The value of biodiversity

A controversial opinion piece on extinction and biodiversity conservation was published Thanksgiving week in the Washington Post by an evolutionary biologist. In the last few days, scathing assessments of the op-ed came across my Twitter feed, but I avoided the article until today. I finally dove in, and here are a few thoughts that emerged during the time I could muster on a Sunday evening.

Diverse assemblage of flowering plants in the understory
of a montane forest in the John Muir Wilderness,
California, summer 2017.

In the op-ed R. Alexander Pyron argues that “extinction is the engine of evolution”, states that almost all species that have ever lived on Earth have already become extinct, and notes that extinctions are inevitable for all currently living species. He argues that despite the loss of a species “the world will be none the poorer from it”. From this assortment of assertions (some obviously true like the inevitability of eventual extinction of all species), he then goes on to build a case that conservation is only prudent in-so-far as it benefits humankind.

In taking a rather extreme view of the role of conservation, the visceral reaction of many biologists to publication of this op-ed in a major media outlet is understandable. But does the author miss the mark? I think so on several major fronts:

1. The author paints an incomplete and superficial view of evolution and the production of biodiversity. Succinctly put, extinction is not the “engine” of evolution as the author claims. Rather, natural selection is the mechanism of evolutionary change, and as another evolutionary biologist S. Claramunt points out in a rebuttal, natural selection operates at the population level, not at the species level that Pyron discusses. Natural selection is one of the key processes of microevolution, which involves the generation of genetic variation within a species (novel genotypes and phenotypes) and its subsequent persistence or demise in the next generation by selection. This initial step in microevolution – the generation of genetic variability such as by mutation or genetic drift – is inherently a creative process, albeit a mostly random and inefficient one. In this light, the two major steps of microevolution (generation of variability and environmental selection) are both productive and destructive. Claramunt and Caroline Tucker address other controversial statements by Pyron here and here.

Where Pyron may be partially correct about extinction is its role in producing biodiversity at the macroevolutionary level. As one example, he cites the radiation of mammals and birds following the global mass extinction that wiped out the dinosaurs. However, while extinction may be an occasionally helpful mechanism for promoting radiations of new lineages over geologic time, it is certainly not necessary to generate new species. Speciation, on the other hand, is requisite for the creation of new biodiversity, and it can proceed easily enough in the absence of extinction through allopatric or sympatric mechanisms. A report just this week suggests the very rapid evolution of a new finch species in the Galapagos stemming from a hybridization event. Many species form from others without the parent lineage going extinct, increasing biodiversity. Moreover, when one surveys the history of life on Earth, despite messy fluctuations over geologic history, there may be more biodiversity today than during any geologic era of the past. For a net increase in global diversity to occur over the long term, long-term speciation rates have been greater than extinction rates. If anything speciation is the “engine” of evolution.

2. Though Pyron advocates for conservation if it serves a direct human need, the extent of species he seems willing to advocate for probably falls far short of the number really needed, even from simply a utilitarian point of view. The problem here is obvious: any argument about selective conservation of a smaller fraction of species fails to recognize the unknown inter-dependency of species in all ecosystems. What of the undiscovered connections and dependencies in the global web of life of which we are still woefully ignorant as ecologists? What of species that hold future drug discoveries, or that will only in the future be discovered to be critical to the persistence of other species or even the functioning of whole ecosystems? Even if impending extinction provokes difficult conservation decisions about which species to save in the future, those decisions need to be informed by understanding the ecological roles of the species and the relative loss of services that could result from extinction. I posit that we presently know very little about the ecological roles of the vast majority of species to be able to effectively triage our conservation efforts.

This notion of the interdependency of life is not just the poetry and song of nature lovers. Rigorous empirical research manipulating biodiversity levels at smaller spatial scales over the last two decades demonstrates that biodiversity often matters in order to sustain ecosystem productivity, stability, or other services upon which humankind depends (Cardinale et al. 2012, Lefcheck et al. 2015). Put simply, a grassland with two or three species is not the same as one with several dozen species; that extra plant biodiversity has measurable effects on the functioning of the grassland ecosystem. The importance of biodiversity for ecological functioning extends to genetic diversity within a species (Hughes & Stachowicz 2004), and by extrapolation (though we cannot experiment on continental or global scales) also reasonably extends to the whole biosphere: global diversity sustains a global suite of diverse ecosystem functions. A prudent, precautionary approach is to conserve as much global biodiversity as possible.

