EPA/600/A-97/071
Jerry 0. Wolff
Department of Fisheries and Wildlife
Oregon State University
Corvallis, OR 97331 USA
Phone: 541-737-2473
FAX: 541-737-3590
Email: woIffj@ccmail.orst.edu
ON APPLYING BEHAVIORAL MODEL SYSTEMS TO LANDSCAPE ECOLOGY.
Jerry O. Wolff
The impact of habitat loss and fragmentation of remaining habitats on the distribution,
persistence, and metapopulation dynamics of plants and animals is a major concern in
conservation biology and landscape ecology (Harris 1984; Wiens et al. 1993; Lidicker 1995;
Hanski and Gilpin 1997). Much of our understanding of how habitat loss and fragmentation
affect native populations is through retrospection, speculation, or modeling rather than direct
quantification or experimentation. Evidence of whether or not experiments and observational
studies corroborate or substantiate predictions of mathematical models is equivocal (Lamberson
et al. 1994; Schumaker 1996). One of the reasons for this discrepancy is that species within a
taxon often are treated as mathematical entities (i.e. all individuals are "average") and
individual-, sex-, and species-specific differences in response to fragmentation are not taken into
account (Andren 1994; Lima and Zollner 1996). Some of the differences in species responses to
fragmentation can be explained by differences in their behavioral systems; dispersal ability, life
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history, trophic level, sociality, and overall responses to changes in habitat size, connectivity, and
type of matrix.
In that experimental studies, or even observational studies are not possible on
endangered, large, or rare species, ecological model species or systems (EMS) are sometimes
used to test predictions of how a species will respond to some perturbation (Ims and Stenseth
1989; Wiens et al. 1993; Ims et al. 1993; Wolff et al. 1997). Several studies have used small
mammals in enclosed or manipulated habitats as EMS's to evaluate responses to loss and
fragmentation of habitat (e.g. Ims et al. 1993; Barrett et al. 1995; Diffendorfer et al. 1995) and
the theoretical application of mammalian responses to landscape ecology have been discussed in
Lidicker (1995). The results from these studies are then applied to other species or situations to
predict similar responses (e.g. comparing territoriality of voles with that of capercaillie grouse
(Tetrao urogallus, Ims et al. 1993). EMS's may have their utility, but whether movements of
voles in enclosures represent movements of cougars in southern California (Beier 1995) or
spotted owls (Strix occidentalis) in western Washington (Lamberson et al. 1994) is doubtful
(scientific names not presented in the text are listed in Appendix 1). I propose that species may
not necessarily be good surrogates for other species per se, but rather behavioral systems might
be more appropriate for making comparisons and predictions among species. Certain aspects of
behavior, such as territoriality, sex-biased dispersal, and sociality might be more similar across
species, than are other traits such as phylogenetie relations, body size, or other aspects of
ecology. An understanding of the behavioral ecology of species should provide further insight
into how species respond to fragmented landscapes. In conjunction with behavior, I describe
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how life and evolutionary history and degree of habitat specialization can affect a species
response to fragmented landscapes.
Colonization of Habitat
Evolutionary History
The rate and(or) probability of a species colonizing distant patches may be in part, a function of
its evolutionary history. If a species evolved in stable continuous habitat it may respond very
differently to fragmented habitats than a species that evolved in a patchy or frequently disturbed
environment (Merriam 1995; Lima and Zollner 1996). In western North America, elk are
frequently associated with mature forests or edge habitat, whereas they apparently spent much of
their evolutionary history in North America as an open steppe habitat species (Guthrie 1968,
Geist 1971). Black bears of eastern United States are primarily forest-dwelling, whereas in
western and northern North America they are frequently associated with partially open habitats
(Powell 1997). Weddell (1991) argued that Columbian ground squirrels never evolved dispersal
strategies suited to colonization of isolated pockets of habitat because steppe vegetation is stable
relative to the lifetime of a ground squirrel. Black-tailed prairie dogs likewise do not migrate to
unoccupied natural patches (Garrett and Franklin 1988). On the other hand, alpine marmots,
which occupy isolated rock outcrops interspersed in alpine mountains appear to be adapted to
dispersal and colonization of this patchy resource (Van Vuren 1994; 1997). White-footed mice
(Peromyscus leucopus) also readily colonize isolated woodlots and persist as a metapopulation
(Middleton and Merriam 1981). Wolves often follow prey such as caribou (Rangifer tarandus)
or deer (Weaver et al. 1996) and lynx disperse over large distances in search of food during
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snowshoe hare declines (Murray et al. 1994). Snowshoe hares, moose, and grassland voles
which exploit early successional or frequently disturbed habitats should also be good colonizers
(Wolff 1980; Hik 1995). Species such as pronghorns (Antilocapra americana) and jack rabbits
that have evolved in open plains habitats and avoid forested areas, probably would not be good
colonists if they had to disperse through barriers of wooded habitats. Thus, various aspects of the
evolutionary history of a species may influence its tendency to move across a habitat mosaic.
Habitat Mosaics: Generalists vs Specialists ,
Most population viability models are based on habitat preferences or a habitat suitability index
(HSI) for the species (Morrison et al. 1992). Unfortunately, most species do not visualize or
utilize habitat based on its description on an aerial photo or landsat image. Rather, many species
have habitat requirements that include a mosaic of habitats, each component being necessary but
not sufficient for successful colonization. For instance, bats typically require a covered roosting
site, often with a narrow access passageway such as caves, tree hollows, or manmade dwellings
(Bradbury 1977). Preferred and suitable foraging areas are not necessarily coincident with
roosting areas. Bats may feed on nectar, fruit, blood, fish, or flying insects, all of which may or
may not be in the immediate vicinity. Opossums and raccoons require hollow trees for nesting,
but frequently forage in open habitats, along streams, or in urban settings. Bears may shift home
range use from mature forest or grazing areas in spring to spawning salmon streams during
summer, and berry patches in fall (Powell 1997; and others), all of which may fall into different
vegetation classifications. Marten typically spend 95% of their time in forest habitats but forage
extensively for voles in adjacent grassland habitats (Zielinski 1982). Male and female ungulates
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typically segregate and use different habitats for much of the year (Main et al. 1996; Bleich et al.
