Signs of Fall #8: Grove Run Trail (part 1), Blister Beetles and Rocks

Photo by D. Sillman

Photo by D. Sillman

(To read more about the Grove Run Trail check out my “Between Stones and Trees” hiking web site))

A couple of weeks ago on a beautiful Saturday morning Deborah and I met Rob and Michele Bridges down in Lynn Run Sate Park for a hike. The woods around Linn Run are a second (or, maybe, even a third or a fourth!) growth forest that date back to the first decade of the Twentieth Century. This was one of the first tracts of land purchased by the State of Pennsylvania (in 1909) in its efforts to reclaim and protect potential forest lands in the Ohio River watershed. When the state bought the land (much to the derision of the local inhabitants), it was a scrubby, tree-less tract dominated by ferns and briars and was almost completely devoid of wildlife or beauty. Not only had the woods been clear-cut by logging companies, but extensive fires (often caused by sparks thrown by the logging railroads) had repeatedly burned off the early successional recovery stages. It was a pretty miserable place!

The passage of time, though, has been kind to this area. With our region’s abundant rainfall and diverse seed reservoirs, a century of robust re-growth of the forest ecosystem followed in spite of the thin, rocky soils and continued sequences of insults and stresses.

Linn Run is shallow, rocky stream. It has a fast pace and lots of splash and foam and now has an abundance of trout and other fish. The forest that fills in the spaces around the narrow road that follows the run is lush and moist with the spray from the creek. Ferns and mosses grow in great abundance along the streamside. Hemlocks, yellow birches, and red maples crowd the edges of the creek and hang their dense branches over the water frequently generating a continuous tree tunnel over the path of the creek. It is a shady, cool place even on the hottest summer day. The hills and ridges around Linn Run through which our hiking trail will pass vary in elevation from 1300 to 2800 feet above sea level. Many of the trails climb up steep slopes in long switchbacks that are carved directly into the hillsides. All of these trails are covered in by layers of cobble-sized rocks that are a great challenge for a hiker’s feet and ankles!

Deborah and I parked in the picnic area of Grove Run (a small tributary of Linn Run) and sat beside a large fire ring to wait for Rob and Michele. Our dog, Izzy, was with us and was very excited to be away from home (or maybe she was terrified at being away from her familiar territory, it’s hard to tell with her sometimes!). She ran from scent to scent in the picnic area adding her scent to the olfactory symphony until she ran dry. She also growled at every large dog (and they were all larger than her!) that walked by. She was full of energy that amazingly did not flag throughout the long, rocky hike that we are about to start.

Photo by D. Sillman

Photo by D. Sillman

Deborah and I watched a male and a female blister beetle walking around in the cleared area around the fire ring. The blue coloration of these beetles announces their presence and also their potential toxicity to any potential predator. This type of warning coloration is called “aposematism,” and it benefits both the beetles (who are able to avoid being eaten) and predators (who avoid getting blasted with the caustic cantharidin secretions produced by the beetle). The physiological steps by which the cantharidin is synthesized and violently released make blister beetles great biological curiosities. They are often used as examples of the unexpected outcomes of evolutionary selection.

The two beetles were mating. The much larger female dragged the attached male around the fire ring. A second male blister beetle showed up but was out of luck for this encounter. This was late in the year for these beetles to be mating. July is usually the peak time for reproduction because the beetle’s eggs and larvae have to have several months to go through all the required developmental changes needed to get them ready to overwinter. The female blister beetle can produce up to six clusters of fifty to three hundred eggs and will deposit these egg masses in the ground or under rocks. A week and half to three weeks later the eggs hatch into first instar larvae which then seek out grasshopper egg cases. The larvae voraciously feed on the grasshopper eggs and go through increasingly larger and more sessile stages until they reach their fifth larval instar. The fat, almost legless fifth instar “grubs” then dig down into the soil where they molt into the sixth instar stage. The sixth instars overwinter and sometimes actually stay in their subterranean hideouts for up to two years! Usually, though, these sixth instars pupate in the spring and then emerge as adults in the late spring or early summer.

Photo by D. Sillman

Photo by D. Sillman

Rob and Michele arrived so we tore ourselves away from the dancing blister beetles and headed off on the old logging road that makes the start of the Grove Run Trail. The lushness of both the undergrowth and the canopy trees is striking. Many tall yellow poplars, red oaks, black oaks, sugar maples, red maples, black cherries, and scattered basswoods, cottonwoods, and American beeches fill up the spaces in the forest.

In 2008 (when I wrote the hiking essay about this trail) there were abundant American chestnut seedlings in the understory of this first section of the woods. I took that as a hopeful sign that some individuals of this formerly abundant tree might be eking out an existence in these ecosystems. I looked carefully to see if the seedlings have survived and grown, but they were no longer here. They must have succumbed to the lethal fungus that causes chestnut blight. The yellow poplars that were growing with them, though, were flourishing.

Photo by D. Sillman

Photo by D. Sillman

On the trail, there is a grace and spacing of the trees that seems almost managed and park-like. This openness is the dominant feature of the trail for many hundreds of yards. As a consequence of this spacing abundant sunlight reaches the forest floor and a rich growth of plants is seen in between the trees. Stinging nettle, cat briar, hay-scented fern, interrupted fern, sensitive fern, Christmas fern, jewelweed, partridgeberry, and extensive patches of blue cohosh grow densely along the trail and out into the surrounding forest. Seedlings of yellow poplar, American beech, red maple, and striped maple grow in clusters among the ground plants and form a dense, green “sea” in between the rich mixture of mature trees. Witch hazel, spice bush, and dogwood generate a scattered understory layer, and near several of the oaks are odd, brown, pine-cone-like patches of squawroot.

The trees are very uniform in diameter (and, therefore, I infer, they are very uniform in age). At the start of the trail trunk diameters of over a foot were common, but soon diameters of significantly less than a foot became the norm. These younger trees generate a “pole forest” that runs up the surrounding hillsides and down the short slopes to the stream. Along the way, there are a few very large, widely dispersed red oaks. These trees might have either survived the early logging or, at the very least, the initial rounds of fire that leveled the recovering forest.

