Levels Of Predation Research Articles

Assessing the Importance of Natural Regulating Mechanisms in Weed Management: The Case of Weed Seed Predation in a Winter Wheat Field and in Adjacent Semi-Natural Habitat in Northern Hungary

Weeds are one group of pests that significantly reduce crop yields and qualities, while herbicide use poses a risk to human health and environment. Weed seed predation has been identified as a potential biocontrol approach offering sustainable weed management. It causes substantial seed losses on weed species in crop fields, and thus may result in a reduction in herbicide use. This study aimed to investigate the relevant seed predation patterns on important weed species, Galium aparine L., Papaver rhoeas L., and Apera spica-venti L., in a winter wheat field and the adjacent semi-natural habitat (SNH) near Gödöllő, Hungary, assuming that weed seeds are likely to be predated, but predation levels may differ by weed species and habitat type. Sampling rounds were performed twice, in 2019 and 2021, before crop harvest, by placing a total of 240 seed cards (120 cards/round) on the soil surface inside both crop field, and in the adjacent SNH. Seed predation was assessed on each card every 24 h, for 5 days in 2019 and 6 days in 2021. The results revealed high intensity (100%) of seed predation on the evaluated weed species, during the exposure periods in both years and habitat types, although weed seeds were significantly consumed (p < 0.001) in 2019 as opposed to 2021. Whereas, seed consumption levels were not significantly different (p = 0.802) among habitat types, and between habitats and years (p = 0.842). The optimum period for measuring weed seed predation was found to be after 48 h of field exposure. Our findings showed that seed predation reduced the number of exposed weed seeds on the soil surface, which may decrease the weed seed banks, and the number of weed seedlings the next cropping season.

Camouflage in lichen moths: Field predation experiments and avian vision modelling demonstrate the importance of wing pattern elements and background for survival.

Background matching is perhaps the most ubiquitous form of defensive camouflage in the animal kingdom, an adaptive strategy that relies on the visual resemblance between a prey organism and its background to promote concealment from predators. The importance of background matching has been acknowledged for over a century, yet despite its renown and apparent pervasiveness, few studies exist that have objectively quantified its occurrence and tested the functional significance of background matching in a specific animal study system. The North Island lichen moth Declana atronivea presents a fascinating system to investigate such anti-predator coloration. This species possesses high contrast black and white forewings that appear to resemble lichen. Here we assessed the contribution of background matching to the antipredator defence of D. atronivea using field predation experiments with realistic models. We found that D. atronivea coloration confers a significant survival advantage against native avian predators when on lichen backgrounds compared to bark backgrounds, with an intermediate level of predation occurring when models were near, but not on lichen. This suggests that D. atronivea wing patterns are an adaptation for background matching. We subsequently used calibrated digital photography, avian vision modelling and image analysis techniques to objectively quantify the degree of background matching exhibited by D. atronivea and assessed the contribution of different visual elements (colour, luminance and pattern) to camouflage in this species. Only the pattern elements of D. atronivea presented a close match to that of the lichen backgrounds, with both chromatic and achromatic cues found to be poor predictors of background matching in this species. This study is one of the first to integrate vision modelling, quantitative image analysis and field predation experiments using realistic models to objectively quantify the level and functional significance of background matching in a real species, and presents an ideal system for further investigating the interrelation between multiple mechanisms of camouflage.

Measurement of post-dispersal invertebrate seed predation of some relevant weed species in maize fields in Hungary: An ecosystem service provided in crop fields contributing to weed management

