Physiological Responses of Mesodinium major to Irradiance,Prey Concentration and Prey Starvation

Ciliates within the Mesodinium rubrum/Mesodinium major species complex harbor chloroplasts and other cell organelles from specific cryptophyte species. Mesodinium major was recently described, and new studies indicate that blooms of M. major are just as common as blooms of M. rubrum. Despite this, the physiology of M. major has never been studied and compared to M. rubrum. In this study, growth, food uptake, chlorophyll a and photosynthesis were measured at six different irradiances, when fed the cryptophyte, Teleaulax amphioxeia. The results show that the light compensation point for growth of M. major was significantly higher than for M. rubrum. Inorganic carbon uptake via photosynthesis contributed by far most of total carbon uptake at most irradiances, similar to M. rubrum. Mesodinium major cells contain ~four times as many chloroplast as M. rubrum leading to up to ~four times higher rates of photosynthesis. The responses of M. major to prey starvation and refeeding were also studied. Mesodinium major was well adapted to prey starvation, and 51 d without prey did not lead to mortality. Mesodinium major quickly recovered from prey starvation when refed, due to high ingestion rates of > 150 prey/predator/d.     

Reproductive Responses of Northern Goshawks to Variable Prey Populations

ABSTRACT Developing comprehensive conservation strategies requires knowledge of factors influencing population growth and persistence. Although variable prey resources are often associated with fluctuations in raptor demographic parameters, the mechanisms of food limitation are poorly understood, especially for a generalist predator like the northern goshawk (Accipiter gentilis). To determine the reproductive responses of goshawks to variable prey populations, we evaluated 823 goshawk breeding opportunities on the Kaibab Plateau, Arizona, USA, during 1994–2002. Concurrently, density was estimated for 4 prey species (2 avian, 2 mammalian). We explored the relationship between goshawk reproduction and prey density at one temporal scale (year) and 2 spatial scales (study area, forest type). Prey density for all 4 species combined accounted for 89% of the variation in goshawk reproduction within the entire study area (P < 0.001), 74% in mixed conifer forest (P = 0.003) and 85% in ponderosa pine (Pinus ponderosa) forest (P < 0.001). We found that an incremental increase in prey density resulted in a greater increase in goshawk reproduction in ponderosa pine forest than in mixed conifer forest, suggesting that the denser structural conditions of mixed conifer forest may have reduced prey availability. Red squirrel (Tamiasciurus hudsonicus) density explained more annual variation in goshawk reproduction within the study area (r² = 0.87, P < 0.001), mixed conifer forest (r² = 0.80, P = 0.001), and ponderosa pine forest (r² = 0.85, P < 0.001) than did any other individual species. Although certain prey species were more strongly correlated with fluctuations in goshawk reproduction than were others, the high model selection uncertainty and the strong relationship between total prey density and number of goshawk fledglings produced indicated that alternate prey species were readily substituted for one another. Therefore, conservation strategies concerned with the status of goshawk populations should incorporate forest management practices that increase the abundance, diversity, and availability of prey resources.     

Behavioral Responses of the Social Wasp Polistes myersi to Prey Infected with Fungi Used in Biological Control

Metarhizium anisopliae and Beauveria bassiana are commonly used entomopathogenic fungi, but their non-target effects over generalist predatory insects, which can contribute to pest control, are not well known. We studied the capacity of the social wasp Polistes myersi to detect the pathogens in either a powdered form or in Galleria mellonella larvae infected with either of the two pathogens offered as prey. The effects of these treatments were compared considering wasp behaviors such as prey preference, frequency, duration and transitions of both hunting and grooming behaviors. Additionally, the effects of each entomopathogenic fungus on the wasp’s mortality were measured. Wasps seem not to detect the pathogens in powdered form but preferred healthy over infected larvae. Seventeen behavioral units for hunting and 34 for grooming were recognized. There were no differences in grooming frequency but there were significant differences on grooming duration, hunting behaviors and the patterns of transitions. Exposure of wasp colonies to either B. bassiana or M. anisopliae had no detectable impact on the mortality of adults, but mortality of larvae increased. For the first time, this study documented behavioral changes that indicated the capacity of social wasps to detect pathogens before physical contact and the display of hygienic strategies once contact occurs. The study also suggested a potential non-target effect of these entomopathogenic fungi on a generalist predator.

