The silent invasion

My office window looks out over our raised-bed gardens and into our front yard.  It's still chilly early spring here in upstate New York -- things won't really start greening up for another couple of weeks -- but we're seeing signs of the coming explosion of growth that tell us warm weather will soon be here.  We actually got out and did some yard work this past weekend, despite clouds and a high of 45 F.  Mostly clean-up that never got done last fall, but we did plant the early peas and lettuce, transplanted some clumps of chives that were taking over one corner of the vegetable garden, and moved a yucca plant that was getting a little too enthusiastic.

From where I sit right now, I can see our bit of grassy lawn, but also the bare branches of a purple lilac, a couple of still-leafless roses, the gnarled branches of a sawtooth oak, the reddish buds of peonies just starting to unfurl, the bright green spikes of daylily leaves, the stubble of the ornamental Miscanthus grass that by midsummer will be taller than I am.  Clumps of brilliant daffodils, crocus, scilla, and chionodoxa already in full flower.

All cool stuff, promising lots of beauty to come.  But you know what all of the plants I've mentioned have in common?

Not one is native to the United States.

Not even the grass.  Just about all the lawn grasses grown in North America are European natives.  Chances are, unless you have deliberately set out to do natives-only landscaping, the vast majority of the plants in your yard are imports as well.  Of everything I can see from my window, only one is native to upstate New York -- a hedge of ninebark (Physocarpus opulifolius).  Two others are eastern natives but originally from a good deal farther south, the Carolina silverbell (Halesia carolina) and black locust (Robinia pseudoacacia).

Thing is, like everything, the situation with exotics is complex.  Not all exotics are a problem.  The charming little bright-blue scilla (Scilla siberica) that pop up everywhere in the very early spring, including all over my lawn, are pretty harmless.  (Contrary to the name, they're not native to Siberia, but to southwestern Russia, the Caucasus, and northern Turkey.)  Garlic mustard (Alliaria petiolata), on the other hand, is an unmitigated thug -- since its introduction in the 1800s, it has spread like wildfire, each plant producing hundreds of seeds, and in many areas has crowded out native plant species.  It's also toxic to a lot of native herbivores, including several species of butterflies.  We've tried for years to rid our yard of this nuisance, without much success.

And don't get me started about multiflora rose (Rosa multiflora).  The Wikipedia page says it's native to Asia, but I'm convinced it was imported directly from hell.  It has pretty white flowers, but more than makes up for that by razor-sharp thorns borne on long, tough, wiry stems that seem to have a deliberate vicious streak.  In general I love roses, but this one is an absolute hazard.

Of course, here in New York, we still have a great many native species that are doing well.  Consider the situation in Hawaii, though -- where on the more populated islands, there are barely any native species left.

Oh, it looks good.  On O'ahu, there are lush forests -- guava, plumeria, cinnamon, peppertree, Kahili ginger, several species of acacia and eucalyptus, banyan, satinleaf -- and flocks of showy birds like the red-billed leiothrix, red-whiskered bulbul, zebra dove, common mynah, and red-crested cardinal.  But not one is native.  The Hawaiian lowland ecosystems were completely destroyed for agriculture and settlement; accidental introduction of the southern house mosquito (Culex quinquefasciatus), and the avian malaria it carried, wiped out nearly all of the birds living below five hundred meters of elevation.  If you want to see native Hawaiian species -- what's left of them -- you have to go up into the mountains, and even there, they're struggling to hang on.

Aarhus University ecologist Jens-Christian Svenning, who has been studying Hawaii's ecology for almost a decade, calls the current situation a "freakosystem."  What's interesting, Svenning says, is that the situation has re-established a healthy, interactive community of species -- just not the ones that were there only two hundred years ago.

"These are wild but changed ecosystems," Svenning said.  "They have passed some critical threshold which means they are unlikely to ever go back to how they were before.  If you removed all people from the planet, Hawaii would be on a different evolutionary ecological trajectory going forward."

Hawaii's iconic plumeria trees, whose flowers are used to make leis, were introduced from the Caribbean in the 1800s  [Image licensed under the Creative Commons Varun Pabrai, Plumeria rubra-4, CC BY-SA 4.0]

Hawaii, however, is just the canary in the coal mine.  A study by Svenning and his colleagues indicates that between thirty and forty percent of all terrestrial ecosystems have "transformed into novel states;" that percentage is projected to rise to fifty by 2100.

