Wildlife population fluctuations

 

Fluctuations in the abundance of wildlife populations in any given area are often a normal occurrence in nature. They may be quite minor or rather large, they may last only a few years or may last many years. Management reaction to a change can depend on why the population level changed, if the change was significant enough to be of concern or just a minor fluctuation, if humans can do anything about it, and whether it is felt the change was desirable or undesirable.

Opinions on desirable or undesirable will likely vary among people depending on if that person likes, or dislikes, the particular species involved. Regardless of personal opinion, the impact the population level change may have on other species, the environment or habitat also should be considered. When we especially like a species, we tend to want it to be very abundant; even if that would be detrimental to other species, public safety, other people’s property/livelihood, or the environment.

The populations of some species fluctuate on fairly regular cycles. The small mammal study I wrote about earlier found that red-backed voles in this area have a population cycle of 3 to 5 years. It has been known for many decades that both snowshoe hare and ruffed grouse have about a 10-year population cycle. In the case of ruffed grouse, studies have found this occurs whether the birds are subjected to hunting or live in areas closed to hunting.

A number of factors can have major impacts on population levels. Weather can be either favorable or unfavorable to animal populations. Without going into examples and descriptions of weather impacts, extreme amounts and duration of both hot and cold temperatures, drought, and precipitation can be devastating to both wildlife and habitat. Wild animals are subject to infection by many parasites and diseases that can be deadly to them. Transmission of these to others of both that species and to other species which may be susceptible is increased by excessively high population levels.

Locally, we have seen the impact of both brain worm and winter ticks on moose. Recently there has been concern about bird flu; not only regarding commercial flocks, but hawks, owls, eagles and a number of other birds seem especially susceptible to it. It, too, could impact wild birds in this area.

Even without the influence of any outside factor, the abundance of a wildlife species in an area is likely to change in response to natural changes in the habitat over time. This may involve young trees growing into mature trees or from the gradual change of the dominant tree species being replaced by different tree species. Through these changes, the abundance and species composition of both the shrub and ground-level vegetation often change. This can be detrimental to the abundance of some species, but favorable to other species.

Rapid changes in habitat, such as by fire, logging, strong winds, or deliberate actions undertaken specifically to benefit a particular wildlife species, can quite quickly result in changes in the use of an area by wildlife. If these occur at appropriate time intervals and locations, the overall population level of a species in the area may fluctuate very little. However, those actions could be detrimental to other species that may already be far too scarce. Determining appropriate population levels is difficult as it involves more interests and considerations than just wildlife.

Considering that so many things can affect the abundance of wildlife populations, perhaps population stability is a rarity; especially for more than a dozen, or so, years at a time. But, are stable population levels the best management strategy for either wildlife or the environment/habitat? A requirement to achieve and then maintain a specific population level for a particular species can make it very difficult to take any action to help other species which are being adversely impacted by the favored species.

In regards to habitat, what we may consider to be an acceptable population level of an herbivore (especially deer, moose, elk, etc.) and it is within the capability of their primary food resources to maintain that level; it may be too high for the long term health of the habitat. They do not eat just their primary foods; it is common for them to prefer and therefore seek out other less abundant (even rare) plants and nearly eliminate them in that area. Some will say “so what?” From an ecological standpoint that is undesirable as those plants may be very important to that plant community. Diversity is important to environmental health.

Another aspect involving a habitat’s carrying capacity for a species is that species’ tolerance of crowding. Species which normally live in small groups, or even herds, can do well at higher densities (that are still within what the habitat can support) than can more individualistic species such as moose. Crowding creates stress which can result in decreased reproduction and in habitat damage not necessarily involving the food resources available.

Major population crashes or explosions are of concern and deserve to be evaluated regarding potential management responses. Most people prefer stable population levels, but minor fluctuations are normal and sometimes even fairly large decreases can be beneficial for both the habitat and the animal population itself.

Rigid adherence to trying to maintain a specific population level of a species in a particular area in spite of new information or major environmental changes over which we have no control is not realistic. Management requires being able to reassess policy decisions as situations change or be doomed to failure. There is an old saying in science that “The only thing constant in nature is change.”

One final item I should bring up regarding population levels is that the common belief that Arctic lemmings commit mass suicide every few years in response to over population is false. The 1958 Disney film “White Wilderness” that purported this myth, staged the scene by pushing dozens of lemmings over a cliff and into the water below. It is common for nature films to stage many scenes, but that one was in particularly poor taste and untruthful. When lemmings have consumed the available foods, they leave that area in large groups and seek an area which has ample food for them.