     

Prey Responses to Predator Chemical Cues: Disentangling the Importance of the Number and Biomass of Prey Consumed

To effectively balance investment in predator defenses versus other traits, organisms must accurately assess predation risk. Chemical cues caused by predation events are indicators of risk for prey in a wide variety of systems, but the relationship between how prey perceive risk in relation to the amount of prey consumed by predators is poorly understood. While per capita predation rate is often used as the metric of relative risk, studies aimed at quantifying predator-induced defenses commonly control biomass of prey consumed as the metric of risk. However, biomass consumed can change by altering either the number or size of prey consumed. In this study we determine whether phenotypic plasticity to predator chemical cues depends upon prey biomass consumed, prey number consumed, or both. We examine the growth response of red-eyed treefrog tadpoles (Agalychnis callidryas) to cues from a larval dragonfly (Anax amazili). Biomass consumed was manipulated by either increasing the number of prey while holding individual prey size constant, or by holding the number of prey constant and varying individual prey size. We address two questions. (i) Do prey reduce growth rate in response to chemical cues in a dose dependent manner? (ii) Does the magnitude of the response depend on whether prey consumption increases via number or size of prey? We find that the phenotypic response of prey is an asymptotic function of prey biomass consumed. However, the asymptotic response is higher when more prey are consumed. Our findings have important implications for evaluating past studies and how future experiments should be designed. A stronger response to predation cues generated by more individual prey deaths is consistent with models that predict prey sensitivity to per capita risk, providing a more direct link between empirical and theoretical studies which are often focused on changes in population sizes not individual biomass.     

Distribution Patterns of Birds and Insect Prey in a Tropical Riparian Forest

Spatial subsidies of energy and nutrients can influence the distribution of consumers in riparian habitats. This study compared the abundance and composition of bird assemblages and the availability of volant insect prey within the riparian zone (≤ 30 m from the stream) and further inland (100–250 m away) within a secondary forest in monsoonal Hong Kong. Replicated point-counts of birds and insect light trapping were conducted in each zone during the wet and dry season of 2006–2007. The biomass of adult aquatic insects in the riparian zone was nine to 12 times higher than inland during both seasons, however, total insect biomass (aquatic plus terrestrial insects) in the riparian zone was only 49 percent (wet season) and 18 percent (dry season) greater. More birds (both numbers of individuals and species) were recorded in the riparian zone, and this difference was particularly conspicuous during the wet season. Most of the wet-season difference was due to the greater number of insectivorous birds in the riparian zone (123% greater than inland), and may have reflected the relative availability of adult aquatic insects. These findings confirm the importance of riparian zones as feeding habitats for forest birds, and have implications for conservation planning and setting the boundaries of protected areas.     

Responses of Plants and Arthropods to Burning and Disking of Riparian Habitats

Abstract: Alteration of Iowa, USA, landscapes for agricultural production has resulted in a loss of >99% of the original prairie and >95% of native wetlands. This conversion has included riparian areas, which, as interfaces between terrestrial and aquatic ecosystems, are important to many wildlife species. Farm Bill programs have resulted in the reestablishment of millions of hectares of grasslands and wetlands nationwide, including >100,000 ha in riparian areas of the Midwest. We assessed plant and arthropod responses to burning and disking of riparian grasslands in east-central Iowa in 2001 and 2002. Burning altered the plant community by removing litter and standing dead vegetation and had negative effects on several arthropod taxa, including Hemiptera and Lepidoptera. However, we observed no differences in vegetation or arthropods between burned and unburned fields during the second year postburning (P > 0.05). Disking decreased the cover of grasses, litter, and standing dead vegetation and increased plant species richness and the cover of forbs and bare ground (P < 0.05). Arthropod abundance and dry biomass were greater on disked than undisked portions of fields (P < 0.05). Increases in the abundance and biomass of arthropods associated with changes in vegetation structure and composition likely improved habitat quality for a number of breeding bird species. Both burning and disking appear to be effective management options for maintaining or enhancing riparian grasslands for wildlife.     