3. Finally, the op-ed fails on the ethical front. I won’t argue from a particular religious or philosophical point of view here, but rather simply from a humanistic one. To appreciate, conserve, and cultivate biodiversity is an inherently human experience. We need look no further than zoos and gardens to understand our intrinsic desire to connect with other species. As much as Homo sapiens is a destructive, warlike, compulsive, and competitive species, we are also inherently caring, empathetic, altruistic, and prudent. Biodiversity enriches our human experience, spiritually and aesthetically. And conservation of a mere fraction of Earth’s species upon which we are most dependent for food and shelter will not satisfy that enduring need for connection to the biosphere. Pyron’s anthropocentric arguments about conservation were taken to an extreme in the op-ed, and in so doing that viewpoint paradoxically harms our species by artificially disconnecting us from our deep human need for biodiversity.

The global, bipartisan efforts we put towards conservation, towards preservation of wilderness, towards city and national parks attest to the value we place on the conservation of other species. We cannot escape the deep connection (the “biophilia” of E.O. Wilson) that we have as humans to other forms of life. Though they lived long before the term “biodiversity” was coined, naturalists such as Humboldt, Haeckel, and Muir intuitively assessed the interconnected nature of life through observation of the natural world (Wulf 2015). Muir understood this dependency of all species on each other and asked a powerful ethical question useful as an antidote to an overly anthropocentric view of the value of biodiversity: “Why ought man to value himself as more than an infinitely small unit of the one great unit of creation?”

References

Cardinale et al. 2012. Biodiversity loss and its impact on humanity. Nature 486:59-67.

Hughes AR,  Stachowicz JJ. 2004. Genetic diversity enhances the resistance of a seagrass ecosystem to disturbance. Proceedings of the National Academy of Sciences 101:8998-9002.

Lefcheck et al. 2015. Biodiversity enhances ecosystem multifunctionality across trophic levels and habitats. Nature Communications 6:6936.

Wulf A. 2015. The Invention of Nature. Vintage Books, New York.

Yosemite VI: Wapama Falls at Hetch Hetchy

Our final Yosemite destination last weekend was Hetch Hetchy, my second visit to this remarkable and controversial valley at the northern end of Yosemite National Park. The valley is beautiful despite the reduction in its dimensions and grandeur by the controversial decision to build a dam and flood the valley a century ago. I cannot help but feel some sadness over that outcome, one that John Muir vigorously opposed in his last days. Only he and others of that era saw the valley before it was drown to satiate San Francisco’s thirst for water. I can only hope that the valley will be restored someday, with the water supply and hydroelectric energy the dam provides being provided elsewhere, though that presently doesn’t seem politically or legally likely.

Farther up the valley, beyond the reach of the dam lies an area of the park known as the “Grand Rapids of the Tuolumne River”, a backpacking destination that I hope I can visit someday. Backcountry wilderness trails crisscross the area to the north and south of Hetch Hetchy.

Crossing over the dam and through a tunnel blast into rock, a trail starts at the northern end of the reservoir heading along the west rim of the valley. The vegetation along the slopes is as much chaparral and shrub as forest, with manzanita, bay laurels, and oaks in abundance. At the four km point from the parking lot one reaches Wapama Falls which crashes down a steep granite face at the northern end of the valley. There are some pools near the base of the falls before it descends a bit further to reach the reservoir. Though not many plants are in bloom at this season in Yosemite, the rocky wetland gardens where the trail crosses the falls had a population of small attractive bright yellow flowers of the monkey flower genus Mimulus.

Wapama Falls on the north side of the Hetch Hetchy valley in the spring of 2011 (left) and fall of 2017 (right).

Flowers of Mimulus floribundus near
pools at the base of Wapama Falls.

