Rebuilding the web

One of the (many) ways people can be shortsighted is in their seeming determination to view non-human species as inconsequential except insofar as they have a direct benefit to humans.

The truth, of course, is a great deal more nuanced than that.  One well-studied example is the reintroduction of gray wolves to Yellowstone National Park, something that was opposed by ranchers who owned land adjacent to the park, hunters who were concerned that wolves would reduce numbers of deer, elk, and moose for hunting, and people worried that wolves might attack humans visiting the park or the area surrounding it.  The latter, especially, is ridiculous; between 2002 and 2020 there were 489 verified wolf/human attacks worldwide, of which a little over three-quarters occurred because the animal was rabid.  Only eight were fatal.  The study, carried out by scientists at the Norwegian Institute for Nature Research, stated outright that the risks associated with a wolf attacking a human were "non-zero, but far too low to calculate."

Fortunately, wiser heads prevailed, and the wolf reintroduction went forward as scheduled, starting in 1996.  The results were nothing short of spectacular.  Elk populations had skyrocketed following the destruction of the pre-existing wolf population in the early twentieth century, resulting in such high overgrazing that willows and aspens were virtually eradicated from the park.  This caused the beaver population to plummet, as well as several species of songbirds that depend on the insects hosted by those trees.  The drop in the number of beaver colonies meant less damming of streams, resulting in small creeks drying up completely in summer and a resultant crash of fish populations.

In the years since wolves were reintroduced, all of that has reversed.  Elk populations have returned to stable numbers (and far fewer die of starvation in the winter).  Aspen and willow groves have come back, along with the beavers and songbirds that depend on them.  The ponds and wetlands are rebuilding, and the fish that declined so precipitously have begun to rebound.

All of which illustrates the truth of the famous quote by naturalist John Muir: "When we try to pick out anything by itself, we find it hitched to everything else in the Universe."

The reason this all comes up is a recent story in Science News about a project that should give you hope; the restoration of mangrove forests in Kenya.  You probably know that mangroves are a group of trees that form impenetrable thickets along coastlines.  They've been eradicated in a lot of places -- particularly stretches of coast with sandy shores potentially attractive to tourists -- resulting in increased erosion and drastically increased damage potential from hurricanes.  A 2020 study found that having an intact mangrove buffer zone along a coast decreased the damage to human settlements and agricultural land from a direct hurricane strike by an average of 24%.

[Image is in the Public Domain courtesy of NOAA]

The Kenyan project, however, was driven by two other benefits of mangrove preservation and reintroduction -- carbon sequestration and increased fish yields.  Mangrove swamps have been shown to be four times better at carbon capture and storage as inland forests, and their tangled submerged root systems are havens for hatchling fish and the plankton they eat.  The restoration has been successful enough that similar projects have been launched in Mozambique and Madagascar.  A UN-funded project called Mikoko Pamoja allows communities that are involved in mangrove restoration to receive money for "carbon credits" that then can be reinvested into the community infrastructure -- with the result that the towns of Gazi and Makongeni, nearest to the mangrove swamps and responsible for their protection, have become economically self-sufficient.

I have the feeling that small, locally-run projects like Mikoko Pamoja will be how we'll save our global ecosystem -- and, most importantly, realizing that species having no immediately obvious direct benefit to humans (like wolves and mangroves) are nevertheless critical for maintaining the health of the complex, interlocked web of life we all depend on.  It means taking our blinders off, and understanding that our everyday actions do have an impact.  I'll end with a quote from one of my heroes, the late Kenyan activist Wangari Maathai: "In order to accomplish anything," she said, "we must keep our feelings of empowerment ahead of our feelings of despair.  We cannot do everything, but still there are many things we can do."

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Islands in the sky

About fifteen years ago, I fulfilled a lifelong dream to go to Ecuador, a country I've been fascinated with since I was a kid.  I'm a fanatical birder, and that tiny country is home to no less than one-sixth of the world's nine-thousand-odd bird species, including over three hundred different kinds of hummingbirds.  (Where I live, in upstate New York, we have exactly one, and it's only here in the summer.)