Invertebrate seed predation is a potential ecosystem service that substantially reduces weed seeds in crop fields, decreasing the seedling emergence and, thus, limiting the weed competition next season. It may, thus, be considered as a natural component of the long-term weed management toolbox. This study aimed to measure the post-dispersal invertebrate seed predation levels of the following relevant weed species in Hungarian maize fields: Ambrosia artemisiifolia, Datura stramonium, Chenopodium album, and Echinochloa crus-galli, and to compare the predation levels among them. We hypothesised that invertebrate seed predators will predate weed seeds, but the predation levels may vary with the weed species. Two sampling rounds were performed, in November 2019 and October 2020, in Gödöllő, Hungary. A total of 100 seed cards/round were placed on the soil surface inside a maize field prior to harvest, 10 m from the field’s edge, along 25 transects, with four cards/transect. A distance of 10 m was set between the transects and 1 m between the cards. Twenty seeds of each weed species were glued onto sandpaper (25 × 10 cm, P-60), and a wire mesh was used to exclude vertebrate predators. The seed removal was calculated every 24 h, for seven days in 2019 and for five days in 2020, and then the seed predation was measured using the number of removed seeds on each card. The results showed high seed predation levels on all the seed cards, with an overall average of 85.9 ± 13.7%. Besides, there was a decrease in the % of remaining seeds on the cards starting from the first day after exposure due to seed predation in both years. The optimum exposure period for measuring the seed predation was found to be three to four days, though the number of predated seeds on days 3 and 4 significantly differed between years (P < 0.001), with higher predation rates in 2020 than in 2019. However, no differences were detected in the predation rates among the weed species (P = 0.962, 0.079). These findings indicate the potential contribution of seed predation by invertebrates to weed management in Hungarian maize fields.

Demographic study of a peripheral population of the rare amphicarpic species Scrophularia arguta

Scrophularia arguta (Scrophulariaceae) is a rare amphicarpic annual species with a fragmented distribution in North Africa, part of the Arabian Peninsula, and Macaronesia, with several peripheral populations on the Iberian Peninsula (south-western Europe) as well. The Iberian populations have a disjunct distribution: several endangered or critically endangered populations are present in the southeast versus a few non-listed ones representing a relict lineage with a unique plastid haplotype inhabiting the west-central region (Extremadura). In this study, we examined the largest and most important population of this relict lineage to assess potential threats to its survival. We evaluated pollination and reproductive systems, floral rewards, fruit and seed set from chasmogamous and cleistogamous flowers, and population dynamics (i.e., phenology, survival, reproductive success, and predation level). We found that the main threats to the population are predation by wild herbivores, such as red deer and, to a lesser extent, Cucullia scrophulariae caterpillars. These threats decrease reproductive success to such an extent that population survival may be in jeopardy if no action is taken to reduce the effects of herbivores. In addition, the existence of nearby beehives alters the presence and density of wild pollinators that contribute to gene flow via pollen transfer and increase genetic variability. Cleistogamous seeds may help maintain the population in specific microhabitats (mainly quartzite rock cracks), although at the cost of reducing genetic variability. Finally, we recommend that regional/national administrations responsible for biodiversity matters adopt measures to ensure the conservation and survival of west-central populations. Scrophularia arguta predation by vertebrates. Left, group of several individuals before and after vertebrate predation. Right, vertebrate predation level. • Wild vertebrates and caterpillars threaten a relict Scrophularia arguta population. • Managed honeybees displace natural pollinators. • The conflict between plant and animal conservation requires monitoring. • The action of regional/national administrations is needed to conserve this species.

Predation thresholds for reintroduction of native avifauna following suppression of invasive Brown Treesnakes on Guam.

The brown treesnake (BTS) (Boiga irregularis) invasion on Guåhan (in English, Guam) led to the extirpation of nearly all native forest birds. In recent years, methods have been developed to reduce BTS abundance on a landscape scale. To help assess the prospects for the successful reintroduction of native birds to Guåhan following BTS suppression, we modeled bird population persistence based on their life history characteristics and relative sensitivity to BTS predation. We constructed individual-based models and simulated BTS predation in hypothetical founding populations for each of seven candidate bird species. We represented BTS predation risk in two steps: risk of being encountered and risk of mortality if encountered. We link encounter risk from the bird's perspective to snake contact rates at camera traps with live animal lures, the most direct practical means of estimating BTS predation risk. Our simulations support the well-documented fact that Guåhan's birds cannot persist with an uncontrolled population of BTS but do indicate that bird persistence in Guåhan's forests is possible with suppression short of total eradication. We estimate threshold BTS contact rates would need to be below 0.0002-0.0006 snake contacts per bird per night for these birds to persist on the landscape, which translates to an annual encounter probability of 0.07-0.20. We simulated the effects of snake-proof nest boxes for Sihek (Todiramphus cinnamominus) and Såli (Aplonis opaca), but the benefits were small relative to the overall variation in contact rate thresholds among species. This variation among focal bird species in sustainable predation levels can be used to prioritize species for reintroduction in a BTS-suppressed landscape, but variation among these species is narrow relative to the required reduction from current BTS levels, which may be four orders of magnitude higher (>0.18). Our modeling indicates that the required predation thresholds may need to be lower than have yet been demonstrated with current BTS management. Our predation threshold metric provides an important management tool to help estimate target BTS suppression levels that can be used to determine when bird reintroduction campaigns might begin and serves as a model for other systems to match predator control with reintroduction efforts.

