More about this simplified version of the model

This version of the Porcupine Caribou Herd model is designed to look at what happens if you control the levels for two climate variables: average temperature during the summer (which affects insect activity) and snow accumulation during the winter. Everything else affecting the caribou is kept constant. This is, of course, a very simplistic approach--in real life the factors affecting the caribou are all interrelated and would vary from year to year. However, running this model will give you an idea of how certain changes in climate might alter the population over several years.

• The model is built on years of research on:
  • how the Porcupine Caribou spend their time (activity budgets);
  • how they fulfill their feeding requirements (diet and energy intake); and,
  • how these factors (plus harvest, predation and other forms of mortality) affect the Herd's population structure and dynamics.
• The relationships used in the model are based on field observations. At least three years of data were collected for each of 15 seasonal periods over a span of eight years. The range of values used is therefore restricted to what actually occurred during those years. For example a "high" level of snow means the highest snow depth measured during three winters.
• During the winter, caribou feed by pawing the snow to get at the ground vegetation. The snow depth affects the amount of the caribou's feeding time that is actually spent eating--the greater the snow depth, the higher the percent of feeding time spent pawing away the snow. This is taken into account in the model.
• Snow depth also affects the energy used by the caribou--it takes more energy to walk through and paw deep snow. This is also taken into account in the model.
• In hot weather, when insects are very active, caribou spend more time standing and less time feeding, reducing their overall intake of food. This is taken into account in the model
• In real life, if the summers are hotter, they will also likely be longer--resulting in a longer period of insect activity and a further decrease in summer food intake. This has not been taken into account in this version of the model.
• Spring and fall conditions, as well as season timing, have been kept constant in this version of the model. Climatologists predict that springtime will come earlier in northwestern North America due to the increase of greenhouse gases. Earlier appearance of nutritious young plants would have an impact on the caribou during their calving period. There would be a benefit early in the season, but a cost later in the season because the best food would not be available when it is most needed. Caribou would not adapt readily to a shift in seasons because the timing of giving birth is related to changes in daylength, not to temperature or the availability of food. This aspect of predicted climate change has not been taken into account in this version of the model.