Carnivore Predation Research Articles

Experimental Taphonomy of Benthic Chaetognaths: Implications for the Decay Process of Paleozoic Chaetognath Fossils

Abstract. Despite their small sizes (ca. 2–120 mm), chaetognaths, or arrow worms, are the most important planktonic carnivorous predators both in terms of biomass and abundance, and they represent the second most important component of modern marine ecosystems. The fossil record of chaetognaths is patchy and only consists of five Paleozoic species, which are still the object of a vigorous debate due to their unclear state of preservation. The two main diagnostic characters for the assignment of a fossil to chaetognaths are the presence of caudal and lateral fins as well as the existence of grasping spines on both sides of the head. However, among the five putative chaetognaths from the Paleozoic, none shows simultaneously these two characters. Our new experiments on the decay process of benthic chaetognaths Paraspadella gotoi demonstrate the differential alteration of various diagnostic characters through time. Six individuals were dissected and their decay was checked regularly in separate dishes contain...

Herpetofaunal Remains from Khonkho Wankane, an Urban and Ceremonial Centre in the Southern Lake Titicaca Altiplano: Unique Behavioural Correlates to Osseous Taphonomy

This research reports the herpetological (reptile and amphibian) remains from Khonkho Wankane, an urban and ceremonial centre in the southern Lake Titicaca region of the Bolivian Altiplano, which fluoresced during the Late Formative period. The total n = 1710, including a minimum of six taxa and representing a significant portion of the relatively depauperate modern herpetofauna recorded for the Lake Titicaca area. A lizard of the genus Liolaemus (Tropiduridae) was identified. Amphibians are represented by Andean toad Rhinella spinulosa (Bufonidae) and by at least four taxa of frogs: [cf. Gastrotheca marsupiata (Hylidae) and Pleurodema marmorata or P. cinerea and Telmatobius spp. (Leptodactylidae)]. The latter genus does not include members of the giant variants (T. culeus) that dwell in Lake Titicaca. The question of how these remains were incorporated into the site deposits is examined taphonomically. No indicators of human or small carnivore predation were detected. Significant spatial clustering of amphibian remains was detected, with two clusters contributing n = 1562 or 92.4% of the amphibian total (n = 1690). These concentrations also are characterised by a depressed ratio of cranial versus postcranial elements, which cannot be explained by recovery methods. These concentrations of herpetofaunal remains likely represent in-burrow deaths of species sheltering for thermoregulatory benefits away from this harsh Altiplano environment, with the lowered recovery of cranial elements hypothesised to have resulted from a lack of ossification. The bulk of herpetofaunal remains recovered therefore likely were recent intrusions into the site deposits and do not represent the residue of human exploitation during the occupation of Khonkho Wankane. Copyright © 2011 John Wiley & Sons, Ltd.

Human Activity Helps Prey Win the Predator-Prey Space Race

Predator-prey interactions, including between large mammalian wildlife species, can be represented as a “space race”, where prey try to minimize and predators maximize spatial overlap. Human activity can also influence the distribution of wildlife species. In particular, high-human disturbance can displace large carnivore predators, a trait-mediated direct effect. Predator displacement by humans could then indirectly benefit prey species by reducing predation risk, a trait-mediated indirect effect of humans that spatially decouples predators from prey. The purpose of this research was to test the hypothesis that high-human activity was displacing predators and thus indirectly creating spatial refuge for prey species, helping prey win the “space race”. We measured the occurrence of eleven large mammal species (including humans and cattle) at 43 camera traps deployed on roads and trails in southwest Alberta, Canada. We tested species co-occurrence at camera sites using hierarchical cluster and nonmetric multidimensional scaling (NMS) analyses; and tested whether human activity, food and/or habitat influenced predator and prey species counts at camera sites using regression tree analysis. Cluster and NMS analysis indicated that at camera sites humans co-occurred with prey species more than predator species and predator species had relatively low co-occurrence with prey species. Regression tree analysis indicated that prey species were three times more abundant on roads and trails with >32 humans/day. However, predators were less abundant on roads and trails that exceeded 18 humans/day. Our results support the hypothesis that high-human activity displaced predators but not prey species, creating spatial refuge from predation. High-human activity on roads and trails (i.e., >18 humans/day) has the potential to interfere with predator-prey interactions via trait-mediated direct and indirect effects. We urge scientist and managers to carefully consider and quantify the trait-mediated indirect effects of humans, in addition to direct effects, when assessing human impacts on wildlife and ecosystems.

