Introduction Of Predators Research Articles

When the neighbourhood goes bad: can endangered black robins adjust nest‐site selection in response to the risk of an invasive predator?

AbstractThe introduction of exotic predators into new areas has had significant impacts on naïve prey species, which initially lack behavioural mechanisms to avoid predation. Understanding a species’ ability to respond appropriately to novel threats may inform in situ management options for threatened island populations. In the presence of nest predators, physical characteristics of the nest site can influence the likelihood that eggs or chicks are lost to predation. Some birds that evolved under high nest predation pressure show predictable changes in nest‐site selection following nest predation, but the ability of naïve island birds to alter nest‐site decisions based on experience with novel nest predators has not been well studied. We examined nest‐site choices of re‐nesting Chatham Island black robins Petroica traversi following nest predation by invasive European starlings Sturnus vulgaris. Robins whose first nests were depredated re‐nested in a new location that was significantly lower to the ground than pairs whose first nests were lost through other causes. As predation risk increases with nest height, the lower placement of re‐nests is consistent with a movement towards safer nest sites. The cause of nest failure did not influence the choice of substrate for a replacement nest, nor did individual pairs re‐nest further away from depredated nests. Changes in nest‐site selection did not carry over into subsequent nesting seasons. Our results suggest that some evolutionarily naïve species may be capable of assessing immediate risk through individual experience with novel predators, and modifying their nest‐site decisions accordingly.

Impact of the historical introduction of exotic fishes on the chironomid community of Lake Azul (Azores Islands)

Little is known about the effect of top predator introduction in historically fishless communities, especially on remote islands. This issue is important because it might strongly affect climate reconstructions derived from biota assemblages such as chironomids. Head capsule larval remains of chironomids have been studied in a 660years lacustrine sedimentary sequence from Lake Azul (Sao Miguel Island, Azores archipelago) to assess the extent and timescale of the effect of the predator introduction occurring in this historically fishless lake. Analysis of similarity showed that the chironomid assemblage was statistically different before and after predator introduction (R=0.78; p<0.001). Abundance of chironomids was about 40% greater in the fishless lake period compared to the period in the presence of predator. Results show major change in chironomid assemblage coinciding with the first time of goldfish introduction (around 1790CE), followed by carp (1890CE) and pike (1979CE) introductions. The composition of feeding group guilds changed following a pattern characterized by a decrease in abundance of detritivorous and predaceous taxa and an increase in abundance of grazing chironomid taxa. This study suggests that predator introduction was the most important factor affecting the chironomid assemblages in this natural, Azorean fishless lake, but predators did not affect all chironomid species. Other external forcings like major climate oscillations, anthropogenic activities in the catchment basin, and volcanic eruptions seem to play an additional role. The latest stage of the warm and arid Medieval Climate Anomaly (1000–1300CE) favoured the occurrence of some warm-adapted chironomid taxa, which were absent through the Little Ice Age (ca. 1450–1850CE) cool period.

Testing the link between perceived and actual risk of predation: mosquito oviposition site selection and egg predation by native and introduced fish

SummaryAccording to the threat‐sensitivity hypothesis, prey avoidance behaviour should reflect the magnitude of predation risk. Since predation can strongly affect reproduction success, ovipositing females are expected to adaptively adjust their predator avoidance response, or local breeding patch selectivity, in accordance with the perceived level of threat posed for their progeny by specific predators. However, association between avoidance and predation can be disrupted when the prey and the predator lack spatiotemporal opportunities to co‐evolve, such as in cases of non‐native predator introductions.We examined the interactions between mosquitoes (from the genusCulex) and three species of sympatric predaceous freshwater fish, a native cyprinidBarbus paludinosus, a cichlidPseudocrenilabrus philanderand an introduced poeciliid, the western mosquitofishGambusia affinis.In an outdoor mesocosm experiment, we quantified patterns ofCulexoviposition site selection across fish species using free‐roaming, caged and fish‐free treatments. In a complementary laboratory experiment, we tested the effectiveness of each fish species as predators of mosquito eggs and larvae.Synthesis and applications. We found evidence for: (i) mosquito egg raft predation by free‐roaming fish; (ii) fish‐specific avoidance by ovipositingCulex; and (iii) a positive association between fish‐specific oviposition avoidance and fish‐specific efficiency as an egg predator. These results contribute towards a better understanding of predator–prey co‐evolution, predator‐borne cue recognition, and suggest local native fish, the southern mouthbrooderPseudocrenilabrus philander, as an alternative toGambusiafor the biocontrol ofCulexmosquitoes.

