Effects of food supplementation on home-range size,
reproductive success, productivity and recruitment in a
small population of Iberian lynx
J. V. Ló pez-Bao, F. Palomares, A. Rodrı́guez & M. Delibes
Department of Conservation Biology, Estación Biológica de Doñana-CSIC, Seville, Spain
Keywords
spatial behaviour; productivity; body
condition; survival; dispersal rates;
recruitment.
Correspondence
José V. López-Bao, Department of
Conservation Biology, Estación Biológica de
Doñ ana-CSIC, C/Américo Vespucio s/n,
41092 Seville, Spain. Fax: +34 954 466 700
Email: jvlb@ebd.csic.es
Abstract
In a conservation context, food supplementation is a management tool used to
reverse the decline of food-limited populations by means of positive changes in
behaviour and fitness that may be reflected in population parameters. The
critically endangered Iberian lynx Lynx pardinus has suffered a dramatic decline
primarily because of the severe drop of its main prey, the European wild rabbit
Oryctolagus cuniculus. To reverse this situation, a food supplementation programme has been implemented in Donana, south-west Spain, since 2002. In this
study, we assess the utility of providing artificial food to reduce home-range (HR)
size, and to increase productivity, survival and recruitment in a scenario of low
lynx density, as compared with reference data from the same population in the
absence of extra food. Food supplementation produced a significant contraction
of core areas, but not of complete lynx HRs. We did not detect any significant
change in productivity or dispersal rates, but supplementation could have helped
transient adult lynx to settle down. The positive effects of food supplementation
may have been partly countered by factors such as inbreeding, Allee effects and
disease outbreaks, whose effects may have been exacerbated in this small lynx
population. Food supplementation, however, proved useful to retain individuals,
to keep range sizes within their normal range of values, thus maintaining spatial
organization, and to allow lynx reproduction and kitten survival in areas with very
low prey density. Therefore, we recommend keeping an extensive and intensive
supplementary feeding programme until the density of wild rabbits will enable the
viability of this endangered lynx population.
Introduction
Supplementary feeding, the artificial supply of food in foodlimited populations, has the potential to produce alterations
in behaviour such as changes in territory size (Ims, 1987),
territorial behaviour (Humbird & Neuford, 2008) or social
organization (Cochran & Solomon, 2000). Moreover, food
addition may have positive effects on fitness components
such as body condition (Lunn & Stirling, 1985; Lindstrom,
1989), reproductive rates (Persson, 2005) or litter and clutch
size (Angerbjorn et al., 1991; Koskela et al., 1998), and on
population parameters such as rates of survival (Schoech
et al., 2008), dispersal (Warrick, Scrivner & O’Farrell, 1999)
or recruitment (Boutin, 1990; Galindo-Leal & Krebs, 1998).
However, although many food addition experiments evaluate the influence of supplemental food on these parameters
(Boutin, 1990; Jones & Reynolds, 2008; Robb et al., 2008),
few studies have explicitly examined its utility as a conservation tool and whether its implementation reaches specific
conservation goals (Elliot, Merton & Jansen, 2001;
Gonzalez et al., 2006; Schoech et al., 2008). Moreover, few
studies have been carried out when the target species had a
very low density primarily due to food shortage, and could
therefore react more clearly to the addition of extra food.
The critically endangered Iberian lynx Lynx pardinus
(IUCN, 2008) is a specialist carnivore that feeds almost
exclusively upon European rabbits Oryctolagus cuniculus
(Delibes, Rodrıguez & Ferreras, 2000) and currently survives in two isolated populations, Sierra Morena and
Donana in south-western Spain (Ferreras et al., 2009; Fig.
1). Rabbit scarcity after the spread of introduced zoonoses,
myxomatosis in 1953 and rabbit haemorrhagic disease in
1989 (Rogers, Arthur & Soriguer, 1994; Villafuerte, Jordan
& Angulo, 2000), has been identified as a major factor of
lynx decline (Rodrıguez & Delibes, 2002). As a result of
rabbit decline, rabbit density does not reach the threshold
that allows regular lynx reproduction in a large proportion
of its geographic range (Palomares et al., 2001; Rodrıguez &
Delibes, 2002; Real et al., 2009).