Photo by D. Sillman

Photo by D. Sillman

There are many downed trees and fallen branches along the trail. Large trees, often wind-thrown with huge, still attached root balls lay in regular lines mostly perpendicular to the path. Some of these fallen trees are old and are covered with mosses, lichens, fungi, and even stands of robustly growing tree seedlings. Others of the fallen trees have bare, intact bark and look like they might have come down quite recently. Most of the fallen trees are yellow poplars with a much smaller number of oaks. Most of the seedlings, though, growing on and around these fallen trees are yellow poplars. The shallow, rocky soil of this ridge undoubtedly was the cause these very numerous wind throws. The cycle of canopy disruption, light influx, and the consequential growth of seedlings favors the very rapidly growing, sun-loving yellow poplars over the oaks. It is possible that this “dynamic equilibrium” of wind throw disturbance and re-growth will result in a persisting, yellow poplar “climax community.”

On past hikes of the Grove Run Trail we have seen abundant birds. In particular many species of warblers were active in the dense forest understory vegetation. Today, though, there are no birds. We are far too late in the season for them. We heard what might have been a grouse chucking in the distance, but no warblers, no woodpeckers, and no towhees sang us along the trail. There were not even any crows raising commotions up in the trees!

The trail followed the curve of the hollow back into deeper and deeper forest. As we hiked up away from Grove Run, the trees grew closer and closer together. The forest and the trail got darker and quieter. The breeze faded away and the undergrowth supported more and more ferns. There are some very large yellow poplars here and increasingly abundant basswoods and red maples. There are also more downed trees that are surrounded by dense growths of yellow poplar and striped maple seedlings. We climbed along the slope on a laboriously carved side-slope trail that was cut all the way down into the underlying rock. There were many rocks and fallen trees all up the sides of the ravine. The uneven trail surface and the necessity of climbing over fallen tree trunks became more and more exaggerated as we go along! THIS was a hard 4 miles!

Michele and Deborah and Izzy walked out ahead of Rob and I. Soon we no longer could see or even hear them. The forest was dense and quiet and surprisingly dry. The surrounding creeks and rills were quiet and have hardly any trickles of water flowing in them. The trail was marked with red blazes. There were older, blue blazes, too, often on downed trees and sometimes painted over with a slap of red

Downed logs have been sawed and pushed off the path, and, very significantly, the stinging nettle and greenbrier has been cut back from the narrow path to make a three or four foot wide swath through the woods. Warm weather, to me, demands hiking shorts (and it was seventy degrees at the peak of our hike!), but the abundance of greenbrier and nettle on this trail might make one consider wearing long pants.

(continued next week!)

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Signs of Fall #7: Falling Leaves and Compost

Photo by D. Sillman

Photo by D. Sillman

I am waiting for the leaves to start to fall from my trees. It is an event that occurs at the same time each year (sometime after Columbus Day and before Halloween) but it always seems to be late in coming. I am not sure why I am always so eager to get on with the Fall, it just means that winter is closing in on us and that the color green is going away for five months!

There are so many “truths” and “myths” about tree leaves and what you need to do with them after they fall. One lawn product company stated on their web site that you need to rake up and dispose of these leaves or else “you will get rats in your yard.” Yeah, right. One of my neighbors piles his leaves in a great mass on top of his cleaned out garden and sets them on fire (or tries to set them on fire, anyway). The resulting smudgy, smoky mess smolders for hours and hours and triggers asthma in everyone for blocks around. One of my other neighbors runs her riding mower over and over her yard to scoop any stray leaves. I am not sure what she does with the mower bag’s contents. Another neighbor runs his leaf blower from August to November pushing his leaves to somewhere out of sight. His hearing must be destroyed by the din of that blower!

Photo by D. Sillman

Photo by D. Sillman

I usually rake up my leaves into several large, strategically located piles around my yard and leave them to nourish the worms and beetles and other invertebrates that will shred and grind them up into food for fungi and bacteria. In the old days my kids and I would jump in the leaves and further accelerate their fragmentation. Now I just rely on the worms to do the job with less noise and vigor (and much less fun, too!). Through the next spring and summer birds (especially the robins and the cardinals) peck at and dig around in the leaf piles looking for insect larvae and earthworms. These leaf piles are a great source of nutrition for these hunters and gleaners. By the time the next fall rolls around, the piles are remarkably reduced in size and are ready to be renewed by the freshly raked up leaves. One pile down in my orchard was kept in this yearly equilibrium for over twenty years. The rich, humus that accumulated at the bottom of the pile eventually was raked up and added to the soil of my tomato patch.

In a forest, the fallen leaves spread out in a thin layer over a broad area. Often earthworms start working on these leaves right away, pulling them into their middens and burrows, grinding them up with their muscular mouth-parts and gizzards, mixing them up with ingested soil, and defecating them out in nutrient rich, erosion resistant pellets. In soils without earthworms, numerous arthropods of many sizes begin to slowly chew away the leaf materials making a fine powder of organic residues enriched with bacteria. Both the worms and the arthropods are setting the table for the bacterial and fungi that then steadily work away at the less resistant molecules in the leaves. Like in my leaf piles, by the time the next fall comes around what’s left of the old leaves serves as the base for the new and the decomposition process grinds on.

Photo by D. Sillman

Photo by D. Sillman

Another fate of some of the leaves that fall in my yard is my household compost bin and pile. I collect a couple of trashcans of dry, freshly fallen red maple and apple leaves each fall and store them over the winter in my garage. When I charge up my composting bin in the spring, I throw in a good amount of the dry leaves to serve as a carbon source for the brewing compost and to give the dense, wet kitchen materials (usually dominated by coffee grounds!) some structure and air spaces. After some weeks in the bin (with regular turning and weekly additions of fresh kitchen materials) I shovel out some of the compost and transfer it to my nearby compost pile. Then I add some more leaves to the bin. By the end of the summer I have a rich pile of compost ready to be used in my garden or Deborah’s flower beds.

My leaf piles decompose more slowly than the managed compost piles primarily because of an innate nutrient imbalance in systems made up simply of leaves. There is too much carbon on these piles and not enough nitrogen. In the compost bin and pile the kitchen materials (especially all of those coffee grounds!) need the extra carbon of the leaves to balance out their decomposition. On the forest floor the richness of the chewing and shredding and burying organisms add nitrogen to the leaf materials via their feces and accelerate and balance the decomposition of leaves.

Natural decomposition is best thought of as an ensemble effort of an entire community of organisms where the products of one group of species becomes foods of another group of species until the food energy in the decomposing leaves is exhausted and only humus is left.

An old friend and mentor of mine, Daniel Dindal, summarized this community concept of composting into a very visual diagram that he called the “Food Web of a Compost Pile.” Please look over this marvelous work of art and science!

