Possible Extinction Vortex for a Population of
Iberian Lynx on the Verge of Extirpation
FRANCISCO PALOMARES,∗ ‡ JOSÉ ANTONIO GODOY,† JOSÉ VICENTE LÓPEZ-BAO,∗
ALEJANDRO RODRÍGUEZ,∗ SEVERINE ROQUES,∗ MIREIA CASAS-MARCE,† ELOY REVILLA,∗
AND MIGUEL DELIBES∗
∗
Department of Conservation Biology, Estación Biológica de Doñana (CSIC), Avda. Américo Vespucio s/n, Isla de la Cartuja 41092
Sevilla, Spain
†Department of Integrative Ecology, Estación Biológica de Doñana (CSIC), Avda. Américo Vespucio s/n, Isla de la Cartuja 41092
Sevilla, Spain
Abstract: Theory suggests that demographic and genetic traits deteriorate (i.e., fitness and genetic diversity
decrease) when populations become small, and that such deterioration could precipitate positive feedback
loops called extinction vortices. We examined whether demographic attributes and genetic traits have changed
over time in one of the 2 remaining small populations of the highly endangered Iberian lynx (Lynx pardinus)
in Doñana, Spain. From 1983 to 2008, we recorded nontraumatic mortality rates, litter size, offspring survival, age at territory acquisition, and sex ratio. We combined these demographic attributes with measures
of inbreeding and genetic diversity at neutral loci (microsatellites) and genes subjected to selection (major
histocompatibility complex). Data on demographic traits were obtained through capture and radio tracking,
checking dens during breeding, track surveys, and camera trapping. For genetic analyses, we obtained blood or
tissue samples from captured or necropsied individuals or from museum specimens. Over time a female-biased
sex ratio developed, age of territory acquisition decreased, mean litter size decreased, and rates of nontraumatic mortality increased, but there were no significant changes in overall mortality rates, standardized
individual heterozygosity declined steadily, and allelic diversity of exon 2 of class II major histocompatibility
complex DRB genes remained constant (2 allelic variants present in all individuals analyzed). Changes in sex
ratio and age of territory acquisition may have resulted from demographic stochasticity, whereas changes
in litter size and nontraumatic mortality may be related to observed increases in inbreeding. Concomitant
deterioration of both demographic attributes and genetic traits is consistent with an extinction vortex. The
co-occurrence, with or without interaction, of demographic and genetic deterioration may explain the lack of
success of conservation efforts with the Doñana population of Iberian lynx.
Keywords: extinction dynamic, genetic variability, Iberian lynx, MHC, mortality rate, reproductive output, sex
ratio
Posible Vórtice de Extinción en una Población de Lince Ibérico al Borde de la Extirpación
Resumen: La teorı́a sugiere que los atributos demográficos y genéticos se deterioran (i.e., la adaptabilidad
y la diversidad genética decrecen) cuando las poblaciones son pequeñ as y que ese deterioro podrı́a precipitar
lazos de retroalimentación denominados vórtices. Examinamos si los atributos demográficos y las caracterı́sticas genéticas han cambiado en 1 de 2 poblaciones remanentes del crı́ticamente en peligro lince ibérico
(Lynx pardinus), en Doñ ana, Españ a. De 1983 a 2008, registramos tasas de mortalidad no traumática,
tamaño de camada, supervivencia de crı́as, edad de adquisición de territorio y proporción de sexos.
‡email ffpaloma@ebd.csic.es
.