Because rabbit scarcity was extremely high in some areas
of Donana, in 2002, food supplementation was implemented
as an emergency conservation measure targeted at the local
Effects of food supplementation in small populations
J. V. López-Bao et al.
Figure 1 Approximate distribution of the two
lynx populations remained in the Iberian Peninsula (DO,Doñana; SM,Sierra Morena) and
the two lynx subpopulations (1 = VE, 80 km2;
2 = CR, 25 km2) studied in the Doñana area
(3500 km2), south-west Spain. Doñana Natural
Reserve is highlighted in grey (dunes and
scrubland) and stippled (marshes).
lynx population. Food supplementation was apparently
useful to feed and retain lynx during several years of severe
rabbit scarcity (Lopez-Bao, Rodrıguez & Palomares, 2008),
but its potential to increase lynx carrying capacity remains
unclear. An increase in carrying capacity is expected to be
indirectly favoured by supplemental food through reduction
of home-range (HR) size (Sandell, 1989; Litvaitis et al.,
1996; Fuller & Sievert, 2001; Mitchell & Powell, 2004), and
an increase in reproductive success, litter size, kitten’s
condition and survival (Boutin, 1990; Angerbjorn et al.,
1991; Dewey & Kennedy, 2001), which may translate at the
population level into reduced dispersal and increased immigration followed by settlement (Boutin, 1990; Galindo-Leal
& Krebs, 1998; Warrick, Scrivner & O’Farrell, 1999).
This study evaluates the efficiency of a supplementary
feeding programme to augment carrying capacity in the
small Donana population of Iberian lynx, through reduction of HR size as well as increase in productivity and
recruitment. Compared with non-supplemented individuals
or subpopulations, for lynx exposed to supplementary feeding we expected (1) lower HR sizes; (2) an increase of
productivity, measured as reproductive success, litter size,
kitten’s condition and survival of kittens and juveniles; (3) a
higher recruitment of dispersing individuals as well as higher
settlement rates of individuals born in non-supplemented
areas.
Methods
Lynx subpopulations and the supplementary
feeding programme
We provided supplementary food to two lynx subpopulations within the most protected area of the Donana Natural
Reserve (Donana National Park, DNP; 37110 0 N, 6123 0 W;
Fig. 1), called Vera (VE) and Coto del Rey (CR). VE and
CR have traditionally played the role of sources within the
Donana metapopulation (Gaona, Ferreras & Delibes,
1998), and have been intensively studied during the last
25 years. As a result, 90 lynx have been radio-tracked, and
more than 16 000 positions recorded (Ferreras et al., 1997,
2004; Palomares et al., 2001). Habitat quality (vegetation
structure and prey abundance), and consequently lynx
density, in VE was lower than in CR (Ferreras et al., 1997;
Palomares et al., 2001).
From 2002 to 2008, six lynx breeding territories, three in
each subpopulation, were supplied with alive domestic
rabbits kept in 4 x 4 m enclosures (see details about the
structure of feeding stations in Lopez-Bao et al., 2008).
Iberian lynx accessed easily to feeding stations and 99% of
rabbits consumed in the feeding stations used regularly by
lynx were by the target species (Lopez-Bao, Rodrıguez &
Palomares, 2008). Each breeding territory contained on
average 3.3 randomly placed feeding stations (range = 1–9).
The supplementation schedule guaranteed a predictable and
abundant food supply to lynx. Supplementation was continuous throughout the year and feeding stations were
usually checked every other day (see details in Lopez-Bao
et al., 2008). Indeed, only 38% of rabbits supplied were
consumed by lynx, which suggest that food provision was ad
libitum (Lopez-Bao et al., 2008).
When the food supplementation programme started, lynx
density in VE was lower (5 individuals 100 km—2) than in CR
(24 individuals 100 km—2). Moreover, the average rabbit
density in VE in the low rabbit abundance period (autumn)
was 100 times lower (0.012 rabbits ha—1) than the threshold
value that allows a normal lynx reproduction (1 rabbit ha—1;
equivalent to 80 rabbit pellets m—2; Palomares, 2001; Palomares et al., 2001). However, in CR, rabbit densities were
only slightly lower than the threshold value for this period
(0.6 rabbits ha—1).
