Archive for the ‘Ecology’ Category

Hippos in Colombia

April 2, 2020

I like to watch the Neflix series, Narcos, but I’m always disappointed in the ending of the story arcs.  The series chronicles the real story of the Colombian drug cartel.  The drug kingpins ingeniously avoid capture for most of the season until DEA agents eventually capture or kill them in the season finale.  This disappoints me because I root for the cartel.  These supposed bad guys are providing a product that people want, and that makes them heroes in my opinion. It’s the law enforcement agents who aim to ruin everyone’s fun.  The first 2 seasons featured the infamous Pablo Escobar, a man elected to Colombia’s parliament but was not allowed to take his seat due to his massive illegal drug operation.  (Decades of Civil War could have been avoided, if he had been allowed to serve in the legislature.) Pablo gave tens of millions of pesos to poor peasants–more than the Colombian government did.  Unfortunately, during 1993, American DEA agents murdered him.

Who Really Killed Pablo Escobar? - A&E

Pablo Escobar.  Why do U.S. taxpayers pay the government to murder citizens in 3rd world countries?

Pablo Escobar loved animals and had his own private zoo.  Following his death, hippos from his zoo escaped into the wild and they are flourishing.  From a founding population of 4 the hippos in Colombia have increased to between 80-100, and biologists predict it could reach between 400-500 or possibly even 5,000 by the year 2050.  Hippos begin bearing young at 3 years of age and can keep giving birth every 2-3 years until they die between the ages of 40-50.  Adult hippos, even in Africa, have almost no natural predators other than man.  (Lions, with difficulty, can kill juvenile hippos.)

Pablo Escobar's Hippos Are Thriving in Colombia and Wreaking Havoc ...

Hippos in Colombia.

Some researchers fear hippos, as an invasive species not native to South America, may be detrimental to the Colombian environment.  Concentrations of hippos can foul non-flowing water holes with excessive manure that turns them anoxic.  The concentrated nitrogen leads to algal overgrowth, resulting in water with no dissolved oxygen in it–killing all the fish.  However, other scientists think hippos may be filling an ecological niche formerly held by extinct Pleistocene megafauna and maybe  in some ways beneficial to the environment.  Hippos in Colombia inhabit floodplain lakes, cattle tanks, and streams.  75% of their range has been man-modified into farmland including cow pastures and palm oil plantations while the balance consists of the original tropical forest. In some areas, especially where the water flows, hippo manure fertilizes aquatic plants and increases fish and insect populations.  This means more food for birds.  Hippo wallowing and movement breaks up thick vegetation, and their aquatic trails connect ponds, allowing fish to migrate and colonize new areas.  Their close cropping of streamside vegetation creates lawn-like habitats that attract some species of birds.

Hippos may be a modern day substitute for the Pleistocene haplomastodons that used to occur in this part of South America.  Haplomastodons, a species of gompothere, were probably semi-aquatic. North American mastodons definitely were semi-aquatic–they ate aquatic plants and had fur similar to that of otters and beavers.  Some notoungulates endemic to South America may have also been semi-aquatic, but not enough is known about them to determine this for sure.

Haplomastodon | Dinopedia | Fandom

Illustration of a haplomastodon.  Fossils of this species have been found in Colombia.

Hippos are in Colombia to stay.  Years ago, some government jerks with a stick up their ass decided to start eliminating the hippos, and they killed a male popular with the locals and tourists.  The outrage among most Colombians put a stop to this.  Animal rights groups sued, and there are now no plans to wipe them out.

References:

Subalusky, A; et al

“Potential Ecological and Socio-Economic Efforts of a Novel Megaherbivore Introduction: The Hippopotamus in Colombia.”

Oryx December 2019

Svenning, J., and Soren Faulby

“Pre-historic and Historic Baselines for Trophic Rewilding in the Neotropics”

Perspectives in Ecology and Conservation 15 (4) 2017

The Red River Raft

February 21, 2020

I came across this remarkable phenomenon while re-reading America as Seen by Its First Explorers by John Bakeless. About 900 years ago, a flood washed a bend of land and all the trees on it into the Red River.  (The red clay substrate makes the water red, hence the name.) The trees and sediment caused a logjam and subsequent floods kept washing more and more debris into it so that by 1830 the logjam, known as the Red River Raft, was an incredible 165 miles long.  The sediment was so deep trees, bushes, bamboo, and grass sprouted on the logjam.  Forests of cypress, cedar, cottonwood, willow, sycamore, oak, and persimmon grew over the river, and many pioneers didn’t even realize they were passing over a river when they crossed it. Some of the trees were 10 inches in diameter. The logjam forced the river to shift positions, often leaving behind fertile soil where the Caddo Indians planted crops.  The impenetrable thickets and unnavigable river protected the Caddo Indians from European settlers and kept them isolated from other hostile tribes.  The logjam created 5 major lakes as well, and these attracted huge flocks of waterfowl.  Natural channels wove their way through the logjam, but it was impossible to travel through it by boat.