1997). Sexual segregation into different microhabitats also was recorded for cotton rats (Lidicker
et al, 1992). Therefore, specific habitat requirements that include all the requisites for life must
be considered for species that have different feeding and nesting areas, seasonally available
resources, and sex-specific requirements.
In contrast, some species which are habitat specialists avoid mosaics and perceive them
as a barrier to dispersal. In a comparison of colonization ability of North American and
European rodents, Liro and Szacki (1995) concluded that bank voles and chipmunks (Tamias
striatus) were forest habitat specialists and would not be good colonists in fragmented habitats
whereas yellow-neck mice (Apodemns jlavicollis) and deer mice, habitats generalists, would
readily cross habitat mosaics and be good colonists. North American red-backed voles
{Clethrionomys spp.) and Peromyscus would be similar to European Clethrionomys and
Apodemus species (see also Wegner and Henein 1991). Marten (Maries spp) also are forest
specialists and seldom travel greater than 25 m into open habitat (Bissonette and Broekhuizen
1995) which probably restricts their ability to colonize new patches interdispersed among an
open habitat matrix. Laurance (1995) concluded that arboreality also might decrease a species
chances of colonizing patchy habitats. In a study of the distribution of mammal species in an
Australian landscape, Laurance found that populations of terrestrial generalists were more stable
and evenly distributed across a landscape whereas arboreal marsupials were more apt to go
extinct or be absent from forested habitat fragments. North American tree squirrels should
respond similarly. Forest-dwelling spotted skunks should have a more difficult time dispersing
across open fields than would striped skunks which are adapted to fragmented landscapes.
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Similarly raccoons and opossums which are adapted to urbanization should be able to cross
human-occupied areas more readily than would wolverines and fishers which tend to avoid
human contact.
Species that live on habitat islands such as hyraxes (Procavia johnstoni and
Heterophyrax brucei) which occupy rock outcrops in Africa (Hoeck 1982), muskrats which are
confined to ponds (Messier et al. 1990), and pikas which occupy isolated talus slopes (Smith and
Ivins 1983) are apparently reluctant to leave their island habitats. Thus, species that evolved
within and even may require a mosaic of habitats should be better colonists than habitat
specialists that have evolved within a given habitat type and are probably reluctant to cross
habitat matrices.
Spacing Behavior - Female Territoriality
Perhaps one of the most influential factors that determine how a species responds to changes in
habitat area is territoriality. Territoriality is defense of an area such that it becomes relatively
exclusive with respect to rivals (Maher and Lott 1995). In that successful colonization of a patch
requires immigration and establishment of females, I limit my discussion to situations in which
females actively defend territories against other females to provide exclusive access to breeding
space (Wolff 1997).
Population viability models rely extensively on females occupying exclusive space such
that only one breeding effort takes place on a given home range area at a time (e.g. Lamberson et
al. 1.994; Schumaker 1996). For many species of mammals this is appropriate; for others it is not
(Wolff 1997). Fpmale territoriality occurs in species that have nonmobile altricial young that are
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deposited in a den or protected nest site. Mammal species with precocial young and(or) altricial
young that are carried with the mother (such as marsupials and primates) are not territorial
(Wolff 1997). Therefore, female territoriality commonly occurs among the insectivores, rodents
(squirrels, mice, and voles), rabbits, carnivores, and prosimian primates, and does not occur
among the ungulates, hystricognath rodents, hares, marsupials, and most anthropoid primates. In
territorial species such as red squirrels, tarsiers, wolves, and rabbits, females require an
individual territory to breed (see exceptions below), whereas in nonterritorial species, exclusive
space is not a requisite for reproduction (Wolff 1997). For instance, in ungulates such as bighorn
sheep, elk, or bison (Bison bison), all females have the opportunity to breed irrespective of space.
Social pressures do not prevent any female from breeding in nonterritorial species. The
important point here, is that in territorial species, the size of breeding population is limited by the
number of breeding sites (territories) available in a habitat (Wolff 1997). This same relationship
does not hold for nonterritorial species.
Some exceptions to the one-female-one-breeding-effort/territoiy rule occur. The social
structure of most mammal species is that young males disperse from the social unit and daughters
are philopatric and remain in or near their natal site (Greenwood 1980; Pusey 1987; Brandt 1992;
Wolff 1993 and see Dispersal section below). Female philopatry often results in the formation of
kin groups or female alliances that share the same space such that if space is limited, daughters
can breed on their mother's territories. This pattern of shared space commonly occurs among
prairie dogs (Hoogland 1995), marmots (Armitage 1981) and many species of mice and voles
(Jannett 1978; Wolff 1985,1994; McGuire and Getz 1991; Lambin 1994; Salvioni and Lidicker
1995). In contrast, only one female breeds on a territory in red foxes (Allen and Sargeant 1993),
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wolves (Mech 1970), dwarf mongooses (Helogale parvula; Creel et al. 1992) red squirrels (Price
and Boutin 1993), and common marmosets (Callithrix jacchus; Digby 1995). Thus, an
understanding of the social relationships among related females and their tolerance of shared
breeding space will allow more accurate predictions of the reproductive potential for a given area
of habitat.
