Fur Management

Population Dynamics

A study of population dynamics helps explain why wildlife populations must be managed and how.

A population is a group of animals of the same kind that occupy a particular area. Dynamics refers to motion or change from within. Population dynamics, therefore, means the changes that occur in a population over time. The study of population dynamics helps explain why wildlife populations must be managed and how.

Two major factors affect the population dynamics of wildlife: the birth rate and the death rate.

Birth Rate
Most wildlife species have a high birth rate. The smaller, short-lived species of wildlife have higher birth rates than the larger, long-lived species. The most important factors that affect the birth rate are:

  • age at which breeding begins
  • number of young per birth or litter
  • number of births or litters per year

Death Rate
The death rate of most wildlife species is high. The smaller species of wildlife have higher death rates than the larger species. The principal factors affecting the death rate are:

  • availability of food and cover
  • predation
  • weather
  • human activities
  • disease and parasites

Note that these are generally the same factors discussed earlier in relation to limiting the carrying capacity of a habitat.

If the birth rate is greater than the death rate, wildlife numbers increase. If the death rate is greater than the birth rate, wildlife numbers decrease. When the birth and death rates are equal, population numbers do not change. However, populations of wildlife are not static – they rise and fall over time, sometimes by large amounts, other times by small amounts.

Seasonal Changes – Population Growth and Decline
Wildlife has a tremendous capacity for reproducing and increasing its numbers. But this growth cannot continue indefinitely. There is always some factor – usually food or cover – that becomes limiting. Let’s look at a situation that occurs each year in wildlife populations.

In the spring, the breeding stock (animals needed for breeding to replenish the population) begin having their young. The population reaches its peak in the spring and summer. At that time, the population numbers have become greater than the carrying capacity of the habitat. The population then begins to decline because the habitat cannot support the excess animals. The decline continues through the spring of the following year.

Though many animals will die over the spring, summer and fall, winter is the period of heaviest mortality.

In winter, the ability of habitat to support a large number of animals is reduced, often drastically. Those animals in excess of the number that the habitat can then support (carrying capacity) become surplus and may be lost to starvation and other factors. This cycle occurs every year. Although the peaks in population numbers may vary according to the birth and death rates, the shape of the curve is the same for all species of wildlife. This annual mortality is part of the natural cycle. All that nature requires is that a sufficient number of animals – the breeding stock – survive until the spring, then the cycle starts over.

Surplus wildlife cannot be stockpiled and saved for future use. A surplus is either used by man or recycled in its natural system.

The average life span of most wildlife species is less than three years. All forms of wildlife are living creatures that will inevitably die and be removed from the population. This loss is replaced by the birth and addition of new individuals to the population.

Man’s ability to control and manipulate both the rate of depletion and the factors that influence the rate of production of a wildlife population forms the basis for wildlife management.

Game Management and Conservation
Using the basic principles of ecology, wildlife managers attempt to maintain and manage wildlife populations. Wildlife is one of our valuable resources, and in this context wildlife managers are really resource managers.

Natural resources are those resources supplied to us by nature, for example, plants, water, soil, minerals and wildlife.

Some resources, once drawn upon and used, are then no longer available to us. Coal, gas and oil are examples of natural resources than cannot be replenished or replaced once they have been used. They are called “non-renewable” resources. Other kinds of natural resources, if managed properly, can replenish themselves through natural means and thus continue to remain available for future use. These resources, such as vegetation and wildlife, are called “renewable resources.”

Game Management
Game management can be thought of as a field of “applied ecology” and is in many respects very similar to the practice of agriculture or forestry. A forester plants trees, allows them to grow and eventually harvests them. A rancher must continually remove and market animals from his herd to keep it within the carrying capacity of the range he has available for grazing. If he did not do this, the yearly addition of

calves to the herd would increase the number of animals to a point beyond the capacity of the land to support them.

Similarly, game managers try to control game populations. A sufficiently high breeding population is maintained to maximize the reproductive potential of that population. As with the rancher, there is a need to remove or harvest a portion of that population to keep it within the ability of the habitat available to support it.

In essence, game manager “farm” certain species of wildlife just as the rancher manages his herds. Through hunting and trapping, the wildlife manager crops portions of game populations just as the rancher removes and markets the surplus portion of his herd.

66 Years of Wildlife Management in North America

This article reprinted from the BC Trappers Education Manual