Perceived Body Condition is Associated with fear of a Large Carnivore Predator in Humans

Natural selection affects emotional and behavioural patterns, such as anti-predator adaptations, that enhance human survival. Fear is a basic emotion that activates behavioural responses upon encountering a predator, being consistently higher in females than in males. In this study, we investigated associations between fear of a large carnivore predator and perceived physical condition in a sample of Slovakian participants (n = 943). When testing evolutionary hypotheses explaining gender differences in fear of predators, we found partial support for the “physical condition” hypothesis, because females either reported lower perceived body condition than males and their perceived body condition showed significant correlation with fear of brown bear, Ursus arctos. The negative association between fear and perceived body condition was stronger in males suggesting that fear evolved as a response to higher predation pressures on males in our evolutionary past, indirectly supporting the “predation pressure” hypothesis. Males and participants with higher fear of bears wanted to exterminate bears by shooting more than others, suggesting that future management strategies should be oriented on elimination of fear of predators, as primary predictor of extremely negative attitudes toward bears.

From Energy Gradient and Natural Selection to Biodiversity and Stability of Ecosystems

The purpose of this paper is to incorporate well-established ecological principles into a foodweb model consisting of four trophic levels --- abiotic resources, plants, herbivores, and carnivores. The underlining principles include Kimura's neutral theory of genetic evolution, Liebig's Law of the Minimum for plant growth, Holling's functionals for herbivore foraging and carnivore predation, the One-Life Rule for all organisms, and Lotka-Volterra's model for intra- and interspecific competitions. Numerical simulations of the model led to the following statistical findings: (a) particular foodwebs can give contradicting observations on biodiversity and productivity, in particular, all known functional forms -- - positive, negative, sigmoidal, and unimodal correlations are present in the model; (b) drifting stable equilibria should be expected for ecosystems regardless of their size; (c) resource abundance and specific competitions are the main determining factors for biodiversity, with intraspecific competition enhancing diversity while interspecific competition impeding diversity; (d) endangered species are expected always and loss in lower trophic endangered species are expected at trophication, i.e. the establishment of a higher trophic level of a community. These findings may shed lights on some ongoing debates on biodiversity. In particular, finding (a) implies that the diversity vs. ecosystems functioning debate is most likely the result of incompatible particular observations each cannot be generalized. In particular, general causality should not be expected between diversity and productivity. Finding (b) does not support May's theory that large ecosystems are inherently unstable nor Eton's theory that stability requires diversity. However, it lends a strong support to the energetic theory for the latitudinal diversity gradient. Finding (c) supports Darwin's observation on the effect of interspecific competition on diversity. Finding (d) implies that loss of diversity is inevitable with the appearance of a super species like the human race. Our method and result also suggest that although the evolution of particular species cannot be predicted, some general statistic patterns appear to persist. In addition to the aforementioned findings, these persisting patterns include: the trophic succession, the trophic biomass separation in orders of magnitude, the upper bounds in biodiversity in relationship to the intensities of specific competitions despite the enormous possible number of species allowed by genetic mutations.

Bovid mortality profiles in paleoecological context falsify hypotheses of endurance running–hunting and passive scavenging by early Pleistocene hominins