Sociality and Compecific Attraction
Smith and Peacock (1990) already have demonstrated that conspecific attraction can affect
metapopulation colonization rates. Weddell (1991) reported that in ground squirrels colonization
of new habitats did not occur because emigrants settled near other squirrels rather than in vacant
patches. Similar results were found for prairie dogs (Garrett and Franklin 1988). New coteries
or populations of prairie dogs and ground squirrels are formed by fusion or fission of established •
colonies (Michener 1983; Halpin 1987) and not by colonization of individuals into vacant
patches. In contrast, the tendency to disperse and colonize distant patches should be less affected
by conspecifics in asocial species, or those that are not attracted to conspecifics per se, such as
hares, mink, opossums, and moose.
Patch Occupancy and Optimal Group Size
Another factor that determines the number of individuals in a habitat patch is that which affects
optimal group size. Optimal group size in turn is dependent on several ecological and social
factors. Optimal group size in African hunting dogs is based on hunting energetics (Creel and
Creel 1995) whereas in lions, group size apparently is not based on predator efficiency, but rather
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on the success of the pride in protecting cubs against infanticide or in defense of carcasses
(Packer et al. 1990). Optimal group size in this case is dependent on the size of other groups in
the area. Optimal group size in ungulates such as bighorn sheep, pronghorn, and bison may be
based on predator vigilance such that a minimum group size is a necessary trade-off between
time spent in vigilance and eating (Berger 1978; Belovsky 1986). A minimum group size is
apparently also required for colonial or communal species such as prairie dogs and ground
squirrels such that colonies do not exist below a minimum threshold number regardless of patch
size (Weddell 1991; Hoogland 1995).
Source-sink Habitats and Reproduction
Just because members of a given species are found in a given habitat, does not mean that the
habitat is optimal or even adequate for the species. Animals will often occur in suboptima! or
sink habitat (Pulliam 1988), but may not necessarily reproduce there. Weddell (1991) found that
some dispersing subordinant male Columbian ground squirrels temporarily settled in unoccupied
habitat, but were not successful colonists. J. Wolff (unpubl.) found a small group of "bachelor"
taiga voles in suboptimal habitat; there were no females in the habitat and the males were not
breeding. Robinson et al. (1992) and Diffendorfer et al. (1995) similarly found that small rodents
were occupying small grassland patches, but successful breeding occurred only in larger patches.
Typically in ungulates, dominant males occupy the best habitats and groups of subordinant
bachelor males are relegated to suboptimal habitats (Jarman 1974, Gosling 1986). Thus, the
suitability for reproduction of a given habitat must be taken into consideration when concluding
if occupation is synonymous with successful "colonization".
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Dispersal
Barriers and Colonization
An important component of mammalian behavioral systems is dispersal (Stenseth and Lidicker
1992). From an ecological perspective, dispersal has demographic consequences for a population
in that it can stabilize densities and provide gene flow and genetic panmixia. From a behavioral
perspective, dispersal separates opposite-sex relatives and reduces the chances of inbreeding
(Pusey 1987; Brandt 1992; Wolff 1993,1994). On the other hand, delayed dispersal can result in
delayed sexual maturation (e.g. Creel and Creel 1991; Wolff 1992, 1997 and references cited
therein), cooperative breeding (Powell and Fried 1994; Solomon and French 1997), or possible
inbreeding (Smith and Ivins 1983). In large continuous populations, animals are free to move
throughout the habitat without consideration of ecological or physical barriers. However, in
fragmented landscapes, dispersal can be deterred or prevented depending on the type of barrier
and presence and absence of corridors (Fahrig and Merriam 1985).
Ecological Barriers
What constitutes a barrier will vary depending on the mobility, natural history, and habitat
specialization of a species. Small fossorial mammals such as shrews, moles, and gophers should
have a difficult time crossing interstate highways, rivers, and even small streams whereas more
mobile and terrestrial species such as bats and larger mammals can cross such barriers with ease.
On the other hand, aquatic habitats provide an avenue for dispersal for species such as water
shrews (e.g. Sorex palustris), otters, beavers, and nutria (Afyocastor coypu), whereas terrestrial
habitats are a barrier to movement of these species. A 15-m strip of mowed grass was a partial
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barrier to movement for tundra voles (Microtus oeconomus, Andreassen et al. 1996a) and a 4-m
strip of barren ground was a barrier to movement in gray-tailed voles (Microtus canicaudus,
Wolff et al. 1997); whereas deer mice readily cross open areas greater than 12-m wide (J. Wolff
unpubl) and white-footed mice cross open fields >1 km (S. Vessey pers. comm.). Microtus voles
in general have evolved in grasslands which provide considerable cover, whereas Peromyscus are
more open-habitat generalist species (Baker 1968); therefore what is a barrier to a Microtus, may
not be a barrier to a Peromyscus.
Behavioral Barriers - Corridors
The negative effects of fragmentation on populations can be reduced by connecting isolated
fragments by narrow strips of habitat referred to as movement corridors (Harris 1984; Bennett .
1990, Simberloff et al. 1992). Empirical evidence for if and(or) how animals use corridors,
however, is minimal (Hobbs 1992; Simberloff et al. 1992; LaPolla and Barrett 1993; Andreassen
et al. 1996b; Davis-bom 1997) and may not fit the assumption that bigger is better (Noss 1987;
Harrison 1992). For instance, optimal width of corridors for meadow voles (LaPolla and Barrett
1993) and tundra voles (Andreassen et al. 1996b) was 1 m. Voles were reluctant to enter
narrower corridors while linear movement in wider corridors was hampered by cross-directional
movements. Wider corridors may be perceived as habitat rather than an avenue for directional
movement and become permanently occupied. Occupancy of corridors should affect territorial
and nonterritorial species differently. For instance, if an individual establishes a territory that
encompasses the width of the corridor, other individuals will be less able to move along the
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corridor to adjacent patches than if the corridor were not occupied. For nonterritorial species
movement should not be deterred along such stretches of habitats.
