Snow Leopard Dietary Preferences and Livestock Predation Revealed by Fecal DNA Metabarcoding: No Evidence for Apparent Competition Between Wild and Domestic Prey

Accurate assessments of the patterns and drivers of livestock depredation by wild carnivores are vital for designing effective mitigation strategies to reduce human-wildlife conflict. Snow leopard’s (Panthera uncia) range extensively overlaps pastoralist land-use and livestock predation there is widely reported, but the ecological determinants of livestock consumption by snow leopards remain obscure. We investigated snow leopard dietary habits at seven sites across the Sanjiangyuan region of the Qinghai–Tibetan Plateau (QTP), an area central to the species’ global range. Snow leopard abundance, wild prey composition, and livestock density varied among those sites, thus allowing us to test the effects of various factors on snow leopard diet and livestock predation. Using DNA metabarcoding, we obtained highly resolved dietary data from 351 genetically verified snow leopard fecal samples. We then analyzed the prey preferences of snow leopards and examined ecological factors related to their livestock consumption. Across the sites, snow leopard prey was composed mainly of wild ungulates (mean = 81.5% of dietary sequences), particularly bharal (Pseudois nayaur), and supplemented with livestock (7.62%) and smaller mammals (marmots, pikas, mice; 10.7%). Snow leopards showed a strong preference for bharal, relative to livestock, based on their densities. Interestingly, both proportional and total livestock consumption by snow leopards increased linearly with local livestock biomass, but not with livestock density. That, together with a slight negative relationship with bharal density, supports apparent facilitation between wild and domestic prey. We also found a significant positive correlation between population densities of snow leopard and bharal, yet those densities showed slight negative relationships with livestock density. Our results highlight the importance of sufficient wild ungulate abundance to the conservation of viable snow leopard populations. Additionally, livestock protection is critically needed to reduce losses to snow leopard depredation, especially where local livestock abundances are high.

Rapid increase in snake dietary diversity and complexity following the end-Cretaceous mass extinction

The Cenozoic marked a period of dramatic ecological opportunity in Earth history due to the extinction of non-avian dinosaurs as well as to long-term physiographic changes that created new biogeographic theaters and new habitats. Snakes underwent massive ecological diversification during this period, repeatedly evolving novel dietary adaptations and prey preferences. The evolutionary tempo and mode of these trophic ecological changes remain virtually unknown, especially compared with co-radiating lineages of birds and mammals that are simultaneously predators and prey of snakes. Here, we assemble a dataset on snake diets (34,060 observations on the diets of 882 species) to investigate the history and dynamics of the multidimensional trophic niche during the global radiation of snakes. Our results show that per-lineage dietary niche breadths remained remarkably constant even as snakes diversified to occupy disparate outposts of dietary ecospace. Rapid increases in dietary diversity and complexity occurred in the early Cenozoic, and the overall rate of ecospace expansion has slowed through time, suggesting a potential response to ecological opportunity in the wake of the end-Cretaceous mass extinction. Explosive bursts of trophic innovation followed colonization of the Nearctic and Neotropical realms by a group of snakes that today comprises a majority of living snake diversity. Our results indicate that repeated transformational shifts in dietary ecology are important drivers of adaptive radiation in snakes and provide a framework for analyzing and visualizing the evolution of complex ecological phenotypes on phylogenetic trees.

Prey preferences of invasive (Hemigrapsus sanguineus, H. takanoi) and native (Carcinus maenas) intertidal crabs in the European Wadden Sea