Field methods
Changes in HR size were studied by means of radio-tracking. We focused on adult resident females (42-year old and
Effects of food supplementation in small populations
J. V. López-Bao et al.
maintaining site fidelity for at least 10 months) on the basis
that female territory size is a function of prey availability in
solitary carnivores (Sandell, 1989). Out of 15 adult resident
females that were caught with box-traps and fitted with
radio-collars between autumn 1985 and autumn 2007, six
were and nine were not provided with supplemental food.
Three females provided with supplementary food were also
studied during a period before the onset of the supplementary feeding programme. Females were usually located
between two and four times per week and normally at a
distance o1 km to decrease triangulation error (estimates of
telemetry error using test transmitters were o100 m in our
study area). Radio-tracking procedures (cf. Ferreras et al.,
1997; Palomares et al., 2001) were exactly the same for
non-supplemented and supplemented animals, so we assumed that telemetry errors and estimates of HR size were
comparable.
Data on breeding events were obtained by radio-tracking
females combined with observations of females with kittens.
Between 1993 and 2008, reproductive success and productivity (litter size) was determined by tracking females daily
during the breeding season (March–May), which allowed us
to identify the den site and to check litter size. Three weeks
after detection of its birth, we recorded sex and biometric
data of kittens (Palomares et al., 2005).
We used lynx sightings, camera-trapping, captures and
radio-tracking (Ferreras et al., 1997, 2004; Palomares et al.,
2001), as well as a continuous monitoring with cameras
in feeding stations to estimate survival, dispersal and
settlement.
Data analyses
HR size
For each adult female, we used the extension Home Range
for ArcView GIS 3.2 (Rodgers & Carr, 1998) to calculate the
size of fixed kernel estimates of HR (area with 90% of
positions) and core areas (CA; area of highest use defined by
50% of positions, exclusive between females). HR and CA
were estimated yearly (from December to November) and
seasonally. We defined three seasons according to female
behaviour and rabbit abundance (Palomares et al., 2001):
(1) December–March (mating season and medium rabbit
abundance); (2) April–July (kitten rearing and high rabbit
abundance); (3) August–November (females accompanied
by juveniles, predispersal phase, and low rabbit abundance).
HR size was calculated using at least 30 independent positions (time interval between consecutive positions to assume
independence 46 h; Ferreras et al., 1997).
Range size estimates were log transformed to meet the
assumption of normality. Generalized linear mixed models
(GLMMs) with normal errors and identity link were used to
analyse the influence of food supplementation on estimates
of range size. As several females were tracked during several
years, we included individual and year as random factors in
all models. In addition, we included area, rabbit abundance
and the breeding status of females as fixed factors in the
models. The two areas differ in habitat quality, rabbit
abundance affects HR size (Palomares et al., 2001; Fernandez et al., 2003), and breeding may limit the movements of
adult females (Dahle & Swenson, 2003). To estimate spatial
variations in rabbit abundance we counted rabbits from a
vehicle along fixed transects 1 h before sunset during three
consecutive days per month, and selected the highest count
per month (Moreno et al., 2007). Monthly counts were
averaged to produce an annual estimate of rabbit abundance per area. For years o2004 we used estimates obtained
with the same method by Moreno et al. (2007) and
the Donana Biological Station Monitoring Team. Finally,
for each individual we included the mean number of
positions per month as a covariate representing radiotracking effort.
Between 2005 and 2006, for all three resident females
living in CR we calculated HR size before and after food
supplementation. Then, we additionally explored whether
food supplementation influenced the size of HR and CA
using Wilcoxon’s matched pairs tests.
Reproductive success and productivity
We evaluated whether food supplementation affected reproductive success (expressed as the ratio between the number
of females that bred and number of adult females per year),
litter size and kitten’s condition. We only considered litters
for which we knew the exact number of kittens born and the
date of birth. We estimated condition with the index BCI,
defined as the residual value obtained in a reduced major
axis regression of log mass on log head–body length
(Schulte-Hostedde et al., 2005). Regressions were fitted
separately for females and males, yielding high correlation
indices (40.99). We used GLMMs with the Poisson errors
and log link for the analysis of litter size and, normal errors
and identity link for the analysis of condition. We included
the index of rabbit abundance in the models to separate the
effects of supplemental food and food availability on productivity. We also included the age of kittens (days) to
control the effect of the age on BCI. The identity of the
mother and the year were included as random factors in the
models.