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Map of the Red River and some of its tributaries.

Great Raft

Photo of part of the Red River Raft after it reformed during the 1870s.

Henry Shreve (the city of Shreveport was named after him) began dismantling the Red River Raft during the 1830s.  He used a giant winch on a steam boat to remove logs from the bottom up and he dug channels through the raft itself.  He successfully cleared the Red River Raft but warned that it could reform, and a few decades later it did.  Eugene Woodruff dismantled the reformed raft during 1873, but this increased water flow through the Mississippi River and flooded parts of Louisiana.  The Army Corps of Engineers was forced to build the Old River Control Structure to prevent disastrous flooding downstream.

Great Raft

Boat with winches used to clear trees from the Red River Raft.

Log jams over 100 miles long must have occurred sporadically during the Pleistocene, providing unique habitat for land and aquatic flora and fauna.

Proxy Evidence for an Increase in Human Populations at a site in South Carolina Circa 12,838 Years BP

December 14, 2019

The Younger Dryas Impact Hypothesis, or YDIH for short, is a crank theory that has been thoroughly debunked.  The YDIH proposes a comet impact on a glacier in the Northern Hemisphere 12,900 years ago sparked continent wide fires, caused a sudden drastic climate reversal, and resulted in the extinction of Pleistocene megafauna.  The Younger Dryas was a climate stage that lasted for about 1500 years; and it was a sudden return to cold, arid Ice Age conditions, following thousands of years of warmer, wetter climate.  It’s named for a flower that flourished in Europe during this climate phase.

The Dryas octopetala flower

Dryas octopetalus likes open, cold, landscapes.

The YDIH is fatally flawed.  There is no known impact crater, dating to the proposed time of impact.  The Hiawatha Crater recently discovered in Greenland has been proposed as the possible impact crater, but the lack of a young ejecta blanket suggests it is millions rather than thousands of years old.  Its ejecta blanket has eroded away–a process that would take a very long time.  There is no evidence of continent wide fires.  Instead, the sites first noted by YDIH proponents to have evidence of the fires dated to many different ages both before and after 12,900 years BP, and the fires were most likely caused by lightning or humans.  Many of the other claimed impact indicators date to different ages.  Megafauna extinctions and extirpations also occurred at various ages–not all at 12,900 years BP.  Some of the so-called impact indicators are not necessarily diagnostic of an impact but can have terrestrial origins.  Other scientists looking for impact markers have not been able to replicate the results of the original YDIH studies.

The Younger Dryas was caused by well understood cyclical climate variations known as Heinrich Events.  12,900 years ago, an ice dam in Canada broke, leading to an enormous influx of cold fresh water into the North Atlantic.  This shut down thermohaline circulation, causing temperatures in the Northern Hemisphere to plunge.  This is the explanation for the Younger Dryas I accept.  Nevertheless, the ridiculous YDIH just will not die.  A paper advocating this bizarre almost pseudo-scientific belief was published as recently as October of this year.  Though I reject the YDIH, this paper had interesting data that I interpret differently from the authors.

Scientists who published this paper took a 1 meter core of sediment from White Pond in South Carolina. White Pond is a ~32,000 year old Carolina Bay.  Carolina Bays are bodies of water formed by wind and water erosion during dry climate phases of Ice Ages, and they are found throughout the Carolinas and Georgia.  The scientists dated the sediment layer by layer and looked for charcoal and sporomiella.  The abundance of charcoal indicates fire in the environment, and sporormiella is a fungus that grows on megafauna feces and is used as proxy evidence for the abundance of large mammal populations.  The scientists found charcoal amounts peaked at 12,838 years ago, indicating lots of fire on the landscape.  Megafauna populations declined to a low point 12,752 years ago.  The authors of this study think the fire was caused by the comet impact, and the resulting changes in the environment led to the local extirpation of the megafauna.

figure1

Location of White Pond where this study took place.  Image from the below reference.

My interpretation is different.  I think the fires were set by humans to improve habitat for megafauna. (Indians set fire to southeastern landscapes until Europeans removed them from the region.)  Then it took 86 years for humans to wipe out megafauna at this locality.  Nomadic hunters possibly moved away after eliminating most of the big game, allowing megafauna populations to rebound until 10,399 years BP when they disappear again from the region, this time permanently.

figure2

Graph from the below referenced paper.  Note how megafauna populations rebounded until 10,399 years ago–2500 years after the proposed comet impact.  This suggests the proposed comet impact could not have been a factor in their extinctions.

