Predicting Predatory Outcomes in the Context of Carryover Effects: Interactions between Juvenile Frogs and Spider Predators

As representatives of organisms with complex life histories, frogs provide an ideal system to study predator‐induced carryover effects: how the risk of predation in one life stage can impact predator–prey interactions in a later stage. Invertebrate predation on frogs has been widely reported, although studies of the behavioral mechanisms underlying their interactions in the terrestrial stage have been lacking. We made detailed observations of interactions between a wolf spider (Tigrosa helluo) and Blanchard's cricket frog (Acris blanchardi) to determine factors that predict capture success and to evaluate potential carryover effects from aquatic predation risk. Juvenile frogs, reared with or without dragonfly predator cues, were placed in an arena with or without spider cues and allowed to interact with a spider. Spiders captured frogs, and an interaction between frog size and activity predicted frog survival. We found no evidence that either aquatic or terrestrial cues altered frog behavior or survival. By preying upon a demographically important life stage, spiders may contribute to population dynamics in frogs.     

Effects of Seed Predators of Different Body Size on Seed Mortality in Bornean Logged Forest

Background

The Janzen-Connell hypothesis proposes that seed and seedling enemies play a major role in maintaining high levels of tree diversity in tropical forests. However, human disturbance may alter guilds of seed predators including their body size distribution. These changes have the potential to affect seedling survival in logged forest and may alter forest composition and diversity.

Methodology/Principal Findings

We manipulated seed density in plots beneath con- and heterospecific adult trees within a logged forest and excluded vertebrate predators of different body sizes using cages. We show that small and large-bodied predators differed in their effect on con- and heterospecific seedling mortality. In combination small and large-bodied predators dramatically decreased both con- and heterospecific seedling survival. In contrast, when larger-bodied predators were excluded small-bodied predators reduced conspecific seed survival leaving seeds coming from the distant tree of a different species.

Conclusions/Significance

Our results suggest that seed survival is affected differently by vertebrate predators according to their body size. Therefore, changes in the body size structure of the seed predator community in logged forests may change patterns of seed mortality and potentially affect recruitment and community composition.     

Stage-Specific Behavioral Responses of Ageneotettix deorum (Orthoptera: Acrididae) in the Presence of Lycosid Spider Predators

Grasshoppers must gather food while avoiding size-selective predation from other arthropods, especially spiders, potentially leading to a trade-off between foraging and defensive behaviors. This trade-off becomes less intense as prey grow larger and are less susceptible to arthropod predation. Activity budgets were constructed for three nymphal (third- to fifth- instar) and adult life cycle stages of Ageneotettix deorum, a common rangeland grasshopper, for three conditions of predation risk by lycosid spiders (spider absence, spider presence, and presence of a nonlethal, chelicerae-modified spider). In third and fourth instars, exposure to predators resulted in reduced feeding activity, increased time spent in antipredator and defensive behaviors, and reduced general activity compared to individuals not exposed to spiders. No significant shifts in behaviors were observed for fifth-instar nymphs and adult A. deorum in response to spider presence. Activity levels in functional spiders and chelicerae-modified spiders were statistically indistinguishable.     

An Advantage of Large Seed Size: Tolerating Rather than Succumbing to Seed Predators1

Although large seeds might be more attractive and apparent to seed predators, large seed size could enable tolerance of seed predators. If seeds are large enough to sustain damage that would kill smaller seeds yet still produce viable seedlings, investment above the minimum by the maternal plant could be advantageous. I tested this hypothesis by removing 0–80 percent of the cotyledons of four large-seeded (4–180 g) tree species from Papua New Guinea and monitoring germination and seedling growth for eight months. All species showed little negative effect on seedling size with up to 50 percent removal of cotyledons and the larger species showed a less serious effect on growth than smaller-seeded species above 50 percent removal. Large-seeded species clearly have more than the minimum-required cotyledonary reserves. Observations of viable seedlings with heavily damaged cotyledons suggest that these species withstand attack by rodents and beetles by virtue of their large size.     

