Research

Coyote Data, Thus Far

We have learned a great deal about animal movement and activity patterns from collecting and analyzing pictures in Statesville’s green patches and neighborhoods.

If you look at Figure 1, time (24-hour) is displayed on the x-axis while activity level is displayed on the y-axis. Activity level is simply the number of detections (pictures) within a particular hour divided by the total number of detections. Figure 1 shows us that coyotes in Statesville are primarily nocturnal. In fact, our data for the past six years show that coyotes are 76.5% nocturnal. In some of our neighborhood plots, that percentage gets as high as 88.9%. This is calculated by dividing the total number of night coyote pictures by the total number of coyote pictures. Night is defined at the time right after sunset to the time right before sunset. Of course, this time frame varies throughout the year, but we have data analysis software that will calculate this for us.

Figure 2 shows coyote activity patterns alongside two other urban carnivores that we have in Statesville, the red fox and grey fox. There may be some slight differences that we could tease out between the three species, but for the most part, they all follow the same nocturnal pattern.

Figure 1

Figure 2


While it’s hard to gather accurate population counts with camera traps, there are analyses that will give us an idea of how abundant coyotes are in Statesville compared to other urban animals.

We looked at and analyzed one particular data set from this past spring. We placed one group of cameras in green spaces that bordered rural areas and another group of cameras in several neighborhood corridors, all within Statesville city limits.

Statesville Green Space
The green space area covered approximately 175 acres. The cameras ran continuously for 126 nights. Coyote pictures made up 1.5% of the total pictures taken. In comparison, raccoons and opossums combined for 49.4% of the total pictures taken. Over the 126 days we recorded 9 independent sightings of coyotes (87 independent sightings for raccoons). As part of our protocol, a sighting was considered independent if two photos with the same sighting were taken at least thirty minutes apart. So, the coyote that hangs around a certain camera for 2-3 hours only counts as 1 independent sighting.

We also analyzed the abundance index of each animal that we captured in this area. This index takes into account the number of independent sightings for a species and the total number of nights (in this case 126). The calculation is as follows:

# of independent sightings/# nights x 100

The abundance index for coyotes was 7.1. For raccoons, it was 69.0. Figure 1 shows the indices for the rest of the animals captured.

Statesville Neighborhood Corridors
Our neighborhood cameras were placed in natural corridors, which are areas in backyards (between houses) where you can see animal trails. These data are important because it lets us know what animals are moving through yards. The downside, however, is that the abundance index for each species and number of detections get inflated because these are trails animals use a lot.

These cameras ran for 78 nights. Coyotes comprised 15% of the total pictures taken. Raccoons and opossums combined for 54%. The abundance index for coyotes was 60.3 (again, the corridor factor inflated this). The index for raccoons was 105.1. Figure 2 shows the rest of the animals captured in neighborhoods.

Relatively speaking, coyotes are not the most abundant urban animal we have in Statesville.

Figure 3

Figure 4


We don’t know for sure the percentage of certain species that make up the diet of Statesville’s coyotes. We have pictures with coyotes walking by with rabbits in their mouths. Students will be using a protocol this year to study scat. Even though we don’t know about the specific coyotes in Statesville, we do know what coyotes eat from other studies.

Coyotes are not just hanging around harassing dogs and cats. They are not sitting and waiting on cats to cross a trail so that they can scoop them up. If cats were #1 on their list of prey, we would not have any more domestic/feral cats in Statesville. In most studies, cats only make up 1-2% or less of the diet of urban coyotes (MacCracken 1982, McClure et al. 1995, and Bollin-Booth 2007). Coyotes are actively engaged in the ecosystem as urban predators. They are influencing ecosystems by mostly eating small rodents and rabbits. They have been also known to scavenge deer carcasses. On occasion, they may be able to bring down deer. None of these are bad for the ecosystem since we do not currently have a rodent, rabbit, or deer shortage in Iredell county.

Coyotes are not only directly influencing the movement patterns of their prey, they are also influencing competitors. We have been able to analyze our camera trap data in such a way to look at the overlap of activity between two species. Figure 5 shows the activity pattern of coyotes compared with squirrels. Squirrel activity peaks between 9-10am, and then again around 5pm. Both are these times are when coyote activity is decreasing. Squirrel are not active at night when coyotes are. This is smart if you’re a squirrel.

Figure 5

What if you’re a deer? Figure 6 shows coyote/deer overlap. Deer activity seems to peak between 7-8am, but then again around 8pm when coyote activity is high. This may indicate that, in Iredell county, coyotes are not a threat to deer. Deer activity stays higher than coyotes during the day, but slightly lower than coyotes through the night.

