Journal of Animal Ecology

A continental scale trophic cascade from wolves through coyotes to foxes

Journal of Animal Ecology

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Newsome, Thomas; Oregon State University, Department of Forest Ecosystems and Society Ripple, William; Oregon State University, Department of Forest Ecosystems and Society

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Key-words:

Standard Paper

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Complete List of Authors:

JAE-2014-00241.R1

apex-predator, bottom-up, interference competition, mesopredator release, species interactions, top-down, trophic cascades

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Re North America's top-predator, the grey wolf (photo credit: D. McLaughlin) 105x79mm (180 x 180 DPI)

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A continental scale trophic cascade from wolves through

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coyotes to foxes

3 4 5 Thomas M Newsome* a and William J Ripple a

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Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, United States *

Corresponding author: [email protected]

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Top-down processes, via the direct and indirect effects of interspecific

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Summary

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competitive killing (no consumption of the kill) or intraguild predation

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(consumption of the kill), can potentially influence the spatial distribution of

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terrestrial predators, but few studies have demonstrated the phenomenon at a

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continental scale.

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For example, in North America, grey wolves (Canis lupus) are known to kill

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coyotes (Canis latrans), and coyotes, in turn, may kill foxes (Vulpes spp.),

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but the spatial effects of these competitive interactions at large scales are

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unknown.

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Here, we analyse fur return data across eight jurisdictions in North America

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to test whether the presence or absence of wolves has caused a continent-

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wide shift in coyote and red fox (Vulpes vulpes) density.

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Our results support the existence of a continental scale cascade whereby coyotes outnumber red foxes in areas where wolves have been extirpated by

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humans, whereas red foxes outnumber coyotes in areas where wolves are

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present. However, for a distance of up to 200 km on the edge of wolf

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distribution, there is a transition zone where the effects of top-down control

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are weakened, possibly due to the rapid dispersal and reinvasion capabilities

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of coyotes into areas where wolves are sporadically distributed or at low

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densities. 5

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Our results have implications for understanding how the restoration of wolf

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populations across North America could potentially affect co-occurring

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predators and prey. We conclude that large carnivores may need to occupy

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large continuous areas to facilitate among-carnivore cascades and that studies

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of small areas may not be indicative of the effects of top-down mesopredator

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control.

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Key-words: apex-predator, bottom-up, interference competition, mesopredator

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release, species interactions, top-down, trophic cascades

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Introduction

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A key process that results in the direct displacement of a competitively subordinate

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individual is interference competition (Palomares & Caro 1999; Linnell & Strand

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2000), often manifested via the direct and indirect effects of interspecific competitive

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killing (no consumption of the kill) or intraguild predation (consumption of the kill)

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(Lourenço et al. 2013). Such agonistic interactions are thought to be an evolved

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behavioural response to broad-scale exploitation competition (Peterson 1996),

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because species that overlap in their use of the environment and resources are at an

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immediate and selective disadvantage if growth or reproduction is suppressed

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(Conner & Bowers 1987).

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Among carnivores, interference competition may be symmetrical (both species kill

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each other) or asymmetrical (one species kills the other), but dominance is typically

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based on size (Peterson 1996; Palomares & Caro 1999). This has generated interest

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in determining how large carnivores shape and drive community structure (Terborgh

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& Estes 2010; Estes et al. 2011; Ritchie et al. 2012; Ripple et al. 2014). It has also

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led to widespread predictions that the loss of large predators will release populations

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of smaller predators, as depicted by the mesopredator release hypothesis (Crooks &

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Soulé 1999; Ritchie & Johnson 2009).

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The ecological effects of mesopredator release, via predation and competition, can be

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dramatic and affect a wide range of faunal elements (Ripple et al. 2013). Yet, despite

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great interest in such interactions, there remains considerable debate about the

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relative efficacy of top-down control in terrestrial ecosystems because the outcomes

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of interactions between predators may vary with resource availability, habitat

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structure and the complexity of predator communities (Elmhagen & Rushton 2007;

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Ritchie & Johnson 2009). We propose that this debate arises because few studies

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have been conducted at spatial scales large enough to fully detect inverse patterns

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between carnivore abundances. There may also be different spatial effects of

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competition at the local or regional scale in comparison to the scale of the entire

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geographic ranges of one or more species (Conner & Bowers 1987). In order to fully

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understand the effects of cascading species interactions it is therefore crucial to

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conduct studies at multiple spatial scales.

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In North America, interference competition between grey wolves (Canis lupus),

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coyotes (Canis latrans) and foxes (Vulpes spp.) has been well studied at a local

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(landscape) scale. For example, wolves are known to kill both coyotes (Stenlund

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1955; Carbyn 1982; Merkle, Stahler & Smith 2009) and less so foxes (Stenlund

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1955; Mech 1966; Peterson 1977). Coyotes, in turn, may kill foxes (Sargeant &

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Allen 1989; Farias et al. 2005; Gosselink et al. 2007).

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At a broader (regional) scale, inverse relationships between the densities of both

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wolves and coyotes (Berger & Gese 2007), and coyotes and foxes (Fedriani et al.

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2000; Levi & Wilmers 2012) are supported by numerous accounts of spatial and

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temporal separation. For example, in northwest Montana, coyotes maintained

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random separation distances from wolves and there was temporal partitioning

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through differential arrangements of home ranges (Arjo & Pletscher 1999). Red

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foxes (Vulpes vulpes) have similarly been shown to select habitats which coyotes

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generally avoid (Sargeant, Allen & Hastings 1987; Gosselink et al. 2003).

