Archive for the ‘Ecology’ Category

Megafauna Survival in Southeast Asian Landscapes Varies

February 2, 2023

The presence of humans is detrimental to megafauna survival, and humans are responsible for the extinctions and extirpations of many species across the globe. Furthermore, in regions where megafauna still survives, humans depress their overall populations with hunting and habitat degradation. A new study of megafauna in Southeast Asia analyzes the differences in species survival rates in the presence of human impact. An impressive assemblage of megafauna still survives in the region despite a continuous and growing human presence. Humans have lived in the region for 60,000 years. The region enjoys a rich tropical climate with an abundance of food sources and variety of habitats that support megafauna populations. The authors of the study set up camera traps at many sites in Thailand, Malasia, Singapore, and parts of Indonesia. They recorded the abundance of 14 species including tiger, leopard, clouded leopard, dhole, sun bear, sambar deer, Malay tapir, Sumatran rhinoceros, Asian elephant, wild boar, bearded pig, mainland serow (a species of tropical goat), and banteng and guar–2 species of wild cattle. Wild boar was the most common species and was found at 65% of the sites. Sumatran rhinos were the least common species and were not found at all. The study considers Sumatran rhinos to be functionally extinct. Banteng and guar were among the less common species as well. People like to eat their beef. No 2 sites had identical species assemblages demonstrating the varied response of megafauna to human presence.

Megafauna populations decline or are extirpated in regions where they suffer from human hunting and habitat degradation. Some megafauna species in southeast Asia follow this trend, but others defy it. The reasons for this disparity are complex and poorly understood. Chart from the below reference.
Chart showing body size and whether a species was herbivore or carnivore didn’t matter in the frequency of extirpations at different sites in Southeast Asia. Charts also from the below study.

The authors of the study note 74 extirpations of megafauna that formerly ranged throughout the region. 58 extirpations occurred during the Holocene from 11,700 years ago to 1950. 16 extirpations have occurred in the region during the Anthropocene (since 1950). (Scientists don’t agree among themselves about when the Anthropocene began. The Anthropocene is regarded as the time when humans became the dominant force in earth’s environment. Some scientists think it should be considered as beginning in 1611, while others believe 1950 should be the starting date. Still others think the Anthropocene began 50,000 years ago. This study goes by the 1950 date.) They found no pattern for megafauna survival or failure to survive. Size didn’t matter nor did whether or not they were a carnivore or herbivore. Some species actually favored areas where habitat was degraded. Wild boars thrive near human habitations. They benefit from foraging on farmer’s crops, and the local Muslims won’t hunt them because they don’t eat pork. Asian elephants, tigers, and clouded leopards were also common in degraded habitats. However, the most disturbed sites had 2.5 times more extirpations than the least disturbed sites. There is some good news: as long as anti-poaching regulations are enforced, megafauna can survive near human settlements. Unfortunately, large, protected parks in remote areas are hard to patrol, and megafauna can become extirpated in areas that otherwise offer excellent habitat.

Reference:

Amir, Z.; J. Moore, P. Negret, and M. Irvin

“Megafauna Extinctions Produce Idiosyncratic Anthropocene Assemblage”

Science Advances 8 (42) Oct 2022

https://www.science.org/doi/10.1126/sciadv.abq2307

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Pockets of Prairies in Eastern North America

December 15, 2022

The notion a squirrel could have traveled through treetops from the Atlantic Coast to the Mississippi River when Europeans first discovered North America is a myth. Extensive grasslands existed throughout eastern North America then. Many factors contributed to their origin. Indians annually set fire to the woods to improve habitat for the deer, bear, and turkeys they ate. Normally, this created an open woodland environment because many species of trees can survive light grass fires. But in some areas, fires can consume much of the tree cover, creating open grassland. Indians also removed trees when they planted corn fields. Abandoned corn fields became prairie-like for at least 10 years before reverting to forest. Natural lightning ignited fires, tornados, and hurricanes also destroyed forests, creating pockets of prairie within eastern forests. In some locations soil conditions that favor grass over trees resulted in grasslands predominating instead of trees.