How common is gigantism in insular fossil shrews? Examining the ‘Island Rule’ in soricids (Mammalia: Soricomorpha) from Mediterranean Islands using new body mass estimation models

The evolution of organismal body size in extant and extinct ecosystems of islands (Island Rule) is receiving much attention at present. Allometric models are a reliable way to predict the weight of extinct species, but are scarce or even absent for some groups of micromammals. To fill the gap, we carried out regression models with extant species of soricids (N = 63) using measurements of teeth, cranium, and postcranial bones, and applied these to fossil insular species and their mainland ancestors. Almost all models are significant (P < 0.05), except for those based on the width of occipital condyles. The femur can be considered the most reliable body-mass predictor, producing estimations not far from those derived from teeth (excepting molar widths). Predictions of insular species (in grams) show that those belonging to the tribe Nectogalini [Asoriculus burgioi Masini & Sara, 1998, 27.54; Asoriculus similis (Hensel, 1855), 23.68; Nesiotites ponsi Reumer, 1979, 14.58; Nesiotites meloussae Pons-Moya & Moya-Sola, 1980, 24.83; Nesiotites hidalgo Bate, 1945, 26–30] had larger masses than Crocidura sp. [Crocidura sicula esuae (Kotsakis, 1986), 9.50; Crocidura sicula sicula (Miller, 1901), 8.60; Crocidura zimmermanni Wettstein, 1953, 7–10]. Statistical comparisons with their ancestors revealed that certain species (Nesiotites sp. from Mallorca and A. similis from Sardinia) may be considered giants, but not C. zimmermanni (from Crete). Body size is closely related to life history, which is highly influenced by the selective regimes of the environment. Thus, the lower isolation distance of Crete in comparison with Sardinia and Mallorca, suggesting more introductions of competitors and predators, and the presence of a flow with the mainland, may be the reason for the absence of a giant form of C. zimmermanni. However, some biological aspects of species (such as phylogeny or lifestyle) may also have an influential role.

Damage caused by mite Tetranychus merganser (Trombidiformes: Tetranychidae) on Carica papaya (Violales: Caricaceae) plants and effect of two species of predatory mite

ABSTRACTPapaya (Carica papaya L.) is an important crop in all tropical countries including Mexico. Tetranychus merganser Boudreaux was recently detected in Mexico, and represents a potential threat to papaya production. There is little available information on this mite; therefore, research on this species is urgently required. We undertook a series of experiments to assess the effect of different initial densities of T. merganser on the level of leaf damage and photosynthetic activity of papaya; evaluations were made 21, 42 and 63 days after the experiments were initiated. We found that the greatest damage caused by T. merganser occurred after the final sampling time (63 days), regardless of the initial density of T. merganser; there were no differences among treatments in photosynthetic activity or chlorophyll content. We also evaluated how introduction of the generalist mite predators, Amblyseius swirskii Athias-Henriot (Gamasida: Phytoseiidae) or Neoseiulus californicus McGregor (Gamasida: Phytoseiidae), affected the relationship between the level of leaf damage and final densities of T. merganser at the end of the experiment. The introduction of predators resulted in a significant decrease in T. merganser densities. The need for early detection of this pest to reduce damage, and achieve the greatest impact of biological control is discussed.

Current approaches neglect possible agricultural cutback under large-scale organic farming. A comment to Ponisio et al.

Agricultural productivity is the key to global food security. Modern conventional farming has substantially increased food production, but at the expense of serious environmental harm [[1][1]]. By contrast, organic production is regarded as a suitable and more sustainable alternative owing to its

Predator Diet and Trophic Position Modified with Altered Habitat Morphology.