Survival
We evaluated the effect of supplemental food on kitten and
juvenile survival at different age classes: o3, 3–6, 6–9 and
9–12 months. We considered that one individual was alive in
each category when at least one positive contact from any of
the monitoring methods was recorded within each age class.
Survival was presented as the percentage of lynx alive at the
beginning of each age category. GLMMs with binomial
errors and logit link were used to test whether food supplementation affected lynx survival for each age category.
The identity of the mother and the year were included as
random effects.
Effects of food supplementation in small populations
J. V. López-Bao et al.
Recruitment
We compared dispersal rates between juveniles exposed and
not exposed to supplemental food. Dispersal was considered
when an individual left its natal territory and did not return in
at least 1 month (Ferreras et al., 2004). We also compared
settlement rates of transient lynx between supplemented and
non-supplemented areas. We considered that one individual
settled down when it was detected in the same area at least for
6 months and exhibited site fidelity (Palomares et al., 2000).
Results
Effects on HR size
We estimated the size of 31 annual ranges of 15 different
females. Food supplementation apparently did not influence
the HR size significantly, but it was significantly associated
with a reduction in the size of CAs (Tables 1 and 2). The
effect of food supplementation was similar in the two lynx
subpopulations (Table 2). We did not find evidence that
supplemental food influenced seasonal range sizes (Tables 1
and 2).
Mean HR and CA sizes ( ± SD) for the same three females
radio-tracked before (6.7 ± 1.8 km2 for HR
and
1.7 ± 0.3 km2 for CA) and after (4.4 ± 1.7 km2 for HR and
1.3 ± 0.7 km2 for CA) the implementation of food supplementation were 35 and 25% lower, respectively, when
females had access to supplemental food. However, these
differences were not significant (Wilcoxon’s test, T = 0,
P = 0.11 for HR, and T =3, P = 0.99 for CA).
Table 1 Mean ( ± SD) fixed kernel home-range sizes (HR, km2), and
estimated core area sizes (CA, km2) for females with and without food
supplementation in Vera (VE) and Coto del Rey (CR)
Area
Time interval
Non-supplemented females
VE
A
S1
S2
S3
CR
A
S1
S2
S3
Supplemented females
VE
A
S1
S2
S3
CR
A
S1
S2
S3
2
2
HR (km )
CA (km )
n
15.2 ± 10.6
8.6 ± 3.5
17.9 ± 16.9
14.8 ± 8.5
5.2 ± 1.9
5.7 ± 2.8
3.9 ± 1.6
5.5 ± 2.1
3.9 ± 1.9
2.46 ± 0.7
4.83 ± 4.1
4.53 ± 2.1
1.5 ± 0.4
1.7 ± 0.7
1.1 ± 0.6
1.6 ± 0.6
7
7
7
7
13
11
12
9
14.2 ± 6.8
13.8 ± 7.5
13.9 ± 8.6
14.4 ± 5.4
4.67 ± 1.67
4.97 ± 2.26
4.31 ± 3.10
5.13 ± 1.29
3.6 ± 1.8
3.7 ± 1.9
3.8 ± 2.6
4.4 ± 1.9
1.2 ± 0.6
1.3 ± 0.7
1.1 ± 0.8
1.4 ± 0.5
4
4
4
4
6
3
6
6
Annual (A) and seasonal (S1, December–March; S2, April–July; S3,
August–November) range size estimates are presented.
n, number of ranges measured. Annual range size estimates are
marked in bold.
Effects on reproductive success and
productivity
Eight adult females used supplemental food between 2002
and 2008. Out of 18 female-year occasions with exposure to
supplementation, females bred in 12 occasions (66%). This
percentage was lower than that for non-supplemented
females (83%, n = 29, Palomares et al., 2005) but differences
were not significant (Z-test = 0.782, P = 0.434). Reproduction in supplemented females occurred mainly in March
(87%), in agreement with previous reports for non-supplemented females (Palomares et al., 2005).