Hempstead Prairie on Long Island, New York is an example of a prairie pocket within the eastern forest. It originally was 50 square miles in extent and hosted grassland species of birds such as upland sandpiper, prairie chickens, and eastern meadowlark. This was tall grass prairie with 5-foot-tall grasses and a great variety of flowering plants. It was still mostly intact until about 1969, but suburban development during the 1970s destroyed most of it. Today, just 19 protected acres remain. Homeowners are encouraged to plant native species of plants in their yards, but it will never be the same.

Hempstead Prairie on Long Island, New York. Until suburban development during the 1970s, this prairie was 50 square miles. Now, 19 protected acres are all that is left. Photo from the below linked article.

Every region in mostly forested eastern North America had pockets of prairies within the wooded landscape. Below is a map made by surveyors of an area in Arkansas during the early 1800s. Most of the landscape at this time consisted of oak and pine forest and bottomland swampy forests, but there were 5 major prairies and 9 smaller ones in this area. The larger prairies were even given names. Most of eastern North America was forest like this pock-marked with prairies.

Map of prairie pockets within a forested region in pre-settlement Arkansas. Map from the below referenced Midland Naturalist article.

2 species of birds require extensive stretches of grasslands with no trees–upland sandpipers (Bartamia longicauda) and prairie chickens (Tympanuchus cupido). These birds were formerly abundant in eastern North America. Now, upland sandpipers are rare in the east and prairie chickens have been extirpated in the region. I hypothesize some populations of eastern prairie chickens, most notably the heath hen, were unique species. Because these species are so habitat-specific, they can be used as index species in the subfossil record for the presence of grasslands. The remains of both species, dating to the late Pleistocene, have been found in Kingston Saltpeter Cave and Yarbrough Cave in Georgia, and Bell Cave in Alabama. Most of the bird species remains found at these fossil sites are woodland, wetland, or generalist species, but the presence of upland sandpiper and prairie chicken remains is evidence there were pockets of prairies in north Georgia and north Alabama about 13,000 years ago.

Remains of upland sandpipers found at fossil sites can be used as index fossils denoting the nearby presence of prairies during the time of deposition.
Prairie chicken fossil or sub-fossil remains can also be used as index fossils that suggest the presence of nearby prairies during the time of deposition.

References:

Bragg, Don. C.

“Natural Pre-settlement Features of the Ashley County, Arkansas Area”

American Midland Naturalist 2003

Marinelli, Janet

“Amid the Sprawl, A Long Island Prairie Makes a Quiet Comeback”

Yale Environmental 360 December 2022

https://e360.yale.edu/features/hempstead-plains-long-island-wildlife-conservation-gardens?fbclid=IwAR1bV3MQJg6SS0O5wGnE6i432bHuXllCAEiKY8ohHvgb1IUwaTUG-SmjCmQ

The Wilds, a Reclaimed Strip Mine in Southeastern Ohio

November 3, 2022

Big Muskie was the largest excavator ever manufactured. This monstrous machine was 6 stories high and as wide as an 8-lane highway. A single scoop from Big Muskie’s bucket contained 325 tons of rock and dirt, and it could remove 19,000 tons of overfill in an hour. Big Muskie operated from 1969-1991 when the Central Ohio Coal Company, a subsidiary of American Electric Power (a utility corporation), used it to strip-mine at the Muskingham Coal Mine. Eventually, changing economic conditions combined with stricter environmental regulations ended operations at the mine. A 1947 Ohio state law required American Electric Power to restore the land they had destroyed with their strip-mining. Some forest and prairie had never been touched by the mining operation, but many trees and other plants had to be planted. Now, the land has been reclaimed and is known as The Wilds. Since 1984, the land has been used as an area to breed rare and endangered animals in conjunction with the Columbus Zoo.

Location of the Wilds. All the images in this blog entry are from the linked reference below.
Big Muskie, the largest excavator ever manufactured. It operated from 1969-1991 and could remove 19,000 tons of dirt in an hour.
Another view of Big Muskie. It was 6 stories high. A crew of 7 operated it.
Before and after view of the Muskingham Coal Mine, now known as The Wilds. A 1947 Ohio state law required companies that strip mined to restore the land. In conjunction with the Columbus Zoo rare and endangered species are bred here, and native and non-native plants have been planted. It’s also a haven for native wildlife.