Empirical patterns that emerge from an examination of food webs over gradients of environmental variation can help to predict the implications of anthropogenic disturbance on ecosystems. This “dynamic food web approach” is rarely applied at the coastal margin where aquatic and terrestrial systems are coupled and human development activities are often concentrated. We propose a simple model of ghost crab (Ocypode quadrata) feeding that predicts changing dominant prey (Emerita talpoida, Talorchestia sp., Donax variablis) along a gradient of beach morphology and test this model using a suite of 16 beaches along the Florida, USA coast. Assessment of beaches included quantification of morphological features (width, sediments, slope), macrophyte wrack, macro-invertebrate prey and active ghost crab burrows. Stable isotope analysis of carbon (13C/12C) and nitrogen (15N/14N) and the SIAR mixing model were used to determine dietary composition of ghost crabs at each beach. The variation in habitat conditions displayed with increasing beach width was accompanied by quantifiable shifts in ghost crab diet and trophic position. Patterns of ghost crab diet were consistent with differences recorded across the beach width gradient with respect to the availability of preferred micro-habitats of principal macro-invertebrate prey. Values obtained for trophic position also suggests that the generalist ghost crab assembles and augments its diet in fundamentally different ways as habitat morphology varies across a highly dynamic ecosystem. Our results offer support for a functional response in the trophic architecture of a common food web compartment (ghost crabs, macro-invertebrate prey) across well-known beach morphologies. More importantly, our “dynamic food web approach” serves as a basis for evaluating how globally wide-spread sandy beach ecosystems should respond to a variety of anthropogenic impacts including beach grooming, beach re-nourishment, introduction of non-native or feral predators and human traffic on beaches.

Feeding Ecology and Establishment of the Naturally-Colonized Freshwater Cichlid, &amp;lt;i&amp;gt; Sarotherodon galilaeus &amp;lt;/i&amp;gt; (Pisces: Actinopterigii: Perciformes) from a Man-Made Lake, South-Benin, West Africa

The freshwater cichlid, Sarotherodon galilaeus (Linne, 1758) is an economically and commercially important fisheries species that has naturally colonized and dominated a sand-dragged man-made freshwater lake of Ahozon (South-Benin) where the species made about 85.21% of the fish community. We investigated the feeding ecology of S. galilaeus in order to evaluate resource exploitation and the establishment of this species in Lake Ahozon. During wet, flood and dry seasons, 1189 individuals of S. galilaeus have been monthly sampled in the open water and in the aquatic vegetation habitats. The study showed that S. galilaeus consumed about seventy (70) food items dominated by algae (52.88%) composed of 28 families and 52 genera from blue-green algae, green algae, desmids, and diatoms, sand particles (23.95%), detritus (12.27%) and protozoans (7.68%). Minor preys were rotifers, copepods, cladodera, crustacea and insect parts. Foods items with higher diet occurrence were sand particles with a percentage occurrence of 72.33%, detritus (69.47%), and some algae such as Scenedesmus (58.96%), Closterium (55.68%), and Microcystis (51.30%). Significant (P ≤ 0.05) ontogenetic variations of empty stomachs were recorded. S. galilaeus exhibited a wide diet breadth (DB) ranging between 5.55 and 7.29 that tended to increase with fish sizes. Diet overlaps (Ojk) varied from 0.77 to 0.97, indicating high diet similarities between different life stage categories. The slope b = 0.560 obtained from Log (body weight)-Log (gut length) linear regression, and the mean ratio of GL/SL = 6.72 ± 2.23 support our findings that S. galilaeus exhibited detritivorous, herbivorous and omnivorous food habits. The broad spectrum of food resources consumed/utilized and the high diet breadth recorded leading to allometric growth, the active breeding and the high propagation of the species, were some indicators of the successful establishment of S. galilaeus in the man-made lake of Ahozon. Sustainable fisheries/ aquaculture exploitation of S. galilaeus and successful valorization of the man-made lake of Ahozon require an integrated management of the lake including the prevention of domestic waste dumpings, the protection of the foraging and spawning grounds, the fertilization of the lake, the introduction of predators to control the population of S. galilaeus , the protection of lake margin to avoid erosion, a planned harvest of the fish stock and a periodic ecological monitoring of Lake Ahozon.

Little evidence for morphological change in a resilient endemic species following the introduction of a novel predator.