Drawing by D.L.Dindal

Drawing by D.L.Dindal

Up on campus we have started a composting system for the materials generated in the Café. We have three fence-sided compost bins into which we are putting kitchen and post-use “waste” materials. We are monitoring the rates and directions of the composting process, and I have three students who are conducting experiments on various stages of the composting system. Hopefully, in the spring we will have some rich compost to add to the flower beds and tree plantings around campus.

 

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Signs of Spring 6: Return of the Stink Bugs!

Photo by D.Sillman

Photo by D.Sillman

When I sit at my writing desk I spend as much time as possible looking out the window at the ongoing events in my backyard. A few days ago my view of a blue jay digging around in my compost pile (he was looking for, finding and eating fragments of egg shells!) was interrupted by the arrival of an organism that I haven’t seen since the end of June: the brown marmorated stink bug (which is frequently referred to as “BSMB”)!
One of these exotic invasive stink bugs attached itself onto the outside of my window screen and was walking around in a tight circle. When I looked back up a minute or so later, there were seven of them slow dancing around each other. They have been increasing in numbers ever since.

These stink bugs have spent the summer out in the surrounding vegetation (especially in my grape vines and apple trees, I am sure). They are the progeny of those stink bugs that survived their winter hibernations and managed to mate this past spring. Each mated female could have laid three hundred eggs which would have quickly hatched into the first of five immature, instar stages. These growing immature stink bugs spent the next two months feeding and growing and hiding out in the vegetation until they molted into their adult forms. They then started to look for a safe place to spend the upcoming winter.

Bill O’Hara (Dee’s husband) caught thousands of adult BMSB’s last fall. He used one liter, plastic, screw-top bottles with some soap solution in the bottom and took advantage of the typical escape behavior of the stink bug (they drop straight down when disturbed!) to induce them to fall into the bottle and the killing soap. Deborah and I had tried to be tolerant of the BMSB’s but their numbers finally overwhelmed even our ecological sensibilities. We used the “O’Hara method” this past spring as thousands of stink bugs emerged from their winter hibernaculae inside and around our house. We filled up several bottles a week with dead and dying stink bugs. When we had house guests we gave everyone their own stink bug bottle so that they could contribute to the correction of this exotic species invasion! We were the perfect hosts!

D. Lance Wikimedia Commons

D. Lance Wikimedia Commons

As I mentioned last year, the brown, marmorated stink bug (scientific name: Halyomorpha halys) is a relatively new sign of fall here in Western Pennsylvania. It is a native of northeast Asia (Japan, Korea, and China) and, apparently, is just as annoying there as it is here! Its use of human habitations as hibernation refuges, and its ability to communicate via pheromones and then aggregate in great numbers in some selected house, barn, porch, garage, or any other stink-bug-determined-suitable building makes their presence both in their native and also in their invasive regions impossible to ignore.

It is thought that this insect was first released into the United States in Allentown, PA in 1996. It apparently traveled from northeast Asia in a shipping container that was delivered either to the port of Philadelphia or Elizabeth, New Jersey and then trucked to Allentown. Five years later this new, alien, invasive species was recognized and identified by entomologists at Cornell University, but by then large populations were established throughout eastern Pennsylvania, New Jersey and New York. This insect has now spread to thirty-five states primarily in the eastern United States. It has very large populations in Pennsylvania, Maryland, Virginia, New York, New Jersey, Massachusetts, Delaware, Ohio, and North and South Carolina. It has also spread to California and Oregon allegedly in a car driven by a person traveling from Pennsylvania to California in 2005.

Here in Western Pennsylvania our first, massive fall outbreak of brown marmorated stink bugs was in 2010. Two of my students since then have gotten interested in the species and have done some research into their biology and ecology and even conducted some experiments to determine the species’ habitat selection preferences. I had hoped that their research would result in an effective stink bug trap, but we’re still working on that!

There is a consortium of university and government researchers who are looking into the basic ecology and biology of the brown marmorated stink bug. Their goal is to come up with effective control measures to stem this growing biological invasion. The group (called “Stop BMSB”) is funded by the US Dept. of Agriculture and includes fifty researchers from ten universities (including Penn State!). They are even conducting a “citizen’s science” survey this fall to try to determine some of the ecological and behavioral features of this bug. Their “2014 Great Stink Bug Count” asks homeowners to go out around their houses every day to determine the numbers and locations of any stink bugs that are present. If you are interested in participating, the URL for the group is www.stopbmsb.org. Maybe they can figure out what that better stink bug trap should be!

So far, the stink bugs are only on the outside of the house, but they will start to slip in soon. We are saving up screw top bottles. Drop by anytime for a lesson in the O’Hara technique!

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Signs of Fall #4: Leaf Changes

Photo by D. Sillman

Photo by D. Sillman

During most summers we hit a dry spell and several types of trees respond to the lack of water with leaf loss. The two, tall, skinny black locusts out on the back edge of my field lose half of their leaves in a typical July. Sudden breezes send swirling clouds of yellow leaflets down onto the lush, green grass, and the black locusts, which are typically one of the last trees to leaf out in the spring, stand mostly denuded but increasingly watertight against the summer drought. Cherry trees (black and sweet cherries) have the same response to drought but don’t shed their leaves quite as extensively as the locusts. I do remember, though, back in 2010 that the cherry trees along the Baker Trail lost at least thirty percent of their canopies in the dry summer. The trail surface was littered with bright, yellow leaflets all through July and August.

This summer both the locusts and the cherries have kept their leaves and are only just now starting to show any color changes or leaf losses. The abundant and remarkably steady rainfall this year (May through August we were three and half inches above average) is probably the reason: no water stress, no leaf changes or leaf losses until the seasonal cues kick in that push the deciduous trees into their winter physiologies.

Leaf loss is a purely “economic” decision for a tree. Leaves are the organs for photosynthesis and energy acquisition, but they also lose incredible quantities of water via transpiration. In the summer the black locusts and the cherries balance their needs for energy (for growth, reproduction, repair etc.) with the necessity of maintaining an acceptable water balance in their tissues and cells. In wet summers these trees can keep all of their leaves, fix abundant energy, and transpire water without damage. In dry summers, the limiting factor of water availability makes the tree give up some of its photosynthetic potential in order to maintain its water balance.

