How a customer in a shopping mall is like a predator-prey system

(A dead caribou calf that was picked off by a J.C. Penney merchant as the calf was passing by the front of the store.)

I spent a thoroughly enjoyable, scintillating, and memorable 3 hours walking around the Crossgates Mall in Albany, NY yesterday (can you hear the sarcasm in my voice?).   As we strolled leisurely along (with me complaining bitterly about wasting my life here, and telling my wife that she is not the boss of me), I felt exactly as I did as a kid when I went to one of those old-time carnivals.  As you walked down the midway, you would invariably pass a "barker" who tried to get you to come inside, and spend a hard-earned dime to see the 2-headed cow, or snake boy, or some other bizarre freak of nature.  I'm always on the lookout for blog topics, so I tried to open my mind and absorb as much of the inane trivia as I could in this super-stimulating environment of lights and sounds and food courts.  And then, as I passed in front of the 177th store out of the 250 shops and restaurants in this giant shopping center, the topic for today's blog came to me.

In behavioral ecology there is a concept called "swamping the predator".  The idea goes like this. In any predator-prey system, there is an evolutionary race going on between the predator that wants to capture the prey and eat it, and the prey that is trying not to be captured and eaten.  One evolutionary strategy for the prey is to give birth to their babies within a short, circumscribed period of time.  The result is that these easy-to-capture baby prey are born en masse; predators can capture them easily, but predators can only capture and eat so many babies during any given day or week.  In addition, with every passing day, the babies are growing larger and faster and, therefore, they soon escape the "window of vulnerability" to the predators.  The result is that a smaller percentage of prey are killed than if they were dribbled out over a longer period of time.  That is, the prey have swamped the predator with overabundance during a short period of time, with the result that more prey survive overall than they would if they had been born a little at a time over a longer period of time.  This model is exactly what caribou do in the presence of wolves.  Any female who gives birth outside of the high-birth period has a much higher probability of losing their calf to wolves than if they had enjoyed the relative protection of the high synchronicity of births by all the other females.

Back to the mall.  The shops are the predators and the people walking around the mall are prey.  And we are susceptible prey.  After all, why would we be meandering around that place like a baby caribou if we did not have cash or credit cards in our pockets and some tendency to want to use some of it?  The shop owners know that and we know that they know it.  And if you are carrying packages from purchases already made, it is like the wolf seeing a limping calf. You are dead meat.  Other merchants know by this sign that you are vulnerable, that you have already deposited your big toe in Victoria's Secret, and that you will likely leave a finger with them next.  We can be consumed by many predators on a single day, at least until we run completely out of money. Bits and pieces of us can be consumed by the insatiable appetite of a dozen different stores in an afternoon.

But this system is different than the wolf-caribou system in a couple of important ways.  First, in the mall, the predator is not mobile; the shop stays where it is located within that building.  It can not run us down and rip the dollars from our pants and purses.  Similarly, we can choose NOT to be prey as long as we want; we can choose NEVER to be prey if that suits us.  So the weapon of the predator in this system is their ability to entice us into their lair with music, sexy displays of underwear in their store window, attractive fragrances emanating from their front door, and well-dressed and attractive young people working as clerks inside.  Once inside, they rely on the persuasiveness of those clerks, large 25% OFF signs next to their merchandise, and cash-back offers if you use a plastic card issued by them.  Second, most of us will be prey, sooner or later, but we get to choose exactly who our predator will be--The Gap, Ruby Tuesday, Best Buy.  And the third difference between the wolf/caribou system and that of the shopping mall/consumer system is this.  When we use our credit card, we are not being eaten today, but we are promising we will allow ourselves to be devoured within 30 days, when the bill comes due.  As Wimpy used to say, "I would gladly pay you Tuesday for a hamburger today."

It is said that the holiday season is a season of giving.  As a behavioral ecologist, I see it as a killing field.  I see the frozen tundra, with dead caribou littering the horizon as far as the eye can see.  I see white snow with random scrawling of red blood dripped around a decorated pine tree.  I hear the howling of wolves and the bleating of baby caribou, and the entire scene scares me to death.

Cats: our feline friends, or are they?

(Cat eating a bird it has just killed.)

About a decade ago I had a student in my Conservation Biology class named Scott Boomer. We were discussing the problem of non-native organisms that week, and Scott told me he had kept some interesting records on the behavior of three cats that he and his wife had at that time. The cats (one male, two females, and all neutered) had access to food and water in Scott’s apartment around the clock. The three natural predators had the habit of capturing prey outside and bringing it back to Scott, often dropping it at his feet or putting it in their bathtub. Scott is a biologist and he was able to identify all the prey items returned to his apartment over a 2-year period.

The list included:

Mammals: 5 deer mice, 2 woodland jumping mice, 5 Eastern chipmunks, 4 meadow voles, 1 gray squirrel, 6 star-nosed moles, 4 short-tailed shrews, 1 cinereus shrew, 2 little brown bats, 1 Eastern cottontail

Amphibians: 2 green frogs

Reptiles: 1 Eastern painted turtle, 3 Eastern garter snakes

Birds: 3 common yellowthroats, 2 black-capped chickadees, 1 house wren

Total: 43 animals

Now, there are about 90 million cats in the U.S., according to the 2005-2006 National Pet Owners Survey. A certain percentage of those cats never go outside. But anyway you run the numbers, the collective mortality on native wildlife by U.S. cats must total millions of individuals of dozens of species. In some places in the world, feral cats, those that have gone completely wild, are responsible for the demise of rare species of birds. The Stephens Island wren (a flightless species) in New Zealand went extinct in the late 1800’s due to the island’s cats, or so that story goes. The wedge-tailed shearwater in Hawaii is also impacted by cats. Conservation biologists actively control cats (as well as non-native rats, mongoose, etc.) in such places today, especially on oceanic islands.

We hear a lot these days about our “ecological footprint”, or the impact that a human has on the earth’s natural resources and ecosystems. I doubt that our pet ownership is included in these calculations. Remember that I tend to think in terms of quantity and quality of habitat for biodiversity. I usually think of our “habitat footprint” as defined by the boundaries of our house and the lawn surrounding it. But the effect of that living space penetrates further depending on the chemicals we use on the property, how far away we or our children trounce on the environment, and the influence of our pets, of which cats are probably the worst offenders. There are zones of concentric circles beginning with the epicenter of the house itself, which include areas of decreasing influence on the fauna and flora that is there now, as one moves respectively outward. Cats probably have an effect in each of those zones, but they may represent the only threat in the outermost circle, which is perhaps several hundred meters from the edge of the house.

In fact, last year someone built a new house about 100 meters from the edge of my woodlot. For the past few months, I have had two cats roaming my property that I am sure live at that house. I have not had cats on my property in 20 years. And so it goes. We increase our collective ecological footprint, we chip away at the quantity and quality of wildlife habitat and, in my opinion, the quality of life is diminished just a little bit more---again.

In these few paragraphs I wanted to increase your awareness of an idea that perhaps you have not thought much about--- how that lovable pet cat of yours is possibly reducing the biological diversity in your neighborhood. I do not intend to explore a detailed solution to this problem, although attaching a simple bell to your outdoor cat would probably reduce its kill rate. You might be thinking that cats kill organisms that people do not like very much anyway, so what the heck. But I can assure you that every one of those species killed by Scott’s cats represents a unique and interesting biological story. Remember that not so long ago, nearly everyone thought it was fine to shoot, trap, or poison wolves, mountain lions, and eagles.