Human activities, such as species introductions, are dramatically and rapidly altering natural ecological processes and often result in novel selection regimes. To date, we still have a limited understanding of the extent to which such anthropogenic selection may be driving contemporary phenotypic change in natural populations. Here, we test whether the introduction of the piscivorous Nile perch, Lates niloticus, into East Africa's Lake Victoria and nearby lakes coincided with morphological change in one resilient native prey species, the cyprinid fish Rastrineobola argentea. Drawing on prior ecomorphological research, we predicted that this novel predator would select for increased allocation to the caudal region in R.argentea to enhance burst-swimming performance and hence escape ability. To test this prediction, we compared body morphology of R.argentea across space (nine Ugandan lakes differing in Nile perch invasion history) and through time (before and after establishment of Nile perch in Lake Victoria). Spatial comparisons of contemporary populations only partially supported our predictions, with R.argentea from some invaded lakes having larger caudal regions and smaller heads compared to R.argentea from uninvaded lakes. There was no clear evidence of predator-associated change in body shape over time in Lake Victoria. We conclude that R.argentea have not responded to the presence of Nile perch with consistent morphological changes and that other factors are driving observed patterns of body shape variation in R.argentea.

Introduction to the Special Issue: Advances in island plant biology since Sherwin Carlquist's Island Biology.

Sherwin Carlquist's seminal publications-in particular his classic Island Biology, published in 1974-formulated hypotheses specific to island biology that remain valuable today. This special issue brings together some of the most interesting contributions presented at the First Island Biology Symposium hosted in Honolulu on 7-11 July 2014. We compiled a total of 18 contributions that present data from multiple archipelagos across the world and from different disciplines within the plant sciences. In this introductory paper, we first provide a short overview of Carlquist's life and work and then summarize the main findings of the collated papers. A first group of papers deals with issues to which Carlquist notably contributed: long-distance dispersal, adaptive radiation and plant reproductive biology. The findings of such studies demonstrate the extent to which the field has advanced thanks to (i) the increasing availability and richness of island data, covering many taxonomic groups and islands; (ii) new information from the geosciences, phylogenetics and palaeoecology, which allows us a more realistic understanding of the geological and biological development of islands and their biotas; and (iii) the new theoretical and methodological advances that allow us to assess patterns of abundance, diversity and distribution of island biota over large spatial scales. Most other papers in the issue cover a range of topics related to plant conservation on islands, such as causes and consequences of mutualistic disruptions (due to pollinator or disperser losses, introduction of alien predators, etc.). Island biologists are increasingly considering reintroducing ecologically important species to suitable habitats within their historic range and to neighbouring islands with depauperate communities of vertebrate seed dispersers, and an instructive example is given here. Finally, contributions on ecological networks demonstrate the usefulness of this methodological tool to advancing conservation management and better predicting the consequences of disturbances on species and interactions in the fragile insular ecosystems.

Global ecological impacts of invasive species in aquatic ecosystems.

The introduction of invasive species, which often differ functionally from the components of the recipient community, generates ecological impacts that propagate along the food web. This review aims to determine how consistent the impacts of aquatic invasions are across taxa and habitats. To that end, we present a global meta-analysis from 151 publications (733 cases), covering a wide range of invaders (primary producers, filter collectors, omnivores and predators), resident aquatic community components (macrophytes, phytoplankton, zooplankton, benthic invertebrates and fish) and habitats (rivers, lakes and estuaries). Our synthesis suggests a strong negative influence of invasive species on the abundance of aquatic communities, particularly macrophytes, zooplankton and fish. In contrast, there was no general evidence for a decrease in species diversity in invaded habitats, suggesting a time lag between rapid abundance changes and local extinctions. Invaded habitats showed increased water turbidity, nitrogen and organic matter concentration, which are related to the capacity of invaders to transform habitats and increase eutrophication. The expansion of invasive macrophytes caused the largest decrease in fish abundance, the filtering activity of filter collectors depleted planktonic communities, omnivores (including both facultative and obligate herbivores) were responsible for the greatest decline in macrophyte abundance, and benthic invertebrates were most negatively affected by the introduction of new predators. These impacts were relatively consistent across habitats and experimental approaches. Based on our results, we propose a framework of positive and negative links between invasive species at four trophic positions and the five different components of recipient communities. This framework incorporates both direct biotic interactions (predation, competition, grazing) and indirect changes to the water physicochemical conditions mediated by invaders (habitat alteration). Considering the strong trophic links that characterize aquatic ecosystems, this framework is relevant to anticipate the far-reaching consequences of biological invasions on the structure and functionality of aquatic ecosystems.