Photo by D. Sillman

Photo by D. Sillman

With the approaching winter the leaves for all deciduous trees are shed primarily to help the trees withstand the dry conditions of winter (also, the freezing of the water in the leaves would destroy their cellular structures and render the leaves useless as photosynthetic organs!). The types of trees that keep their leaves (the coniferous, or “evergreen” trees) do so by making a tougher, more water tight “leaf” (often very tightly pored needles that are wrapped in layers of waxes) and by some elegant physiological adaptations that go on inside the cells of the needles. This winter acclimation adaptation includes altering the chemical nature of the lipid molecules inside the cells (making the lipids more “unsaturated” and, therefore, more twisted and bent and thus less able to join together in a solid form (this significantly reduces the freezing temperature of the cells!). The cells also increase the cytoplasmic concentrations of these freeze-resistant lipids to amplify this antifreeze effect. The cells also add other solutes to their cytoplasm and break up some of their intracellular proteins into many smaller pieces. Both of these responses act to further decrease their freezing points.

The cells in these conifer needles also alter their plasma membranes to allow water to move across the membrane more freely. Then, as ice begins to form in the spaces around the cells, the water of cytoplasm is drawn out into the surrounding ice crystals and away from triggering possible freeze events inside the cell itself! An interesting side note is that the freezing of this surrounding liquid water to form ice releases a small amount of heat energy (the “heat of fusion”) and the cells of the leaf take advantage of this added heat to help maintain their internal liquidity!

Photo by D. Sillman

Photo by D. Sillman

When the deciduous trees get ready to shed their leaves in the fall, they undergo several well defined stages of change. First, in response to the duration of the dark period of the day reaching a critical length, the leaves begin to generate large numbers of cells right at the junction of the leaf’s stem and its branch. These cells greatly increase in number but not, at first, in their individual sizes. This layer of cells (the “abscission layer”) slowly starts to interfere with the flows of sugars out of the leaf and nutrients into the leaf. The lack of nutrients entering the leaf stops the synthesis of new chlorophyll molecules that are needed to replace the ones that wear out in the ongoing process of photosynthesis. Chlorophylls are, of course, the pigments that give plants their characteristic green colors. Initial cessation of chlorophyll production makes the leaves appear a bit paler and less intensely green than they were during the height of summer. Continued breakdown of the chlorophylls then starts to unmask the other pigments (the “accessory” pigments of photosynthesis: the carotinoids and xanthophylls) that had been present in the leaves all summer long). As these pigments are “revealed” the leaves then “turn” orange (from the carotinoids) or yellow (from the xanthophylls) before they finally fall. The accumulation of the sugars in the leaves also has an effect on eventual leaf color. These sugars stimulate the synthesis of anthocyanin pigments in the leaf. These pigments generate purple or bright red colors in the leaf and are thought (by W. D. Hamilton, the famous “Bill Hamilton” of biology!) to possibly protect the leaf (and particularly next year’s delicate leaf buds) from insect damage.

The deciduous trees in our area will be turning their autumnal colors very soon. The breakdown of the chlorophyll and the revealing of the accessory pigments is inevitable in our climate zone. In some years, though, the intensity of the reveled colors is much more extreme than in other years. The weather patterns of the fall and of the preceding spring and summer all contribute to the magnitude of the final color response.

Good, healthy abundant leaves are favored if the previous spring had adequate rainfall. A normal to wet summer will then insure that these leaves persisted intact through their active photosynthetic seasons. Warm, sunny autumn days combined with cool but not freezing autumn nights will maximize sugar production and anthocyanin synthesis in the leaves. These accumulating anthocyanins then give the leaves their brilliant red and crimson colors that seem to define a “good” color year in the forest!

The way this year is working out, we should have some very spectacular colors around us, and that is almost everyone’s favorite Sign of Fall!

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Signs of Fall #3: Feral Cats

Photo by Stavrolo, Wikimedia Commons

Photo by Stavrolo, Wikimedia Commons

A couple of weeks ago I received an email from my friend and fellow environmental enthusiast Patrick Kopnicky asking me for my opinion about feral cats and their impacts on their environments. Patrick and his wife Mardelle, as I have mentioned in several previous postings, head up the Environmental Learning Center and the Friends of Harrison Hills organization at Harrison Hills Park (Allegheny County). The feral cat discussion that he was involved in centered on not only the maintenance of some area feral cat colonies but the proposed establishment (and support) of new colonies in some of the county’s other public parks.

So let’s get some facts lined up about feral cats. A feral cat is defined as a domesticated cat (Felis catus (or Felis sylvestris catus , if you prefer)) that has returned to the wild. A feral cat is not the same as a “stray” cat. Stray cats are domesticated cats that are lost or abandoned although the kittens of stray cats can, indeed, grow up to be feral cats. Feral cats typically live in colonies of three to twenty-five individuals. They are wild animals that live by consuming human refuse or by hunting small mammals, reptiles and birds (and it is the magnitude of this hunting that is the crux of the problem concerning feral cat populations!). It is estimated that there may be up to ninety million feral cats in the United States alone!

Photo by S. Golemon, Wikimedia Commons

Photo by S. Golemon, Wikimedia Commons

Some feral cat colonies are tended by human caretakers. These volunteers provide food, shelter and a degree of protection for the colony. Attention to disease and parasite prevention is also a part of this colony maintenance. These tended feral cat colonies are made up of animals that have very similar levels of health, vigor, and expected life spans that are seen in populations of domesticated (“house pet”) cats. A notable exception to this concerns rates of disease and mortality in kittens which are much higher in feral cat colonies than in “housecat” cohorts.

Cats are not native to North America. Feral cats, then, by definition, are alien, exotic species in our ecosystems, and they can have impacts on small mammal, reptile and bird populations that are, potentially, quite significant. The Smithsonian Institution and U.S. Fish and Wildlife Service released a study recently in which they estimated that up to 3.7 billion birds and 20.7 billion mammals are killed by cats in the United States each year. “Un-owned” cats (strays, feral cats, and barn cats) kill three quarters of these small animals while “owned” housecats are responsible for the remainder of kills.

Photo by Brisbane City Council, Wikimedia Commons

Photo by Brisbane City Council, Wikimedia Commons

Cats of all definitions are marvelously efficient hunters. It is this ability to hunt and kill that led the World Conservation Union to list the cat as one of the world’s one hundred worst invasive species. I have found a number of specific studies that correlate the presence of cats to the decline in the populations of many types of birds. One of the most compelling papers that I read described a seabird chick survival study set on two of the smaller islands in the Hawaiian chain. The island that had established populations of cats had a sea bird chick survival rate of 13%, while the island that had no cats had a sea bird chick survival rate of 83%. Cats are very active hunters!