Intermediate Levels of Predation and Nutrient Enrichment Enhance the Activity of Ibuprofen-Degrading Bacteria.

Water is the most indispensable natural resource; yet, organic pollution of freshwater sources is widespread. In recent years, there has been increasing concern over the vast array of emerging organic contaminants (EOCs) in the effluent of wastewater treatment plants (WWTPs). Several of these EOCs are degraded within the pore space of riverbeds by active microbial consortia. However, the mechanisms behind this ecosystem service are largely unknown. Here, we report how phosphate concentration and predator-prey interactions drive the capacity of bacteria to process a model EOC (ibuprofen). The presence of phosphate had a significant positive effect on the population growth rate of an ibuprofen-degrading strain. Thus, when phosphate was present, ibuprofen removal efficiency increased. Moreover, low and medium levels of predation, by a ciliated protozoan, stimulated bacterial population growth. This unimodal effect of predation was lost under high phosphate concentration, resulting in the flattening of the relationships between predator density and population growth of ibuprofen degraders. Our results suggest that moderate nutrient and predation levels promote the growth rate of bacterial degraders and, consequently, the self-purifying capability of the system. These findings enhance our understanding of the mechanisms by which riverbed communities drive the processing of EOCs.

Predation probabilities and functional responses: How piscivorous waterbirds respond to pulses in fish abundance

How predators respond to changes in prey abundance (i.e., functional responses) is foundational to consumer–resource interactions, predator–prey dynamics, and the stability of predator–prey systems. Predation by piscivorous waterbirds on out-migrating juvenile steelhead trout (Oncorhynchus mykiss) is considered a factor affecting the recovery of multiple Endangered Species Act-listed steelhead populations in the Columbia River basin. Waterbird functional responses, however, may vary by predator species and location, with important implications to predator management strategies. We used a 13-year dataset on waterbird abundance across seven breeding colonies (three Caspian tern [Hydroprogne caspia], two double-crested cormorant [Nannopterum auritum], and two California and ring-billed gull [Larus californicus and Larus delawarensis] colonies) and steelhead tag-recovery data (>645,000 tagged and >32,000 recovered steelhead) to quantify weekly predation probabilities and functional responses across waterbird species, colonies, and years. Weekly predation probabilities were highly variable, ranging from 0.01 to 0.30 at tern colonies, 0.01 to 0.20 at cormorant colonies, and 0.03 to 0.13 at gull colonies. Per capita predation probabilities were an order of magnitude higher at inland tern and cormorant colonies relative to estuary colonies of the same species. Terns displayed Type II functional responses across colonies and years, where predation probabilities peaked at low steelhead abundances and declined as steelhead abundance increased (i.e., predator swamping). Cormorants nesting at the large estuary colony (several thousand birds) displayed a Type III functional response, but cormorants nesting at the smaller inland colony (several hundred birds) displayed a Type II response. Consumption probabilities of steelhead by gulls remained consistent across a large range of steelhead availability, suggesting a Type I or a Type III functional response, but a lack of colony abundance data prevented quantifying functional responses. The level of tern predation combined with Type II functional responses indicate possible population-level impacts that could destabilize small or declining prey populations. Conversely, the apparent Type III functional responses of gulls and estuary nesting cormorants are indicative of prey switching behaviors targeted at periods of high steelhead abundance. Our results illustrate the complexity of predator–prey interactions and the importance of quantifying predator- and location-specific functional responses when predicting the efficacy of management strategies to enhance prey populations.

Effectiveness of electric harps in reducing Vespa velutina predation pressure and consequences for honey bee colony development.