The Wilds currently includes 4600 acres of pasture and grasslands with 700 acres of native prairie, 4000 acres of forest, and 1400 acres of ponds, streams, and marshes. The forests consist of oak, maple, ash, beech, and tulip. Native wildlife thrives here, notably deer, bobcat, beaver, and eastern meadowlark. Endangered animals bred in captivity on The Wilds includes 2 species or oryx, Bactrian camels, Bactrian deer, King Pere’s deer, banteng (a species of wild cattle), Persian onager (a species of wild donkey), Pryzelwalski’s horse, zebra, giraffe, white rhino, Asian rhino, Chinese wild goat, African wild dogs, dhole, cheetah, red-crowned crane, trumpeter swan, ostrich, and eastern hellbender. The scimitar-horned oryx was actually extinct at its original range in North Africa, but individuals raised here were used to re-establish a population on their original range. Tourists can take safari tours of The Wilds. If I lived closer, I would definitely visit.

Reference:

https://thewilds.columbuszoo.org/home/discover/training-center/restoration-ecology

Open Woodlands at Chickamauga Battlefield Park

October 20, 2022

I visited Chickamauga National Battlefield Park last week for the first time in many years. We were in northwest Georgia to see my mother-in-law for a couple of days. She lives in the Chickamauga Valley, and I’m familiar with the natural history of the region. Next week, I’m going to cover the history of the battle itself along with the horrors of war (for my annual Halloween blog post), but this week I want to focus on the natural history of the park. The landscape consists of large, mowed fields bordered by open woodlands.

Turkey and deer thrive in this type of environment.
An open woodland is defined as an environment with 50%-75% canopy cover. A forest is defined as an environment with >75% canopy cover. I estimate this is woodland, not forest.
Some of the trees here grow quite large.
Men were shooting, stabbing, and clubbing each other to death at this site 158 years ago.

An open woodland is defined as an area with 50%-75% tree canopy cover, while a forest is considered an area with >75% tree canopy cover. A woodland has widely spaced trees that allow enough light for grass, and shade intolerant shrubs and saplings to grow. Species of trees I found growing at Chickamauga Battlefield Park included white oak, black oak, northern red oak, scarlet oak, willow oak, black walnut, hickory, southern sugar maple, box elder, tulip, ash, Kentucky coffee tree, cedar, shortleaf pine, and loblolly pine. Botanists believe chestnut was formerly a co-dominant tree here on soils underlain by dolomite, but chestnut blight wiped them out a century ago. Many of the trees in the park now are over 100 years old. Shallow well-drained acidic soils predominate, and they are underlain by dolomite, limestone, shale, and sandstone.

Cedar trees are not fire tolerant. Open woodlands at this site are maintained by mowing and a high population of foraging deer, not fire.
This is either field thistle (Cirsium discolor) a native of North America or bull thistle (C. vulgaris), a native of Europe that has colonized North America. Enough sun reaches the woodland floor that shade-intolerant species can grow. Thistles attract many species of bees and butterflies and seed-eating birds.

Open woodland has probably been the most common environment on this site for millions of years. During the Pleistocene, megafauna foraging, ice storms, and windy conditions likely prevented the tree canopy from getting thick. More recently, Indians set fire to the woods frequently, thus keeping tree canopy open with thermal pruning. Now, I hypothesize a high density of white-tailed deer is keeping this woodland open. There is no hunting inside the park, though it occurs in adjacent areas. I suspect herds of deer find refuge here, and they thin out saplings with their hungry appetites. This habitat is ideal for deer and turkey, and I saw both while driving through the park. Road-killed coyotes are a common site on nearby roads. Fox, skunk, raccoon, possum, squirrel, woodchuck, and rabbit can be found in the park too.

