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Macronutritional Consequences of Food Generalism in an Invasive Mammal, the Wild Boar

Authors:

Abstract

We apply a recently established nutritional framework for defining dietary generalism to global populations of wild boar (Sus scrofa). Across its range, wild boar consume a diversity of foods that vary in nutritional composition. The macronutrient (carbohydrate, protein and fat) composition of the diets composed from those foods also varies substantially between countries, particularly in terms of proportion of energy from protein. These results suggest that as a species wild boar have a wide fundamental macronutrient niche, which likely contributes to the success of the species as an invader of novel environments.
Mammalian
Biology
81
(2016)
523–526
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Mammalian
Biology
jou
rn
al
hom
epage:
www.elsevier.com/locate/mambio
Short
communication
Macronutritional
consequences
of
food
generalism
in
an
invasive
mammal,
the
wild
boar
Alistair
M.
Seniora,b,,1,
Catherine
E.
Grueberc,d,1,
Gabriel
Machovsky-Capuskaa,c,e,
Stephen
J.
Simpsona,e,
David
Raubenheimera,c,e
aCharles
Perkins
Centre,
The
University
of
Sydney,
Sydney,
Australia
bSchool
of
Mathematics
and
Statistics,
Faculty
of
Science,
The
University
of
Sydney,
Sydney,
Australia
cSchool
of
Life
and
Environmental
Sciences,
Faculty
of
Veterinary
Science,
The
University
of
Sydney,
Sydney,
Australia
dSan
Diego
Zoo
Global,
San
Diego,
CA,
USA
eSchool
of
Life
and
Environmental
Sciences,
Faculty
of
Science,
The
University
of
Sydney,
Sydney,
Australia
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
14
March
2016
Accepted
7
July
2016
Handled
by
Francesco
Ferretti
Available
online
18
July
2016
Keywords:
Diet
Invasive
species
Niche
Nutrition
Sus
scrofa
a
b
s
t
r
a
c
t
We
apply
a
recently
established
nutritional
framework
for
defining
dietary
generalism
to
global
pop-
ulations
of
wild
boar
(Sus
scrofa).
Across
its
range,
wild
boar
consume
a
diversity
of
foods
that
vary
in
nutritional
composition.
The
macronutrient
(carbohydrate,
protein
and
fat)
composition
of
the
diets
com-
posed
from
those
foods
also
varies
substantially
between
countries,
particularly
in
terms
of
proportion
of
energy
from
protein.
These
results
suggest
that
as
a
species
wild
boar
have
a
wide
fundamental
macronu-
trient
niche,
which
likely
contributes
to
the
success
of
the
species
as
an
invader
of
novel
environments.
©
2016
Deutsche
Gesellschaft
f¨
ur
S¨
augetierkunde.
Published
by
Elsevier
GmbH.
All
rights
reserved.
Diet
is
commonly
used
to
classify
species
along
the
generalist-
specialist
spectrum
(Machovsky-Capuska
et
al.,
2016a).
However,
dietary
generalism
has
been
coarsely
defined
historically,
with
the
role
of
nutrition
poorly
considered
(Machovsky-Capuska
et
al.,
2016a).
This
is
problematic,
because
nutrition
is
a
fundamental
determinant
of
the
environments
an
animal
is
able
to
inhabit
(Raubenheimer
et
al.,
2012).
Dietary
macronutrient
composition,
in
particular,
has
been
shown
to
impact
many
fundamental
bio-
logical
traits,
including
foraging
behaviour,
lifespan
and
individual
fitness
(Le
Couteur
et
al.,
2015;
Machovsky-Capuska
et
al.,
2016b;
Senior
et
al.,
2015).
Recently,
Machovsky-Capuska
et
al.
(2016a)
developed
a
frame-
work
for
integrating
nutrition
and
ecological
niche
theory,
and
provided
a
definition
of
dietary
niche
that
allows
a
species
to
be
classified
as
a
generalist
across
three
functional
levels:
1)
the
range
Corresponding
author
at:
Charles
Perkins
Centre,
The
University
of
Sydney,
Sydney,
Australia.
E-mail
addresses:
alistair.senior@sydney.edu.au
(A.M.
Senior),
catherine.grueber@sydney.edu.au
(C.E.
Grueber),
g.machovsky@sydney.edu.au
(G.
Machovsky-Capuska),
stephen.simpson@sydney.edu.au
(S.J.
Simpson),
david.raubenheimer@sydney.edu.au
(D.
Raubenheimer).