An observation closer to home concerning the impacts of feral cats comes from a conversation I had a few years ago with John and Marilou McNavage. They told me (and recently confirmed that this is still the situation) that no longer had any chipmunks around their house. They correlated the lack of chipmunks to the presence of a near-by feral cat colony.

Now I have written about my two cats in this blog on a number of occasions. Two years ago I proposed “Housecat Day” as a logical (and ecologically sound) February alternative to Groundhog Day, and, as I write this, one of my cats is laying half across my computer key board and is purring so loudly that is hard to keep a train of thought going.
In short, I love cats very much! I also acknowledge, though, that they are incredibly efficient predators!

The Audubon Society endorses the American Bird Conservancy’s “cats indoors” campaign. The Audubon web site states that “worldwide cats may have been involved in the extinction of more bird species than any other cause except habitat destruction.” The American Association for the Prevention of Cruelty to Animals (“ASPCA”) states on their web site that feral cats mostly hunt and kill rodents not birds. The Smithsonian data listed above agrees with that: a cat will on average kill 5.6 small mammals for every bird. But, although the kill ratio seems to favor rodent control, the numbers of birds killed each year is still staggeringly high!

The ASPCA estimates that a feral cat without human intervention has an expected life span of about two years if it survives its time as a kitten. With human intervention and management of a feral cat colony the expected life span of the cats is ten years. The ASPCA also states that if a feral cat colony is eradicated (i.e. the cats are killed) a “vacuum effect” occurs and cats from outside the colony come into the area and rapidly re-establish the colony. Killing feral cats, then, only opens up resources for other feral cats.

The ASPCA and many other animal welfare groups advocate programs of Trapping…Neutering…and Releasing (“TNR”) as the most effective way to deal with feral cat populations (a variation on the TNR is “TVHR” (Trap-Vasectomy-Hysterectomy-Release) and there are studies that compare the relative effectiveness of each type of population control program). These types of programs have been used extensively in the United States and also in Europe. How effective are they? Studies in North Carolina and Florida showed 36% declines in colony populations in TNR treated feral cat colonies after two years and an 85% decline after eleven years. In Rome (the feral cats of the Coliseum!) there was a 32% decline in treated feral cat populations after six years.

TNR (or TVHR) works. The treated feral cat colony slowly declines in numbers and should, if there are no additional cats added to its population via stray or abandoned animals, result in the eventual extinction of the colony.

So what do I think about feral cats? Having some of these small predators in our ecosystems actually might be a benefit (we have far too many white-footed mice out there for, example, and these mice are important intermediate hosts for the bacterium that causes Lyme disease. Increasing predator control of these mice might be a way to get our local Lyme epidemic under control!), but having ninety million of these small predators out in our ecosystems is excessive. I personally could not go out and trap and kill a cat, but we need to control their numbers (via TNR and TVHR?) and also deal with the source of the feral animals, irresponsible pet owners who do not spay or neuter their cats and allow them to reproduce so excessively that the numbers of abandoned pet cats that head off into feral existences explosively increases each year.

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Signs of Fall #2 American Chestnut Trees

Forest History Society

Forest History Society

The American chestnut was once one of the most abundant trees of the eastern United States. It is estimated that up until the early part of the Twentieth Century thirty percent of the trees in our eastern forests were American chestnuts. It was a tall, although not the tallest, tree in the forest. It was a tree of great, spreading mass with huge trunks ten or twelve feet diameter and thick, extending, shading branches (as in the poem “Under the spreading chestnut tree, the village Smithie stands…”) that covered over remarkably large areas (Photo of virgin American chestnut trees used with permission from the Forest History Society).

The American chestnut also produced large numbers of extremely palatable nuts that were eaten not only by squirrels, birds, deer, and bears but also humans. These nuts were produced in abundance every year (unlike oak trees, say, that make their acorns over multi-year, boom and bust cycles), and many animals relied on this predicable production of chestnuts to sustain their populations.

The wood of the chestnut was strong as oak but lighter and more easily worked. The bark yielded tannins for small scale leathering, and even the leaves were thought to have medicinal value. It was a beautiful shade tree and was widely preserved and planted in the growing towns and cities throughout America.

Public Domain Wikimedia Commons

Public Domain Wikimedia Commons

In 1904, though, the American chestnuts lining the roads and walkways of the Bronx Zoo began to sicken. Their leaves withered and great lesions appeared in their bark. The trees then died one by one. They were the first recorded casualties of Chestnut Blight epidemic that swept through the eastern United States. There is evidence that the fungus responsible for this disease had been present in the southern U.S. since the 1820’s, but the death of the chestnuts in New York set off alarms that reverberated through the country. By 1950, the American chestnut was for all intents and purposes “gone.” It was no longer a reliable source of nuts or timber. It was no longer a tree of size and majesty.

The species, though, persisted even in the face of this awful disease. The fungus is transported either via insects or on the wind and infects a tree through cracks in its bark. The fungal mycelia then grow into the cambium layer of the tree (the part of the tree’s vascular system that transports sugars and nutrients). The tree responds to the infection by sealing off the infected cambium with a dense callus tissue, but the fungus grows faster than the callus and eventually the tree loses its ability to transport nutrients and dies. The fungus, though, does not affect the tree’s roots. New chestnut trees are thus able to sprout from the still living roots and stumps. Depending upon the site density of the chestnut trees and the abundance of the fungal spores, these new sprouts may grow for ten to fifteen years before the fungal infection kills them. They can reach heights of fifteen to twenty feet and can even produce nuts for several years before they die back. This growth and die-back cycle has caused the American chestnut to become more of a tall shrub than a tree!

Photo by D. Sillman

Photo by D. Sillman

Out in my yard and field I have had a small number of American chestnuts scattered among the oak, maple, apple, crab apple, locust, and spruce trees. Several of these trees have gone through cycles of growth and die-back in the 25 years I have lived here. Three trees, though, clustered into a corner of my field have lasted more than twenty years and to date have shown no sign of the fungus. They have grown to heights of 30 to 35 feet and last year produced an abundance of chestnuts in their spiky encasing burrs. I had to fight the squirrels for my share.

There are two associations that are working hard to develop a blight resistant American chestnut tree. The American Chestnut Foundation (which includes Penn State) and The American Chestnut Research and Restoration Center (which is based at one of my alma maters, The State University of New York College of Environmental Science and Forestry). Through incredible time and effort the scientists of these groups are now very close to developing American chestnut tree strains that are not affected by the blight. The thought that we might soon be able to re-establish these magnificent (and ecologically significant) trees throughout our eastern forests is one of the most hopeful and exhilarating pieces of environmental news that I have heard in decades.

