Deer Herbivory Alters Plant and Bird Species Composition

Cades Cove, located within Great Smoky Mountains National Park, is 1 of my favorite places in the world. I visited Cades Cove during June of 2017 and saw lots of deer, a few black bears, a turkey, and an herd of tame horses. It’s 1 of the best places to see wildlife east of the Mississippi. Cades Cove is known for its high density of white-tailed deer and is 1 of many areas where deer herbivory and its effect on plant species diversity and abundance has been studied. High density deer populations reduce tree regeneration and alter plant species composition and forest successional patterns. Areas where deer are abundant can also see a shift in natural communities to an alternate state, while plant species diversity becomes reduced, influencing other species of wildlife. Results of studies on the interaction between deer and plant community vary, depending upon geographical location. Some species thrive or can at least survive in high density deer locations, while these same species in a different geographical location my suffer. I’ll review some of these studies below.

Plant growth inside and outside a deer exclosure in Wisconsin.

Cades Cove, located within the Great Smoky Mountains National Park, is an area considered to have an high density of deer.

Deer in Cades Cover are not hunted, and they have little fear of people.

Look at how close these stupid asses got to this bear in Cades Cove. That bear could be mauling them in about 2 seconds.

Scientists studying the effect of deer herbivory on plant species composition use exclosures, or in other words they construct deer proof fences on certain plots to prevent deer from feeding on the plants inside the fence. They then compare plant composition and abundance inside and outside the fence. A study at the Clemson Experimental Forest found that after 2 years the difference between inside and outside exclosures was negligible. The differences aren’t noticeable until 5-20 years after the exclosure is constructed. At Callaway Gardens near Columbus, Georgia deer exclosures were in use for 20 years. Here, there were significant differences between the inside and outside of the enclosures. Inside the exclosures strawberry bush (Eunonymous americanus not to be confused with the strawberry people eat–Fragaria virginianus) and greenbriar, 2 favorite deer foods, grew taller and more dense than outside the exclosure. There was also an increase in red maple, black cherry, white oak, and sassafras inside the exclosure. Outside the exclosures there was an increase in sweetgum, wax myrtle, hop hornbeam, shining sumac, water oak, and willow oak. Black cherry benefitted from the absence of deer at this location, but at a site in northwest Pennsylvania, this species was found to be resistant to deer browsing.

Violet responds differently to deer herbivory at different locations as well. Scientists studying deer herbivory on the upper peninsula of Michigan found deer eradicated violets, but at Cades Code, though it is often eaten by deer, violet still regenerates. The scientists in Michigan identified “winners” and “losers” among plants in high density deer sites. “Winners included wind pollinated sedges and grasses in the Poa genus, along with hazelnut, blueberry, wood anemone, and wood fern. “Losers” in addition to violets were forbs such as big leaf aster, blue beard lily, strawberry, and thimbleberry. In some areas of Wisconsin deer can reduce tree sapling abundance by 90%, and they can eliminate white cedar and red oak. Oddly enough, yellow birch trees require moderate deer population densities. This species didn’t regenerate if deer populations were too low or too high.

The effects of deer herbivory were studied in a forest located in northwest Pennsylvania. The forest consisted of sugar maple, striped maple, black cherry, fire cherry, beech, and sweet birch. Tree regeneration failed in 25%-40% of clear cut plots. Species of trees that were browse resistant included beech, black cherry, striped maple, ash, and hackberry. A number of common bird species were absent from Pennsylvania forests with high deer population densities. This list includes wood peewees, cerulean warblers, yellow-billed cuckoos, and indigo buntings.

Ironically, heavy deer populations can accelerate forest successional patterns. By feeding upon pioneer species of plants, deer reduce competition for space with species that normally don’t dominate until later stages of forest succession.

References:

Thrift, J.