1These
two
authors
contributed
equally
to
this
manuscript.
of
dietary
macronutrient
compositions
on
which
the
animal
is
able
to
succeed,
or
its
“fundamental
macronutrient
niche”;
2)
the
range
of
food
nutritional
compositions
from
which
it
is
able
to
compose
a
diet
that
falls
within
the
macronutrient
niche,
and
3)
the
range
of
ecological
and
physical
attributes
of
foods
that
it
is
able
to
exploit.
While
these
three
levels
interact
to
determine
the
diet
of
a
species,
the
fundamental
macronutrient
niche
has
particular
ecological
rel-
evance
because
animals
that
are
nutritionally
flexible
are
more
likely
to
persist
in
the
face
of
substantial
changes
to
their
nutri-
tional
environment
(e.g.
loss
of
a
food,
or
translocation
to
a
new
environment).
The
wild
boar
(Sus
scrofa)
is
considered
among
the
100
world’s
most
effective
invasive
species,
now
established
on
all
continents
except
for
Antarctica
(Lowe
et
al.,
2000).
Wild
boar
prey
on
native
wildlife,
and
their
rooting
behaviour
destroys
plant
cover,
seed
banks
and
crops
(Ballari
and
Barios-Garcia,
2014).
Wild
boar
diets
comprise
a
variety
of
foods
that
differ
in
their
ecological,
physical
and
nutritional
properties,
and
as
such
the
species
is
widely
consid-
ered
a
generalist
omnivore
(reviewed
in
Ballari
and
Barios-Garcia,
2014).
In
the
context
of
functional
dietary
generalism,
wild
boar
can
thus
be
classified
as
food
exploitation
and
food
composition
generalist
(i.e.
a
generalist
at
levels
2
and
3
above).
http://dx.doi.org/10.1016/j.mambio.2016.07.001
1616-5047/©
2016
Deutsche
Gesellschaft
f¨
ur
S¨
augetierkunde.
Published
by
Elsevier
GmbH.
All
rights
reserved.
524
A.M.
Senior
et
al.
/
Mammalian
Biology
81
(2016)
523–526
However,
to
understand
the
relationship
between
the
nutri-
tional
environment,
adaptation
and
population
persistence,
it
is
important
to
also
establish
a
species’
fundamental
macronutri-
ent
niche,
as
this
represents
the
range
of
dietary
compositions
on
which
a
population
can
actually
persist
(Machovsky-Capuska
et
al.,
2016a).
It
is
unclear
whether
wild
boar
consume
a
range
of
ecologically
different
foods
in
order
to
regulate
macronutrient
intake,
as
is
seen
in
many
other
mammals
(Raubenheimer
et
al.,
2015;
Simpson
and
Raubenheimer,
2012)
including
domesticated
pigs
(Kyriazakis
and
Emmans,
1991).
It
is
also
unclear
whether
wild
boar
populations
are
capable
of
persisting
on
diets
that
vary
widely
in
macronutrient
composition
(i.e.
have
a
broad
fundamen-
tal
macronutrient
niche).
We
applied
a
recent
framework
using
the
right-angle
mixture
triangle
(RMT;
Machovsky-Capuska
et
al.,
2016a;
Raubenheimer,
2011),
to
infer
the
fundamental
macronutri-
ent
niche
of
wild
boar.
Data
were
extracted
from
published
reports
of
wild
boar
diets
from
geographically
separated
populations,
fol-
lowing
the
approach
previously
applied
to
examine
the
diets
of
omnivorous
predators
(Remonti
et
al.,
2015).
From
a
recent
review
of
wild
boar
diets
in
native
and
introduced
ranges
(Ballari
and
Barios-Garcia,
2014),
we
collected
studies
that
provided
estimates
of
the
percentage
contribution
(by
mass)
of
foods
to
the
diet
of
populations
of
wild
boar
(based
on
stomach
contents).
We
also
updated
the
previous
search
by
using
the
same
criteria
to
find
material
published
between
2013
and
2016,
and
by
searching
within
literature
citing
the
aforementioned
review.
We
were
able
to
obtain
a
total
of
16
articles
that
met
our
criteria,
pro-
viding
dietary
data
for
28
populations.
“Populations”
within
articles
were
considered
independent
if
samples
were
taken
from
different
studies,
countries,
geographical
regions,
seasons,
or
segregated
by
sex
(Appendices
Files
S1,
S2
in
Supplementary
material).
Foods
within
diets
were
listed
in
published
articles
to
varying
specificity,
e.g.
some
studies
listed
the
contribution
of
leaves
from
specific
plant
species,
while
others
gave
broad
categorisations
of
foods
(e.g.
