What Happens When Predators Do Not Completely Consume Their Prey?

A mathematical model is presented for the dynamics of predator-prey interactions when predators do not consume prey (or clumps of prey) in their entirety. Using a combination of analytical and numerical methods, I demonstrate that predator-mediated changes in the distribution of intact and partially consumed prey can affect the outcome of competition between predators in unexpected ways. In some cases, two predators can coexist on a single prey species owing to tradeoffs between the ability to consume prey completely and other competitive abilities. In other cases, predators exhibit frequency-dependent dynamics in which the first predator to occupy the habitat can prevent the other from invading. Conditions for stable coexistence usually expand if the larger predator scatters uneaten prey parts, if prey renewal includes both small and large items, or if the predator with the smaller retrieval capacity is poor at catching intact prey relative to the other predator.     

Do Behavioral Foraging Responses of Prey to Predators Function Similarly in Restored and Pristine Foodwebs?

Efforts to restore top predators in human-altered systems raise the question of whether rebounds in predator populations are sufficient to restore pristine foodweb dynamics. Ocean ecosystems provide an ideal system to test this question. Removal of fishing in marine reserves often reverses declines in predator densities and size. However, whether this leads to restoration of key functional characteristics of foodwebs, especially prey foraging behavior, is unclear. The question of whether restored and pristine foodwebs function similarly is nonetheless critically important for management and restoration efforts. We explored this question in light of one important determinant of ecosystem function and structure--herbivorous prey foraging behavior. We compared these responses for two functionally distinct herbivorous prey fishes (the damselfish Plectroglyphidodon dickii and the parrotfish Chlorurus sordidus) within pairs of coral reefs in pristine and restored ecosystems in two regions of these species' biogeographic ranges, allowing us to quantify the magnitude and temporal scale of this key ecosystem variable's recovery. We demonstrate that restoration of top predator abundances also restored prey foraging excursion behaviors to a condition closely resembling those of a pristine ecosystem. Increased understanding of behavioral aspects of ecosystem change will greatly improve our ability to predict the cascading consequences of conservation tools aimed at ecological restoration, such as marine reserves.     

“Prey Play”: Learning about Predators and Prey through an Interactive,Role-Play Game

“Prey Play” is an interactive role-play activity that provides fifth-grade students with opportunities to examine predator–prey interactions. This four-part, role-play activity allows students to take on the role of a predator and prey as they reflect on the behaviors animals exhibit as they collect food and interact with one another, as well as limiting factors. Through this activity, students will enhance their communication and observation skills and showcase their creativity.     

Motive for Killing: What Drives Prey Choice in Wild Predators?

Carnivorous animals are assumed to consume prey to optimise energy intake. Recently, however, studies using Nutritional Geometry (NG) have demonstrated that specific blends of macronutrients (e.g. protein, fat and in some cases carbohydrates), rather than energy per se, drive the food selection and intake of some vertebrate and invertebrate predators in the laboratory. A vital next step is to examine the role of nutrients in the foraging decisions of predators in the wild, but extending NG studies of carnivores from the laboratory to the field presents several challenges. Biologging technology offers a solution for collecting relevant data which when combined with NG will yield new insights into wild predator nutritional ecology.     

Community Response of Mammalian Predators and Their Prey to Motorways: Implications for Predator–Prey Dynamics

Understanding the interactions between predators and prey is essential for predicting the effects of disturbances to ecosystems. Motorways produce changes in the surrounding biotic and abiotic environment and hence have multiple impacts on wildlife. Some species are known to change their activity patterns in the proximity of motorways but the implications for the structure of food webs are unknown. This study analyzes the activity patterns of both mammalian predators and their prey species near nine motorways in attempt to clarify how motorways affect the mammalian community. Habitat structural variables were also sampled to control the effects of microhabitat on relative prey abundance. Our results revealed different activity patterns of both predators and prey near motorways that are independent of structural differences in microhabitat. Both the red fox and small mammals were found to use the zone close to the motorways more frequently, whereas lagomorphs and mustelids were less active there. These differences suggest that motorways favor the population of the predator that is most tolerant of human activity, the red fox, whose activity could have both direct and indirect effects on that of other members of the predator and prey community. On the one hand, the red fox seems to act as “top predator” and mustelids to follow a “safety match” strategy avoiding the area close to the motorway where fox is more active. On the other hand, abundances of prey species are negatively associated with the activity of their most frequent predators. This study is the first to assess how the proximity to motorways affects the activity of mammals in two levels of the food web and opens the field for research to understand the processes driving the detected patterns. Moreover, such effects at the community scale should be taken into account when evaluating the impacts of motorways on the surrounding ecosystems.     