Prey Responses to Predator's Sounds: A Review and Empirical Study

Many animals assess their risk of predation by listening to and evaluating predators' vocalizations. We reviewed the literature to draw generalizations about predator discrimination abilities, the retention of these abilities over evolutionary time, and the potential underlying proximate mechanisms responsible for discrimination. Broadly, we found that some prey possess an ability to respond to a predator after having been evolutionarily isolated from a specific predator (i.e., predators are allopatric) and that some prey are predisposed to respond to certain types of predators that they coevolved with but without having ecological experience. However, these types of studies are lacking, and relatively, few studies have examined predator discrimination abilities in ungulates. To begin addressing these knowledge gaps, we performed field experiments on Mule deer (Odocoileus hemionus) in which we investigated the ability of deer to discriminate among familiar predators [coyotes (Canis latrans) and mountain lions (Puma concolor)] and an evolutionary relevant predator with which deer have had no recent exposure [locally extinct wolves (Canis lupus)]. We found that Mule deer respond to and discriminate among predators based on predator vocalizations and have retained an ability to respond to wolves that have been extinct from the study area since the early 20th century. Previous playback studies have shown that responses vary among human‐habituated and non‐habituated populations and differ according to human proximity. Deer greater than 0.5 km from human residences allocated more time to heightened responses both before and after stimulus playback. Our findings may help predict how prey–predator interactions may change as a result of the recovering wolf population with a basis in ecological and evolutionary experience in predator discrimination and desensitization.     

River Food Web Response to Large-Scale Riparian Zone Manipulations

Conservation programs often focus on select species, leading to management plans based on the autecology of the focal species, but multiple ecosystem components can be affected both by the environmental factors impacting, and the management targeting, focal species. These broader effects can have indirect impacts on target species through the web of interactions within ecosystems. For example, human activity can strongly alter riparian vegetation, potentially impacting both economically-important salmonids and their associated river food web. In an Olympic Peninsula river, Washington state, USA, replicated large-scale riparian vegetation manipulations implemented with the long-term (>40 yr) goal of improving salmon habitat did not affect water temperature, nutrient limitation or habitat characteristics, but reduced canopy cover, causing reduced energy input via leaf litter, increased incident solar radiation (UV and PAR) and increased algal production compared to controls. In response, benthic algae, most insect taxa, and juvenile salmonids increased in manipulated areas. Stable isotope analysis revealed a predominant contribution of algal-derived energy to salmonid diets in manipulated reaches. The experiment demonstrates that riparian management targeting salmonids strongly affects river food webs via changes in the energy base, illustrates how species-based management strategies can have unanticipated indirect effects on the target species via the associated food web, and supports ecosystem-based management approaches for restoring depleted salmonid stocks.     

Developmental Instability and Sexual Selection in Stag Beetles from Chernobyl and a Control Area

Radioactivity may have both phenotypic and genetic effects through its disruption of physiological processes and mutations. I studied the size and asymmetry of secondary sexual and ordinary morphological characters of stag beetles ( Lucanus cervus ) in two areas in the Ukraine: near Chernobyl, where levels of radiation are high, and in a control area with low background radiation. Developmental instability of morphological characters was estimated from the degree of fluctuating asymmetry using the restricted maximum likelihood parameter estimation (REML) method to partition measurement error from asymmetry. The degree of asymmetry estimated from unsigned differences in size of right and left secondary sexual character was similar to estimates based on the REML method. Beetles from the contaminated area had a significantly elevated level of fluctuating asymmetry in the secondary sexual character compared with animals from the control area. Male stag beetles found with a female had significantly lower asymmetry than males found alone. While mated males did not differ in asymmetry between areas, unmated males from Chernobyl were much more asymmetric than unmated males from the control area. These findings provide evidence for radiation disrupting developmental homeostasis, and thereby affecting the mating status of free-living beetles.     

Riparian Beetles,a Unique,but Vulnerable Element in the Fauna of Fennoscandia

A survey of the distribution and ecology of riparian beetles in Fennoscandia and adjacent countries is presented and the conservation value of, and threats to, the element are discussed. Contrary to most other taxa or ecological groups, the number of riparian species increases from south to north in Scandinavia. The inner parts of the counties of Sør-Trøndelag (STI) in Central Norway and Troms (TRI) in North Norway have the largest total number of riparian species, the largest number of vulnerable (red-listed) riparian species, and the largest importance index, rarity factor and algorithmic ranking in Fennoscandia. These provinces may be regarded as hot spots for riparian species in northwestern Europe and therefore have high conservation value. In addition to river regulation, river banks are exposed to a number of impacts such as removal of sediment and fluvial woodlands, wear and tear, construction of flood-prevention walls, canalization and various other developments (road building, industrial activity, etc.). These impacts seem to be more severe in Norway than in Northern Sweden and Finland. Due to human impacts, riparian carabid beetles have become extinct in parts of their former range in Scandinavia. The possibility of re-invasion of species after restoration is discussed.     