“vertebrates”).
To
evaluate
the
percentage
of
macronu-
trients
in
the
diet,
we
first
estimated
the
percentage
contribution
of
each
food
type
to
the
total
diet.
We
then
estimated
the
nutrient
composition
(in
terms
of
digestible
content,
then
in
terms
of
pro-
tein,
carbohydrate
and
fat,
assuming
dry
mass),
of
each
food
using
published
data
and
the
USDA
National
Nutrient
Database
for
Stan-
dard
Reference
(US
Department
of
Agriculture,
2015)
(Appendices
Files
S2,
S3
in
Supplementary
material).
We
were
unable
to
obtain
proximate
composition
of
reported
foods
using
data
that
were
temporally
and
spatially
contemporary
with
the
wild
boar
stom-
ach
contents
sampled.
While
this
might
introduce
error
around
estimates
of
the
composition
of
specific
foods
(e.g.
the
nutritional
content
of
a
specific
forage
may
vary
spatially/temporally;
Rothman
et
al.,
2012),
it
is
unlikely
to
substantially
impact
on
differences
in
diet
estimates
between
populations,
which
are
driven
by
vari-
able
proportions
and
foods
types
(i.e.
the
ratio
of
different
forages
and
animal
matter)
in
the
diet
(Remonti
et
al.,
2015).
Following
Raubenheimer
and
Rothman
(2013),
macronutrient
masses
of
the
foods
obtained
from
the
literature
were
converted
to
energy
using
protein/carbohydrate
=
17
Kj/g
and
lipid
=
37
Kj/g.
Our
dataset
included
ten
countries
(Fig.
1A),
although
for
analyt-
ical
purposes
we
pooled
data
from
France
and
Luxembourg.
Of
these
countries
wild
boar
are
invasive
in
Australia,
New
Zealand
and
the
USA.
Data
from
seven
countries
were
reported
as
being
based
on
samples
pooled
over
multiple
seasons.
For
five
countries
data
were
available
from
discrete
seasons
enabling
temporal
examination
of
diet
(Fig.
1A
and
B).
Two
studies
did
not
clearly
report
sample
size,
but
for
the
remainder
the
mean
number
of
wild
boar
examined
per
population
was
102.5
(range
3–1200).
We
recorded
43
food
types
present
in
the
stomach
contents
of
wild
boar,
which
varied
sub-
stantially
in
their
nutritive
content
(round
points
shown
on
Fig.
1A
and
B);
foods
ranged
from
<1%
to
91%
protein
(dry
mass),
0–95%
carbohydrates
(dry
mass)
and
<1–78%
fats
(dry
mass).
Researchers
reported
an
average
of
8.8
food
types
per
population
(range
5–13).
Where
data
were
based
on
samples
pooled
from
multiple
seasons,
the
macronutrient
composition
of
wild
boar
diets
var-
ied
between
countries.
In
New
Zealand,
diets
had
higher
protein
content
than
in
other
countries
(Fig.
1A).
The
pattern
of
dietary
variation
among
countries
was
also
seen
among
those
data
that
were
recorded
seasonally:
in
spring
and
summer,
for
example,
New
Zealand
diets
showed
substantially
higher
protein
content
than
those
from
USA
and
Ukraine
(Fig.
1B).
Across
all
seasons,
intra-country
variation
in
protein
composition
was
relatively
low
in
comparison
to
inter-country
variation
(Fig.
1B).
Analyses
using
linear-mixed
models
confirmed
a
high
degree
of
between-country
variance
in
dietary
proportions
of
protein
(estimated
between-
country
SD
=
0.51,
2=
55.8,
d.f.
=
1,
p
<
0.001;
see
Appendix
File
S4,
Tables
A1
and
A2
in
Supplementary
material).
A
moderate
degree
of
between-country
variation
in
carbohydrates
was
also
estimated,
although
this
was
not
quite
statistically
significant
(esti-
mated
between-country
SD
=
0.31,
2=
3.34,
d.f.
=
1,
p
=
0.07).
There
was
no
between-country
variation
in
proportion
of
energy
from
fat
(estimated
between-country
SD
=
0).
Accordingly,
residual
variance
of
each
model
(interpretable
as
variation
among
populations
within
each
country)
was
low
for
protein,
moderate
for
carbohydrate,
and
high
for
fat
(Tables
A1
and
A2
in
Supplementary
material).