It's not, of course, that these kinds of changes can't happen through natural processes.  Three years ago I wrote a piece about the effect that continental collisions can have on the species that live there; and, after all, even less dramatic events than that can lead to extinction.  What strikes me here is the speed with which it's happening.  We've tampered with ordinary ecological succession with no forethought, and as a result, triggered what (to judge by the rates) will rank up there with the "Big Five" mass extinctions -- the Ordovician, Devonian, Permian-Triassic, Late Triassic, and Cretaceous.

So maybe it's time to start thinking about this.

It's too late to undo the silent invasion of exotic species; here in upstate New York, I'm afraid lawn grass is here to stay, as are garlic mustard and multiflora rose, and lilacs, peonies, and daffodils.  At least the last three are pretty and don't seem to be especially harmful.  But we'd better wise up about what we're doing, and fast.  Because remember that as prideful as we get sometimes, to the biosphere we're just another animal species.  We're no more guaranteed survival than anything else.

Let's hope we learn that lesson before it's too late.

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Lightning rod

In 1904, biologist Joseph Grinnell formulated what has since become known as the Competitive Exclusion Principle: if two species overlap in their niches, the degree of overlap correlates to the degree of competition between them.  If the competition becomes too high, eventually one of them is outcompeted and dies out.

Contrary to the "Nature is red in tooth and claw" view of the natural world, however, many species solve the problem of competitive exclusion in remarkable peaceable ways.  Some partition the habitat -- for example, species of insect-eating warblers in my part of the world avoid competing for food by splitting up where they forage, with some species mostly staying in the treetops, others in the the forest midstory or undergrowth.  Elaborate cooperative strategies are also remarkably common -- witness lichens, which are a symbiotic pairing of an algae species and a fungus, where the fungus gives the algae housing, and the algae photosynthesizes and donates some of the nutrients to its host.

So despite how it's often characterized, nature doesn't always land on the violent solution.

Sometimes, though...

There's a rain forest tree found in Panama called the almendro (Dipteryx oleifera).  It's in the bean family, Fabaceae, which you can tell if you look at its pinnately-compound leaves and showy flowers:

It can get up to 55 meters tall, which is a necessity in the rain forest.  Dense patches of rain forest have such a thick covering of leaves that only two percent of the incident sunlight reaches the forest floor.  Understory plants have evolved to cope with the perpetual twilight -- this is one of the reasons why rain forest plants often have very dark green leaves.  The density of pigments allows them to trap every photon of light they manage to receive.

Trees, though, compete by elbowing each other out of the way, trying to grow as tall as possible so as to access light, and in the process, shade out the abundant competition.  But not only do rain forest trees have to worry about nearby trees, they also have to deal with lianas, vining species that twine up tree trunks and drape themselves over the canopy, hitching a ride on their taller, sturdier neighbors, and shading them out in the process.

Well, the almendro has evolved a strategy for dealing with all of that at once.

A study this week in New Phytologist looked at a peculiar pattern that ecologist Evan Gora, of the Cary Institute of Ecosystem Studies, had noticed: almendros seemed to have an unusually high likelihood of being struck by lightning, but almost never sustained any significant damage from it.  Well, after a five-year study, Gora and his collaborators found that almendros that were struck usually just lost some leaves and small branches, while other species sustained significant damage, with 64% of the struck trees dying within two years.

Not only that, but the lightning strikes completely wipe out any lianas.  Almendros that were hit by lightning not only recovered quickly, they had their tangle of vines blown to smithereens.  And neighboring trees that were jolted by the strike -- through sparks jumping from the almendro -- often died, too, freeing up more living room.

The data shows that living near an almendro raises a neighboring tree's likelihood of being killed by a lightning strike by 48%.  "Any tree that gets close," Gora said, "eventually gets electrocuted."

How the almendro has managed to evolve into a natural lightning rod is uncertain, but it has been found that the cells in its wood have wider channels for water transport, making the wood more electrically conductive.  Most of the damage to trees from lightning strikes occurs because internal resistance causes the electrical energy to dissipate as heat, making the sap boil and triggering the trunk to explode.  Lowering the electrical resistance allows the current to pass through the trunk and safely into the ground with less heating.  This means that not only does the almendro not suffer as much damage, it actually attracts lightning -- electrical discharges tend to follow the path of least resistance.