Figure 6

Figure 7 shows coyote/rabbit overlap using a large dataset. You can see that rabbit activity is the greatest in the morning, just a little earlier than squirrels. However, when we break down our data into green spaces versus back yards, we see a different pattern. Figures 8 and 9 show coyote/rabbit overlap in green spaces and back yards, respectively. “Dhat1” measures overlap on a scale from 0-1, with 0 being no overlap in activity and 1 being 100% overlap in activity. There’s a higher overlap in green spaces. Also, the back yard rabbits seem to like to be out right after midnight. Maybe coyotes are influencing the behavior of rabbits in Statesville.

Figure 7

Figure 8

Figure 9

What about other animals that aren’t prey? Figures 10 and 11 show the overlap between coyotes/raccoons and coyotes/cats, respectively. Raccoons look to be even less active during the day than coyotes and more active during the night. Cats, on the other hand, are all over the place. Their activity peaks around 7pm, right before coyote activity during the night peaks.

Figure 10

Figure 11

Coyotes are carnivores. Coyotes are active. Coyotes are clever and curious. However, for the most part, they want nothing to do with you or your pets.


We should be careful when we speculate. For example, it is hard to determine whether domestic/feral cats disappeared because of coyotes or for another reason. Just because a pet disappears does not mean that coyotes “got” it. Blaming coyotes for everything only increases the fear factor.

One way we can better understand how (or if) coyotes are influencing other animals is to look at how other species use habitats with a coyote presence compared with how they use habitats with no coyote presence. This “intensity” is measured by the # of detections/total # of detection days (duration). Figure 12 shows us what we would expect. Squirrels are not detected as much in areas where coyotes are present. Again, this is good for the squirrel. Figure 13 shows us the same pattern with deer. Maybe this is just coincidence or maybe it means that deer simply don’t stay in coyote-occupied habitats too long. Figure 14 seems to show us something unexpected. It looks like, at least in Iredell county, that raccoons thrive in the presence of coyotes. It doesn’t look like they are impacted at all. Finally, figure 15 shows us domestic/feral cats and dogs decrease activity in habitats that are occupied by coyotes.

Figure 12

Figure 13

Figure 14

Figure 15

Coyotes may influence how intensely certain species use certain habitats. Coyotes probably play a part in influencing the activity of certain species. However, this does not mean they coyotes are responsible for the disappearance of all pets.


Is it fair to call coyotes “non-native” or “invasive”? To properly answer this question, we need to explore the issue and find out where they came from, how they got here, and why they came. Also, it doesn’t hurt to delve into the latest research on canine genetics. It does no good to speculate or simply rattle off stories that you have heard from sources that were probably not reliable.

Let’s debunk some myths. We do know is that coyotes were not introduced into NC by state officials because they had made a deal with insurance companies. This story states that NC officials released them to help control the deer population because there were too many automobile accidents. It’s simply not true.

In 2008, Iredell County Animal Services and Control sent out a publication that says at one point in the past, foxes were in so much demand for hunting that someone transported coyotes from Virginia into Iredell County to replace them. Hurricane Hugo, which came through the county in 1989, supposedly demolished the coyote pens, and they all escaped into the wild. These coyotes then reproduced and created the current problem. Some people believe that these hunters were solely responsible for bringing coyotes to NC. This is also not entirely true.

The most probable way coyotes infiltrated Iredell county is by a natural process we call migration. Hunters bringing coyotes to Iredell county in the 1980’s may have helped them spread faster into the area, but coyotes expanded into the area naturally by moving into a territory that was once occupied by wolves.

As you can see in the illustration, coyotes have recolonized North America over the last 100 years. There is no doubt that our eastern coyote here in Statesville is a hybrid. What’s remarkable is the evolutionary story this creature has to tell. Studies show that the eastern coyote is actually a mixture of 3 species: coyote, dog, and wolf. Here’s the breakdown by genes:

Genome of coyotes in the Northeast 60%-84% coyote, 8-25% wolf, and 8%-11% dog

Genome of coyotes in Virginia 85% coyote, 2% wolf, and 13% dog

Genome of coyotes in the Deep South 91% coyote, 4% wolf, and 5% dog

As you can see, this mixture changes as you move south along the eastern region of the U.S. Even though coyotes show evidence of hybridization, most researchers do not think they are still naturally mating with dogs or wolves. We have no wolves here in North Carolina, except for the tiny population of red wolves along the coast. Even those red wolves show a mixture of gray wolf and coyote genes.

