Animal communities are based on mutually beneficial relationships that help maintain equilibrium between the flora and fauna in a complex environment. We’ve looked at the relationships between predators and prey species, but of equal interest and importance is the interaction and competition between like species.
Most of the predators that we hunt live within structured social families that are based on aggressiveness and intolerance—the dominance of individual animals over others. These hierarchies maintain order and structure and provide a mechanism that guards against interbreeding, disease, over-crowding and the devastation of available resources.
Dispersal (which occurs as young animals are pushed from their home ranges and seek out new territories) allows for population growth and distribution of the species as a whole.
There is also competition between different predatory species that vie for the same territories and their resources. Again, the most dominant species generally inhabit the most desirable and productive locales while subordinate species seek out habitat niches where they can avoid being attacked.
Population regulation and territory acquisition involve competition for resources among members of the same species. Ecologists refer to this as intraspecific competition. This rivalry becomes vigorous when prime habitat is in short supply and food sources are scarce.
During many hunts in the high desert regions of Arizona, for instance, I have observed as many as four coyotes responding to a call at one time, often arriving from different directions. This type of fierce competition makes for exciting hunts and confirms the effectiveness of using food source sounds where predator populations are high and food is sparse.
Intraspecific competition leads to dispersal in predator populations. Instead of dealing with the stress of limited food sources and constant attacks from more dominant members of the society, young adult animals often flee and seek vacant habitat areas. These are often less desirable localities with fewer resources. Some predators perish from starvation or are killed by those animals whose territories they have trespassed upon.
As these animals gain maturity and dominance, many are able to migrate to better territories or occupy areas that have become vacant for whatever reason. Fur trappers know that they can set traps at the same locations year after year with continued success: As animals are removed from prime habitat, other animals will find these open, desirable niches and repopulate them.
In his book Elements of Ecology, Robert Leo Smith explains that more important to population regulation is dispersal that takes place when the population density is low or increasing, but well before the population reaches a density at which food and cover are overexploited.
“Individuals who participate are not a random selection of the population but ones that are in good condition, belong to any sex or age group, have a good chance of survival, and show a high probability of settling in a new area. Some evidence exists that such individuals are genetically predisposed to disperse.
“Such individuals can maximize their fitness only if they leave their birthplace. When intraspecific competition at the home place is intense, dispersers can locate in habitats where resources are more accessible, breeding sites are more available and competition is less. Further, the individual reduces the danger of inbreeding. At the same time, dispersers also incur risks. They are living in unfamiliar terrain; their hybrid young, produced with wholly unrelated individuals, may not be well adapted to the environment.”
Dispersal is a function of population density control and population expansion. A good example is provided by the relatively recent movement of coyotes into the eastern reaches of the North American continent. And while this is a function of intraspecific competition and dispersal, it has also been a function of competition between different predatory species.
Historically, wolves kept coyote populations at bay where they coexisted, and coyotes were not found in abundance in the East. When man stepped in and removed wolves, this opened up new territories and paved the way for the coyote’s eastward migration.
Interspecific competition concerns the competition for resources among different species. The classic relationship between coyotes and red foxes in North Dakota provides a good example. These predators compete vigorously for the same limited food sources contained in optimal habitat niches.
The coyote occupies a higher position on the food chain and considers the red fox unwanted competition. Coyotes will run off or kill the smaller predators that infringe on their territories. But foxes must survive under the constant threat posed by the larger predator and, essentially, find niches in the habitat that coyotes find less desirable.
“It’s not a friendly relationship, let’s put it that way,” describes Steve Allen, retired furbearer biologist for the North Dakota Wildlife Division. Allen, an avid predator hunter, participated in a number of studies that observed the relationships between red foxes and coyotes in North Dakota. He says that the results are interesting from a hunter’s perspective as well as from that of a biologist.
“It’s the same with all the canines. Each species likes its own kind, but everybody hates the other guy,” Steve says. “And that particularly holds true in the case of coyotes and red foxes. Coyotes drive red foxes from their territories, often killing them. Smart foxes figure this out and go where there aren’t any coyotes. That’s how coyotes end up in some areas and foxes end up in others.”
A study published in 1987 looked at the relationships between these two predators and came up with some interesting findings regarding how the animals utilize the North Dakota landscape. It was found that coyotes center their activities, especially pup rearing, on relatively large roadless areas where cropland is least abundant. Foxes live closer to farmsteads and roads where cropland is most abundant.
The study concluded that coyotes and red foxes tended to avoid interspecific encounters. This explained the absence of red foxes from much of the area where there was little cropland, the areas where coyotes were most abundant.
This relationship holds true where coyotes and gray foxes share the same habitat. For example, in Texas, gray foxes are generally less abundant where coyotes are common. However, on ranches where coyotes have been removed by trappers and hunters because of the threat they pose to sheep and other grazing livestock, gray foxes are plentiful. It appears that coyotes hold gray foxes numbers in check where the two species occupy the same territory.
All predators stake out territories and vigorously defend them from poachers. Territoriality is one mechanism whereby the population density of a species is adjusted to the availability of resources such as food and water. Each territory holder is defending itself and its family. When all the critical resources (i.e., food) have been divided between territories, any remaining animals face little more than the prospect of starvation (or at least not breeding) until they can establish a territory that becomes vacant.
In the North Dakota study, it was found that coyotes and red foxes avoided contact with each other. Foxes avoided coyotes, which caused foxes to shy away from occupying central portions of coyote family territories and to limit their use of areas within coyote territory. To frequent coyote territory could cause conflict, which could result in the deaths of foxes.
The study also found that age and social status might be important factors affecting relationships between individual coyotes and foxes. Young foxes are probably most vulnerable to mortality from coyotes, especially when dispersing, because they are inexperienced and travel through unfamiliar terrain, including coyote territories.
Smith points out that the degree of aggressive behavior among individuals might limit the size of their home range. Dominant males can control highly desirable locations, especially in relation to food and females, and force subdominant animals to occupy the areas that are left. Restriction to a home area also confers security. Animals become familiar with the location of food, shelter and escape cover.