It was when I was reading up on the hummingbirds in the Ecuadorian bird guide before leaving on the trip that I noticed something odd.  A number of the species had extremely narrow ranges.  A good example is the exquisite Violet-tailed Sylph (Aglaiocercus coelestis):

[Image licensed under the Creative Commons Joseph C Boone, Violet-tailed Sylph 2 JCB, CC BY-SA 4.0]

The Violet-tailed Sylph is only found in a narrow band a couple of kilometers wide on the Pacific slope of the Andes.  North-to-south, though, its range spans over sixteen hundred kilometers.  The reason for this bizarre geographical distribution is obvious if you consider the topography; the range of the Violet-tailed Sylph, and the majority of the other hummingbirds, is driven by altitude, so their ranges run in thin strips parallel to the Andes Mountains.  A lot of it has to do with food specialization; they're nectar-feeders, and many of them have bills shaped to fit only a single species of flower.  Many tropical plants are very temperature- and moisture-sensitive, and that depends strongly on altitude, so they have equally restricted ranges.  In the case of the lovely little Sylph, its food sources are mostly found in the cloud forests that run along the mid-slope of the Andes at an elevation of about a thousand meters.

The combination of phenomenal overall biodiversity with extremely narrow ranges that you find in Ecuador draws some parallels with the fascinating ecological model called island biogeography studied in the 1960s by Robert MacArthur and E. O. Wilson.  They were trying to find patterns to explain why some islands (such as Trinidad) have extensive and diverse ecosystems, and others (such as Tristan da Cunha) have very low diversity.  They found two factors that made the most difference; island size and the proximity of the island to the nearest mainland.

The dependence on island size is easy to see; the bigger the island, the more resources there are, and the greater the number of species it can support.  The proximity factor comes from the likelihood of immigration (defined as a new species arriving and becoming established); more distant islands are farther away from a source of new species.  The math gets a little complicated, but the basic gist is that islands end up in an equilibrium between immigration and extinction, and that equilibrium results in a predictably higher number of species on larger islands that are closer to the mainland.

Where this gets interesting is that the mathematical model even works for metaphorical islands -- marshes surrounded by desert, isolated springs and lakes, hydrothermal vents on the floor of the deep ocean, and -- as with our hummingbird -- narrow ecosystems in mountain ranges that are restricted by altitude.  In fact, it's this last one that got me thinking about this topic in the first place; last week, a really cool study by a team led by Martha Kandziora of Charles University (Prague) looked at diversity in African "sky islands," ecosystems high up on mountains that are defined by cold temperatures, low rainfall, and harsh sunlight.  The authors write:

Tropical alpine floras are renowned for high endemism, spectacular giant rosette plants testifying to convergent adaptation to harsh climates with nightly frosts, and recruitment dominated by long-distance dispersal from remote areas.  In contrast to the larger, more recent (late Miocene onward) and contiguous expanses of tropical alpine habitat in South America, the tropical alpine flora in Africa is extremely fragmented across small patches on distant mountains of variable age (Oligocene onward)...  Although some of the mountains are old... most lineages appear to have colonized the afroalpine during the last 5 or 10 My.  The accumulation of species increased exponentially toward the present.  Taken together with recent reports of extremely low intrapopulation genetic diversity and recent intermountain population divergence, this points to a young, unsaturated, and dynamic island scenario.  Habitat disturbance caused by the Pleistocene climate oscillations likely induced cycles of colonization, speciation, extinction, and recolonization.

One of the things driving the study is that these regions are seriously threatened by anthropogenic climate change.  While species like the Violet-tailed Sylph could potentially respond to warming trends by moving farther up-slope, the African sky islands have nowhere to go.  If the climate gets significantly hotter, the great likelihood is that these ecosystems with their unique and bizarre flora will simply disappear.

Tragic to think that we're losing biodiversity and in many cases only poorly understand what's being lost.  Perhaps these odd species with their extreme specialization and tiny ranges don't have much impact on our day-to-day lives, but without them, we would live in a sadly impoverished world.

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Out of sight, out of mind

Humans have amazingly short memories.

I suppose that there's at least some benefit to this.  Unpleasant events in our lives would be far, far worse if the distress we experienced over them was as fresh every single day as it was the moment it happened.  That's the horror of PTSD; the trauma gets locked in, triggered by anything that is even remotely similar, and is re-experienced over and over again.