See also: https://markgelbart.wordpress.com/2021/05/20/deer-herbivory-alters-plant-and-bird-species-composition/

Reference:

Wharton, Charles

The Natural Environments of Georgia

Georgia Department of Natural Resources 1978

Railroad Ecology

September 15, 2022

George Stephenson invented the first workable steam engine locomotive in 1814, and he designed the first working rail system in 1820. The British government approved the construction of this first track used for hauling coal. The first rails were made of wood, but they wouldn’t hold locomotives filled with heavy loads of coal. The type of iron available then was also not strong enough to hold all that weight, so Stephenson invented an improved type of iron that could. Americans bought this technology and constructed our first working railway track in 1828. It was the Baltimore-Ohio Railroad and was 8 miles long. Tavern keepers opposed the construction of railways because they feared losing business when railway tracks were constructed far from their establishments, and religious nuts who thought railroads were sinful also fought against their construction, but the free market eventually won. Today, there are over 800,000 miles of railway tracks around the world.

George Stephenson invented the first workable locomotive steam engine in 1814. He also invented the iron used on railway tracks.

The many miles of railway tracks across the world have a big impact on the environment. They increase mortality of large animals, and they serve as migratory barriers for smaller animals, especially amphibians. Herbicides used to suppress vegetation influence the types of species that can live near railway embankments. Grassland corridors on railway embankments cut through forest facilitate the spread of invasive plant species. The impact is so extensive that railroad ecology has become a subset within the science of ecology. Railroad ecology has been more studied in Europe than the United States, but more and more scientists here are starting to pay attention to it.

A study in southern Poland looked at the influence of railway embankments on bird populations. This study counted 1644 individuals of 67 species. They found railway embankments hosted a greater diversity of species, but total number of birds was about the same as found in agricultural fields. They counted 923 individuals of 58 species found on railway embankments. The 3 most abundant in order were starlings, skylarks, and white-throated sparrows. 17 species were only found on railroad embankments, while 9 species were only found in agricultural fields. Railway transects had higher diversity, but birds were most abundant where railway embankments passed over wetlands, wet meadows, slopes, and bushy areas.

A scientific study found skylarks were the 2nd most common species of bird found on railroad embankments in southern Poland.

A study in Alberta Canada looked at wildlife mortality caused by train collisions with large mammals. This study determined 646 large mammals were killed by trains along 1 major track between 1995-2018. Species killed by trains here included grizzly and black bears, white tail and mule deer, bighorn sheep, moose, wolf, coyote, and Canadian lynx. 50 bears, 27 large carnivores, and 560 ungulates were killed. Areas with increased train speed and near water resulted in greater casualties. Trains coming around bends also caught large mammals by surprise.

This moose was rescued, but many large mammals are killed by trains every year.

References:

Cassady, Colleen, V. Whittingham, A. Forshner, A. Gangadhare, and D. Lietze

“Railway Mortality for several Mammal Species Increases with Train Speed, Proximity to Water, and Truck Curvature”

Scientific Reports 20776 2020

Kajzer-Bonk, J. et. al.

“The Effect of Railways on Bird Diversity in Farmland”

Environmental Science and Pollution Research 26 2019

2 Uninhabited Forests in Mozambique

September 1, 2022

Scientists used google earth to find 2 uninhabited forests in Mozambique. Outside of isolated mountain forests like these, Mozambique has 0% virgin forest left. The first is Mount Lico, a granite mountain surrounded by agricultural lowlands. Mt. Lico is classified as an inselberg or isolated mountain. It is made of erosion-resistant granite. Formerly, it was about the same elevation as the surrounding land, but over time precipitation caused the surrounding land to erode away, leaving this isolated mountain. The forest growing on top of this mountain has been isolated for millions of years. Scientists first explored Mt. Lico in 2018, and every expedition finds species new to science. Though pottery has been found on Mt. Lico, the locals say no one in recent history has scaled the cliffs to get there. Scientists have already named 9 new species found here including mistletoe, 2 snakes, 2 pygmy chameleons, a bat, and 3 kinds of butterflies. Potentially, there will be more new species named because they found numerous amphibians, a catfish, more butterflies, crabs, and small mammals not known to science. There are hundreds of unknown species of fungi here as well. Mt. Lico is an important refuge for species of birds that prefer closed canopy forests, now rare elsewhere in the region. Of the 126 species of birds found here, 9 are considered endangered. Mt. Lico is now protected.

