Acorns and Adaptation: On Oaks and the Struggle for Existence By Teresa Helms It is remarkably improbable for a mature oak tree to even exist. Of the abundance of acorns produced every few years—an irregular cycle linked to predator satiation—many will be parasitized by acorn weevils and similar insects. The majority of what remains will be foraged by wildlife. Perhaps a few will get lucky and end up in the cache of a less-than-lucky rodent, left to sprout after their keeper has been predated. Of those that manage to germinate, another percentage will succumb to unideal climatic conditions or be browsed by deer and moose before the seedlings are able to grow out of reach. Ultimately, only about one in every 10,000 acorns will develop into a tree. And yet, Quercus contributes more biomass to northern temperate forests than any other genus of woody plants, its species providing critical sources of hard mast sustenance for wildlife populations. Ubiquitous and essential to these ecosystems, every oak in the forest is inherently unlikely, a testament to persistence, grit, and random chance; Darwin’s “struggle for existence” at play before our eyes. In the grand scheme of evolution, oak species display a certain tenacity, with numerous lineages that have diverged and dominated across the Northern Hemisphere. At the individual level, physiology contributes to this resilience, including long tap roots that prove useful in times of drought. Globally, the Quercus genus boasts roughly 435 species of oaks. Of this array, 60 percent occur in North America, a subset that can be broken down into two major lineages: white oaks and red oaks. Variation between these groups presents itself both genomical-
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ly and functionally. Beyond this distinction, however, the lines of biology become blurred. When determining speciation among organisms, the most foundational methodology is Ernst Mayr’s biological species concept, which defines a species as a group of organisms that may successfully interbreed to produce fertile offspring. This theory generally holds that certain reproductive characteristics allow for populations to remain distinct, restricting gene flow within closed systems. Oak species complicate this with their readiness to hybridize. Many white oak species are known to hybridize naturally, and red oak varieties are even more apt to do so—black oak, for instance, is particularly promiscuous, frequently found hybridized with northern red oak, plaguing dendrologists and confounding the scientific community. Subsequently, many scientists posit that these “species” may not be distinct, but rather phenotypic variations of singular species. This appears to defy such a central tenant of biological thought: oaks expand beyond their categories. Or, perhaps, is it more accurate to say that our categories fail to account for their complexity? Rather than attempting to restrict the natural world to our understanding, we might allow room for the morethan-human world to exist as is. W. John Hayden, in his paper “Hybrid Oaks: Full of Vexation and Wonder,” asks us to embrace this complexity, arguing that “[rather] than vexation, maybe we should adopt an attitude of awe and respect for the complexity of biological processes that, playing out on continental scales, involving untold millions of individual trees, and millennial time