The world’s first archaeological traces from 2.6 million years ago (Ma) at Gona, in Ethiopia, include sharp-edged cutting tools and cut-marked animal bones, which indicate consumption of skeletal muscle by early hominin butchers. From that point, evidence of hominin meat-eating becomes increasingly more common throughout the Pleistocene archaeological record. Thus, the substantive debate about hominin meat-eating now centers on mode(s) of carcass resource acquisition. Two prominent hypotheses suggest, alternatively, (1) that early Homo hunted ungulate prey by running them to physiological failure and then dispatching them, or (2) that early Homo was relegated to passively scavenging carcass residues abandoned by carnivore predators. Various paleontologically testable predictions can be formulated for both hypotheses. Here we test four predictions concerning age-frequency distributions for bovids that contributed carcass remains to the 1.8 Ma. old FLK 22 Zinjanthropus (FLK Zinj, Olduvai Gorge, Tanzania) fauna, which zooarchaeological and taphonomic data indicate was formed predominantly by early Homo. In all but one case, the bovid mortality data from FLK Zinj violate test predictions of the endurance running-hunting and passive scavenging hypotheses. When combined with other taphonomic data, these results falsify both hypotheses, and lead to the hypothesis that early Homo operated successfully as an ambush predator.

Differential routing of ‘new’ nitrogen toward higher trophic levels within the marine food web of the Gulf of Aqaba, Northern Red Sea

Mesozooplankton communities in the meso-oligotrophic Gulf of Aqaba, Northern Red Sea, were investigated over a 2 years period (2005–2007) with emphasis on the trophodynamic relations among different taxonomic groups ranging from primary consumers to carnivorous predators. Based on stable isotope analyses, we present evidence for a strong contribution of ‘new’ nitrogen mainly derived from the utilization of aerosol nitrate by unicellular cyanobacteria especially during summer stratification and the propagation of exceptionally low δ15N onto higher trophic levels. In contrast, N2-fixation by diazotrophs seemed to play a minor role, while the utilization of deep water nitrate by cyanobacteria and eukaryotic algae might be of importance during winter mixing. Based on 15N enrichment of consumers, clear differences between exclusively herbivorous organisms (doliolids, appendicularians, pteropods) and those with omnivorous feeding modes were detected. The category of omnivores comprised a large variety of taxons ranging from small meroplanktonic larvae to non-calanoid copepods (harpacticoids, cyclopoids and poecilostomatoids) that together form a diverse and complex community with overlapping feeding modes. In addition, distinct seasonality patterns in δ15N of copepods were found showing elevated trophic positions during periods of winter mixing, which were most pronounced for non-calanoid copepods. In general, feeding modes of omnivores appeared rather unselective, and relative contributions of heterotrophic protists and degraded material to the diets of non-calanoid copepods are discussed. At elevated trophic positions, four groups of carnivore predators were identified, while calanoid copepods and meroplanktonic predators showing lowest 15N enrichment within the carnivores. The direct link between ‘new’ nitrogen utilization by primary producers and the 15N enrichment of consumers in the planktonic food web of the Gulf of Aqaba emphasizes the significant contribution of ‘new’ nitrogen to the nitrogen budget and ecosystem functions in subtropical and tropical oligotrophic oceans.

Testing the threat-sensitive predator avoidance hypothesis: physiological responses and predator pressure in wild rabbits

Predation is a strong selective force with both direct and indirect effects on an animal's fitness. In order to increase the chances of survival, animals have developed different antipredator strategies. However, these strategies have associated costs, so animals should assess their actual risk of predation and shape their antipredator effort accordingly. Under a stressful situation, such as the presence of predators, animals display a physiological stress response that might be proportional to the risk perceived. We tested this hypothesis in wild European rabbits (Oryctolagus cuniculus), subjected to different predator pressures, in Doñana National Park (Spain). We measured the concentrations of fecal corticosterone metabolites (FCM) in 20 rabbit populations. By means of track censuses we obtained indexes of mammalian predator presence for each rabbit population. Other factors that could modify the physiological stress response, such as breeding status, food availability and rabbit density, were also considered. Model selection based on information theory showed that predator pressure was the main factor triggering the glucocorticoid release and that the physiological stress response was positively correlated with the indexes of the presence of mammalian carnivore predators. Other factors, such as food availability and density of rabbits, were considerably less important. We conclude that rabbits are able to assess their actual risk of predation and show a threat-sensitive physiological response.