By most accounts, coyotes are described as “non-native” and “invasive.” Those are two words that may not be suitable in this case. Should we refer to a species as non-native if it came into an area naturally? To call a species invasive, you would need to show that it is negatively impacting the ecosystem. Are coyotes doing this? It seems that they are simply occupying a niche that was left open when the wolves that once roamed NC disappeared.

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Coyote Misconceptions

The recent coyote attack in Iredell county is unfortunate and sad. Someone lost a pet in a matter of seconds. Human fear and emotions are real and for good reason. The dog was likely attacked with no warning at all.

In situations like this, comments like, “What do we expect? We have built houses in their habitat” are not helpful. It also does no good to simply say, “If I see one, I am going to just shoot it!” or to argue whether or not you can actually shoot a coyote within city limits. These comments bring little comfort to the people who have seen coyotes in their neighborhoods and are frightened. What may actually help is understanding coyote behavior and knowing what the scientific literature says about this urban carnivore.

For the past 6 years, researchers at Mitchell Community College have surveyed areas around Statesville using motion-activated trail cameras. The following picture shows where coyotes have been observed (highlighted in yellow).

Figure 1. Statesville, NC coyote habitat. Diagram is based on data collected from Mitchell Community College Trail Camera Studies.

As you can see, if there is a green patch within city limits, these animals can be successful. Individual coyotes or pairs can typically have smaller home ranges in urban environments because resources (i.e. food) are greater. Below, we have attempted to provide answers to some coyote questions by compiling data from scientific articles. We have also used some of our own camera trap data from Statesville.

1) Have coyotes just recently learned to live with people? Nope.

In a recent news article, a N.C. Wildlife Resources Commission biologist was quoted as saying coyotes are “getting used to people.” This makes it sound like the co-existence between coyotes and humans is relatively recent. It’s not. Coyotes have never been solely wilderness creatures. For the 15,000 years since humans have inhabited North America, coyotes have been living alongside us (Flores 2016). Besides, we do not ever want coyotes to get used to us to the point where they feel comfortable.

2) Are coyotes “non-native” and “invasive”? It depends on how you define “non-native.” As far as invasive goes, not by a long shot.

It is probably accurate to say that coyotes are the most persecuted animal in North America, with 500,000 of them killed every year (Flores 2016). What makes them different than any other urban animal is that they are deemed a “problem” just because of their presence. By most accounts, coyotes are described as “non-native” and “invasive.” Those are two words that may not be suitable in this case.  In 2008, Iredell County Animal Services and Control sent out this publication. It states that at one point in the past, foxes were in so much demand for hunting that someone transported coyotes from Virginia into Iredell County to replace them. Hurricane Hugo, which came through the county in 1989, supposedly demolished the coyote pens, and they all escaped into the wild. Judging by how fast coyotes have spread into other counties throughout North Carolina, it is unclear whether this single event helped coyotes spread into the area faster than they normally would have. Even though coyotes may not have always inhabited North Carolina, red wolves once did. Since recent genetic research has shown that 80% of the red wolf genome is similar to coyotes, you could make an argument that coyotes (their genes, anyway) are native (VonHoldt 2011).

3) Are coyotes beneficial to urban ecosystems? Yes.

As is the case in Statesville, coyotes are the top predator in most urban ecosystems. Crooks and Soule (1999) showed that coyotes regulate a trophic cascade mechanism within fragmented landscapes. In the absence of coyotes, mesopredator (like raccoons or cats) populations increase. When mesopredators increase, songbirds tend to decrease, so you could make the argument that coyotes benefit native songbirds. Coyotes can also influence foxes, cats, raccoons, and skunks through direct competition. They may even influence behavior in domestic cats in urban environments (Kays et al. 2015). At our urban green patch sites, we did not catch any domestic cats. However, at our backyard sites over the same period of time, we had 22 independent captures of cats. So, maybe cats know where to go and where not to go. Through direct predation, coyotes do regulate rodent, rabbit, and in some areas, deer populations. For example, look at both Figures 2 and 3.  Coyote and rabbit activity overlap is higher in Statesville green spaces (Figure 2) than in backyards (Figure 3). You will also notice that rabbit activity peaks soon after midnight in backyards where coyotes are less dense (Figure 3). In Statesville green patches, rabbit activity peaks a little before 6 a.m. and right after 6 p.m. Are coyotes changing the behavior of rabbits in urban environments?