Modelling the Effects of Prey Size and Distribution on Prey Capture Rates of Two Sympatric Marine Predators

Understanding how prey capture rates are influenced by feeding ecology and environmental conditions is fundamental to assessing anthropogenic impacts on marine higher predators. We compared how prey capture rates varied in relation to prey size, prey patch distribution and prey density for two species of alcid, common guillemot (Uria aalge) and razorbill (Alca torda) during the chick-rearing period. We developed a Monte Carlo approach parameterised with foraging behaviour from bird-borne data loggers, observations of prey fed to chicks, and adult diet from water-offloading, to construct a bio-energetics model. Our primary goal was to estimate prey capture rates, and a secondary aim was to test responses to a set of biologically plausible environmental scenarios. Estimated prey capture rates were 1.5±0.8 items per dive (0.8±0.4 and 1.1±0.6 items per minute foraging and underwater, respectively) for guillemots and 3.7±2.4 items per dive (4.9±3.1 and 7.3±4.0 items per minute foraging and underwater, respectively) for razorbills. Based on species'' ecology, diet and flight costs, we predicted that razorbills would be more sensitive to decreases in 0-group sandeel (Ammodytes marinus) length (prediction 1), but guillemots would be more sensitive to prey patches that were more widely spaced (prediction 2), and lower in prey density (prediction 3). Estimated prey capture rates increased non-linearly as 0-group sandeel length declined, with the slope being steeper in razorbills, supporting prediction 1. When prey patches were more dispersed, estimated daily energy expenditure increased by a factor of 3.0 for guillemots and 2.3 for razorbills, suggesting guillemots were more sensitive to patchier prey, supporting prediction 2. However, both species responded similarly to reduced prey density (guillemot expenditure increased by 1.7; razorbill by 1.6), thus not supporting prediction 3. This bio-energetics approach complements other foraging models in predicting likely impacts of environmental change on marine higher predators dependent on species-specific foraging ecologies.     

Understanding Statin Non-Adherence: Knowing Which Perceptions and Experiences Matter to Different Patients

Background

Non-adherence to statins is substantial and is associated with numerous perceptions and experiences. However, time limits in clinical practice constrain in depth explorations of these perceptions and experiences.

Objectives

To propose and examine a strategy aimed at an efficient assessment of a wide array of perceptions and experiences regarding the efficacy, side effects, and practical problems of statins. Furthermore, to assess associations between this wide array of experiences and perceptions and non-adherence and to examine whether patients'' ''perceived self-efficacy'' moderated these associations.

Methods

Patients were recruited through community pharmacies. A wide array of specific patient perceptions and experiences was efficiently assessed using the electronic Tailored Medicine Inventory that allows people to skip irrelevant questions. Adherence was measured through self-report and pharmacy refill data.

Results

Of the two-hundred twenty-nine patients who participated (mean age 63.9, standard deviation 10.2), 40%-70% doubted the necessity of or lacked knowledge about the efficacy of statins, 20%-35% of the patients were worried about joint and muscle side effects or had experienced these, and 23% had encountered practical problems regarding information about statins, intake of tablets, the package, or the blister. Experiencing more practical problems was associated with increased unintentional non-adherence (Odds ratio 1.54, 95%CI:1.13–2.10, P < 0.01), whereas worrying about side effects was associated with increased intentional non-adherence (Odds ratio 1.90, 95%CI:1.17–3.08, P < 0.01). Higher ''perceived self-efficacy'' did not moderate these associations.

Conclusions

Insight into patients'' specific barriers with regard to appropriate statin use may reveal personal reasons for being non-adherent. The Tailored Medicine Inventory is a promising tool to devise individualized intervention strategies aimed at improving adherence by the clinician-patient alliance.     