Myosin VI: How Do Charged Tails Exert Control?

Molecular dynamics simulations and single molecule experiments are used to suggest that charged helices in the medial tail domain participate in myosin VI dimerization (Kim et al., 2010), which reinforces the mechanism that unfolding of the three helix bundle in the proximal tail serves as a lever arm extension.     

Resistance to Plant Invasion? A Native Specialist Herbivore Shows Preference for and Higher Fitness on an Introduced Host

The response of native herbivores to the introduction of a new plant to the community has important implications for plant invasion. Under the Enemy Release Hypothesis introduced species become invasive because of reduced enemy control in the new range, while under the New Association Hypothesis introduced species lack effective defenses against native enemies because they do not share an evolutionary history. I tested the response of a native South-American specialist herbivore Utetheisa ornatrix (Lepidoptera: Arctiidae) to a native (Crotalaria incana) and an introduced host (Crotalaria pallida) (Fabaceae: Papilionoideae). I compared seed predation rates between the two hosts in the field, and I tested preference and performance traits with common garden experiments. Utetheisa ornatrix caused much higher seed predation rates on the introduced host than on the native host. Females also preferred to oviposit on the introduced over the native host. Additionally, larvae feeding on the introduced host had higher fitness (higher pupal weight) than larvae feeding on the native host. I discuss how the response of this specialist herbivore to this introduced host plant contradicts the predictions of the Enemy Release Hypothesis and support the New Association Hypothesis. This study shows that the New Association Hypothesis can also be true for specialist herbivores.     

Size-structured Interactions between Native and Introduced Species: Can Intraguild Predation Facilitate Invasion by Stream Salmonids?

Dynamics of biological invasions may be complicated in size-structured animal populations. Differences in timing of life history events such as juvenile emergence create complex interaction webs where different life stages of native and non-native species act as predators, competitors, and prey. Stream salmonids are an ideal group for studying these phenomena because they display competition and predation in size-structured populations and have been introduced worldwide. For example, introduced rainbow trout (Oncorhynchus mykiss) are invading streams of Hokkaido Island, Japan and have caused declines in native masu salmon (O. masou) populations. However, age-0 rainbow trout emerge later than age-0 masu salmon and are smaller, which raises the question of why they are able to recruit and therefore invade in the face of a larger competitor. We conducted experiments in laboratory stream channels to test effects of increasing density of age-0 and age-1 rainbow trout on age-0 masu salmon. Age-1 rainbow trout dominated age-0 masu salmon by aggressive interference, relegating them to less favorable foraging positions downstream and reducing their foraging frequency and growth. The age-1 trout also reduced masu salmon survival by predation of about 40% of the individuals overall. In contrast, age-0 rainbow trout had little effect on age-0 masu salmon. Instead, the salmon dominated the age-0 trout by interference competition and reduced their survival by predation of 60% of the individuals. In each case, biotic interactions by the larger species on the smaller were strongly negative due to a combination of interspecific competition and intraguild predation. We predict that together these produce a positive indirect effect in the interaction chain that will allow the recruitment of rainbow trout in the face of competition and predation from age-0 masu salmon, and thereby facilitate their invasion in northern Japan.     

Nuisance Ecology: Do Scavenging Condors Exact Foraging Costs on Pumas in Patagonia?