Indications of habitat association of Australopithecus robustus in the Bloubank Valley, South Africa

Establishing the habitat preferences of early hominin taxa is a necessary, though difficult, requirement for understanding the interaction between environmental change and hominin evolution. The environments typically associated with Australopithecus robustus have been reconstructed as predominantly open grasslands situated within a habitat mosaic that included a more wooded component with a nearby perennial water source. Most studies have concluded that the open grassland component represents the habitat preference of the hominins. In this study we investigate indicators of habitat association of A. robustus that are preserved in the animal paleocommunities represented in a series of fossil cave infills in the Bloubank Valley of South Africa, including Swartkrans, Sterkfontein, Kromdraai, and Coopers. Testing for conditions of isotaphonomy reveals a potential bias relating to depositional matrix and perhaps accumulating agent, though such a bias has not unduly influenced the taxonomic composition the assemblages. Correspondence analysis of census data from modern African nature reserves demonstrates that carnivore predation patterns are indicative of animal communities, which in turn are representative of habitats. As a result, modern census data are used to document patterns of habitat preference of large herbivores, thus allowing assignment of fossil taxa to a series of broadly defined habitat categories. Correspondence analysis of fossil assemblages reveals that the abundance profile of A. robustus is most similar to that of woodland-adapted taxa. In addition, fluctuations in the relative abundance of taxa assigned to the broad habitat categories reveal a significant negative correlation between A. robustus and open grassland-adapted taxa, indicating that the more grassland-adapted taxa there are in a given assemblage, the fewer hominins there tend to be. Thus, it appears that the open grasslands that comprise the majority of the paleoenvironments associated with A. robustus do not necessarily indicate the habitat preference of the hominins. Rather, it would appear that in addition to being dietary generalists, A. robustus were also likely to have been habitat generalists.

Substrate exploitation and resistance to biotic disturbance in the brachiopod Terebratalia transversa and the bivalve Pododesmus macrochisma

To test the hypothesis that epifaunal bivalves are more resistant to biotic disturbance than brachiopods, I evaluated abundances and body size of the brachiopod Terebratalia transversa and the anomiid bivalve Pododesmus macrochisma, which co-occur in the San Juan Islands (Washington State, USA, eastern Pacific). The proportion of bare space correlated with intensity of biotic disturbance had negative effects and surface rugosity had positive effects on abundance of T. transversa. Both rugophilic settlement and post-settlement mortality of juveniles due to biotic disturbance restrict T. transversa to crevices and complex substrates formed by solitary ascidians and giant barnacles. Its juveniles are under-represented on flat substrates, implying lower survivorship than in crevices, where juveniles are common. Abundance of the byssally-cemented bivalve P. macrochisma is negatively affected by rugosity and does not decrease with increasing bare space. P. macrochisma size patterns do not differ between crevices and flat substrates. Flat valves and high post-settlement mobility probably increase its juvenile survivorship under grazing pressure. T. transversa is not able to re-attach after settlement and is thus less resistant to grazing effects than P. macrochisma. This study supports the hypothesis that brachiopods are more negatively affected by biotic disturbance than epibyssate bivalves. Although brachiopods can be less preyed upon by carnivorous predators than epibyssate bivalves, T. transversa is affected more negatively by grazing than P. macrochisma. The evolutionary decline of brachiopod abundance in shallow habitats may represent responses to a heavy pressure on juveniles by grazers that evolved during the Mesozoic.

Summer kill rates and predation pattern in a wolf–moose system: can we rely on winter estimates?

So far the vast majority of studies on large carnivore predation, including kill rates and consumption, have been based on winter studies. Because large carnivores relying on ungulates as prey often show a preference for juveniles, kill rates may be both higher and more variable during the summer season than during the rest of the year leading to serious underestimates of the total annual predation rate. This study is the first to present detailed empirical data on kill rates and prey selection in a wolf-moose system during summer (June-September) as obtained by applying modern Global Positioning System-collar techniques on individual wolves (Canis lupus) in Scandinavia. Moose (Alces alces) was the dominant prey species both by number (74.4%) and biomass (95.6%); 89.9% of all moose killed were juveniles, representing 76.0% of the biomass consumed by wolves. Kill rate in terms of the kilogram biomass/kilogram wolf per day averaged 0.20 (range: 0.07-0.32) among wolf territories and was above, or well above, the daily minimum food requirements in most territories. The average number of days between moose kills across wolf territories and study periods was 1.71 days, but increased with time and size of growing moose calves during summer. Over the entire summer (June-September, 122 days), a group (from two to nine) of wolves killed a total of 66 (confidence interval 95%; 56-81) moose. Incorporation of body growth functions of moose calves and yearlings and wolf pups over the summer period showed that wolves adjusted their kill rate on moose, so the amount of biomass/kilogram wolf was relatively constant or increased. The kill rate was much higher (94-116%) than estimated from the winter period. As a consequence, projecting winter kill rates to obtain annual estimates of predation in similar predator-prey systems may result in a significant underestimation of the total number of prey killed.