Prey Selection by the Lady Beetle Harmonia axyridis: The Influence of Prey Mobility and Prey Species

The influence of prey mobility and species on prey selection by the coccinellid Harmonia axyridis Pallas was determined under laboratory conditions for two prey species, Hyaliodes vitripennis (Say) and Tetranychus urticae Koch. Prey selection was influenced by prey mobility. In the presence of active prey, the coccinellid selected T. urticae while in presence of immobilized prey, H. vitripennis was preferred. Harmonia axyridis searching time was longer in the presence of active H. vitripennis than in the presence of active T. urticae. Moreover, the coccinellid capture rate was lower for active H. vitripennis caused by effective defensive mechanisms. Prey suitability was affected by prey mobility and species. Immobilized H. vitripennis were the most profitable prey, i.e. induced a shorter developmental time and no mortality. However, active H. vitripennis were not a suitable food source for H. axyridis. Our results suggested that three factors are involved in prey selection by H. axyridis: (i) prey mobility; (ii) prey defensive mechanisms; and (iii) prey species.     

Responses to Riparian Restoration in the Spring Creek Watershed, Central Pennsylvania

Riparian treatments, consisting of 3‐ to 4‐m buffer strips, stream bank stabilization, and rock‐lined stream crossings, were installed in two streams with livestock grazing to reduce sediment loading and stream bank erosion. Cedar Run and Slab Cabin Run, the treatment streams, and Spring Creek, an adjacent reference stream without riparian grazing, were monitored prior to (1991–1992) and 3–5 years after (2001–2003) riparian buffer installation to assess channel morphology, stream substrate composition, suspended sediments, and macroinvertebrate communities. Few changes were found in channel widths and depths, but channel‐structuring flow events were rare in the drought period after restoration. Stream bank vegetation increased from 50% or less to 100% in nearly all formerly grazed riparian buffers. The proportion of fine sediments in stream substrates decreased in Cedar Run but not in Slab Cabin Run. After riparian treatments, suspended sediments during base flow and storm flow decreased 47–87% in both streams. Macroinvertebrate diversity did not improve after restoration in either treated stream. Relative to Spring Creek, macroinvertebrate densities increased in both treated streams by the end of the posttreatment sampling period. Despite drought conditions that may have altered physical and biological effects of riparian treatments, goals of the riparian restoration to minimize erosion and sedimentation were met. A relatively narrow grass buffer along 2.4 km of each stream was effective in improving water quality, stream substrates, and some biological metrics.     

Ocean Acidification Disrupts Prey Responses to Predator Cues but Not Net Prey Shell Growth in Concholepas concholepas (loco)

Background

Most research on Ocean Acidification (OA) has largely focused on the process of calcification and the physiological trade-offs employed by calcifying organisms to support the building of calcium carbonate structures. However, there is growing evidence that OA can also impact upon other key biological processes such as survival, growth and behaviour. On wave-swept rocky shores the ability of gastropods to self-right after dislodgement, and rapidly return to normal orientation, reduces the risk of predation.

Methodology/Principal Findings

The impacts of OA on this self-righting behaviour and other important parameters such as growth, survival, shell dissolution and shell deposition in Concholepas concholepas (loco) were investigated under contrasting pCO₂ levels. Although no impacts of OA on either growth or net shell calcification were found, the results did show that OA can significantly affect self-righting behaviour during the early ontogeny of this species with significantly faster righting times recorded for individuals of C. concholepas reared under increased average pCO₂ concentrations (± SE) (716±12 and 1036±14 µatm CO₂) compared to those reared at concentrations equivalent to those presently found in the surface ocean (388±8 µatm CO₂). When loco were also exposed to the predatory crab Acanthocyclus hassleri, righting times were again increased by exposure to elevated CO₂, although self-righting times were generally twice as fast as those observed in the absence of the crab.

Conclusions and Significance

These results suggest that self-righting in the early ontogeny of C. concholepas will be positively affected by pCO₂ levels expected by the end of the 21st century and beginning of the next one. However, as the rate of self-righting is an adaptive trait evolved to reduce lethal predatory attacks, our result also suggest that OA may disrupt prey responses to predators in nature.     

