Ecology. How large predators manage the cost of hunting

The effects of prey depletion on dietary niches of sympatric apex predators in Southeast Asia

Resource depletion exerts opposing pressures on co-occurring consumers to expand diets while limiting overlap with competitors. Using foraging theory as a framework, we tested the effects of prey availability on diet specialization and overlap among competing Asian predators: dhole, leopard, and tiger. We used scat analysis from a prey-poor site, combined with a quantitative synthesis of 40 other diet studies, to determine biomass of different prey types consumed by each predator. We then assessed diet composition in relation to prey density, and compared diet breadth and overlap between prey-poor and prey-rich sites. In prey rich areas, all three predators specialized on energetically profitable medium and large ungulates (>30 kg), resulting in narrow, overlapping niches. Each predator shifted toward less profitable small-bodied prey (≤30 kg) as preferred ungulates declined, whereas consumption of preferred ungulates was unrelated to small prey abundance, as predicted by foraging theory. Diet breadths doubled under prey depletion (except leopard), but overlap declined as diets diverged via species-specific traits that facilitated capture of different types of alternative prey. Asia's apex predators adapt similarly to depletion of mutually preferred ungulates by switching to more numerous but less profitable small prey. Yet they can also partition a depleted prey base through intrinsic niche differences, thereby avoiding competitive exclusion. Our findings illuminate the stabilizing properties of adaptive foraging and niche differences in ecological communities, and provide insights into the behavior and resilience of Asia's endangered apex predators in response to prey depletion in the heavily poached forests of this region.

Energetics and evasion dynamics of large predators and prey: pumas vs. hounds

Quantification of fine-scale movement, performance, and energetics of hunting by large carnivores is critical for understanding the physiological underpinnings of trophic interactions. This is particularly challenging for wide-ranging terrestrial canid and felid predators, which can each affect ecosystem structure through distinct hunting modes. To compare free-ranging pursuit and escape performance from group-hunting and solitary predators in unprecedented detail, we calibrated and deployed accelerometer-GPS collars during predator-prey chase sequences using packs of hound dogs (Canis lupus familiaris, 26 kg, n = 4-5 per chase) pursuing simultaneously instrumented solitary pumas (Puma concolor, 60 kg, n = 2). We then reconstructed chase paths, speed and turning angle profiles, and energy demands for hounds and pumas to examine performance and physiological constraints associated with cursorial and cryptic hunting modes, respectively. Interaction dynamics revealed how pumas successfully utilized terrain (e.g., fleeing up steep, wooded hillsides) as well as evasive maneuvers (e.g., jumping into trees, running in figure-8 patterns) to increase their escape distance from the overall faster hounds (avg. 2.3× faster). These adaptive strategies were essential to evasion in light of the mean 1.6× higher mass-specific energetic costs of the chase for pumas compared to hounds (mean: 0.76 vs. 1.29 kJ kg-1 min-1, respectively). On an instantaneous basis, escapes were more costly for pumas, requiring exercise at ≥90% of predicted [Formula: see text] and consuming as much energy per minute as approximately 5 min of active hunting. Our results demonstrate the marked investment of energy for evasion by a large, solitary carnivore and the advantage of dynamic maneuvers to postpone being overtaken by group-hunting canids.

Plants are not sitting ducks waiting for herbivores to eat them

There is a common attitude toward plants, accordingly, plants are waiting around to be found and eaten by herbivores. This common approach toward plants is a great underestimation of the huge and variable arsenal of defensive plant strategies. Plants do everything evolution has allowed them to do in order not to be eaten. Therefore, plants are not sitting ducks and many plants outsmart and even exploit many invertebrate and vertebrate herbivores and carnivores for pollination and for seed dispersal, and even carnivores and parasitoids for defense.

Agouti-related peptide neural circuits mediate adaptive behaviors in the starved state

In the face of starvation, animals will engage in high-risk behaviors that would normally be considered maladaptive. Starving rodents, for example, will forage in areas that are more susceptible to predators and will also modulate aggressive behavior within a territory of limited or depleted nutrients. The neural basis of these adaptive behaviors likely involves circuits that link innate feeding, aggression and fear. Hypothalamic agouti-related peptide (AgRP)-expressing neurons are critically important for driving feeding and project axons to brain regions implicated in aggression and fear. Using circuit-mapping techniques in mice, we define a disynaptic network originating from a subset of AgRP neurons that project to the medial nucleus of the amygdala and then to the principal bed nucleus of the stria terminalis, which suppresses territorial aggression and reduces contextual fear. We propose that AgRP neurons serve as a master switch capable of coordinating behavioral decisions relative to internal state and environmental cues.

Can thermogenic adipocytes protect from obesity?

The role of brown adipocytes and adipocytes of a new beige type in the energy metabolism of a healthy person and in the pathogenesis of obesity has extensively been discussed in recent years. The interest to these cells has been stimulated owing to the application of new noninvasive methods for studying the metabolic activity of tissues. Using these methods, the presence of thermogenically active adipocytes in adults and their reactivity to cold stimuli have been proved. These data, together with the results of animal experiments support the idea of thermogenic fat being a direct regulator of the energy balance of man. However, for several reasons there are some objections to this viewpoint. The main objection is that the total activity of the human thermogenic adipocytes is about 100 kJ/day, i.e., it is negligible. In addition, the burn of excessive nutrients is biologically inappropriate for an organism. Therefore, the idea that obesity is caused by the decreased activity of thermogenic adipocytes is erroneous. The statement that the causes of obesity are associated with the increased efficiency of energy-dependent processes seems more reasonable. The consequence is a reduction in energy expenditure to perform a unit of biological work. This results in excess of nutrients deposited in the form of fat.

Movement, resting, and attack behaviors of wild pumas are revealed by tri-axial accelerometer measurements

BACKGROUND

Accelerometers are useful tools for biologists seeking to gain a deeper understanding of the daily behavior of cryptic species. We describe how we used GPS and tri-axial accelerometer (sampling at 64 Hz) collars to monitor behaviors of free-ranging pumas (Puma concolor), which are difficult or impossible to observe in the wild. We attached collars to twelve pumas in the Santa Cruz Mountains, CA from 2010-2012. By implementing Random Forest models, we classified behaviors in wild pumas based on training data from observations and measurements of captive puma behavior.

RESULTS

We applied these models to accelerometer data collected from wild pumas and identified mobile and non-mobile behaviors in captive animals with an accuracy rate greater than 96%. Accuracy remained above 95% even after downsampling our accelerometer data to 16 Hz. We were further able to predict low-acceleration movement behavior (e.g. walking) and high-acceleration movement behavior (e.g. running) with 93.8% and 92% accuracy, respectively. We had difficulty predicting non-movement behaviors such as feeding and grooming due to the small size of our training dataset. Lastly, we used model-predicted and field-verified predation events to quantify acceleration characteristics of puma attacks on large prey.

CONCLUSION

These results demonstrate that accelerometers are useful tools for classifying the behaviors of cryptic medium and large-sized terrestrial mammals in their natural habitats and can help scientists gain deeper insight into their fine-scale behavioral patterns. We also show how accelerometer measurements can provide novel insights on the energetics and predation behavior of wild animals. Lastly we discuss the conservation implications of identifying these behavioral patterns in free-ranging species as natural and anthropogenic landscape features influence animal energy allocation and habitat use.