Evaluating exotic predator control programs using non-invasive genetic tagging

Carnivorous predators are difficult to detect using conventional survey methods, especially at low levels of abundance. The introduced red fox (Vulpes vulpes) in Australia is monitored to determine the effectiveness of control programs, but assessing population parameters such as abundance and recruitment is difficult. We carried out a feasibility study to determine the effectiveness of using faecal DNA analysis methods to identify individual foxes and to assess abundance before and after lethal control. Fox faeces were collected in two sampling periods over four separate transects, and genotyped at five microsatellite loci. Two transects were subject to lethal control between collection periods. DNA was extracted from 170 fox faeces and, in total, 54 unique genotypes were identified. Fifteen biopsy genotypes from 30 foxes killed during lethal control were detected among the faecal genotypes. Overall, a similar number of genotypes were detected in both sampling periods. The number of individuals sampled in both periods was low (n = 6) and new individuals (n = 24) were detected in the second collection period. We were also able to detect animals that avoided lethal control, and movement of individuals between transects. The ability to identify individual foxes using these DNA techniques highlighted the shortcomings of the sample design, in particular the spatial scale and distances between transects. This study shows that non-invasive DNA sampling can provide valuable insight into pre and post fox abundance in relation to lethal control, individual behaviour and movement, as well as sample design. The information gained from this study will contribute to the design of future studies and, ultimately, control strategies.

Post‐dispersal granivory in a tall‐tussock grassland: A positive feedback mechanism of dominance?

AbstractQuestions: Is post‐dispersal seed predation a factor contributing to a positive feedback mechanism for dominance of tall‐tussock grasslands? Do seeds dispersed into neighbouring microhabitats of contrasting dominance differ in their probabilities of being predated? Does predation rate vary among predator groups? Do seed eaters selectively forage among the available seeds?Location: The southern and flooding sub‐regions of the Argentinian Pampas.Methods: We examined seed predation by vertebrate and invertebrate predators within two microhabitats of grassland mosaics (highly dominated tall‐grass patches vs. scarcely dominated short‐grass matrix) for different seed species in semi‐natural grasslands. Proportion of seeds eaten by different predator groups was estimated through exclusion experiments and analysed using ANOVA for split‐split‐plot designs. Experiments were performed during the autumn of two consecutive years in both Pampa sub‐regions.Results: Removal of seeds after a five day trial was two to four times higher in the tall‐grass patches than in the short‐grass matrix. During the same period, vertebrate predation was six times higher than invertebrate predation in the tall‐grass phase of the Southern Pampa, but it did not differ in the short‐grass matrix. Relative predation among phases showed the same pattern in the Hooding Pampa, where preferences by seed species also varied according to phase.Conclusions: The highest predation intensity shown by vertebrates in the tall‐grass patches indicates that they are the main seed predators in these systems, possibly because this microhabitat grants them refuge against carnivorous predators. This could significantly reduce the available seeds for recruitment of subordinate species after different disturbance events (fires, trampling by large herbivores, burrowing), representing an active filter to the floristic composition of the patch and contributing with other mechanisms to the dominance of tall‐grass species.