Exotic Mammals and Invasive Plants Alter Fire-Related Thresholds in Southern Temperate Forested Landscapes

Human activity has resulted in the emergence of fire-induced forest-shrubland mosaics in many southern temperate forest landscapes. In New Zealand (NZ), this transformation was caused by the introduction of fire to previously very low fire-frequency ecosystems. High levels of seed and seedling predation by exotic mammals and the reduction of avian pollination and seed dispersal further influence vegetation change and can cause successions to become completely arrested. Analogous dynamics occur in many other Southern Hemisphere forest landscapes where changes in fire regimes and the introduction of mammalian herbivores and predators have resulted in forest-shrubland mosaics. We developed a spatially explicit state-and-transition model to disentangle the effects of altered fire regimes; invasive pyrophyllic shrub species; seed and seedling predation by exotic mammals; and lowered rates of long-distance seed movement on long-term landscape dynamics and state transitions. Our modelling highlights a threshold in fire frequency where forest systems move to a fire-induced early-successional shrubland state. Because early-successional vegetation in NZ and many other southern temperate forests is much more flammable than mature late-successional vegetation, this shrubland state will persist until fire is suppressed. Our modelling suggests also that in the absence of fire there are critical thresholds in seed predation beyond which succession may become completely arrested in a mid-successional state. Even moderate levels of predation slow regeneration and move the tipping point at which forests shift to early-successional shrublands in the direction of less frequent fire. The presence of invasive pyrophyllic shrubs in the landscape also influences the location of thresholds in fire frequency at which state shifts occur. Restoring these landscapes to their formerly forested condition will require the removal of fire as well as mammalian seed/ling predators and the reinstatement of pollination and dispersal services. Removal of seed predators may act as an effective component of fire control by allowing secondary successions to proceed more quickly, thereby reducing landscape-level flammability.

Sail or sink: novel behavioural adaptations on water in aerially dispersing species.

BackgroundLong-distance dispersal events have the potential to shape species distributions and ecosystem diversity over large spatial scales, and to influence processes such as population persistence and the pace and scale of invasion. How such dispersal strategies have evolved and are maintained within species is, however, often unclear. We have studied long-distance dispersal in a range of pest-controlling terrestrial spiders that are important predators within agricultural ecosystems. These species persist in heterogeneous environments through their ability to re-colonise vacant habitat by repeated long-distance aerial dispersal (“ballooning”) using spun silk lines. Individuals are strictly terrestrial, are not thought to tolerate landing on water, and have no control over where they land once airborne. Their tendency to spread via aerial dispersal has thus been thought to be limited by the costs of encountering water, which is a frequent hazard in the landscape.ResultsIn our study we find that ballooning in a subset of individuals from two groups of widely-distributed and phylogenetically distinct terrestrial spiders (linyphiids and one tetragnathid) is associated with a hitherto undescribed ability of those same individuals to survive encounters with both fresh and marine water. Individuals that showed a high tendency to adopt ‘ballooning’ behaviour adopted elaborate postures to seemingly take advantage of the wind current whilst on the water surface.ConclusionsThe ability of individuals capable of long-distance aerial dispersal to survive encounters with water allows them to disperse repeatedly, thereby increasing the pace and spatial scale over which they can spread and subsequently exert an influence on the ecosystems into which they migrate. The potential for genetic connectivity between populations, which can influence the rate of localized adaptation, thus exists over much larger geographic scales than previously thought. Newly available habitat may be particularly influenced given the degree of ecosystem disturbance that is known to follow new predator introductions.

Genetic Divergence among Regions Containing the Vulnerable Great Desert Skink (Liopholis kintorei) in the Australian Arid Zone.

