Meta-analysis on the effect of competition between lynx and

wolf on their diets

A literature study

G. Lelieveld

Wageningen, 2013

Meta-analysis on the effect of competition between lynx and

wolf on their diets

A literature study

Glenn Lelieveld 18 March 2013

Part of: MSc Ecology, VU University, Amsterdam.

Supervised by: Peter van Bodegom, senior lecturer sub-department ‘System Ecology’, Faculty of Earth and Life Sciences (FALW), Vrije

Universiteit, De Boelelaan 1085, 1081HV Amsterdam, 020-5986964, p.m.van.bodegom@vu.nl.

Wieger Wamelink, senior researcher team ’Biodiversity & Policy Alterra, Wageningen UR, Droevendaalsesteeg 3, 6708

PB Wageningen, 0317-485917, wieger.wamelink@wur.nl

Performed at:

Team ‘Biodiversity & Policy Alterra, Wageningen UR, Droevendaalsesteeg 3, 6708 PB Wageningen.

Pictures cover:

Lynx Norbert Rosing, http://animals.nationalgeographic.com/wallpaper/animals/photos/baby-

animals/baby-lynx/

Wolf Roeland Vermeulen, FREE Nature

Roe deer André van der Meulen, http://natuurfoto.wordpress.com/2009/05/24/libellenjacht/

Red deer Ed van Zoonen, http://www.edvanzoonen.nl/edelhert.htm

Abstract Behavioural interactions between predators, herbivores and vegetation have a major impact on ecosystem

composition and ecosystem functioning. Changes in these interactions may lead to changes in ecosystem

composition and even trigger a trophic cascade as not only predation affects the ecosystem, but is also

affected by changes in foraging behaviour of herbivores based on the threat of predation. However, many

factors can influence trophic cascades. First, through controlling a mesopredator with a common food

source, top predators can affect herbivore species. Second, different predators preying on the same prey

species exerts a different demographic impact on the prey species. Third, the complexity of the food web

and changes in bioclimatic effects on ecosystem productivity and anthropogenic habitat change can also

explain sudden changes in prey densities and the ecosystem.

Up to now, it is unknown how the re-establishments of lynx and wolf will affect differences in trophic

interactions in Europe. Studies on prey-predator relations between ungulates and large predator such as

lynx and wolf were carried out mostly in single-prey systems in North America and Scandinavia. However,

the ungulate community of the European mainland is different. Therefore, the research question of this

study was ‘What is the influence of competition between lynx and wolf on their diets in temperate and

continental regions of Europe?’. Based on the biology of both species, lynx being a stalking specialist and

wolf being a coursing generalist, it was expected that lynx outcompetes wolf in the predation on roe deer.

Consequently, wolves will have to broaden their niche breadth.

Only studies executed in the mainland of Europe of the last 30 years that contained data on the total diet of

either lynx or wolf were used. For each study site the niche breadth was calculated and were then analysed

using the permutational multivariate analysis of variance (perMANOVA) and Wald’s chi square test. Here,

the presence of the other predator was used as independent and the dependants were the variance in

mean niche breadth and proportions of each prey species in the diet of each species.

Results of this study show that the diet of lynx is affected by the presence of wolves as the lynx diet

significantly changed by presence of wolves for roe deer, wild boar, Leporidae and bird species. While the

proportion of roe deer is highest in areas without wolves, the proportion of Leporidae species in the diet of

lynx shows a contrasting effect. The niche breadth of the diet of wolf is not significantly affected by the

presence of lynx. However, the mean proportion red deer in the wolf diet is highest in areas with lynx, but

this effect was not significant. The permutational multivariate analysis of variance showed no overall

significant change in diets of lynx and wolf.

Because of limited availability of data and selection criteria, the limited number of study sites has serious

implications on the statistical power in this research. Also, the actual availability of prey species could not

be taken into account as this was not investigated in most studies. Still, this research showed that lynx

seems to change their foraging behaviour because of the presence of wolves, whereas wolves do not

change. As both lynx and wolves are in top of their food chain and there seems to be a form of interaction,

one can argue that the relation between lynx and wolf is therefore more complex than merely being two

top predators in the same community. Therefore, I expect that not only the bioclimatic conditions

determine the strength of a trophic cascade, but also the type of top predator and in case of an apical

predator, the presence of other top predators.

