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Chapter

36

Ecological Impact of Wild Boar in Natural Ecosystems

Peter V. Genov, Stefano Focardi, Federico Morimando, Laura Scillitani, and

Atidzhe Ahmed

Introduction

The presence of wild boar (Sus scrofa) (also known as feral pigs

or wild hogs), in many ecosystems of the globe, has raised con-

cerns about the impacts of this species on agriculture, collisions

with vehicles, and because of the expected strong impact on wild

ecosystems and biodiversity. Problems are exacerbated where

this species is alien or in insular ecosystems where the presence

of wild hogs can be devastating.

Several review papers have focused on different aspects of

the ecology of wild boar in native or introduced populations

(Massei & Genov 2004; Barrios-Garcia & Ballari 2012; Bengsen

et  al. 2014). With respect to ecological/biodiversity impacts,

Barrios-Garcia and Ballari (2012) have set the scene. This spe-

cies has a native distribution ranging from the tropical region of

Asia to Siberian forests, including semi-desertic and temperate

ecosystems. The possibility of colonizing this large ecological

range is probably linked to the particular life-history traits of

the species, which is characterized by high population turn-

over, a peculiar pattern of elasticity of demographic parameters

(Servanty et al. 2011), and resilience in the face of predation and

harvest (Gamelon et al. 2012). Its demographic strategy appears

atypical among ungulates of similar size and with similar sexual

dimorphism. Focardi et al. (2008) suggested that these features

are linked to its diet because wild boars consume other animal

species when available, by scavenging or actively preying upon

both vertebrates and invertebrates.

So it is not a big surprise that the wild boar was able to invade

many different habitats in America and Australia, while high pre-

dation risks or interspecific competition appear to have reduced

its capacity to colonize African ecosystems. Barrios-Garcia and

Ballari (2012) noted that most of research was devoted to nega-

tive impacts, but they also pointed out some examples of posi-

tive effects on biodiversity.

It is not worth repeating arguments well developed in the

existing literature. Previous researches have clearly pointed

out that wild boar can be considered an ecosystem engineer.

According to Jones et al. (1997), ‘physical ecosystem engineer-

ing by organisms is the physical modification, maintenance, or

creation of habitats’. It is important to note that ‘trophic interac-

tions and resource competition do not constitute engineering’.

These authors pointed out that physical state changes directly

create non-food resources such as living space, directly control

abiotic resources, and indirectly modulate abiotic forces that,

in turn, affect resource use by other organisms, i.e. ecological

engineers may cause cascading effects in ecosystems. Thus, in

the investigation of the pertinent literature it is important to

keep conceptually distincts direct trophic impacts, for example

predation on ground-nesting birds, from indirect or cascading

effects such as the variations of local biodiversity produced by

the establishment of alien plant species, favoured by rooting or

zoochoria, by wild boar (Barrios-Garcia & Simberloff 2013).

The aim of this chapter is to present a semi-quantitative anal-

ysis of the bulk of the existing literature, including appropriate

references from east European studies, overlooked by previous

reviews, and to discuss the methodologies used in study design,

pointing out the pros and cons of the different approaches used.

We describe how the data set has been built and the multi-

variate approaches used for the analysis. We present basic sta-

tistics about the evidence from literature, and illustrate results

using case studies of special interest. We conclude with remarks

on the methodologies used and the appropriateness of study

design as well as with suggestions for further research.

Methods

We performed a literature survey on the web-of-science accessed

on 21 November 2015, with the following keywords: ‘sus

scrofa’ AND (‘ecosystem’ OR ‘biodivers* OR ‘conserv*’) AND

‘impact’. We found 324 items. Upon inspection of the abstracts,

we retained 127 items. We discarded conference abstracts and

assumed all selected papers have been peer-reviewed, but this

is hard to guarantee, especially for older items. Other biblio-

graphical sources, especially pre-1989, and east European pub-

lications were found in the Library of the Bulgarian Academy

of Sciences or from the authors’ personal reprint collections.

A total of 119 papers were finally retained. We excluded purely

descriptive papers and papers focused on habitat selection or

use by wild boar. We used papers written in English, Italian,

French, Spanish, Russian, Polish, Slovak, and Bulgarian. We

retained those papers that provided some form of experimental

comparison between impacted areas and control plots.

In more recent studies, researchers have mainly used exclu-

sion plots to study the ecological impact of wild boar, while in

many older studies researchers used areas with or without evi-

dent presence of wild boar for estimating impact, by assuming

identical baseline conditions. It is clear that the latter approach

may confound ‘impact’ with habitat selection. In a number of

recent papers, exclusion plots were randomly selected, but in

several cases existing fences were used to save time and money,

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