Measuring Spider Richness: Effects of Different Sampling Methods and Spatial and Temporal Scales

Assessing the richness of invertebrate taxa to aid conservation and management requires a better understanding of the potential sources of error. Patterns of richness for heathland spiders at the species and family levels were compared across three sampling methods, four spatial scales, and monthly intervals (for 16 months). A total of 33 families and 130 species was collected: pitfall traps collected 94% of species, sweep net, 25%, and visual search, 41%. The sampling methods produced variable results. Pitfall trap and sweep net techniques identified significant, yet contrasting spatial differences in the number of families and species at one spatial scale. Pitfall trap data reflected strong temporal variation that influenced spatial patterns in richness (across one spatial scale for families and two for species). The use of broader temporal scales introduced a potential failure to detect significant differences in the richness of ground active spiders, and this risk varied spatially. The sweep net is not recommended for this habitat, although a method that targets the foliage is required for a more complete faunal assessment. Visual searches detected no significant patterns in richness, yet given its potential and increasing use for rapid biodiversity surveys, ways to improve sampling efficiency are suggested.     

Reproductive Asynchrony and the Divergence of Hawaiian Crickets

Asynchrony in reproductive behavior may contribute to reproductive isolation among sympatric species. While the 38 cryptic species of the genus Laupala are primarily distinguished on the basis of variation in pulse rate of male calling songs, additional phenotypes, such as asynchrony in reproductive behavior, may contribute to reproductive isolation in this genus. Here we document similarities and differences in the diel timing of two reproductive behaviors, male singing activity and insemination events. Asynchrony in the diel timing of male singing behavior was observed between two sympatric species, Laupala cerasina and Laupala paranigra, in the field. An interpopulational comparison within L. cerasina did not reveal variation in diel behavior patterns of singing between two locations. Asynchrony in the timing of copulation and sperm transfer between L. cerasina and L. paranigra was documented in the laboratory. The observed pattern of asynchrony in both the field and laboratory could have arisen in a number of ways. One possibility is that species diverged in sympatry because of interspecific interactions, producing a pattern of reproductive character displacement. Alternatively, the observed asynchrony in reproductive behavior may have played a role in the process of community assembly within this recently diverged cricket genus. The presence of interspecific variation and the absence of intraspecific variation revealed by our study do not support a pattern of reproductive character displacement for diel reproductive behavior, suggesting that the differences seen between species were not caused by recent species interactions.     

Interactions Between Two Neotropical Phytoseiid Predators on Cassava Plants and Consequences for Biological Control of a Shared Spider Mite Prey: a Screenhouse Evaluation

The issue of introducing single or multiple natural enemy species for classical biological control has been an area of intense inquiry by ecologists and biological control practitioners. This is particularly relevant to classical biological control of cassava green mite Mononychellus tanajoa (Bondar) (Tetranychidae) in Africa, as this pest mite is shared by several natural enemies in the Neotropics (its area of origin), two of which have been introduced and established widely in Africa. We conducted two screenhouse experiments using the two neotropical phytoseiid predatory mites, Typhlodromalus aripo DeLeon and Typhlodromalus manihoti Moraes, to determine the effects of single and two-predator species on population dynamics of the two predators and on suppression of M. tanajoa populations. The two predators are thought to be complementary in their impact on their shared prey M. tanajoa, due to similarities in their preference for this prey and to differences in their spatial distribution and foraging activities on cassava. The two predator species were released alone or together at low and at high initial densities of M. tanajoa. In all cases, predator releases resulted in significant suppression of M. tanajoa, but the degree of suppression did not differ among single and two-species releases with one exception: at high initial density of M. tanajoa, releases of T. aripo alone had less impact than that of either T. manihoti alone or of the two species together. Typhlodromalus aripo also appeared to be inferior as a competitor of T. manihoti: at low initial density of M. tanajoa, the proportion of T. aripo in the two-predator release treatments gradually declined and was strikingly lower than in the single species release, probably due to intraguild predation on its larvae by T. manihoti. However, T. aripo persisted longer than T. manihoti after elimination of M. tanajoa. On the basis of this study under semi-natural conditions, it appears that either species is sufficient for controlling M. tanajoa populations, with T. manihoti being more efficient at high initial prey densities and T. aripo at low initial prey densities. At high prey density, T. manihoti increased to large numbers and outcompeted T. aripo. Relevance of these findings to larger spatial scale and under natural conditions is discussed.     