Contents

1 Introduction ......................................................................................................................... 5

2 Methods ............................................................................................................................... 8

2.1 Study area .......................................................................................................................................... 8

2.2 Data collection ................................................................................................................................... 8

2.3 Data quality ....................................................................................................................................... 9

2.4 Data preparation ................................................................................................................................ 9

2.5 Data analysis .................................................................................................................................... 10

3 Results ................................................................................................................................ 11

3.1 Lynx diet shifts ................................................................................................................................ 11

3.2 Wolf diet shifts ................................................................................................................................ 12

4 Discussion ........................................................................................................................... 13

5 Conclusion .......................................................................................................................... 15

References ................................................................................................................................. 16

Appendix I ................................................................................................................................... I

Appendix II ................................................................................................................................. II

Appendix III .............................................................................................................................. III

Appendix IV ............................................................................................................................... IV

Appendix V ................................................................................................................................. V

Appendix VI ............................................................................................................................... VI

5

1 Introduction

Behavioural interactions between predators, herbivores and vegetation have a major impact on ecosystem

composition and ecosystem functioning (Beschta & Ripple 2010; Iercek et al. 2010; Kauffman et al. 2010;

Ripple & Beschta 2012b; White et al. 2010). Changes in these interactions, for example due to extinction or

recolonization, may lead to changes in ecosystem composition and even trigger a trophic cascade (Steffan

& Snyder 2010). The original concept of a trophic cascade, also known as the Green World hypothesis,

encompasses that predators reduce the abundance of herbivores, allowing plants to flourish (Hairston et al.

1960). At first this concept was argued to be solely allocated to marine and aquatic systems as these are

communities with fast-growing producers which lack defences against herbivory (Strong 1992). However,

several studies following the reintroduction of wolves (Canis lupus) in Yellowstone National Park (YNP) in

1995 and 1996, showed that trophic cascades may also apply to terrestrial systems (Beschta & Ripple 2009,

2012). In the National Park, elk (Cervus elaphus) were not only affected by predation, but were also

affected by the threat of predation (Berger et al. 2001). Coping with the predation risk costs energy, as the

elk is more alert, has less foraging time and loses energy while escaping a wolf hunt. Predation, the

decrease of energy uptake and increased costs all result in a decreased reproduction, see figure 1.

Figure 1 Flow diagram of predator–prey encounters for wolves and elk in Yellowstone National Park (YNP) since 1926 (Ripple & Beschta 2004)

In addition, elk avoided potentially high-risk sites with limited opportunities for prey to see approaching

wolves or with terrain features that could impede the escape of prey (Ripple & Beschta 2004). At these

sites, willow (Salix spp.) and cottonwood (Populus angustifolia and Populus balsamifera) were released

from the browsing pressure and increased in height, cover and density. This in turn led to an increase of

songbird, bison (Bison bison) and beaver (Castor Canadensis) populations (Painter & Ripple 2012). The

increased willow and cottonwood populations and as result, increased beaver populations reduced widths

of active channels via slower bank, floodplain and terrace erosion. It also decreased the area of

6

unvegetated alluvium, decreased channel incision and decreased braiding. A conceptual visualisation of the

wolf-induced trophic cascade in the Yellowstone National Park is shown below in figure 2.

Figure 2 Trophic interactions due to predation risk and selected ecosystem responses to (a) wolf extirpation (1926–1995) and (b) wolf recovery (post-1995) for northern ecosystems of Yellowstone National Park. Solid arrows indicate documented responses; dashed arrows indicate predicted or inferred responses. (Ripple & Beschta 2004)

Besides, through effects on herbivore species, cascading effects can also take place via a mesopredator

species. One effect that Ripple et al. (2011) hypothesised is that the presence of one top-predator

positively influences the survival of another top predator by controlling a mesopredator with a common

food source. For example, a decrease of pressure by wolves (top predator) on coyotes (Canis latrans,

mesopredator) may have affected lynx (Lynx lynx, top predator) as coyotes increased their predation

pressure on snowshoe hares (Lepus americanus). Recolonizing wolves may control the coyote population

and in doing so alter the survival of hares and lynx (Ripple et al. 2011). Such a case is known from Finland.

Here they identified a relation between top predator (lynx), mesopredator (red fox (Vulpes vulpes)) and

prey (mountain hare (Lepus timidus)) abundance (Elmhagen et al. 2010). In this study, fox biomass was

lower than could be expected from hare density in areas where lynx was abundant, whilst hare were

scarcer than could be expected from primary productivity where fox was abundant and lynx was scarce

(Elmhagen et al. 2010). Also, in a multi-predator community, different predators preying on the same prey

species exerts a different demographic impact on the prey species, even in the same ecological context, as

a direct consequence of their differences in predation patterns (Gervasi et al. 2012).

In addition to trophic cascades, additional changes in bioclimatic effects on ecosystem productivity and

anthropogenic habitat change can explain sudden increases in prey densities (Elmhagen & Rushton 2007).

Elmhagen & Rushton (2007) showed a positive feedback of the mesopredator to declines in top predator

abundance, although ecosystem productivity determined the strength of the trophic cascade. Another

factor influencing the strength of the effects of the trophic cascade is the complexity of the food web. In a

coastal marsh community, it was shown that having a higher predator diversity dampens the effects on

7

herbivores and weakens the trophic cascade (Finke & Denno 2004). Consequently, changes in diversity at

higher trophic levels can significantly alter ecosystem function in natural systems (Finke & Denno 2004).