For us here in Western Pennsylvania the nearby Chestnut Ridge might one day live up to its historical name! Let’s hope that our grandchildren will someday see it covered once again with American chestnut trees!

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Signs of Fall #1: Dog Day Cicadas

M.Szklanny Wikimedia Commons

Photo by M.Szklanny Wikimedia Commons

We have just passed though the period of the year that the ancient Romans called the “dog days” in honor of the rising of the dog star, Sirius, with the morning sun. They thought that the heat and often unbearable humidity of the late summer and start of the fall were due to the combined powers of these two stars bearing down on the Earth. It was said to be a time of madness when wine soured and both man and beast hovered on the edges of despair and rage.

Things are not really that bad, though. The rage and despair common to both students and teachers right now has more to do with the resumption of classes than with the celestial alignments. One positive aspect of these hot, humid days, for me anyway, is the emergence of the annual cicadas (called the “dog day cicadas”). Their buzzing songs high up in the trees gives a pace and a pulse to the hazy days.

The dog day cicadas have life cycles that range from two to five years in length. A given area, though, will have cohorts that reach their adult stages in the late summer of any given year. So, as we go through any given August, we will be greeted by the nearly continuous singing of the “annual” cicadas.

These cicadas begin their lives as eggs deposited in clusters under the bark of small tree branches and twigs. In six to seven weeks the eggs hatch into tiny nymphs which drop to the ground and burrow into the soil. They will live in the soil, feeding primarily on the sap from tree roots (especially oaks, ashes, and maples) for the next two or more years. They grow and undergo molts and metamorphic changes until at last they are at last ready to molt into their adult forms. In the late summer they crawl up out of the soil and climb back up the trunks of the same trees that housed their eggs and whose roots have nourished them for so long. On the trunks and branches of these trees the cicadas carry out their last molt and are transformed into adults. The dry exoskeletons of their pre-adult stages can often be found empty but still clinging to the rough surface of the tree bark!

Male cicadas climb further up the tree and begin to sing. They have thin, exoskeleton membranes (called “tymbals”) on the sides of their abdomens that they can pull inwardly and then release to make a loud “click.” The males’ bodies are also quite hollow and act as amplifying, resonance chambers for the generated sounds. The purpose of the song is, of course, to attract females for mating. The mated females will then lay their cluster of eggs under the bark of a twig or branch of the tree and start the life cycle all over again.

Hhaithait  Wikimedia Commons

Photo by Hhaithait, Wikimedia Commons

Interestingly, the females have very solid, “meaty” bodies. They require more metabolic energy and more elaborate internal organs for the production of their eggs. One consequence of these morphological gender differences is that females are the preferred food for most cicada predators (including birds, squirrels, raccoons, and even people (many cultures include annual cicadas as a popular, seasonal food! Pictured to the left is a dish of deep fried cicadas from Shandong, China ).

A few days ago I watched a blue jay flying hard after a swerving and twisting cicada. The blue jay had his beak open poised to grab the tasty insect when it eluded him by flying into a cluster of spruce branches. The cicada got away (for the moment, anyway).

The soils under our trees are quite rich with developing cicada nymphs and each year a significant number of them mature and emerge. It is thought that the species reduces its overall losses to predation by concentrating its adult emergence into a very narrow time window. Their numbers overwhelm potential predators and then they suddenly disappear. This transient existence also keeps predators from specializing on the cicada adults.

Other cicada species (called the “periodic cicadas”) have taken this idea of transient, predator satiation even further by extending their soil dwelling, nymphal stages out to thirteen or even seventeen years! These periodic “locusts” are so rarely abundant and when out are in such incredible numbers that predatory species are not only overwhelmed (and satiated) but also are stymied from evolving any specialized feeding strategies.

Species of these annual cicadas can be found all around the world. I was listening to a radio report from Liberia this morning. The story was about the West African Ebola outbreak, but the reporter couldn’t help but mention the beauty of humming cicadas high up in the trees all around her. The gentle throbbing of the cicadas formed a background for the gruesome details of the story and felt, to me, like a momentary song of peace against the horrors of the on-going epidemic.

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Signs of Summer 14: Red and Grey Squirrels

Photo by D. Sillman

Photo by D. Sillman

My family has a long history of providing food for birds and, often unintentionally, other types of wildlife, too. My father had a dozen bird feeders around his house in Arkansas and spent many enjoyable years of his retirement feeding and watching the birds. He also had an ongoing war of wits and weapons with the army of grey squirrels that descended onto his feeders every day. He bought “squirrel-proof” birdfeeders and even designed a few squirrel-blocking devices of his own (he was a very talented engineer), but none of them were successful. If the squirrels could not bypass or evade the blockages, they simply tore them apart with their sharp, relentless teeth. The squirrels even got used to my father’s noise makers and pellet guns and effectively adapted to the occasional feeding disturbances by scattering up into the surrounding trees until the prevailing Ozark quiet returned.

At first, I continued my father’s war on squirrels when I finally matured enough to have a yard and spot for birdfeeders, but finally I surrendered to them. The more I made the feeders “squirrel-proof” the more the squirrels were likely to destroy the feeders, and my bird feeding budget was far too modest to keep up with constant “hardware” replacement!
So, I put seed on the ground and even started spreading shelled corn and, in the winter, peanuts around for the squirrels. I also started admiring the incredible acrobatics that the squirrels employed daily just to get some mouthfuls of sunflower seeds! Hanging by one foot from the bottom of feeder, doing free-hanging sit-ups to reach the seeds must be a hard way to eat, indeed! The amazing thing is that once I accepted and facilitated the squirrels’ feeding, the wonton destruction of my feeders stopped and an acceptable (and visually entertaining) staus quo was established.

Photo by D.Dewhurst (USFWS)

Photo by D.Dewhurst (USFWS)

My son, Joe, was home a few weeks ago for a summer visit. He lives in Seattle now and is doing all sorts of things about which I am extremely proud (I’d list them here, but then I would run out of space for the rest of the blog posting!). Anyway, Joe was watching our front feeders one morning and noticed that there were only grey squirrels gorging on the corn and sunflower seeds. He remembered that when he was younger there was a mix of grey and red squirrels at out feeders, and that we often had problems with the red squirrels getting into our attic and chewing through window screens to get to the stash of birdseed on the porch. Where, he wanted to know, did all of the red squirrels go?