The authors of this study note there is an unconformity in the core dating to the Younger Dryas.  Normally, during wet climate cycles sediment builds up as vegetation dies and turns into soil.  But during dry phases when vegetation is sparse, exposed soil erodes and is blown away by wind, and there is little to no sedimentation.  If this is the case, there should be a gap rather than a continuous line in the graph.  I’m not sure how this impacts the conveyed data.  However, the data is interesting to me because I think it shows when humans arrived at this locality in significant numbers, and how long it took them to extirpate the megafauna.

Reference:

Moore. C; et. al.

“Sediment Core from White Pond, South Carolina contains a Platinum Anomaly, Pyrogenic Carbon Peak, and Coprophilous Decline at 12.8 Ka”

Scientific Reports October 2019

https://www.nature.com/articles/s41598-019-51552-8

 

Why the Western Hebrides are Mostly Treeless

November 16, 2019

During fall of 1773 Samuel Johnson and James Boswell traveled together on the western islands of Scotland, also known as the Hebrides.  They wrote separate accounts about this journey, and both are included in  a volume I’ve been reading for the past couple of weeks.  Samuel Johnson frequently noted and joked about the scarcity of trees in the region.  I wondered why a temperate locality with plenty of precipitation was mostly treeless, so I researched the natural history of western Scotland and learned there is a fascinating and complex ecological explanation.

Map courtesy of www.calmac.co.uk

Map of the Western Hebrides.  Johnson and Boswell traveled on the inner islands.

Scottish peat bog and heather.  These are also known as moors.

The first explanation I found on google seemed implausible and I was right.  Some claimed the Vikings stripped the island of trees to prevent rivals from using the wood to build boats.  This is an unlikely explanation because a people who lived by pillaging would not be keen on all the labor required in felling and removing all that lumber.  Moreover, trees would grow back within a generation.  I dug deeper and found a better, more scientifically sound explanation.

During the Ice Age glaciers completely covered Scotland, and there were no trees.  11,400 years ago, the glaciers retreated and a scrub forest of birch, willow, hazel, and rowan advanced over the tundra.  These scrub forests co-existed with peat bogs.  By 8500 years ago, oak, elm, and Scotch pine began to grow as well but were uncommon and local in distribution on the Hebrides.  From 9300 years BP-7900 years BP open woodlands of birch, willow, aspen, and hazel with plenty of grassy meadows between the trees prevailed.  But then, peat bogs began to expand while areas consisting of woodlands contracted so that by 2500 years ago peat bogs were the dominant environment on the Western Hebrides.  This predates the Viking invasion by 1500 years.  Instead, natural disturbance and soil chemistry shaped the landscape of the region.

Severe storm events about 8000 years ago felled the trees.  Without trees drinking up the water, the water table rose.  Tree deaths caused a positive feedback loop for peat bog expansion at the expense of woodlands.  The cool moist climate slows down evaporation, and the water just sits on impervious bed rock.  Water dissolves acids in the rock, further helping the growth of acid-loving sphagnum peat and heath but reducing the fertility in the soil required by trees. Peat bogs are dominated by sphagnum peat, sedges, and carnivorous plants, while heath grows on the better drained sites.  Trees just can’t grow in these conditions.

About 400 years ago humans cleared the remaining woodlands on the islands and converted them to agricultural use.  Now, an organization known as the Hebridean Ark hopes to re-establish at least some forests on the islands.  They’ve planted 100,000 trees including rowan, birch, willow, hazel, juniper, and aspen.  According to Johnson and Boswell, attempts to plant trees on the islands during the 18th century mostly failed.  Modern scientists may have a better idea of what they are doing, however.

References:

Fossitt

“Late Quaternary Vegetation History of the Western Isles of Scotland”

New Phytologist 132 1996

Johnson, S. and James Boswell

A Journey to the Western Islands of Scotland and The Journal of a Tour to the Hebrides

Penguin Classics 1984

Did Pleistocene Tapirs Shit in the Woods?

May 12, 2019

The answer is not as obvious as it might seem.  A new study found extant lowland tapirs (Tapirus terrestris) defecate more often in degraded woodlands than in deep forests.  They spend more time in disturbed forest openings that have been logged or burned because they feed upon young plants sprouting in the increased sunlight after canopy tree removal.  The study suggests tapirs facilitate forest regeneration by defecating viable seeds in their dung.  Scientists estimated the average tapir shits about 10,000 viable seeds per year in disturbed forests–3X more than in undisturbed forests.

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Lowland tapir standing near a forest edge.  They actually shit more next to the woods than in it.