Mt. Lico in Mozambique. The sheer walls protect it from human settlement.
Scientists had to scale a cliff to explore Mt. Lico.
Mt. Lico is an inselberg–a granite mountain that resists erosion. The land surrounding it was formerly the same height, but rain has eroded it away.
Amphibians abound on Mt. Lico.
Pygmy chameleons and hundreds of other animal and plant species new to science live on Mt. Lico.
Mt. Lico from inside the forest.
Mt. Mabu is uninhabited because the natives think the spirits of the dead reside here.
This is 1 of 7 rare species of birds that live on these isolated tropical mountains in Mozambique.

Mt. Mabu is uninhabited for a different reason. The local natives believe spirits of the dead reside here, and they avoid it for superstitious reasons, though limited hunting and gathering takes place here. Researchers say it is eerily quiet, and animal tracks are everywhere. Caterpillars are so abundant that caterpillar scat falls like rain from the treetops. Mt. Mabu is 5600 feet above sea level and 27 square miles in extent. Uninhabited forests like these are getting harder and harder to find as the human population on earth heads towards 10 billion.

References:

Silva, Bettencourt, G., J. Bayless, and W. Conradson

“First Herpetological Survey of Mount Lico and Mount Socone, Mozambique”

Amphibian and Reptile Conservation 14 (2) 2020

Spotteswood, G., and J. Bayless

“Threatened Bird Species on 2 Little Known Mountains (Cheperone and Mabu) in Northern Mozambique

Ostrich–The Journal of African Ornithology 74 (1) 2008

Everglades Hammocks and Snails

June 8, 2022

During Pleistocene climate phases of high sea levels, the Everglades region of south Florida was flat sea bottom dotted with limestone outcrops and coral, and Lake Okeechobee was a saltwater bay. Today, the Everglades is a sea of sawgrass (Cladium jamaicense) dotted with hardwood hammocks that grow on top of the formerly inundated limestone outcrops and coral. Fresh water from Lake Okeechobee, funneled by a coastal ridge, flows south through the Everglades landscape. Sawgrass (technically a sedge not a grass) is a fire-adapted species, and during dry spells it burns, but hardwood hammocks are usually protected from the fires. Trees growing on the limestone-enriched elevated soils drop leaves, and the acidity from the decomposing leaf litter dissolves the limestone surrounding the hammock, creating moats filled with water that serve as fire breaks. Most hardwood hammocks also have an eroded solution hole in their middle, and they are elliptically shaped with 1 end pointed in the direction of the southward water flow.

Typical Everglades landscape–sawgrass wet prairie dotted with hardwood hammocks.

The composition of trees on Everglades hardwood hammocks includes a mix of tropical and temperate species. Tropical species are more common on southern Everglades hammocks, while temperate species predominate on the northern Everglades hammocks. The list of tree species found on these hammocks includes gumbo-limbo, mahogany, cocoplum, wax myrtle, live oak, red maple, hackberry, mulberry, Everglades palm, royal palm, and strangler fig.

Gumbo limbo tree. This is a tropical species common in hardwood hammocks of the southern Everglades. Everglades hardwood hammocks contain a mix of temperate and tropical species of plants.
Royal palms cannot survive frequent frost. Therefore, they are more common in the southern Everglades.

A diverse snail fauna thrives on Everglades hammocks because the limestone outcrops provide a rich source of calcium. Snails need calcium to develop their shells. The relatively frost-free climate also helps them breed year-round. Each hammock hosts a variation of tree snail (Liguus fasciatus) with a different color pattern. Over 58 variations are known. Tree snails feed upon fungus, lichen, and algae. 4 species of large apple snails live on these hammocks. 3 non-native apple snail species from South America are outcompeting the native species (Pomacea paludosa). Apple snails graze on green plant material and are a pest on south Florida vegetable farms. However, the rapidly expanding population of non-native apple snails benefit snail-eating bird species such as limpkins and the Everglades snail kite. The latter species is endangered, but the increase in snail populations has led to a rebound in Everglades kite numbers.

Native Florida apple snail. 3 species of non-native apple snails also thrive on Everglades hammocks.
Over 58 color variations of tree snails have been found on Everglades hammocks. Each hammock hosts a snail with a different color variation.
Limpkins primarily eat snails.
Endangered snail kites are increasing in population, thanks to rapidly spreading populations of non-native apple snails.