So even if sometimes the natural world does evolve nice, friendly, cooperative solutions to the problems of survival, sometimes it... doesn't.  Even the trees don't always.  Like the Ents and Huorns from Tolkien's Fangorn Forest, sometimes the trees deal with their enemies by taking matters into their own... um... branches.

Think about that next time you're going for a nice stroll in the woods.

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Wipeout

252 million years ago, the Earth was hit by a confluence of Very Unfortunate Events.

First, most of the large continental land masses locked up into a single supercontinent, Pangaea.  This had multiple effects, including alterations of oceanic currents, massive desertification, and the collapse of the convection cells powering seafloor spreading at mid-ocean ridges.  The latter caused a drastic lowering of sea level and exposure of continental shelves, reducing habitat for marine species that live in shallow water (which is most of them).

Second, the tinder box that had formed in the Carboniferous Period -- enormous deposits of coal, oil, and limestone produced when the Earth was basically one giant greenhouse -- found its lit match when the Siberian Traps erupted.  This is one of the largest volcanic events known, and produced an almost unimaginable four million cubic kilometers of basaltic lava.  This ripped through all that coal and carbonate rock, releasing catastrophic amounts of carbon dioxide and sulfur dioxide into the atmosphere.  The portion of the excess absorbed into the ocean caused acidification, killing any marine animal with carbonate shells or skeletons.  The resulting temperature rise caused worldwide oceanic anoxia.  It very likely also triggered the unraveling of unstable methane clathrate deposits on the seafloor, releasing gaseous methane and further boosting the temperature.

If that weren't enough, right around this time the Araguainha Impactor hit what is now Brazil.  The spot where it struck was at the time mostly composed of another gift from the Carboniferous -- oil shale.  This was flash-incinerated, releasing yet more carbon dioxide.

The result: the extinction of between 80% and 95% of the species on Earth, depending on how you count them and who you ask.  

What there's no doubt of, though, is that it was devastating.  It's the closest the Earth has come to undergoing a complete wipeout.  Entire taxa went extinct, including eurypterids (sea scorpions), trilobites, blastoids, tabulate and rugose corals, and acanthoid fish; 99% of radiolarian species vanished, as well as 98% of gastropods and 97% of ammonites and foraminiferans.  The entire food web collapsed.

Afterward, the Earth was an overheated, sulfur-smelling, hypoxic, largely lifeless wasteland.

And yet, somehow, it recovered.  How exactly the Earth's living things made it through the largest bottleneck ever is the subject of a paper last week in the Geological Society of America Bulletin, authored by a team from University College Cork, the University of Connecticut, and the Natural History Museum of Vienna.  And what it found was that the bounce-back didn't happen all at once.  It was far from a linear progression toward rebuilding the biosphere -- there were further shifts and setbacks over several million years as life "found a way."

The team focused mainly on the plants, given that they're the base of the food web.  Some of the first recolonizers were conifers, but they suffered a reversal not even a million years after the main pulse of extinctions with the Smithian-Spathian Boundary Event, a further spike in global temperature that ultimately saw sea surface temperatures of 40 C (104 F), but which was then followed by an unexplained and equally rapid drop.  The wild pendulum swings in temperature caused the collapse of the resurgent coniferous forests; ultimately they were replaced by seed ferns and club mosses (the latter were larger than the ones we have today, but not as big as the enormous Lepidodendrons that were around during the Carboniferous).  

An early Triassic seed fern, Lepidopteris [Image licensed under the Creative Commons Vivi Vajd, Stephen McLoughlin, Sam M. Slater, Ola Gustafsson, Allan G. Rasmusson, Lepidopteris life restoration, CC BY 4.0]

Eventually the climate stabilized, but any way you spin it, the Early Triassic Period was a horrible time to be alive.  It was largely hot and dry, but then -- with startling rapidity -- terrestrial biomes were swamped during the weird Carnian Pluvial Episode, a two-million-year-long thunderstorm which I wrote about not long ago.  Then, at the end of the Triassic, there was yet another massive extinction, this one probably caused by the volcanism from the Central Atlantic Magmatic Province (which would ultimately open the Atlantic Ocean).  Things had largely settled down by the beginning of the Jurassic Period, at which point we were heading into a period of lush forests and (mostly) stable climate -- the long, glorious Age of Dinosaurs.

But as you know, even their salad days weren't destined to last forever.