Mean litter size ( ± SD) for supplemented females
(2.4 ± 0.9, n = 9, range = 1–4) was lower than for females in
non-supplemented territories (3.0 ± 0.8, n = 21, range
= 2–5; Palomares et al., 2005), although differences were
not significant (F1,7 = 3.71, P = 0.095). The relative abundance of wild rabbits had no significant effect on litter size
(F1,7 = 0.88, P = 0.379).
We determined the birth date and condition for 30 kittens
from 12 different litters (eight litters and 20 kittens
under food supplementation). Food supplementation had
not a significant effect on kitten condition (F1,18 = 0.02,
P = 0.886) when rabbit abundance (F1,18 = 2.77, P = 0.113)
and the age of kittens (F1,18 = 0.18, P = 0.680) were controlled for.
Effects on survival
The mean proportion of lynx surviving in each category was
similar between supplemented and non-supplemented individuals (Table 3). Mortality was highest during the first
3 months in both scenarios (Table 3).
Effects on recruitment
Out of nine juveniles born under supplementation, 66%
abandoned the natal area. The rate of dispersal for supplemented juveniles was not significantly different than for
non-supplemented juveniles (75%, n = 41; Z-test = 0.137,
P = 0.891). Half (one male, two females) of the six juveniles
that dispersed (four males and two females) left their natal
subpopulations.
We detected eight transient adult lynx born in nonsupplemented areas (three males and five females) that used
supplemental food at least once. All of them were first
detected in VE, and five (62.5%) settled down in supplemented areas: three females and one male in VE and one
male in CR. The other three individuals left the supplemented areas within 3 months; two females settled in nonsupplemented areas and one male disappeared.
Discussion
In the small Iberian lynx population of Donana, supplemental food was significantly associated with a decrease in
the size of CAs of adult female HRs, but little reduction of
whole ranges was observed after provision of additional
food. Because supplemental food was provided ad libitum,
Effects of food supplementation in small populations
J. V. López-Bao et al.
Table 2 Generalized linear mixed models showing the effects of food supplementation on annual and seasonal home range and core area sizes
Parameter estimate ( ± SE)
Model effect
Annual ranges
Intercept
Food supplementation
Area
Food supplementation x area
Relative rabbit density
Breeding status
Radio-tracking effort
Seasonal ranges
Intercept
Food supplementation
Area
Season
Absence
VE
Absence of food supplementation x VE
Absence
VE
December–March (S1)
April–July (S2)
Absence of food supplementation x S1
Absence of food supplementation x S2
Food supplementation x season
Radio-tracking effort
Home range
Core area
2.62 ± 0.12
0.17 ± 0.09
0.41 ± 0.15**
0.05 ± 0.18
0.04 ± 0.01
0.34 ± 0.09*
—0.02 ± 0.01
2.10 ± 0.12
0.17 ± 0.09*
0.34 ± 0.14**
0.11 ± 0.17
0.02 ± 0.01
0.29 ± 0.09*
—0.01 ± 0.01
2.69 ± 0.11
0.02 ± 0.11
0.43 ± 0.07***
—0.06 ± 0.11
—0.14 ± 0.10
—0.02 ± 0.13
0.05 ± 0.12
—0.01 ± 0.01
2.12 ± 0.11
0.02 ± 0.11
0.46 ± 0.07***
—0.08 ± 0.11
—0.19 ± 0.11
—0.01 ± 0.14
0.06 ± 0.13
0.01 ± 0.01
Year and individual identity were included as random factors. The levels ‘Presence of food supplementation’, ‘CR’, ‘Occurrence of breeding
events’ and ‘S3: August–November’ are included in the intercept.
*Significant at Po0.05;
**Significant at Po0.01;
***Significant at Po0.0001.
CR, Coto del Rey; VE, Vera.
