Weathering the storm: how lodgepole pine trees survive mountain pine beetle outbreaks

Climate change leads to phenology shifts of many species. However, not all species shift in parallel, which can desynchronize interspecific interactions. Within trophic cascades, herbivores can be top–down controlled by predators or bottom–up controlled by host plant quality and host symbionts, such as plant-associated micro-organisms. Synchronization of trophic levels is required to prevent insect herbivore (pest) outbreaks. In a common garden experiment, we simulated an earlier arrival time (~2 weeks) of the aphid Rhopalosiphum padi on its host grass Lolium perenne by enhancing the aphid abundance during the colonization period. L. perenne was either uninfected or infected with the endophytic fungus Epichloë festucae var. lolii. The plant symbiotic fungus produces insect deterring alkaloids within the host grass. Throughout the season, we tested the effects of enhanced aphid abundance in spring on aphid predators (top–down) and grass–endophyte (bottom–up) responses. Higher aphid population sizes earlier in the season lead to overall higher aphid abundances, as predator occurrence was independent of aphid abundances on the pots. Nonetheless, after predator occurrence, aphids were controlled within 2 weeks on all pots. Possible bottom–up control of aphids by increased endophyte concentrations occurred time delayed after high herbivore abundances. Endophyte-derived alkaloid concentrations were not significantly affected by enhanced aphid abundance but increased throughout the season. We conclude that phenology shifts in an herbivorous species can desynchronize predator–prey and plant–microorganism interactions and might enhance the probability of pest outbreaks with climate change.     

Colonization and usage of eight milkweed (<Emphasis Type="Italic">Asclepias</Emphasis>) species by monarch butterflies and bees in urban garden settings

Planting milkweeds on public and private lands has emerged as a central conservation strategy for restoring declining North American migratory populations of the monarch butterfly (Danaus plexippus). Nearly all actionable science on this issue has focused on restoring common milkweed (Asclepias syriaca L.) in rural land types. The aim of this study was to develop recommendations for the best milkweeds for managed gardens intended to support both monarch butterflies and bees. Eight milkweed (Asclepias) species varying in height, form, and leaf shape were grown in a common-garden experiment at a public arboretum. We measured milkweed growth, tillering, and bloom periods, conducted bi-weekly counts of eggs and larvae to assess colonization by wild monarchs, and evaluated suitability for growth of monarch larvae. We also quantified bee visitation and compared the bee assemblages associated with six of the eight species, augmented with additional collections from other sites. Monarchs rapidly colonized the gardens, but did not equally use all of the milkweed species. More eggs and larvae were found on taller, broad-leaved milkweeds, but there was relatively little difference in larval performance, suggesting ovipositional preference for more apparent plants. Asclepias tuberosa and A. fascicularis attracted the greatest number of bees, whereas bee genus diversity was greatest on A. verticillata, A. fascicularis, and A. tuberosa. Milkweeds that do not spread extensively by tillering may be best suited for managed gardens. Combining milkweeds that are preferred by ovipositing monarchs with ones that are particularly attractive to bees may enhance conservation value of small urban gardens.     

Potential for exploitative competition,not intraguild predation,between invasive harlequin ladybirds and flowerbugs in urban parks

In aphidophagous insect communities invaded by the harlequin ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae), intraguild predation (IGP) is widely implicated in the displacement of native predators, however, indirect trophic interactions are rarely assessed. Using molecular gut-content analysis, we investigated the relative frequencies of IGP by H. axyridis on the predatory flowerbug Anthocoris nemoralis Fabricius (Heteroptera: Anthocoridae) and prey overlap for a shared prey, the lime aphid Eucallipterus tiliae L. (Hemiptera: Aphididae), in Tilia × europaea crowns in urban parks. The frequency of IGP by H. axyridis was low: 2.7 % of larvae and 3.4 % of adults tested positive for A. nemoralis DNA. The presence of lime aphid DNA in predators was higher: 56.5 and 47.9 % of H. axyridis larvae and adults, respectively, contained E. tiliae DNA, whereas 60.8 % of adult A. nemoralis tested positive for aphid DNA. Incorporating insect densities revealed that the density of H. axyridis larvae had a strong negative effect on the likelihood of detecting aphid DNA in A. nemoralis. Prey overlap for E. tiliae was widespread in space (2–13 m height in tree crowns) and time (May–October 2011) which suggests that interspecific exploitative competition, mediated by predator life-stage, more so than IGP, is an important indirect trophic interaction between co-occurring H. axyridis and A. nemoralis. Whether exploitative competition equates to displacement of A. nemoralis populations requires further investigation. Our results emphasize the need to incorporate indirect interactions in studies of insect communities following invasion, not least because they potentially affect more species than direct interactions alone.     