It always strikes me, when I read papers like this one -- the colossal hubris and ignorance of people who think we can mess around with Earth's ecosystems with complete impunity.  They often shrug off any Cassandras with breezy lines like, "The Earth's climate has had swings in the past, and has always recovered."  And in one sense, sure, that's true.  Faced even with a catastrophic extinction like the Permian-Triassic, enough species made it through the bottleneck -- and the whipsawing that happened afterward, as the climate gradually restabilized -- to repopulate the Earth.

But keep in mind that a great many species didn't make it.  Most of them, in fact.  Then, at the end of the Cretaceous, the non-avian dinosaurs -- that had been the dominant group worldwide for two hundred times longer than humans have existed -- were completely eliminated.  Okay, life recovered once again, but even for the survivors, living through the event itself was no fun.

Oh, and allow me to put this whole grim story into perspective by mentioning the second paper that came out this week; a huge study out of James Cook University and the University of Adelaide showing unequivocally that tropical forests are dying off because of human-induced climate change -- that they're not adapting fast enough to cope with how quickly we're altering the climate.

We are the first species that has sufficient brainpower to understand how our actions affect the biosphere, and (perhaps) enough power to work toward mitigating them.  And instead, we're largely doing nothing, selling out the future in exchange for short-term expediency, a use-it-once-then-throw-it-away lifestyle, and enriching the coffers of corporate billionaires.  The current so-called administration's mottos with regards to the environment are "Deregulate everything," "Cut down more trees," and "Drill, baby, drill."

They, and all of us, should remember: sure, it's likely that whatever we do, in a million years there still will be plenty of life on Earth.  No matter the mistakes we make, the biosphere will survive.

But there is no guarantee that the survivors will include us.

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The lost forests of the Fens

It will come as no surprise to regular readers of Skeptophilia that I have a fascination for considering how the terrain of the Earth has changed over its history.  It's a topic I've come back to again and again as scientists piece together the shifting topography of the continents, molded by plate tectonics and glaciations and even the occasional meteorite impact.

It's tempting to think that you have to go back hundreds of millions of years to see a significant difference from what we have now, as we did in yesterday's post about the peculiar geology of Scotland.  In some cases, though, things have changed on a far shorter time scale, so recently that the remnants of the past lie right beneath the surface of the modern landscape.

The Fens are a region in eastern England, lying in Lincolnshire, Cambridgeshire, and Norfolk.  It's virtually all dead-flat and only a meter or two above sea level, so the whole area is prone to flooding -- water is controlled by a network of levees and drainage channels that crisscross the entire nearly four thousand square kilometer region.  You'd think this would discourage people from living there, but the opposite is true; it's been settled since Mesolithic times, mostly because of the excellent quality of the soil for agriculture.  The largest communities in the Fens are understandably concentrated on the highest ground, which are nicknamed "islands" (and in rainy periods, they sometimes are islands in actual fact).  The largest of these is Ely, a beautiful cathedral city that is now home to twenty thousand people.

Ely Cathedral [Image licensed under the Creative Commons Tilman2007, Ely-071, CC BY-SA 4.0]

It's a strange and surreal landscape, prone to long periods of fog and swirling mist, largely devoid of trees, dominated by wide grassy marshes that are home to a great variety of birds and other wildlife.  The region so impressed composer Ralph Vaughan Williams that he wrote his melancholy and evocative piece In the Fen Country to try to capture the otherworldly beauty of the place.

Wicken Fen, Cambridgeshire [Image is in the Public Domain]

What brings up this topic today is a study by researchers at the University of Cambridge that appeared in the journal Quaternary Science Reviews last week, which showed that only five thousand years ago, the Fens looked very different -- and traces of that vanished landscape still lurk right below the surface.

Farmers plowing the rich soil to plant crops such as grains, vegetables, potatoes, canola, and mustard frequently find their plows getting snagged on heavy logs that then have to be dug up and dragged out.  "A common annoyance for Fenland farmers is getting their equipment caught on big pieces of wood buried in the soil, which can often happen when planting potatoes, since they are planted a little deeper than other crops," said study lead author Tatiana Bebchuk.  "This wood is often pulled up and piled at the edge of fields: it's a pretty common sight to see these huge piles of logs when driving through the area."

Upon analysis, Bebchuk and her team found that nearly all of the wood came from yew trees -- many of them absolutely enormous, on the order of twenty meters tall.  Only five millennia ago, what is now the marshland of the Fens was a huge forest of yew trees.