Combinamos estos atributos demográficos con medidas de endogamia y diversidad genética en loci neutrales (microsatélites) y genes sujetos a selección (complejo mayor de histocompatibilidad). Los datos de
atributos demográficos fueron obtenidos mediante captura y rastreo por radio, revisión de madrigueras
durante la reproducción, muestreo de huellas y cámaras trampas. Para los análisis genéticos, obtuvimos
muestras de sangre o tejido de individuos capturados o muertos o especı́menes de museo. A lo largo del
tiempo se observó un sesgo en la proporción de sexos hacia hembras, la edad de adquisición de territorio
disminuyó, el tamañ o promedio de las camadas disminuyó y las tasas de mortalidad no traumática incrementaron, pero no hubo cambios significativos en las tasas de mortalidad generales, la heterocigosidad
individual estandarizada declinó a ritmo constante y la diversidad alélica de los genes del exón 2 de la clase
II del complejo mayor de histocompatibilidad DRB permaneció constante (2 variantes alélicas en todos los
individuos analizados). Los cambios en la proporción de sexos y la edad de adquisición de territorio pudieron
ser resultado de la estocasticidad demográfica, mientras que los cambios en el tamañ o de la camada y la
mortalidad no traumática pueden estar relacionados con los incrementos observados en la endogamia. El
deterioro concomitante tanto de los atributos demográficos como en las caracterı́sticas genéticas es consistente con un vórtice de extinción. La coocurrencia, con o sin interacción, del deterioro demográfico y
genético puede explicar la falta de éxito de los esfuerzos de conservación de la población de lince ibérico en
Doñana.
Palabras Clave: dinámica de extinción, lince ibérico, MHC, proporción de sexos, rendimiento reproductivo,
tasa de mortalidad, variabilidad genética
Introduction
Theory suggests that population and genetic traits deteriorate (i.e., fitness and genetic diversity decrease) when
populations become small and that this deterioration precipitates positive feedback loops called extinction vortices (Gilpin & Soulé 1986; Fagan & Holmes 2006). In
invertebrates, a few empirical studies have addressed the
dynamics of extinction events and have focused on deterioration of different traits at small population sizes (e.g.,
Saccheri et al. 1998). However, direct empirical evidence
confirming the occurrence of extinction vortices in vertebrate populations is lacking, mostly because long-term
data series and demographic and genetic data are lacking, particularly for long-lived species (Fagan & Holmes
2006). If extinction vortices occur in nature, they may
severely affect the recovery of small and isolated populations of endangered species (Gilpin & Soulé 1986; Fagan & Holmes 2006; Scheffer et al. 2009). This, in turn,
may slow or even counteract the efficacy of conservation
measures (Westemeier et al. 1998; Stephens & Sutherland
1999).
Mostly theoretical studies provide support for Gilpin
and Soulé’s (1986) model (e.g., Caughley 1994). For example, it is well known that small population size can
decrease breeding opportunities because the probability that individuals of the opposite sex will meet is lower
(Stephens et al. 1999). Breeding may be further decreased
by the sex-ratio bias that arises due to demographic or
environmental stochasticity (Ripa & Lundberg 2000). Another mechanism driving the extinction vortex is inbreeding depression (Hedrick & Kalinowski 2000; Tanaka
2000), which refers to the potential negative effects of
reduced genetic diversity and increased inbreeding on
demographic traits, such as birth rate (Madsen et al.
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1999; Rabon & Waddell 2010) and survival (Blomqvist
et al. 2010; Hostetler et al. 2010; but see Bouzat 2010).
Results of both simulation (Tanaka 2000) and empirical
studies (Keller & Waller 2002) show that inbreeding depression affects population dynamics and extinction risk.
We examined whether demographic and genetic traits
changed over time in a small vertebrate population that is
near extirpation. We used the highly endangered population of the Iberian lynx (Lynx pardinus) in Doñana, Spain
(Palomares et al. 2011a) as a model. This population has
remained small and isolated for decades despite considerable conservation efforts, the failure of which may be
due to an extinction vortex (Palomares et al. 2011a).
Methods
Iberian Lynx Populations
The critically endangered Iberian lynx (IUCN 2008) remains in 2 populations, Sierra Morena and Doñana. These
populations occupy about 4000 km2 (Ferreras et al.