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Mountain tapir (T. pinchaque).  This is the only species of extant tapir adapted to cooler climates.  The extinct species of tapir that formerly lived in southeastern North America was likely adapted to temperate climates, like this species.

The extinct Vero tapir (Tapirus veroensis) roamed across southeastern North America during the Pleistocene, and this species likely played an important role in forest regeneration then as well.  Herds of mammoths and mastodons stripped bark from trees, often killing them.  This was especially true during droughts when mammoths, normally grass-eaters, were forced to dine on the edible parts of trees.  Flocks of passenger pigeons also wiped out whole sections of forest.  Tornadoes and ice storms left large gaps in the forest canopy.  Tapirs attracted to these disturbed areas helped them regenerate.

Studies of extinct tapir bone chemistry indicate tapirs preferred to eat plants that occurred in deep forests.  However, they likely ate the young saplings that sprouted in gaps within forests.  Some of the plants tapirs may have consumed included pokeberry, persimmon, pawpaw, Osage orange, honey locust, wild squash, blueberry, composites, maple, and oak. These are plants that quickly colonize forest gaps.  And tapirs didn’t often shit in the woods.  Instead, they crapped on the edge of the woods or in open gaps within the woods.

Reference:

Paolucci, L.; C. Rattis, R. Pereira, and D. Silverio

“Lowland Tapirs Facilitate Seed Dispersal in Degraded Amazonian Forests”

Biotropica Feb. 2019

The Last Glacial Maximum in the Georgia Piedmont–My Abundant Oases Hypothesis

January 13, 2019

Scientists estimate average annual precipitation in Georgia was just 15 inches during the Last Glacial Maximum (~24,000-~19,000 calendar years BP).  I’ve kept a rain gauge in my backyard here in Augusta, Georgia for 17 years, and I’ve carefully recorded precipitation.  Average annual precipitation in my backyard was 47.8 inches over this time period.  The driest year in my records was 2010 when just 29.5 inches of precipitation fell, and the wettest year according to my records was 2017 when 69.8 inches of precipitation fell.  The difference between present day precipitation totals and LGM precipitation suggests the floral composition must’ve been considerably different then, and many modern day species of plants must’ve retreated to small refugia.  However, there is no evidence of this, and in fact a couple lines of evidence indicate species abundant today were just as widespread during the LGM.

Genetic evidence shows that species common in deciduous forests occurred all the way to the glacial boundary during the Ice Age, despite pollen records indicating spruce forests dominated the landscape from north Georgia to the Ice Sheet.  DNA studies of eastern chipmunks, red and sugar maple, shagbark hickory, beech, and yellow birch suggest they all ranged right up to the edge of the glacier which expanded all the way to southern Ohio.  The ranges of at least 17 species of trees including persimmon, sweet gum, and river birch still reach their northern limits at the ghost boundary of where the massive glacier advanced.  (See: https://markgelbart.wordpress.com/2017/03/30/the-ghost-boundary-of-the-last-glacial-maximum-ice-margin/ ) Although genetic evidence reveals discontinuities between populations of species, these appear to be caused by geographical barriers such as major rivers and the Appalachian Mountains.  The genetic evidence suggests multiple diffuse refuges during the LGM for species that are common today.  It seems like a paradox, but I have an hypothesis that can explain this for the Georgia piedmont.  I call it my Abundant Oases Hypothesis, and it can probably be applied north of Georgia as well.

First, temperatures were much cooler during the LGM, so an average annual precipitation total of 15 inches would have gone much further then.  Evapotranspiration rates were much lower, especially during summer.  15 inches of rain and snow may have been the equivalent of 25 inches in today’s climate–similar to an average drought year today.  Second, Georgia’s piedmont soils are mostly clay, and they don’t drain as well as sandy soils.  Water was held longer near the surface when it did receive precipitation.  Third, the hilly terrain of the piedmont was a factor in contributing to oases where flora and fauna could flourish.  Rainwater flowed down hills (this is known as colluvial flow), so the bottom areas between them hosted more plant life.  Although most creeks dried up, there were plenty of areas at the bottom of hills where the water table came close enough to the surface to form intermittent springs.  Beavers dammed springs, making them deeper and helping them hold water longer.  Fourth, major rivers didn’t dry out completely and provided plenty of mesic refuge for species that could expand into oases during phases when annual precipitation increased.

Topographical map of the Piedmont National Wildlife Refuge in Jones County, Georgia.  Note the hilly terrain and abundant creeks.  During the LGM colluvial slope flow, intermittent springs, and lower temperatures helped reduce the negative effect of droughts.