Then, about 4,200 years ago, all of them suddenly died.

The reason, Bebchuk found, was a sudden influx of salt water as the world warmed following a cold period, and sea levels rose.  Within a generation the yew forests were nothing more than a vast expanse of bleached trunks, which ultimately fell and were buried in the marshy soil.  Replacing them was an ecosystem of salt-tolerant marshland grasses that still dominate the region today.

What's curious is that this coincided with significant events in other parts of the world -- a serious drought in China, and the collapse of the Egyptian Old Kingdom and the Mesopotamian Akkadian Empire.  Whether these are all directly related is, of course, impossible to say; it's rare that complex historical events have only a single cause.  Climate change may, however, been a significant contributor -- otherwise this is quite the coincidence.

"We want to know if there is any link between these climatic events," said Bebchuk.  "Are the megadroughts in Asia and the Middle East possibly related to the rapid sea level rise in northern Europe?  Was this a global climate event, or was it a series of unrelated regional changes?  We don't yet know what could have caused these climate events, but these trees could be an important part of solving this detective story."

It's fascinating, and a little scary, to see how rapidly things can change -- and if this doesn't put you in mind of what we're currently doing to the climate, it should.  Consider what landscapes we have today, places that seem like they'll never change, that might be drastically different fifty years from now.

I wonder what the scientists five thousand years in the future will piece together about our current world?

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Do not cross

Back in 1859, renowned British naturalist Alfred Russell Wallace wrote a paper about a peculiar phenomenon, which has since been called Wallace's Line in his honor.  He had noted that west of a wavering line that runs basically from northeast to southwest across Indonesia, the flora and fauna is much more similar to what you find in India and tropical southeast Asia; east of that line, it resembles what you find in Australia and Papua-New Guinea.

Map from Wallace's original paper [Image is in the Public Domain]

The change is striking enough that it didn't take a naturalist of Wallace's caliber to notice it.  Italian explorer Antonia Pigafetta mentioned it in his journals way back in 1521, and various others considered it a curiosity worth noting.  None, though, did the thorough job of studying it that Wallace did, so naming it after him is justified.

However -- even Wallace had no idea why, or how, it had happened.

Ordinarily, faunal and floral assemblages change gradually, unless there's a major geographical barrier.  I saw an example of the latter first-hand when I was in Ecuador -- there's a completely different set of birds as you cross from the west slope to the east slope of the Andes Mountains.  (Some did make the leap, but by and large, you run into a whole different group of species from one side to the other.)

Here, though, there's no obvious barrier.  In fact, if you'll look closely at the map, you'll see that Wallace's Line goes right between the islands of Bali (on the west) and Lombok (on the east) -- a distance of only 35 kilometers, easily narrow enough for birds to cross, not to mention other species swimming or rafting their way from one island to the other.  Even so, the species on Bali are distinctly Asian, and the ones on Lombok distinctly Australian.

On one side, kangaroos and koalas, cockatoos and birds of paradise and cassowaries; on the other, bears and tigers, trogons and drongos and minivets and babblers.

How did this happen -- and more perplexingly, what's kept the line intact?

The explanation for the first part of this question had to wait until the discovery of plate tectonics in the 1950s.  The Australian region and Asia have very different species because they are on different tectonic plates that used to be a great deal farther away from each other; in fact, until 85 million years ago, Australia was connected to Antarctica (something we know not only from our understanding of plate movement, but because prior to that Australia and Antarctica have similar fossils, which began to diverge at that point as Australia moved north and Antarctica moved south).  Australia has been gradually approaching Asia ever since, with its unique assemblage of species riding in like some latter-day Noah's Ark.

What, though, is keeping them from mixing?  The reason the topic comes up today is because of a paper last week in Science that has proposed a neat explanation; the problem is the climate.

Researchers at ETH-Zürich led by evolutionary biologist Loïc Pellissier noted that there were exceptions to the boundary of Wallace's line, but the species that crossed it almost always went one way -- from the Asian region into the Australian region.  Some species of Australian snakes, for example, have their nearest relatives in Asia, as do the wonderful Australian flying foxes.  But there are virtually no examples of species that went the other way.

What was preventing organisms from island-hopping their way from Australia to Asia was Asia's much wetter climate -- if you go from west to east across Indonesia and into Australia, the average rainfall by and large goes steadily downward.  The contention is that it's easier for organisms from a rainy climate to adapt to gradually drying out than it is for extremely dry-adapted organisms to deal with the already high biodiversity (and thus much higher competition with species already well suited to the conditions) found in more rainy regions.

