Introduction
Terrestrial carnivores are some of the most imperiled species today due
to their large home range requirements, high metabolic demands,
sensitivity to habitat fragmentation, and persecution by humans (Crooks,
2002; Palomares & Caro, 1999; W. J. Ripple et al., 2014; Woodroffe &
Ginsberg, 1998). Carnivores are also important top-down regulators in
ecological communities (Beschta & Ripple, 2009; W. J. Ripple &
Beschta, 2006; W. Ripple J. & Beschta, 2012). The loss of key carnivore
species can have devastating ecosystem effects (Effiom et al., 2013; W.
J. Ripple et al., 2014) and changes in abundance or occurrence of
carnivores can trigger trophic cascades (W. Ripple J. & Beschta, 2012).
As such, the recovery of apex predators as a conservation tool to
restore ecosystem functions (termed trophic rewilding) has become
increasingly popular (Jørgensen, 2015; Seddon et al., 2014). Trophic
rewilding is an ecological restoration strategy used to promote
self-regulating ecosystems (Svenning et al., 2016).
Rewilding efforts in the context of apex predators requires not only an
understanding of their ecological interactions within the carnivore
guild, but also the broader context of these interactions including
sources of anthropogenic impacts. Many apex predators readily
reestablish in human-dominated landscapes and exhibit potential
coexistence with humans (Chapron et al., 2014; Lamb et al., 2020).
Although the effects of apex predator recovery in natural landscapes are
relatively well understood, there are significant knowledge gaps
regarding the effects of their recovery in shaping species interactions
(both intraguild and across trophic levels) in human-dominated
landscapes (Dorresteijn et al., 2015). Interactions between carnivores
are complex in nature, but are integral to shaping the ecology and
structure of wildlife communities. Therefore, examining such
interactions in landscapes that harbor viable carnivore populations may
provide important insights into the effects of carnivore recovery on the
mesocarnivore communities that often dominate landscapes where apex
predators have been eliminated.
Grey wolf (Canis lupus ) and Eurasian lynx (Lynx lynx ) are
top predators in many temperate ecosystems in Europe and Asia, but their
co-occurrence has been severely limited by extirpation of one species
(most often wolf). This is particularly the case for most of Western and
Central Europe due to a long history of human habitation and persecution
of carnivore species. Both wolf and Eurasian lynx are recovering in
Europe’s landscapes (Chapron et al., 2014; Kaczensky et al., 2013)
either through natural range expansion (wolf) or reintroductions and
population augmentation (lynx). The wildcat (Felis silvestris ) is
a mesocarnivore that was once common in Europe, has also been
extirpated, and currently at the core of reintroduction programs in some
European Union states. In this context, the Romanian Carpathians
represent one of the few natural areas in Europe that still harbor
intact viable populations of all three species and serve as a stronghold
for carnivore populations in Europe, despite anthropogenic influences
common (hunting, forestry, farming, and livestock production) (Popescu
et al., 2016; Salvatori et al., 2002).
While no work has been conducted on understanding the spatial relations
and interactions between these three species simultaneously, research
exists on pairwise interactions between species, particularly for lynx
and wolf. Lynx and wolf are sympatric across most of their range and
there is some diet overlap between them. Research addressing coexistence
between these species differ in their findings, but recent studies
looking at spatial interactions between these species in Europe found
that these two apex predators coexist and competition between them is
low (Schmidt et al., 2009; Wikenros et al., 2010). In Poland, lynx and
wolf territories overlap and researchers concluded that the
co-occurrence of these two species was facilitated by heterogeneous
habitat and specialization on different prey (Schmidt et al., 2009).
These predictors, habitat heterogeneity and diet, are also explaining
competitive interactions between canids and felids in North America,
with a lack of interference competition in heterogeneous habitat (Dyck
et al., 2022). Therefore, we expect to observe similar co-existence
(high co-occurrence) and little evidence of interference competition
(neutral or positive conditional occupancy values) between lynx and wolf
in our study area. Additionally, we expect to observe differences in
co-occurrence based on seasonal changes in these species’ behaviors. For
example, male lynx move further during the mating season (January-March)
and female lynx move further during periods of extensive kitten care
(May-August) (Jedrzejewski et al., 2002), which could cause increased
interactions with wolves. Research on wildcats is scarce, but a study
conducted in the Jura Mountains of central Europe found no evidence of
avoidance between lynx and wildcat (Zimmermann & Raoul, 2011). No
published research examines interactions between wildcats and wolf,
however interspecific interactions have been assessed between wildcats
and red foxes. A study in Spain found that the two carnivores exhibited
active avoidance towards one another and exhibited aggressive behaviors
during encounters suggesting interference competition (Ruiz-Villar et
al., 2021). Given the size difference between wolf and wildcats and
their different diets, it is likely that the relationship between
wildcats and wolf will be similar to that of wildcats and lynx.
In this study, we aimed to address these knowledge gaps by studying the
intraguild interactions of two apex carnivores, the Eurasian lynx and
the grey wolf, and a mesocarnivore, the wildcat in the Romanian
Carpathians using multispecies occupancy models (Rota et al., 2016).
Unlike traditional occupancy modeling, multispecies occupancy models
allow for the estimation of co-occupancy probabilities for more than two
species and do not assume asymmetric interactions (i. e., dominant and
subordinate species). This is useful for estimating co-occupancy
probabilities between species for which there is not a priori knowledge
about interspecific relationships or for which there is not an obvious
dominant or subordinate species. Multispecies occupancy models also
allow for the estimation of marginal occupancy (occupancy of a single
species irrelative of other species) and conditional occupancy
(occupancy of a single species based on the presence or absence of
another species) probabilities in relation to variables of interest
(e.g., altitude). This approach has been used effectively to assess
habitat use, interspecific interactions of carnivores in a variety of
landscapes (Dechner et al., 2018; Lombardi et al., 2020; Van der Weyde
et al., 2018). Previous research on lynx-wolf and lynx-wildcat
interactions suggests a high capacity for coexistence, low interspecific
competition, and little to no intraguild killing. However, this research
is limited and there has been no work on lynx-wolf dynamics or
interactions of lynx, wildcat, and wolf in the same region.
Additionally, none of the published literature has been conducted in an
area with a fully intact carnivore guild. This information is crucial to
understanding the effects of apex predators on mesocarnivores and the
carnivore guild. By using a multi-species occupancy approach, we can
analyze complex intraguild interactions and better understand
competition and coexistence patterns. Results can elucidate variables
and thresholds important for occurrence and coexistence of elusive
species and help inform management or reintroduction efforts. Our
specific objectives were: 1) evaluate seasonal predictors for occupancy
of each species, 2) characterize the spatial relationships
(co-occurrence) of each species in winter and autumn, and 3) identify
predictors that facilitate co-occurrence. Specifically, we analyzed the
effects of potentially dominant apex carnivores on the occupancy and
detection of a mesocarnivore to understand potential impacts
reintroductions of apex predators may have on smaller carnivores. We
also evaluated seasonal changes is marginal and co-occupancy
probabilities to better understand how species persist and interact
under different environmental conditions.