Primary Prey Species Research Articles

Restoring historical moose densities results in fewer wolves killed for woodland caribou conservation

AbstractWoodland caribou (Rangifer tarandus caribou) are declining across much of their distribution in Canada in response to habitat alteration, leading to unsustainable predation, particularly by wolves (Canis lupus). Habitat alteration can benefit the primary prey species of wolves (moose [Alces alces] and deer [Odocoileus spp.]) by creating early seral conditions that contain more of their preferred food types. This increase in primary prey populations results in elevated wolf abundance and heightened predation pressure on caribou. In response to the elevated wolf populations and the risks to caribou, managers have reduced wolf abundance in key areas. Ecological theory suggests that reducing wolf abundance would release moose from the top‐down effects of wolf predation, potentially allowing moose populations to grow. Elevated moose abundance thus has the potential to cause wolf populations to rebound quickly each year following reductions, suggesting a possible link between moose abundance and the number of wolves killed for caribou conservation. To test this idea we used a unique management situation in British Columbia and Alberta, Canada, where lethal wolf removals were annually conducted across specific southern mountain caribou population ranges and, in some places, moose populations were concurrently reduced via liberalized hunting. We used indices of moose abundance and wolf removal data to test the hypothesis that reducing moose populations to a historical abundance target by hunting leads to fewer wolves killed for caribou conservation. After controlling for habitat quality, wolves removed per km2 was 3.2 times lower in areas with reduced moose density ( = 1.55 wolves/1,000 km2 ± 0.33 [SE]) than in those without reduced moose density ( = 5.02 wolves/1,000 km2 ± 0.52). However, the average number of wolves removed per year decreased under both conditions. After 9 years, there was a 35% reduction in the predicted difference in the annual removal between areas with and without moose reduction. Our results suggest that policies that do not reduce or stabilize moose abundance will result in the removal of more wolves to increase caribou abundance. Like wolf reductions, moose reductions can also be controversial and affect local harvesters. Thus, understanding the consequences of actions that support caribou recovery is essential to supporting evidence‐based policy discussions.

Lethal wolf control elicits change in moose habitat selection in unexpected ways

AbstractMoose (Alces alces) and woodland caribou (Ranger tarandus caribou) are the 2 large prey species for wolves (Canis lupus) in the Nearctic boreal forest in North America. Caribou have declined, with widespread anthropogenic disturbance as the ultimate cause and wolf predation as the proximal cause. To conserve caribou the government of Alberta, Canada initiated a wolf control program to reduce predation rates on caribou populations and contribute to caribou population recovery. Predators play an important role in shaping the structure and function of ecosystems through top‐down forces. We hypothesized that the strongest factors influencing moose occurrences would reflect changes in predation risk before and after the onset of wolf control. We weighed evidence for competing hypothesis by deploying cameras across a highly industrialized landscape in Alberta for 3 years after wolf control (2017–2020), capitalizing on 3 years of existing data before the onset of wolf control (2011–2014). We created generalized linear models representing competing hypotheses about moose response to natural and anthropogenic landscape features before and after wolf control, examining support for each in an information‐theoretic framework. Prior to wolf control, the model containing landscape features providing security cover was best‐supported, but this was scale‐dependent. After wolf control, the model containing landscape features that offer increased forage opportunities was best‐supported. Unexpectedly, the direction of effect was often opposite to predictions, with moose avoiding some features thought to provide security and forage. We demonstrate that lethal predator control affects the spatial distribution of its primary prey species but in ways we do not fully comprehend, highlighting the need for a better understanding of community dynamics following wolf control.

Safeguarding the last stronghold: Ecology and conservation of Asiatic Cheetah's prey species in Turan Biosphere Reserve (Iran)

