outcrossing plant taxa is often highly dependent on the actions of their mutualist pollinators (Burd, 1994; Ashman et al, 2004)
We investigate the relationships among climate, pollinator exclusion, and reproductive fitness components of a winter annual wildflower, Clarkia pulchella
Concurrent work with C. pulchella (Bontrager and Angert, 2018) has indicated that fall, winter, and spring growing conditions play a large role in overall plant growth and reproductive output, we considered flowering season (June-July) climate variables and annual temperature and precipitation for inclusion as predictors
Summary
The reproductive success of primarily outcrossing plant taxa is often highly dependent on the actions of their mutualist pollinators (Burd, 1994; Ashman et al, 2004). Limited resources, including limited water availability, can increase the cost of producing and maintaining attractive floral displays (Galen et al, 1999) This could lead to selection for individuals that can achieve high reproductive success without incurring the costs of showy displays. Mate limitation can occur when populations are small or sparse, or when pollinators are low in abundance or prefer to visit co-occurring species (Knight et al, 2005) These patterns of mate and resource limitation can co-vary with climatic conditions. Patterns in mating system traits may be correlated with the climatic gradients that underlie a species’ geographic distribution (Lennartsson, 2002; Moeller and Geber, 2005) and may covary with geographic range position These climatic gradients may simultaneously affect other plant fitness components (Doak and Morris, 2010), so it may be important to consider multiple plant responses at once (i.e., multiple fitness components or traits)
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