Invasive predators can have wide-ranging effects on invaded ecosystems and identifying the prey spectra and preferences of invaders are important steps in assessing their potential impacts on native biota. In this study, we investigated prey preferences of two invasive crab species (Hemigrapsus sanguineus and Hemigrapsus takanoi) that recently invaded Europe's shores and compared them with preferences of native shore crabs (Carcinus maenas) of similar size. In laboratory experiments, all three crab species preferred animal over algal prey. In general, sessile mussels (Mytilus edulis) were preferred over motile amphipods (Gammarus locusta) by all three crab species but amphipod predation was lower in the invasive compared with the native crabs. For the two invasive crab species, this pattern was the same in treatments where prey was offered separately (no-choice treatments) or simultaneously (choice treatments), while for the native crabs, mussel preference disappeared in choice treatments. The general preference of mussels by all three crab species suggests that local invasions of crabs most likely lead to increased competition among crabs. In addition, given that local densities of invasive crabs are often much higher than those of native crabs, predation pressure on native mussels can be expected to strongly increase at invaded sites. In contrast, local predation pressure on amphipods may be less affected by the crab invasions. Further field studies are needed to establish the magnitude of competition and predation pressure exerted by the invaders under natural conditions.

Detecting Prey Preferences and Prey Switching

In this chapter I consider the question of whether predators switch their preference for different types of prey as those prey change in abundance. There are numerous experiments in the literature focusing on this, but generally they have focused on a simplified analysis that ignores the functional response. Here I show why the functional response is crucial for understanding prey choice, and I show that null expectations considering a multi-species functional response lead to different interpretations than standard null expectations. I also derive null expectations for the proportion of prey consumed given the single-species functional response.

Habitat use and activity patterns of female Deacon Rockfish (Sebastes diaconus) at seasonal scales and in response to episodic hypoxia

We combined a high-resolution acoustic telemetry array with presence/absence receivers to conduct a preliminary study of the seasonal movements, activity patterns, and habitat associations of the newly described Deacon Rockfish (Sebastes diaconus). Eleven mature female Deacon Rockfish were tagged and monitored during an 11-month period, at a nearshore rocky reef off Seal Rock, Oregon, USA, an area of recurring seasonal hypoxia (defined as dissolved oxygen concentration [DO] < 2 mg l−1). Two tags were detected leaving the study area by day 35, indicating predation or emigration. Three tags became inactive within the array, indicating tag loss or fish death. Six “resident” fish inhabited the array for 246–326 days. Resident fish exhibited high site fidelity, small home ranges (mean 95% KDE = 4907 m2), and consistent activity patterns for the duration of the summertime high-resolution array (5 months), except during seasonal hypoxia. Resident fish were strongly diurnal in summer, with high levels of daytime activity above the bottom in relatively rugose habitat, followed by nighttime rest periods in deeper, less rugose habitat. During summertime hypoxia, resident fish exhibited less daytime activity during daytime hours with no rest periods at night, inhabited shallower water depths, and moved well away from their core activity areas on long, erratic forays. During the winter, diel patterns were less evident with higher activity levels at night (than in the summer) and lower activity levels in the day (than in the summer). We propose that some Deacon Rockfish continuously inhabit nearshore reefs throughout the year, but that daily/seasonal movement patterns, seasonally occurring hypoxia, and prey preferences for planktonic organisms influence relocation.

New insight into trophic niche partitioning and diet of mackerel (Scomber scombrus) and herring (Clupea harengus) in Icelandic waters

Understanding the competitive interactions of ecological similar species is essential to determine their role and niche in the ecosystem. Using both conventional dietary methods and stable isotope analysis, we examined the feeding ecology, trophic position and possible niche partitioning of Northeast Atlantic mackerel (Scomber scombrus), Icelandic summer spawning (ISS) herring (Clupea harengus), and Norwegian spring spawning (NSS) herring from Icelandic waters during the spring and summer 2012 and 2014. The stomach analysis showed differences in prey preferences among the species during summer, where mackerel diets were almost exclusively calanoid copepods, while herring ate larger zooplankton, i.e. euphausiids and amphipods. Analysis of isotopic diet contribution of mackerel and herring using Bayesian mixing models, representing mainly the spring consumption, revealed that euphausiids were the main dietary contributor of both mackerel and herring. Fish prey were also an important dietary source for ISS herring, and amphipods were important to the diet of NSS herring. In addition, mackerel encompassed a broad isotopic niche, whereas the two herring stocks had narrower and separated niches from each other. The results from this analysis reveal new and holistic information into the diet of these species, which have various ecological implications.