Knowledge of genetic structure and patterns of connectivity is valuable for implementation of effective conservation management. The arid zone of Australia contains a rich biodiversity, however this has come under threat due to activities such as altered fire regimes, grazing and the introduction of feral herbivores and predators. Suitable habitats for many species can be separated by vast distances, and despite an apparent lack of current geographical barriers to dispersal, habitat specialisation, which is exhibited by many desert species, may limit connectivity throughout this expansive region. We characterised the genetic structure and differentiation of the great desert skink (Liopholis kintorei), which has a patchy, but widespread distribution in the western region of the Australian arid zone. As a species of cultural importance to local Aboriginal groups and nationally listed as Vulnerable, it is a conservation priority for numerous land managers in central Australia. Analysis of mitochondrial ND4 sequence data and ten nuclear microsatellite loci across six sampling localities through the distribution of L. kintorei revealed considerable differentiation among sites, with mitochondrial FST and microsatellite F′ST ranging from 0.047-0.938 and 0.257-0.440, respectively. The extent of differentiation suggests three main regions that should be managed separately, in particular the southeastern locality of Uluru. Current genetic delineation of these regions should be maintained if future intervention such as translocation or captive breeding is to be undertaken.

Traits influencing range contraction in New Zealand's endemic forest birds.

Understanding vulnerability of endemic taxa to predation is clearly important for conservation management. In New Zealand, predation by introduced mammals such as rats and mustelids is widely recognized as the primary factor responsible for declines of indigenous fauna. The aim of our study was to evaluate the vulnerability of New Zealand's surviving endemic forest bird species to impacts of introduced mammalian predators, and identify key life history attributes underlying this vulnerability. We measured range contraction following the introduction of exotic mammalian predators for 23 endemic forest bird species using information on both pre-human and current distributions. We used Bayesian modeling techniques to analyze whether variation in range contraction was associated with life history traits potentially influencing species' predation vulnerability, while accounting for phylogenetic relatedness. Our results showed that the extent of range contraction varied greatly among species, with some species remaining in available forest habitat throughout most of their pre-human range, and others having disappeared completely from the main islands. Cavity nesting was the key trait associated with more extensive range decline, suggesting that cavity-nesting species are more vulnerable to predation than species that nest in more open sites.

Re‐colonization by common eiders Somateria mollissima in the Aleutian Archipelago following removal of introduced arctic foxes Vulpes lagopus

Islands provide refuges for populations of many species where they find safety from predators, but the introduction of predators frequently results in elimination or dramatic reductions in island‐dwelling organisms. When predators are removed, re‐colonization for some species occurs naturally, and inter‐island phylogeographic relationships and current movement patterns can illuminate processes of colonization. We studied a case of re‐colonization of common eiders Somateria mollissima following removal of introduced arctic foxes Vulpes lagopus in the Aleutian Archipelago, Alaska. We expected common eiders to resume nesting on islands cleared of foxes and to re‐colonize from nearby islets, islands, and island groups. We thus expected common eiders to show limited genetic structure indicative of extensive mixing among island populations. Satellite telemetry was used to record current movement patterns of female common eiders from six islands across three island groups. We collected genetic data from these and other nesting common eiders at 14 microsatellite loci and the mitochondrial DNA control region to examine population genetic structure, historical fluctuations in population demography, and gene flow. Our results suggest recent interchange among islands. Analysis of microsatellite data supports satellite telemetry data of increased dispersal of common eiders to nearby areas and little between island groups. Although evidence from mtDNA is suggestive of female dispersal among island groups, gene flow is insufficient to account for recolonization and rapid population growth. Instead, near‐by remnant populations of common eiders contributed substantially to population expansion, without which re‐colonization would have likely occurred at a much lower rate. Genetic and morphometric data of common eiders within one island group two and three decades after re‐colonization suggests reduced movement of eiders among islands and little movement between island groups after populations were re‐established. We predict that re‐colonization of an island group where all common eiders are extirpated could take decades.

A call for applying trophic structure in ecological restoration

Ecological restoration projects have traditionally focused on vegetation as both a means (seeding, planting, and substrate amendments) and ends (success based upon primary productivity and vegetation diversity). This vegetation‐centric approach to ecological restoration stems from an historic emphasis on esthetics and cost but provides a limited measure of total ecosystem functioning and overlooks alternative ways to achieve current and future restoration targets. We advocate a shift to planning beyond the plant community and toward the physical and biological components necessary to initiate autogenic recovery, then guiding this process through the timely introduction of top predators and environmental modifications such as soil amendments and physical structures for animal nesting and refugia.