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At a continental scale, as wolves were eliminated by humans from much of North

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America, coyotes dramatically expanded their historical range (Peterson 1996;

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Gompper 2002). However, little attention has been given to the broader effects of

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competitive interactions across large geographic areas such as those now occupied

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by the coyote. This is critical to understand because the effects of competition could

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alter the distribution of multiple predator-guilds at a continental scale. Therefore, we

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test the hypothesis that the presence or absence of wolves has caused a continent-

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wide shift in coyote and red fox densities due to the cascading effects of competition.

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We hypothesize that the spatial effects will manifest as a gradient that strengthens or

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weakens, depending on the level of human influence that penetrates the ranges of

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wolves.

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To test our hypotheses, we first review long term time series of fur return data over a

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1.3 million km2 area from the provinces of Saskatchewan and Manitoba, in central

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Canada. In those two provinces there is spatial overlap in the distribution of wolves,

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coyotes and red foxes in the northern forested areas. To the south, red foxes and

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coyotes co-occur, but wolves have been extirpated by humans from the crop and

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rangeland areas (Musiani & Paquet 2004). Thus, using the southern edge of wolf

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distribution as our predator divide, we test the hypothesis that the presence of wolves

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has caused a shift in predator-guilds. In particular, we predict that in the presence of

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wolves there will be relatively more fur returns for red foxes than coyotes. In the

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absence of wolves we predict there will be relatively more fur returns for coyotes

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than red foxes. We provide spatial replication and empirical support for our results

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by presenting fur return data from six other jurisdictions across the continent of

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North America.

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Materials and Methods

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HISTORICAL BACKGROUND TO STUDY DESIGN

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Over the last two centuries, widespread predator control resulted in wolves being

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largely restricted to the forested portions of far northern North America. Wolves only

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recently (post 1995) re-occupied 15% of their historic range in the conterminous

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United States (Bruskotter et al. 2013). Thus, during the 20th and 21st century, wolves

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have remained present in the far north of North America, but largely absent to the

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south (Fig. 1).

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Prior to European settlement, native red foxes (including the subspecies Vulpes

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vulpes alascensis, V. v abeitoru, V. v cascadensis, V. v necator, V. v macroura, V. v

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rigalis, and V. v rubricosa) were distributed throughout most of the boreal and

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montane portions of North America (Hersteinsson & Macdonald 1992; Kamler &

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Ballard 2002; Statham et al. 2012). Since the early 1900’s, red foxes may have

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expanded their distribution westward after non-native red foxes, of European origin,

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were introduced throughout the eastern United States and lowland areas in the

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Pacific coast states (Kamler & Ballard 2002). However, red foxes may have also

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expanded their range naturally from populations in Canada, perhaps due to more

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suitable human-altered habitat becoming available (Statham et al. 2012).

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Additionally, red foxes expanded their distribution northward into the higher

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latitudes and altitudes (Hersteinsson & Macdonald 1992). Thus, red fox distribution

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has largely overlapped that of wolves in the far north of North America throughout

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the 20th and 21st century, but red foxes also occur in areas where wolves are absent to

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the south (Fig. 1).

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Coyotes were historically mostly located in central North America (Gompper 2002;

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Fener et al. 2005). However, in the early 1900’s a wolf free corridor through Canada

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allowed for coyotes to disperse from the central United States to as far north as

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Alaska (Peterson 1996). The near-elimination of wolves from the lower 48

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conterminous United States was also followed by coyote dispersal as far east as

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Nova Scotia, which coyotes reached by the 1980’s (Parker 1995). Thus, since the

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early 1900’s, coyotes have been dispersing into areas occupied by wolves and red

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foxes in the north and northwestern portions of North America. There has also been a

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30 year presence of coyotes in the northeast where wolves are absent, but where red

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foxes are present (Fig 1). The historical expansion of coyotes into areas where

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wolves and/or red foxes occur therefore provides the basis of a “natural experiment”

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to examine.

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MAIN STUDY SITES AND DATA

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We first analyse the fur returns of coyotes and red foxes in two large provinces of

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Canada, namely Saskatchewan (651,900 km²) and Manitoba (647,797 km2) (see Fig.

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1 - “Transition Sites”). The northern two-thirds of Saskatchewan and Manitoba are

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dominated by coniferous forest (>75% forest cover). The southern third is dominated

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by rangeland (<10% forest cover) and cropland (0% forest cover). The southern edge

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of wolf distribution generally coincides with the boundary of the forested and open

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areas in both provinces (See Appendix S1 in Supporting Information). Fur returns for

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coyotes and red foxes were collected from 136 wildlife management zones by the

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Government of Saskatchewan each year since 1982 (Appendix S2). Fur returns for

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coyotes and red foxes were collected from 40 wildlife management zones by the

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Government of Manitoba each year since 1996 (Appendix S2). We used these time

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series data sets to test our hypotheses.

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SPATIAL PATTERNS OF PREDATOR DENSITY

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To broadly assess if the presence or absence of wolves results in suppression of

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coyotes or red foxes we divided the total number of coyote fur returns by the number

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of red fox fur returns for each wildlife management zone in Saskatchewan and

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Manitoba. The ratio was used because we were primarily interested in the relative

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abundance of coyotes and red foxes in areas with and without wolves. Thus, we

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assumed a ratio > 1 reflects an area with relatively more coyotes than red foxes

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(Thurber et al. 1992; Peterson 1996).

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For more detailed analyses we focused on the northern predominantly forested areas

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where wolves were present in Saskatchewan and Manitoba (Fig. 1; Appendix S1).