Dispersal Distance
Dispersal is a component of vertebrate behavioral systems that contributes substantially to
colonization of vacant habitats and fragmented landscapes. Estimates of the tendency to disperse
and dispersal distance are used to predict the likelihood of a given species colonizing a vacant
habitat or crossing a fragmented landscape. Estimates of dispersal patterns and distances are also
used in spatially explicit population viability models (e.g. Lamberson et al. 1994; Schumaker
1996). Dispersal patterns vary considerably among species primarily with respect to dispersal
distances, which sex disperses, and the tendency to disperse in the first place, However, various
aspects of a species life and natural history and behavioral system can affect dispersal patterns
among mammals (Koenig et al. 1996). I expand on the paper by Van Vuren (1997) in which
body mass of 33 mammals was used to estimate median dispersal distances for all mammals. I
used data on maximum dispersal distances for species of mammals and discuss the implications
of dispersal distance and various aspects of a species social system and life history that contribute
to dispersal patterns and the propensity for a species to colonize new habitats.
I obtained dispersal distances for as many species as I could find from the original
literature. However, dispersal distances are rarely studied directly for mammals, so data on
dispersal distances often are obtained from basic studies on animal demography or from data that
were obtained inadvertently in radio-telemetry or mark-recapture studies. Much of the data on
dispersal distances are anecdotes and often represent record distances or in some cases minimal
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distances based on the size of the study or census area (see Koenig et al. 1996 for discussion on
data limitations). Though dispersal distances vary considerably by sex, species, age, and habitat,
and sample sizes are always small, I obtained as much reliable data as I could find, and then
regressed log mean maximum dispersal distance against log body mass to estimate dispersal
distances for other species. Many mammalian life history traits scale allometrically to body mass
(e.g. Peters 1983; Calder 1984) including home ranges sizes (McNab 1963; Harestad and Bunnell
1979; Rolling 1992). I used a least squares linear regression of log,0 of "mean maximum
dispersal distances" against log,0 of body mass for 59 species of mammals for which data were
available. The mean maximum dispersal distance was an estimate of the distance within which
most (usually >90%) of the animals were caught. For many species, I found data for only a few
individuals and used these values if they seemed reasonable. I used data primarily on dispersal of
juveniles from the natal site and only adult dispersal data when those of juveniles were not
available. I did not use dispersal data from translocated animals or record dispersal distances.
For some species such as mountain goats, bighorn sheep, and sea otters, I had only total lifetime
movements of animals and used these distances. Body masses for mammals were obtained from
Eisenberg (1981), Chapman and Feldhammer (1982), and Silva and Downing (1995) and if
available I used the same masses as Van Vuren (1997).
The dispersal data are in Appendix I and the allometric relationships between dispersal
distance and body mass are listed in Table 1 and shown graphically in Figs. 1 and 2. The
allometric relationships for dispersal distance as a function of body mass for all mammals gives
an r2 of .868. Carnivores have a steeper slope than do herbivores and omnivores. The slopes are
relatively similar for males and females, however females have a lower intercept than do males
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(Fig. 2). In general, males disperse farther than do females and carnivores farther than do
herbivores or omnivores. Some of the species that show the shortest dispersal distances and fall
below the regression lines in Fig. 1 are those that are highly social such as the ground squirrels or
those that are confined to very patchy habitats such as pikas and pond-dwelling muskrats. Those
mammals that are the farthest below the regression line in Fig. 1 are all females and include the
field and meadow voles, wambenger, pika, muskrat, and gray fox. Although these equations
predict dispersal distances for all mammals, deviations from this expected dispersal distance are
expected to occur for the reasons discussed above and below.
Which Sex Disperses
In most mammal species, females are relatively philopatric often remaining in or near their natal
site and dispersal is male-biased (Greenwood 1980, Pusey 1987, Wolff 1993). Thus, the
probability of colonizing and establishing a breeding population in new sites or distant patches is
often less than would be predicted based on an estimated dispersal distance for the species. Even
though both males and females are listed as dispersing in Appendix 1, males usually disperse
farther and at a much higher frequency than do females in all species except the kangaroo rats,
red squirrels, snowshoe hares, mountain hares, beaver, porcupines, wombats, European badgers,
arctic and red foxes, lynx, coyotes, dingoes, wolves, and opossums. Females do occasionally
disperse in the other species, but in general, females of these species remain relatively close to
their natal home range and often form female kin groups (Greenwood 1980, Holekamp 1984;
Kevles 1986, Boonstra et al 1987, Wolff 1994, 1995,1997). Among large carnivores, female
grizzly bears remain near their natal site and are not likely to colonize new habitat; whereas
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female wolves, lynx, and cougars frequently move long distances (Weaver et al. 1996). General
characteristics of species in which both sexes disperse at comparable rates and distances include
a monogamous mating system (such as exhibited by many species of canids), species in which
both sexes individually defend burrow systems and food caches (such as kangaroo rats and red
squirrels), or species that are not territorial (such as hares, porcupines, and opossums;
summarized in Wolff 1997).