So it's probably better that negative emotions lose their punch over time, that we simply don't remember a lot of what happens to us.  But even so, I kind of wish people would keep important stuff more in mind, so we don't repeat the same idiotic mistakes.  Santayana's quote has almost become a cliché -- "Those who don't remember the past are doomed to repeat it" -- but part of the saying's sticking power is its tragic accuracy.

The reason this comes up is because of some research out of Oxford University that appeared in the journal Trends in Ecology and Evolution this week.  A team led by Ivan Jarić looked at the phenomenon of extinction -- but framed it a bit differently than you may have seen it, and in doing so, turned the spotlight on our own unfortunate capacity for forgetting.

There are various kinds of extinction.  Extirpation is when a species is lost from a region, but still exists elsewhere; mountain lions, for example, used to live here in the northeastern United States, but were eradicated in the late nineteenth and early twentieth century (the last confirmed sighting was in Maine in 1938).  They're still holding their own in western North America, however.  Functional extinction is when the population is reduced so much that it either no longer has much impact on the ecosystem, or else would not survive in the wild without signification conservation measures, or both.  Sadly, the northern white rhinoceros, the northern right whale, and the south China tiger are all considered functionally extinct.  

Extinct in the wild is exactly what it sounds like; relict populations may exist in captivity, but it's gone from its original range.  Examples include the beautiful scimitar oryx, the Hawaiian crow, and the franklinia tree (collected in the Altamaha River basin in Georgia in 1803 and never seen in the wild since).  Such species may be reintroduced from captive breeding, but it tends to be difficult, expensive, and is often unsuccessful.

Then there's global extinction.  Gone forever.  There has been some talk about trying to resuscitate species for which we have remains that have intact DNA, Jurassic Park-style, but the hurdles to overcome before that could be a reality are enormous -- and there's an ongoing debate about the ethics of bringing back an extinct species into a changed modern world.

The new research, however, considers yet another form of extinction: societal extinction.  This occurs when a population is reduced to the point that people basically forget it ever existed.  It's amazing both how fast, and how completely, this can happen.  Consider two bird species from North America -- the passenger pigeon (Ectopistes migratorius) and the Carolina parakeet (Conuropsis carolinensis) -- both of which were common in the wild, and both of which went completely extinct, in 1914 and 1918 respectively.

Illustration of the passenger pigeon by naturalist Mark Catesby (1731) [Image is in the Public Domain]

Actually, "common" is a significant understatement.  Up until the mid-nineteenth century, passenger pigeons were the most common bird in North America, with an estimated population of five billion individuals.  Flocks were so huge that a single migratory group could take hours to pass overhead.  Carolina parakeets, though not quite that common, were abundant enough to earn the ire of fruit-growers because of their taste for ripe fruit of various kinds.  Both species were hunted to extinction, something that only fifty years earlier would have been considered inconceivable -- as absurd-sounding as if someone told you that fifty years from now, gray squirrels, robins, house sparrows, and white-tailed deer were going to be gone completely.

What is even more astounding, though, is how quickly those ubiquitous species were almost entirely forgotten.  In my biology classes, a few (very few) students had heard of passenger pigeons; just about no one knew that only 150 years ago, there was a species of parrot that lived from the Gulf of Mexico north to southern New England, and west into the eastern part of Colorado.  As a species, we're amazingly good at living the "out of sight, out of mind" principle.

The scariest part of this collective amnesia is that it makes us unaware of how much things have changed -- and are continuing to change.  Efforts to conserve the biodiversity we still have sometimes don't even get off the ground if when the species is named, the average layperson just shrugs and says, "What's that?"  Consider the snail darter (Percina tanasi), a drab little fish found in freshwater streams in the eastern United States, that became the center of a firestorm of controversy when ecologists found that its survival was jeopardized by the Tellico Dam Hydroelectric Project.  No one but the zoologists seemed to be able to work up much sympathy for it -- the fact that it wasn't wiped out is due only to the fact that a population of the fish was moved to neighboring streams that weren't at risk from the dam, and survived.  (It's currently considered "threatened but stable.")