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First, we calculated distance (km) from the centroid of each wildlife management

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zone to the closest point along the southern edge of wolf distribution. We then used a

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linear regression to model the relationship between coyote:fox ratios (including on

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the log scale) and distance from the edge of the wolf distribution using software R (R

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Development Core Team). To test for independence (spatial correlation) we plotted

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the standardised residuals from the linear regression against fitted values. We also

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plotted the residuals versus their spatial co-ordinates (Zuur, Ieno & Walker 2009).

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We then examined the spatial and temporal relationship between wolves, coyotes and

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red foxes across three geographic zones in Saskatchewan and Manitoba (i) the south

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where wolves were absent, (ii) a “transition zone” (determined by the above analysis

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as the distance from the edge of wolf distribution where red fox fur returns started to

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outnumber coyote fur returns), and (iii) the north where wolves were present.

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The study site in Manitoba additionally provided an opportunity to assess the

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relationship between wolves, coyotes and red foxes within two forested wolf-occupied

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wildlife management zones surrounded by agricultural lands where wolves were very

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scarce, namely at Porcupine (1948 km2) and Duck Mountain (3616 km2) (see Fig. 2).

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To do so, we plotted yearly numbers of coyote and red fox fur returns to assess which

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predator consistently had more returns.

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SPATIAL REPLICATION AT THE CONTINENTAL SCALE

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To assess if there is additional support for our hypotheses at a continental scale we

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first plotted long term numbers of coyote and red fox fur returns for jurisdictions in

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northwestern North America, where coyotes and red foxes have co-occurred since the

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early 1900’s (Hersteinsson & Macdonald 1992; Peterson 1996). We chose

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jurisdictions where wolves were present within the entire province or state boundary,

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namely the NW Territories, the Yukon and Alaska (Fig. 1). Second, we plotted long

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term numbers of coyote and red fox fur returns for jurisdictions in northeastern North

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America, where coyotes and red foxes have co-occurred since the 1980’s (Fener et al.

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2005). Here we chose jurisdictions where wolves were absent within the entire

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province or state boundary, namely Nova Scotia, New Brunswick and Maine (Fig. 1)

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(but see also Appendix S2 for more details on data sources).

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Results

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SPATIAL PATTERNS OF PREDATOR DENSITY

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The spatial distribution of the coyote:fox ratio values show that red fox fur returns

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outnumber coyote fur returns at sites to the north of wolf distribution in both

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Saskatchewan and Manitoba (Fig. 2). This is supported by the least squares

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regressions which showed a significant relationship between coyote:fox ratios (on

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the log scale) and distance to the edge of the wolf distribution in both Saskatchewan

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(r2 = 0.85, F1,87 = 506.61, P < 0.0001) and Manitoba (r2 = 0.64, F1,33 = 59.04, P <

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0.05) (Fig. 3). There was no indication of south-north spatial correlation based on the

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plots of the standardised residuals against fitted values or the plots of residuals

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versus their spatial co-ordinates in either Saskatchewan or Manitoba (Appendix S3).

233 In Saskatchewan, the linear and non linear fitted lines indicates that red fox fur

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returns start to outnumber coyote fur returns at a distance of approximately 200 km

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from the edge of the wolf distribution (Fig. 3). In Manitoba, red fox fur returns start

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to outnumber coyote fur returns at a distance of approximately 100 km from the edge

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of the wolf distribution (Fig. 3). These results are supported by the plots of fur return

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data on a yearly basis which indicate that coyote fur returns always outnumber red

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fox fur returns in the absence of wolves, whereas the opposite is true north of the

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transitional zone distances of 200 km in Saskatchewan and 100 km in Manitoba (Fig.

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4). This apparent shift occurred despite greater overall numbers of fur returns for

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both coyotes and red foxes in the southern agricultural region compared to the

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northern forested region (Fig. 5). Additionally, in the habitat islands of Duck

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Mountain and Porcupine, which are located within 100 km of wolf range in

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Manitoba, coyote fur returns consistently outnumber red fox fur returns on a yearly

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basis, despite the presence of wolves (Fig. 6).

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SPATIAL REPLICATION AT THE CONTINENTAL SCALE

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In the jurisdictions where wolves were present (NW Territories, the Yukon and

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Alaska; Fig. 1) red fox fur returns always outnumber coyote fur returns (Fig. 7). In

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contrast, in the jurisdictions where wolves were absent (Nova Scotia, New Brunswick

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and Maine; Fig. 1) the plots from 1970 to 2010 show that red fox fur returns generally

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decline as coyote fur returns increase (Fig. 7). By the year 2000, coyote fur returns

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outnumber red fox fur returns in all three jurisdictions in the northeast (Fig. 7)

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Discussion

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Our analysis supports the occurrence of a continent-wide mesopredator cascade from

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wolves through coyotes to red foxes. Across multiple jurisdictions and spatial scales,

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we show that in areas where wolves are present that red fox fur returns outnumber

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coyote fur returns (Fig. 7). In the absence of wolves we show that coyote fur returns

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outnumber red fox fur returns (Fig. 7). In Saskatchewan and Manitoba, the spatial

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distribution of coyote and red fox fur returns was likely also influenced by the

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distribution of wolves (Fig. 4). However, the presence of a large transition zone on the

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edge of wolf distribution, where coyote fur returns outnumber red fox fur returns

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(Figs 2 and 3), suggest that the cascading effects of top-down control on

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mesopredators might only become manifest where wolves occur continuously over a

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large spatial area.