In time, effects of the multiple top-predator induced trophic cascades may become visible throughout

Europe now that the European top predators, lynx and wolf are recolonizing parts of Europe. For example,

lynx and wolf are at the verge to re-establish populations in the Benelux. Previous studies show that at least

parts of the Netherlands have suitable habitat for lynx (Groot Bruinderink 1997) and wolf populations

(Lelieveld 2012; Potiek et al. 2012).

Up to now, it is unknown how the re-establishments of lynx and wolf will affect differences in trophic

interactions in Europe, especially in a densely populated area as the Netherlands. Studies on prey-predator

relations between ungulates and large predator such as lynx and wolf were carried out mostly in single-

prey systems in North America and Scandinavia. However, the ungulate community of the European

mainland is different from North America and Scandinavia, which restrains comparison with other

European studies (Fritts & Mech 1981; Gasaway et al. 1992; Gasaway et al. 1983; Messier 1991; Okarma

1995). Roe deer (Capreolus carpeolus) and wild boar (Sus scrofa) piglets are dominant in the diets of both

lynx and wolf in the West and Central European region, whereas in other parts of the Northern hemisphere

their mainly consist of reindeer (Rangifer tarandus) and moose/Eurasian elk (Alces alces). Reindeer and

moose are both absent in other parts of Western Europe, including the Netherlands (Wagner et al. 2012;

Wikenros et al. 2010).

This literature research therefore aims to gather data on changes in diet by interactions between lynx and

wolf in European landscapes with special interest in the possibilities in the Netherlands. There is no

evidence that wolf and lynx predate on each other (Schmidt et al. 2009), nor is there proof that habitat use

changes (May et al. 2008; Wikenros et al. 2010). In other words, there is no direct effect of one of the

species on the other. Indirect effects via competition over prey have not been done so far, although diets of

lynx and wolf show large overlap in European landscapes, both having roe deer as main prey species

(Wikenros et al. 2010). As both species have large home ranges and tend to avoid people, lynx and wolves

are complex species to investigate (Galaverni et al. 2012; Samelius et al. 2012). However, diets of lynx and

wolf show overlap in European landscapes, both having roe deer as main prey species (Wikenros et al.

2010). This overlap can cause indirect competition, which can have a large impact on the landscape via

diverse cascading effects.

Therefore, the research question of this study was ‘What is the influence of competition between lynx and

wolf on their diets in temperate and continental regions of Europe?’. Theoretically, based on the biology of

both species, lynx being a stalking specialist and wolf being a coursing generalist, it is possible that lynx

outcompetes wolf in the predation on roe deer. As a consequence wolves will have to broaden their niche

breadth, or in other words be more versatile in their diet (Colwell & Futuyma 1971). Possibly, wolves

change their diet to a more red deer and wild boar dominated one. I will test the following hypotheses:

1. The presence of wolves has no influence on the diet of lynx.

2. The proportion of roe deer in the diet of wolves is larger in areas without lynx than in areas with lynx.

3. The niche breadth of the diet of wolf is significantly influenced by the presence of lynx.

These hypotheses will be tested using meta-analysis techniques to sum up overall effects based on the

results from different studies.

8

2 Methods

2.1 Study area

In Europe, the current distribution of lynx and wolf populations is concentrated in Northeastern European

countries, the Alps, the Dinaric Mountains and the Iberian Peninsula (see figure 3-4).

Datasets used in this study were limited to studies executed in the mainland of Europe, since these areas

are supposed to be similar to each other and unique with respect to prey-predator interactions in

comparison to Scandinavia and North America. This makes the study area comparable with the

Netherlands.

The European mainland features a prey community consisting of red deer (Cervus elaphus), roe deer, wild

boar, and different middle-sized mammals like brown hare (Lepus europaeus). Areas that are more

mountainous generally also feature chamois (Rupicapra rupicapra). Instead, the Scandinavian prey

community features moose (Alces alces), roe deer, red deer and reindeer (Rangifer tarandus). Both wild

and semi-domestic reindeer are important prey for both lynx and wolf (Basille et al. 2009; May et al. 2008;

Pedersen et al. 1999).

2.2 Data collection

Lynx and wolf diets within the study area were analysed using all available literature of the last 30 years.

Articles were only included if they contained data on the proportion of the ungulate species and medium-

sized mammals like hares in the diet of wolf, lynx or both. However, incomplete datasets may be useful for

later model parameterization and were therefore collected as well. The data collection was considered

complete when at least five articles in a row give neither new data nor references to available data using

Figure 3 Distribution of constantly occupied lynx (Lynx lynx) areas and lynx observations in Europe. Dark red are the constantly occupied areas, red areas have confirmed single observations. Larger picture and explanation is provided in Appendix II. (Arx et al. 2004)

Figure 4 Estimated present distribution and future expansion of wolves (Canis lupus) in Europe. Grey dots represent sightings of roaming wolves. Yellow dots represent lone wolf territories. Orange dots represent wolf pairs. Red dots represent wolf packs. Numbers in the red circles indicate the number of packs in that region. The solid arrows indicate the current direction of expansion. The dotted arrows indicate expected expansion. The red mash layer indicates distant, yet permanent, wolf populations. Larger picture and explanation is provided in Appendix I. (Natuurmonumenten 2012)

9

the search engines and keywords listed below. In this study, model-based data was not used. All data was

stored in a Microsoft Excel dataset.