You have to wonder what will happen when Australia and Asia finally collide -- something that is, in a sense, already happening, but will result in a complete fusion of the two continents in two hundred million years or so.  This will result in a situation a little like the collision of India with Asia eighty million years ago, which raised the Himalaya Mountains.  (In fact, that collision is ongoing; as India pushes north, like a giant plow, the Himalayas are continuing to rise.  Which is why you find marine fossils at the top of Mount Everest -- the Himalayas aren't volcanic, they're marine and continental debris scooped together and piled up by the motion of India.)

The collision of Australia and Asia will, of course, eradicate Wallace's Line (although the mountain range it will create could still provide a barrier for species mixing, just as the Andes do in Ecuador and Peru).  Of course, two hundred million years is a very long time -- about three times as long as it's been since the extinction of the non-avian dinosaurs -- so who knows what species will have evolved in the interim?

Or if we'll have any distant descendants of our own around to see it?

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The mysteries of the deep

I've heard it said that we know more about the surface of the Moon than we do about the deep oceans on the Earth.

I've never seriously attempted to find out how accurate this is (and honestly, don't know how you'd compare the two), but I suspect it's substantially correct.  About seventy percent of the Earth's surface is covered by water, and given the difficulty of seeing what's down there -- even by remote telemetry -- it's no wonder we're still finding things in the ocean we never knew existed.

Take, for example, the study that appeared in Current Biology last week about the Clarion-Clipperton Zone.  The CCZ is the region between the Clarion Fracture Zone and the Clipperton Fracture Zone in the central Pacific, with an area of about six million square kilometers.  It contains several (apparently dormant or extinct) volcanoes, a number of submarine troughs of uncertain seismic activity, and a rough, mountainous topography.

[Image is in the Public Domain courtesy of the United States Geological Survey and the Department of the Interior]

The prevailing wisdom has been that most of the open ocean has relatively low biodiversity.  To put it more simply, that there just ain't much out there.  If you're in the middle of the ocean, any given cubic meter of water is unlikely to have many living things in it beyond single-celled plankton.  And -- supposedly -- the floor of the deep ocean, with crushing pressures, no light, and constant temperatures just above the freezing point of water, is often pictured as being pretty much devoid of life except for the bizarre hydrothermal vent communities.

That concept of the deep oceans needs some serious re-evaluation.  Last week's paper featured a survey of the abyssal life in the Clarion-Clipperton Zone, and found nearly six thousand species of animals...

...of which 92% were unknown to science.

The coolness factor of this research is tempered a little by the reason it was conducted.  The CCZ is being studied because of its potential for deep-sea mining.  The seafloor there has a rich concentration of manganese nodules, concretions of metal oxides and hydroxides (predominantly manganese and iron, with lower concentrations of other heavy metals), which are of immense value to industry.  Add to that the fact that the CCZ is in international waters -- so, basically, there for whoever gets there first -- and you have a situation that is ripe for exploitation.

What makes this even more complex is that the metals in the nodules are used, amongst other things, for high-efficiency electronics, including renewable energy systems.  The cost, though, might be the destruction of an ecosystem that we've only begun to study.

"There are some just remarkable species down there," said Muriel Rabone, of the Natural History Museum of London, who co-authored the study.  "Some of the sponges look like classic bath sponges, and some look like vases.  They’re just beautiful.  One of my favorites is the glass sponges. They have these little spines, and under the microscope, they look like tiny chandeliers or little sculptures.  There are so many wonderful species in the CCZ, and with the possibility of mining looming, it’s doubly important that we know more about these really understudied habitats."

So much of what humans have done seems to be blundering around blindly and only afterward seeing what the consequences are.  Perhaps we should investigate the ocean's mysteries before we attempt to use it for profit.

It seems fitting to end with a quote from H. P. Lovecraft, whose fascination with the ocean returns time and time again in his fiction: "But more wonderful than the lore of old men and the lore of books is the secret lore of ocean.  Blue, green, grey, white, or black; smooth, ruffled, or mountainous; that ocean is not silent.  All my days have I watched it and listened to it, and I know it well.  At first it told to me only the plain little tales of calm beaches and near ports, but with the years it grew more friendly and spoke of other things; of things more strange and more distant in space and in time.  Sometimes at twilight the grey vapours of the horizon have parted to grant me glimpses of the ways beyond; and sometimes at night the deep waters of the sea have grown clear and phosphorescent, to grant me glimpses of the ways beneath.  And these glimpses have been as often of the ways that were and the ways that might be, as of the ways that are; for ocean is more ancient than the mountains, and freighted with the memories and the dreams of Time."