“Effects of White-Tailed Deer Herbivory on Forest Plant Communities”

Clemson University Thesis 2007

Wiegmann, S.; and D. Waller

“Fifty Years of Change in Northern Upland Forest Understory. Identity and Traits of “Winner” and “Loser Plant Species”

Biological Conservation 129 2006

Chinese Privet (Ligustrum sinense) is Beneficial for Birds

During the 1927 college football season the Georgia Bulldogs won 9 consecutive games before playing their hated rival, the Georgia Tech Yellow Jackets. The Bulldogs always played the Yellow Jackets in Atlanta during this era because their own home games were played at rocky Herty Field–a poor quality gridiron. The Bulldogs were a fast team that year, so some Yellow Jacket officials watered down the field before the game, turning it into a muddy quagmire that negated Georgia’s speed advantage, and the Yellow Jackets upset the Bulldogs 12-0, ruining their unbeaten season. Georgia officials were furious and vowed to build their own stadium where they could play Tech at home every other year. Sanford Stadium was completed in 1929. Hedges of Chinese privet were planted near the sidelines, and Georgia home games are referred to as being played “between the hedges.” I’m a big Georgia Bulldog fan, and I was excited to discover 1 specimen of Chinese privet that recently popped up on its own near my back door.

Gardeners planted Chinese privet in Sanford Stadium during 1929. Traditionally, college football games played in Athens, Georgia are said to be played “between the hedges.” Photo from Gun and Garden Magazine.

I’m a big Georgia Bulldog fan, so I was excited to discover this Chinese privet that popped up near my back door.

Cardinal eating a privet berry. At least 16 species of birds use privet thickets for food and/or cover. Photo ripped off from google images.

Chinese privet, as the name would suggest, is native to China, and it was introduced to North America during 1852 as an ornamental plant. Privet is a tough species and thrives in both wet and dry locations on just about any kind of soil. In the wild privet grows on disturbed sites and originally depended upon elephant foraging, human activity, fires, or wind storms to open up the forest canopy, so it could take over a location. Privet can survive fire and will come back from the roots. In addition to spreading through sucker roots, privet is spread by birds eating its fruit and defecating the still viable seeds throughout the environment. It grows fast. The 1996 Olympic soccer matches were played at Sanford Stadium, and the privet hedges were temporarily removed and transplanted. Upon their return to Sanford Stadium they grew enough in 1 week that one couldn’t tell they’d ever been moved.

Chinese privet flowers are very fragrant. This is what attracted my attention to the bush, but I did not recognize it. I posted a photo on a Facebook page known as Weakley’s Flora of Southeastern North America. I learned plant conservationists revile Chinese privet because it crowds out native plants. The man who identified it for me told me to destroy it. I told him I liked it and was not destroying it. Numerous other shmucks called me a troll, and one suggested I was a fake account who signed up for this group just to troll about Chinese privet. (Facebook suggested the group based on my interests. That’s why I joined.) Another person suggested I use an app for plant identification because I must not be interested in ecology and didn’t belong in the group. (I’ve been writing this blog about Pleistocene ecology for over 10 years.) Yet another putz encouraged me to breath the flowers in deeply in the hopes I would suffer an uncomfortable allergic response. The internet makes it easy to expose people for their mean spirited attitudes.

Now, I am trolling them. I found a scientific study that determined Chinese privet benefits birds. Thickets of Chinese privet host the same abundance and species diversity of birds as other more natural areas during spring, summer, and fall; but during winter bird species diversity and abundance is even higher than in the surrounding landscape. Privet berries ripen in late fall/early winter when most native berries are gone. Birds that benefit from food and/or cover provided by privet include cedar waxwings, cardinals, bluebirds, robins, Carolina wrens, chickadees, brown thrashers, flickers, mockingbirds, purple finches, blackbirds, blue jays, crows, doves, sparrows, bobwhite quail, turkey, and feral chickens. Mockingbirds are the most common songbird in my neighborhood, and I suspect this was the species that inadvertently planted the bush in my backyard when it defecated the seed. The berries are toxic to humans. Deer and cotton rats eat privet foliage and also benefit from the presence of the plant. This same study did find privet does crowd out native plants.