During a quick scan of available literature, I came across several related articles. With these articles, I

started my research. The list of the articles is mentioned in Appendix III.

For additional information, I searched for reviews or specific articles using in order of importance:

Search engines: Scopus (Web of Science) / JSTOR, Wageningen UR Library (also http://

library.wur.nl/desktop/direct/), Vrije Universiteit Library, Google Scholar.

Keywords: Canis lupus, wolf, Lynx lynx, lynx, diet, feeding behaviour, predation, competition,

food abundance, prey abundance, Capreolus capreolus, roe deer, Cervus elaphus,

red deer, Dama dama, fallow deer, Sus scrofa, wild boar, Lepus europaeus, hare,

Ovis musimon, moufflon, Rupicapra rupicapra, chamois.

2.3 Data quality

Meta-analyses can have two disadvantages that can impede the data quality. The first problem is whether

unpublished studies are included to avoid publication bias (file drawer problem). It is not possible to know

how many studies have been conducted and never reported. This type of problem can seriously bias the

results of any meta-analysis. To prevent this from happening, I tried to get to unpublished datasets by

correspondence with authors who refer in their article to the dataset, but did not publish them.

Unfortunately, this was not successful.

The second problem has to do with the quality of the original studies, as a good meta-analysis of badly

designed studies will still result in unusable results. This can be the case when small datasets are compared

to large datasets. Smaller datasets can be more prone to abnormalities and generally, but statistical

analysis can generally deal with this. However, as this study deals with proportional data of community

composition and composition of prey, this study only used datasets with at least 100 scat samples per

dataset to ensure data quality. In addition, this study aimed to give insight in the competition of lynx and

wolf over prey in natural systems. Therefore, diet datasets that have a proportion 10% or more of domestic

animals or a proportion 10% or more of unidentified species in them were excluded from analysis. After

data collection, 11 studies with 21 unique locations were processed into a database. A detailed overview of

the processed studies and the used sites is provided in Appendix III.

2.4 Data preparation

To investigate the differences in diet among the study sites, all datasets were put into a new dataset with

one specific format, suitable for analysis in SPSS20 (see Appendix IV for the format of the dataset). In case a

study had multiple study sites, the dataset was split into data per site. In case a site had multiple study

periods, these were accumulated into one dataset per site. In some studies, it was necessary to transform

the data into fractions of the total diet. After these preparations, the niche breadth (Levins 1968) was

calculated with the following formula:

∑

Where B = Levin’s measure of niche breadth

= The proportion of individuals per species found in the diet

Next, the data was put into SPSS20, grouped (see Appendix IV) and put into R (version 2.15, package

‘vegan’) for further analysis.

10

2.5 Data analysis

The groups for lynx and wolf studies were separately analysed on variance in total diet using a

permutational multivariate analysis of variance (perMANOVA), where the presence of the other predator

was used as independent. Syntax code of the perMANOVA can be found in Appendix V. In addition, the

relative contributions of prey species to the variance in total diet were studied using R. To investigate

whether these contributions of prey species were significantly different, I used the Wald’s statistics in SPSS.

Here, the presence of the other predator was used as independent and the dependants were the variance

in mean niche breadth and proportions of each prey species in the diet of each species.

The used studies regarding wolf diet in areas where lynx is present had a large proportion of unidentified

cervids. For a more meaningful comparison with areas where there are no lynx, I corrected the abundance

of roe deer, red deer and fallow deer for the unidentified cervids while respecting the proportional ratio

between the species with the simple equation: (CervidN / (Cervid∑N + unidentified cervids)) / all cervids.

11

3 Results

3.1 Lynx diet shifts

When testing whether the diet of lynx is affected by the presence of wolves, the permutational multivariate

analysis of variance showed no overall significant change in diet (N = 6, F = 2.03, df = 1, p = 0.147).

