Introduction and Wolf Ecology

Territoriality is a fundamental aspect in the ecology of many mammals, particularly predatory animals such as wolves, lions, hyenas, African wild dogs and badgers, and it has been widely studied. In the case of wolves, whose prey are mainly moose and deer, an immediate question arises as to how the predator and prey coexist if the land is divided up into predator territories.1 This in turn leads to the question of how territories are determined and maintained. It is clearly important in the ecology of such predatory animals. In this chapter we consider the question of mammalian territory formation, specifically as it applies to wolves, and its role in wolf-deer survival for which there is a considerable amount of data. In spite of the numerous studies on how pack territories are formed and maintained it was not addressed mechanistically until the mid-1990's with the mathematical modelling work of Lewis and Murray (1993), White (1995), White et al. (1996a,b), Lewis et al. (1997,1998), Moorcroft et al. (1999) and Lewis and Moorcroft (2001) who studied the spatiotemporal effects on territory formation, territory maintenance and wolf-deer survival. Most of the material we describe in detail in this chapter is based on their work. First we give some background ecology on wolves.

The book (which has many beautiful photographs) by Mech (1991), who has studied wolves for nearly 40 years, is the best general introduction to the biology and ecology of wolves. It gives an excellent overview of the major aspects of wolf behaviour and social organisation; he also discusses some practical aspects of wolf conservation. Through his work, Mech has done much to change the often held traditional (erroneous) view of these splendid animals. He also points out that the stories of wolves attacking humans are mainly myths. He notes 'I have no doubt that if a single wolf—let alone a pack—wanted to kill someone, it could do so without trouble. When I have watched wolves close-up killing prey, they were swift and silent. A few good bites, and a human would be dead. The fact remains, however, that there is no record of an unprovoked, non-rabid wolf in North America seriously injuring a person.'

11 first became intrigued by this question during a visit to the University of British Columbia in the late 1970's when, over dinner, in a discussion on animal intelligence it was mentioned how particularly clever and intelligent wolves are, as has been noted regularly since at least Roman times. In Canada their main food source is often the moose. I started to wonder how, if wolves are so clever, did the moose manage to survive. It was not until the early 1990's that Mark Lewis and I started to look at the question from a mathematical modelling point of view being joined soon afterwards by Jane White.

Wolf Formation

Figure 14.1. The past and present geographic distribution of wolves from Mech (1991). (Reproduced with permission of Voyageur Press Inc. (copyright holder)) With the recent reintroduction of wolf packs into the western U.S., in particular into Yellowstone National Park, the range has been extended below the 49th parallel, which separates Canada and the U.S.

Figure 14.1. The past and present geographic distribution of wolves from Mech (1991). (Reproduced with permission of Voyageur Press Inc. (copyright holder)) With the recent reintroduction of wolf packs into the western U.S., in particular into Yellowstone National Park, the range has been extended below the 49th parallel, which separates Canada and the U.S.

Wolves used to be one of the most widely distributed animals in the northern hemisphere. Figure 14.1 shows the present and past distribution of wolves.

Wolves are social carnivores typically belonging to a pack which is a family unit consisting of 3-15 wolves. The extensive field studies which have been carried out on different packs in northeastern Minnesota, often using radiotracking techniques, have provided information on the land use by wolves from different packs. Pack territories are maintained over several years and are spatially segregated, rarely overlapping in the boundary regions; see Figure 14.2.

Territorial boundaries are usually avoided to lessen the chance of interpack conflict which often leads to death of one or more of the pack leaders (the alpha pair) which, in turn, can result in pack disintegration. In northeastern Minnesota, territories range in size from 100-310 km2. These boundary regions between neighboring packs, known as 'buffer zones' are rarely visited by pack members. The buffer zones, which are a kind of 'no-mans-land,' are about 2 km wide and can account for as much as 25-40% of the available area.

Some of the most striking spatial patterns evident in wolf territories have been described by Mech (1973) and van Ballenberghe et al. (1975) and these provided the modelling basis for a mechanism as to how wolves and their prey may coexist in relatively close proximity (Lewis and Murray 1993, White 1995, White et al. 1996a,b, 1998). Our goal was to develop a mechanistic, spatially explicit model incorporating wolf movement, scent marking and wolf interactions that produces the spatial patterns evident in a wolf ecosystem specifically in northeastern Minnesota. Understanding pack territory formation and home range patterns is crucial if we are to understand the ecol-

Figure 14.2. Radiolocations and home range boundaries of five adult and yearling timber wolves radiotracked in northeastern Minnesota during the summer of 1971. (Redrawn from van Ballenberghe et al. (1975) and reproduced with permission from the Wildlife Society (copyright holder))

ogy of many mammalian societies. Of course, other aspects are also important such as the social organization, mating and demography (see, for example, Clutton-Brock 1989). The literature is large and diverse; we give only a few references (see the numerous references cited in these). White (1995) gives an extensive review of the literature and modelling studies and the articles by Lewis et al. (1998) and Moorcroft and Lewis (2001) review some of the more recent theoretical studies with the latter presenting some interesting field data on coyotes using the mechanistic models discussed in this chapter.

