Archive for February, 2023

Pleistocene Gray Foxes (Urocyon cinereoargenteus)

February 23, 2023

Almost every major Pleistocene-aged fossil site in southeastern North America yields specimens of the gray fox. Bones of this species have been found at 58 sites across North America and 22 sites in Florida alone. The gray fox is an extremely successful species and has existed for at least 10 million years, though paleontologists assign the scientific name Urocyon cinereoargenteus just to those individuals that have lived over the past 300,000 years. Its evolutionary ancestors are barely distinguishable from modern day gray foxes. (Scientists are quick to make up new scientific names, so they can claim they discovered a new species.) The Miocene gray fox (U. webbi) grew a little larger than modern day gray foxes. The Pliocene gray fox (U. progressus and U. galushia) are known from just a few specimens and were apparently also slightly larger. The early Pleistocene gray fox (U. citrinus) in Florida anatomically resembled modern western subspecies of gray foxes, while the mid Pleistocene gray fox (U. minicephalus) in Florida resembled modern eastern gray foxes. This is consistent with a genetic study that determined eastern and western gray foxes became isolated from each other for a while 800,000 years ago. Gray foxes prefer wooded habitat, and the eastern and western halves of North America must have been separated by unsuitable arid habitat then. Eastern gray foxes evolved some minor differences during this separation that occurred during the mid-Pleistocene. This same study found northern populations of gray foxes are less diverse, reflecting their recolonization of the region following the retreat of Ice Age ice sheets. Gray foxes are considered the most primitive canid species, and they are not closely related to any other living canids.

Gray fox range map. Western and eastern populations of gray foxes diverged 800,000 years ago, but they are still the same species. The Urocyon genus is at least 10 million years old.

This gray fox entered my yard in October of 2019. They are relatively common in my neighborhood.

Gray foxes are 1 of only 2 species of Canids that can climb trees. This helps them escape larger predators.

Part of the reason for the success of the gray fox is their ability to climb trees, making them capable of escaping larger predators. Of the 35 species of canids, they are 1 of 2 species that can climb trees. (Raccoon dogs, native to east Asia, are the other species that can climb trees.) They are omnivorous–another reason for their success. They can eat a wide variety of foods, including rabbits, rodents, birds, lizards, carrion, fruit, and acorns. At the present time their main predators and competitors are bobcats and coyotes. Studies show gray foxes will live and roam closer to suburban and urban habitats than bobcats or coyotes often will. This also helps them avoid predators. Bobcats and coyotes that kill gray foxes usually will not eat them, showing they are viewed more as competition than food. Gray foxes live in my neighborhood, and I see them on occasion. Once, my wife and I saw a gray fox carrying a squirrel in its mouth in front of our house. Red foxes (Vulpes vulpes) are less common near my vicinity, but I have seen them as well. They prefer more open country in contrast to the gray fox’s favored wooded habitat. Unlike gray foxes, red foxes are a recent immigrant to North America, having crossed the Bering land bridge about 15,000 years ago.


Geffen, E.; A. Mercure, P. Gorman, D. Macdonald, A. Wayne

“Phylogenetic Relationship of the Fox-like Canids: Mitochondrial DNA Restructure Fragment, Site, and Cytochrome B Sequence Analysis”

Journal of Zoology September 1992

Reding, D. et. al.

“Mitochondrial Genomes of the U.S. Distribution of Gray Fox (Urocyon cinereoargenteus) Reveal a Major Phylogeographic Break at the Great Plains Suture Zone”

Frontiers of Ecological Evolution and Population Genetics June 2020

Tedford, R.; X. Wang, and B. Taylor

“Phylogenetic Systematics of the North American Fossil Caninae (Carnivora: Canidae)”

Bulletin of the American Museum of Natural History 325 2009


Some Ecologists Think an Overpopulation of Deer could be Considered a Natural Disturbance