However, when analysed for the relative contributions of prey species, it shows that roe deer, wild boar

and Leporidae contribute most to the between-group variance. Species proportions in the lynx diet

significantly changed by presence of wolves for roe deer (N = 6, χ² = 8.3, df = 1, p = 0.004), wild boar (N = 6,

χ² = 12.8, df = 1, p = 0.000), Leporidae (N = 6, χ² = 8.3, df = 1, p = 0.004) and bird species (N = 6, χ² = 32.6, df

= 1, p = 0.000). Figure 5 shows that all ungulate species, except for roe deer, seem of minor importance to

the lynx when looking at the mean proportion of these species in the lynx diet. While the proportion of roe

deer is highest in areas without wolves (61.5% versus 27.8%), the proportion of Leporidae species in the

diet of lynx shows a contrasting effect as the proportion of Leporidae is on average only 3.3% in areas

without wolves and 20.7% in areas with wolves. These changes resulted in a significant difference at the

level of total ungulate (N = 6, χ² = 8.2, df = 1, p = 0.004) and total medium sized mammals (N = 6, χ² = 5.7, df

= 1, p = 0.017) species groups, and a near significant effect of the presence of wolves on the niche breadth

of lynx (N = 6, χ² = 3.6, df = 1, p = 0.058). The diet of lynx is furthermore complemented by other medium

sized and small mammals, birds and plant material. More detailed statistical results of the occurrence of

prey species in the diet of lynx is supplemented in Appendix VI.

Figure 5 Frequency of occurrence of prey species in lynx scats were significant different (* = <0.05, ** = <0.01, *** = <0.005) for roe deer (N = 6, χ² = 8.3, df = 1, p = 0.004), wild boar (N = 6, χ² = 12.8, df = 1, p = 0.000), Leporidae (N = 6, χ² = 8.3, df = 1, p = 0.004) and bird species (N = 6, χ² = 32.6, df = 1, p = 0.000).

0

10

20

30

40

50

60

70

80

Fre

qu

en

cy o

f o

ccu

rern

ce in

lyn

x sc

ats

Wolf absent (N = 4)

Wolf present (N = 2)

***

***

***

***

12

3.2 Wolf diet shifts

When testing whether the diet of wolf is affected by the presence of lynx, the permutational multivariate

analysis of variance showed no significant effect (F = 1.00, df = 1, p = 0.39). Relative contributions of prey

species to the between-group variance was dominated by red deer. There was no significant effect of the

presence of lynx on the niche breadth of wolves (N = 9, χ² = 0.7, df = 1, p = 0.400). In the uncorrected

analysis, red deer proportion was significantly different (N = 9, χ² = 4.2, df = 1, p = 0.041) between areas

with and without lynx, as well as small mammals (N = 9, χ² = 5.9, df = 1, p = 0.015) and birds (N = 9, χ² = 7.0,

df = 1, p = 0.008). Still, wolf diet is dominated by roe deer, red deer and wild boar. When corrected for the

large proportion of unidentified cervids, figure 6 shows that the mean proportion red deer in the wolf diet

is higher in areas with lynx (32.5% versus 20.3% in areas without lynx) . More detailed statistical results of

the occurrence of prey species in diet of wolf is supplemented in Appendix VI.

Figure 6 Frequency of occurrence of prey species in wolf scats corrected for unidentified cervids. Proportions were significant different (* = <0.05, ** = <0.01, *** = <0.005) for small mammals (N = 9, χ² = 5.9, df = 1, p = 0.015) and birds (N = 9, χ² = 7.0, df = 1, p = 0.008).

0

10

20

30

40

50

60

70

80

Fre

qu

en

cy o

f o

ccu

ren

ce in

wo

lf s

cats

Species occuring in the studied wolf scats

Lynx absent (N = 7)

Lynx present (N = 2)*

13

4 Discussion

In this research, the limited number of study sites (N = 15) I used has serious implications on strength of the

conclusions. First reason for the limited number of studies is simply the limited availability of data. To draw

conclusions that still have meaning for the Netherlands required a first selection of studies based on the

geographical location. However, lynx and wolves are not present in all of the study area and are difficult

species to study, and even in a vast region as central Europe, diet studies on lynx and wolf are limited. To

increase the number of used studies, one can increase the larger geographical range by grouping species

from the entire Northern Hemisphere into species groups. The lynx-predator group would then not only

contain the European lynx (Lynx lynx), but also the threatened Iberian lynx (Lynx pardinus), Canadian lynx

(Lynx canadensis) and the bobcat (Lynx rufus). More importantly, prey species can then be grouped in size,

evasiveness, abundance and risk classes, allowing study on trade-offs between the prey selection factors in

areas with one or more top predators.

In the database, studies were selected based on two criteria. The first criterion was that each study site had

to have studied at least 100 scats so that the retrieved data had as minimum deviation as possible of

stochastic deviations. The second criterion was that no studies with 10% or more domestic animals in the

scats were used as this study investigated the natural diet of lynx and wolf. There is a trade-off between

using more study sites or holding on to only using the most relevant study sites. In this study, the focus was

on the relevance of the study site. However, if all the study sites were used, the statistical power would

have been greater.

Unfortunately, the actual availability of prey species could not be taken into account as this was not

investigated in most studies. When comparing the prey availability and diet proportions at the same time,

prey selectivity can be investigated by using selection coefficients (Ivlev 1961). These derived selection

coefficients can help to give an in-depth understanding of what factors influence prey selectivity instead of

using prey occurrence in the diet alone.