Factors Contributing to Variance in Dispersal Distances
Density, Territoriality, and Dispersal
The rate of dispersal of individuals away from their natal site is, in part, a function of the species
behavioral system. Territoriality can impede movement of animals if all the suitable space is
occupied and individuals are thus not able to cross undefended space. This type of barrier to
movement is referred to as a social fence (Hestbeck 1982) and results in an inverse density-
dependent dispersal pattern in territorial species (Wolff 1997). In contrast, in nonterritorial
species in which habitat is not actively defended, individuals can move without social
impediment at any density. Thus in nonterritorial species, emigration should be density-
independent (Wolff 1997). A decrease in emigration rate has been reported for high densities of
several species of territorial mammals (e.g. montane voles, Microtus montanus, Jannett 1978;
white-footed mice; Wolff 1992; prairie voles, M. ochrogaster; Maguire and Getz 1991). On the
other hand, emigration should not be delayed in species such as deer, elk, porcupines, opossums,
and other species that do not defend territories.
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Delayed Emigration
Any type of barrier, whether it be ecological, physical, or behavioral can result in delayed
emigration and its demographic consequences (e.g. frustrated dispersal, Lidicker 1975). A
common consequence of delayed emigration is delayed body growth and reproductive
suppression of young females as long as they remain in their family group or in the presence of
other adults. The proximate mechanisms for reproductive suppression may be to reduce
competition within the natal site (Abbott 1984; Digby 1995), to prevent inbreeding with close
relatives (Wolff 1992; 1997), or in response to the threat of infanticide from adult females
(Wasser and Barash 1983; Abbott 1984; Digby 1995; Wolff 1997). Delayed emigration can also
lead to cooperative breeding (Powell and Fried 1994; Creel and Waser 1994; Solomon and
French 1997). In all of these situations, reproductive suppression is a response to immediate
behavioral situations that are created because normal dispersal patterns are prevented.
Behavioral reproductive suppression does not appear to occur in nonterritorial species. Thus, the
behavioral and demographic responses to delayed dispersal should be a function of the species
behavioral system.
Delayed Emigration and Longevity
What does lifespan have to do with the demographic consequences of delayed emigration and
delayed reproduction? The probability of extinction, colonization, and persistence of a species in
a fragmented landscape is a function of life expectancy. In general, in long-lived species with
high annual survival rates, delayed sexual maturation and(or) foregoing a reproductive event has
relatively little long-term consequences compared to a species with a short life expectancy. For
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instance, whether a bear, wolf, or elk breeds as a 3-year old or reproduction is delayed until the
age of 5 or even 6, should have less consequences than if a vole or mouse delays sexual
maturation for even 3- to 4 weeks. The reproductive lifespan for most voles is 3-5 months with
2-week survival rates typically around 0.8 (Taitt and Krebs 1985; Schauber et al. 1997) compared
to >10 years longevity and 0.9 annual survival rates for larger mammals (Read and Harvey 1989;
Promislow et al. 1991). In Belding's and golden-mantled ground squirrels (S. beldingi and S.
lateralis), (which may live for up to 9 years) reproduction may be curtailed in years of
unfavorable weather with little long-term demographic consequences (Morton and Sherman
1978; Phillips 1984; Smith and Johnson 1985). If ecological or behavioral conditions are
temporarily unfavorable for reproduction in a short-lived species, a population can go extinct in a
few months, whereas long-lived species would be less affected. Population instability and the
probability of local extinctions is much greater for short-lived species than it is for long-lived
species (Pimm 1991). Thus, those aspects of a species life history that contribute to life
expectancy and lifetime reproductive potential should be considered when predicting the effects
of habitat fragmentation on a species.
Ecological Model Systems or Behavioral Model Systems?
What makes a good ecological model system? The EMS concept was first described by Ims and
Stenseth (1989) and later by Ims et al. (1993) and Wiens et al. (1993), but has had little
application to natural systems. If voles are to be used as EMS's, for what systems are they good
models? Voles, per se, probably are not good models for anything but voles. The problem has
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been that researchers have been studying voles or other species and have not addressed the
attributes of a species that makes them an EMS for other systems. Voles are not good ecological
models for capercaillre grouse and mice are not good models for moose or any other species.
The argument that I make above is that certain aspects of behavior are the feature that is the
model that can be used to predict how another model system will respond in a similar situation.
For instance, voles are not good ecological models for capercaillie grouse, but territoriality is the
common feature that makes both species respond the same way to fragmentation (Ims et al.
1993). Similarly, voles are not good ecological models for brown bears, but the reason they have
similar colonization potential is that both species have female philopatry and male-biased
dispersal. In contrast, snowshoe hares and porcupines have greater colonization potential than
predicted by their body size because they are not territorial and females disperse as often and far
as do males. The common feature of ground squirrels, naked mole rats (Heterocephalus glaber),
and mountain sheep is their sociality or conspecific attraction that inhibits individual dispersal.
Thus, behavioral models systems (BMS) might be a more appropriate concept than the EMS's
and research should be designed to test hypotheses regarding the role of specific behavioral
systems in dispersal and response to fragmented landscapes.
The relative influence of the above BMS factors on the ability for mammal species to
colonize fragmented landscapes is summarized in Table 2. Specific examples for how each of
these parameters is predicted to affect the propensity for various representative mammal species
to colonize patchy habitats is presented in Table 3. The various parameters are presented as their
relative contribution to whether or not a given species is more or less likely to disperse and
successfully colonize and persist in a patch of habitat than is predicted by body size alone
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(Appendix 1, Table 1). The values for each factor are expressed as + (positive = more likely to
colonize), - (negative = less likely to colonize), or 0 neutral. The success of a species in
colonizing habitat patches will be a function of the +/- ratio; with a higher value increasing the
species chances for colonizing habitat patches. For instance, the red fox would be a good
colonizer, the muskrat a poor colonizer, and the opossum intermediate. I compared the observed
and predicted dispersal distances for 17 species from Appendix I that represent all trophic levels
and a range of body sizes and life history traits (Table 3). Observed dispersal distances of 15 of
these 17 species fit those predicted by the traits listed in the table. The five variables listed in
Table 3 may not all be weighted the same, such as habitat specialist may have a greater influence
on colonization potential than mode of life or sociality greater than trophic level. The list of
variables and ranking is meant to be used as a relative ranking scheme to predict why some
species should be better colonists than others.