Vespa velutina has become a species of concern in invaded regions of Europe and Asia, due to its impacts on biodiversity, apiculture and society. This hornet, a ferocious hunter of pollinating insects, poses a serious threat to biodiversity and pollination services. Despite ongoing efforts, its extermination in continental Europe is hampered by a lack of effective control methods, thus effective mitigation measures are primary concerns. The aims of this work were: (i) to study the effects of V. velutina predating on honey bee colonies, and (ii) to assess the effectiveness of electric harps in reducing hunting pressure and predation. We assessed the predation pressure and compared honey bee colony performance, body weight of workers, and winter survivorship for protected versus unprotected colonies in 36 experimental hives across three apiaries. Electric harps protected honey bees by reducing predation pressure and therefore mitigating foraging paralysis. Consequently, foraging activity, pollen income, brood production and worker body weight were higher in protected colonies which in turn showed greater winter survivorship than those that were unprotected, especially at sites with intermediate to high levels of predation. The predation of V. velutina affects foraging activity, breeding, body weight and colony survivorship of Apis mellifera. Electric harps contribute significantly to mitigate the impact of this invasive hornet on apiaries; however, they should be deployed in tandem with additional measures to preserve honey bee colony stocks, such as facilitating access to food sources for colonies during the periods of highest predation pressure. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

On the Fitness of Predators with Prey-Induced Dispersal in a Habitat with Spatial Heterogeneity.

This study considers a situation in which a predator can change its dispersal rate according to its satisfaction with foraging prey in a predator-prey interaction. However, since it is impossible to accurately determine the magnitude of the density of prey that is favorable to a predator's survival in an area, the predator determines the movement rate through inaccurate judgment. In this situation, we investigate the effect of the predator's decision about its movement on fitness. To achieve our goal, we consider a predator-prey model with nonuniform predator dispersal, called prey-induced dispersal (PYID), in which the spread of predators is small when the prey density is larger than a certain value, and when the prey density is smaller than a particular value, a large spread of predators occurs. To understand how PYID affects the dynamics and coexistence of the system in a spatially heterogeneous region, we examine a model with Holling-type II functional responses under no-flux boundary conditions wherein the predators move according to the PYID. We study the local stability of the semitrivial solution of models with PYID and linear dispersal where the predator is absent. Furthermore, we investigate the local/global bifurcation from the semitrivial solution of models with two different dispersals. We conclude that in most cases, nonuniform dispersal of predators following PYID promotes predator fitness; however, there is a case in which PYID does not increase predator fitness. If a predator's satisfaction degree regarding the prey density is higher than a certain level, there may exist a case that is not beneficial for predators in terms of their fitness. However, if the satisfaction level of predators regarding prey density is relatively low, predators following PYID will take advantage of fitness. More precisely, if predators are dissatisfied with the amount of prey in a region and move quickly, even for abundant prey density, they may not benefit from PYID. Meanwhile, if predators change their motility when they are appropriately satisfied with the amount of prey, they will obtain a survival advantage. We obtain the results by analyzing an eigenvalue problem at the semitrivial solution from the linearized operators derived from the models.

Modeling total predation to avoid perverse outcomes from cat control in a data-poor island ecosystem.

Data hungry, complex ecosystem models are often used to predict the consequences of threatened species management, including perverse outcomes. Unfortunately, this approach is impractical in many systems, which have insufficient data to parameterize ecosystem interactions or reliably calibrate or validate such models. Here we demonstrate a different approach, using a minimum realistic model to guide decisions in data- and resource-scarce systems. We illustrate our approach with a case-study in an invaded ecosystem from Christmas Island, Australia, where there are concerns that cat eradication to protect native species, including the red-tailed tropicbird, could release meso-predation by invasive rats. We use biophysical constraints (metabolic demand) and observable parameters (e.g. prey preferences) to assess the combined cat and rat abundances which would threaten the tropicbird population. We find that the population of tropicbirds cannot be sustained if predated by 1607 rats (95% credible interval (CI) [103, 5910]) in the absence of cats, or 21 cats (95% CI [2, 82]) in the absence of rats. For every cat removed from the island, the bird's net population growth rate improves, provided that the rats do not increase by more than 77 individuals (95% CI [30, 174]). Thus, in this context, one cat is equivalent to 30-174 rats. Our methods are especially useful for on-the-ground predator control in the absence of knowledge of predator-predator interactions, to assess whether 1) the current abundance of predators threatens the prey population of interest, 2) managing one predator species alone is sufficient to protect the prey species given potential release of another predator, and 3) control of multiple predator species is needed to meet the conservation goal. Our approach demonstrates how to use limited information for maximum value in data-poor systems, by shifting the focus from predicting future trajectories, to identifying conditions which threaten the conservation goal. This article is protected by copyright. All rights reserved.