My Abundant Oases Hypothesis is speculative.  There are no pollen studies dating to the LGM from piedmont Georgia.  There is 1 site in Winder, Georgia known as Nodoroc where pollen was collected that dates to just before the LGM when temperatures were warmer and precipitation was higher.  Oak and pine were the dominant species, and they co-occurred with hickory, fir, and spruce.  Beech, chestnut, birch, and maple were present.  The shrub layer consisted of hazelnut and blueberry/rhododendron.  There is no sediment dating to between 28,000 years BP-5000 years BP, suggesting land was eroding rather than accumulating sediment during this time period.

This is how I envision the Georgia piedmont landscape during the LGM.  The tops of hills were covered with widely spaced shortleaf pine and post oak.  These were slow growing and ancient because reduced CO2 levels in the atmosphere caused slow plant growth.  Grass, herbs, thorny patches with prickly pear cactus, exposed boulders and rocks, and bare earth occurred between the trees.  Following rare rain events, the ground burst into flower, but most of the year it looked dull and brown.  Deep gullies, red from exposed clay, were common on the hillsides–a result of erosion that commonly occurred due to storms and a lack of topsoil.  The bottoms of hills stayed green longer, and in some low areas hosted springs surrounded by marshy vegetation and deciduous woods of oak, maple, and beech.  These are the oases of my hypothesis.  Megafauna game trails connected these oases with each other, and the river systems where even more deciduous woodlands existed.  This system of oases is what supported the continued existence of species that were able to expand when climatic conditions improved.

Reference:

Soltis, et al.

“Comparative Phylogeography of Unclaciated North America”

Molecular Ecology 2006

 

 

Ants, Flies, and Trillium

November 12, 2018

Woodland herbs in the trillium family have evolved interesting traits that lure insects into helping them reproduce.  The trillium family belongs to the lily plant order, and it includes 45 species and 5 hybrids found in North America and Asia.  More species live in North America and the center of trillium evolutionary origin is probably the southern Appalachians.  Species of trillium were likely widespread in the tropical to temperate forests that occurred across both continents during the Miocene over 5 million years ago.   This is likely when trillium evolved a dependent relationship with bees, ants, and flies.  Some species of trillium, such as the great white (Trillium grandiflorum) produce flowers that attract bees and wasps with a sweet smell.  But others, such as the inaptly named little sweet betsy (T. cunacateum), have flowers that smell like rotting meat, and the red color looks like flesh, so they attract flies.  These flying insects help pollinate the trillium plants.

Image result for Fly pollinating little sweet betsy

Little sweet betsy–more accurately known as bloody butcher because they smell like rotting meat. The flesh color and carrion smell of the flowers attract flies, and in turn the flies pollinate the flowers.

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By contrast the flowers of the great white trillium smell sweet and attract bees and wasps for pollination help.

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Ants disperse trillium seeds throughout the forest.  Aphaenogaster picca is an example of an ant species that mostly preys on termites but takes advantage of the passive trillium seeds when they have a chance.

Trillium produce a fruit with over a dozen fat covered seeds that attract ants.  This layer of fat is known as the elaiosome, and it surrounds a hard seed.  The ants carry the fat rich seeds back to their nest, but discard the hard seeds after consuming the nutritious coating.  This helps spread the species throughout the environment. Most of the species of ants that consume trillium seeds normally prey on termites, worms, and grubs–the trillium seeds are an easier meal that puts up no resistance.  Plants that depend upon ants to disperse their seeds are called myrmecochorous.

For years many scientists were mystified at how trillium and other plant species so rapidly recolonized land formerly covered by glaciers. This is known as Reid’s paradox defined as the unexplained mystery of how some plant species apparently recolonized post glacial habitats faster than their modern dispersal rates suggest.  It is mathematically impossible for ants to have dispersed trillium across New England and parts of Canada in less than 10,000 years. However, scientists recently discovered deer feces containing viable trillium seeds.  Apparently, white tail deer eat trillium fruit and spread the seeds into new territory.  This would answer Reid’s paradox.  However, high populations of white tail deer can be detrimental to trillium populations.  Trillium plants are perennials, capable of surviving from the same root for up to 25 years, but repeated deer consumption of the leaves can kill the plant.  Deer also choose to eat the largest trillium plants, thus selecting for smaller and less productive individual trillium plants.  I hypothesize extinct tapirs and possibly long-nosed peccaries also fed upon and dispersed trillium during the Pleistocene.

The relict trillium (T. reliquum) is known from just 50 sites along the fall line, mostly in Georgia. A genetic study determined this species survived in 2 different Pleistocene refuges during Ice Ages when much of the landscape became desert like.  There is actually greater genetic diversity on the eastern and western parts of its range rather than in the central part.