2010). The populations are 240 km apart, and there is
no evidence of recent contact between them (Ferreras
et al. 2010). The Sierra Morena population contains threequarters of the remaining Iberian lynx, but this population declined by 83% from 1985 to 2005 (Palomares et al.
2011a). In contrast, the Doñana population remained relatively stable, at approximately 50 individuals, over the
same period (Palomares et al. 2011a). Despite the stability of the Doñana population, over the last 25 years the
probability of its extirpation has greatly increased due to
the reduction of potential source areas within Doñana
National Park (Palomares et al. 2011a). Clusters of individuals within the Doñana lynx population are spread
across 2000 km2 , and persistence of the metapopulation
depends critically on birth and dispersal from clusters
in the park (Revilla & Wiegand 2008). From 1985 to
2005, the percentage of lynx inside the park decreased
from 78% to 38% (Palomares et al. 2011a). In 1989–1990,
an outbreak of rabbit haemorrhagic disease severely decreased the abundance of European wild rabbits (Oryctolagus cuniculus) (Villafuerte et al. 1995), the primary
prey of Iberian lynx (Ferreras et al. 2010). The lack of prey
in many areas of the park limited lynx breeding events
after 1990 to a single area inside the park, Coto del Rey
(Ferreras et al. 1997; Palomares et al. 2001).
Acquisition and Organization of Data
We obtained demographic data (mortality, litter size,
age of territory acquisition, age at first reproduction,
sex ratio) on the Doñana lynx population for the years
1983–2008 through capture and radio tracking, track surveys, and camera trapping, following the methods described in Ferreras et al. (1992, 1997), Palomares et al.
(2001, 2005), and Meli et al. (2009). In some years data
on some variables were not collected. We obtained blood
and tissue for genetic analyses from captured or necropsied individuals and from museum specimens in the collection of Doñana Biological Station.
We considered individuals 2- to 10-year-old adults because within this range of ages animals may breed and
hold territories (Palomares et al. 2005; Vargas et al. 2009;
Gañan et al. 2010). From 1983 to1999, the age of most
lynx was determined mainly through canine radiographs
and cementum annuli enumeration (Zapata et al. 1997).
The birth dates of some individuals were known exactly
because their mothers were radio tracked. From 1993 onward, transponders were implanted in all trapped lynx.
Age was, therefore, known for all individuals captured as
neonates and juveniles. In addition, the ages of some untagged lynx were determined on the basis of when they
were first recorded in camera traps as 3- to 6-month olds
and later identified from their unique pattern of spots
(López-Bao et al. 2009). Accuracy in age assignation was
within 1 year for 15 individuals from the 150 used in this
study.
To test whether demographic and genetic traits
changed over time, we compared the values obtained
from early and late periods in the study. Unless otherwise stated, the early period was from 1983 to 1998, and
the late period was from 2002 to 2008. For analyses for
which we had a yearly sequence of data, we also looked
for changes in these data.
Mortality Rates of Adult Resident Lynx
We estimated annual adult mortality rates for radiotracked resident lynx (n = 36). An adult lynx was considered resident when it maintained site fidelity (as described in Palomares et al. 2000) for at least 10 months.
To remove the potential effect of land protection (lynx
may occur inside or outside Doñana National Park) on
mortality rates, we considered only adult resident lynx
living primarily inside the park (i.e., >60% of their home
ranges located inside the park). We used the extension
Home Range in ArcView GIS 3.2 (Rodgers & Carr 1998)
to calculate the size of 90% fixed-kernel estimates of lynx
home ranges. Radio-tracked location data were available
for the early period and the late period. We estimated annual total and nontraumatic (primarily disease) mortality
rates with Micromort (Heisey & Fuller 1985). Lynx were
radio tracked for 26,820 days (annual mean [SE] = 1341
days [148.81], range = 425–2724, n = 20 years) during which 18,496 lynx locations were recorded (annual
mean = 924.8 locations [141.74], range = 392–733, n =
20). The sum of the number of years some individuals had
a tag was 98 (annual mean = 4.9 [0.50], range = 2–10,
n = 20).