Irrational exuberance and deception — Why markets spin out of control

This article reports on a field study of 457 US participants that identifies the intimate link between three constructs: disconnection (dis-anchoring) from the bundle of needs, goals, and preferences (NGPs), irrationality, and indebtedness. We combine these three mental states that together influence deceitful borrowing behaviors to define irrational exuberance. When using linear regressions and path analyses, we find that together they form a self-reinforcing wheel of misfortune that may spin out of control and generate market frictions, as suggested by US market data. A predatory dynamic drives this loop whereby market agents position themselves at various levels of financial predation (as either predators, prey, or a mix thereof). The theoretical implications of our findings are that we integrate this loop into the literature on debt, something that has not been done before in financial or economic theory. Thus, we enrich the understanding of why market agents – lenders and borrowers alike, either individuals or organizations – mislead each other and why markets consequently tend to deviate from normalcy. The managerial implication is that a better psychological appraisal of borrowers’ mental states and behaviors would likely improve lending risk assessment, may reduce default outcomes, and, on a macroeconomic level, could alleviate the symptoms of impending financial crises.

The First Ex-Situ Germination and Dispersal Mechanisms of the Rare, Critically Endangered Tree, Pleodendron costaricense

Background and Research aims The extinction of relict and rare tree species is accelerated by habitat loss and climate change. Pleodendron costaricense is a critically endangered tree, with only four mature individuals known in Southern Pacific Costa Rica. With the discovery of three additional trees, we set out to learn more about P. costaricense’s natural history and attempt the first successful germination. Methods We collected fruits from two trees and carried out preliminary germination trials in a nursery at the study site. We also used camera traps in one of the fruiting mother-trees to understand natural dispersal mechanisms of the species. Results Although plagued by excessive levels of invertebrate predation, we were able to germinate and produce 59 saplings ready for restoration planting. Five mammal species were detected on the camera traps feeding on the fruits, along with one primate potentially using the fruits as a topical medicine. Conclusion P. costaricense can be propagated ex-situ, potentially with greater success using stimulating hormones. To improve production rates, future efforts should focus on the protection of germinating seeds and saplings from seed predators. We also identified numerous potential natural mammalian seed dispersers, mostly in the family Procyonidae. Implications for Conservation Given the propagation knowledge we have developed, the active restoration efforts of the saplings by Osa Conservation to help increase population numbers, and the strict protection of the two fruiting mother trees, there is now the possibility to attain a positive conservation outcome for this critically endangered species.

Who to help? Helping decisions in a cooperatively breeding bird with redirected care

Cooperative breeding sometimes occurs when adult breeders form groups following natal dispersal and mating. In such cases, individuals typically face a choice of social partner with whom to cooperate. Selecting appropriate social partners is crucial to maximising the fitness payoffs from cooperation, but our understanding of the criteria guiding partner choice is limited. Here, we analyse helping decisions by long-tailed tits (Aegithalos caudatus), which may redirect their care to assist breeders in raising offspring following the failure of their own nests. In this species, helpers prefer to help relatives at nearby nests, but it is unclear whether other criteria that may affect helper fitness also influence helping decisions. When choosing among broods of equivalent kinship, we found that helpers did not prefer those broods that offered the greatest indirect fitness returns. Further analyses revealed that helpers did not choose nests on the basis of brood size or age, but were more likely to help broods that were closer to their own failed nests and that were already being cared for by other helpers. Both effects likely reflect the limited choice available to helpers: although individuals breed close to relatives within kin neighbourhoods, a high rate of nest predation constrains helpers’ choice of broods. In other species where cooperatively breeding groups form after natal dispersal, a greater range of options may be available and here detailed analysis of group formation will be helpful for determining the decision rules that underpin partner choice and permit stable cooperation in the face of alternative options.Significance statementCooperative breeding occurs most frequently when offspring delay dispersal from their natal site and help to care for their younger siblings. In some species, however, individuals first disperse and then come together as adults to cooperate in rearing young. In the latter case, multiple social partners may be available — what then determines which partner is helped? We studied partner choice in long-tailed tits, which may help to feed other broods if their own brood fails. When multiple related broods were available, individuals were more likely to help those close by but showed no preference for broods offering the greatest indirect fitness returns. One explanation for this result is that helping options for most individuals are limited by high levels of nest predation, favouring a simpler decision-making process based on identifying close relatives breeding in close proximity.