Sometimes you need some distance from a place to see its changes. Joe’s five summers away from home gave him just the right perspective, and he was right about the red squirrels. There used to be a rotating pattern of grey and red squirrels at the feeders. Now the greys were seemingly there all day! Watching closely, though, we did see a single red squirrel at the feeder in the later afternoon.

Where did the red squirrels go?

They are also asking this question in Great Britain, but we have to be careful about linking the two discussions. It is another case of “common names” and “scientific names” that we talked about in a previous posting (“True Names”). The “red” squirrel in Great Britain is Sciurus vulgaris. The North American “red” squirrel is Tamasciurus hudsonens. Very different animals!

In Great Britain the alarming decline in their red squirrels is due to two main factors: loss of coniferous forests (due to logging, land clearing, and climate change), and the introduction (in 1876) of the North American grey squirrel (Sciurus carolinesis). The loss of coniferous forests removes the principle food source of the red squirrel, the seed-rich cones of pine and spruce trees. The small red squirrel is well adapted to finding and gathering these cones and seeds and is able to out-compete most other seed eaters in these ecosystems. Red squirrels can live in deciduous forests, too, and are able to eat “mast” sources like acorns. They do not, however, digest these acorns very efficiently and, thus, have less food energy to sustain their activities and their rates of reproduction.

The introduction of the North American eastern grey squirrel to Britain was intentional but not historically clearly explained. The excitement of having an “exotic” squirrel species in the woods around Henbury Park, Cheshire is a likely explanation, but these grey squirrels responded as exotic invasive often do by multiplying and spreading all through their new habitats. Grey squirrels are now found in most areas of Great Britain. The grey squirrel does not directly interfere with or harm the red squirrels (in fact there are more recorded examples of red squirrels chasing off larger (although usually immature) grey squirrels from feeding areas than vice-versa). The grey squirrel does, however, consume a great deal of the seed and mast resources in a deciduous forest ecosystem and thus leaves less and less food for the less efficient red squirrel. So, as deciduous forests increased in Great Britain, red squirrels found it harder and harder to “make a living,” and their numbers declined. Grey squirrels also carry a virus that causes the disease called “squirrel pox.” The British red squirrels were not as resistant to this virus as the invasive greys, so the virus took its toll on the red squirrel numbers.

But, this isn’t exactly what has happened back here in Apollo, Pennsylvania!

The North American red squirrel like the British red squirrel does favor coniferous forests and does thrive when cones and seeds are available. The decline in coniferous forests in North America, though, has not been as extensive as it has been in Great Britain (although the long term impacts of climate change are casting a foreboding shadow over these ecosystems!), and the overall numbers of red squirrels in North America does not seem to be declining. North American red squirrels are moving into deciduous forest habitats but, as has been observed in Great Britain, they end up with less energy available for life processes are compete poorly against the more mast-adapted grey squirrels. Maybe most significantly, North American red squirrels are not as vulnerable to squirrel pox as the British red squirrels.

So what happened in Apollo? There is a local decline in red squirrels, but this decrease is not a part of a continental decline in the species’ numbers. What has happened here over the past decade?

As I discussed in a previous post, nine years ago a series of thunderstorms blew across our hill here in Apollo and knocked down eight (of the original twelve), fifty year old spruce trees (a mix of Norway and Blue spruces). My theory is that the removal of these cone and seed producing trees decreased the carrying capacity of our property for red squirrels. So, instead of having dozens of red squirrels running around (and chewing their way into the attic and porch) we now have just a few red squirrels that feed on the much smaller number of cone producing spruces (and whatever birdseed that they can glean).

The other side of Joe’s observation (that the grey squirrels are so abundant) may be due to the growth of the new oaks trees where the spruces once stood. These trees, as I have also previously mentioned, are starting to produce acorns and are, thus, increasing the food resource base for the acorn-loving grey squirrels. Another possibility to explain the surge in the numbers of the grey squirrels is the recognized détente between them and me. All of those scoops of sunflower seeds, piles of shelled corn, and bags of peanuts must have an impact on the grey squirrel biomass!

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Signs of Summer 13: A Monarch Update and True Names

Photo by D. Sillman

Photo by D. Sillman

Monarch update! There have been several monarchs fluttering around my stand of milkweed plants. I am watching closely for caterpillars! These will be the larvae of the migrating butterflies, the ones that will fly all the way to Mexico. I am sure that one of the monarchs was a female, and I hope that she was laying eggs!

But, back to this week’s blog!

There are two kinds of names for biological organisms: common names and scientific names. Common names are familiar, usually generalized, and are easy to remember. Scientific names sound like Latin (because most of them are!), are hard to spell and pronounce, and are often very difficult to remember with any degree of precision. So why don’t we just use common names?

Let’s think of the common name “red worm.” That name fits two different species of earthworms, a roving “bristle worm” found in estuaries, a large nematode parasite found in herons and egrets (and a bunch of intermediate hosts, too), and a thin, freshwater sediment dwelling worm that is an EPA indicator species and often used as fish food. And, that’s just a partial list! So, if I wrote an essay about a “red worm” there would definitely be a high level of uncertainty about what organism I was discussing.

That’s where the Latinized, scientific names come in. While their spellings and pronunciations seem more than a bit strange, they always refer to just one type of organism! So if we say Eisenia foetidia or Lumbricus rubellus we know which type of “red worm” earthworm we are referring to. Or, if it’s Neris diversicolor, or Eustrongylides ignatus, then we know that we are talking about the errantial polychaete out in the estuary or the parasitic nematode in a blue heron. Or, if it’s Tubifex tubifex, we know that we’re talking lake or river sediment worms (or fish food).

There are lots of rules for writing scientific names. One very important one is that they are written in italics (or underlined). It’s like the title of a journal, or a book, or a web site in a bibliography, the italics sets the scientific name apart and emphasizes its singularity and importance. I’ll save the other rules for my biology students, but it is quite amazing how often they are ignored in newspapers, magazines, web sites, and sophomore biology research papers!

So, in my postings for this blog I have tried to be as precise as possible as to which species I was talking about. I try to include the scientific name in the post (and work very hard to spell it correctly!).

There are, though, two very different views of scientific names in biology, and these views seem to be based on a degree of appreciation of the importance of organisms in our view of life. It’s very interesting to realize that there are many biologists who really have had no training in or experience with actual, living organisms! These molecular biologists live in a world of proteins and nucleic acids and are exploring the depths of the reality of life well away from the requirements of looking at intact animals, plants, fungi, or even bacteria.