Another study determined privet thickets host fewer bees and butterflies than privet-free zones, but this study is misleading and seriously flawed. Privet was mechanically removed from locations in a botanical garden and a nature reserve in Athens, Georgia. Forest service scientists trapped bees and butterflies 5 years after the removal and counted species abundance and diversity. The title of the article is misleading–“Removing Chinese Privet from a Riparian Corridor Benefits Pollinators 5 years later.” From the title one would assume they counted bees and butterflies at the same location before the privet was removed, but this is not what they did. Instead, they compared bee and butterfly composition from this location to different locations within the Oconee National Forest including 2 sites with privet and 2 sites without. This is quite flawed because some sites might be better for pollinators based on factors unrelated to privet. (And see below…an obvious factor.) Moreover, the sites where privet was removed were embedded within a botanical garden and a nature reserve where humans deliberately plant flowers that attract bees and butterflies. Populations of pollinators in these areas are artificially boosted due to anthropogenic activities. They are even higher than in the natural privet-free zones used as control groups in the study. A better study would take inventory of pollinators before and after privet removal in the same location.

Even without human interference nature would eventually control privet populations. During the 1996 transplanting of the Sanford Stadium privet, horticulturalists discovered the privet was slowly dying of a nematode infestation. They treated it, but many wild stands of privet may be dying from nematode infestations. Left alone, after centuries, native plants could retake space where privet previously took over.

References:

Hudson, J.; J. Handa, and S. Kim

“Removing Chinese Privet from Riparian Forest Still Benefits Pollinators 5 Years Later”

Biological Conservation 167 November 2017

Wilcox, J; and C. Beck

“Effects of Ligustrum sinense (Chinese privet) on Abundance and Diversity of Songbirds and Native Plants in a Southeastern Nature Preserve”

Southeastern Naturalist 6 (3) 2007

Tigers (Panthera tigris) Suppress Dhole (Cuon alpinus) Populations.

A new study determined tigers suppress dhole pack sizes in India. Dhole packs are smaller in areas with higher densities of tigers, even if there is an higher density of potential prey species. The scientists conducting the study used camera traps to estimate pack size and tiger numbers. In Tadoba-Andhari Tiger Reserve where tiger density is high, there were 7 dhole packs averaging 6.4 dholes per pack. In Navegaon-Naziri Tiger Reserve where tiger density is lower, there were 5 dhole packs averaging 16.8 dogs per pack. Pack sizes were 2.6 times greater in areas with lower tiger density. Both reserves are in a subtropical dry deciduous forest zone dominated by teak, argun, and giant crepe myrtle trees. The terrain is somewhat hilly. Leopards are another important large predator in the reserves, and the leopard population is also negatively impacted by tigers. Common prey species in the reserves include spotted deer, sambar deer, barking deer, nilgai antelope, wild boar, and gaur–a large species of cattle. Dhole pack sizes do increase in areas with greater prey density, but the abundance of tigers is a greater influence on pack size. Dholes tend to prey on smaller animals in areas with lots of tigers, so they can consume more of the animal before a tiger drives them away from the kill. Tigers depress dhole populations by directly hunting them and by chasing packs away from their kills.

Map of tiger reserves where the below referenced study took place. Map from the below referenced study.

Tigers totally dominate dholes. The authors of the study saw tigers kill dholes on 5 different occasions and drive packs away from their kills 23 times. They saw no instances of dholes killing tigers or driving them away from their kills.

Spotted deer are an important prey item for tigers and dholes.

Nilgai antelope, also known as blue buck are another important prey item for tigers and dholes. Hunters introduced nilgai antelope to Texas about 100 years ago, and now there is a feral population of 37,000 in that state.

India has the highest dhole population in the world. There are small packs in the northern montane forest, and larger packs in the dry deciduous forests of central and south India. Since tigers were eliminated from Laos, dhole populations have increased there. Dholes formerly ranged across most of Asia, and during the Pleistocene they ranged into North America, though fossil evidence there is limited to 1 site in Mexico.

Siberian tigers are known to depress wolf populations, and lions depress hyena and hunting dog populations in Africa. I wonder if big cats suppressed canid populations in Pleistocene North America. Saber-tooths were very powerful fanged cats, and American lions grew larger than any big cat species. Pleistocene jaguars grew as large or larger than modern tigers and are at least as common as dire wolves in the fossil record of Florida. There really is no way to know because abundance in the fossil record doesn’t necessarily reflect actual abundance in life.