The biological background and data used in constructing the mechanistic models is largely based on the wide-ranging radiomarking studies of wolves (Canis lupus) in northeastern Minnesota over the past 25 years. These have greatly facilitated the observation of wolf territories. The well-known and the most detailed quantitative studies of wolf numbers, however, is from the Isle Royale Project.

The Isle Royale National Park, an island of just over 200 square miles, is in Lake Superior close to the Minnesota-Ontario border. During a particularly cold winter in 1949, when the island was joined to the mainland by ice, some wolves crossed over to the island. They established themselves on the island where their main prey is the moose. Since 1959 the actual wolf and moose numbers, among many other things (such as beaver colonies and otter numbers), have been recorded thereby providing a remarkable data set on the wolf and moose interaction and their survival. Dr. Rolf Peterson (School of Forestry and Wood Products, Michigan Technical University, Houghton, Michigan 49931-1295, U.S.A.) is the director of the project. The report (Peterson 1999)

for the 1998 to 1999 year gives an overview and some quantitative details of the ecology of the island. Some of the data on wolf-moose numbers and wolf pack territories are given below. This long term study of more than 40 years is immensely important and has allowed a wide variety of studies to be carried out. For example, other than wolf population and territorial distribution, the effect of inbreeding, disease pathology and so on are of major current interest as are the dynamics of other animal populations and interactions on the island. The data are an excellent source for modelling investigations of population interactions. Figure 14.3 shows the wolf-moose populations, the wolf pack territories and the moose distribution on Isle Royale in 1999.

Wolves can cover around 50 km in a 24-hour period and so could cover a significant portion of their territory in a day. Even so, relative to pack size, the size of territories in northeastern Minnesota really means that physical presence can not provide a sufficient defensive mechanism to protect the territory. Based on many years of field observations, Mech (1991) suggests that wolf territories are formed and maintained by interpack aggression in conjunction with two warning systems: scent marking and howling, and that the result is a mosaic of territories covering the wolves' range. While howling may provide temporary information on a pack's location, elaborate spatial patterns of scent marks serve to advertise precise information about territorial claims even in the absence of any pack members. We shall include scent marking in our models.

As with other carnivores, olfaction (smell) is the primary sense.2 Wolves use a variety of olfactory signs but behavioral studies indicate that raised leg urination (RLU) is the most important one in territory marking and maintenance. RLU markings occur throughout the territory along wolf trails but, more importantly, they increase significantly around the buffer region giving rise to high concentrations of RLU markings from all packs in this region: Figure 14.4 sketches typical RLU markings around a pack territory. Unlike the other olfactory signs used by wolves, RLU shows little correlation with pack size because they are made by only a few mature dominant wolves in each pack. These are primarily the alpha pair who reproduce and who dominate the other pack members: wolf packs are highly structured socially. Observations also indicate aversion to the scent from RLUs made by neighbouring packs.

White-tailed deer are the main prey for wolves in northeastern Minnesota and their distribution varies seasonally. During the summer months, deer are dispersed on large home ranges but in the winter months they tend to congregate in yards as shown in Figure 14.5. In spite of the relative homogeneity in food and habitat across the study region, the deer in both summer and winter tend to remain in the buffer zones between pack territories. It has been suggested that this deer heterogeneity could be due to differential predation rates caused by the territorial nature of the wolf.

As mentioned, the main motivation for the work described here is from the wolf-deer data from northeastern Minnesota. By following the movements of radiomarked individual members from a pack, or cooperative extended family group, it has been possible to deduce distinct spatial patterns in wolf distribution. Wolves typically remain within well-defined territories (Mech 1973, Van Ballenberghe et al. 1975) that, to some

2As noted earlier, the domesticated male silk moth (Bombyx mori) uses an optimally designed antenna filter to detect molecules of the sex-attractant chemical, Bombykol, emitted by the female. The male silk moth cannot fly so it has to walk up the concentration gradient to find the female: in some experiments it walked upwind as much as a kilometre!

Moose-Wolf Populations

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