Populations grow exponentially until a limiting factor dampens the increase into a, potentially dynamic,

optimum. For both lynx and wolf it follows that only when the availability of prey is a limiting factor,

competition over prey affects the population dynamics. Although previous studies show the two species do

not compete on a spatial scale (Schmidt et al. 2009; Wikenros et al. 2010), home ranges can be a function

of prey density (Jedrzejewski et al. 2007; Nowak et al. 2008). In the diets of lynx and wolf at 15 independent

study sites over the mainland of Europe, lynx seems to change their foraging behaviour because of the

presence of wolves, whereas wolves do not change.

As both lynx and wolves are in top of their food chain and there seems to be a form of interaction, one can

argue that the relation between lynx and wolf is therefore more complex than merely being two top

predators in the same community. Lynx is a top predator, but at the same time, its diet is affected by the

presence of wolf. Definitions in the literature of top predator include ‘relatively large vertebrates that

regularly feed on other vertebrates’ (Sergio et al. 2008) and ‘species on which nothing else in the [food] web

feeds’(Pimm et al. 1991). Naturally, both definitions are correct when describing lynx and wolf, but this

does not take the relation between the two species into consideration. In literature, this is described as

follows: ‘The apical predator is the top predator that holds the maximum trophic position, and therefore

resides at the apex of the food web. Within any one food web, there can be many top predators, but there

can be only one apical predator.’ (Post & Takimoto 2007).

Following the results of this study, I consider the wolf as apical predator and I believe that this difference

between lynx and wolf might affect the level of impact each top predator can have on the ecosystem. I

expect that recolonization of lynx will trigger only small effects on its environment, whereas recolonization

of wolves has a larger impact on the environment, especially in areas where it also influences the behaviour

14

of another top predator. In other words, I expect that not only the bioclimatic conditions determine the

strength of a trophic cascade, but also the type of top predator and in case of an apical predator, the

presence of other top predators.

15

5 Conclusion

In this study, I tested if there are significant effects of the presence of lynx or wolves on the diet of the

other top predator based on the following hypotheses:

- The presence of wolves has no influence on the diet of lynx

- The proportion of roe deer in the diet of wolves is larger in areas without lynx than in areas with lynx

- The niche breadth of the diet of wolf is significantly influenced by the presence of lynx

It seems that roe deer is the most preferred prey species of lynx and one of the most preferred prey species

of wolves. Additionally, results of this study show that when the roe deer population is under pressure of

lynx and wolf predation, lynx change their diet by hunting more wild boar, hares, rabbits and birds, whereas

the diet of wolves does not significantly change. I therefore conclude that my three hypotheses are not

correct, as wolves seem to influence the diet of lynx and are not influenced by lynx.

Based on this study, I conclude that there is interaction between lynx and wolf and that this may diversify

the effects these predators have when recolonizing to new areas, especially in areas where the other top

predator is already present.

16

References

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Barja, I. 2009. Prey and prey-age preference by the Iberian wolf Canis lupus signatus in a multiple-prey ecosystem. Wildlife Biology 15:147-154.

Basille, M., I. Herfindal, H. Santin-Janin, J. D. C. Linnell, J. Odden, R. Andersen, K. A. Hogda, and J. M. Gaillard. 2009. What shapes Eurasian lynx distribution in human dominated landscapes: selecting prey or avoiding people? Ecography 32:683-691.

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I

Appendix I

Distribution of constantly occupied lynx areas and lynx observations in Europe

Figure 7 Distribution of constantly occupied lynx (Lynx lynx) areas and lynx observations in Europe. Dark red are the constantly occupied areas, red areas have confirmed single observations, pink areas have unconfirmed single observations. (Arx et al. 2004)

II

Appendix II

Estimated present distribution and future expansion of wolves in Europe

Figure 8 Estimated present distribution and future expansion of wolves in Europe. Grey dots represent sightings of roaming wolves. Yellow dots represent lone wolf territories. Orange dots represent wolf pairs. Red dots represent wolf packs. Numbers in the red circles indicate the number of packs in that region. The solid arrows indicate the current direction of expansion. The dotted arrows indicate expected expansion. The red mash layer indicates distant, yet permanent, wolf populations. (Natuurmonumenten 2012)

III

Appendix III

List of literature with which I will start the study: (Barja 2009; Basille et al. 2009; Gorini et al. 2012; Herfindal et al. 2005; Jedrzejewska et al. 1997; Jedrzejewska et al. 1994;

Jedrzejewski et al. 1996; Jedrzejewski et al. 2000; Jedrzejewski et al. 1989; Jedrzejewski et al. 2005; Jedrzejewski et al. 1993;

Jedrzejewski et al. 2002; Kamler et al. 2008; Kawata et al. 2008; Kusak et al. 2012; Linnell et al. 1998; Melis et al. 2010; Melis et al.