Reference:

Bhanda, A.; P. Ghaskodbi, P. Nigram, and B. Habib

“Dhole Pack Size Variation: Assessing the Effect of Prey Availability and Apex Predator”

Ecology and Evolution March 29, 2021

Squirrels and Blue Jays vs Acorn Tannins

For over 10,000 years acorns were the most important source of food for Native Americans wherever oak trees were common.  Acorns are an important source of food for animals too for everything from mice to bison.  However, acorns contain tannins, a substance difficult to digest and even toxic for some animals.  For example horses that eat too many acorns may die. Oak trees rely on animals to spread their seed, but if too much of their seed is consumed, their populations will decline.  The nutritional value in acorns attracts hungry animals, but the tannins act as a semi-deterrent.  Acorns from species in the white oak family evolved a different strategy for coping with acorn predation than species in the red oak family.  White oak acorns contain less tannins and are more palatable, so squirrels and jays prefer these and spread them throughout the landscape, but they germinate as soon as they are buried in the fall.  When a squirrel or jay tries to retrieve them later, it is too late.  White oaks only lose acorns that are consumed immediately.  Acorns from oaks in the red oak family are high in tannins, but the tannins are concentrated in the bottom half of the acorn.  Squirrels gnaw on the top half and abandon the bottom half.  If enough of the bottom half is left, the acorn can still germinate, though red oak acorns don’t need to germinate until spring because squirrels and other animals don’t want to eat the part of the acorn with such an high concentration of tannins. This year the sand laurel oaks (Quercus hemispherica), the most common oak species in my neighborhood, are producing a bumper crop of acorns, and the squirrels are gnawing the tops of them but leaving the bottoms.

Squirrels eat the tops of acorns from oak trees in the red oak family.  These acorns, found in my backyard, are from a sand laurel oak. also known as Darlington oak.  The top part of acorns have less tannins which are hard for most animals to digest.  Nevertheless, squirrels risk death from the 8 cats that live in my backyard to exploit this food source.  Oaks can germinate from acorns with the tops gnawed off.

Squirrels fed a diet of just red oak acorns in an experiment ate less.  Blue jays fed a diet of red oak acorns in an experiment actually lost weight.  Squirrels living in a location with mostly red oaks must vary their diet with other foods such as white oak acorns, nuts, fungi, berries, and insects.  Blue jays fed a diet of red oak acorns and acorn weevil larva maintained their weight, showing how blue jays can survive in the wild on a diet of mostly red oak acorns because the infestation rates of acorns by weevil larva are high.  Incidentally, oak trees were able to quickly colonize New England and southern Canada following deglaciation at the end of the Ice Age because of the acorns that were spread by blue jays.

Tannins posed an obstacle for hungry Native Americans as well.  According to Euell Gibbons, Native Americans processed the acorns by boiling them in water to leech out the tannins.  It’s necessary to periodically change the water–a tedious process.  I tried this years ago with the sand laurel oak acorns in my yard.  After dumping the water out and replacing it 8 times, I got tired of the process and gave up.  The acorns were becoming less bitter, but still not palatable enough to eat in a satisfying quantity.  Native Americans with no modern day supermarkets were most persistent from necessity.

References:

Chang-Macoubrey, A;  A.E. Hagerman, and R. L. Kirkpatrick

“Effects of Tannins on Digestion and Detoxification Activity in Gray Squirrel (Sciurus carolinensis)”

Physiological Zoology 20 (3) 1997

Johnson, W., Libby Thomas, and Curtis Adkinson

“Dietary Circumvention of Acorn Tannins by Blue Jays: Implications for Oak Demography”

Oecologia 99 (2) 1993

 

 

Wilderness Rebounded Following the Black Death

The recent ill-advised lockdown that failed to stop the spread of the coronavirus reduced human activity for several months, and the wildlife noticed.  Deer and coyote, normally more active at night, began roaming big city streets in broad day light.  It doesn’t take long for wilderness to rebound when the presence of humans is diminished or eliminated.  The Chernobyl Exclusion Zone is now 1 of the greatest nature reserves in the world, thanks to radiation fallout which makes the area an unpopular place for people to reside.  Past epidemics have led to the rebound of wilderness.  Europeans introduced many infectious diseases to the Americas, resulting in an 80% reduction in Indian populations.  Many Europeans then mistakenly believed the Americas had always been a sparsely populated segment of the world.  They collectively forgot their own past history with the bubonic plague.