Identifying suitable habitats for wild felids is essential for effective area-based conservation efforts. However, modeling habitat suitability for extremely rare and endangered taxa such as the Asiatic Cheetah (Acinonyx jubatus venaticus) is challenging due to limited data availability. To address this, our study focused on analysing the distribution factors of the Asiatic Cheetah's main prey species, including the Wild Goat (Capra aegagrus), Urial (Ovis vignei), Goitered Gazelle (Gazella subgutturosa), Jebeer Gazelle (Gazella bennettii), and Cape Hare (Lepus capensis) in the Turan Biosphere Reserve (TBR), a critical Cheetah habitat in Iran. To determine habitat suitability for these prey species, we conducted a systematic field survey along 30 transects measuring 16 km each by collecting data in each 1 km interval, resulting in 1172 direct observations of their presence. These observations were then correlated with 44 variables grouped into four categories: bioclimatic, topography, vegetation, and distance to anthropogenic and natural features. Suitability maps were generated using a hierarchical modeling approach. Among the observed prey species, Urial had the highest frequency of sightings (675 visual observations over eight seasons), followed by Goitered Gazelle (564 observations), Cape Hare (278 observations), Jebeer Gazelle (232 observations), and Wild Goat (208 observations). The most influential predictors affecting prey species distribution were mean summer temperature (with optimal ranges at lower temperatures), terrain relief roughness (with optimal ranges at intermediate roughness), distance to wells (with optimal ranges at shorter distances), and distance to corrals (with variable optimal ranges across species). Our findings indicate that the western and eastern mountainous areas, along with their hilly surroundings, as well as the northwest and western plains of TBR, constitute the most suitable habitats for these five prey species. These models and suitability maps provide crucial evidence for implementing conservation measures in the vulnerable habitats of the Asiatic Cheetah and its primary prey species. Environmental conditions can be enhanced through the management of water sources, roads, corrals, and livestock grazing. In addition, the fragmentation of suitable areas within TBR highlights the importance of preserving corridors between these fragmented habitats. We recommend re-evaluating and expanding the boundaries of Turan National Park, Turan Wildlife Refuge, and Turan Biosphere Reserve to ensure the long-term conservation of this threatened felid species and its associated ecosystems.

Evaluation of shoreline rotenone application to control Largemouth Bass recruitment in small impoundments

AbstractObjectiveReducing Largemouth Bass Micropterus salmoides recruitment and therefore population density could benefit recreational fisheries in small impoundments by improving individual growth rates and increasing the average size and condition of Largemouth Bass. To achieve these effects, methods of controlling Largemouth Bass recruitment should avoid reducing the productivity of their primary prey species, the Bluegill Lepomis macrochirus.MethodsWe tested this hypothesis by evaluating the effects of shoreline rotenone application on the density of Bluegill and the density, growth, and survival of age‐0 and age‐1 Largemouth Bass in 15 Alabama small impoundments.ResultAfter treatment, Largemouth Bass age‐0 densities declined and mean age‐1 length increased, whereas Bluegill populations were not significantly reduced.ConclusionOur study indicates that shoreline rotenone application may be a valuable method for reducing Largemouth Bass recruitment and increasing the growth of age‐1 Largemouth Bass in small impoundments. However, further research is needed to understand the effects of treatment on nontarget fishes and to better assess the effects of factors such as impoundment surface area and treatment frequency and duration on the ultimate utility of the approach.

Numerical response of predator to prey: Dynamic interactions and population cycles in Eurasian lynx and roe deer

AbstractThe dynamic interactions between predators and their prey have two fundamental processes: numerical and functional responses. Numerical response is defined as predator growth rate as a function of prey density or both prey and predator densities [dP/dt = f(N, P)]. Functional response is defined as the kill rate by an individual predator being a function of prey density or prey and predator densities combined. Although there are relatively many studies on the functional response in mammalian predators, the numerical response remains poorly documented. We studied the numerical response of Eurasian lynx (Lynx lynx) to various densities of its primary prey species, roe deer (Capreolus capreolus), and to itself (lynx). We exploited an unusual natural situation, spanning three decades where lynx, after a period of absence in central and southern Sweden, during which roe deer populations had grown to high densities, subsequently recolonized region after region, from north to south. We divided the study area into seven regions, with increasing productivity from north to south. We found strong effects of both roe deer density and lynx density on lynx numerical response. Thus, both resources and intraspecific competition for these resources are important to understanding the lynx population dynamic. We built a series of deterministic lynx–roe deer models, and applied them to the seven regions. We found a very good fit between these Lotka–Volterra type models and the data. The deterministic models produced almost cyclic dynamics or dampened cycles in five of the seven regions. Thus, we documented population cycles in this large predator–large herbivore system, which is rarely done. The amplitudes in the dampened cycles decreased toward the south. Thus, the dynamics between lynx and roe deer became more stable with increasing carrying capacity for roe deer, which is related to higher productivity in the environment. This increased stability could be explained by variation in predation risk, where human presence can act as prey refugia, and by a more diverse prey guild that will weaken the direct interaction between lynx and roe deer.