Predation risk describes the energetic cost an animal suffers when making a trade off between maximizing energy intake and minimizing threats to its survival. We tested whether Andean condors (Vultur gryphus) influenced the foraging behaviors of a top predator in Patagonia, the puma (Puma concolor), in ways comparable to direct risks of predation for prey to address three questions: 1) Do condors exact a foraging cost on pumas?; 2) If so, do pumas exhibit behaviors indicative of these risks?; and 3) Do pumas display predictable behaviors associated with prey species foraging in risky environments? Using GPS location data, we located 433 kill sites of 9 pumas and quantified their kill rates. Based upon time pumas spent at a carcass, we quantified handling time. Pumas abandoned >10% of edible meat at 133 of 266 large carcasses after a single night, and did so most often in open grasslands where their carcasses were easily detected by condors. Our data suggested that condors exacted foraging costs on pumas by significantly decreasing puma handling times at carcasses, and that pumas increased their kill rates by 50% relative to those reported for North America to compensate for these losses. Finally, we determined that the relative risks of detection and associated harassment by condors, rather than prey densities, explained puma “giving up times” (GUTs) across structurally variable risk classes in the study area, and that, like many prey species, pumas disproportionately hunted in high-risk, high-resource reward areas.     

Do Predators Condition the Distribution of Prey within Micro Habitats? An Experiment with Stoneflies (Plecoptera)

The selection of habitat by macroinvertebrates living in running waters may be influenced by the physical characteristics of the substratum, as well as by the presence of other species. In this study, an artificial river with three different substrata (pebbles, detritus, and leaves) was utilized to analyze the microhabitat preference of two Plecoptera prey species (Amphinemura sulcicollis and Brachyptera risi), both in absence and in presence of a Plecoptera predator species (Perla marginata). In the absence of predators, both prey species showed a clear preference for the leaf microhabitat. When the predators were present, only Brachyptera risi showed a change of microhabitat selection, with a decrease of leaves and an increase of pebbles and detritus utilization. Amphinemura sulcicollis did not change their substratum utilization. This study demonstrates that the presence of a predator may affect microhabitat selection through a switch from the preferred to the less preferred substrata, although not all species change their habitat utilization in response to predator presence. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Functional and Numerical Responses of Predators: Where Do Vipers Fit in the Traditional Paradigms?

Snakes typically are not considered top carnivores, yet in many ecosystems they are a major predatory influence. A literature search confirmed that terrestrial ectotherms such as snakes are largely absent in most discussions of predator‐prey dynamics. Here, we review classical functional and numerical responses of predator‐prey relationships and then assess whether these traditional views are consistent with what we know of one group of snakes (true vipers and pitvipers: Viperidae). Specifically, we compare behavioural and physiological characteristics of vipers with those of more commonly studied mammalian (endothermic) predators and discuss how functional and numerical responses of vipers are fundamentally different. Overall, when compared to similar‐sized endotherms, our analysis showed that vipers have: (i) lower functional responses owing primarily to longer prey handling times resulting from digestive limitations of consuming large prey and, for some adults, tolerance of fasting; (ii) stronger numerical responses resulting from higher efficiency of converting food into fitness currency (progeny), although this response often takes longer to be expressed; and (iii) reduced capacity for rapid numerical responses to short‐term changes in prey abundance. Given these factors, the potential for viperids to regulate prey populations would most likely occur when prey populations are low. We provide suggestions for future research on key issues in predator‐prey relationships of vipers, including their position within the classical paradigms of functional and numerical responses.     

Predators,Prey and Habitat Structure: Can Key Conservation Areas and Early Signs of Population Collapse Be Detected in Neotropical Forests?