CONSUMER–RESOURCE BODY-SIZE RELATIONSHIPS IN NATURAL FOOD WEBS

It has been suggested that differences in body size between consumer and resource species may have important implications for interaction strengths, population dynamics, and eventually food web structure, function, and evolution. Still, the general distribution of consumer-'resource body-size ratios in real ecosystems, and whether they vary systematically among habitats or broad taxonomic groups, is poorly understood. Using a unique global database on consumer and resource body sizes, we show that the mean body-size ratios of aquatic herbivorous and detritivorous consumers are several orders of magnitude larger than those of carnivorous predators. Carnivorous predator-prey body-size ratios vary across different habitats and predator and prey types (invertebrates, ectotherm, and endotherm vertebrates). Predator-prey body-size ratios are on average significantly higher (1) in freshwater habitats than in marine or terrestrial habitats, (2) for vertebrate than for invertebrate predators, and (3) for invertebrate than for ectotherm vertebrate prey. If recent studies that relate body-size ratios to interaction strengths are general, our results suggest that mean consumer-resource interaction strengths may vary systematically across different habitat categories and consumer types.

Cascading effects of predator diversity and omnivory in a marine food web

AbstractOver‐harvesting, habitat loss and exotic invasions have altered predator diversity and composition in a variety of communities which is predicted to affect other trophic levels and ecosystem functioning. We tested this hypothesis by manipulating predator identity and diversity in outdoor mesocosms that contained five species of macroalgae and a macroinvertebrate herbivore assemblage dominated by amphipods and isopods. We used five common predators including four carnivores (crabs, shrimp, blennies and killifish) and one omnivore (pinfish). Three carnivorous predators each induced a strong trophic cascade by reducing herbivore abundance and increasing algal biomass and diversity. Surprisingly, increasing predator diversity reversed these effects on macroalgae and altered algal composition, largely due to the inclusion and performance of omnivorous fish in diverse predator assemblages. Changes in predator diversity can cascade to lower trophic levels; the exact effects, however, will be difficult to predict due to the many complex interactions that occur in diverse food webs.

Seasonal, diel and ontogenetic variation in feeding patterns of small yellow croaker in the central Yellow Sea

Stomach contents of 1603 small yellow croaker Pseudosciaena polyactis, sampled from seasonal bottom trawl surveys in the central Yellow Sea between March 2001 and January 2002, were examined. The results showed that small yellow croaker was a carnivorous predator and >30 prey species were identified from stomach contents analysis. Crustaceans (mainly euphausiids and decapods) were the most important prey, occurring in 93·1% of the stomachs containing food, and accounting for 77·6% of the total food by mass. Feeding activity was highest in autumn and lowest in spring and winter. Decapods were more important in summer, whereas euphausiids were more important during other seasons. Ontogenetic differences were found in the diet composition and feeding activity within the range of size (standard length, LS) studied. The importance of fishes and decapods increased with LS, whereas euphausiids, copepods and amphipods decreased in importance with LS. Dietary breadth increased markedly for adults. A positive relationship was found between LS and prey size. In each season the maximum diel feeding activity occurred at 0800 and 2400 hours, indicating that there was crepuscular and nocturnal feeding by small yellow croaker.

Trophic Cascades and Historic Aspen Recruitment in the Gallatin Elk Winter Range of Southwest Montana

The extirpation of the gray wolf (Canis lupus) by 1930 in Yellowstone National Park (YNP) provided us with an opportunity to study historic aspen (Populus tremuloides ) recruitment with and without a top carnivore predator present. Herbivory, climate trends, fire records, and current conifer invasion were also examined within the context of aspen recruitment. We obtained tree cores and diameter at breast height measurements to create an aspen age-diameter relationship which we used to approximate aspen origination dates. One elk (Cervus elaphus) exclosure, erected in 1945 within the same elk winter range, was compared to the rest of the winter range. Consistent recruitment inside the exclosure began in the 1940s and has continued into the present. Outside of the exclosure, aspen recruitment began decreasing in the 1930s and ceased in the 1950s. Within the scope of the study, we found little correlative evidence between aspen decline and climate trends, conifer invasion, or fire suppression. The results are suggestive of a trophic cascade between aspen recruitment, and historical elk browsing activities as affected by the absence or presence of wolf predation.