Stream Resource Gradients Drive Consumption Rates of Supplemental Prey in the Adjacent Riparian Zone

Decades of research have revealed the crucial roles of cross-system energy flows (spatial subsidies) in mediating trophic interactions in recipient systems. Food web theory predicts that the responses of subsidized consumers are a key to understanding the net impacts of spatial subsidies on in situ prey/resources of recipient systems. However, less is known about the factors triggering the cascading biotic interactions across coupled ecosystems. Here, we quantify how riverine productivity (donor system) mediates terrestrial food web interactions through spatial subsidies to simplified gravel bar communities. Our comparative study in Japan indicated that higher algal biomass in aquatic systems led to increased supplies of emerging aquatic insects, which were associated with greater densities of terrestrial consumers (Carabid beetles) and enhanced consumption rates of supplemental in situ prey on gravel bars. Our results highlight the potential of donor productivity to drive cascading biotic interactions across coupled ecosystems. Because cross-system energy flows should originate, at least in part, from primary producers of donor systems, our fundamental finding may form the basis of future studies exploring the driving factors of cross-system trophic interactions.     

Responses of the Toad Bufo bufo (L.) to Stationary Prey Stimuli1

In the present work toads (Bufo bufo) are shown to respond with prey catching to stationary dummies without previous or accompanying visual or olfactory stimulation. The subjects very rarely showed jerky head movements which, therefore, cannot be necessary for perception of stationary objects. Size preference with respect to stationary stimuli is about the same as in experiments with moving stimuli. However, differences exist between the effects of stationary and moving stimuli with respect to shape and orientation. If a square measuring 10 times 10 mm and a rectangle measuring 5 times 20 mm, oriented either horizontally or vertically, are presented within the frontal-vertical plane, the square is preferred to the rectangles, and among these the horizontal rectangle is to the vertical one. This latter preference is due to the negative effect of the vertical extension: If the vertical rectangle is reduced in length, it becomes more effective as compared to the horizontal rectangle. In the horizontal (X-Z) plane the square and the rectangle oriented parallel to the Z-axis are equally superior to the bar oriented parallel to the X-axis. At presentation of a pair of stimuli in both planes, the one in the frontal-vertical plane is always preferred to that in the horizontal plane. Correspondences and differences of these results to those from experiments with moving prey dummies are discussed.     

Prey Capture Behaviour in the Social Spider Anelosimus eximius (Araneae: Theridiidae): Responses to Prey Size and Type

Some species of web building spiders use different capture tactics for different prey types. The main factors influencing the attack behaviour are the ability of the insect to escape, the risks of injury to the spiders and prey size. This study evaluated the effects of size and prey type on prey capture behaviour of the social spider Anelosimus eximius as influenced by the number of spiders attracted by prey movements that did not bite until the immobilization (bystanders) and the number of spiders that contributed to prey immobilization (catchers). We carried out a two‐factor (prey size and type) experiment offering prey belonging to four orders: Diptera, Lepidoptera, Hymenoptera and Orthoptera, in a size gradient within each prey type. Both factors influenced the number of spiders recruited as bystanders, but only prey body size influenced the number of catchers in the subduing process. The possible advantages of the presence of bystanders around the interception site are discussed.     

Winter Prey Selection of Canada Lynx in Northwestern Montana

ABSTRACT The roles that diet and prey abundance play in habitat selection of Canada lynx (Lynx canadensis) in the contiguous United States is poorly understood. From 1998–2002, we back-tracked radiocollared lynx (6 F, 9 M) for a distance of 582 km and we located 86 kills in northwestern Montana, USA. Lynx preyed on 7 species that included blue grouse (Dendragapus obscurus), spruce grouse (Canachites canadensis), northern flying squirrel (Glaucomys sabrinus), red squirrel (Tamiasciurus hudsonicus), snowshoe hare (Lepus americanus), least weasel (Mustela nivalis), and white-tailed deer (Odocoileus virginianus). Snowshoe hares (69 kills) accounted for 96% (4-yr average, range = 94–99%) of prey biomass during the sample period. Red squirrels were the second-most-common prey (11 kills), but they only provided 2% biomass of the winter diet. Red squirrels contributed little to the lynx diet despite low hare densities. A logistic regression model of snowshoe hare, red squirrel, and grouse abundance, as indexed by the number of track crossings of use and available lynx back-tracks, was a significant (Wald statistic = 19.03, df = 3, P < 0.001) predictor of habitat use. As we expected, lynx (P < 0.001) selected use-areas with higher snowshoe hare abundance compared to random expectation. However, the red squirrel index had a weak (P = 0.087) negative relationship to lynx use, and grouse was nonsignificant (P = 0.432). Our results indicate that lynx in western Montana prey almost exclusively on snowshoe hares during the winter with little use of alternative prey. Thus, reductions in horizontal cover for hares would degrade lynx habitat.