Mortality caused by traumatic events (e.g., collision
with a vehicle or poaching) was easily identified. When
no signs of trauma were apparent on a corpse, we attributed death to disease. We used a z test to determine whether there were significant differences in the
observed changes in mortality rates between study periods due to nontraumatic mortality (Heisey 1995).
Reproductive Output, Age of Territory Acquisition, and Age of
First Reproduction
Litter size and offspring survival during the first 3 months
were determined for the early period (Palomares et al.
2005) and the late period (2002–2008) following the
method described in Palomares et al. (2005) (also see
López-Bao et al. 2010). We tested whether litter size
(Mann–Whitney rank sum test) and survival (z test) differed between the 2 periods. Individuals that gave birth
in each study period belonged to different cohorts. Thus,
all females monitored in the early period were born from
1987 to 1998, whereas those monitored in the late period
were born after 1998.
We compared ages of territory acquisition within the
potential source areas of the park between a late period of
intensive radio tracking, 2005–2008, and an earlier lessintensive period of radio tracking 1983–1992, conducted
by Ferreras et al. (1997). We used a z test to examine
whether the age individuals acquired territory differed.
Because lynx acquiring territory during the late period
were often <3 years old, the age previously suggested by
Palomares et al. (2005) as age of first reproduction, we
reviewed the data on breeding success from free-ranging
lynx and captive females to determine the age of first
reproduction in the absence of mating constraints. Data
from 2- and 3-year-old captive females (n = 23) were obtained for 2005–2008 from Vargas et al. (2009). These
captive females mated with males that were ≥3 years
old, the age at which males have high breeding potential (Gañán et al. 2010). We obtained similar data for
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free-ranging females (n = 19) for 1994–2008, and, in all
cases, these females shared territory with only males ≥3
years old. For captive females, it was possible to know
whether they were pregnant or had live births, but this
information was not usually available for free-ranging females. Therefore, to make the data from free-ranging and
captive females comparable, any breeding attempt was
considered successful if offspring survived the first week
of life. We used a chi-square test to examine whether
the proportion of individuals that breed in each age class
differed. We obtained data on reproductive success for
2- and 3-year-old free-ranging males (n = 9) from 2005 to
2008. We considered only cases in which the male shared
his territory with a mature female (females 3–6 years old,
except one case in which the female was 2 years old) and
when paternity of the offspring could be confirmed genetically. We used composite microsatellite genotypes of
the offspring and their known mothers and a maximum
likelihood approach as implemented in CERVUS (version
3.0) (Kalinowski et al. 2007) to assign paternity. We considered as potential fathers all genotyped males known
to be mature and alive according to the field data. The
average probability that an unrelated individual was not
excluded from parentage of a given offspring when the
genotype of the second parent was known was 0.0033.
Sex Ratio of Offspring and Adult Resident Lynx
We calculated young (<3 months old) and adult (2–10
years old) annual sex ratios, expressed as the proportion of males, if at least 6 offspring from at least 2 different litters were recorded per year and if data on at
least 6 monitored adults existed for the breeding period
(December–February). Monitored lynx were those that
had working radio collars or were detected by cameras.
The criteria for inclusion in sex-ratio estimation were met
for offspring born from 1993 to 2007, when on average
of 8.1 offspring (SE 0.60) were sexed per year (range =
6–10), and were met for 1986 to 2008 for adults, when
on average 12.8 adults (SE 1.33) were monitored per year
(range = 6–27, n = 23 years). We examined whether
there was a trend in adult sex ratio with regression analyses and used a t test with data from the early and the late
periods. We used Spearman rank correlation to determine
whether adult and offspring sex ratios were correlated.
Genetic Diversity
After the rabbit hemorrhagic disease outbreak, most
breeding events occurred in the Coto del Rey population nucleus, which was usually inhabited by 3 lynx pairs
(Palomares et al. 2001; López-Bao et al. 2009). For all
adult lynx alive in 2008, we recorded whether they, their
mothers, or their grandmothers were born in the Coto
del Rey nucleus. These data provided an indirect measure of the potential for reproduction between closely
related individuals.
