Why Do Dogs Eat Grass?

Why do dogs eat grass?

It's a common question, but in asking the question, an assumption is revealed.

The assumption is that dogs are not supposed to eat grass.

After all, no one asks why we humans eat chicken, corn on the cob, fish, or strawberries.

The short answer is that dogs eat grass because it tastes good and it provides some nutrition.

It is not a sign of worms, an upset stomach, or any kind of nutritional deficit.

That's the short answer.

Now let's look at the question a bit deeper.

Do wolves, fox, coyotes, and dingoes, also eat vegetable matter?

The answer is "yes."

Wolf biologist David Mech notes that grass appears in 14-43% of all wolf scat found in North America and Eurasia. Plant material in fox and coyote scat, including grass, is so common as to be unremarkable.

Leopards, jaguars, mountain lions, and bobcats also eat surprising amounts of grass. A sample of 215 leopard scats collected in the Tai National Forest of the Ivory Coast, for example, found 17% had a considerable amount of grassy vegetable matter.

Bears too eat a lot of plant material. Though classified as the largest carnivores in the world, bears eat more vegetable matter in their diet than flesh, and grass is a major food source.

So why do "carnivores" so often eat grass?

For the same reason you and I eat most of the foods we eat; it tastes good.

Of course the other answer is that it is maladaptive for them not to do so.

Let's explore that idea a bit more.

Specialization in food sources is a terrific idea so long as the world stays exactly the same, day in and day out, season after season, year in and year out.

But, the world is both temperamental and unreliable.

Crippling winters, blistering summers, and poorly timed rains can decimate populations of prey species.

Disease can wipe out herds, migration routes can change without warming, and new species can invade.

Water holes may dry up, salt licks may disappear, and predators can injure themselves in the chase.

And yet every few days, a predator must eat.

And that's the problem: The chain of life is so easily snapped.

For a meat-eating predator, the weakest link is the absence of ready prey, easily caught, day in and day out, in good health and bad, dry season and wet, winter and summer, year after year.

And so wolves, coyotes, dingoes, bears, lions, bobcats and jaguars have all evolved to eat plants, as well as flesh -- a way of "hedging the bet" for a few days against the vicissitudes of life.

Yes these animals will try to bring down a deer- or rabbit-sized meal if they can. But if they cannot, then they will try to catch a few rats or mice, a lizard or a snake, a frog or a turtle.

And if push comes to shove, there's always grasshoppers, crickets, and verdant grass along the creek. And it does not hurt at all that some of that grass actually tastes pretty good!
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Lion Grooming

Like so many things, lion grooming looks very easy and relaxed from the cheap seats, same as sword swallowing, but if you intend to try this at home, bring a gallon of iodine as you may need it at the end!
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Islands of Wolves, Rats, Lions and Dogs

Isle Royale, Michigan.  An island of wolves.

In the real world, population bottlenecks are not always quite as big a problem as some people imagine, nor are they quite as easy to correct as some people hope. 

If that sounds like two statements in direct opposition, then you have grasped a core message of this post, which is that not all animal populations are the same, that few real-world cases line up squarely with simple theory, and that there are multiple facets to both genetic isolation and genetic rescue.

In order to understand a little more, let's look at four real-world animal populations:

Imagine a pregnant rat jumps ship on to a large island that is 200 square miles in size.  The population of rats multiplies very rapidly but without any apparent long term problems due to inbreeding.  How is that possible?  Answer:  With rats, massive population numbers within a short period of time are possible, and a mid-sized island of 200 square miles (over 259,000 acres) can easily hold a million rats.  In this situation, genetic drift and mutation will eventually result in a population with little or no obvious genetic dysfunction.  On an island with 1,000,000 rats, in which each rat lives for a year or so, a 100-year old population of theoretically "inbred" rats will have very low coefficients of inbreeding, no inbreeding depression, and no discernible early mortality due to genetic weakness.  To be clear, this is not a theory; rats have colonized almost every island in the world exactly this way.