蜘蛛神经节的解剖与神经细胞的分离培养

报道了虎纹捕鸟蛛(Ornithoctonus huwena)食道下神经节的解剖以及神经细胞的分离培养方法。为开展蜘蛛神经生物学实验方法的研究,创立了一种蜘蛛神经细胞解剖方法——去胸甲解剖法。神经节细胞培养基为NaCl2 23 mmol/L;KCl6.8 mmol/L;CaCl28 mmol/L;MgCl2 5.1 mmol/L;Sucrose 5 mmol/L;Hepes 10 mmol/L;谷氨酰胺1mmol/L;青霉素200IU/ml;链霉素200μg/ml;小牛血清20%;pH7.4。在温度(27±2)℃的培养箱中培养2~4h。实验结果表明与传统方法相比较,去胸甲解剖法具有取材简便、准确、快捷和高效的特点。改进的培养基非常适合蜘蛛离体神经细胞的培养。培养的细胞状态好、数量多,细胞体呈椭圆形,细胞形状近似汤勺,有一个长的单极突起,其大小为10~30μm。     

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.     

Body Size Overlap,Habitat Partitioning and Living Space Requirements of Terrestrial Vertebrate Predators: Implications for the Paleoecology of Large Theropod Dinosaurs

Ecological studies of extant tetrapod predators indicate that morphologically similar species which coexist in the same habitats routinely reduce interspecific competition for food by regular spacing of body size. The biggest predator species in the assemblage often differ more from one another in size than the smallest species. When coexisting carnivore species do not differ greatly in size, they commonly show morphological differences related to prey handling that may reduce dietary overlap. If carnivore species are very similar in both size and morphology, competition is avoided by habitat partitioning. Two tyrannosaurid species from the late Campanian Dinosaur Park Formation of western Canada are similar in both size and morphology, suggesting that they were segregated on the basis of habitat and/or biogeographic province. However; consideration of the living-space requirements of predator species of such large body size suggests that this kind of spatial separation would only have been possible had tyrannosaurids been more like ectotherms than endotherms in their metabolic rates. Distribution of different large theropod species across different, and surprisingly small (for the size of the animals) portions of Mesozoic landscapes may also account for the remarkably high diversity of morphologically similar large theropods in other dinosaur faunas.     

Predation Risk Avoidance by Terrestrial Amphibians: The Role of Prey Experience and Vulnerability to Native and Exotic Predators

We studied avoidance, by four amphibian prey species (Rana luteiventris, Ambystoma macrodactylum, Pseudacris regilla, Tarichia granulosa), of chemical cues associated with native garter snake (Thamnophis elegans) or exotic bullfrog (R. catesbeiana) predators. We predicted that avoidance of native predators would be most pronounced, and that prey species would differ in the intensity of their avoidance based on relative levels of vulnerability to predators in the wild. Adult R. luteiventris (presumably high vulnerability to predation) showed significant avoidance of chemical cues from both predators, A. macrodactylum (intermediate vulnerability to predation) avoided T. elegans only, while P. regilla (intermediate vulnerability to predation) and T. granulosa (low vulnerability to predation) showed no avoidance of either predator. We assessed if predator avoidance was innate and/or learned by testing responses of prey having disparate levels of prior exposure to predators. Wild‐caught (presumably predator‐exposed) post‐metamorphic juvenile R. luteiventris and P. regilla avoided T. elegans cues, while laboratory‐reared (predator‐naive) conspecifics did not; prior exposure to R. catesbeiana was not related to behavioural avoidance among adult or post‐metamorphic juvenile wild‐reared A. macrodactylum and P. regilla. These results imply that (i) some but not all species of amphibian prey avoid perceived risk from garter snake and bullfrog predators, (ii) the magnitude of this response probably differs according to prey vulnerability to predation in the wild, and (iii) avoidance tends to be largely learned rather than innate. Yet, the limited prevalence and intensity of amphibian responses to predation risk observed herein may be indicative of either a relatively weak predator–prey relationship and/or the limited importance of predator chemical cues in this particular system.     