Figure 2. Coyote and rabbit activity overlap in urban green patches.

Figure 3. Coyote and rabbit activity overlap in urban backyards.

4) Do coyotes pose a danger to pets? Obviously, yes, but conflicts are rare.

Occasionally, coyotes do kill pets, but it is hardly a common occurrence. Contrary to popular belief, coyotes do not simply eat garbage and harass pets. It’s not the dumpsters or the small cats that attract coyotes to urban areas. Coyotes are top-level carnivores here in Statesville, and they are actively engaged as predators. Most conflicts with pets are because coyotes view small dogs and cats as competitors, not as food. In fact, this competitive response is similar to the response that coyotes show towards smaller foxes. Coyotes in urban ecosystems do not depend on pets as food (Gehrt 2007).  If they did, we would not have any pets left. In most studies, cats only make up 1-2% or less of the diet of urban coyotes (MacCracken 1982, McClure et al. 1995, and Bollin-Booth 2007). Our studies have shown that coyotes prefer cottontails in Statesville.

5) Are coyotes dangerous to humans in urban environments? Typically, not at all.

Coyotes have been documented attacking people. In 1981, a small child died from a coyote attack (Howell 1982). In 2009, White and Gehrt classified 142 U.S. and Canadian coyote attack reports. They categorized the attacks as follows:

Predatory- 37%

Investigative- 22%

Pet related- 6%

Defensive- 4%

Rabid- 7%

Like the recent attack in Statesville, most of the attacks occurred during pup-rearing season (May-July). “Problem” coyotes seem to be those that have become habituated to humans. Most urban coyotes avoid humans by shifting to more nocturnal activities. Our data certainly indicate this. Over 126 days, we collected 56 independent coyote captures on our cameras within city limits. Our data show that coyotes within city limits are, on average, 68% nocturnal. Four capture sites in one particular area showed that coyotes were 89% nocturnal.

Habituation could be the result of intentional or unintentional feeding of wildlife or avoiding them when they are seen. To successfully live with these predators, it is always best to yell and scream at them if you see them in your neighborhood. Make sure they stay wild, but also make sure they stay nervous.

6)  Are coyotes frequently reported as rabid wildlife species? Nope.

Rabies is a common fear among those of us that live in the city. The Center for Disease Control reports that raccoons account for most of the rabies outbreaks in the U.S., followed by bats, skunks, and foxes. Unlike raccoons, the coyote-strain rabies (except for a tiny population in South Texas) has not been an issue in the U.S (Clark and Wilson 1995). However, raccoon-strain rabies or raccoon rabies virus (RRV) can spillover into coyote populations. This has happened only occasionally (Wang 2010).

7) Can you ever get rid of all the coyotes? It doesn’t look like it.

If a pest-control company tells you they can take care of the “problem” and eliminate coyotes, they can’t (at least not permanently). Most predators are either solitary (mountain lions) or social (gray wolves), but not both. Coyotes, however, can be both. They can also catch a variety of prey, from small mice to deer. These are just some of the characteristics that allow them to live just about anywhere. Also, coyotes seem to be somewhat immune to exploitation. Knowlton et al. (1999) showed that unexploited coyote populations tend to have older age structure, high adult survival rates, and low reproductive rates. However, in highly exploited populations, coyotes are characterized by younger age structures, lower adult survival rates, and increased percentages of yearlings reproducing, and increased liter sizes. What can you do? Removal programs that target problem coyotes on an individually basis may be more cost-effective. It is important to remember how you define “problem”. Not all individual coyotes are problems just because of their presence.

 

References

Bollin-Booth, H. A. 2007. Diet analysis of the coyote (Canis Latrans) in metropolitanpark systems of northeast Ohio. Master’s thesis. Cleveland State University, Ohio.

Crooks, K. R., and M. E. Soule. 1999. Mesopredator release and avifaunal extinctions in a fragmented system. Nature, 400: 563-566.

Flores, D. 2016. Coyote America: A Natural and Supernatural History. Basic Books: New York, NY.

Gehrt, S. D. 2007. Biology of coyotes in urban landscapes. Pages 303-311 in D. L. Nolte, W.M. Arjo, and D. H. Stalman, eds. Proceedings of the 12th Wildlife Damage Management Conference. Corpus Christi, TX.

Howell, R. G. 1982. The urban coyote problem in Los Angelos County. Pages 21-23 in R. E. Marsh, ed Proceedings of the tenth Vertebrate Pest Conference. University of California, Davis.