2009; Nilsen et al. 2009; Nowak et al. 2005, 2008; Nowak et al. 2011; Odden et al. 2008; Odden et al. 2006; Okarma 1995; Okarma

et al. 1995; Okarma et al. 1997; Okarma et al. 1998; Panzacchi et al. 2008; Rigg et al. 2011; Ripple & Beschta 2012a; Schmidt et al.

2009; Selva et al. 2005; Sidorovich et al. 2003; Wagner et al. 2012; Wikenros et al. 2010)

Table 1 Characteristics of the processed study sites. Six sites were not used in the study because of small sample size (1) or a too large occurrence of domestic animals in the diet.

Predator Other predator

Country Region Period Scats / kills

Source Used in study

Wolf no Germany Eastern Germany 2001-2009 Scat (Wagner et al. 2012)

Wolf no Spain Galicia 1998-2002 Scat (Barja 2009) No 2

Wolf no France Western Alps 1999-2002 Scat (Marucco et al. 2008)

Wolf no Italy Apennines 1988-2000 Scat (Mattioli et al. 2011)

Wolf yes Poland Bialowieza Forest 1985-1996 Scat (Jedrzejewski et al. 2000)

Wolf no Poland Bydgoszcz Forest 2002-2009 Scat (Nowak et al. 2011) No 1

Wolf no Poland Wałcz Forest 2002-2009 Scat (Nowak et al. 2011)

Wolf no Poland Rzepin Forest 2002-2009 Scat (Nowak et al. 2011)

Wolf no Poland Lower Silesian Forest 2002-2009 Scat (Nowak et al. 2011)

Wolf no Poland Other 2002-2009 Scat (Nowak et al. 2011) No 1

Wolf yes Estonia 1996-1997 Scat (Valdmann et al. 2005)

Wolf yes Latvia 1996-2001 Scat (Valdmann et al. 2005) No 1

Lynx yes Estonia 1998-2000 Scat (Valdmann et al. 2005)

Lynx yes Latvia 1997-2001 Scat (Valdmann et al. 2005) No 1

Lynx no Slovenia / Croatia

Dinaric Mountains 1993-2010 Scat (Krofel et al. 2011)

Lynx yes Poland Bialowieza NP 1985-1995 Scat (Okarma et al. 1997)

Lynx no Switzerland North-western Alps 1983-2000 Kill (Molinari-Jobin et al. 2007)

Lynx no Switzerland Central Alps 1986-1989 Kill (Molinari-Jobin et al. 2007)

No 1, 2

Lynx no Switzerland Jura Mountains 1988-1997 Kill (Molinari-Jobin et al. 2007)

Lynx no Switzerland North-eastern Switzerland

2001-2004 Kill (Molinari-Jobin et al. 2007)

IV

Appendix IV

Groups in the dataset

Group number Diet of which predator Presence of other predator Group size (number of sites)

1 Lynx No wolves 4

2 Lynx Wolves present 2

3 Wolf No lynx 7

4 Wolf Lynx present 2

Format of the combined dataset in SPSS17

V

Appendix V

Syntax code for R 2.15 with package ‘vegan’

Lynx (study groups 1 and 2) library(vegan)

input_PCA2 <- read.table("glen_permanova_input12.txt", header=TRUE)

input_PCA3<-input_PCA2[,2:ncol(input_PCA2)]

Groups<-input_PCA2[,1]

perm12 <- adonis(input_PCA3 ~ factor(Group), input_PCA2, method="euclid")

perm12$aov.tab

perm12$coefficients

output12 <-perm12$coefficients

write.table(output12, "output12.txt")

dist12<-vegdist(input_PCA3, method="euclidean")

perm_disp12 <- betadisper(dist, Groups)

permutest(perm_disp12, pairwise = TRUE)

Wolf (study groups 3 and 4) library(vegan)

input_PCA2 <- read.table("glen_permanova_input34.txt", header=TRUE)

input_PCA3<-input_PCA2[,2:ncol(input_PCA2)]

Groups<-input_PCA2[,1]

perm34 <- adonis(input_PCA3 ~ factor(Group), input_PCA2, method="euclid")

perm34$aov.tab

perm34$coefficients

output34 <-perm34$coefficients

write.table(output34, "output34.txt")

dist34<-vegdist(input_PCA3, method="euclidean")

perm_disp34 <- betadisper(dist34, Groups)

permutest(perm_disp34, pairwise = TRUE)

VI

Appendix VI

Statistical output

Table 2 Results of the Wald’s chi square statistical test. Niche breadth was calculated as by Levins (Levins 1968). Other ungulates

1 encompasses moufflon, elk, and moose.