The Role of Body Size in Mating Interactions of the Sexually Cannibalistic Fishing Spider Dolomedes triton

Some arachnids display extreme sexual size dimorphism (SSD) with adult females being several times larger than adult males. One explanation for SSD in species that exhibit pre‐copulatory sexual cannibalism (female attack, kill and consumption of the male prior to mating) is that smaller males may be less likely victims of predatory attacks by females. However, in some sexually cannibalistic species SSD is relatively moderate (i.e. males are similar in size to females) suggesting benefits of large male body size. Here, I report the results of an experiment designed to explore the ramifications of body size in mating interactions of the sexually cannibalistic, North American fishing spider (Dolomedes triton). Results suggest that male size does not influence courtship behavior, the likelihood of being attacked, or the male's ability to secure a mounting. However, large males were superior at gaining copulations once mounted. Sexual cannibalism may also be predicated on female size. Female condition (mass/cephalothorax area) did not explain any of these behaviors from the copulatory sequence, however, females with a smaller cephalothorax area were more likely to attack courting males. Finally, analysis of the ratio of female size to male size showed that when SSD is weak males are more likely to escape attacks and mate successfully. Results are discussed in light of several hypotheses for sexual cannibalism, and the benefits of large male body size illustrated here are put forth as potential explanations for the relatively moderate extent of SSD found in this sexually cannibalistic species.     

Impact of Different Carbon Dioxide Concentrations in the Olfactory Response of Sipha flava (Hemiptera: Aphididae) and its Predators

The increasing level CO₂ may altered host plant physiology and hence affect the foraging behavior of herbivore insects and predator. Hence, the aim of this study was provides evidence that host plants grown at different levels of CO₂ can alter the choice behavior of aphid, Sipha flava and their natural enemies, Cycloneda sanguinea and Diomus seminulus. The plant used was Pennisetum purpureum, cultivar Cameron Piracicaba growing in greenhouse (mean value of CO₂?=?440 ppm), climatic chamber with constant value of CO₂?=?500 ppm and climatic chamber with fluctuating CO₂ (mean value?=?368 ppm). A glass Y-shape olfactometer was used to verify the insects responses towards elephant grass plants cultivated under different conditions. The aphids were statistically more attracted by plants grown with constant CO₂ level (500 ppm) than by plants grown with fluctuating CO₂ level or plants grown in greenhouse. There was no difference in S. flava preference to non-infested versus infested plants by conspecifics. The predator C. sanguinea did not show difference between plants grown with constant CO₂ level and infested or not with S. flava. However, the predator D. seminulus showed higher preference to plants grown with constant CO₂ level and infested with S. flava. This study showed that the response of S. flava and its predators were affected by plants grown under different levels of CO₂.     

Divergence between the Courtship Songs of the Field Crickets Gryllus texensis and Gryllus rubens (Orthoptera, Gryllidae)

Acoustic mating signals are often important as both interspecific prezygotic isolating mechanisms and as sexually selected traits in intraspecific mate choice. Here, we investigate the potential for cricket courtship song to act as an isolating mechanism by assessing divergence between the courtship songs of Gryllus texensis and Gryllus rubens , two broadly sympatric cryptic sister species of field crickets with strong prezygotic isolation via the calling song and little or no postzygotic isolation. We found significant species-level differences in the courtship song, but the song has not diverged to the same extent as the calling song, and considerable overlap remains between these two species. Only two related courtship song characters are sufficiently distinct to play a possible role in prezygotic species isolation.     

Size Assortative Mating and Reproductive Success of the Funnel-Web Spider, Agelena limbata (Araneae; Agelenidae)

Field observations and laboratory experiments were conducted to assess the relation between male size and reproductive success in the funnel-web spider, Agelena limbata Thorell (Agelenidae), in 2 years. In this species, the body size of males is similar to that of females. In the field, size assortative mating occurred in both years. In 1 year, partial correlation coefficient analysis indicates that male cephalothorax width is a beter predictor of the copulated female cephalothorax width than of the date of pairing. In laboratory experiments, females tended to reject courting males that were smaller in relative body size, and males that were larger in relative body size had greater copulation success. Consequently female rejection of smaller courting males has some contribution to size assortative mating. Since larger females deposited more numerous eggs in the field, larger males are expected to have a higher reproductive success.