The bubonic plague is believed to have originated in the Gobi Desert, possibly in the gerbil population.  Fleas spread the dangerous bacteria (Yersinia pestis) to the Mongolian raiders descended from Ghengis Khan who then carried it to Europe during hostile invasions and through free trade.  During 1347 a merchant ship with an 100% infection rate arrived in Venice, Italy and soon the plague spread throughout Europe in fleas carried by rats.  People slept on straw mats, crowded together in unsanitary condition, and bubonic plague outbreaks exploded.  In addition to being flea-borne the bacteria could be transmitted through the air between people in close contact with each other. The plague is an horrible disease, killing people in 3-4 days, and the victims die in agony–their lymph glands literally burst with toxic bacterial waste and white blood cells.  The victims turn back, hence the name “Black Death.”  50% of the population died.  Not enough agricultural workers remained alive to harvest the crops, and combined with bad weather from the onset of The Little Ice Age, famine soon followed the plague.  Wild animals and wilderness soon took over much of rural Europe.

Bubonic plague, originating in Asia, decimated European populations for 2 centuries and wilderness areas rebounded.

Birch and aspen trees quickly sprouted in abandoned fields that were soon replaced by oak forests with trees that eventually grew 150 feet tall.

Huge oak trees like this grew on abandoned agricultural land following the Black Death.

Grass growing in abandoned grain fields fed herds of wild cattle and horses recently freed from their dead human masters, and these escapees interbred with their wild cousins.  Bison expanded their range.  Soon birch and aspen forests sprouted in the fields, and moose invaded the new natural areas to feed on the saplings.  Brown bears enjoyed the fruits of long neglected orchards.  Eventually, oak trees shaded out the birch forests, and they grew to enormous size–the acorns feeding wild boars and roe deer.  Lynx and wolves reclaimed land they’d lost in the previous centuries.

The aurochs, the ancestor of modern cows, along with cattle that went feral roamed the European countryside in the years following the Black Death.  The Black Death likely delayed the extinction of the aurochs by centuries.  They didn’t become extinct until 1527.

Red deer and horse populations increased when human populations decreased.

King Jagiello escaped an outbreak of the plague in 1426 when he retreated to an hunting manor in the Bialowitza woods.  No roads or bridges penetrated this vast wilderness.  Royalty protected this wilderness for centuries, and today it is just a partial remnant of the post Black Death rebound of nature.

Wolf packs took over when humans disappeared from large areas of Europe.

Eastern Range Extensions of Western Fauna on Xeric Limestone Prairies

I wrote an article a few years ago about roadrunners (Geococcyx californiannus). (See: https://markgelbart.wordpress.com/2016/08/05/pleistocene-roadrunners-geococcyx-californianus/ ) I noticed roadrunners ranged into Arkansas–a curious eastern range extension–and I wondered why.  A few weeks ago, a scientist sent me a box of science books, and I found the answer to my question in 1 of them.  Xeric limestone prairies in Arkansas and Missouri provide excellent habitat for 3 species of western fauna including roadrunners, collared lizards (Crotophytus collaris), and Texas brown tarantulas (Aphonopelm hentzi).  Xeric limestone prairies are openings in woodlands that are created naturally but may be maintained with or without human influence.  Dry shallow soils, not more than 3 feet deep, on a bed of limestone or dolomite, favor the growth of grass over trees. Little bluestem grass dominates xeric limestone prairies, but Indian grass, side oats gramma, and big bluestem also grow on them with the summer annual grass, poverty dropseed, on areas with even shallower soils.  Grazing and fire help maintain these openings, but the dry shallow soils high in calcium can remain open without these influences.  Nevertheless, in the absence of fire or grazing woody encroachment can occur.  Juniper, blackjack oak, and black hickory may invade some xeric limestone prairies.

 Xeric Limestone Prairie in West Virginia.

Roadrunners primarily are a western species, but they have an eastern range extension into Arkansas because they like limestone prairies.

Texas brown tarantulas also range into limestone prairies in Arkansas.

Dry limestone prairies provide habitat for an eastern range extension of the collared lizard.