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We calculated standardized individual heterozygosity
(Supporting Information) for 150 lynx born from 1983
through 2008 (mean [SE] = 5.8 individuals/year [0.59],
range = 1–14, n = 26 years) and tested whether heterozygosity changed over time with regression analyses.
We tested whether each locus and all loci were at HardyWeinberg equilibrium by simulating 1000 permutations
of alleles among individuals within each population (implemented in FSTAT [Goudet 2001]) (Supporting Information). We assessed variation at exon 2 of class II major histocompatibility complex DRB genes (an important
component of genetic diversity relative to disease immunity) in 85 individuals born 1985–2007 (mean [SE] =
3.7/year [0.46], range = 1–8, n = 23 years) (Supporting
Information).
Results
Mortality Rates of Adult Resident Lynx
From 1983 to 2008, 14 adult Iberian lynx living in
Doñana National Park were found dead (39% of the total sampled individuals; n = 36). We recorded cause
of death as disease for 5 individuals, although cause of
death was confirmed through necropsy for only 4 (Meli
et al. 2009, 2010). The condition of the body of the
fifth lynx was too poor to test for disease. Four of these
deaths occurred after 2005. Mortality rate due to nontraumatic causes during the late period (0.20, 95% CI =
0.02–0.34) was 10 times higher (Z = 2.18, p = 0.01)
(Fig. 1a) than during the early period (0.02, 95% CI =
0.00–0.05). However, the difference in overall mortality
rate during the 2 periods was not significant (0.23, CI =
0–0.37 and 0.15, CI = 0–0.23, respectively; Z = 0.83,
p = 0.21).
Reproductive Output, Age of Territory Acquisition, and Age of
First Reproduction
Litter size in the early period was on average 3.11 kittens
(SE 0.17) (n = 19 litters from 7 females, range = 2–5),
and 75% of these offspring (n = 63) survived for at least
3 months. Reproductive output, however, decreased significantly in females during the late period to a mean
litter size of 2.27 (SE 0.14) (27% decrease, n = 11 litters
from 6 females, range = 2–3). Mann–Whitney rank sum
test for litters (data from the same females included) (U
= 105.0, p = 0.005) and for females (only average litter
size per female considered) (U = 21.5, p = 0.001) (Fig.
1b) indicated that differences were significant. Offspring
survival to 3 months also was lower (61%; n = 18) in
the late period, although differences were not statistically significant (Z = 0.87, p = 0.38). The small sample
size precluded statistical analyses of the possible effects
of the age of females on litter size, but data suggest age
did not affect litter size (Supporting Information).
The age at which lynx acquired and held territories in
the early period varied from 3 to 7 years for females and
from 4 to 7 years for males (n = 6 individuals; Ferreras
et al. 1997). However, only one individual (a female)
within this age range acquired and held a territory in the
late period. The other 5 females were 2 years old, and
6 males were 1 year old (n = 1), 2 years old (n = 2), 3
years old (n = 2), and 8 years old (n = 1). Proportion of
individuals in each study period that acquired territory
within the age range observed in the early period was
statistically significant (Z = 3.25, p = 0.001).
Individuals younger than 3 years old had a markedly
lower breeding success than 3-year-old lynx (Table 1).
A 2-year-old male fathered the offspring of a 3-year-old
female only once. In 23% of cases, a 2-year-old female
raised kittens compared with a breeding success of 76%
for 3-year-old females (χ 2 = 8.3, df = 1, p < 0.01).
Sex Ratio of Offspring and Adult Resident Lynx
Adult sex ratio (measured as the proportion of males)
became significantly female-biased throughout the study
period (1986–2008; y = 27.72–0.01X, t = 3.22, p < 0.01)
(Fig. 1c), but this trend was particularly noticeable since
1998 when mean sex ratio was 0.34 (SE = 0.023; test for
sex ratio equal to 0.5: t = –6.93, df = 10, p < 0.001).