Differential developmental rates and demographics in Red Kangaroo (Osphranter rufus) populations separated by the dingo barrier fence.

Decommissioning the dingo barrier fence has been suggested to reduce destructive dingo control and encourage a free transfer of biota between environments in Australia. Yet the potential impacts that over a century of predator exclusion might have had on the population dynamics and developmental biology of prey populations has not been assessed. We here combine demographic data and both linear and geometric morphometrics to assess differences in populations among 166 red kangaroos (Osphranter rufus)-a primary prey species of the dingo-from two isolated populations on either side of the fence. We also quantified the differences in aboveground vegetation biomass for the last 10 years on either side of the fence. We found that the age structure and growth patterns, but not cranial shape, differed between the two kangaroo populations. In the population living with a higher density of dingoes, there were relatively fewer females and juveniles. These individuals were larger for a given age, despite what seems to be lower vegetation biomass. However, how much of this biomass represented kangaroo forage is uncertain and requires further on-site assessments. We also identified unexpected differences in the ontogenetic trajectories in relative pes length between the sexes for the whole sample, possibly associated with male competition or differential weight-bearing mechanics. We discuss potential mechanisms behind our findings and suggest that the impacts of contrasting predation pressures across the fence, for red kangaroos and other species, merit further investigation.

Free-ranging livestock affected the spatiotemporal behavior of the endangered snow leopard (Panthera uncia).

Long recognized as a threat to wildlife, particularly for large carnivores, livestock grazing in protected areas can potentially undermine conservation objectives. The interspecific interactions among livestock, snow leopards (Panthera uncia), and their wild prey in fragile Asian highland ecosystems have been a subject of debate. We strategically deployed 164 camera traps in the Wolong National Nature Reserve to systematically investigate the activities of snow leopards, their primary wild ungulate prey species, and free-ranging livestock. We found that snow leopard habitat use was influenced by both wild prey and livestock. Blue sheep served as the main wild prey that spatially attracted snow leopards and coexisted with yaks while free-ranging yaks significantly restricted snow leopard habitat use both temporally and spatially. This study challenges the conventional understanding that livestock indirectly impacts large carnivores by competing with and displacing wild prey. Our findings highlight that free-ranging yaks within the alpine canyon terrain could directly limit snow leopard habitat use, suggesting a potential risk of grazing in reducing apex predator distribution and jeopardizing their populations. Consequently, managing their coexistence in shared habitats requires a more nuanced approach. Furthermore, our research underscores the importance of further research efforts aimed at enhancing our comprehension of the complex interplay within animal communities and ecosystems. This knowledge will contribute to the development of informed, evidence-based conservation strategies and policies.

Spatiotemporal predictions of the alternative prey hypothesis: Predator habitat use during decreasing prey abundance

AbstractThe alternative prey hypothesis supposes that predators supported by a primary prey species will shift to consume alternative prey during a decrease in primary prey abundance. The hypothesis implies that during declines of one prey species, a predator modifies their behavior to exploit a secondary, or alternative, species. Despite occurring in many systems, the behavioral mechanisms (e.g., habitat selection) allowing predators to shift toward alternative prey during declines in the abundance of their primary prey are poorly understood. We evaluated habitat selection and use by a generalist predator with respect to two prey species during a dramatic decrease in the abundance of primary prey. Further, we evaluated how spatial variation in access to primary prey affected habitat selection, and assessed similarity and overlap between habitats used by each prey species. Coyotes (Canis latrans) exhibited decreasing selection for cottontail rabbits (Sylvilagus spp.; primary prey) during population decreases but did not shift habitat selection toward neonate mule deer (Odocoileus hemionus; alternative prey). Use of rabbit habitat remained high even during historically low rabbit abundance, while mule deer habitat was used in proportion to its availability. Coyotes seemingly do not make large shifts in habitat selection toward alternative prey following spatial and temporal decreases in the abundance of primary prey, but instead, take advantage of habitat overlap to facilitate prey‐switching behavior. Our work extends previous research conducted under the alternative prey hypothesis by explicitly evaluating the influence of habitat overlap between prey species and variation in access to prey habitat as factors affecting prey‐switching behaviors in predators.