Reptiles like to sun themselves on the limestone rocks scattered throughout these prairies, and this attracts roadrunners that prefer open areas with lots of the insects, reptiles, and rodents they prey upon.  Collared lizards are 1 of the reptiles that like to sun themselves on rocks, and they may become prey for roadrunners,  but they are also predators that hunt insects and other lizards in this habitat..  Collared lizards are cannibalistic.  Texas brown tarantulas, yet another western species extending their range east on limestone prairies, are large spiders reaching 6 inches in length with a 4 inch leg span.  They can weigh as much as a McDonald’s quarter-pounder.  Their venom is not harmful to humans unless the person is allergic.  But their fangs are large and can cause a painful bite that may get infected.

Other species of animals common on xeric limestone prairies in Arkansas include 6-lined race runners, southern coal skinks, fence lizards, slimy salamanders, leopard frogs, box turtles, Bachman’s sparrows, field sparrows, prairie warblers, cerulean warblers, Kentucky warblers, painted buntings, brown thrashers, hawk wasps, and numerous species of grasshoppers.

Xeric limestone prairies are not confined to Arkansas and Missouri but are also found in parts of West Virginia, Alabama, Tennessee, Georgia, Indiana, Illinois, Ohio, and Pennsylvania.  However, limestone prairies in those states don’t host as many species of western fauna as those in Arkansas and Missouri.  The Mississippi River must be too big an hurdle for them.

Reference:

Cartwright, Jennifer and William Wolfe

“Insular Ecosystems of the Southeastern United States: A Regional Synthesis of Support Biodiversity Conservation in a Changing Climate”

U.S. Geological Survey Professional Paper 1828 2016

New Study of the Seda-DNA in Hall’s Cave, Texas

A new study of seda-DNA and bone DNA from Hall’s Cave documents the changes over time in the plant and animal communities on the Edward’s Plateau in Texas.  Previously, scientists had collected and identified thousands of bones in Hall’s Cave from 56 species of mammals, 30 species of birds, 9 species of amphibians, 3 species of reptiles, and 2 species of fish.  The bones date from the Last Glacial Maximum (~20,000 years BP) to the early Holocene (~9,000 years BP).  The new study extracted DNA from the bones but in addition took samples of DNA from the sediment. (Scientists call DNA from sediment samples, “seda-DNA.”)  Sampling DNA from the sediment has the added advantage of detecting the presence of plant remains that were otherwise unidentifiable, and the presence of animals that perchance left no skeletal remains at all in the cave.  For example 2/36 bone samples were from cat but 7/10 sediment samples detected cat.  Jaguars and bobcats urinated, defecated, and shed hair in the cave but left no skeletal remains.  The seda-DNA samples detected 36 of the 56 species of mammals known to have  occurred in the cave from fossil evidence but they found an additional 7 species of mammals as well as additional species of birds not collected as fossils here, including ducks and geese.  They also determined which species of woodrat lived in the cave, an identification not really possible by just looking at the bones.

Deer mouse, cottontail rabbit, and eastern woodrat were the most common species of small mammals found in the cave since the Last Glacial Maximum, and these species occurred throughout all climate phases.  White-tailed deer and bison were the most common large mammals found in the cave and they too were found throughout all climate phases, though they became less abundant over time.  Hackberry and oak were the most common plant species found in the cave, and they were found throughout all climate phases.  Hackberry still grows near the entrance of the cave.  According to local pollen studies, pine was the most common tree growing on the Edward’s Plateau during the Ice Age, but it is absent from the cave.  Pine simply didn’t grow near the cave.

Hall’s Cave.

Location of Edward’s Plateau.

Dendrogram of species found via DNA sampling in Hall’s Cave.  From the below referenced study.

The study sheds light on the changes that occurred on the Edward’s Plateau since the Last Glacial Maximum.  During the height of the last Ice Age weather patterns differed from those of today–more precipitation fell on southwestern North America whereas southeastern North America was more arid.  As a result, the Edward’s Plateau hosted a prairie environment with trees found at scattered locations.  Soils were much thicker because dense grass regularly decayed.  Deeper soils were good environments for prairie dogs, 13-lined ground squirrels, pocket gophers, and marmots.  Common large mammals included camel, pronghorn, and flat-headed peccary that were preyed upon by saber-tooths, dire wolves, and giant short-faced bears.  Birds that preferred treeless plains–prairie chickens, upland sandpipers, horned larks–abounded here then.