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The relict trillium, also known as the Confederate wake robin.  It is an ancient species that became rare because of Ice Ages.

References:

Gonzalez, E.; and J.L. Hamrick

“Distribution of Genetic Diversity among Disjunct Populations of the Rare Forest Understory T. reliquum”

Heredity 95 2005

Velland, Mark; et. al.

“Dispersal of Trillium Seeds by Deer: Implications for Long Distance Migration of Forrest Herbs”

Ecology 84 (4) 2003

The Vice-Versa Climate Phases of South Florida during the Late Pleistocene

September 3, 2018

Drastic climatic fluctuations occurred during Ice Ages.  Sudden warm spikes in average annual temperatures followed by rapid onsets of much colder climate phases altered the quantitative composition of plant species in the environment.  In most of North America oaks and other broad-leafed trees increased in abundance during warm wet interstadials but waned during arid cold stadials when coniferous parkland forests consisting of pine and spruce expanded in response to the changing climate.  These fluctuations were part of a feedback loop.  The warmer temperature phases gradually caused giant ice dams to weaken and break.  Torrents of cold freshwater from glacial lakes with floating icebergs flooded the North Atlantic, shutting down the Gulf Stream which during present day conditions moderate temperatures.  These deluges of iceberg studded meltwater are known as Heinrich Events, and they caused average annual temperatures to drop by 15-20 degrees F within decades.  In response to the drop in temperatures the Ice Sheets expanded for thousands of years until the next warm phase.  Climate also became drier because moisture for potential precipitation became locked in glacial ice.  However, evidence from a lake in south Florida suggest climate there was out of sync with the rest of North America north of the Rio Grande.

Graph depicting Heinrich Events and the subsequent fall in temperature.  Pollen evidence from sediment in Lake Tulane, Florida reveals the floral response to these climatic shifts, including the most recent 6 Heinrich Events.

Location of Avon Park in Highlands County, Florida.

Lake Tulane is located near Avon Park, Florida.

Scientists have taken numerous cores of sediment from Lake Tulane, located in south central Florida.  Lake Tulane is a very old body of water and has probably existed for almost 5 million years since this region emerged above sea level.  The sedimentary record goes beyond the limits of radio-carbon dating (50,000 years). The pollen composition in these cores shows the local environment’s response to Heinrich Events, but curiously it is the opposite from that of the rest of North America.  When the rest of North America experienced a warm wet interstadial, south Florida became cooler and drier (though mostly not sub-freezing).  The landscape transformed into an environment dominated by scrub oak, Florida hickory, red cedar, ragweed, grass, asters, staggerbush (Lyonia sp.), and rosemary (Ceratiola).  Scrub oak thickets surrounded by open spaces prevailed.  These are all drought-tolerant but shade-intolerant species, and red cedar is fire-intolerant, indicating the rarity of lightning-induced fires.  Conversely, when the rest of North America suffered cold dry stadials south Florida was warmer and wetter and pine forests spread across the land because lightning-induced fire frequency increased, and pine is fire tolerant.  Scientists find macrofossils of aquatic plants in the sediment representing dry phases because the lake was shallow enough to support emergent marsh vegetation, but these are absent during the wetter phases.

A brand new study introduced a new line of evidence that supports assumptions based on the earlier pollen evidence.  The authors of this study looked at variations in carbon and oxygen isotopes from Lake Tulane plant leaf waxes.  Scientists can understand the historical precipitation characteristics by studying the isotopic composition of plant leaf waxes.  (Plants synthesize organic compounds by using hydrogen atoms they absorb from water molecules.  The isotopes vary depending upon their source.)  They discovered that during climatic phases when scrub oak and ragweed dominated, average annual precipitation dropped by 22%.  The source of precipitation was different too.  Oak phase precipitation mostly came from storm fronts, but pine phase precipitation originated from tropical oceanic storms.

The vice-versa climate of south Florida was tied to the shifting Gulf Stream.  Under non-Ice Age conditions the Gulf Stream carries tropically-heated water to the North Atlantic as far as the coast of Canada, moderating temperatures.  When it shut down following Heinrich Events, the warm water stayed near the coast of south Florida, keeping it warm and wet while the rest of North America suffered dry cold conditions.  The Gulf Stream eventually restarted, bringing warmer wetter temperatures north, but this caused cooling and aridity in south Florida.

I hypothesize the Gulf Stream periodically began to restart within stadials, then shut down with new influxes of meltwater.  These partial changes likely influenced temperatures near the coasts of Georgia and South Carolina.  The climate may have temporarily been warmer in this region even during colder climate stages, and the composition of species here may have varied as well, though it involved different species than the Florida endemics.  Eventually, when the Gulf Stream restarted for longer periods, coastal Georgia may have experienced warmer climates centuries before northern latitudes of North America did.