Summary
I attempted to look for a general conceptual model to identify those features associated with a
predisposition for a given mammal species to colonize new habitats. The overall pattern appears
to be associated with various aspects of the species' evolutionary and natural history, degree of
ecological specialization, trophic level, behavioral system, and body mass. Dispersal distance is
a function, of body mass, but also is influenced by ecological factors such as the distribution,
predictability, and renewability of food resources and the type of habitat matrix between patches,
Behavioral aspects that affect dispersal, colonization, and persistence are territoriality, sex-biased
dispersal, and degree of sociality or conspecific attraction. These features should in turn affect
19
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home range size and(or) annual movements. In species that have a predictable and(or) stationary
and renewable food source, females appear to be relatively philopatric and are not adapted to
long range movements or colonization of vacant habitats. Species that are adapted for colonizing
new habitats are likely those that have evolved under conditions that require long-distance
movements within the lifetime of individuals. These conditions should include seasonally
available food (e.g. winter and summer range) and(or) unpredictable or a mobile food source, and
frequent habitat disturbance such as early successional or fire-regime habitats.
Acknowledgments
This work was supported by NSF Grant 9508319 and cooperative agreements PNW 92-0283
between the U.S. Forest Service and Oregon State University, CR 824682 between the U.S.
Environmental Protection Agency and Oregon State University, Interagency agreement DW-
129J5631 between the U.S. Environmental Protection Agency and the U.S. Forest Service, and
DOD SERDP Project No. 241-EPA. The manuscript has been subjected to the U. S. EPA's peer
and administrative review and it has been approved for publication as an EPA document.
Mention of trade names or commerical products does not constitute endorsement of
recommendation for use. George Batzli and William Lidicker, Jr. provided helpful comments on
the manuscript. This is manuscript No. 11185 of the Oregon Agricultural Experiment Station.
20
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42
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Table 1.
Allometric relationships between dispersal distance and body mass of mammals
(data are from Appendix 1).
Formula for dependent variable = ab* where a = constant, b = mass, x = slope
Log(dispersal distance in km) = Iog(body mass in grams) x slope + intercept.
Trophic
intercept
Slope
status
N
(+SE)
(± SE)
r
P
Carnivores
23
-1.369 ±0.389
0.761 ±0.109
0.701
<.001
Herb/omnivores
51
-1.375 ±0.126
0.597 ±0.040
0.907
<001
All mammals
74
-1.420 ±0.150-
0.670 ±0.045
0.868
<.001 .
Males
22
-1.095 ±0.207
0.638 ±0.065
0.828
<.001
Females
17
-1.769 ±0.306
0.720 ±0.103
0.767
<.001
43
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Table 2.
Characteristics of species that make them good or poor colonizers of fragmented landscapes as
measured by dispersal ability.
Life, behavioral characteristics Dispersal ability
Mode of life aerial > terrestrial > arboreal > fossorial > freshwater
Degree of specialization generalists > specialists
Spacing behavior nonterritorial > territorial
Sex females = males
Body size large > small
Trophic level carnivores > omnivores > herbivores
Mobility migratory > nonmigratory
Sociality asocial > social (conspecific attraction)
44
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Table 3.
The relationship between the potential for colonization of representative terrestrial mammal species and
behavioral, ecological, and life history traits.
Species
Habitat
generalist/
specialist
Trophic
level
Mode
of life
Sociality
Dispersing
sex
Overall
rating
Observed
dispersal
distance
Predicted
disersal
distance
deer mouse
+
0
+
+
-
+++
1.0
0.2
meadow vole
-
-
+
+
-
++
0.1
0.4
red squirrel
-
-
-
+
+
++
1.0
1.2
pika
-
-
+
+
0
++
0.05
0.9
white-tailed
prairie dog
+
-
+
-
-
+
2.7
2.9
muskrat
-
-
-
-
-
-
.5
2.9
striped skunk
+
0
+
+
+
++++
12
4.6
marten
+
+
+
+
- •
i I t I .
45
9.4
opossum
+
0
+
+
-
+++
4.9
4.6
raccoon
•f
0
+
+
-
+++
23
8
45
-------
black-tailed
deer
+
-
+
+
-
+++
26
31
bighorn sheep
-
-
+
-
-
+
46
40
ermine
+
+
+
+
-
++++
7
2.6
porcupine
+
-
0
+
+
++++
10
9
red fox
-f
+
+
+
+
t I 1 i I
46
29
coyote
+
+
+
+
+
i i i11 i
116
67
gray wolf
+
+
+
+
+
i I i i I
128
128
Habitat: generalist (+), specialist (-)
Trophic level: carnivore (+), omnivore (0), herbivore (-)
Mode of life: terrestrial (+), arboreal (-), fossorial (-), fieshwater aquatic (-)
Sociality: asocial (+)» social (-)
Dispersing sex: females (or both sexes +), males (-)
Overall rating for potential to colonize (based on predicted dispersal distance as a function of body size): number of +'s indicate
potential for colonization (poor 0 to good -H-+++) , ' .
Observed and predicted dispersal distances are from Appendix I and formulas in Table 1.
46
-------
List of Figures
Figure 1. Allometric relationship between logI0 of dispersal distance and log10 of body mass
for carnivores and herbivores and omnivores. Data are from Appendix 1.
Figure 2. Allometric relationship between log10 of dispersal distance and log,0 of body mass
for males and females of all mammals. Data are from Appendix 1.