The environment changed here about 15,000 years ago during the Boling/Alerod Interstadial when temperatures and precipitation increased.  The prairie converted to open woodland and forest with widely spaced oak, ash, juniper, walnut, mulberry, and hackberry trees.  Plenty of grass still grew between the trees…enough to support a population of horses.  Many of the open plains animals disappeared from the record here including the pronghorn, camel, and flat-headed peccary.  Black-tailed jackrabbits, northern grasshopper mice, and prairie chickens all left the area as well.  However, turkey, bobwhite quail, and barking tree frogs moved onto the Plateau because they liked the newly expanded tree and thicket habitats.

12,900 years ago, during the Younger Dryas cold phase, the climate suddenly became much colder and dryer.  Vegetation decreased and the region became desert-like.  Small and large mammal and plant diversity decreased.  Following the end of this cold phase, temperatures and precipitation increased, though rainfall didn’t increase to the levels of the LGM and Boling/Alerod Interstadial.  Soils of the Edward’s Plateau were still thinner than they were during the LGM and today the region is dominated by a plant community of live oak, juniper, and hackberry.  Plant and small animal diversity rebounded but large mammal diversity did not.  The authors of this paper suggest man is likely responsible.  Plant and small mammal ranges adjusted to climate change, and they disappear and re-appear in the seda-DNA samples over time.  If not for overhunting by man, the same should hold true for large mammals.  14 species of large mammals that lived on the Edward’s Plateau during the late Pleistocene are either extinct or extirpated from the region.

Plant and animal composition does not stay constant, and the study found some non-analogue components living side by side.  Today, white-tailed jack rabbits and barking tree frogs have ranges that do not come close to overlapping, but both species lived on the Edward’s Plateau during the Boling/Alerod Interstadial.    Bog lemmings and least weasels ranged much farther south then and co-occurred with species of more southerly affinities.  Animal and plant communities are dynamic and always changing.

Range of barking tree frog.

Range of white-tailed jack rabbit.  White tailed jack rabbits and barking tree frogs both lived on the Edward’s Plateau during a warm interstadial of the last Ice Age, indicating the existence of non-analogue environments dissimilar to any that occur today.

Reference:

Seersholm, F.; et al

“Rapid Range Shifts and Megafaunal Extinctions Associated with Late Pleistocene Climate Changes”

Nature Communications 2020

https://www.nature.com/articles/s41467-020-16502-3#:~:text=Large%2Dscale%20changes%20in%20global,impacted%20ecosystems%20across%20North%20America.&text=Instead%2C%20five%20extant%20and%20nine,the%20end%20of%20the%20Pleistocene.

Squirrel Monkeys (Saimiri oerstedii) and their Co-Horts

Several species of birds follow foraging squirrel monkeys through the jungle tree tops of Central and South America.  Troops of squirrel monkeys look for insects and fruit to eat, often overturning leaves and thrashing branches.  Their actions dislodge hiding insects and lizards, and this exposes them to predators.  Double-toothed kites (Harpagus bidentatus) perch on nearby branches, looking for insects or lizards forced to leave their hidden refuges.  Normally, their prey blends in with their surroundings, but the kites are attracted to the exposed prey forced to move.  Gray-headed tanagers (Eucometis pencillata) and tawny-winged woodcreepers (Dendrocineeb anabatina) also find insects this way.  These birds also follow white-throated capuchin monkeys, and they are among the many species that follow army ants. This behavior has occurred for tens of millions of years, ever since monkeys accidentally rafted over from Africa.

Squirrel Monkey

Gray-Headed Tanager

Tawny winged woodcreeper

Double-toothed kite

Army ant columns attract even more birds than troops of monkeys do.   Fleeing insects and small vertebrates become prey to a family of 18 species of antbirds known as the Thamnophilidae, as well as cuckoos, thrushes, and chats.  The bird-ant relationship is parasitic.  Studies determined army ants obtain 30% less food when they are followed by antbirds.  It’s not always a beneficial relationship for the birds either.  4 ant stings is all it takes to kill the small birds.