Now imagine that a pregnant wolf lands on an island that is 200 square miles in size.  The wolf whelps five pups, and the pups interbreed and the population grows for a time until it hits some sort of food-availability threshold.  A boreal island that is 200 square miles in size and with a sizable moose population can, for a while, feed a population of 50 wolves, but eventually that population can be expected to collapse down to as few as dozen individuals before it rises again and falls again due to the vagaries of disease and weather which will impact prey species such as moose, deer and rabbit.  After 75 years, the population of wolves on this island will be very inbred, and infecundity and disease will be common.  The reason for this is simple:  wolves typically live between six or seven years in the wild, and the smaller number of wolves on the island, combined with the smaller number of generations, means that there will be very little room for genetic drift or mutation.  Is is possible to import a single individual wolf to achieve a "genetic rescue" of this heavily inbred wolf population?  A single wolf, sadly, is not likely to do it.  The reason for this is simple:  the small number of wolves on the island (a population of 24, on average) and their high rate of infecundity due to inbreeding, means that the genes of the new male wolf will quickly dominate.  Inbreeding will then continue as before.  Though there may be a short temporal  improvement in population health, that may not be observed if there is a counter-balancing downtick in food sources occurring at the same time.  To be clear, this scenario is not one I have made up; it appears this is exactly what happened with the wolves on Isle Royale, Michigan.

Now imagine a large population of lions that has been reduced by hunting to just 30 individuals living on an isolated isthmus 200 square miles in size.  The population is so isolated that the coefficients of inbreeding within the lion population begin to rise, and a rise of infecundity and an increase in genetic defect is feared.   The good news, however, is that this isthmus is not at carrying capacity for lion, and so eight completely unrelated female lions are imported from another country more than 1,000 miles away -- a 25% population boost representing a massive increase in genetic diversity.  What happens?   A rather significant improvement in species health and fecundity seems to occur, and the lions begin colonizing more space on the isthmus.  Why did this genetic rescue work?  Well, for one thing, the original 30-lion population was more diverse than it at first appeared.  Remember that these 30 lions did not actually spring from a closed registry of two individuals, but were the remainder left from a massive population that once numbered scores of thousands.  While inbreeding to failure appeared to threaten this lion population, the actual genetic diversity beating under the hood was likely to be quite a bit more expansive than a purely mathematical population model would suggest.  Factor in the relative size of the genetic infusion coming from the other side of the country, and the ground is set up for a successful genetic rescue.  To be clear, this scenario is not one I have made up; this is exactly what happened with the lions of Southern Florida (aka, the Eastern Puma, Florida Panther, or Eastern Mountain Lion).

Now imagine a pair of dogs that are mated and their pups are then inbred to each other for 25 years at which time another dog is added to the population and the result is further inbred for another 40 years.  The result is a population of about 180 potential breeding dogs (30 dogs are born a year, and not all dogs will be bred) which have a Coefficient of Inbreeding of 80 percent.  What would it take to have a successful genetic rescue here?  If we use the Florida Panther model as a guide, we would need to see an addition of 45 new dogs to the gene pool.  Would the addition of  one or two dogs be enough to turn the tide?   Probably not.   The addition of only a handful of dogs in a show-breed situation, where dominant sire selection will continue unabated, will not provide the genetic fix needed to turn things around.  Remember we are starting here with a very high COI, and the public demand for these dogs is apparently quite low; this is a breed that hits its consumer "carrying capacity" with just 30 to 40 puppies a year.  To be clear, this scenario is not one I have made up; the dog presented here is the Cesky terrier, a breed that has never been very popular.

So what's the point? 
 
The point is this:  the issues associated with population bottle necks are not quite as simple as some imagine.  Yes, the relative size of the founding population matters, but so too does the genetic health of the founding population, the total number of animals bred, the number of generations it took for the population to achieve a large size, and whether the animal in question was breeding randomly or within an organized scheme that encouraged (or discouraged) genetic diversity.