Hetch Hetchy has been described as a companion valley to the much more famous and visited Yosemite Valley to the south. John Muir described it thus: “…it is a wonderfully exact counterpart of the great Yosemite, not only in its crystal river and sublime rocks and waterfalls, but in the gardens, groves, and meadows of its flowery, park-like floor”.

Views of the Hetch Hetchy Valley today from the north rim of the valley. At right
in center of photo is Kolana Rock.

Presently it is hard to gauge the original dimensions of the valley, but historical photos of the valley show its former glory. About 100 meters of water cover the valley floor currently. Taber’s historical photo from 1908 shows meadows (some perhaps actively grazed), wetlands, and a meandering Tuolumne River on the valley floor. Another photo taken a few years later farther up stream depicts the beautiful canyon and its forested and rocky slopes.

The Hetch Hetchy Valley in 1908 before dam construction. Wapama Falls can be seen at
center right in. Photo by Isaiah Taber, published in the Sierra Club Bulletin. Source.

Historical photo of the Grand Canyon of the Tuolumne River by F. Matthes of the USGS
in about 1914. The photo faces west towards the valley with Kolana Rock at center. Source.

Crossing over the dam to the north side of the reservoir, none of the information placards I viewed that are placed to inform the public show any such historical photos of what Hetch Hetchy looked like before its burial, something I note with some cynicism. With its swelling population and capricious annual precipitation, a reliable water supply is critical for California. However, there are alternatives to a dam at Hetch Hetchy, but like so many issues in conservation, the choice comes down to priorities and values. At a minimum we can strive to ensure that another decision like Hetch Hetchy is never made again in our most cherished national landscapes.

References

Wenk E. 2015. Wildflowers of the High Sierra and John Muir Trail. Wilderness Press, Birmingham, AL.

Worster D. 2008. A Passion for Nature. The Life of John Muir. Oxford University Press, New York, NY.

The O'Shaughnessy Dam as seen from the southwest
on the drive towards Hetch Hetchy Valley.

Yosemite V: To Nevada Falls

I’m not a fan of crowded trails, but the trail from Yosemite Valley up through Vernal and Nevada Falls is one of my favorite destinations in Yosemite National Park despite the swell of people it attracts.

Thankfully we started the hike early enough to avoid the swell. From the southeast corner of Yosemite Valley, the trail begins with a modest ascent towards the south and then to the east to gain a view of the Illilouette Valley. A footbridge across the Merced River offers the first glimpse of Vernal Falls in the distance to the east. A short while later one arrives at the southern side of the falls where there is a steep incline up the granite bedrock up to the top of the falls. In wetter seasons, Vernal Falls is a wide white ribbon that cascades over a sharp lip of granite, but at the tail end of a long dry season, the November falls were broken into three independent streams of water flowing down the rock.

Despite the diminished flow, Vernal Falls still seemed to have more water than some of the other waterfalls in the Valley, notably Yosemite Falls which was barely a humble trickle of water. I rather prefer to see Vernal Falls at this lower level of flow; the waterfall produced trickles and ribbons of water rather than a huge thunderous gush. The effect at the base of the falls is very different too since a full cascade of water produces so much spray that the trail becomes doused in mist.

Vernal Falls.

Nevada Falls.

At the top of Vernal Falls, the trail levels out to commanding views of the Illilouette Valley to the west, and the greeting of Emerald Pool, a temporary tranquil rest stop for Sierra snow melt before it plunges over the Vernal. The trail continues east and then crosses over the Merced River again back to its northern bank. Then the trail ascends steeply again in anticipation of reaching the top of Nevada Falls.   

Nevada Falls exceeds Vernal Falls in height, but the latter is more elegant in my opinion since it the sheer 90 degree drop at the crest of the falls results in an elegant plunge of water. At the head of Nevada Falls, the water seems to shoot out more forcefully where it then drops nearly vertically for some distance and finally hits a more sloping granite face where it slides further in sheets down the rocks. Anywhere else, a waterfall such as Nevada Falls would be the chief highlight of the area, but in Yosemite where there are an abundance of natural waterworks, one can be more choosy.