Reference:

Boinski, S.; Peter Scott

“Association of Birds with Monkeys in Costa Rica”

Biotropics 20 (2) 1988

The Co-Existence of Feral Hogs and Peccaries in the Americas

An old episode of Anthony Bourdain’s No Reservations sparked my interest in Brazil’s Pantanal region.  Bourdain searched eastern Brazil in vain for a rare species of fish he wanted to eat.  He was told it was still abundant in a remote part of western Brazil, so he purchased a charter flight to take him there and satisfy his culinary curiosity. The pilot flew the small aircraft through storms, and Bourdain and his crew weren’t sure they were going to make it.  Then, after arrival, Bourdain suffered the worst back pain he’d ever felt, and his producer fell ill with a tropical fever.  Nevertheless, they continued filming and I was impressed with the quantity and quality of wildlife.  It reminded me of 18th century descriptions of Kentucky and early 19th century accounts of Oklahoma.  On a boardwalk through a jungle Bourdain saw a red monkey that no one could identify.  Though there are riverine forests, most of the Pantanal consists of vast treeless plains, variously flooded here and there.  The indigenous people who sparsely populate the Pantanal use it as pastureland, and large herds of feral hogs and peccaries intermingle with cattle.  Caimans and capybaras abound in the flooded parts, and huge flocks of wading birds crowd the water holes.  Incidentally, Bourdain did get to sample the fish.

Map of Brazil’s pantanal.

The Brazilian Panatanal is 1 of the richest wildernesses left on earth.  It encompasses 75,000 square miles and includes at least 12 different types of ecosystems.  463 species of birds, 209 species of fish, and 236 species of mammals live in the region.  It has the healthiest population of jaguars in the world.  Peccaries and wild pigs are the most common ungulates.

Feral hog and vultures feeding upon a dead cow in Brazil’s pantanal region.

Collared peccary.

White lipped peccaries.

Peccaries and pigs are superficially similar in appearance, but they are separated by over 25 million years of evolution.  There are 2 species of peccaries native to the Pantanal–the aggressive white-lipped (Tayassu pecari) and the collared (Pecari tajacu).  Feral hogs (Sus scrofa) are not native to the Pantanal and were introduced hundreds of years ago.  Scientists who study the interrelationships between peccaries and pigs expect the latter to be detrimental to the former, but their studies find this is not true.  A recent study examined the consumption of 37 plant foods among the 3 species, and they found minimal dietary overlap.  Feral hogs favored grugru palm nuts (Acrocomia aculeata), collared peccaries preferred bay cedar (Guazuma sp.), and white-lipped peccaries liked the fruit of a plant in the coffee family (Alibertia sessilis).  All 3 species did feed upon the fruit of Astralea phaleratata, a type of palm.  Palm nuts taste coconut-like.  There was more overlap in diet between white-lipped peccaries and wild hogs than between collared peccaries and wild hogs.  Collared peccaries foraged at times when they could avoid pigs and white-lipped peccaries.

Chart showing diet overlap between the 3 species.  From the below referenced paper.

Palm nuts from the grugru palm are the favorite food of feral hogs in the Pantanal.

Alibertia sessilis fruit ( relative of coffee)  is the favorite food of the white-lipped peccary in this region.

The study determined bay cedar was the favorite food of the collared peccary.

During the Pleistocene new species of mammals periodically crossed the Bering Land Bridge and invaded the Americas, and vice versa.  Like pigs and peccaries, many of the co-existed.  Deer, bear, and big cats came from Eurasia.  Horses and camels went from the Americas to Eurasia.  Co-existence was not always permanent.  Felids from Eurasia outcompeted many species of canids, a group of carnivores originating in North America.  Deer from Eurasia outlasted 3-toed American horses.  The composition of mammals on both continents changed over time, and co-existence between species can be temporary or long lasting.

Reference:

Galetti, M. ; et al

“Diet Overlap and Foraging Activity Between Feral Pigs and Native Peccaries in the Pantanal”

PLOS ONE 2015

 

Hippos in Colombia

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.

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.)

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.

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