I’ve seen apple snails for sale in Asian food markets. I was not impressed with my lone snail-eating experience after I bought a can of imported escargot. They were relatively inexpensive, but they had no flavor at all. Escargots are traditionally served with butter and garlic sauce. I think eating snails is an excuse to dunk French bread in the butter and garlic sauce.

Survival of the Fittest During the Anthropocene

December 9, 2021

Humans are a part of the natural world, and human activities have an enormous impact on worldwide ecosystems. The impact is so great, some scientists think the current geological era we live in now should be known as the Anthropocene. The animals and plants that are best able to adapt to Anthropocene living conditions have the best chance of surviving into the future. I call it survival of the fittest during the Anthropocene. When I used this phrase on twitter in defense of cats, whiny woke wimps showered their fury at me. One anonymous jerk called me a ninny, short for pickaninny, a derogatory term for a black child. Darren Naish, a world-renowned vertebrate zoologist, clicked on the like button for this racist tweet, then blocked me because I don’t agree that cats are detrimental to the environment. I don’t think Naish is a racist–he probably didn’t know ninny was a racist term. He may be an expert on vertebrate zoology, but his knowledge of other topics is apparently limited.

Darren Naish liked a post from someone who referred to me using a racist term, then he blocked me because I don’t agree that feral cats are detrimental to the ecosystem.
A man on twitter called me a ninny, short for pickaninny, a derogatory racist term. Darren Naish clicked on the like button.

I like animals capable of thriving during the Anthropocene. Cats are 1 of the best examples of an organism well adapted to living alongside humans. They can survive with or without people, existing in conditions ranging from being pampered to total neglect. Cats are a commensal species with humans and will occur wherever humans live, whether woke ecologists like it or not. Some scientists unfairly demonize cats. Most of the studies purporting to show how cats are detrimental to ecosystems are so bad I can’t understand how they get published in peer-reviewed scientific journals. Perhaps, the most famous paper (widely regurgitated without question in the media) claimed cats killed an estimated 94 million birds per year in the U.S. The author of that paper simply made-up numbers using wild guessing. Cats do kill birds on occasion, but they are taking the place of natural predators that would live in the area, if it had remained wilderness. Some species of songbirds have artificially inflated populations in suburban locations because humans create favorable nesting structures, maintain bird feeders, and suppress natural predator populations. A cat killing a songbird in the suburbs is actually restoring a balance. Moreover, cats control rodents and rabbits, species that spread disease and actually compete with humans for food.

My outdoor cats. They control rodent populations and provide companionship.

Ross Barnett is another scientist always whining about cats on twitter. The sadistic hypocrite favors bringing the lynx back to Great Britain where they have been extirpated, but he participated in a cat eradication program in Australia. Cat eradication programs in that part of the world have been disastrous. Rat and rabbit populations exploded wherever cats were eliminated. Rats ate all the birds the eradication programs were supposed to protect, and rabbits denuded the landscape. How can Barnett lament the loss of the lynx, but favor the destruction of an animal so similar? His reasoning makes no sense.

I don’t like the term, invasive species. Every successful organism has been invasive at some point in its evolutionary history. They originated at 1 location and invaded surrounding territory. I prefer to call them newly colonizing species, and I think they increase diversity. House sparrows are 1 of my favorite newly colonizing species, and they are well adapted to surviving the Anthropocene. They are commonly found in grocery store parking lots, and some even live inside the stores. Few other birds (with the exceptions of pigeons and ring-billed gulls) can be found thriving in parking lots.

House sparrows are one of my favorite newly colonizing species. They are common in grocery store parking lots, and some times even live inside the stores.

Bradford pears are another 1 of my favorite newly colonizing species. Many ecologists revile this species because of the way they take over abandoned fields at the expense of native species. I think they contribute greatly to the beauty of the landscape. They provide white flowers in spring, attractive foliage in fall, and food and nesting for birds.

Flowering Bradford pear tree in an old field. I love this species. Woke horticulturalists suggest replacing them with native serviceberry. What a stupid suggestion. Serviceberry won’t successfully grow in most locations, like Bradford pear trees can.