The
breadth
of
dietary
compositions
that
we
observed
shows
that
wild
boar
are
dietary
generalists
in
terms
of
the
diversity
of
food
types
exploited,
the
compositions
thereof,
and
the
composi-
tion
of
diets
that
can
sustain
a
population.
Previous
synthesis
of
wild
boar
diet
has
focussed
on
food
types,
rather
than
the
nutritional
composition
of
foods
and
overall
diet.
Ballari
and
Barios-Garcia
(2014)
concluded
that
temporal/spatial
variations
in
availability
were
major
contributors
to
the
foods
selected
by
wild
boar.
Along
with
these
variations,
our
analyses
suggest
that
wild
boar
shows
a
wide
tolerance
of
macronutrient
dietary
compositions
across
the
whole
range.
For
example,
in
New
Zealand,
wild
boar
diets
were
substantially
higher
in
protein
than
in
native
ranges,
a
difference
that
seemingly
persists
across
seasons.
In
New
Zealand,
it
is
likely
that
animals
make
up
a
larger
component
of
wild
boar
diets
than
in
native
ranges
(Ballari
and
Barios-Garcia,
2014).
The
extent
to
which
the
inter-population
differences
in
diet
that
we
observed
result
from
food
availability
(e.g.
habitat-type
or
proximity
to
human
settlement)
and/or
selection
(i.e.
the
regulatory
behaviours
of
the
species)
is
difficult
to
say
based
on
our
data.
Additionally,
the
rel-
ative
consistency
that
we
observe
in
proportion
of
energy
from
protein
across
seasons
in
our
dataset
may
not
necessarily
be
ubiq-
uitous.
Studies
on
European
wild
boar
populations
have
shown
that
animals
adjust
their
foraging
to
take
advantage
of
abundant
agri-
cultural
crops
in
summer
(Keuling
et
al.,
2009).
It
remains
to
be
seen
how
such
changes
in
habitat
use
impact
the
macronutrient
compo-
sition
of
the
diet.
Nevertheless,
our
results
suggest
that
as
a
species,
wild
boar
populations
are
not
intrinsically
constrained
to
diets
of
a
narrow
macronutrient
range,
and
that
other
non-physiological
processes
are
likely
to
influence
the
distribution
of
the
species.
It
is
interesting
to
consider
how
variation
in
dietary
compo-
sition
influences
life-history
traits
and
population
demography.
Studies
in
model
organisms
indicate
that
higher-protein
diets
are
associated
with
increased
reproductive
output
(Lee
et
al.,
2008;
Solon-Biet
et
al.,
2015).
Furthermore,
in
production
populations,
sows
on
higher-protein
diets
are
quicker
to
reach
oestrous
after
weaning
their
first
litter
(King
and
Dunkin,
1986).
There
is
abun-
dant
evidence
that
food
intake
influences
reproduction
in
wild
boar,
with
females
tending
to
give
birth
to
larger
litters
in
seasons
where
food
is
more
abundant
(Frauendorf
et
al.,
2016;
Gamelon
et
al.,
2013;
Geth ¨
offer
et
al.,
2007;
Servanty
et
al.,
2009).
The
degree
to
which
this
is
driven
by
an
increase
in
total
energy
per
se,
or
an
increase
in
the
intake
of
specific
macronutrients
(e.g.
protein)
that
A.M.
Senior
et
al.
/
Mammalian
Biology
81
(2016)
523–526
525
% Protein
% Carbohydrate
A.
B.
%Fat
[0]
[20]
[40]
[60]
[80]
0
20
40
60
80 10
0
020406080100
Australia (
Invasive)
France &
Lux
embourg
Germany
Italy
Japan
NZ (Invasive)
Pakist
an
Poland
Ukraine
USA
(Invasive)
% Pr
otein
% Carbohydrate
0
25
50
75
100
0255075100
Spring
% Pr
otei
n
% Carbohydrate
0
25
50
75 10
0
0255075100
Summer
% Pr
o
t
ein
% Carbohydrate
0
25
50
75
100
0255075100
Autu
mn
%
Pro
t
ei
n
% Carbohydrate
0
25
50
75 10
0
0255075100
Winter
Fig.
1.
Right-angle
mixture
triangles
showing
the
nutritional
composition
of
foods
(points)
and
diets
(stars)
consumed
by
wild
boar
in
terms
of
%
energy
from
protein
(x-axis),
carbohydrate
(y-axis)
and
fat
(implicit
axis;
diagonal
lines)
in
different
countries.
Data
are
based
on
samples
that
were
A)
pooled
from
several
seasons,
and
B)
sampled
in
discrete
seasons.