Stable isotope analysis to assess the trophic level of arthropod in sugarcane ratoon agroecosystem

Abstract. Prabowo H, Rahardjo BT, Mudjiono G, Rizali A. 2022. Stable isotope analysis to assess the trophic level of arthropod in sugarcane ratoon agroecosystem. Biodiversitas 23: 2871-2881. Arthropods represent one of the main components of soil inhabitants and play an important role in maintaining soil health, as well as providing ecosystem services. The description of the trophic level of the ratoon sugarcane agroecosystem is needed to describe the role of organisms in the ecosystem to maximize the role of detritivores, predators, and parasitoids in the ratoon sugarcane agroecosystem. The stable isotope approach is widely used in various studies to describe trophic levels in an agroecosystem. The stable isotope technique, especially the one that uses stable isotopes of carbon (?13C) and nitrogen (?15N), can measure the trophic position that integrates energy assimilation or mass flow through all the different trophic pathways leading to an organism. Stable isotopes ?13C and ?15N can be used to identify the roles of arthropods in the ratoon sugarcane agroecosystem by identifying the composition of both isotopes. The ratio of arthropod's carbon assimilation (?13C) to sugarcane ranges from-1.4 to-5.45‰. In contrast, the ratio of nitrogen assimilation (?15N) of arthropod to sugarcane ranges from 3.86 to 39.7‰. The values of stable isotope ?13C and ?15N on predator and parasitoids are varied. The stable isotope value of carbon (?13C) for predators varies from-10.14 to-11.62‰. In contrast, the predator's stable isotope value of nitrogen (?15N) varies from 9.17 to 18.1%. The parasitoids' carbon stable isotope value (?13C) varies from 10.5 to 11.05‰. In contrast, parasitoids' nitrogen stable isotope value (?15N) varies from 12.8 to 17.05‰. The value of carbon (?13C) stable isotope assimilation between herbivores and predators varies from 0.006 to 1.38‰. While the value of nitrogen (?15N) stable isotope assimilation varies in the range of 0.33 to 10.3‰. Furthermore, the value of carbon (?13C) stable isotope assimilation between herbivores and parasitoids varies in the range of 5.3 to 9.23‰. While the value of nitrogen (?15N) stable isotope assimilation varies in the range of 3.79 to 10.3‰. Isotope content (?13C) shows the food resources of arthropods in the agroecosystem, while isotope value (?15N) shows the roles of arthropods in the sugarcane ratoon agroecosystem. Carbon stable isotope values of predator and parasitoids are close to zero. While the stable nitrogen isotope (?15N) values on arthropods are averagely above 10‰, values are suspected of having roles as predators or parasitoids. Knowing the trophic level of predators and parasitoids through stable isotopes in agroecosystems can be used to conserve and optimize natural enemies to suppress the development of herbivores.

Woody perennial polycultures increase ant diversity and ant-mediated ecosystem services compared to conventional corn-soybean rotations

The role plant diversity has played in regulating insect communities has been of interest for decades. Recent syntheses from agroecosystems suggest increasing plant diversity can positively affect beneficial insects like predators, reducing pest pressure and increasing yield. However, the agricultural landscape of the Midwestern United States is dominated by just two crops—corn and soybean—which cover approximately 180 million acres of arable land yearly. New ideas to conserve wildlife that additionally provide economic opportunities for farmers must be developed in order to promote sustainable and resilient ecosystems. Here we tested the capacity of an alternative cropping system to support more diverse insect populations than conventional cropping systems. We quantified differences in the diversity of an insect taxon, ants (Hymenoptera: Formicidae), over an annual cycle using pitfall traps in thirty-two 2-m2 plots of either woody perennial polycultures that contained apples, chestnuts, currants, hazelnuts, and raspberries or conventional corn-soybean rotations. In doing so, we found that woody perennial polycultures supported 2.4-fold more ant species and maintained a unique fauna of specialist and predatory ants. The observed differences in diversity were linked to higher levels of predation as 18.2-fold more sentinel prey were consumed during each month of the growing season. Combined, our results suggest that agricultural landscapes in the Midwestern United States can be modified to support important beneficial insects like ants while still producing commodities that can be economically beneficial to farmers.