Are the diets of sympatric Pygoscelid penguins more similar than previously thought?

In recent years, functional changes in Southern Ocean are becoming more noticeable, due to climate change and increasing human impacts, including a growing fishery that is concentrating in the Antarctic Peninsula (AP) region. Antarctic krill Euphausia superba is often the primary prey species for animals such as Pygoscelis penguins, a sentinel species for ecosystem monitoring and management. During the last two decades in the AP gentoo penguin numbers (Pygoscelis papua) have increased and their range has shifted southward, in contrast to the decline in numbers of Adélie (P. adeliae) and chinstrap (P. antarcticus) penguins. Given divergent population trends, the goal of this study was to examine differences in their diet, and size structure of Antarctic krill recovered from penguin diet samples. The study is based on diet samples collected during the austral summers on King George Island (South Shetland Islands) where P. adeliae, P. antarcticus, and P. papua breed in mixed colonies. Results indicate that the penguins consumed krill of similar sizes during the breeding period. In contrast to prior diet studies, we found higher proportions of krill in the gentoo diet and changes in the percentage of krill in the diet relative obtained during 1970s. The similarity in diets among all three species suggests that the availability prey items (e. g., fishes) may be changing and driving higher dietary overlap. Moreover, we also check differences in krill length among penguin individuals and we did not find any statistically significant differences. We also found plastic debris in penguin stomachs during both summers.

Disappearance of an ecosystem engineer, the white-lipped peccary (Tayassu pecari), leads to density compensation and ecological release

Given the rate of biodiversity loss, there is an urgent need to understand community-level responses to extirpation events, with two prevailing hypotheses. On one hand, the loss of an apex predator leads to an increase in primary prey species, triggering a trophic cascade of other changes within the community, while density compensation and ecological release can occur because of reduced competition for resources and absence of direct aggression. White-lipped peccary (Tayassu pecari—WLP), a species that typically co-occurs with collared peccary (Pecari tajacu), undergo major population crashes—often taking 20 to 30-years for populations to recover. Using a temporally replicated camera trapping dataset, in both a pre- and post- WLP crash, we explore how WLP disappearance alters the structure of a Neotropical vertebrate community with findings indicative of density compensation. White-lipped peccary were the most frequently detected terrestrial mammal in the 2006–2007 pre-population crash period but were undetected during the 2019 post-crash survey. Panthera onca (jaguar) camera trap encounter rates declined by 63% following the WLP crash, while collared peccary, puma (Puma concolor), red-brocket deer (Mazama americana) and short-eared dog (Atelocynus microtis) all displayed greater encounter rates (490%, 150%, 280%, and 500% respectively), and increased in rank-abundance. Absence of WLP was correlated with ecological release changes in habitat-use for six species, with the greatest increase in use in the preferred floodplain habitat of the WLP. Surprisingly, community-weighted mean trait distributions (body size, feeding guild and nocturnality) did not change, suggesting functional redundancy in diverse tropical mammal assemblages.

Predation patterns on the tundra—genetic barcoding of scats from two sympatric fox species

In the Arctic tundra, climate-induced emergence of the red fox ( Vulpes vulpes (Linnaeus, 1758)), a competitor to the Arctic fox ( Vulpes lagopus (Linnaeus, 1758)), is predicted to influence predation patterns of both fox mesopredators. In this study, we (i) identified predator species from scats through an established barcoding approach and (ii) explored the use of a cheap, quick barcoding method of fox feces ( n = 103). We investigated differences in diet between the red fox (predicted generalist predator) and Arctic fox (predicted specialist predator) over 2 years with varying prey abundance. We amplified short DNA fragments (<200 bp) from small rodents, birds and hares. For both predators, there was a high frequency of occurrence of rodents (38%–69%) identifying them as primary prey species and birds as secondary prey species (13%–31%). This demonstrates the strength of a straightforward DNA barcoding method for dietary analyses in sympatric fox predators, with species-level resolution of prey. Barcoding is a promising tool for future dietary studies; however, a few methodological improvements, along with extended sampling, are needed for a more complete assessment of fox predation patterns. Integrating high-resolution dietary analyses have great potential to enhance our understanding of predation patterns in Arctic tundra communities.