In contrast, adult sex ratio did not differ from 0.5 before
1998 (mean = 0.56, SE = 0.044, t = 1.30, df = 11, p =
0.22) (Fig. 1c). Adult female-biased sex ratio was partially
a consequence of the sex ratio in predispersing 3- to 6month-old kittens, as the sex ratio of adults was correlated
with the sex ratio of 3- to 6-month-old kittens 2 years prior
(Spearman rank correlation; r s = 0.63, p = 0.03, n = 11
years) (Fig. 1c).
Genetic Diversity
At least 70% of adult lynx living in the Doñana area by
2008 (n = 23 individuals) were born or descended from
lynx born in the Coto del Rey population nucleus.
The null hypothesis of Hardy Weinberg equilibrium
could not be rejected for the overall sample for any locus. Observed heterozygosity ranged from 0.04 to 0.64
(in both cases all the loci were typed), and the average was 0.31. Standardized individual heterozygosity declined steadily during the study period (y = 16.73–0.01x,
t = 2.09, p = 0.04) (Fig. 1d). Mean heterozygosity of lynx
born from 1983 to 1998 was significantly higher than
that of lynx born from 1999 to 2008 (t = 2.13, df = 148,
p = 0.04, pooled variance). In addition, although the sample size did not allow for a robust statistical comparison,
genotyped breeding females during the late period had a
lower mean heterozygosity (0.87 [SE 0.223]) than breeding females during the early period (1.00 [SE 0.103]).
In the major histocompability complex, 2 allelic variants (Lypa-DRB∗ 01 and Lypa-DRB∗ 02) occurred in all 85
Doñana lynx. The analyses of father–mother–offspring
trios suggest these alleles corresponded to 2 different
genes that seem to have been fixed in the Doñana population from 1985 to 2007.
Discussion
Our results provide empirical evidence of how demographic and genetic traits may change concurrently and
quickly over time in a small, free-ranging vertebrate population at high risk of extirpation. Several demographic
and genetic traits were associated with lowered individual fitness (e.g., lower reproductive rate or increased susceptibility to disease), despite that the population has remained small [Palomares et al. 2011a]). Gilpin and Soulé
(1986) theorize demographic and genetic traits will deteriorate in small populations in extinction vortices. Fagan
and Holmes (2006) provide indirect empirical evidence
of such deteriorations. They found that a small population
is less likely to persist a few years before extirpation than
the same population at the same size several years earlier,
which implies that demographic traits deteriorate as extirpation becomes imminent. Our results and the results
of Palomares et al.’s (2011a) population-viability models
provide plausible evidence that the Doñana population
of Iberian lynx may be in extinction vortices. But, our
results here provide only correlative evidence, and our
data do not reveal the potential synergies between demographic and genetic factors inherent to an extinction
vortex.
Demographic stochasticity in the Doñana population
of Iberian lynx may explain biased sex ratios and reduced
mating opportunities (i.e., the Gilpin and Soulé [1986] R
vortex), whereas low genetic diversity may be indirectly
reducing reproductive performance and increasing susceptibility to disease (i.e., the Gilpin and Soulé F vortex). Although our results may suggest the existence of
the Gilpin and Soulé R vortex in the Doñana population,
Table 1. Reproductive success of Iberian lynx soon after reaching reproductive maturity.∗
Males (n, %)
Age (years)
2
3
Females (n, %)
offspring
no offspring
offspring
no offspring
1, 25
4, 80
3, 75
1, 20
3, 23
22, 76
10, 77
7, 24
∗ Males
were free-ranging individuals that shared territories with mature females (one female was 2 years old). Females were from both captive
(n = 23) (Vargas et al. 2009) and free-ranging populations (n = 19).