Higher Rate of Male Sexual Displays Correlates with Larger Ventral Posterior Amygdala Volume and Neuron Soma Volume in Wild-Caught Common Side-Blotched Lizards, Uta stansburiana

Several areas of the vertebrate brain are involved in facilitating and inhibiting the production of sexual behaviors and displays. In the laboratory, a higher rate of sexual displays is correlated with a larger ventral posterior amygdala (VPA), an area of the brain involved in the expression of sexual display behaviors, as well as larger VPA neuronal somas. However, it remains unclear if individuals in the field reflect similar patterns, as there are likely many more selective pressures in the field that may also modulate the VPA architecture. In this study, we examined variation in VPA volume and neuron soma volume in wild-caught common side-blotched lizards (Uta stansburiana) from two different populations. In a population from Nevada, males experience high predation pressure and have decreased sexual display rates during the breeding season, whereas a population in Oregon has lower levels of predation and higher rates of male sexual displays. We found that wild-caught males from the population with lower display rates also exhibited decreased VPA volume and VPA neuron cell soma volume, which may suggest that decreased display rate, possibly due to increased predation rate, covaries with VPA attributes.

Natural biological control of Bagrada hilaris by egg predators and parasitoids in north-central California

Bagrada bug, Bagrada hilaris Burmeister (Hemiptera: Pentatomidae), is an invasive stink bug from Asia that has become a major pest of cruciferous crops (Brassicaceae) in California. Conventional insecticides are currently the most effective means for controlling this pest. In organic production, options are limited and generally ineffective. As part of an effort to develop a biological control program for bagrada bug, we documented attack rates by resident parasitoids and predators on sentinel bagrada bug eggs throughout north-central California, including the Salinas Valley, which is the largest cruciferous crop growing region in the US. A total of 51 sites were sampled over three years. Sentinel eggs were placed on the ground, where bagrada bug lays most of its eggs, and in foliage, where all other known stinkbug species deposit their eggs and resident egg parasitoids are most likely to search. Predation rates exceeded 20% per day on some sample dates (averaging 7.2, 7.4 and 6.3% per day in 2017, 2018 and 2019, respectively) and were generally higher on the ground than in the foliage, although temporal patterns were inconsistent and predation levels varied among the sampled regions. Burying eggs in sand did not consistently reduce predation rates, indicating that bagrada bug’s habit of burying its eggs provides only partial protection from predators. Of the 25,387 eggs deployed over the three years of this study that were not predated or missing (out of the 35,673 total eggs that were deployed), only 47 (0.19%) were parasitized. Gryon aetherium Talamas (Scelionidae), a biological control agent for bagrada bug that is currently undergoing testing, was found at one site. Only five of the parasitized sentinel eggs were on the ground, suggesting that few resident parasitoids in north-central California attack bagrada bug eggs, particularly on the ground. These results show that a parasitoid that co-evolved with bagrada bug in its native range is necessary to provide successful biological control of bagrada bug in California.

Are the Interactions between Oaks and Pre-Dispersal Seed Predators Retained in Urban Environments? An Analysis of Two Quercus Species in Southern Mexico City