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An ancient invasion

Just about anywhere you are in the world, you are confronted constantly with invasive species.

Some are so ubiquitous we've stopped even noticing them.  Here in the United States, for example, most lawn grasses are non-natives (including, amusingly, Kentucky bluegrass), as are dandelions, daisies, burdock, garlic mustard, multiflora rose, bush honeysuckle, and thistle.  None of our domesticated animals are native to North America, but neither are such ridiculously common creatures as house mice, the various species of rats, Japanese beetles, pigeons, starlings, house sparrows, and goldfish.  

It's tempting to lump all these species together and say "exotic = bad," but that's a vast, and inaccurate, oversimplification.  Some have clearly had devastating effects on native species; feral and owned-but-outdoor cats, for example, kill an estimated two billion birds a year in the United States alone.  (Yes, that's billion, not million.  Cats are responsible for more bird deaths than any other single cause.)  Other exotics have had far less impact; dandelions may be in every lawn in North America, for example, but they don't seem to do much in the way of outcompeting other species.  (And, as I said earlier, lawn grasses are exotics themselves anyhow.)

A lot of effort by environmental agencies has been put into eradication of exotics, to varying levels of success.  Rats and mice, for example, are generally a lost cause, given their fast reproductive rate and ability to survive on damn near any kind of food; but some isolated islands have done pretty well, most notably South Georgia, which wiped out their rat and mouse infestation in 2018 in order to save endangered birds that nest there.

The southeastern United States, however, has had almost zero success controlling kudzu, also called "mile-a-minute vine" because of its stupendous growth rate.  Introduced in 1876, and hailed as a source of browse for cattle and starch-rich roots that could be used in place of potatoes, the vine went on to cover trees, barns, and slow-moving individuals, and to this day blankets acres during its growing season.

Kudzu in Atlanta, Georgia [Image is in the Public Domain]

Where it gets interesting is the observation by one of my AP Environmental Science students a while back, who said, "But if you go back far enough, isn't everything exotic?"  It's a point well taken.  Species move around, and introductions happen by accident pretty much continuously.  (In fact, there's a whole mathematical model called island biogeography that has to do with the effects of such factors as island size and distance from the mainland on immigration rate and stable biodiversity.)  Our own deliberate and accidental introductions are only continuing a process that has been going on for a long time.

A very long time, to judge by the research of Ian Forsythe (of the University of Cincinnati) and Alycia Stigall (of the University of Tennessee - Knoxville).  They've been studying the "Richmondian Invasion" -- a sudden influx of new species into the shallow sea that covered what is now northern Kentucky, southwestern Ohio, and southeastern Indiana that occurred during the Late Ordovician, 450 million years ago.

The invasion was surprisingly rapid.  Due to exceptionally well-preserved strata, they were able to show that the new species were introduced from the north, as rising seas allowed them to cross what had been a low ridge of dry land, over only a few thousand years.  And what Forsythe and Stigall found was despite the magnitude of the invasion, and the speed with which it occurred, it didn't have very much effect on the recipient ecosystem's pre-existing species.

The reason, Forsythe and Stigall say, is that most of the invaders were low on the trophic ladder -- they were filter-feeders and grazers on phytoplankton.  It'd have been a different story if the invaders had been high-trophic-level predators.

All of this should inform our decisions on where to put our limited resources for environmental management.  High-impact, high-trophic-level invaders -- feral cats, rats, and the like -- are more critical to control than low-level herbivores like pigeons and house sparrows.  (It bears mention, though, that just being a herbivore doesn't mean "harmless;" here in the northeastern United States, whole forests of ash trees are being killed by the emerald ash borer, and farmers and viticulturists are rightly flipping out about the wildfire-spread of the spotted lanternfly.)

So it's a complex subject.  But it's fascinating that an analysis of an exotic invasion 450 million years ago might inform our decisions about how to manage exotics today.  Yet another indication of the value of pure research -- it can give us an angle on real-world problems that we wouldn't have arrived at otherwise.

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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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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!]