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Although our analysis is correlative, our conclusions are based on plausible

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mechanisms of asymmetrical interference competition and size based dominance

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among canids (Peterson 1996). For example, at a smaller spatial scale than our

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analyses, Levi & Wilmers (2012) showed that as wolves suppress coyote populations

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that foxes are released from top-down control by coyotes. A major factor potentially

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influencing our results is the bounty price paid for coyote and red fox fur returns.

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However, fur prices of coyotes and red foxes are correlated on a year-to-year basis in

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both Saskatchewan (r = +0.85, P < 0.001) and Manitoba (r = +0.82, P < 0.05)

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(Appendix S4). Other factors that could influence the harvest rates include (i)

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background fluctuations in populations, (ii) poor weather conditions for trapping and

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(iii) regulatory changes. However, with respect to the first two factors, these apply

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equally to coyotes and red foxes because of their biological similarities (McDonald et

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al. 2008; Levi & Wilmers 2012). There has also been a consistent bounty on coyotes

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and red foxes for the time period of our study and no regulatory changes that could

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have influenced their harvest rates. We are therefore confident that our ratio values

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reflect the relative abundance of coyotes versus red foxes in both provinces.

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In any case, we provide spatial and temporal replication providing compelling support

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for our hypotheses. In northwestern North America, where wolves are present,

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coyotes and red foxes have co-occurred since the early 1900’s (Hersteinsson &

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Macdonald 1992; Peterson 1996). While the northward expansion of coyotes was

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aided by wolf control in some areas (Peterson 1996), the fur return data suggest that

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coyotes never outnumbered red foxes in the northwest (Fig. 7). Indeed, in Alaska,

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coyotes only became common in localised areas where wolves were reduced

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(Peterson 1996). In northeastern North America, where wolves are absent, coyotes

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and red foxes have only co-occurred since the 1980’s (Fener et al. 2005). Despite this

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short timeframe, the fur return data suggest that it only took coyotes 20-30 years to

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outnumber red foxes in the absence of wolves (Fig. 7). These trends are also

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independent of bounty price because coyote and red fox fur prices are generally

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correlated in North America dating back to the early 1900’s (Appendix S4).

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Additionally, our analyses does not include data from pre-20th century when all

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species of foxes were combined into one category, and when wolves and coyotes were

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also frequently misidentified (Novak et al. 1987) (Appendix S2). Nor does it include

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fur records from ranch (farmed) foxes, or exclude records based on whether or not

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they were tagged or “sealed” (Novak et al. 1987) (but see Appendix S2 for further

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details). Thus, we are confident that our data outside of Saskatchewan and Manitoba

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also reflect the relative abundance of coyotes versus red foxes.

306 Further support for our hypotheses is provided by comparing fur return data across

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three geographic regions in Saskatchewan and Manitoba (Fig. 4). In both provinces,

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coyote fur returns always outnumber red fox fur returns in the absence of wolves. In

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the presence of wolves, to the north of the transition zones, red fox fur returns always

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outnumber coyote fur returns (Fig. 4). The fact that red fox fur returns are lower in the

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north (where wolves are present) compared to the south (where wolves are absent)

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does not disprove our hypothesis. For example, it could be interpreted that wolves

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negatively affect red foxes because there are fewer red fox fur returns in the north

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compared to the south (Fig. 5). However, in the context of our study it is not the

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direction of change in abundance that matters, it is whether or not red foxes start to

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outnumber coyotes as you move north into wolf range, and this is what we

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demonstrate. Indeed, the scale of effect is dramatic with coyote fur returns

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outnumbering red fox fur returns in the south by up to 10:1 and red fox fur returns

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outnumbering coyote fur returns at an extreme of 517:1 in the north (Appendix S5).

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It could also be interpreted that changes in land-use and habitat influence the

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northward expansion of coyotes. For example, it could be argued that red foxes are

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more suited to the northern forested areas than coyotes. However, our spatial scale

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analysis predominantly considers forested habitat within wolf range and there is no

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change in land-use or habitat at the point where red fox fur returns start to outnumber

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coyote fur returns in Saskatchewan and Manitoba (Appendix S1). Indeed, the change

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from predominantly coniferous forest to a transitional and tundra forest is well over

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500 km from the edge of wolf distribution (Appendix S1). Thus, there is insufficient

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evidence to suggest that the northward expansion of coyotes is limited by changes in

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land-use and habitat. This reflects the fact that coyotes and red foxes have similar

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habitat requirements (McDonald et al. 2008; Levi & Wilmers 2012). Our results

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therefore accord with those of Levi & Wilmers (2012) who demonstrated that bottom-

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up factors, land-use changes and habitat differences are insufficient to explain the

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pattern of spatial relationships between wolves, coyotes and foxes.

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The discovery of the transition zones in Saskatchewan and Manitoba and the large

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scale of our analysis distinguishes our study from others. In particular, we quantified

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the extent to which top-down mesopredator control occurs on the edge of wolf

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distribution. This has implications for understanding how competitive interactions

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influence the spatial distribution and density of predators. For example, coexistence

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between wolves and coyotes may be facilitated where wolves leave carcases of large

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prey for coyotes to scavenge (Paquet 1992). Thus, the distribution of wolves and

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coyotes throughout North America could be related to the distribution, abundance and

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diversity of prey species, in conjunction with wolf prey selection (Paquet 1992).

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However, the strong negative linear relationship between the coyote:fox ratios and

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distance to the southern edge of wolf distribution are more suggestive of a “ramp”

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effect due to very low densities of wolves on the periphery of their distribution

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(Caughley et al. 1988).