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Common ragweed.  It was much more common in south Florida during the late Pleistocene than it is today.

There is no modern analogue for the abundance of ragweed (Ambrosia artemisifolia) in south Florida during the late Pleistocene.  Ragweed prefers cooler nights than occur in present day Florida for germination, and its abundant presence during the late Pleistocene indicates cooler nights prevailed, even during the out of phase warmer climate stages.  Ragweed is a tough plant that grows on disturbed sites such as abandoned agricultural fields and vacant lots.  It produces up to 32,000 seeds per plant, so it is able to survive heavy foraging by herbivores.  The seeds persist indefinitely and can wait for centuries before germinating when an environment transforms into a sunny one.  This means it can lay dormant through several stages of forest succession, and then colonize the habitat when conditions become favorable.  This may explain why it was so successful during the late Pleistocene when both sudden climatic fluctuations and megafauna foraging greatly disturbed and altered the landscape.  Many animals consume ragweed.  Rabbits and meadow voles eat the leaves while birds including juncos, cowbirds, quail, purple finch, mourning dove, goldfinch, and red-bellied woodpeckers eat the seeds.  Rabbits and meadow voles were common in south Florida during the Pleistocene, though the latter is presently restricted to 1 county in the state.  Farmers report livestock prefer giant ragweed (Ambrosia trifida) over clover.  It’s unclear if this species lived in south Florida during the late Pleistocene.  It is found in a couple counties, and this may represent relic populations, but they also may be invasive.  Livestock will also eat common ragweed, though they don’t like it as much.  Pleistocene megafauna such as horses, bison, and mammoth likely ate ragweed and grass, and they probably occurred in large herds during both climatic phases.  Other species probably common during the oak phase were Harlan’s ground sloth, northern pampathere, flat-headed peccary, and giant tortoise.  Flat-headed peccaries preferred thorny thickets, and the other 3 liked open environments.  Predators such as saber-tooths, lions, jaguars, and dire wolves fed upon the herbivores.  Ragweed survived megafauna foraging by producing large numbers of seeds, but 2 other plant species in this environment survived because their leaves were toxic–rosemary and staggerbush.  I think both climatic phases in Florida supported approximately similar populations of megafauna.

References:

Arnold, T. Elliott; et. al.

“Climate Response of the Florida Peninsula to Heinrich Events in the North Atlantic”

Quaternary Science Reviews 194 2018

Grimm, Eric; et. al.

“A 50,000 year old record of Climate Oscillation from Florida and its Temporal Correlation with Heinrich Events”

Science 9 July 1993

Grimm, Eric: et. al.

“Evidence for Warm Wet Heinrich Events in Florida”

Quaternary Science Review 25 Sept 2006

Gulf Fritillary and Passion Flower Vine

August 21, 2018

Butterfly migration is even more amazing than bird migration.  Bird migration includes the same generation, but butterflies that begin migrating north never live long enough to return south.  Instead, butterflies gradually expand their range north as the weather warms; breeding, laying eggs, and dying.  The next generation advances farther north.  Then, several generations later, they begin moving south, retreating before killing frosts.  The gulf fritillary (Augraulis valinae) is an example of a migratory butterfly.  They winter in Florida, south Texas, and Mexico, but generations of them migrate as far north as Pennsylvania.  Gulf fritillaries were named because they are some times seen fluttering over the Gulf of Mexico.  Their larva feed upon passion flower vine (Passiflora incarnata) foliage.  The adults obtain their energy from nectar in flowers , and as the below photo represents, they often find some nutrition in animal feces.  Gulf fritillaries are particularly fond of lantana, a non-native shrub that rapidly colonized Florida during early Spanish occupation.

Gulf fritillary snacking on dog feces.

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Passion flower.  Spanish conquistadors thought it symbolized the passion of Christ.

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The fruit of passion flower is edible.  The seeds are covered in a gelatinous substance with a sweet-sour flavor and a tropical aroma.  Brazil produces and consumes the most passion fruit.  Imported passion fruit is occasionally available in the grocery store.

There are between 520-700 species of passion flower vine–taxonomists disagree about the number of species.  96% of them occur in the Americas, indicating this is where they originated.  Other species live in southeast Asia, Australia, and Pacific islands.  They probably colonized these regions by rafting on clumps of debris ripped from the land by  tropical storms.  P. incarnata and the crinkled passion flower (P. gracilis) are the only species that evolved to live in temperate climates.  P. gracilis  is restricted to 1 county in South Carolina, while P. incarnata ranges throughout eastern North America.  During the Miocene when most of North America was sub-tropical there were probably many species of passion flower native to North America, but just 2 evolved the ability to survive frosty seasons.