Table 3 Percentage of Iberian lynx Lynx pardinus that survived to
different age categories in supplemented and non-supplemented
territories of the Vera (VE) and Coto del Rey (CR) subpopulations
NonTime interval Supplemented supplemented Food
kittens
kittens
supplementation
(months)
o3
3–6
6–9
9–12
72%
81%
100%
100%
(n =27)
(n =21)
(n = 12)
(n =12)
62%
81%
100%
88%
(n =52)
(n =32)
(n =26)
(n =26)
F1,55 = 0.67 P = 0.417
F1,30 = 0.33 P= 0.543
F1,19 = 0.01 P= 0.998
The number of lynx is given within parentheses. The significance of
food supplementation on kitten and juvenile survival is also shown. No
dead lynx was detected for the age class 6–9 months.
accessible and regularly used by lynx (Lopez-Bao et al.,
2008), our results suggest that not only food abundance
determine female HR size. Other factors such as intruder
pressure (Hixon, 1980; Schoener, 1983), optimal use of
resources (Mitchell & Powell, 2007), the spatial dispersion
of natural and supplemental food (Macdonald, 1983;
Adams, 2001) and other essential resources as refuge or
water (Palomares et al., 2001) could also be influential, and
could limit quantitatively the usefulness of supplementation
to increase carrying capacity through territory compaction.
Optimal foraging rules predict that animals will tend to
use intensively areas with high density of resources (Ford,
1983). Contraction of CAs may be associated with an
increase in the use of space around feeding stations by adult
females. Our findings are also consistent with the idea that
variation in the distribution of one essential resource (food
availability) in the short term is unlikely to change substantially HR size (Cooper et al., 2006; Fernandez, Delibes &
Palomares, 2007). In addition, mean range size varied little
in both areas irrespective of supplementation and large
initial variation in range size between areas, which supports
that landscape structure may greatly influence HR size
(Fernandez et al., 2003). Little variability of HR size in the
short term may partly result from the fact that breeding
females usually inherit their maternal territories (Ferreras
et al., 1997). Indeed, despite the remarkable rabbit decline in
VE, HR size and location continued to be the same.
Food addition generally increases the proportion of
individuals that are reproductively active and the length of
the breeding season (Boutin, 1990). However, we found a
slight decrease in this proportion for resident adult females.
We also found that supplementation did not increase the
length of the breeding period (Palomares et al., 2005).
Productivity is expected to increase with food abundance
(e.g. Fuller & Sievert, 2001), and many food addition
experiences conform to this expectation (Boutin, 1990;
Schoech et al., 2008). We expected that this effect would be
strong under the conditions of extremely low rabbit abundance that occur in the VE area. However, we did not find
any significant change in productivity, which suggests that
productivity was not only limited by food. Indeed, reproduction rates and litter sizes tended to be lower in presence
Effects of food supplementation in small populations
of supplementation, perhaps reflecting a cumulative deterioration of reproductive performance in the Donana lynx
population after several decades of isolation (Rodrıguez &
Delibes, 2002). Genetic variability of the Donana population has decreased during the last 10 generations (Johnson
et al., 2004). Reduced reproduction and productivity, even
after supplementation, might be a demographic consequence of inbreeding (Hedrick & Kalinowski, 2000). Moreover, in small populations, the influence of an exceptionally
good or bad breeder on mean productivity is magnified. For
18 breeding female-year in the Donana lynx population,
50% of cases without breeding records (n = 6) belonged to
the same female. The other half came from two females
sharing their territory with a single adult male, which had
not been successfully mated previously. These examples
illustrate how, in small populations, stochasticity in reproductive performance may interfere at the population level
with potentially positive effects of supplementary feeding.
Previous studies about the effects of food supplementation on juvenile survival have shown a variety of responses:
no effect on survival (Doonan & Slade, 1995), increase
in survival (Dewey & Kennedy, 2001) and, more rarely,
decrease in survival (Fordham, 1971). We found little effect
on lynx survival, and the slight increase in survival for
kittens o3 months old could not be clearly related to food
supplementation.