47
-------
m
o
m
%
'"V
lu
£
m
CL
m
13
Ui
o
Trophic level
A Carnivores
o Herb/omnivores
3 4 5 6
Log body mass
48
-------
Log dispersal distance, km
fb 1* O • ¦ IV3 w
o
n
-------
Appendix 1,
Mean body mass, mean dispersal distance, and primary dispersing sex (M = males, F = females, B = both sexes, ? not reported) for 59
species of mammals.
Species Mass Mean Primary
Sex kg distance dispersing References
km sex
Herbivores
Field vole, Microtus arvalis
F
.02
0.05
M
Boyce and Boyce 1988
Field vole, Microtus arvalis
M
.02
0.54
M
Boyce and Boyce 1988
Bank vole, Clethrionomys glarelous
M
.02
1.0
M
Steen 1994
Field mouse, Apodemus agrarius
M&F
.02
1.0
M
Szaki and Liro 1991
Deer mice, Peromyscus maniculatus
M&F
.02
1.0
M
Burt 1940
Cotton mouse, Peromyscus gossypinus
M
.02
0.9
M
Pournelle 1950
-------
Cotton mouse, Peromyscus gossypinus
F
.02
Meadow vole, Microtus pennsylvanicus
F
.04
Least chipmunk, Tamias minimus
M&F
.04
Yellow pine chipmunk Tamias amoenus
M
.05
Yellow pine chipmunk Tamias amoenus
F
.05
Merriam's kangaroo rat
Dipodomys merriami
M
.04
Merriam's kangaroo rat
Dipodomys merriami
F
.04
Stephen's kangaroo rat,
Dipodomys stephensi
M
.07
Stephen's kangaroo rat,
Dipodomys stephensi
F
.07
Taiga vole, Microtus xanthognathus
M
.1
Water vole, Arvicola terrestris
M
.12
Banner-tailed kangaroo rat
0.15 M Pournelle 1950
0.1 M McShea and Madison 1992
0.53 M Meredith 1974
1.0 M Meredith 1974
0.5 M Meredith 1974
0.27 B Jones 1989
0.17 B Jones 1989
0.4 B Price etal. 1994
0.4 B Price et al. 1994
0.8 M Wolff and Lidicker 1980
1.3 M Leuze 1980
51
-------
Dipodomys spectabilis M&F .12
Pika, Ochotona princeps M&F . 16
Red squirrel, Tamiasciurus hudsonicus M&F .25
Red squirrel, Sciurus vulgaris M&F .3
Pocket gopher, Thomomys talpoides ? . 1
Valley pocket gopher, Thomomys bottae .1
Columbian ground squirrel
Spermophilus columbianus F .47
Columbian ground squirrel
Spermophilus colombianus M .47
California ground squirrel,
Spermophilus beecheyi M&F .6
E. Gray squirrel, Sciurus carolinensis M&F .5
Jones et al. 1988, Waser and Jones
1989, Amarasekare 1994
Smith and Ivins 1983
Price and Boutin 1993
Wauters et al. 1994
Vaughan 1963
Lidicker and Patton 1987
Hackett 1987, Wiggett and.Boag
1989
Hackett 1987, Wiggett and Boag
1989
Evans and Holdenreid 1943
Cordes and Barkalow 1972
-------
Fox squirrel, Sciurus niger ? .8
Fox squirrel, Sciurus niger ? .8
Black-tailed prairie dog,
Cynomys ludovicianus M .8
Black-tailed prairie dog,
Cynomys ludovicianus F .8
White-tailed prairie dog Cynomys leucurus M&F 1.2
Muskrat, Ondatra zibethicus ? 1.2
Snowshoe hares, Lepus americanus M&F 1.5
Striped skunk, Mephitis mephitis M&F 2.6
Opossum, Didelphis virginiana M&F 2.7
Opossum, Didelphis virginiana M 2.7
Mountain hare, Lepus timidus ? 3.0
Marmot, Marmota Jlaviventris M 3.6
1.2
16.1
M
M
Baumgartner 1938
Allen 1943
3.1 M Garrett and Franklin 1988
1.7, M Garrett and Franklin 1988
2.7 M Clark etal. 1971
0.5 M Beshears 1951, Errington 1951
1.5 B O'Donoghue and Bergman 1992,
Keith et al. 1993
10-12 B Sargeant etal. 1982
3.2-4.9 B Van Druff 1971
B Reynolds 1945
10 B Hewson 1990
5.2 M Salsbury and Armitage 1994,
VanVuren and Armitage 1994
53
-------
Marmot, Marmota flaviventris F 3.6
Porcupine, Erethizon dorsatum M&F 7.8
European badger, Meles meles M 9
European badger, Meles meles F 9
Raccoon, Procyon lotor M&F 7
Beaver, Castor canadensis M&F 18
Black-tailed deer, Odocoileus hemionus M&F 64
Mule deer, Odocoileus hemionus M&F 64
White-tailed deer, Odocoileus virginianus M&F 91
Mountain goat, Oreamnos americanus M&F 80
Salsbuiy and Armitage 1994,
VanVuren and Armitage 1994
Dodge and Barnes 1975, Marshall et
al. 1962
Cheeseman et al. 1988
Cheeseman et al. 1988
Giles 1943, Priewert 1961, Lynch
1967, Fritzell 1978
Beer 1955, Libby 1957, Hodgdon
1978, Chubbs and Phillips 1994
Brown 1961, Bunnell and Harestad
1983
Brown 1992
Nelson and Mech 1992, Nelson
1993, Nixon et al. 1994
Richardson 1961
-------
Bighorn sheep, Ovis canadensis
M&F 1.00
Black bear, Ursus americanus F 70
Black bear, Ursus americanus M 125
Grizzly bear, Ursus arctos M 204
Elk, Cervus elaphw! M&F 204
Carnivores
Townsend's hiole, Scapanus townsendii
M&F
.14
Ermine, Mustela erminea
F
.12
Ermine, Mustela erminea
M
.23
Wambenger, Phascogale tapoatafa
F
.16
Wambenger, Phascogale tapoatafa
M
.2
Mink, Mustela vison
M
1.1
Welles and Welles 1961, Spalding
and Mitchell 1970
Rogers 1987
Rogers 1987
Craighead 1980
Brazda 1953, Cole 1969
Giger1973
Erlinge 1977
Erlinge 1977
Soderquist and Lill 1995
Soderquist and Lill 1995