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Figure 1. Annual (a) mortality rates (black circles,
total mortality; white circles, nontraumatic mortality;
black and white circles, total and nontraumatic
mortality have the same value; 95% CI excluded for
clarity) for resident adult Iberian lynx (no data were
available between 1999 and 2004); (b) mean litter
size (SE); (c) sex ratio of 3- to 6-month-olds (black
circles) and adults (white circles); and (d) mean
standardized observed heterozygosity (SE) for lynx
born from 1983 to 2008 (n = 150).
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they are not clearly consistent with the existence of the
F vortex.
The female-biased adult sex ratio in the Doñana population could have resulted partly from higher deterministic mortality rates of males during dispersal (Ferreras
et al. 1992). The hypothesis that demographic stochasticity also contributes to a female-biased adult sex ratio, however, was supported by the correlation between
the sex ratio of adult lynx and that of 3- to 6-monthold juveniles 2 years earlier. In contrast, our correlative
results do not unequivocally demonstrate that the deterioration of the demographic traits (particularly litter
size and disease-related mortality) was a direct effect of
inbreeding. For example, reduction of litter size may
also occur when population density increases (Trinkel
et al. 2010), but this was not the case with the Doñana
population.
A decrease in prey abundance may also reduce litter size and prevent breeding in adult females (e.g.,
O’Donoghue et al. 2010). In the Doñana population of
lynx, this phenomenon is not the reason for reduced litter sizes and reproductive outputs. All potential breeding
females under study when the reduction of litter size was
detected inhabited areas where rabbit abundance was
high or were part of a supplementary feeding program
(López-Bao et al. 2009, 2010). In other cases, resident
females may not have bred because they or their potential partners were sexually immature. Furthermore, the
high level of relatedness among individuals in the recent adult population of Doñana and the reduction of
the population’s heterozygosity suggest that inbreeding
may be coincident with the deterioration of demographic
traits.
The 2 allelic variants found in the major histocompability complex of the Iberian lynx were identical to the
alleles Lyly-DRB∗10 and Lyly-DRB∗07, 2 of 13 alleles detected in a sample of 16 Eurasian lynx (Lynx lynx) from
China (Wang et al. 2009). The low level of genetic variation at class II major histocompability complex loci may
be limiting the immune response in the Iberian lynx.
Jiménez et al. (2008) provides further evidence of a decreased immune response in Iberian lynx. We, however,
did not detect changes over time in major histocompability complex that were correlated with changes in mortality rates due to infectious disease. There are 2 likely reasons for these changes in mortality, despite the seeming
decreased immune response we detected throughout the
entire study. First, Iberian lynx populations are susceptible to new or rare diseases (Millán et al. 2009). Thus, an
increase in chance contact with infectious disease agents
may explain the increase in infectious diseases during
the last years of the study (Palomares et al. 2011b). Second, because the domestic rabbits used in supplementary feeding contain high levels of antibiotics, their consumption may increase mortality from disease (Palomares
et al. 2011b). The inclusion of a higher number of individuals from the historical population and the analysis of
additional immune-related genes would be needed to
draw stronger inference.
The striking changes in demography and genetic traits
between the early and late periods may be related to
the large decline in rabbit abundance and distribution
that occurred in 1989–1990 (Villafuerte et al. 1995). The
number of breeding females in the area decreased (P. Ferreras, personal communication), and most litters were
produced within an area inhabited by only 3 breeding
pairs (Palomares et al. 2001). Most of the lynx reproducing before 1998–1999 were born before or near the time
of the collapse of the rabbit population. Seven of 12 adult
reproductive individuals (7 females and 5 males) that reproduced in 1993–2002 (i.e., the first period when litter
size was studied) were born between 1986 and 1992,
and the rest were born in 1993–1997. There was only
one adult male in the Coto del Rey area during the 1998
reproductive season, which may have further increased
the level of inbreeding.