Consider, for a moment, a dog breed that was drawn into a closed registry 120 years ago with 150 dogs in its foundation registry.  The breed grew rather quickly so that after 40 years it had a worldwide population of 125,000 dogs; a population it has maintained for the last 80 years.  Coefficients of inbreeding in the modern population of this dog will, on the whole, be quite low, and though the apparent "effective population size" may have dropped from 150 dogs to 80 dogs due to dominant sire selection, effective population size is quite a meaningless number when you have bred well north of 1 million dogs over a 100-year span.  In a situation like this diversity is not destroyed over time, but created through the sheer beat of numbers over vast distances.
 
Of course, there is another factor in all this, and it is an important one, and one that is too often left out.

You see, in the world of Kennel Club dogs there has always been a little "pedigree leakage."  

Pedigree leakage may be small or even nonexistent in a very rare breed where everyone knows everyone else, and the dog in question is likely to look a bit odd or extreme and not have an obvious analog in another breed or cross-breed.

But what of the other more popular breeds, where there are a lot more dogs in the wind, and only a small number are likely to ever see the inside of a show ring, and analogs exist all over? 

In a situation like this, instead of a reduction in effective population size, there may actually be a little growth! 

After all, a Labrador Retriever with five-generation pedigree papers from the AKC may, in fact, have a Flat-coated sire, or even be whelped by a cross-bred dog of "pedigree unknown." 

A Miniature Poodle may have a little Maltese coursing through its veins only a generation or two back. 

And what does it matter?  Not a whit if the cross was a sound one and did not add a new or heavier genetic load to the mix.

The bottom line is that there is more to population genetics than any one number, and while it's important to be worried, and to take action to increase breed genetic diversity, it's equally important to recognize that one can fall in love with less than robust genetic theory and falsely specific numbers just as easily as one can fall in love with cocked up doggy histories and the romance of breed purity.   In the end, population science and genetics is about more than one number; it's about a small stack of numbers meeting a real gene pool coursing through the flesh and blood of a real population that is living in a real environment (whether wild or artificial, free-feeding or subsidized).

Yes, let us work to increase diversity, but let us also look towards Mother Nature as well. 

Remember that while Mother Nature abhors closed breed pools, she also manages to work out solutions for most of those that wash up as single or paired animals on tropical islands or are introduced to foreign lands.  Observe the birds in the park.  How many Starlings did we start off with here in America?  How many English Sparrows?  How many Red Fox?   How many wolves in Yellowstone?  They are clearly thriving.  How is that possible?  And, of course, the answer is that they colonized in vast numbers over a vast space of land, and in the slow beat of numbers and space they managed forge their own genetic health.
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Does Your Local Zoo Have a Dirty Little Secret?

One of the big stories in the news today is that a depressed and distressed owner of a private zoo in Ohio opened up all the cages to release his bears, lions, tigers, wolves, and other animals on the public.... just before he shot himself in the head.

The call is already going out to ban all private zoos and only salute the public ones.

Not said: much of the stock in those private zoos can be traced back to the breeding and dumping of animals by public zoos and semi-public places like Busch Gardens.

As I noted in a post a few years ago:

Zoos routinely over-breed animals because tiger cubs and baby zebras boost attendance and generate profits. Cute baby animals quickly grow up, however, and that's a problem. It turns out that the world has more caged lions, tigers and zebras than it knows what to do with.

Now to be clear, zoos do not trumpet their actions and their economics. Instead, they trumpet the fact that they have a Species Survival Plan (SSP) which calls for sophisticated program of maintaining "valuable gene pools" so that endangered species "may be preserved for future generations through captive breeding."

O.K. True enough, as far as that goes. But every "Species Survival Plan" produces surplus animals. What happens to them?

Some of these undiscussed animals are moved to other public zoos, but some are sold off to private zoos where they may end up in backyard menageries or even canned hunts after passing through the hands of third-party dealers later on.

This is the dirty little secret of the zoo business, and it's not just a phenomenon of the private zoos, but the public ones too.

To be fair, the Association of Zoos and Aquariums is now working hard to stop over breeding of zoo animals and the sale of excess animals to such venues as circuses. But this push is pretty new. Most of the backyard tigers, lions and Great Apes we have in America today are just one or two generations removed from commercial zoo and circus stock.

