The Capacity to Carry

[Note: The following was first published in the September 2016 Alberta Outdoorsmen.]

Copyright © 2016 Don H. Meredith, All Rights Reserved.

We’ve seen the signs on the sides of trucks specifying the maximum weight the vehicle can handle safely. Likewise, certain containers label the maximum volume or weight they can transport safely. We’ve also seen signs in auditoriums or theatres expressing the maximum number of people the room can safely hold. These maximums are the “carrying capacities” of these chambers and vessels.

The concept of carrying capacity is also used in population biology, including wildlife biology, to describe the maximum number of a particular species a certain prescribed habitat can hold without affecting the health of that population or habitat. For example, 100 square kilometres of prairie habitat might have a carrying capacity of 400 white-tailed deer. Now, one must keep in mind we are talking about capacity here, the maximum number the habitat can support. The actual population figure is most likely significantly lower as a result of many factors.

yarded deer

When snow gets too deep, deer yard-up, only going to a portion of the food available in their winter habitat.

The amount of food in a habitat is the chief factor used to calculate carrying capacity. Knowing how much food a deer or moose requires each day and comparing that to the amount of browse available in winter or green vegetation in summer can give you a rough estimate of the gross carrying capacity of that particular environment for each species. But of course, other factors come into play. There might be two species of deer competing for the available food. Likewise, moose and other animals compete with deer for certain foods. All animals compete for space, particularly if certain food items are found in small patches.

Another factor might be snow depth. Even though a habitat might have lots of good winter food, the snow depth can cause deer to “yard-up” and only go to the few areas where the deer fed prior to the snow becoming too deep for travel to other areas. The result can be that many deer starve despite the carrying capacity being high.

Time of the year is also important in determining carrying capacity. A habitat can support many more individuals in the spring and summer when a lot more food is available, and indeed that is when young are born and populations increase. In winter, however, there is a lot less food available and populations are lower as a result of predation (hunting), migration or disease/starvation. Hence the ultimate carrying capacity of a habitat is the winter one.

So, at first glance the concept of carrying capacity can seem quite simple but in practice quite complicated. Where the concept gets intense is when a species-at-risk confronts dwindling habitat. A case in point would be our woodland caribou. Now, I know I harp on caribou a lot in this column, but I feel our treatment of woodland caribou represents our true attitude toward our environment; that is, the caribou are nice to have as long as they don’t get in the way of our perceived prosperity (ignoring the fact that the caribou and our environment are part of that prosperity). And that is how we let the A La Peche and Little Smoky caribou herds go to the edge of extinction: we drastically cut the capacity of their habitat to carry them. Resource extraction companies were allowed to mow down critical caribou winter habitat (contiguous old-growth forests). The new government has realized this shortcoming and is attempting to do something about it. But its draft range plan for the two herds falls far short.

well site construction

Resource development sites and their infrastructure eliminate habitat and reduce the carrying capacities of many species.

Instead of increasing the carrying capacity for the caribou as quickly as possible, it allows logging and energy development to continue in “historic” areas. In place of increasing capacity by allowing a significant amount of habitat to develop, the new plan calls for 1) the wolf cull to continue, 2) the numbers of moose, deer and elk to continue to be lowered, and 3) the construction of a 100 km2 “caribou rearing facility” to increase caribou numbers under protected conditions, releasing yearlings to the outside where little new habitat will be available for them. If you don’t increase the carrying capacity of these areas, what’s the point?

Perhaps it’s time to admit defeat with these two herds. If maintaining our rate of resource extraction in these areas is so important, perhaps we should write-off these herds, wait until actual new habitat develops in 50 or more years and then repopulate the caribou with introductions from the northern herds where more protection is to be provided. If we’re not going to be serious about protecting these animals and their habitats, why spend all this time, money and effort?

Of course, I know why. It has to do with the so-called optics of the situation. The government doesn’t want to go on record as abandoning their responsibilities to a species-at-risk. So, culling wolves and building a rearing facility shows they’re doing something even though it’s not near enough to bring these herds back from the brink.

Human Carrying Capacity
Discussions about carrying capacity, especially among population biologists, often go to the “elephant-in-the-room” that few other people wish to discuss; that is, human carrying capacity. Just how many people can Alberta, Canada or this old Earth carry? As many know, the human population of the earth exceeded 7 billion not too long ago; and that population continues to grow, as the number of human deaths does not keep up with the number of births. Despite what some economists would have us believe, the human population cannot grow forever. There is a limit.

Eminent biologist Edward O. Wilson wrote in his 2003 book, The Future of Life, that the gross human carrying capacity of the earth is around 10 billion people, provided that every bit of arable land on the planet is put into maximum agricultural production and all people become vegetarians (a lot more vegetarians can be supported than meat eaters). Of course, that’s not going to happen. Over the last few decades much cropland has been paved over, contaminated, and lost to climate change (e.g., desertification, floods, rising sea levels), and meat eating is an important component of many cultures.

As we approach or exceed our carrying capacity, life will not be that comfortable for more and more people. Indeed, we are already seeing this in terms of increases in worldwide poverty and violence, and the number of people migrating from distressed areas. So, what is a carrying capacity that will allow most people to live comfortable lives? Good question and there is much debate about the answer. Some believe it is 3.5 to 4 billion people, or the population of the earth back in the 1970s. Others believe it could be 5 to 7 billion people, provided we can maintain our current agricultural production.

One thing that is becoming obvious is that the denser our population becomes, the more people will see a degradation of their quality of life. We are already seeing that here in Alberta in terms of outdoor activities: fewer opportunities in fishing and hunting, overused wild regions, competition for space with resource extraction companies, and loss of species like the woodland caribou.

It need not all be gloom and doom. We can still make changes to ensure a better future for our children but we need governments to recognize the problems and make the hard decisions.

Comments are always welcome (below).

Interested in reading an award-winning outdoor adventure novel? Check out The Search for Grizzly One and Dog Runner.


About Don Meredith

I am a writer and biologist living in Alberta, Canada. I wrote a monthly column for the Alberta Outdoorsmen magazine, and have published articles for several other magazines.
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