Tropical forests with a low human population and absence of large-scale deforestation provide unique opportunities to study successful conservation strategies, which should be based on adequate monitoring tools. This study explored the conservation status of a large predator, the jaguar, considered an indicator of the maintenance of how well ecological processes are maintained. We implemented an original integrative approach, exploring successive ecosystem status proxies, from habitats and responses to threats of predators and their prey, to canopy structure and forest biomass. Niche modeling allowed identification of more suitable habitats, significantly related to canopy height and forest biomass. Capture/recapture methods showed that jaguar density was higher in habitats identified as more suitable by the niche model. Surveys of ungulates, large rodents and birds also showed higher density where jaguars were more abundant. Although jaguar density does not allow early detection of overall vertebrate community collapse, a decrease in the abundance of large terrestrial birds was noted as good first evidence of disturbance. The most promising tool comes from easily acquired LiDAR data and radar images: a decrease in canopy roughness was closely associated with the disturbance of forests and associated decreasing vertebrate biomass. This mixed approach, focusing on an apex predator, ecological modeling and remote-sensing information, not only helps detect early population declines in large mammals, but is also useful to discuss the relevance of large predators as indicators and the efficiency of conservation measures. It can also be easily extrapolated and adapted in a timely manner, since important open-source data are increasingly available and relevant for large-scale and real-time monitoring of biodiversity.     

Introduced Alien or Persecuted Native? Resolving the Origin of the Viperine Snake (Natrix Maura) on Mallorca

The viperine snake (Natrix maura) is an important agent of decline of the threatened midwife toad (Alytes muletensis) of Mallorca. However, there is a paucity of biological data to support the notion that the viperine snake is an introduced species to the island. Here we compare mitochondrial cytochrome b gene sequences and genomic ISSR-PCR fingerprints from Mallorcan and mainland European viperine snakes. Identical or nearly identical haplotypes and very similar ISSR-PCR profiles provide strong evidence that N. maura arrived only recently to Mallorca. There is no indication of a recent natural colonization of the island by transmarine dispersal. The data therefore support historical information that N. maura was introduced to Mallorca by human agency comparatively recently, and that management measures to reduce the impact of the snake on toad populations are justified.     

Native and alien invasive plants: more of the same?

We compare the ecological and habitat characteristics of alien and native vascular plants which have recently expanded in range m England, Scotland, the Republic of Ireland and the Netherlands In the great majority of respects, expanding aliens and natives are functionally indistinguishable However, there are a few consistent differences aliens are more likely than natives to be clonal, polycarpic perennials with erect, leafy stems, and to have transient seed banks We discuss these trends m the context of the difficulties faced by aliens in invading mostly closed plant communities in relatively cool, damp climates Our results are consistent with some predictions of the attributes of'ideal'invaders, but contradict others We argue that the ecological attributes of successful alien invaders are strongly habitat-dependent     

Stress and the developing hippocampus: a double-edged sword?

The mechanisms that regulate neuronal function are a sum of genetically determined programs and experience. The effect of experience on neuronal function is particularly important during development, because early-life positive and adverse experience (stress) may influence the still “plastic” nervous system long-term. Specifically, for hippocampal-mediated learning and memory processes, acute stress may enhance synaptic efficacy and overall learning ability, and conversely, chronic or severe stress has been shown to be detrimental. The mechanisms that enable stress to act as this “double-edged sword” are unclear. Here, we discuss the molecular mediators of the stress response in the hippocampus with an emphasis on novel findings regarding the role of the neuropeptide known as corticotropin-releasing hormone (CRH). We highlight the physiological and pathological roles of this peptide in the developing hippocampus, and their relevance to the long-term effects of early-life experience on cognitive function during adulthood.     

Oxidative Stress and Alzheimer Disease: The Autophagy Connection?

Intraneuronal accumulation of amyloid beta-protein (Abeta) is believed to be responsible for degeneration and apoptosis of neurons and consequent senile plaque formation in Alzheimer disease (AD), the main cause of senile dementia. Oxidative stress, an early determinant of AD, has been recently found to induce intralysosomal Abeta accumulation in cultured differentiated neuroblastoma cells through activation of macroautophagy. Because Ab is known to destabilize lysosomal membranes, potentially resulting in apoptotic cell death, this finding suggests the involvement of oxidative stress-induced macroautophagy in the pathogenesis of AD.

Addendum to:

Autophagy of Amyloid Beta-Protein in Differentiated Neuroblastoma Cells Exposed to Oxidative Stress

L. Zheng, K. Roberg, F. Jerhammar, J. Marcusson and A. Terman

Neurosci Lett 2006; In press