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A ramp effect could occur if an attribute such as density is low at the periphery but

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rises progressively towards the core of distribution (Caughley et al. 1988). The

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possibility of a ramp effect in our study is strengthened by the observation that the

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ramp extends for 200 km in Saskatchewan but only 100 km in Manitoba, where the

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presence of physical barriers (lakes) produces a steeper ramp, or “step” effect

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(Caughley et al. 1988). For example, should density step at the range boundary, the

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factor controlling the position of the boundary is likely to be a substrate or physical

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barrier (Caughley et al. 1988). Thus, if wolf density progressively declines towards

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the edge of their distribution, the strength of top-down control may also progressively

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decline towards the edge of wolf distribution, as indicated by the strong negative

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linear relationship between the coyote:fox ratios and distance to the southern edge of

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wolf distribution in our study (Fig. 3).

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An additional factor to consider is the rapid dispersal and reinvasion capabilities of

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coyotes. For example, densities of coyotes may vary spatially and temporally in

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accordance with wolf abundance (Berger & Gese 2007), but they also may relate to

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coyote movements. In a insular example, lack of dispersal from adjacent areas may

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facilitate complete exclusion of competitively subordinate individuals, such as when

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coyotes were eliminated from Isle Royale a decade after wolves arrived (Peterson

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1996). The opposite is true where reinvasion of coyotes is possible. In fact, despite

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wolves being present within the small habitat islands of Porcupine and Duck

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Mountain in Manitoba, red fox fur returns never outnumber coyotes (Fig. 6). Coyotes

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were also abundant within the wolf occupied area of the nearby Riding Mountain

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National Park, but the park is also relatively small in size (2976 km2) and surrounded

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by agricultural lands where coyotes were common and wolves generally absent

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(Carbyn 1982; Paquet 1991).

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localised areas by up to 39% after wolf reintroduction (Berger & Gese 2007), but

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there was no drastic overall suppression of coyote populations in the Greater

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Yellowstone Ecosystem (72519 km2) (Berger & Gese 2007). The high dispersal

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capacity of coyotes potentially allows them to penetrate tens of kilometres into wolf

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ranges (Peterson 1996). Indeed, our data suggest that coyotes can penetrate up to 200

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km within wolf range. The interactions between wolves and coyotes within Riding

385

Mountain and Yellowstone National Park are therefore unsurprising given they are

386

both relatively small habitat islands (Fig. 2). However, the amount of coyote dispersal

387

into wolf range could reflect local resource conditions, especially if coyotes persist at

388

high densities in human altered landscapes on the edge of wolf distribution.

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Our results have implications for understanding how the restoration of wolf

391

populations in North America will affect species interaction webs. For example,

392

coyotes were historically mostly restricted to central North America, but in less than

393

two centuries they colonised most of the continent (Gompper 2002; Fener et al. 2005).

394

As a consequence, there have been widespread predictions that in the absence of

395

wolves coyotes will exert intense predation pressure on their typical prey (Miller et al.

396

2012; Ripple et al. 2013). Indeed, coyote depredation after wolf extirpation has been

397

linked to the decline of jack-rabbit (Lepus spp.), cottontail (Sylvilagus spp.) and

398

pygmy rabbit (Brachylagus idahoensis) populations, among others (Ripple et al.

399

2013). Moreover, in the province of Nova Scotia, there has been a decline in white-

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400

tailed deer (Odocoileus virginianus), coincident with the arrival of coyotes

401

(unpublished data, Nova Scotia Department of Natural Resources 2013). Thus, if wolf

402

populations expand and suppress coyotes, it is possible that a release of foxes will

403

result in wolf and fox dominant prey being consumed (Levi & Wilmers 2012). The

404

expansion of wolves may also provide positive outcomes for some lineages of

405

montane red foxes that are potentially threatened by coyote predation (Sacks et al.

406

2010).

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However, our results suggest that wolves may need to occupy large areas to facilitate

409

an among-carnivore cascade given that the effects of top-down mesopredator control

410

are weakened on the edge of wolf distribution for up to 200 km. No study has

411

previously quantified the size of the “border region” or “transition zone” that

412

influences the effectiveness of top-down mesopredator control. Nor has it previously

413

been appreciated that the border region may be of this magnitude. The spatial area that

414

wolves occupy is therefore an important factor to consider when assessing their ability

415

to assert top-down control. For example, the apparent variation in top-down control

416

that we found suggests that large carnivores may need to occupy large continuous

417

areas to facilitate among-carnivore cascades, and further, that the spatial scale of a

418

study can contribute significantly to variation in the results obtained. Indeed, given

419

that wolves only occupy 15% of their former range in the United States (Bruskotter et

420

al. 2013), and that much of their current range is surrounded by agricultural lands

421

where coyotes are common, the potential for wolves to suppress coyotes may be

422

limited.

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Consideration of spatial scales also has broader implications for understanding

425

competitive interactions between predators in other systems. For example, in

426

Australia the dingo (Canis dingo) is considered a top-predator and potential trophic

427

regulator that can suppress the activity or abundance of the invasive red fox and

428

possibly also the feral cat (Felis catus) (Johnson, Isaac & Fisher 2007; Glen et al.