Factor Wald’s Chi Square Df Significance

Niche breadth 3.6 1 0.058

Roe deer 8.3 1 0.004

Red deer 1.2 1 0.273

Fallow deer - 1 -

Unidentified cervids 0.3 1 0.604

Wild boar 12.8 1 0.000

Other and unidentified ungulates1

0.7 1 0.414

Total ungulates

8.2 1 0.004

Domestic animals 0.1 1 0.746

Leporidae 8.3 1 0.004

Other medium sized mammals 0.1 1 0.732

All medium sized mammals 5.7 1 0.017

Small mammals 0.4 1 0.525

All mammals 2.4 1 0.124

Bird species 32.6 1 0.000

Fish species - 1 -

Plant material 0.6 1 0.448

Carrion 0.3 1 0.607

Unidentified material 4.0 1 0.046

Table 3 Comparison of mean proportion per species and standard deviation in the lynx diet in areas where wolves are absent (N = 4) and where wolves are present (N = 2). Other ungulates

1 encompasses

moufflon, elk, and moose.

Species Wolves absent (N = 4) Wolves present (N = 2) Mean SD Mean SD

Roe deer 61.5 8.3 27.8 29.7 Red deer 1.1 2.3 2.8 1.6 Fallow deer 0 - 0 - Unidentified cervids 20.3 14.3 29.1 41.2

Wild boar 0 - 1.8 1.4 Other and unidentified ungulates

1 0.5 0.9 0 -

Total ungulates

83.4 13.9 61.5 16.4

Domestic animals 0.4 0.7 0.6 0.8 Leporidae 3.3 2.7 20.7 16.4 Other medium sized mammals 4.3 2.7 5.1 4.0 All medium sized mammals 8.0 5.3 26.3 19.7

Small mammals 5.4 8.4 2.1 1.4 All mammals 96.8 6.3 89.9 6.5

Bird species 0.5 0.9 3.6 0.4 Fish species 0 - 0 - Plant material 2.3 4.5 5.1 7.2 Carrion 0.5 0.9 0.8 1.1 Unidentified material 0 - 0.6 0.8

VII

Table 4 Results of the Wald’s chi square statistical test. Niche breadth was calculated as by Levins (Levins 1968). Other ungulates

1 encompasses moufflon, elk, and moose.

Wald’s Chi Square Df Significance

Niche breadth 0.7 1 0.400

Roe deer 1.7 1 0.199

Corrected roe deer 0.136 1 0.712 Red deer 4.2 1 0.041 Corrected red deer 0.8 1 0.374 Fallow deer 1.5 1 0.221 Unidentified cervids 13.0 1 0.000

Wild boar 0.7 1 0.409 Other and unidentified ungulates

1 0.2 1 0.676

Total ungulates

1.1 1 0.292

Domestic animals 0.3 1 0.592 Leporidae 1.1 1 0.297 Other medium sized mammals 0.0 1 0.849 All medium sized mammals 0.0 1 0.957

Small mammals 5.9 1 0.015 All mammals 0.0 1 0.954

Bird species 7.0 1 0.008 Fish species - 1 - Plant material 0.1 1 0.708 Carrion - 1 - Unidentified material 0.3 1 0.564

Table 5 Comparison of mean proportion per species and standard deviation in the wolf diet in areas where lynx are absent (N = 7) and where lynx are present (N = 2). Other ungulates

1 encompasses

moufflon, elk, and moose.

Species Lynx absent (N = 7) Lynx present (N = 2) Mean SD Mean SD

Roe deer 44.0 14.3 27.4 33.6 Corrected roe deer 45.0 13.7 40.5 31.8 Red deer 19.7 9.1 6.5 9.2 Corrected red deer 20.3 9.3 32.5 45.9 Fallow deer 1.9 2.4 0 - Unidentified cervids 1.7 2.0 39.1 38.6

Wild boar 23.9 16.0 15.2 2.4 Other and unidentified ungulates

1 2.6 7.1 0.9 1.3

Total ungulates

94.0 4.9 89.0 13.0

Domestic animals 2.8 4.3 1.3 0.4 Leporidae 1.6 1.2 1.9 1.8 Other medium sized mammals 1.1 2.2 1.4 1.2 All medium sized mammals 5.5 4.7 5.7 5.5

Small mammals 0.3 0.7 5.1 7.2 All mammals 99.8 0.6 99.8 0.2

Bird species 0 - 0.2 0.3 Fish species 0 - 0 - Plant material 0.1 0.3 0.1 0.1 Carrion 0 - 0 - Unidentified material 0.1 0.3 0 -

VIII

Figure 9 Frequency of occurrence of prey species in wolf scats were significant different (* = <0.05, ** = <0.01, *** = <0.005) for red deer (N = 9, χ² = 4.2, df = 1, p = 0.041), small mammals (N = 9, χ² = 5.9, df = 1, p = 0.015) and birds (N = 9, χ² = 7.0, df = 1, p = 0.008).

0

10

20

30

40

50

60

70

80Fr

eq

ue

ncy

of

occ

urr

en

ce in

wo

lf s

cats

Lynx absent (N = 7)

Lynx present (N = 2)*

*