Kays, R. et al. 2015. Cats are rare where coyotes roam. Journal of Mammalogy, 96: 981-987.

Knowlton, F. F., E. M. Gese, and M. M. Jaeger. 1999. Coyote depradation control: An interface between biology and management. Journal of Range Management, 52: 398-412.

MacCracken, J. G. 1982. Coyote foods in a Southern California suberb. Wildlife Society Bulletin, 10: 280-281.

McClure, M. F. et al. 1995. Diets of coyotes near the boundary of Saguaro national monument and Tucson, Arizona. Southwestern Naturalist, 40: 101-104.

VonHoldt, B. M. et al. 2011. A Genome-Wide Perspective on the Evolutionary History of Enigmatic Wolf-Like Canids. Genome Research, 8: 1294-1305.

Wang, X. et al. 2010. Aggression and Rabid Coyotes, Massachusetts, USA. Emerging Infectious Diseases, 16: 357-369.

White, L. A., & Gehrt, S. D. 2009. Coyote Attacks on Humans in the United States and Canada. Human Dimensions of Wildlife, 14(6), 419–432. http://doi.org/10.1080/10871200903055326

 

Suggested Readings

Bekoff, M. 1977. Canis latrans. Mammal Species, 79:1-9.

Gehrt, S. D., Wilson, E. C., Brown, J. L., & Anchor, C. 2013. Population Ecology of Free-Roaming Cats and Interference Competition by Coyotes in Urban Parks. PLoS ONE, 8(9), e75718–11. http://doi.org/10.1371/journal.pone.0075718

Gehrt, S. D., C. Anchor, and L. A. White. 2009. Home range and landscape use of coyotes in a major metropolitan landscape: Coexistence or conflict? Journal of Mammalogy, 90: 1045-1057.

Gehrt, S. D., & Prange, S. 2006. Interference competition between coyotes and raccoons: a test of the mesopredator release hypothesis. Behavioral Ecology, 18(1), 204–214. http://doi.org/10.1093/beheco/arl075

Heinrich, R.E., Strait, S.G., and Houde, P. 2008. Earliest Eocene Miacidae (Mammalia: Carnivora) from northwestern Wyoming. Journal of Paleontology, 82: 154–162.

Kays, R., Curtis, A., and Kirchman, J. 2010. Rapid adaptive evolution of northeastern coyotes via hybridization with wolves. Biology Letters, 6:89-93.

Kilgo, J., Ray, S., Vukovich, M., Goode, M., and Ruth, C. 2012. Wildlife Management, 76:1420-1430.

Meachen, J., Janowicz, A., Avery, J., and Sandleir, R. 2014. Ecological Changes in Coyotes (Canis latrans) in Response to the Ice Age Megafaunal Extinctions. PLoS ONE 9(12): e116041. doi:10. 1371/journal.pone.0116041

Meachen, J. and Samuels, J. 2012. Evolution in coyotes (Canis latrans) megafaunal extinctions. PNAS, 109: 4194-4196.

Mech, L. D. 1974. Canis lupus. Mammal Species, 37:1-6.

Newsome, S. D., Garbe, H. M., Wilson, E. C., & Gehrt, S. D. 2015. Individual variation in anthropogenic resource use in an urban carnivore. Oecologia, 178(1), 115–128. http://doi.org/10.1007/s00442-014-3205-2

Tallian, A., Smith, D. W., Stahler, D. R., Metz, M. C., Wallen, R. L., Geremia, C., et al. 2017. Predator foraging response to a resurgent dangerous prey. Functional Ecology, 96, 1151–12. http://doi.org/10.1111/1365-2435.12866

 

A Relationship Older Than Dirt

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Lichen and moss living together on an oak

No one made chasing down ancient artifacts cooler than Indiana Jones. He would leave the safety of his classroom, which required battling bad guys, to track down artifacts. Fortunately for us, all we have to do is step outside to be in the midst of something much more primitive than anything Dr. Jones collected.

Take a walk, and you will easily find yourself in the presence of a species from another age. It surrounds us, but we rarely notice it. Some researchers even think it may have even laid the foundation for terrestrial life. It’s not just one species. It’s two different species intertwined as one, which creates various types of colors and structures.

Lichen is actually a symbiotic relationship between two partner species. The mycobiont partner is a fungus that gives structure to the lichen. Fungi are made up of eukaryotic cells, meaning the internal structure is made up of organized compartments and also a membrane-bound nucleus that stores and protects the delicate genetic code. As such, fungi are heterotrophic organisms,  obtaining their nutrients externally. In the case of fungi, food comes in the form of fixed carbon, which is often acquired through the process of decomposition. If not through decomposition, the fungus must get the required carbon through a symbiotic relationship with a partner.