There's another problem with getting rid of private zoos in America: they hold a hell of a lot of animals representing a fair amount of genetic diversity. As this article notes:

More than 8,000 tigers live in the U.S., far more than live in the wild globally. Of the 8,000, only a few hundred live in accredited zoos. The rest live in backyards.

So, to put a point on it, getting rid of backyard tigers, in the absence of thousands of more zoos in the United States and around the world, is to green light the killing of more tigers in America than exist in the wild in all the rest of the world.

Are we ready to salute that?  Why? 

Some claim that many of the exotics in private hands are not "pure" subspecies of one type or another, and so they have no value and should be euthanized.

But why is one tiger that has 10% Sumatran blood running through it deemed to be worthless, while another tiger with a "pure" gene stock (cough, cough) is deemed to be priceless? Whiskey, tango, foxtrot. Subspecies are not species, and Mother Nature has no problem with out crosses and diversity, so why are we listening to the people embracing mass-death solutions and forced sterilization for animals that have slightly more diverse pedigrees? Does the Indian tiger with a little Sumatran blood kill a Sambar any differently than a 100% pure-blood animal? If the tigers are not finicky about patrolling their gene pool, and the Sambar are pretty certain it is all the same, and the offspring are all fertile, then isn't this all "theory trumping reality?"

And what about those public zoos? Are they really running picture perfect shops as far as animal welfare?

Nope, not a chance.

Nor are all the private zoos horror shows. Many have caring owners and some have very decent set ups. The notion that taxpayer-funded always equals "good," while privately-funded always equals "bad" is simply not true in the world of animals.

So what's the solution?  

Surely between "shoot them all dead" and "anyone should be able to get one," there is a place for mandatory training, mandatory licensing, mandatory insurance, mandatory inspection, and mandatory cash bonds with some animals still being held in private hands?

The good news is that this seems to be the direction that the world is going.

Will there be a long period of transition until we get there?

Sure.  Elephants live a long time, and so too do many of the big cats and large ungulates.

The transition will not be smooth, and a lot of private menagerie owners and zoo keepers are going to bitch and moan about the cost and the regulation.  I am OK with that. 

But should we ban all private ownership of all exotics and rush 8,000 tigers to their death prematurely because of this sad case in Ohio?  

Is the proper response to this tragedy to compound senseless death with more senseless death?




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Deer v. Lion at National Zoo in D.C.

A wild deer from Rock Creek Park jumped into the lion exhibit at the National Zoo on Sunday afternoon.

One word: maladaptive.

A female lion went after the deer, mashed it to the ground, and then let it go. The deer dived into the moat and got got away. Zoo officials cleared visitors from the area and rescued the deer, but its injuries were too serious and it was euthanized.

• Related Posts
  ** The Missing Birds of Rock Creek Park
  ** The U.S. Now Has More Lions Than Africa
  ** Deer are Designing Forests
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How to Tame a Lion Poisoner

Link

Over the course of the last 20 years, Africa's lion population has crashed from 200,000 to 30,000, and the numbers continue to drop fast.

One of the big reasons is that an American company -- FMC -- has sold a highly toxic, tasteless pesticide to African countries where herders are using it to indiscriminately wipe out all predators -- lions, cheetahas, leopards, hyenhas, etc.

Though FMC says it no longer sells Furadan (carbofuran) in Kenya, and is now trying to buy up stock that may still be on shelves, FMC has not said it will stop selling the drug in neighboring African countries or around the world.

To be clear, Furadan is such a horrible chemical that in July 2008, the Environmental Protection Agency initiated action to ban the chemical's use in the U.S. as it presented unacceptable dietary risks, especially to children, from consuming food or water with carbofuran residue in it or on it.

Want to help take action?

Send an email to Jim Fitzwater, FMC's corporate flak at james.fitzwater@fmc.com or call him directly at 215.299.6633.

Your message does not have to be long, and it does not help to be rude. It is enough to simply say that you want FMC to stop making this toxic poison, and that you are passing on this notice to 20 of your friends.

Make some heat, and maybe FMC will yet see the light!

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