Juvenile dispersal rates under supplementation tended to
be somewhat lower than the reference scenario. Nevertheless, this trend could have resulted from factors other than
supplementary feeding. Two juvenile males settled down in
vacant territories previously held by adult males that died in
an outbreak of feline leukaemia virus (Meli et al., 2009). The
other juveniles abandoned their natal territories apparently
due to intra-specific competition, which uses to be the
proximate triggering mechanism of dispersal (Ferreras
et al., 2004). Only one female settled down in her natal
area apparently aided by supplemental food, but this new
territory also showed the highest relative density of rabbits
of our study area, which makes both effects difficult to
separate.
Several food addition experiments have shown that the
increase in density in supplemented areas is mainly the result
of immigration, instead of reproduction or reduction in
dispersal rates (Galindo-Leal & Krebs, 1998; Yunger,
2002). In our study, five of the 15 adult lynx living in
supplemented areas between 2005 and 2008 were immigrants, and all immigrants that settled down were adults, in
agreement with the findings of Galindo-Leal & Krebs
(1998). We expected lynx to be attracted to supplemented
areas regardless their habitat quality or the presence of
conspecifics. However, only one female settled down in a
supplemented empty area, whereas other lynx settled
down in areas already occupied by conspecifics. One male
left one supplemented area without adult females and settled
down in another supplemented area with three adult
females. These results suggest that the presence of conspecifics is an important factor determining settlement of
transient lynx.
J. V. López-Bao et al.
Conclusions and implications for
conservation
Food supplementation proved useful to feed Iberian lynx
regularly and to preserve local lynx populations during long
periods of severe prey scarcity (Lopez-Bao et al., 2008). In
addition, where rabbit abundance was below the threshold
for lynx reproduction, supplemental food retained lynx,
kept their range sizes around reference values (Ferreras
et al., 1997; Palomares et al., 2001) and enabled the reproduction of females and the survival of kittens. We believe
that food supplementation have played an important role in
the maintenance of these lynx subpopulations and the
stability of their spatial organization. Without supplemental
food, lynx might have abandoned these areas, changed their
spatial behaviour or even reduced drastically their per capita
productivity and survival rates, particularly in VE.
However, because consumption of supplemental food
was enough to have a significant impact on the lynx population (Lopez-Bao et al., 2008), our results suggest that
additional positive effects of food supplementation such as
density increase through contraction of HRs and higher
productivity were tiny, maybe because the action of stochastic factors associated with the small population size of our
study population and social interactions countered the
positive effects of food addition. Small sample size (typical
in small threatened populations) may have also reduced the
power of analyses and made difficult to detect the expected
effects; this could have been the case for kitten survival or
dispersal rates.
Despite these considerations, previous studies on food
supplementation have shown that major population declines
cannot be prevented by food addition alone (Boutin, 1990),
and other extrinsic and intrinsic factors should also be
considered (Ferrer & Penteriani, 2008; Oro et al., 2008).
For example, we found a significant reduction in the size of
CAs, but not in the size of HRs. Therefore it might not be
possible to increase carrying capacity through territory
compaction without altering lynx territorial behaviour (i.e.
increasing the extent of HR overlapping).
In summary, our results suggest that, at present, carrying
capacity could hardly be increased through HR compaction
or through an increase in productivity in the Donana lynx
population. However, the potential of supplemental food to
increase carrying capacity through settlement of transient
lynx in supplemented empty areas remains to be explored.
Acknowledgements
This research was funded by the Spanish Ministry of
Education and Science (Project-CGL2004-00346/BOS), the
Spanish Ministry of the Environment under the National
Parks research programme (Grant-17/2005) and BP-Oil
Spain. The Consejerıa de Medio Ambiente (Junta de Andalucıa) partially financed the supplementary feeding programme under the project LIFE-02NAT/8609 and helped
with the fieldwork. The staff of Donana Natural Reserve
J. V. López-Bao et al.
provided data obtained with their camera traps. LandRover Espana S.A. kindly lended the vehicles for this work.
P. Ferreras supplied additional data on lynx dispersal
events. J.V.L.B. was supported by a FPU fellow (Ministry
of Education). Radio-tracking data on Iberian lynx from
1983 to 2000 was available thanks to the work of numerous
scientists, technicians, students and volunteers of the Carnivore Ecology Group, EBD-CSIC. M. Vogeli and M. Pereira
made useful suggestions on a previous draft of the paper.
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