A photobiont is the second partner into this lichen relationship.  Either green algae or cyanobacteria can fulfill the needs of the fungus because they can both photosynthesize. Green algae belongs to the plant kingdom and cyanobacteria is a prokaryotic organism so they are not even grouped together. However, they both have the ability to harness light energy from the sun and use it to make food in the form of glucose, or sugar (carbon source). This works out well for the fungus. The photobiont provides an endless supply of glucose for the fungus, and in return, the fungus provides structure and protection. This partnership seems to have set the stage in primitive times for two important events.

In 2001, results from a massive genetic study revealed that early plants and fungi played a major role in instigating the environment in such a way that global glaciation and the evolution of land animals eventually both took place. The process of photosynthesis, presumably from the photobiont partner, was a major player because it takes up carbon dioxide, thus lowering atmospheric levels, and at the same time, increases oxygen levels. Here’s what the overall process looks like:

                                                                       sunlight
                 Carbon dioxide + Water  —————>  Oxygen + Glucose (carbon-based sugar)

This particular study looked at when, specifically, plants and fungi colonized land. Earlier studies had concluded that both came on land about 480 million years ago (mya). Before that, supposedly only rocks and bacteria covered the land. Campbell Biology, a popular academic text, states, “But it was only within the last 500 million years that small plants, fungi, and animals joined them (bacteria) ashore.” Heckman et al. (2001) concluded that for plants actually colonized land 700 mya and fungi around 1300 mya. This is significant because this would mean that these two groups colonized land during the Precambrian, the oldest geological eon. If land fungi and plants did appear during the Precambrian, how exactly could they have played a role in both ice age events and the explosion of various animal forms that we see in the fossil record?

screenshot-2017-01-21-13-57-41

Figure 1. Geological time By United States Geological Survey [Public domain], via Wikimedia Commons

To understand this, it is important that one understands just how hard it is to live on land. Compared with living in the water, or at least near water, plants need to have certain vascular tissue like roots, stems, and leaves to transport water and sugars. Some plants benefit from having a thick waxy layer on leaves to keep too much water from escaping. Living on land is tough, and it would have been especially hard 700 mya. This is where lichen come into the picture.

The terrestrial plants and fungi were not living separately during this early time. They were living in this lichen relationship. It was this relationship that allowed them to live in these harsh conditions. Lichen can live without rain for months, which explains why it is found in harsh places like the arctic and the hottest deserts. Early in the earth’s history, the green algae needed protection, which is exactly what the fungi provided. Now, photosynthesis could work on a large scale. Carbon dioxide levels in the atmosphere decreased and oxygen levels increased.

When carbon dioxide levels decrease, global temperatures decrease. Photosynthesis probably was the main reason why the Earth experienced global glaciation events from 750 mya to 580 mya. This time period lines right up with the appearance of lichen and early land plants like moss (seen mixed in with lichen in above picture). There may have been some other explanations for the decreased carbon dioxide levels. One may have been the mosses and early land plants that are made up of lignin. Lignin is a tough organic compound that does not easily decompose. Carbon gets “locked” up in the lignin and cannot get out. This ends up eventually producing fossil fuels if the plant material gets buried over years and years. Another event that may have helped the decrease of carbon dioxide levels could have been the fact that the first lichen may have produced acids that dissolved the rocks they were living on. This acid released calcium from the rock. When calcium is washed away, calcium carbonate limestone forms, which prevents carbon atoms from forming carbon dioxide in the atmosphere.

There was an increase in atmospheric oxygen during the Neoproterozoic era, right before what scientists refer to as the Cambrian explosion. Campbell Biology explains the Cambrian period this way, “Early in the Cambrian period, some 530 million years ago, and immense variety of invertebrate animals inhabited the Earth’s oceans.”  In fact, from 535 mya to 525 mya, the oldest fossils of nearly half of all extant animal phyla have been found, including the first arthropods, chordates, echinoderms, and the precursor organisms to vertebrates. The lichen (and the moss) may have been responsible for this oxygen increase that led to this evolution boom of animals.

According to a recent study, soil has only been around for the last 450 mya. If this is true, this lichen relationship is truly older than dirt. The next time you are walking in the woods or even in your own backyard, pay close attention to the lichen growing on the trees and rocks. Then, to show respect to your elder, give a slight nod of the head.