Instead of lamenting all of the organisms incapable of surviving during the Anthropocene, people should appreciate the tough species that can survive in a world dominated by humans.

Wet Climate Phases during the Pleistocene Probably Supported Higher Megafauna Populations in Southeastern North America

October 8, 2021

I love the fungus that grows on manure. I know that sounds weird, but the dung fungus spore concentration in sediment samples is the best evidence paleo-ecologists have of determining past megafauna populations. It is the perfect proxy because if dung fungus spores are high in a sample, megafauna populations must have been high during that time period. There is no hiding all the defecation that was occurring then. Low dung fungus spore concentrations are evidence of low megafauna populations. The latest dung fungus spore study was from a core of sediment taken beneath Lake Peten-Itza in Guatemala. The core was over 120 feet long and included radio-carbon dated time periods from 42,000 years BP-4,000 years BP. The dung fungus concentrations were compared with the pollen composition within each time period to determine what types of environments existed when megafauna populations were high or low. The types of environments fluctuated with known climate phases, alternating between oak and myrtle-dominated woodlands, pine-dominated woodlands, dry acacia-grassland scrub, and seasonal rain forest (the predominating present day environment). Oak-dominated woodlands prevailed during wet interstadials; acacia scrub grasslands prevailed during dry stadials. Megafauna populations were highest in this region during phases of climate that favored oak-dominated woodlands. I also noticed on the chart below that grass pollen was higher during this phase as well, suggesting wildlife had abundant grass and acorns to eat. Nearby fossil sites show horse, llama, mammoth, gompothere, and glyptodont occurred in this region during these time periods. Megafauna populations were lowest during dry stadials.

Location of the study site. Image from the below referenced study. Scientists took the core from 1 of the deepest parts of the lake that never dried out during dry climate phases.
Chart showing abundance of dung fungus (sporomiella) with pollen composition from a >120 foot core taken from sediment beneath Lake Peten-Itza. Megafauna populations were most abundant during wetter climate phases. Chart from the below reference.
Lake Peten-Itza today. It is surrounded by a seasonal rain forest, but during different climatic phases of the Pleistocene the surrounding environment varied between oak-dominated woodlands, pine-dominated woodlands, poor quality scrub grasslands, and seasonal rain forests. This lake is old and over 500 feet deep in some places.
Lucky Oak Woodland in Indiana. Much of central Georgia probably looked like this during wet interstadials of the Pleistocene.
Oak woodland in Ellijay, Georgia. Over 10,000 years ago this was prime habitat for Jefferson’s ground sloths, long-nosed peccaries, and tapirs. At least deer still occur here.

Other regions of the world weren’t the same. The mammoth steppe, a grassland and forb-dominated environment, located from northern Europe across Asia to Beringia, supported higher megafauna populations during cold stadials than other climate phases that favored forests and woodlands. The arid acacia scrub grasslands that occurred in Central America during stadials may have been nutrient poor and just did not support high populations of megafauna. Much of the region may have been bare soil.

I hypothesize populations of megafauna in the piedmont region of southeastern North America were also higher during interstadials. Pollen evidence indicates oak trees increased in abundance during these climate phases. Wetlands expanded and more grass, herbaceous plant growth, and acorns were available with increased precipitation; thus providing more potential food for wildlife. I think megafauna were likely limited to oasis-like habitats in this region during cold dry stadials. These habitats probably occurred in river valleys where stream flow was much reduced, and instead of meandering continuous rivers like those of today, the waterway was more like a chain of pools clogged with sand bars.

Many folks imagine Pleistocene-environments to resemble the modern day Serengeti, but this was not always the case. During cold dry climatic phases large areas may have hosted scarce wildlife populations restricted to shrinking water holes. Wildlife populations rebounded whenever climate phases shifted to more moist conditions. I’m sure wildlife populations fluctuated in parts of North America just like they did in Guatemala.

Reference:

Rozas-Davila, A.; A. Correa-Metreo, N. McMichael, M. Bush

“When the Grass wasn’t Green: Megafaunal Ecology and Paleodroughts”

Quaternary Science Review 266 August 2021

Deer Herbivory Alters Plant and Bird Species Composition

May 20, 2021

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