Big maggots dig deeper: size-dependent larval dispersal in flies.

The ability of individual animals to select habitats optimal for development and survival can be constrained by the costs of moving through the environment. Animals that seek overwintering sites underground, for example, may be constrained by the energy required to burrow into the soil. We conducted field and laboratory studies to determine the relationship between individual size and overwintering site selection in the tephritid flies, Rhagoletis juglandis and Rhagoletis suavis. We also explored the effect of site selection on pupal mortality, parasitism, and the ability to emerge from overwintering sites after eclosion. In both species, and in both lab and field tests, larger pupae were found at deeper soil depths. In addition, marginally non-significant trends indicated pupae in deeper sites were 48% more likely to survive the overwintering period. Finally, larger individuals were more likely to eclose and emerge from the soil at a given depth, but flies in deep overwintering sites were less likely to emerge from those sites than flies in shallow sites. Our data indicate that overwintering site selection represents a trade-off between avoiding predators and parasites that occur at shallow sites, and the energetic and mortality costs of burrowing to, overwintering in, and emerging from, deeper sites. The size-dependent overwintering site selection demonstrated here has implications for population dynamics and pest control strategies. Some fly control measures, such as the introduction of parasites or predators, will be mitigated when the deepest and least accessible overwintering pupae represent a disproportionately large amount of the population's reproductive capacity.

Interplay of Functional Responses and Weak Allee Effect on Pest Control via Viral Infection or Natural Predator: An Eco-epidemiological Study

We propose and analyze a deterministic eco-epidemiological system where the susceptible pest exhibits a weak Allee effect due to mating limitation. We make the following assumptions: (i) Allee effect is built in the reproduction process of susceptible pest where infected pest has no contribution; and (ii) growth rate of natural predator is negative for consuming infected pest. We also assume that the functional response of predator for susceptible pest is linear, hyperbolic, or sigmoidal, whereas for infected pest is linear, as infected pest are weakened and easy to catch. We study the dynamics of the system around each of the ecological feasible equilibrium and observe some interesting features of the system dynamics. The reduction of disease eradication, and predator–pest coexistence are observed around the predator free and disease free equilibrium respectively. It is also observed that the interior equilibrium is always unstable and the result is true for any choice of functional responses. Our results suggest that introduction of predator or natural enemies with sigmoidal functional response is a good candidate to represent disease eradication.

A novel bacterial pathogen of Biomphalaria glabrata: a potential weapon for schistosomiasis control?

BackgroundSchistosomiasis is the second-most widespread tropical parasitic disease after malaria. Various research strategies and treatment programs for achieving the objective of eradicating schistosomiasis within a decade have been recommended and supported by the World Health Organization. One of these approaches is based on the control of snail vectors in endemic areas. Previous field studies have shown that competitor or predator introduction can reduce snail numbers, but no systematic investigation has ever been conducted to identify snail microbial pathogens and evaluate their molluscicidal effects.Methodology/Principal findingsIn populations of Biomphalaria glabrata snails experiencing high mortalities, white nodules were visible on snail bodies. Infectious agents were isolated from such nodules. Only one type of bacteria, identified as a new species of Paenibacillus named Candidatus Paenibacillus glabratella, was found, and was shown to be closely related to P. alvei through 16S and Rpob DNA analysis. Histopathological examination showed extensive bacterial infiltration leading to overall tissue disorganization. Exposure of healthy snails to Paenibacillus-infected snails caused massive mortality. Moreover, eggs laid by infected snails were also infected, decreasing hatching but without apparent effects on spawning. Embryonic lethality was correlated with the presence of pathogenic bacteria in eggs.Conclusions/SignificanceThis is the first account of a novel Paenibacillus strain, Ca. Paenibacillus glabratella, as a snail microbial pathogen. Since this strain affects both adult and embryonic stages and causes significant mortality, it may hold promise as a biocontrol agent to limit schistosomiasis transmission in the field.