Passion flower vines are shade intolerant but drought tolerant.  They prefer disturbed areas, and I’ve found them growing on vacant lots in my neighborhood.  This species was well adapted to live during the Pleistocene when rapid climate change and megafauna foraging often drastically altered local landscapes.  Mammoths and other large animals girdled and uprooted trees, opening up the canopy so shade intolerant passion flower vines could thrive.  Many vertebrates, perhaps peccaries, fed on the fruit and distributed the still viable seeds in their dung.  Long Ice Age droughts also killed trees and let passion flower vine spread in the available sunshine, climbing over grass and tree saplings and across bare sandy soils.

When the Spanish conquistadors conquered the Americas, they found passion flower vine growing everywhere.  The soldiers were super religious, though they ignored 1 of the 10 commandments when they were butchering the Indians.  They thought passion flowers symbolized the crucifixion of Christ, known as the passion by religious zealots.  Supposedly, the 5 petals and 5 sepals represent the 10 apostles.  The 72 filaments = the number of thorns in Jesus’s crown.  The 3 stigmas = the cross.  The 3 stamens = the wounds in Jesus’s hands.  The leaf lobes resemble the spear wounds.  The dark spots under the leaves represent the 33 pieces of silver given to Judas to betray Jesus.  The flowers die after just 1 day, just like Jesus died after a day on the cross.  And the petals reclose like the tomb enclosed Jesus.  Some superstitious priest sure had an overactive imagination.

Did Large Carnivores Influence Dune Formation in Ice Age Georgia?

July 26, 2018

Over 100 years ago Australians built a 3480 mile long fence to keep dingoes away from livestock. For ecologists this provides a grand experiment of how the exclusion of a large predator influences ecosystems. However, there exists a considerable amount of conflicting scientific literature about this. Many studies report overgrazed regions on the dingo-less side of the fence that have poor soils as a result. The fence bisects a national park. One study confined to part of this park counted 85 dingoes and 8 kangaroos on the side of the fence with the dingoes, and 1 dingo and 3200 kangaroos in a comparably sized lot on the side that is supposed to be without dingoes. Tame livestock, feral goats and hogs, and rabbits along with the kangaroos contribute to these overgrazed landscapes. Parma wallabies, the greater bilby, and small rodents thrive on the side of the fence with the dingoes because the large canines suppress populations of smaller predators. Another study that claims to be more comprehensive than any other found no differences between either side of the fence. The authors of this study suggest there are no differences because dingoes have never been completely eliminated on the supposedly dingo-less side of the fence. They say other studies concluding there is a difference are local and anecdotal.

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Dingo on a sand dune.

I think the most interesting study is a recent paper that found the presence of dingoes influenced sand dune formation in arid regions. On the dingo-less side of the fence sand dunes were larger and stabilized with shrubby plants growing on top. On the side of the fence with dingoes sand dunes were more shallow, bald, and dispersed by wind because plant growth was sparse. This seems counterintuitive. But this difference in dune formation is caused by the suppression of small carnivore populations. Dingoes reduce populations of foxes and feral cats (neither of which are native to Australia). In turn dusky hopping mice and rabbit populations increase, and they eat the seeds of plants and shrub saplings that keep dunes stabilized.

This last study is most interesting to me because sand dunes rolled across parts of Georgia during the coldest driest stages of Ice Ages, and I wonder if large predators influenced their shape and pattern. The arid climate caused some small rivers in Georgia to run dry. Wind blew the riverine sand into big dunes that are still evident today, though scrubby vegetation has since stabilized them. (See: https://markgelbart.wordpress.com/2012/04/09/the-ohoopee-sand-dunes/ ) I’ve hypothesized overgrazing by megafauna alongside shrinking water holes located in the river bed may have contributed to the erosion leading to sand dune formation. But maybe the presence of large carnivores played a role as well. Dire wolves, jaguars, and cougars suppressed populations of bobcats and foxes; causing an increase in rodent and rabbit numbers. The small herbivores stripped the vegetation bare, allowing sand dunes to roll. On the other hand hawks, owls, and snakes probably always remained abundant, and they likely provided a check on rodent and rabbit populations. Nevertheless, the notion large carnivores may have influenced dune formation in Georgia is an intriguing idea.

References:

Glen, A.; and C. Dietman, M. Soule, and B. Mackey
“Evaluating the Role of the Dingo as a Trophic Regulator in Australian Ecosystems”
Australian Ecology August 2007

Harris, Emma
“Dingoes have Changed the Actual Shape of the Australian Desert”
The Atlantic July 6, 2018