A temporal refuge from predation can change the outcome of prey species competition

Generalist predators whose primary prey undergoes cyclic fluctuations, will predate on alternate food sources when the abundance of their primary prey is low. In this paper we have developed a general model of a predator that switches predation between its primary prey and two alternative, competing, prey species. When the predators primary prey is at high abundance, predation of the alternate, competing, prey species is low, which provides periods of temporal refuge for the alternate prey from predation. When the inter‐specific interactions between the competing prey species lead to different dynamical outcomes in the presence and absence of predation, increasing the duration of the temporal refuge promotes dominance of a competitively superior species that is vulnerable to predation. The general theoretical framework was extended to consider a key case study system of pine marten predation on red and grey squirrels. In the absence of predation, grey squirrels out‐compete red squirrels but preferential predation by pine marten on grey squirrels can suppress grey squirrel density and allow red squirrel recovery. A temporal refuge for both squirrel species can arise due to prey switching by pine marten in years when field voles, their primary prey in the UK, are abundant. The duration of the temporal refuge, quantified as the relative length of the multi‐annual vole population cycle where vole density is above a population threshold, is a critical factor determining the persistence of red and grey squirrels. Our findings therefore provide insights for the conservation of the endangered red squirrel in the UK and the Republic of Ireland and more generally on the influence of the population dynamics of primary prey species in determining community composition.

Whole-lake nanosilver additions reduce northern pike (Esox lucius) growth

Nanosilver (AgNP) is an anti-microbial agent widely used in consumer products, with significant potential for these nanoparticles to be released into aquatic environments. Laboratory studies involving short-term exposures of fish to AgNP show a range of toxicological effects, but these studies do not address potential responses in long-lived organisms resulting from chronic exposures. A collaborative study involving additions of AgNP to environmentally relevant concentrations over two field seasons took place at the IISD-Experimental Lakes Area, providing an opportunity to study the impacts of chronic exposures to long-lived fish species. In the present study, we evaluated the abundance and growth of an apex predator, Northern Pike (Esox lucius), collected from Lake 222 before, during and after the AgNP dosing period and compared results to those from a nearby unmanipulated lake (Lake 239). While the abundance of Northern Pike from Lake 222 during the study period was essentially stable, per capita availability of their primary prey species, Yellow Perch (Perca flavescens) declined by over 30%. Northern Pike fork length- and weight-at-age (indices of growth rate) declined following AgNP additions, most notably in age 4 and 5 fish. No similar changes in prey availability or growth were observed in Northern Pike from the reference lake. Body condition did not change in Northern Pike collected from either Lake 222 or Lake 239. Our results indicate that declines in the growth of Northern Pike chronically exposed to AgNP likely resulted from reduced prey availability but direct sublethal effects from AgNP exposure could also have been a factor. The persistence of reduced growth in Northern Pike two years after the cessation of AgNP additions highlight the potential legacy impacts of this contaminant once released into aquatic ecosystems.

Landscape patterns in the occupancy of jaguars (Panthera onca) and their primary prey species in a disturbed region of the Selva Maya in Mexico

Abstract In order to prioritize the conservation and management efforts to protect jaguars (Panthera onca), it is of utmost importance to determine their tolerance in face of human disturbances, habitat modifications and varying degrees of prey availability. We assessed the occupancy probability of jaguars and five of their most common prey species throughout a heterogeneous landscape in the Selva Maya in southern Mexico: armadillo (Dasypus novemcinctus), coati (Nasua narica), paca (Cuniculus paca), white-tailed deer (Odocoileus virginianus), and collared peccary (Dicotyles tajacu). Additionally, we projected prey and Jaguar occupancies onto a 5993 km2 landscape based on the habitat type in the area. We averaged the best prey models ranked by QAICc and found that white-tailed deer had the highest average occupancy probability of 0.72 ± 0.06 and paca the lowest with 0.14 ± 0.04. The average occupancy probability for jaguars was 0.35 ± 0.07 and the strongest predictor of jaguar occupancy was a positive effect of collared peccary occupancy. These findings support previous studies that show that predator distribution is largely influenced by their prey availability, even in the midst of degraded habitats, and underlies the essential need to incorporate protection plans for prey species in jaguar conservation strategies.