As urbanization proceeds, natural ecosystems surrounding cities are transformed, but usually some elements persist, notably trees from forest ecosystems. However, it is still unknown the extent to which isolated trees, immersed in an urban matrix, maintain their interactions with insects that feed on their seeds. In this work we analyzed pre-dispersal seed predation by the two main groups of insects, weevils (Coleoptera; Curculionidae) and moths (Lepidoptera: Tortricidae), whose larvae feed on the acorns of two oak species (Quercus rugosa and Q. castanea). We compared these interactions between trees located in a protected forested area and trees isolated in an urban matrix. Our hypothesis was that, since pre-dispersal seed predation depends on insect dispersal, acorns from isolated trees would have lower predation levels than acorns from trees in the forest. A second hypothesis, based on reports that moths exhibit larger dispersal distances than weevils, was that isolated trees would have higher predation levels from moths than from weevils compared to their respective proportions in forest trees. Finally, we expected that moth predation would increase with seed size, as it does in weevils. We collected 1200 acorns of the two oak species (ten trees per species) in a protected oak forest and a nearby highway in southern Mexico City. From the whole sample, 17.3% of the acorns were predated by weevils and 3.8% by moths. The probability of predation was larger in acorns from trees in the forest (0.30) than in those from isolated trees (0.07), which confirmed the first hypothesis; tree species identity did not have a significant effect on the proportion of predated acorns. When only predated acorns were analyzed, predation by weevil larvae was larger than predation by moths in both oak species, although the probability of predation by weevils was higher in the oak species having large acorns (Q. rugosa, 0.93), than in the species with small acorns (Q. castanea, 0.63). Inversely, predation by moths was higher in Q. castanea (0.37) than in Q. rugosa (0.07). Seed predation decreased similarly for weevils and moths in isolated trees, so we failed to find support for our second hypothesis. A positive relationship between seed predation by weevils and seed size was found in Q. rugosa but not in Q. castanea; seed size did not affect predation by moth larvae. Therefore, although isolated trees in the urban matrix harbor smaller populations of pre-dispersal seed predators than forest trees, their interactions with the two main groups of insects feeding on acorns are maintained, which points to their importance for the conservation of urban biodiversity.

Coastal infrastructure alters behavior and increases predation mortality of threatened Puget Sound steelhead smolts

AbstractFundamental movements of migratory species can be substantially influenced by marine habitat disruptions caused by coastal infrastructure. The Hood Canal Bridge (HCB) spans the northern outlet of Hood Canal in the Salish Sea, extends 4.6 m (15 ft) underwater, and forms a partial barrier for steelhead migrating from Hood Canal to the Pacific Ocean. Spatial mark–recapture survival models using acoustic telemetry data indicate that only 49% (2017; 95% confidence interval (CI) = 40%–58%) and 56% (2018; 95% CI = 48%–65%) of the steelhead smolts encountering the HCB survived past the bridge and 7 km to the next array. We studied fine‐scale movements of more than 300 steelhead smolts to understand how migration behavior was affected across the entire length of the HCB and to quantify spatial and temporal patterns of mortality. Individually coded acoustic telemetry transmitters implanted in juvenile steelhead were used in conjunction with an extensive array of acoustic receivers surrounding the HCB to obtain approximations of the path each steelhead took as they encountered the bridge structure. Steelhead survival past the HCB appeared unaffected by tidal stage, population‐of‐origin, approach location, current velocity, or time of day, but was influenced by week of bridge encounter. Behavioral data from transmitters with temperature and depth sensors ingested by predators are consistent with high levels of marine mammal predation. This study confirms the considerable impact of the HCB on Endangered Species Act‐listed steelhead smolt survival, and provides detailed information on the behavior of steelhead smolts and their predators at the HCB for use in planning recovery actions.

Scale dependence of drilling predation in the Holocene of the northern Adriatic Sea across benthic habitats and nutrient regimes

AbstractPredation has strongly shaped past and modern marine ecosystems, but the scale dependency of patterns in drilling predation, the most widely used proxy for predator–prey interactions in the fossil record, is a matter of debate. To assess the effects of spatial and taxonomic scale on temporal trends in the drilling frequencies (DFs), we analyzed Holocene molluscan assemblages of different benthic habitats and nutrient regimes from the northern Adriatic shelf in a sequence-stratigraphic context. Although it has been postulated that low predation pressures facilitated the development of high-biomass epifaunal communities in the eastern, relatively oligotrophic portion of the northern Adriatic shelf, DFs reaching up to 30%–40% in the studied assemblage show that drilling predation levels are comparable to those typical of late Cenozoic ecosystems. DFs tend to increase from the transgressive systems tract (TST) into the highstand systems tract (HST) at the local scale, reflecting an increase in water depth by 20–40 m and a shift from infralittoral to circalittoral habitats over the past 10,000 years. As transgressive deposits are thicker at shallower locations and highstand deposits are thicker at deeper locations, a regional increase in DFs from TST to HST is evident only when these differences are accounted for. The increase in DF toward the HST can be recognized at the level of total assemblages, classes, and few abundant and widespread families, but it disappears at the level of genera and species because of their specific environmental requirements, leading to uneven or patchy distribution in space and time.