429

2007; Letnic & Koch 2010; Letnic et al. 2011). However, assessments of

430

correlations between dingo and red fox densities typically reveal a triangular

431

relationship, whereby dingo abundance sets an upper limit on the abundance of red

432

foxes (Johnson & VanDerWal 2009). In other words, when dingoes are abundant,

433

red foxes are consistently rare, whereas the strength of top-down mesopredator

434

control is weakened when dingoes are uncommon. This suggests that when control

435

programs reduce dingo abundance that top-down suppression may be weakened (see

436

also Wallach et al. 2010). Thus, where there are gradients of human influence that

437

penetrates the size of dingo ranges over large spatial areas, similar results to those

438

obtained in our study could be present.

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Alternatively, the strength of top-down control by dingoes may be influenced by

441

bioclimatic effects and from anthropogenic habitat change. For example, after

442

wolves and lynx (Lynx lynx) populations declined in northern Europe, there was

443

accelerated growth rates of red foxes in productive regions, whilst the release effect

444

was negligible in unproductive regions (Elmhagen & Rushton 2007). But, here we

445

show that coyotes could feasibly disperse large distances into wolf range and that the

446

effects of top-down control are also weakened in systems where there is a gradient of

447

human influence that penetrates the size of wolf ranges. Thus, where there is

448

sporadic distribution of a top-predator, like the wolf in the parts of the conterminous

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Page 20 of 40

449

United States (Fig. 1) and the dingo in Australia (Letnic, Ritchie & Dickman 2012),

450

we suggest that the spatial effects of competition might be reduced. We therefore

451

reemphasise that in order to facilitate the suppression of mesopredators it may

452

require establishment of top-predator communities over large continuous areas where

453

they remain at ecologically effective densities. This remains one of the greatest

454

conservation challenges in a world where large carnivores are in significant decline

455

because of human-wildlife conflicts (Ripple et al. 2014).

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Acknowledgements

458

The manuscript was greatly improved after reviews by Taal Levi, Chris Dickman

459

and Aaron Wirsing. The work was made possible by funding from the Australian-

460

American Fulbright Commission.

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Figure legends

607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654

Figure 1 Study areas in relation to the current distribution of wolves (Canis lupus), coyotes (Canis latrans) and red foxes (Vulpes vulpes) in North America. Figure 2 The ratio of coyotes (Canis latrans) to red foxes (Vulpes vulpes) based on the total number of fur returns collected from 136 wildlife management zones by the Government of Saskatchewan from 1982-2011 and from 40 wildlife management zones by the Government of Manitoba from 1996-2010. Note that fur returns from the open trapping areas 1-5 are pooled by the Government of Manitoba.

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Figure 3 The ratio of coyote (Canis latrans) to red fox (Vulpes vulpes) fur returns within wolf (Canis lupus) range in Saskatchewan and Manitoba (see Fig. 2) against the distance from the centriod of each wildlife management zone to the southern edge of wolf distribution. Data from the open trapping areas in Manitoba within wolf range (see Fig. 2) have been excluded from the analysis because fur return counts are pooled across areas with and without wolves. Three sites with no coyotes or no red foxes were also excluded from the analysis.

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Figure 4 Total number of coyote (Canis latrans) and red fox (Vulpes vulpes) fur returns for three comparable geographic zones in Saskatchewan and Manitoba.

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Figure 5 Average number of coyote (Canis latrans) and red fox (Vulpes vulpes) fur returns for three comparable geographic zones in Saskatchewan (1982-2011) and Manitoba (1996-2010) (±95% confidence intervals). Figure 6 Total number of coyote (Canis latrans) and red fox (Vulpes vulpes) fur returns in two forested wildlife management zones surrounded by cleared land and on the edge of wolf (Canis lupus) distribution in Manitoba (see Fig. 2 for locations).

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Figure 7 Total number of coyote (Canis latrans) and red fox (Vulpes vulpes) fur returns in six jurisdictions in North America with and without wolves (Canis lupus). Coyotes colonised the three wolf absent areas starting in the 1970’s.

Appendix S1 Landcover map for Saskatchewan and Manitoba showing that there is no major change in land-cover 200 km north of the wolf (Canis lupus) distribution edge in Saskatchewan or 100 km north of the wolf distribution edge in Manitoba. Data was sourced from the Canadian Government vegetation and land cover mapping project derived from the advanced very high resolution radiometer sensor (AVHRR) (available at http://geogratis.gc.ca/geogratis/search?lang=en). Appendix S2 Additional notes on data sources. Appendix S3 Plots of standardised residuals obtained from the linear regression model (of coyote:fox ratios (on the log scale) and distance from the edge of wolf distribution in Saskatchewan and Manitoba) against fitted values (a) and their spatial coordinates (b). In (b) the blue circles are positive residuals, and open circles are negative residuals. In (b) for both Saskatchewan and Manitoba there is no major indication of south-north 24

Journal of Animal Ecology

spatial correlation because there is no spatial pattern or clustering in that direction (e.g. groups of positive and negative residuals close to each other) (see Zuur, Ieno & Walker 2009). Appendix S4 Historical fur prices ($ CAD) for coyotes (Canis latrans) and red foxes (Vulpes vulpes) for jurisdictions in North America relevant to the study. Data were not available for all years relevant to the study and no data were available for Maine and Alaska, but see trends for North America. Overall, coyote fur prices are consistently correlated with red fox fur prices. See Appendix S2 for notes on data sources. Appendix S5: The ratio of red fox (Vulpes vulpes) to coyote (Canis latrans) fur returns within wolf (Canis lupus) range in Saskatchewan and Manitoba against the distance from the centriod of each wildlife management zone to the southern edge of wolf distribution. Data from the open trapping areas in Manitoba within wolf range (see Fig. 2) have been excluded from the analysis because fur return counts are pooled across areas with and without wolves. Three sites with no coyotes or no red foxes were also excluded from the analysis. Here we show that red fox fur returns outnumber coyotes at an extreme of 517:1 at one site in Manitoba.