Identification of Little Tern (Sternula albifrons) Prey in Inland Andong Lake, Korea Using Video Image Analysis

Little Tern (Sternula albifrons) prey composition was studied on a sandy islet in inland Andong Lake, Republic of Korea, during the breeding season (April to July 2018). Two remote-control video cameras with 4K-resolution were set on the islet to identify prey and determine whether prey species composition or size differed among breeding stages. On still images in which terns had prey in their bills (n = 1,275), prey species were identified, classified to five length-categories, and compared among breeding stages. Freshwater fishes dominated the observed diet (100%; 11 species overall), where the landlocked pond smelt (Hypomesus nipponensis; 80.8%) and largemouth bass (Micropterus salmoides; 13.7%) were main prey species. The mean prey length was 51.0 ± 20.89 mm, where 50.1–75.0 mm prey was the most frequent in the diet (42.2%) and varied significantly among breeding stages; 50.1–75.0 mm prey were most frequent during courtship and incubation stages, whereas 1.0–25.0 mm prey were most frequent at the chick-rearing stage. Surface water temperatures exceeded the upper thermal tolerance of the primary prey species at a date coincidental with tern departure from the colony.

Forage quality in grazing lawns and tall grasslands in the subtropical region of Nepal and implications for wild herbivores

Subtropical grasslands interspersed in forests often present mosaics of tall grasslands and grazing lawns with a high variation in structure, biomass and nutrient concentration. However, the impact of such variation on forage quality is still poorly known. We quantified physical and chemical properties of grasses of grazing lawns and tall grasslands, interspersed in the forested region of Bardia National Park, Nepal during the hot-dry season. This area falls within Cwa-climate (Köppen-Geigen climate classification). We found that grasses in grazing lawns had an average bulk density of ~5400 g.m-3 whereas tall grasslands had an average bulk density of ~1000 g.m-3 only. Forage in grazing lawns was comprised of a higher percentage of green leaf (up to 60%) compared to tall grassland (up to 40%). Phosphorus levels in green leaves were below maintenance requirements of wild herbivores (especially for grazers and mixed feeders) on both grazing lawns and tall grasslands. However, average crude protein levels in green leaves from both the grazing lawns and tall grasslands could meet the herbivores maintenance requirement (~7%). Only green leaves on grazing lawns had crude protein levels sufficient enough (9.7%) to meet the requirements of herbivores for maintenance and gestation, though not for lactation. We conclude that, during the hot-dry season, grazing lawns provide forage with a higher quantity and quality than tall grasslands. Consequently, grazing lawns can make a significant contribution to the maintenance or even growth of the grassland dependent wild ungulate population, such as chital (Axis axis), a primary prey species of the endangered tiger (Panthera tigris) in Bardia National Park. The insight of this study will provide a basis for restoring grazing lawns for quality forage, and aid in the conservation and management of wild grazers and mixed feeders.

Direct evidence of a prey depletion “halo” surrounding a pelagic predator colony

Colonially breeding birds and mammals form some of the largest gatherings of apex predators in the natural world and have provided model systems for studying mechanisms of population regulation in animals. According to one influential hypothesis, intense competition for food among large numbers of spatially constrained foragers should result in a zone of prey depletion surrounding such colonies, ultimately limiting their size. However, while indirect and theoretical support for this phenomenon, known as "Ashmole's halo," has steadily accumulated, direct evidence remains exceptionally scarce. Using a combination of vessel-based surveys and Global Positioning System tracking, we show that pelagic seabirds breeding at the tropical island that first inspired Ashmole's hypothesis do indeed deplete their primary prey species (flying fish; Exocoetidae spp.) over a considerable area, with reduced prey density detectable >150 km from the colony. The observed prey gradient was mirrored by an opposing trend in seabird foraging effort, could not be explained by confounding environmental variability, and can be approximated using a mechanistic consumption-dispersion model, incorporating realistic rates of seabird predation and random prey dispersal. Our results provide a rare view of the resource footprint of a pelagic seabird colony and reveal how aggregations of these central-place foraging, marine top predators profoundly influence the oceans that surround them.