A great example of this new type of biologist is the person who led the team that sequenced the genome of the Neanderthals, Svante Paabo. In his book (Neanderthal Man: In Search of Lost Genomes) he refers to the instructions that he gives to his graduate students who use Latin, scientific names in their manuscripts, “I always delete the Latin and sometimes even snidely ask who they are trying to impress by saying Pan troglodytes instead of chimpanzee.” Now Paabo is a brilliant molecular biologist, and his book on the search for the Neanderthal genome is excellent, but his attitude toward zoology in general (he admits to not knowing that insects were animals) and taxonomy in particular (“a sterile, academic exercise”) needs some expansion.

Carl von Linne (Public Domain)(Wikimedia Commons)

Carl von Linne (Public Domain)(Wikimedia Commons)

In another book, The Species Seekers, by Richard Conniff the religious fervor of Carolus Linnaeus (to use the Latin version of his name!) and his students to both see and describe (and name) all of the species on Earth and to put them in a taxonomic order “for the greater glory of God” is vividly described. Many of Linnaeus’ students were so driven by this quest that they committed themselves to some of the far ranging voyages of exploration of the Eighteenth Century (and about half of them died on these expeditions!). Theirs was not a sterile exercise, but a flesh and blood drive to see and know!

Reality, as is usually the case, is somewhere in between these two extremes. We need to appreciate the detail and meaning of our scientific nomenclature without having to throw ourselves out to sea in leaky, wooden boats.

 

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Signs of Summer #12: Green Apples, Symbioses and the Gene Pool

Photo by D. Sillman

Photo by D. Sillman

Deborah and I were sitting out on our deck a few nights ago watching the flurry of activities that always precedes sunset. The main event of the evening involved two squirrels playing tag and chase up in one of the apple trees down in the orchard. They were bumping into each other, jumping over each other, and just having a great time. They shook the branches of the apple tree so hard with their acrobatics that a steady rain of tiny, green apples poured onto the ground. Standing under the apple tree were two fawns, and they were happily eating the sour, green apples as quickly as they fell.

Squirrels and deer interacting via the apple tree, who would have predicted that?

Ecology is the scientific study of the interactions going on in an ecosystem. These interactions can be between organisms and also between an organism and the non-living parts of its environment. A word that has grown in meaning over recent decades is “symbiosis.” At one time symbiosis meant two species that interacted and benefited each other, but now it defines all types of interactions between species. Symbiosis, then, is the essence of what is studied in ecology! Symbiosis is what was going on in and under our apple tree!

Looking out at my yard and field I can see many examples of symbioses. There are the young oak trees shading out the older spruce trees and grape vines wrapping up and over the crowns of the arbor vitae (both are examples of “perfect competition:” one species will “win” and one species will “lose”).

Photo by D. Sillman

Photo by D. Sillman

There are lichens growing on the rocks and also on a number of the tree trunks around the yard. Lichens are fungi that have algae living inside of their cells. The fungus relies on the algae to make sugars via photosynthesis, and the algae rely on the fungus to give it a place to live. Both organisms benefit from this interaction. It is a type of symbiosis called “mutualism.”

There is a cardinal’s nest up in the branches of one of the blue spruce trees. This interaction is a great benefit for the cardinal but has no real impact on the spruce. When one species is benefited in an interaction and the other is unaffected this sets up a symbiosis called “commensalism.”

On the ground beneath the spruce tree a robin pulls an earthworm out of my leaf pile. This is a symbiosis called “predation.” The robin benefits but the worm is harmed.

In any given time frame in an ecosystem a whole array of symbioses will occur. Out front in the yard a sharp-shinned hawk flies from her perch near the top of the spruce tree and dives down toward the birdfeeder. A blue jay perched in the lilac bush near the feeder sees the hawk coming and screeches an alarm. The feeder birds have an extra second or two to fly into the protection of the arbor vitae or scattered out across the street away from the hawk’s dive path. The hawk does not get a kill, and flies off chased out of the area by several blue jays including the one that raised the initial alarm.

The hawk gets negatively affected in all of these interactions (no supper and a blue jay chase squad ruining any chances for another attack!). The feeder birds are benefited in their interaction with the blue jay, but how does the hawk or the feeder birds in turn affect the blue jay? I would say that they didn’t affect him at all. Now, if there had been blue jay fledglings or some flock members at the feeder, then there would have been a self-benefit in sounding the alarm, but there weren’t. So, the interaction between the blue jay and the hawk generates harm to the hawk and no effect on the blue jay (a symbiosis called “amensalism”).

And, what about the observation that started this whole flow of ideas: the squirrels and fawns around the old apple tree? What kind of symbiosis is this? The fawns are definitely benefiting by the fresh abundance of apples, and the squirrels are neither harmed nor helped. So, it’s another example of commensalism! And what does the apple tree get out of this? Its fruit have seeds that are spread around the yard, the field, and the whole neighborhood in the feces of the deer (there is a lot of deer feces everywhere!). The apple tree, then, gets the chance to generate new apple trees far from the parental tree. The deer are benefited, the apple tree is benefited, so it’s another example of mutualism!

In an ecosystem there is a complex matrix of interactions that often influence each other in unexpected ways. The impact of predators on their prey species is a great example of this. Take our sharp-shinned hawk and the bird feeder community of small bird species. Sharp shinned hawks swooping in on a feeder are most likely to take the slowest, the least experienced, or the individuals that are physically impaired as their prey. The individuals most likely to survive the attack are the healthiest or the “most fit” individuals. The impact of a predator that is in balance with its prey populations, then, is improvement of the quality of the prey’s population! This has been observed in birds around suburban bird feeders, it has also been observed in the elk in Yellowstone after wolves were introduced, and in wildebeests in Tanzania in areas where a healthy population of lions are active!

I am glad that there are no lions lurking in my back yard, but it is good that there are small predators working the flocks and clusters of the various prey species out there. I like to think that my yard will have a very healthy, nimble, and fit chipmunk population because of the predation pressure exerted by my cat, Mazie, and that maybe my dog Izzy’s impact by chasing rabbits around the field each morning will be to make the rabbits more alert and somehow wilder. Izzy has never come close to catching any of the rabbits, of course, and probably wouldn’t know what to do with them if she ever did! But, if ever one of the rabbits was slow (or stupid) enough to be caught by a scatterbrain terrier who runs with her eyes closed, then the removal of that individual from the population would do nothing but improve the gene pool!

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