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Page 26 of 40

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Study areas in relation to the current distribution of wolves (Canis lupus), coyotes (Canis latrans) and red foxes (Vulpes vulpes) in North America. 155x96mm (300 x 300 DPI)

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Page 28 of 40

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The ratio of coyotes (Canis latrans) to red foxes (Vulpes vulpes) based on the total number of fur returns collected from 136 wildlife management zones by the Government of Saskatchewan from 1982-2011 and from 40 wildlife management zones by the Government of Manitoba from 1996-2010. Note that fur returns from the open trapping areas 1-5 are pooled by the Government of Manitoba. 164x125mm (300 x 300 DPI)

Page 29 of 40

Journal of Animal Ecology

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The ratio of coyote (Canis latrans) to red fox (Vulpes vulpes) fur returns within wolf (Canis lupus) range in Saskatchewan and Manitoba (see Fig. 2) against the distance from the centriod of each wildlife management zone to the southern edge of wolf distribution. Data from the open trapping areas in Manitoba within wolf range (see Fig. 2) have been excluded from the analysis because fur return counts are pooled across areas with and without wolves. Three sites with no coyotes or no red foxes were also excluded from the analysis. 156x100mm (300 x 300 DPI)

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Re Total number of coyote (Canis latrans) and red fox (Vulpes vulpes) fur returns for three comparable geographic zones in Saskatchewan and Manitoba. 168x124mm (300 x 300 DPI)

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On Average number of coyote (Canis latrans) and red fox (Vulpes vulpes) fur returns for three comparable geographic zones in Saskatchewan (1982-2011) and Manitoba (1996-2010) (±95% confidence intervals). 174x213mm (300 x 300 DPI)

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Total number of coyote (Canis latrans) and red fox (Vulpes vulpes) fur returns in two forested wildlife management zones surrounded by cleared land and on the edge of wolf (Canis lupus) distribution in Manitoba (see Fig. 2 for locations). 118x108mm (300 x 300 DPI)

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Total number of coyote (Canis latrans) and red fox (Vulpes vulpes) fur returns in six jurisdictions in North America with and without wolves (Canis lupus). Coyotes colonised the three wolf absent areas starting in the 1970’s. 171x135mm (300 x 300 DPI)

Journal of Animal Ecology

Page 34 of 40

Appendix S1 Landcover map for Saskatchewan and Manitoba showing that there is no major change in land-cover 200 km north of the wolf (Canis lupus) distribution edge in Saskatchewan or 100 km north of the wolf distribution edge in Manitoba. Data was sourced from the Canadian Government vegetation and land cover mapping project derived from the advanced very high resolution radiometer sensor (AVHRR) (available at http://geogratis.gc.ca/geogratis/search?lang=en).

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Appendix S2 Additional notes on data sources. Data sources Government of Manitoba

Data types Coyote and red fox fur returns from wild harvests and prices paid.

Relevant provinces (year) Manitoba (1996-2010)

Other relevant notes and considerations  Detailed fur return data collected at the individual wildlife management zone level by the Government of Manitoba each year based on payments made to trappers and hunters.  No fur farm data are included in our analyses.  There is no requirement to tag or “seal” coyote or fox furs in Manitoba (this could bias the results if only sealed returns are counted).

Government of Saskatchewan

Coyote and red fox fur returns from wild harvests and prices paid.

 Detailed fur return data collected at the individual wildlife management zone level by the Government of Saskatchewan each year based on payments made to trappers and hunters.

Saskatchewan (1982-2011)

Fo rR

Coyote and red fox fur returns from wild harvests and prices paid.

 There is no requirement to tag or “seal” coyote or fox furs in Saskatchewan. NW Territories (1970-2009)

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Statistics Canada Database (http://www5.statcan.gc.ca/cans im/a03?lang=eng&pattern=0030013,003-0014,003-0015)

 No fur farm data are included in our analyses.

 For details on data sources and methodology see web site link provided.

Nova Scotia (1970-2010) Additional notes:

New Brunswick (1970-2010)

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 No fur farm data are included in our analyses.

The Yukon (1970-2009) Canada price trends (1970-2009)

 Data are based on a census survey on the number and value of wildlife pelts produced in Canada through provincial administrative sources.

 Quality is viewed as excellent as the data are closely scrutinized by each individual province and corrected before being provided to Statistics Canada where the data are validated by comparing it to previous periods and other provinces.

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 The data accuracy of this census survey is high as the response rate is normally 100%, although occasionally reports are provided late.

 Our data includes all fur returns and is therefore not biased by tagging or “sealing” requirements. National Furbearer Harvest Statistics Database (www.fishwildlife.org/files/AF WA_Fur_Harvest_2012.xls)

Coyote and red fox fur returns from wild harvests and prices paid.

Maine (1970-2010)

 For details on data sources and methodology see web site link provided.

Alaska (1970-1997) Additional notes:  For red foxes and coyotes in Alaska and Maine the data are based on wild harvests, largely from trapping.  No fur farm data are included in our analyses.

Journal of Animal Ecology

Page 36 of 40  Based on inspection of trapping guidelines available from Alaska there has been no requirement to tag or “seal” coyote or fox furs from 1970 onwards. Thus, our data includes all fur returns and is therefore not biased by tagging or “sealing” requirements.

