1. Introduction
Dogs (
Canis familiaris) are globally the most widespread human-introduced carnivores [
1]. Originating roughly 14,000 years ago [
2], the dog population grew alongside the human population, with estimates nearing a billion worldwide [
3]. Through their long-term association with humans, dogs have become integral members of human society, fulfilling various roles, such as pets, protectors, and guards for agriculture and livestock [
4,
5]. Across the globe, dogs exhibit varying degrees of free-ranging behavior, bringing them into interactions with wildlife on multiple levels [
1]. Particularly in developing nations, the threat of free-ranging dogs escalates as human populations expand into natural areas in search of suitable agricultural land and natural resources [
6]. Despite their long history as human companions and workers, the impact of dogs on wildlife hinges on their management practices, whether they are fully domesticated and leashed, roam freely, rely on human-provided food or lead independent lives. Additionally, the proximity of dogs to natural reserves or urban pockets of wildlife plays a significant role in the frequency and nature of interactions with wildlife [
6,
7].
Despite their morphological differences from wolves due to domestication, dogs retain characteristics of the carnivore guild [
1,
4]. In certain regions, dogs have emerged as the most abundant carnivores, disrupting ecosystems [
8] and negatively impacting wildlife. Dog behaviors, including direct predation, harassment, and competition can lead to fear-induced behavioral changes in wildlife and affect their resource base and ultimately their fitness. In addition, the mere presence of dogs can lead to disease transmission [
9,
10,
11]. Prominent review articles provide insightful analyses of the complex dynamics of human-dog-wildlife interactions, highlighting the need for effective management strategies to mitigate adverse effects on biodiversity [
1,
4,
7,
14,
15]. However, there remains a need to understand how dogs are increasingly impacting individual species of wildlife as humans expand their agricultural areas.
Primate species represent one of the most diverse groups of mammals, totaling 504 species [
14]. Unfortunately, approximately 65% of these species are currently under threat of extinction due to habitat loss and resource depletion [
15]. Primate habitats are becoming significantly fragmented as a result of rising human demand for agricultural land, industrial growth, and the extraction of natural resources (e.g., mining, fuelwood), [
16,
17]. Tropical and subtropical forests, which are home to a large diversity of primates worldwide, have over 50% of their habitats fragmented [
16]. In these fragmented landscapes, encounters between primates and invasive species, notably dogs, are growing, as primates often fall victim to dog attacks while navigating patchy landscapes and fragmented forests [
19,
20]. For example, dogs have been hunting and eating white-tailed small-eared Galagos (
Otolemur garnettii lasiotis) in Kenya's fragmented landscapes [
19]. Similarly, in Madagascar, dogs have also been observed preying on wild ring-tailed lemurs (
Lemur catta) [
20], and similar incidents involving langurs and macaques have been reported from comparable landscapes in Asia [
21,
22,
23,
24]. The presence of predators, including dogs, profoundly influences primate behavior and activity patterns. Primates, like many other species, have adapted to minimize the risk of predation through behavioral strategies such as alarm calls, vigilance, and counter-attacking [
26,
27]. Studies conducted in various ecosystems have demonstrated how the perceived risk of predation alters vigilance behavior [
27], movement patterns [
28], foraging strategies [
29], and social dynamics [
30].
Anthropogenic impacts on animal behavior result from both direct human disturbances, like fragmentation, and indirect disturbances, such as the introduction of alien species [
31]. The initial reactions of animals to these changes are often behavioral, helping them adapt to new conditions [
32,
33,
34]. Primates living in anthropogenically disturbed areas regularly show changes in habitat use, foraging, and activity budget [
36,
37]. For instance, chimpanzees (
Pan troglodytes verus) in Guinea, West Africa, demonstrated a preference for traveling, resting, and socializing in habitat types with lower levels of human-induced pressure [
37]. Compared to natural processes, anthropogenic pressures expose animals to environments they have not experienced in their evolutionary history, and behavioral changes are occurring at faster rates [
38]. Even though these behavioral adaptations might have short-term benefits, they may also disrupt other long-evolved, fitness-related behaviors (e.g., social structure, reproductive strategies), which could negatively impact species persistence and have cascading effects on ecosystems [
35,
40].
Shared agroforest environments offer a complex web of opportunities and costs to wildlife. Our study species, Central Himalayan Langurs (CHL) inhabit Himalayan high-altitude agroforest landscapes. CHL dwell within fragmented natural oak forests and rely on seasonal crops (May-June and September-October) as well as on the leaves of fodder trees that grow along the edges of agricultural fields year-round [
41,
42]. However, foraging within agricultural fields exposes the langurs to their main predator, feral dogs [
20,
43], and increases the likelihood of frequent negative encounters with local people [
40,
43]. Predator presence can create a ‘landscape of fear’, and can influence the behavior and distribution of prey species within an ecosystem. Thus, ecological dynamics for CHL in such agroforest landscapes are not solely driven by the availability of resources, but also by the fear of predation and the strategies animals employ to mitigate that risk [
45,
46,
47]. By understanding how animals adapt their behavior to minimize risks while maximizing opportunities in shared landscapes, we can develop more effective approaches for managing human-wildlife interactions and fostering sustainable coexistence.
While a growing number of case studies describe behavioral responses to human-induced rapid environmental change in specific systems [
46], our understanding of such changes due to predatory feral dogs remains limited. We know that the presence of dogs can impact the activity of wild animals [
3,
7,
13,
49], but how animals respond to such changes has not been previously addressed, to our knowledge. We investigate how the fear landscape created by humans and predators affects the activity patterns of CHL in agroforest environments. By investigating how these primates deal with the simultaneous threats of humans and predators, we aim to understand more about the complex structure of fear behavior and how it impacts interactions between humans and wildlife. We hypothesized that H1: The predator-induced landscape of fear will have an impact on the activity patterns of CHL; H2: The human-induced landscape of fear will have an impact on the activity patterns of CHL; H3: CHL will modify their behavior in the habitat associated with these landscapes of fear. We predicted that in the landscapes of fear induced by predators and human activities, CHL will prioritize moving and feeding behaviors over socializing to maximize their fitness.
Author Contributions
Conceptualization, H.N., VN., and K.H.G.; methodology, H.N.; software, H.N., and K.H.G; formal analysis, H.N.; investigation, H.N., and V.M; resources, H.N., and J.T; data curation, H.N., VN., and K.H.G.; writing—original draft preparation, H.N., K.H.G.; writing—review and editing, H.N., VN., K.H.G., J.T., D.S., and R.D; visualization, H.N., V.M., and D.S.; supervision, J.T., D.S., and R.D.; funding acquisition, H.N., V.M., and J.T. All authors have read and agreed to the published version of the manuscript.