Heckman, D. S. et al. 2001. Molecular Evidence for the Early Colonization of Land by Fungi and Plants. Science, 293: 1129-1133.

Reece, J. B. et al. 2014. Campbell Biology. Boston: Benjamin Cummings/Pearson.

 

Holding Tight

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American Beech trees, still holding leaves in January, are scattered throughout the understory of a local forest.

And to this very day, when all the other trees lose their leaves, the great oaks (and for the sake of this post, the American Beech) keep theirs in memory of their ancestor’s promise. Only in Spring’s time, when the other trees grow new leaves, do the oaks drop theirs. Winter cannot steal spring away and control the weather forever.”

As the days get shorter and colder, trees have an important “decision” to make. They must shed their leaves or hold tight through the winter. Evergreens hold tight to their needles or leaves, but in evolutionary terms, evergreens are old. Over time, trees diversified and accumulated many beneficial adaptations. One of those was the ability to lose leaves. It is these deciduous trees that dominate areas like Statesville, where there are patches of mixed evergreen and deciduous forests. Between evergreens and deciduous trees, there seem to be some that do not obey all the rules. Tree such as oaks and beeches belong somewhere in the middle.  To understand why these trees hold their leaves longer than others, we must first understand why deciduous trees shed in the first place.

Shorter periods of daylight coupled with colder temperatures trigger a hormone in deciduous trees that sends a chemical message to every leaf. This message is to, essentially, “get off.” Cells then appear at the exact point where the leaf and stem meet. These cells start to rapidly divide, creating what is called an abscission layer. The division of these “abscission” cells prevents nutrients from reaching the leaves and also prevents chlorophyll from being replaced. Therefore, the leaves start to die just as other pigments (yellow, red, and orange) start to be seen and enjoyed by many people. Abscission comes from the Latin word abscissio, meaning “breaking off” (think scissors).

Leaves are the main food producers for trees through the process of photosynthesis. The leaves trap energy from the sun and use it to convert water and carbon dioxide into glucose (food) and oxygen. On short, cold days, food production decreases significantly. Deciduous trees choose to push these food producers away rather than keep them around with decreased productivity. Not that there’s anything wrong with retaining what gives you food. Evergreens do it. For example, one of the luxuries that a southern magnolia, a broad-leaved evergreen, has is it is able to produce food through photosynthesis all year long. Another advantage of retaining leaves would be that the tree would not have to allocate energy and resources into growing new ones every year. For deciduous trees, though, the bad outweighs the good.

If there happened to be several warm days in the winter, the leaves would resume photosynthesis (which requires water). If this warm spell was following by a frost, the leaves would be in trouble. The water would be trapped and would freeze. Because water expands when it freezes, the ice crystals would damage internal structures beyond repair, killing cells and tissue. In areas where snow and ice accumulates, entire branches could even be pulled off of trees, putting the tree in serious danger. So, for many trees, abscission keeps trees from becoming damaged and also helps conserve water and energy.

Even with the risks, the American Beech tree, Fagus grandifolia, decides to hold most of its leaves throughout the winter. The process of retaining dead plant organs that are normally shed is called marcescence. How do beech trees get away with this strategy and is there any advantage? There are three main theories, but these theories trigger more questions than answers.

Marcescence could be a trait found in both juvenile trees and/or lower branches of older trees. Holding on to leaves throughout the winter could benefit younger trees simply because after the taller trees shed leaves, more sunlight would reach the bottom. This would allow these understory trees to take advantage of the increased sunlight and photosynthesize longer. The American Beech tree does really well in the shadows of larger maples, oaks, and birches. Could it be that retaining leaves is what allows the beech to be so shade-tolerant? It’s hard to imagine that the beech trees are able to take advantage the increased food production process since their leaves look to be out of chlorophyll in the winter (see the yellowish, brown leaves above).

Another idea is that having these leaves “stick” around plays an important role in nutrient cycling for the tree. If the leaves shed in autumn, they would join all the other leaves on the forest floor and start the decomposition process. There’s a chance that the nutrients produced from this decomposition could leach away and the trees would have none for the spring when they are growing. Instead, the beech trees wait to drop their leaves in the spring to ensure that are some nutrients in the soil. This could be important for small understory trees that have small root systems. However, the problem with this theory is that big leaves often take months to decompose. Maybe there’s another answer.