Novak et al. (1987).

Coyote and red fox fur returns from wild harvests and prices paid.

Alaska (1934-1969)

Relevant notes on data sources and methodology (from Novak et al. 1987):

NW Territories (1919-1969) The Yukon (1919-1969) North America price trends (1918-1970)

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 In Canada, separate records have been kept for each species and each colour phase since 1919 (Statistics Canada 1920-1985). However, prior to the 194344 season the total fox harvest reported in Catalogue 23-207, Fur Production (Statistic Canada 1920-1985) included the production of ranch foxes. For those years, it was necessary to subtract the total ranch fur production given in Catalogue 23-208, Fur Farms of Canada (Statistics Canada 1920-1944) from the grand total given in Catalogue 23-207 to arrive at the wild fur harvest figure. In the United States, separate data are available for the arctic fox from 1934-35 to the present. From 1934-35 to 1953-54, the remaining U.S data for foxes are a composite of gray, red, and kit/swift foxes. In this period, some jurisdictions listed gray foxes or swift foxes separately, but most reported a combined figure so we have reported combined figure for these years. From 1954-55 to 1969-70, the swift fox harvest was generally not recorded and gray and red foxes were lumped together. From 197071 to the present, separate data are available for all fox species.

ly

On

 Novak et al. (1987) does not state that tagging or “sealing” requirements may have biased the results. However, there was a requirement to tag fox furs but not coyote furs prior to Alaska becoming a State in the late 1950’s. This could influence the data in Alaska from 19341959, however we provide trapping data for Alaska from 1960-1997 and provide spatial replication in two neighbouring jurisdictions to support our results.  No fur farm data are included in our analyses (see notes above).  Data on the harvest of coyotes are only available for the 20th century. Even in the 20th century, there are periods in some jurisdictions where the harvest for coyotes and wolves are combined.  Novak et al. (1987) states that where wolves and coyotes have been combined they used the same total for both species. This would overestimate, not underestimate the coyote population, so our conclusions are not biased because of misidentification.

Page 37 of 40

Journal of Animal Ecology

Appendix S3 Plots of standardised residuals obtained from the linear regression model (of coyote:fox ratios (on the log scale) and distance from the edge of wolf distribution in Saskatchewan and Manitoba) against fitted values (a) and their spatial coordinates (b). In (b) the blue circles are positive residuals, and open circles are negative residuals. In (b) for both Saskatchewan and Manitoba there is no indication of south-north spatial correlation because there is no spatial pattern or clustering in that direction (e.g. groups of positive and negative residuals close to each other) (see Zuur, Ieno & Walker 2009).

Saskatchewan (a)

iew

ev

rR

Fo ly

On

(b)

60.00

59.00

58.00

57.00

56.00

55.00

54.00

53.00

52.00 -110.00

-108.00

-106.00

-104.00

-102.00

Journal of Animal Ecology

Page 38 of 40

Manitoba (a)

iew

ev

rR

Fo (b)

58.00 57.00

ly

On

59.00

56.00 55.00 54.00

53.00 52.00 51.00 50.00 -102.00

-100.00

-98.00

-96.00

-94.00

-92.00

Page 39 of 40

Journal of Animal Ecology

Appendix S4 Historical fur prices ($ CAD) for coyotes (Canis latrans) and red foxes (Vulpes vulpes) for jurisdictions in North America relevant to the study. Data were not available for all years relevant to the study and no data were available for Maine and Alaska, but see trends for North America. Overall, coyote fur prices are consistently correlated with red fox fur prices. See Appendix S2 for data sources.

Historical fur prices ($)

Saskatchewan (1982-2011)

Manitoba (1996-2010)

80

Fox

80

Fox

70

Coyote

70

Coyote

60

60

50

50

40

40

30

30

20

20

10

10

0

0

Fo

NW Territories - wolf present (1970-1998) 120

80 60

20

40

iew

80

60

0

Yukon - wolf present (1970-2009) 100

80

20

0

120

100

ev

40

rR

100

New Brunswick - wolf absent (1970-2009) 120

Nova Scotia - wolf absent (1970-2009)

120 100 80

40

40

20

20

0

0

ly

60

On

60

North America trends (1918-1970) and Canada trends (1970-2009) 120

100

80

60

40

20

0

Journal of Animal Ecology

Page 40 of 40

Appendix S5: The ratio of red fox (Vulpes vulpes) to coyote (Canis latrans) fur returns within wolf (Canis lupus) range in Saskatchewan and Manitoba against the distance from the centriod of each wildlife management zone to the southern edge of wolf distribution. Data from the open trapping areas in Manitoba within wolf range (see Fig. 2) have been excluded from the analysis because fur return counts are pooled across areas with and without wolves. Three sites with no coyotes or no red foxes were also excluded from the analysis. Here we show that red fox fur returns outnumber coyotes at an extreme of 517:1 at one site in Manitoba.

Saskatchewan

450

450

350

350

250

250

150 50

0

400

50

600

2.5

400

600

800

3

iew

1.5

1

1

y = 0.0041x - 0.736 R² = 0.8534

-0.5

0.5

y = 0.0042x - 0.0047 R² = 0.6415

0

-0.5 -1

Distance to wolf distribution edge (km)

-1.5

On

-1 -1.5

200

2

1.5

0

0

2.5

2

0.5

-50

800

ev

Log10 fox:coyote ratio

3

200

150

rR

-50

Manitoba

550

Fo

Fox:coyote ratio

550

Distance to wolf distribution edge (km)

ly