"It is important to note that the majority of species actually cannot become societally extinct, simply because they never had a societal presence to begin with," said study lead author Ivan Jarić, in an interview with Science Daily.  "This is common in uncharismatic, small, cryptic, or inaccessible species, especially among invertebrates, plants, fungi and microorganisms -- many of which are not yet formally described by scientists or known by humankind.  Their declines and extinctions remain silent and unseen by the people and societies."

Which is honestly kind of terrifying.  It's bad enough to lose species that are, as it were, right in front of our eyes; how many more are we losing that are familiar names only to biologists, or aren't even yet known to science?  And keep in mind that little-known doesn't mean unimportant.  There are plenty of "uncharismatic, small, cryptic, or inaccessible species" that are pretty damn critical.  One that springs to mind immediately are mycorrhizae, a group of underground fungi that form a symbiotic relationship with plant roots.  The relationship is mutually beneficial; the plant has its capacity to absorb minerals and water greatly increased, and the fungus gets a home and a source of food.  By some estimates, 95% of plant species have a mycorrhizal partner, and some -- notably orchids -- are completely dependent on it, and die if they are separated from their fungal symbiont.  Even plants that aren't entirely reliant on them benefit from the relationship; there is increasing evidence that adding mycorrhizal spores to an ordinary vegetable garden can decrease dependence on chemical fertilizers, improve drought resistance, and increase crop yield (some experiments have seen it as much as double).

Incredibly cool.  But not what most of us would consider "charismatic."  I doubt, for example, that micrographs of mycorrhizae will ever usurp the wolves and eagles and elephants on the pages of the calendars we hang on our walls.  I mean, I would buy one, but I suspect I'm in the minority.

What this highlights to me is that we need to fight this tendency to overlook or forget about the organisms in our world that aren't obvious -- the rare, the small, the hidden.  The fact that their plight is not as obvious as the whales and the elephants and the tigers doesn't mean they're unimportant.  We need to become conscious of what's around us, and committed to protecting it.  Another comparison that's become almost a cliché is comparing biodiversity to a tapestry, but the symbolism is apt.

Pull out enough threads, and the entire thing comes to pieces.

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Floral invaders

I used to ask a question to my biology classes, during the unit on ecology: what are the only two commonly-eaten fruits that are native to North America?

Some of the most frequent wrong answers -- and where those plants are actually native:

• Apples ("American as apple pie," right?)  Nope, native to Europe, brought over in the early seventeenth century by the French settlers of eastern Canada and now naturalized across the continent.
• Peaches, apricots, and pears -- native to central Asia.
• Plums -- native to China (although there are a few wild North American plum varieties, they're not the ones you ever see in the grocery store).
• Kiwi fruit -- native to east Asia.
• Cherries, strawberries, blackberries, and raspberries -- native to Europe.
• Citrus fruits -- native to southern Asia and Australia.
• Pineapples -- native to South America.
• Bananas -- native to southeast Asia, Papua-New Guinea, and Australia.

Some students -- knowing their botany -- thought I was being tricky and had in mind plants whose product are fruits in the botanical sense, but not to be found in the fruit section of the grocery store, like cucumbers (south Asia) and tomatoes (Central and South America), but no.

The only two commonly-consumed fruits that are native to North America are blueberries and cranberries.  (Squash is also an example, if you count introductions that preceded European colonization; they were widely used by Indigenous Americans, but even they originally came from Mexico and Central America.)

It might be especially hard to believe this apropos especially of blackberries and raspberries, which have gone wild and in many places (like my back yard) form nearly impenetrable thorny thickets of vines.  We have the birds to thank for this; birds consume the berries and then carry the seeds far and wide, a dispersal strategy that is effective enough that both species are now found in every state in the continental United States and every province of Canada.

[Image is in the Public Domain]

Well, so what?  Why does this matter?  The problem is the degree to which non-native (or exotic) species have infiltrated ecosystems -- and changed them.  I could just as well used garden flowers as my example group, but most high school students know fruits way better than flowers.  And I'm ignoring what might be the single most common group of exotic plants in the United States, so ubiquitous that we hardly even think about them; the various common species of lawn grasses.