Habitat connectivity for endangered Indochinese tigers in Thailand

Habitat connectivity is crucial for the conservation of species restricted to fragmented populations within human-dominated landscapes. However, identifying habitat connectivity for apex predators is challenging because trophic interactions between primary productivity and prey species influence both the distribution of habitats, and predator movement. Our goal was to assess habitat connectivity for Indochinese tigers (Panthera tigris) in Thailand. We quantified suitable habitat and dispersal corridors based an ensemble species distribution model that included prey distributions, primary productivity, and abiotic variables and was based on camera-trap data from 1996 to 2013 in 15 protected areas. We employed graph theory to evaluate the relative importance of habitat patches and dispersal corridors to the overall connectivity network. We found that tiger occurrence models with and without prey distributions performed well (Area Under the Curve: 0.932–0.954). However, inclusion of prey distributions significantly improved model performance (P < 0.001). Protected areas with tigers at the time of our surveys were highly isolated with high resistance to movement within the dispersal corridors, and four of them have lost their tiger populations since. Potential habitat patches outside of protected areas were also mostly isolated, but it was encouraging to find that there is ample potential habitat that tigers are not occupying. The Huai Kha Kaeng - ThungYai habitat patch and Kaeng Krachan dispersal corridor were the most important for overall habitat connectivity. Generally, integrating prey distributions into assessments of connectivity is a promising approach that can be widely applied to predict species occurrence and delineate dispersal corridors, thereby supporting conservation planning of tigers and other large carnivores.

Comparison of mechanical sorting and DNA metabarcoding for diet analysis with fresh and degraded wolf scats

AbstractDNA metabarcoding has become a powerful technique for identifying the species present in a bulk environmental sample. The application of DNA metabarcoding to wildlife diet analysis is a particularly promising tool for exploring trophic interactions. The extent to which molecular approaches agree with traditional approaches, and how this varies with the quality of field‐collected scats, is unknown. Here, we compare diets from wolf scats profiled using both mechanical sorting and metabarcoding of amplified vertebrate DNA sequences. Our objectives were to (1) compare findings from mechanical sorting and metabarcoding as a method of diet profiling and (2) use results to better understand diets of wolves on Prince of Wales Island, a population of conservation concern. We predicted metabarcoding would reveal both higher diversity of prey and identify rare species that are overlooked with mechanical sorting. We found that there was substantial overlap in the diets revealed using both methods, indicating that deer, beaver, and black bear were the primary prey species, but metabarcoding revealed a more diverse diet with greater occurrence of rare species. However, there was a large discrepancy in the occurrence of beaver in scats (52% and 25% from mechanical sorting and metabarcoding, respectively) explained by the high rate of false positives with mechanical sorting methods. While the number of wolf sequence reads for fresh scats was nearly eight times higher than in degraded scats, neither the number of prey sequence reads nor the quantity of DNA to be sequenced varied between fresh and degraded scats suggesting that metabarcoding is sensitive enough to determine prey assemblages in degraded scats. Even using scats from extremely wet conditions hostile to DNA preservation, we found that metabarcoding was more effective than mechanical sorting in describing diet.

Surface behaviors correlate with prey abundance and vessels in an endangered killer whale (Orcinus orca) population

AbstractSouthern Resident killer whales (SRKWs) (Orcinus orca) are an endangered population in the United States and Canada, partly due to declines of their primary prey species, Chinook salmon. Prey availability influences various aspects of SRKW behavior, including distribution patterns and social structure. Yet, it is unclear to what extent a limited prey source influences the frequency of surface‐active behaviors (SABs), behaviors with important ecological implications. Here, we used long‐term datasets (1996–2019) to examine the relationships between the abundance of Chinook salmon, vessel presence, and the frequency with which SRKWs perform SABs. Salmon abundance was a significant predictor of SAB frequency, with fewer SABs performed in times of lower salmon abundance. SRKWs displayed more SABs when more whale watching vessels were present, and the whales spent a greater amount of time in the study area, performing more milling as opposed to traveling behavior, when vessel numbers were higher. Lastly, we found pod‐specific differences, such that K pod displayed significantly fewer SABs than either J or L pods. The observed relationships between SRKW behavior and both salmon abundance and vessel presence have implications for social network cohesion and foraging success. Our study adds to a growing body of literature highlighting factors affecting SRKW behavior as they experience increased threats from decreased prey availability, habitat loss, and anthropogenic disturbance, with implications for trans‐boundary management and conservation efforts.