Mitchell 1961; Gerell 1970
-------
Marten, Martes americana
M
1.2
Marten, Martes americana
F
1.2
Fisher, Mustela pennanti
F
2.3
Fisher, Mustela pennanti
M
4
Gray fox, Urocyon cinereoargenteus
M
3.6
Gray fox, Urocyon cinereoargenteus
F
3.6
Red fox, Vulpes vulpes
M&F
5.4
American badger, Taxidea taxus
F
6
American badger, Taxidea taxus
M
8
Otter, Lutra lutra
M
8
Otter, Lutra canadensis
F
7
Otter, Lutra canadensis
M
8
40
M
Hawley and Newby 1957
50
M
Latouretal, 1994
22.6
M
Arthur etal. 1993
23.0
M
Arthur etal. 1993
24
B
Nicholson et al. 1949
3
B
Nicholson et al. 1949, Sheldon 1953
46
B
Pils and Martin 1978, Trewhella et
al. 1988, Allen and Sargeant 1993,
Zimen 1984
52
M
Messick and Hornocker 1984
110
M
Messick and Hornocker 1984
16
M
Erlinge 1968
14
M
Melquist and Hornocker 1983
42
M
Melquist and Hornocker 1983
-------
Bobcat, Felts rufus
M&F
9
25
Lynx, Felis lynx M&F 10 20
Wolverine, Gulogulo M&F 12 100
Coyote, Canis latrcms M&F 16 116
Sea otter, Enhydra lutris M 32 96
Gray wolf, Canis lupus M&F 37 128
Cougar, Felis concolor M&F 70 99
57
Rollings 1945; Erickson 1955;
Robinson and Grand 1958; Knick
1990
Saunders 1963; Nellis and Wetmore
1969; Mech 1977
Magoun 1985, Gardner et al. 1986
Bekoff 1982; Bowen 1982; Harrison
1992
Jameson 1979
Kelsall 1968; Mech 1970; van Camp
and Gluckie 1979; Ballard et al.
1983; Gese and Mech 1991; Mech et
al. 1995
Hemker et al. 1965; Beier 1995
-------
NHEERL-COR-2152A
TECHNICAL REPORT DATA
(Please read instructions on the reverse before com
1EFAWo/A-97/07!
2.
3,
4, TITLE AND SUBTITLE
On applying behavioral model systems to landscape ecology
5. REPORT DATE
6. PERFORMING ORGANIZATION
CODE
7. AUTHOR(S) Jerry Wolff
8. PERFORMING ORGANIZATION REPORT
NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Fisheries and Wildlife
Oregon State University
Corvallis, Oregon 97331
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
US EPA ENVIRONMENTAL RESEARCH LABORATORY
200 SW 35th Street
Corvallis, OR 97333
13. TYPE OF REPORT AND PERIOD
COVERED
14. SPONSORING AGENCY CODE
EPA/600/02
15. SUPPLEMENTARY NOTES:
16. Abstract;
The impact of habitat loss and fragmentation of remaining habitats on the viability of plant and animal species is a
major concern in conservation biology and landscape ecology. Because experimental and observational data on species
responses to habitat loss and fragmentation are costly to collect, and impossible to collect for rare, endangered, and
large species, "ecological model species" (EMS) are frequently used to predict how other species will respond to these
disturbances. For example, experimental studies using small mammals (e.g., voles) in enclosed or manipulated habitats
have been used to predict how other species (e.g., cougar or grouse) might respond to similar situations.
Unfortunately, little attention has been paid to what attributes make a given species an appropriate EMS for other
species. Dr. Jerry Wolff, onsite cooperator from Oregon State University at NHEERL's Western Ecology division,
reviewed the available literature on species' response to habitat fragmentation and potential for habitat colonization.
Based on this evidence, he concludes that certain aspects of behavior play a major role in determining how species
respond to fragmented landscapes and that "behavioral model systems" might be a more appropriate basis, than the
EMS concept, for making comparisons and predictions among species. Dr. Wolff found that behavioral traits, such as
mobility, territoriality, sex-biased dispersal, mode of life (aerial, terrestrial, arboreal, fissural, freshwater,) degree of
specialization, degree of sociality or conspecific attraction, and trophic level, were related in a consistent and
predictable manner to the potential for a species to colonize fragmented habitats. The Pacific Northwest Research
Program at WED is evaluating the effects of large-scale landscape change on terrestrial vertebrate biodiversity, as well
as other ecological endpoints. The "behavioral model system" proposed in this paper will be used eventually to improve
model predictions of species viability and the effects of habitat loss and fragmentation in the Northwest on terrestrial
biodiversity.
1 7. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED
TERMS
c. COSATI Field/Group
habitat loss, landscape ecology,
conservation biology.
18. DISTRIBUTION STATEMENT
1 9. SECURITY CLASS (This Report1
21. NO. OF PAGES: 57
20. SECURITY CLASS (This page)
22. PRICE
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