Drivers of synchrony of acorn production in the valley oak (Quercus lobata) at two spatial scales.

Walter D Koenig,Mary V Ashley,Mario B Pesendorfer,Johannes M H Knops,David N Zaya

doi:10.1002/ecy.2010

Abstract

We investigated spatial synchrony of acorn production by valley oaks (Quercus lobata) among individual trees at the within-population, local level and at the among-population, statewide level spanning the geographic range of the species. At the local level, the main drivers of spatial synchrony were water availability and flowering phenology of individual trees, while proximity, temperature differences between trees, and genetic similarity failed to explain a significant proportion of variance in spatial synchrony. At the statewide level, annual rainfall was the primary driver, while proximity was significant by itself but not when controlling for rainfall; genetic similarity was again not significant. These results support the hypothesis that environmental factors, the Moran effect, are key drivers of spatial synchrony in acorn production at both small and large geographic scales. The specific environmental factors differed depending on the geographic scale, but were in both cases related to water availability. In addition, flowering phenology, potentially affecting either density-independent pollination failure (the pollination Moran effect) or density-dependent pollination efficiency (pollen coupling), plays a key role in driving spatial synchrony at the local geographic scale.

Highlights

The mechanisms driving spatial synchrony—the tendency for the size or density of spatially disjunct populations to correlate through time—is a subject of debate despite the ubiquity of this phenomenon (Liebhold et al 2004a)
One is flowering phenology, which potentially affects both densitydependent pollination efficiency and density independent pollination failure (Pearse et al 2016). The latter is expected to be driven primarily by a mechanistic response to weather (Pearse et al 2014), and since previous work has demonstrated a strong relationship between weather and phenology in this population (Koenig et al 2012, 2015), it is likely that a pollination Moran effect is in play and that flowering phenology has a strong effect on spatial synchrony
The saturated model explained 40.2% of the variance in spatial synchrony in acorn production observed between sites. These analyses offer several insights regarding the drivers of spatial synchrony in acorn production in the valley oak Quercus lobata, a masting tree species that exhibits highly significant spatial synchrony

Summary

Introduction

The mechanisms driving spatial synchrony—the tendency for the size or density of spatially disjunct populations to correlate through time—is a subject of debate despite the ubiquity of this phenomenon (Liebhold et al 2004a). Typically weather (Moran 1953, Ranta et al 1997)—and enhanced pollination efficiency or “pollen coupling”, in wind-pollinated species (Kelly et al 2001, Kelly and Sork 2002). The first of these processes is almost always potentially significant given that both temperature and precipitation exhibit geographically widespread spatial synchrony, often up to distances of 1000+ km, across all continents (Koenig 2002). One is flowering phenology, which potentially affects both densitydependent pollination efficiency (pollen coupling) and density independent pollination failure (pollination Moran effect) (Pearse et al 2016). The latter is expected to be driven primarily by a mechanistic response to weather (Pearse et al 2014), and since previous work has demonstrated a strong relationship between weather and phenology in this population (Koenig et al 2012, 2015), it is likely that a pollination Moran effect is in play and that flowering phenology has a strong effect on spatial synchrony

Methods

Results

Conclusion