Retaining leaves may help to deter large herbivores, such as deer, from browsing. At least one researcher thinks that the leaves protect buds and twigs from being chewed off because the leaves are less nutritious and palatable. Svendsen (2001) showed that the European beech tree, Fagus sylvatica, was browsed significantly more by weight and number of branches when the leaves were removed. Chemical analyses revealed that the protein and fiber content of beech twigs was higher of higher quality when compare to marcescent leaves. Maybe these leaves do act as an herbivore deterrent.

No one seems to know for sure why these trees chose to not give in to peer pressure and drop their leaves. It could be one of the previous theories. It could, in fact, be a combination of these theories. It could be something yet to be discovered.

Ah, the beauty of nature.


Svendsen, C. R. 2001. Effects of marcescent leaves on winter browsing by large herbivores in northern temperate deciduous forests. Alces, 37: 475-482.

Huggin’ Trees by Design

By Tim Ross (Own work) [Public domain], via Wikimedia Commons

By Tim Ross (Own work) [Public domain], via Wikimedia Commons

How do you survive if you’re not the most dominant canine in an area? If you have to share space and potential food with your faster and sometimes much larger cousin, how do you and your kin thrive day in and day out? These are questions the gray fox, Urocyon cinereoargenteus, must answer.

The common gray fox is a crepuscular and nocturnal canid whose home range averages around 1.5 square miles. This range contracts during the spring when they mate and have pups and then expands during the fall while they search for food. Their diet, like both red foxes and coyotes, consists of small mammals and even birds. Unlike other canids, the gray fox’s digestive system is better equipped to handle much more fruit.

In many parts of the southeast, including Statesville, gray foxes live with both red foxes and coyotes. Not much is known about how red foxes and gray foxes divide habitat in areas where they overlap. What is known is that red foxes seem to prefer more open terrain while gray foxes stick to the woods. it’s certainly possible that these two species use time-share strategies to avoid interactions.

Having to share space and resources with coyotes, however, could cause major, or fatal, problems for the foxes. Coyotes have been implicated in the decrease of red fox populations in certain areas (Cypher 1993). However, gray fox populations do not seem to be impacted as much by the larger coyote. Our small data set from greenway patches seem to support the idea that gray foxes tolerate coyotes better than red foxes. The following shows the number of pictures of each species we have collected from two camera traps from August to December during both 2015 and 2016:

                               Camera A             Camera B
Coyotes             25                         10
Gray fox            24                           2
Red fox                1                           2

Is the explanation just that the diets of gray foxes and coyotes are different or is it that gray foxes avoid coyotes spatially and/or temporally?

Both Cypher (1993) and Neale and Sacks (2001) found that there was actually a high dietary overlap among coyotes and gray foxes year-round. The implication is that this means, more than likely, that there is interspecific competition when they live in the same area. Neale and Sacks (2001) also used scat analyses to determine that gray foxes did not avoid coyotes in space. Our data (Figure 1) suggest that gray foxes don’t avoid coyotes in a temporal (time) dimension either.

rplot

Figure 1. Gray fox versus Coyote

The answer to how gray foxes avoid coyotes seems to be found in their evolutionary past. Gray foxes were the first canid to diverge from the rest of the canid family. They are a primitive species that branched off from the rest of the canids around ten million years ago (Lindblad-Toh et al. 2005). As a matter of fact, there is scientific support that states that the gray fox should not even be considered a canine or a vulpine (red fox). The gray fox is what geneticists call a basal canid, meaning it represents an ancient lineage.

Gray fox climbing in Statesville

Gray fox climbing in Statesville

As a result of this ancient lineage, the gray fox has many unique characteristics. Some features are only shared with another ancient species, the raccoon dog (Nyctereutes procyonoides). Gray foxes have hooked claws and the ability to rotate their forearms. This, coupled with the fact that they have the shortest leg-to-body ratio of any wild canid, allows them to easily hug tree trunks or branches and climb. Ecologically, they are more like cats. When pursued, gray foxes are not really interested in running. They would rather scamper up a tree. It’s this ability that helps them minimize conflict with coyotes.

Next time you are out in the forest, take the time to look up into the trees. You may get a peek at one of these cat-like dogs.

Gray fox foraging

Gray fox foraging


Cypher, B. L. 1993. Food Item Use by Three Sympatric Canids in Southern Illinois. Transactions of the Illinois State Academy of Science, 86: 139-144.

Lindblad-Toh et al. 2005. genome sequence, comparative analysis, and haplotype structure of the domestic dog. Nature, 438: 803-819.

Neale, J. C. C. and Sacks, B. N. 2001. Food habits and space use of gray foxes in relation to sympatric coyotes and bobcats. Canadian Journal of Zoology, 79:1794-1800.