Predation risk and the functional response of elk–aspen herbivory

Hypotheses for trembling aspen ( Populus tremuloides) decline in Rocky Mountain national parks include long-term high herbivory by elk ( Cervus elaphus), decreased disturbance, climate change, and long-term low elk herbivory. Predation theory, as applied to herbivores, was used to describe alternative functional responses predicted by each hypothesis. Further, we postulated that elk behavioral patterns resulting from predation risk could also influence aspen herbivory. We tested predictions by sampling aspen density and browsing conditions in spatially separate watersheds in the Canadian Rockies, with three areas in each of three elk density levels (<2, 2–4, >4 elk/km 2), and in each of four tree cover classes: recently disturbed (<25 years ago), and low, moderate, and high. Plot elk use was indexed with pellet group counts classed by habitat patch type, aspen condition (open or thicket), and different distances from trails or park boundaries used by predators, hunters, or park visitors. The herbivory rate on aspen saplings (>1 m height and <1 cm diameter at breast height, DBH) fitted the predictions of a Type 2 functional response (e.g. increased rate of herbivory with decreased sapling density). The Type 2 response appeared to result from low elk use in dense aspen thickets when predation risk is high. An interaction effect in the tree cover×elk density factorial analysis indicated that recent disturbances (<25 years) have incrementally increased the number of aspen saplings, but did not cause a major shift to an abundant sapling state in areas of high and moderate elk density. These results best supported the predictions of the low elk herbivory hypothesis. Anthropogenic burning combined with human and carnivore predation effects on elk (behavioral and numeric) appeared to be important in aspen’s long-term persistence, and its recent decline.

HABITAT-RELATED DIFFERENCES IN RABBIT (ORYCTOLAGUS CUNICULUS) ABUNDANCE, DISTRIBUTION, AND ACTIVITY

The European rabbit (Oryctolagus cuniculus) is a key prey species in Mediterranean ecosystems and is ecologically plastic. However, ecological responses of rabbits to different habitats are poorly understood. We present data on abundance, distribution, activity, and survival in 3 neighboring habitats in southwestern Spain differing in refuge and forage availability. Scrubland presents dense cover but low forage abundance; grassland offers little protective vegetation but high food availability; the ecotone provides intermediate levels of both resources. Rabbits reached the highest abundance in ecotone, whereas low food and refuge availability seemed to limit their abundance in scrubland and grassland, respectively. In scrubland, rabbits were dispersed among the cover. In grassland, rabbits were linked to aggregated burrows. In ecotone, rabbits dug burrows in the bordering bushes that abutted grassy feeding pasture. Predation by raptors was low in scrubland, and mortality due to mammalian carnivores was higher in spite of more diurnal rabbit activity. Carnivore predation also caused higher mortality in grassland, where rabbits were more nocturnal. In ecotone, the effect of both mammalian carnivores and raptors on rabbits was similar. Mortality by disease seemed to be linked to level of rabbit aggregation.

Glycerotoxin from Glycera convoluta stimulates neurosecretion by up-regulating N-type Ca2+ channel activity.

We report here the purification of glycerotoxin from the venom of Glycera convoluta, a novel 320 kDa protein capable of reversibly stimulating spontaneous and evoked neurotransmitter release at the frog neuromuscular junction. However, glycerotoxin is ineffective at the murine neuromuscular junction, which displays a different subtype of voltage- dependent Ca(2+) channels. By sequential and selective inhibition of various types of Ca(2+) channels, we found that glycerotoxin was acting via Ca(v)2.2 (N-type). In neuroendocrine cells, it elicits a robust, albeit transient, influx of Ca(2+) sensitive to the Ca(v)2.2 blockers omega-conotoxin GVIA and MVIIA. Moreover, glycerotoxin triggers a Ca(2+) transient in human embryonic kidney (HEK) cells over-expressing Ca(v)2.2 but not Ca(v)2.1 (P/Q-type). Whole-cell patch-clamp analysis of Ca(v)2.2 expressing HEK cells revealed an up-regulation of Ca(2+) currents due to a leftward shift of the activation peak upon glycerotoxin addition. A direct interaction between Ca(v)2.2 and this neurotoxin was revealed by co-immunoprecipitation experiments. Therefore, glycerotoxin is a unique addition to the arsenal of tools available to unravel the mechanism controlling Ca(2+)-regulated exocytosis via the specific activation of Ca(v)2.2.