I hiked just a bit beyond Nevada Falls along the John Muir Trail where it heads into the Little Yosemite Valley and crosses into the Yosemite wilderness. Venturing a little off trail, I went just a ways up the eastern slope of Liberty Cap where there was an excellent view of the valley to the east. A pair of granite domes were visible some miles in the distance to the east. The domes appeared to be composed of sheets of granite, like Half Dome itself.  Where the sheets were partly broken, the laminar fractures produced dark shadows on the rocks. These patterns are one of my favorite manifestations of the diversity of granitic composition in the Sierra.

Panorama (looking east) of Little Yosemite Valley from the eastern slope of Liberty Cap.

The trail continues several miles to the summit of Half Dome and the broader Yosemite wilderness for overnight backpacking. Permits are required for both, and while both adventures sound very appealing, I’d prefer to find a time to when the crush of the crowds can be avoided. 

Sheets of water at the base of Nevada Falls.

Monterey's marine gardens

Rocky intertidal at Pt Pinos, with pelicans cruising in
 from the east.

The Monterey Peninsula juts out into the Pacific Ocean at the south end of Monterey Bay along the central California coast. The area is well known for posh homes, golf courses, and tourism, but has an equally wealthy abundance of marine life and history of human connection to the sea. The peninsula is well populated and busy with visitors, hardly wilderness on the terrestrial side, but the rocky intertidal and near-shore subtidal very quickly attenuates human presence and is the realm of rich marine diversity.

Point Piños is situated on the northwest tip of the peninsula and has been a tidepooling destination of mine for years. The intertidal shoreline here consists of smooth bedrock and boulders with only relatively small beaches of coarse sand linking the rocks to the low-elevation upland. Most of the rest of the peninsula is in fact rocky as well, miles of coastline that would take many years of low tides to thoroughly explore.

Yesterday afternoon’s tide was not particularly low, but sufficiently amenable to exploration because the water was calmer than I had expected given the weekend rain that has moved though the northern half of California. There was a light to moderate breeze and partial cloud cover. As the tide dropped, mounds of bright green surf grass (Phyllospadix) that covered low intertidal rocks became exposed. At slightly higher elevations, red seaweeds (many appearing more black then red) dominated the intertidal space. A bit higher still there were carpets of the rockweed Silvetia compressa.

Selected seaweeds at Point Pinos. Upper left: Codium setchellii; upper right: Bryopsis sp.; lower left: Silvetia compressa; lower right: Sarcodiotheca gaudichaudii.

Kelps were not particularly abundant, but I noted three species in the section of coastline that I explored. The feather boa (Egregia menziesii), nearly ubiquitous at all rocky intertidal sites along the Pacific coast, was the most abundant species. A more interesting species to me, Dictyoneurum californicum, was present in a few patches very low in the intertidal. This species grows as a mass of skinny brown blades that sway in unison as the surge flushes in and out of the low intertidal. The other kelp species was the perennial Laminaria setchellii, also quite frequent along the west coast of the US, though this species was not particularly abundant at Pt. Piños and seemed a little tattered by this time of year. 

Brown pelican in flight.

As the sun drifted lower on the horizon, an abundance of bird life filled the skies. Flocks of birds, some in more organized patterns like the lines of brown pelicans, cruised from east to west. In fact, all of these marine birds may have been there all along, but I was more oblivious to their presence as I focused on taking notes of seaweeds at the site.

The peninsula is well protected legally from resource exploitation and is also a conservation-minded community. Much of the rocky coastline and near shore areas of the peninsula are protected in state marine reserves or state marine conservation areas that completely limit take of all species (marine reserves) or allow limited fishing (conservation areas). Pt Piños itself is in the Pacific Grove Marine Gardens State Marine Conservation Area. Monterey is also at the center of the Monterey Bay National Marine Sanctuary, a large NOAA-administered marine protected area that extends along the outer coast from the Bay Area to Cambria south of Big Sur. Sanctuary status protects the nearshore region from oil drilling and mining.