In
all
plots
the
greyed
out
area
corresponds
to
the
convex
hull
of
all
diets
(i.e.
stars
in
A
and
B
pooled),
providing
an
estimate
of
the
fundamental
macronutrient
niche
for
reference.
Food
compositions
have
been
jittered
(small
amount
of
random
noise
added),
to
make
overlaying
points
visible.
Note
that
seasonal
data
for
New
Zealand
are
based
on
Auckland
Island
populations
whereas
annual
data
are
based
on
the
North
and
South
Islands.
Number
of
articles
(number
of
populations)
for
Australia
=
1
(1),
France
&
Luxembourg
=
3
(3),
Germany
=
1
(8),
Italy
=
1
(2),
Japan
=
1
(1),
New
Zealand
=
4
(5),
Pakistan
=
1
(1),
Poland
=
1
(1),
Ukraine
=
1
(5)
and
USA
=
3
(8).
accompanies
increased
total
food
intake,
has
yet
to
be
studied
in
wild
boar.
It
is
hypothesised
that
higher
reproductive
rates,
earlier
age
at
reproduction
and
more
generally
the
adoption
of
‘r-type’
strategies
are
associated
with
successful
colonisation
by
invaders
(reviewed
in
Sakai
et
al.,
2001).
Additionally,
it
is
believed
that
traits
favour-
ing
increased
reproductive
output
are
selected
for
at
the
forefront
of
an
expanding
range
(Phillips
et
al.,
2010).
We
hypothesise
that
the
broad
fundamental
macronutrient
niche
of
wild
boar
may
favour
successful
population
establishment
by
two
mechanisms:
1)
pro-
526
A.M.
Senior
et
al.
/
Mammalian
Biology
81
(2016)
523–526
viding
the
flexibility
required
for
populations
to
survive
across
nutritional
environments,
and
2)
where
ecological
constraints
allow,
populations
may
consume
diets
that
affect
life-history
traits
so
as
to
favour
invasion
success.
In
the
future
it
will
be
interesting
to
examine
whether
widespread
correlations
between
macronutrient
niche
breadth,
diet,
and
life
history
are
observed
in
other
successful
invaders.
Acknowledgements
AMS
is
supported
by
a
Coffey
fellowship
from
the
Charles
Perkins
Centre,
The
University
of
Sydney.
DR
is
an
affiliate
of
the
New
Zealand
Institute
for
Advanced
Study.
SJS
was
supported
by
an
Australian
Research
Council
Laureate
Fellowship.
GEMC
is
supported
by
a
Loxton
fellowship
from
the
Faculty
of
Veterinary
Science,
The
University
of
Sydney.
DR
and
SJS
are
supported
by
Australian
Research
Council
grantLP140100235.
Finally,
we
would
like
to
thank
Dr
Jan
Buchmann
for
translating
papers.
Appendix
A.
Supplementary
data
Supplementary
data
associated
with
this
article
can
be
found,
in
the
online
version,
at
http://dx.doi.org/10.1016/j.mambio.2016.07.
001.
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... is considered one of the world's best invaders having now colonized every continent excluding Antarctica (Lowe et al., 2000). Generalist habitat and dietary requirements are considered the primary reasons the wild boar is such a successful invader (Senior et al., 2016). ...
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BACKGROUND Determining factors influencing animal movements at a temporal scale that is similar to that at which management actions are conducted (e.g., weekly) is crucial for identifying efficient methods of wildlife conservation and management. Using GPS data from 49 wild pigs in the southeastern U.S., we constructed weekly 50% and 95% utilization distributions to quantify the effects of biotic and abiotic factors on weekly core area and home range size, as well as home range shape. RESULTS We found vegetative composition (i.e., proportion of bottomland hardwoods), season (based on forage availability), meteorological conditions (i.e., temperature and pressure), and sex influenced wild pig weekly home range and core area size, while vegetative composition (i.e., proportion of upland pines) and landscape features (i.e., distance to streams) also were important factors influencing home range shape. At close distances to streams, wild pigs had more elongate home ranges when their home ranges comprised less upland pine habitat; however, farther from streams, there was no change in home range shape across fluctuating proportions of upland pines. CONCLUSION These results demonstrate that fine-scale wild pig home ranges and movements are pliable from week to week and influenced by several habitat, landscape, and meteorological attributes that can easily be quantified from available land use and meteorological databases. These findings are important for designing monitoring studies, identifying high risk zones for disease transmission, planning response to disease emergence events, and allowing more effective and efficient short-term management planning. This article is protected by copyright. All rights reserved
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