February 16, 2023

In 1943 Aldo Leopold conceived the notion an overpopulation of deer degraded the natural environment. He was an early expert on wildlife management science, but he was also a biased hunter perhaps seeking an excuse to kill deer. He proposed the extirpations of wolves and cougars meant human hunting was necessary to control deer populations, or they would exceed the carrying capacity of the land. Most modern ecologists still accept his doctrine and assume deer populations are above historical averages, and they believe natural environments should consist of high tree density. A new paper takes an alternative view and proposes an overpopulation of deer or high densities of deer could be considered a natural disturbance that benefits the ecology of the landscape. The authors of this study (referenced below) also take issue with the assumption modern deer populations exceed historical averages. The modern deer population in eastern North America is estimated to be about 21 million, but the authors of this study estimate the historical average was 24 million, although both estimates are guesses. Nobody was surveying deer populations from the time Columbus discovered America through the 19th century. Moreover, colonization of eastern North America by coyotes resulted in an effective replacement for wolves and cougars. Coyotes are more omnivorous and exist in higher numbers than larger predators ever did. And humans can not eliminate them. Megaherbivores were even more abundant during the Pleistocene than they are now or during written history. In addition to deer mammoths, mastodons, ground sloths, horses, bison, llamas, tapirs, and peccaries roamed the land. This suggests that what humans consider environmental degradation by large populations of herbivores should actually be considered a normal natural disturbance.

Map of deer population by state. I wrongly thought the deer population was higher in Pennsylvania than Georgia. This info is 20 years old, and it might not be the same today.

An overpopulation of deer contributes to the development of open woodlands with abundant herbaceous growth. Deer eat saplings thus thinning a forest, but they don’t repress grass and fern growth.

Conventional ecologists believe an overpopulation of deer is detrimental to the environment, but some ecologists now believe it mimics Pleistocene environments, and they think it should be considered a natural disturbance like lightning-ignited fires and windstorms.

The benefits of a higher population of deer include a reduction of the fuel loads thus reducing wildfire intensity, and the maintenance of an open woodland environment. Many species of birds, reptiles, and insects thrive in more open environments. Open woodlands also allow the growth of herbaceous plants. Grass, flowers, and ferns require areas with more sunlight. Reduced competition from other saplings lets surviving trees grow into magnificent specimens with wide spreading limbs that foster higher mast production. Deer help spread seeds in their dung and on their fur. Many species of plants are adapted to having their seeds cling to deer hides (known as endozoochoric).

The authors of the paper acknowledge a high population of deer can have some negative results. Although deer suppress populations of palatable non-native plants such as multiflora rose and bittersweet, unpalatable non-native plants increase with less competition from palatable native plants. Rabbits prefer brushy habitats and may decline when deer suppress dense vegetation. Deer do consume some rare and endangered plants. However, most negative results are economic rather than ecological. High deer populations can destroy farmer’s crops, and they can cause frequent car accidents. I’ve lived in my house for 30 years, and there have been 3 deer-car collisions in front of it, since I moved in. It is in a quiet suburban neighborhood–not even on a busy highway.

Whether or not deer populations degrade the environment is a human conceived construct. Throughout earth’s history, wildlife populations have always fluctuated, sometimes wildly. Large herds of megaherbivores grazing and browsing their way through a landscape should probably be viewed as a natural disturbance like a lightning-ignited fire, a hurricane, a flood, or an ice storm.


Hanberry, B; and E. Faison

“Re-framing Deer Herbivory as a Natural Disturbance Regime with Ecological and Socioeconomic Outcomes in the Eastern U.S.