There are two commonly-cited problems with non-natives. Certainly the best known is that when exotic organisms take hold, they can outcompete and replace native species.  The most successful exotics are the ones that are ecological generalists, able to utilize a wide variety of resources and habitats, and those have especially taken hold in the disturbed ecosystems of cities; consider where you are most likely to find dandelions, burdock, pigeons, house sparrows, and rats, for example.  A second is the accidental introduction of pests that end up destroying native organisms -- three we're constantly fighting here in the northeastern United States are Japanese beetles, the spotted lanternfly, and the emerald ash borer.  (Once again, there's another example in this category you may not have thought about -- feral cats, which take a tremendous toll on native birds.  But I'm guessing the cat lovers in my readership won't appreciate my labeling cats as "exotic pests...")

A third, and less-explored, aspect of the transport of species into new regions is homogenization.  Enough new introductions, and previously diverse and unique ecosystems start looking very much alike.  This was the subject of a paper last week in Nature Communications by a team led by Qiang Yang of the University of Konstanz (Germany), detailing a way to quantify this loss of uniqueness.  

The authors write:

Regional species assemblages have been shaped by colonization, speciation and extinction over millions of years.  Humans have altered biogeography by introducing species to new ranges.  However, an analysis of how strongly naturalized plant species (i.e. alien plants that have established self-sustaining populations) affect the taxonomic and phylogenetic uniqueness of regional floras globally is still missing.  Here, we present such an analysis with data from native and naturalized alien floras in 658 regions around the world.  We find strong taxonomic and phylogenetic floristic homogenization overall, and that the natural decline in floristic similarity with increasing geographic distance is weakened by naturalized species.  Floristic homogenization increases with climatic similarity, which emphasizes the importance of climate matching in plant naturalization.  Moreover, floristic homogenization is greater between regions with current or past administrative relationships, indicating that being part of the same country as well as historical colonial ties facilitate floristic exchange, most likely due to more intensive trade and transport between such regions.  Our findings show that naturalization of alien plants threatens taxonomic and phylogenetic uniqueness of regional floras globally.  Unless more effective biosecurity measures are implemented, it is likely that with ongoing globalization, even the most distant regions will lose their floristic uniqueness.

The problem is, halting this trend is going to be tough.  In a lot of ways, that ship has already sailed.  We can act on local scales -- like my wife's and my effort to convert a section of our property into a native wildflower meadow -- but there has already been too much pot-stirring to have a chance of separating the mixture back to its original configuration of ingredients.  It may be that the best we can do is to mitigate the damage to the extent we can; replacing lawn, choosing to plant natives, removing unwanted exotics when you find them -- and keeping your cats indoors. 

And, of course, remember the somewhat encouraging truth that even introduced species can eventually come into equilibrium with the natives.  European Starlings, introduced into North America in the late nineteenth century, had multiplied into such enormous numbers that in many regions they were the most common bird around, but in the last fifty years have declined to more reasonable (and stable) numbers.  (The only scary thing about this is that we don't have a clear idea of why they've declined -- by some estimates, to fifty percent of the total population in 1970 -- and scarier still, there's been a commensurate decline in native species during the same time frame.)

But the harsh fact is that we've already made irreparable changes to the world's ecosystems, and that's not going to stop any time soon.  The important thing now is to learn from past mistakes -- and do what we can to protect what's still left of our beautiful and unique biodiversity.

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One of my favorite writers is the inimitable Mary Roach, who has blended her insatiable curiosity, her knowledge of science, and her wonderfully irreverent sense of humor into books like Stiff (about death), Bonk (about sex), Spook (about beliefs in the afterlife), and Packing for Mars (about what we'd need to prepare for if we made a long space journey and/or tried to colonize another planet).  Her most recent book, Fuzz: When Nature Breaks the Law, is another brilliant look at a feature of humanity's place in the natural world -- this time, what happens when humans and other species come into conflict.

Roach looks at how we deal with garbage-raiding bears, moose wandering the roads, voracious gulls and rats, and the potentially dangerous troops of monkeys that regularly run into humans in many places in the tropics -- and how, even with our superior brains, we often find ourselves on the losing end of the battle.

Mary Roach's style makes for wonderfully fun reading, and this is no exception.  If you're interested in our role in the natural world, love to find out more about animals, or just want a good laugh -- put Fuzz on your to-read list.  You won't be disappointed.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]