After Masting Aftermath

As I was composing the earlier masting story ("Masting Aftermath", posted 2-3 weeks ago) about our local oak trees, I read an article in the autumn 2012 issue of Living Bird magazine (from Cornell University), on a similar process that is unfolding in the western US. It’s another fascinating tale about the close relationship between animals and trees that periodically mast—this time in the higher elevations of Arizona and New Mexico. It’s a very intimate alliance that has been forged for millions of years between two species that even share the same name: the pinyon pine and the Pinyon Jay. (It’s an interesting byproduct of scientific custom that the bird’s name merits capital letters, while the tree must suffice with lower case letters.)

The symbiotic partnership between the bird and the tree has evolved over time, to the point that today, neither one of them can survive without the other. It is referred to by biologists as a mutualistic relationship—wherein each species derives benefit from their interdependence. The Pinyon Jay’s beak is long and sharp, having evolved specifically to extract seeds from pinyon pine cones. The seeds are very nutritious, but when not available, the birds nearly starve and their chicks—if they have any that year—will not survive.

As part of its bargain, the bird will plant the tree’s large seeds at distant locations, caching thousands of them during the years when the pines mast. The Pinyon Jay has evolved a special throat pouch, into which it can stuff over four dozen seeds! (And any one seed nearly fills its bill!) Monogamous mates will jam their pouch with the plentiful seeds and then fly off, wing-to-wing, and carefully cache the seeds, poking them into the ground. They specifically choose a location where no pinyon pines currently grow. (If that’s not a wonderful example of inherent intelligence, I don’t know what is!) Even though the bird’s memory is so good that researchers have determined it later retrieves some 95% of all its hidden seeds, a few do get forgotten, and some pinyon pines may later sprout in a new location.

This old partnership is in peril, however—threatening both the tree and the jay. Pinyon pine habitat is dramatically diminishing, as development, forest fires, and climate change take their toll on the trees. Recent dry years have fostered more fires; and those fires have worsened because of mistaken forest management in the west, that has discouraged forest fires in recent years and allowed an abundance of dry tinder to accumulate. Conservationists have monitored an alarming decrease in the population of both bird and tree.

The situation is aggravated by climate change—which is causing droughts and heat to worsen. The fates of the Pinyon Jay and the pinyon pine—inextricably linked to each other—is shaky. There is a ray of hope here, however. The mutualistic connection between bird and tree has existed for millennia, and as climate change occurred in past eras, the pines were moved to more favorable locations, thanks to the propensity for the Pinyon Jay to cache seeds in virgin territory.

Will the Pinyon Jay be smart enough (they are a corvid, like crows, and are very intelligent) to find favorable new habitat for the pine, as climate change increases? The future is very uncertain for these two intertwined species. It’s just one more example of the threat to many of nature’s species, as the globe warms and weather becomes increasingly chaotic.

Fig-Wasp Mutualism

The deeper biologists delve into the workings of nature, the more they come to appreciate and understand the complexity and entanglement that exists between species. No living entity is in isolation. Every plant and creature has a relationship with and depends upon countless other life forms around it. The web of life connects us all, with varying degrees of interdependency.

Remove one species and there will be manifold types of impact on all species connected to it—even those remotely connected. The web of life has evolved to be so interdependent that if one link is severed, the whole thing might not collapse but it will surely change. We humans are causing the ongoing extinction of numerous species every day, with little comprehension of how we are upsetting the exquisite balance of nature.

Mutualism is the strongest kind of tie between two species, wherein both of them benefit from and depend on each other. Pollination is a common type of mutualism. For example, most flowering plants depend on bees, birds, and bats to spread pollen to other plants of the same species—completing the process of sexual reproduction. In return, the plant may offer the pollinator sweet nectar or some of its pollen for food. If the critter is pleased with the meal, it will fly off—carrying some pollen with it—to seek another plant of the same species, and thus fulfilling the sex act.

Modern agriculture relies heavily on bees for pollination of fruits and vegetables. Many bee colonies are being decimated in the last few years, however, and agricultural folks are in a panic. Is the bee-plant balance being degraded?

Some plant-pollinator mutual relationships evolve to become so specialized that only one kind of insect is able to pollinate one kind of plant. They become completely dependent on each other. If one goes extinct, the other must follow. There are numerous species of tree for which there are no further offspring possible, because their pollinator has died off. On the island of Mauritius, for example, there have been no tambalacoque saplings for some 300 years, because the dodo bird—which once spread the tree’s seeds—went extinct in the late 1600s, having been hunted down by people who arrived on the island. Only ancient tambalacoque trees are left. Soon they may also be gone (unless a new pollinator can step in).

One of the more spectacular examples of complete mutualism exists between fig trees and the wasps that pollinate them. There are some 750 species of fig tree around the world (mostly in tropical climates) and 750 species of wasp—one for each kind of fig. The fruit of the fig is hollow, with one end open and with a tiny array of flowers inside the fruit. The wasp climbs inside, lays her eggs on a flower and promptly dies. Later, her eggs hatch, larva eat some of the flower’s seeds, and pupate. Yet later the adult wasps emerge, mate, and the males then promptly die. The impregnated females—now coated with pollen, as they’ve mucked around inside the flower for some time—fly off to find another fig tree of the same species, crawl inside the fruit, and pollinate its flowers.

I don’t believe that such an exclusive example of mutualism exists around me. Most local plant and animal species are generalists. But I can’t help watching a bee or butterfly, loaded with pollen, and wish that it fly on and visit many kinds of flowers and help to bring about more of them. And I can’t help but wonder what delicate examples of mutualism do exist around here, that are in danger of being interrupted. Every critter is precious!