Science of the Total Environment 868 (1) 2023

The Megafauna Release Hypothesis

February 9, 2023

The Megafauna Release Hypothesis postulates the extinction of the megafauna at the end of the Pleistocene caused an increase in the populations of species of plants that were preferred food for the megaherbivores, an increase in fire frequency due to the greater fuel load of uneaten vegetation, and the spread of non-analogue forests with no modern floral composition equivalent. Oak trees and maples did increase in abundance after megafauna extinctions because herds of animals were no longer eating acorns and saplings. And the hardwood trees were growing next to spruce trees in strange kinds of forests that no longer exist. A new study (Perotti 2022) attempted to test this hypothesis with new data from 5 sediment cores taken from lake bottoms at 5 sites, and they compared this with existing data from 14 other sites. Scientists took samples of mud from lake bottoms and carbon dated the layers. They analyzed the pollen composition to determine the abundance of various genera of plants, and they looked at the abundance of dung fungus spores used as a proxy for megafauna populations. They also looked at the amount of charcoal to determine fire frequency. With all this data they can get a general idea of the environment during past time periods. The authors of this study found the Megafauna Release Hypothesis held up well in Northeastern and Midwestern North America but did not for Southeastern North America.

Megafauna declined in abundance in the Northeast and Midwest about 14,600 years ago, and by 14,400 years ago there was a marked increase in hardwood tree abundance. However, fire frequency increased slightly before this–a clue humans were on the scene setting fires and overhunting the megafauna. In Southeastern North America the timeline doesn’t support the Megafauna Release Hypothesis. Hardwood trees began increasing about 16,300 years ago, preceding megafauna population decline by 2000 years. I have no doubt the extinction of megafauna had a major impact on floral composition, but I believe climate was a much bigger factor. I think the non-analogue forests in all regions can be explained by rapid climate fluctuations that led to temperate species growing with boreal species.

Graph showing pollen and foraminifera abundance from a core of sediment located off the coast of Georgia. The layers of sediment date from ~130,000 years ago-50,000 years ago. Oak increased during wet warm climate stages. Spruce increased during cold dry climate stages. Pine stayed relatively constant. Graph from the below reference by Huesser and Oppo.

A study of sediment taken from Ocean Drilling Project 1059A covers the period from 130,000 years BP to 50,000 years ago, long before megafauna became extinct. The location of the core is the South Atlantic off the Georgia coast. The time period includes the Sangamonian Interglacial and the first half of the Wisconsinian Ice Age. I wrote about this study in a long blog article about 12 years ago. (See: ) During warm wet climate phases hardwood trees such as oak increased in abundance, while spruce decreased. During cold dry climate cycles spruce increased in abundance, while hardwood trees decreased. Pine abundance stayed relatively stable during all climate phases. Broadleaf trees thrive in atmospheres high in carbon dioxide concentrations with higher precipitation rates, and they outcompete spruce trees under these conditions. Spruce trees are more resistant to the windy and icy conditions that occur during Ice Ages, and they can tolerate lower carbon dioxide levels as exist during a stadial. Transitions between stadial and interstadial likely always fostered transition (non-analogue) forests.

The extinction of megafauna has a big impact on various species of plant and animal abundance. A new study posits the impact was greater in the Midwest and Northeast than in the Southeast. Illustration from the below reference by Gallett et. al.

Landscapes were much richer when megaherbivores roamed the land. Their foraging and trampling created a variety of different habitats. They fertilized the soil and spread seeds with their dung. They provided food for predators, scavengers, and parasites. Their extinction had a major impact on the environment, but it was less than the influence of climate.


Gallett, M.; M. Moleon, P. Jordeno, and J. Suenim

“Ecological and Evolutionary Legacy of Megafauna Extinction”

Biological Reviews October 2007

Huesser, L. and D. Oppo

“Millennial and Orbital Scale Climatic Variability in Southeastern United States during MIS 5: Evidence from Pollen and Isotope in ODP site 1059A”

Earth and Planetary Science Letters 214 (2003)

Perrott, A. et. al.

“Diverse Response of Vegetation and Fire after Pleistocene Megaherbivore Extinction across the Eastern United States”

Quaternary Science Review 294 October 2022

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.


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

“Megafauna Extinctions Produce Idiosyncratic Anthropocene Assemblage”

Science Advances 8 (42) Oct 2022