Twenty-five years ago there were 10 Iberian lynx populations on the Iberian Peninsula (Rodrı́guez & Delibes
1992; Castro & Palma 1996), and intensive measures were
undertaken to prevent extirpation of at least 4 of the populations (Palomares et al. 2011a). Eight of the 10 populations had been extirpated by 2000, and in the 2 remaining
populations, Sierra Morena and Doñana, the number of
individuals declined by 83% or remained stable, respectively, where conservation efforts have been particularly
intense in the last 3 decades (Palomares et al. 2011a).
Management efforts may have merely delayed the extirpation of those populations, and our results suggest how
difficult it can be to recover a small and isolated vertebrate population. The mechanisms that underpin extinction vortices, such as reductions in reproductive output
and survival, may have prevented the recovery of the
Doñana population and, as suggested by Rodrı́guez and
Delibes (2003), may have accelerated the extirpation of
the other small lynx populations that remained 25 years
ago but were not in protected areas or were not the target
of conservation actions.
Although reasons other than an extinction vortex may
explain the failure of conservation efforts (Palomares
et al. 2011a), we believe that potential extinction vortices are important to consider in the recovery of small
populations. Theoretical models predict extinction vortices (Tanaka 2000; Oborny et al. 2005), but empirical examples of populations that exhibit deterioration of demographic and genetic traits, despite conservation actions,
are few (Caughley 1994; Fagan & Holmes 2006; but see
Westermeier et al. 1998 and Hostetler et al. 2010).
We do not believe stochastic factors better explain the
conservation status of the Iberian lynx than deterministic factors. It is simplistic to conclude that Iberian lynx
in Doñana are threatened with extirpation due only to
changes in the values of some stochastic factors. Palomares et al. (2011a) suggest the recovery of habitat and
prey populations should be undertaken immediately to
prevent extirpation of the Doñana population (Palomares
et al. 2011a). Here, we found correlative evidence that
supports, under the extinction vortex model, the suggestion that some demographic traits should be manipulated
to counteract the effects of deterministic factors.
The recovery of small vertebrate populations subject
to an extinction vortex may be particularly difficult. For
Doñana Iberian lynx to escape the extinction-vortex dynamic, restoration of habitat to increase carrying capacity and manipulation of demographic traits to increase
genetic variability are necessary.
Acknowledgments
This research was funded by Spanish Ministries of Education and Science (projects 944, PB87–0405, PB90–1018,
PB94–0480, PB97–1163, CGL2004–00346/BOS, and
CGL2006–10853/BOS) and Environment (048/2002 and
17/2005), project LIFE of the European Union, Instituto
para la Conservación de la Naturaleza, and the Consejerı́a
de Medio Ambiente of the Junta de Andalucı́a (projects
LIFE-02NAT/8609 and LIFE 06/NAT/E/209). Land-Rover
España kindly loaned us the vehicles for this work.
Doñana National Park and Junta de Andalusia staff provided some field data, and some of the samples for genetic analyses were obtained by the staff of the LifeNature Project for Iberian Lynx Conservation in Andalusia, the Iberian Lynx Ex situ Programme, and the Centro
de Análisis y Diagnóstico de la Fauna Silvestre. J.J. Aldama, P. Ferreras, J. Calzada, J. Román, N. Fernández, G.
Ruiz, J.C. Rivilla, A. Pı́riz, L. Soriano, S. Conradi, and numerous students and volunteers helped gather the data.
J. Donázar and P.W. Hedrick reviewed a previous draft
and D.B. Stouffer reviewed the English. J.V.L.B. was supported by a Formación de Personal Universitario fellowship (Ministry of Education) and M.C. was supported by a
Junta para la Ampliación de Estudios fellowship. The collection group of the Doñana Biological Station provided
the museum specimens.
Supporting Information
Details of genetic analyses (Appendix S1) and the age of
breeding females and their litter sizes (Appendix S2) are
available online. The authors are solely responsible for
the content and functionality of these materials. Queries
(other than absence of the material) should be directed
to the corresponding author.
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