Fish invasion alters ecosystem function in a small heterotrophic stream

The strength of trophic cascade effects in aquatic ecosystems depend, in part, on the identity of the top predator involved. We examined whether an invasive benthic fish (round goby, Neogobius melanostomus) altered the strength of cascade effects in a heterotrophic stream and in a controlled mesocosm experiment relative to the effects of a functionally similar, native fish. In the stream, the introduced fish had a direct effect on grazer and shredder abundance which led to a significant increase in periphyton chlorophyll a, a significant reduction in leaf breakdown rate, an increase in leaf biomass remaining, but no change in periphyton ash-free dry mass. In mesocosms, native and introduced fish similarly reduced shredder abundance, but this did not lead to an indirect effect on leaf breakdown rates or biomass remaining at the end of the experiment. Indirect effects of introduced fish on periphyton biomass and chlorophyll a in mesocosms were both significant and were stronger than in the field, but were the result of grazer behavioral modification and not reduced grazer abundance. Collectively, these results suggest non-native fish have the ability to initiate trophic cascades in heterotrophic streams, and that both fish identity and environmental context are important in determining the strength of cascades.     

Herbivore population suppression by an intermediate predator, <Emphasis Type="Italic">Phytoseiulus macropilis</Emphasis>, is insensitive to the presence of an intraguild predator: an advantage of small body size?

Recent work in terrestrial communities has highlighted a new question: what makes a predator act as a consumer of herbivores versus acting as a consumer of other predators? Here we test three predictions from a model (Rosenheim and Corbett in Ecology 84:2538–2548) that links predator foraging behavior with predator ecology: (1) widely foraging predators have the potential to suppress populations of sedentary herbivores; (2) sit and wait predators are unlikely to suppress populations of sedentary herbivores; and (3) sit and wait predators may act as top predators, suppressing populations of widely foraging intermediate predators and thereby releasing sedentary herbivore populations from control. Manipulative field experiments conducted with the arthropod community found on papaya, Carica papaya, provided support for the first two predictions: (1) the widely foraging predatory mite Phytoseiulus macropilis strongly suppressed populations of a sedentary herbivore, the spider mite Tetranychus cinnabarinus, whereas (2) the tangle-web spider Nesticodes rufipes, a classic sit and wait predator, failed to suppress Tetranychus population growth rates. However, our experiments provided no support for the third hypothesis; the sit and wait predator Nesticodes did not disrupt the suppression of Tetranychus populations by Phytoseiulus. This contrasts with an earlier study that demonstrated that Nesticodes can disrupt control of Tetranychus generated by another widely foraging predator, Stethorus siphonulus. Behavioral observations suggested a simple explanation for the differing sensitivity of Phytoseiulus and Stethorus to Nesticodes predation. Phytoseiulus is a much smaller predator than Stethorus, has a lower rate of prey consumption, and thus has a much smaller requirement to forage across the leaf surface for prey, thereby reducing its probability of encountering Nesticodes webs. Small body size may be a general means by which widely foraging intermediate predators can ameliorate their risk of predation by sit and wait top predators. This effect may partially or fully offset the general expectation from size-structured trophic interactions that smaller predators are subject to more intense intraguild predation.     

Suitability of Different Prey Aphids on the Growth,Development and Reproduction of <Emphasis Type="Italic">Chrysoperla zastrowi sillemi</Emphasis> (Esben-Petersen) (Chrysopidae: Neuroptera)

The prey preference of polyphagous predator, green lacewing (Chrysoperla zastrowi sillemi (Esben-Petersen)) was evaluated against five prey aphids viz., mustard aphid (Lipaphis erysimi), green peach aphid (Myzus persicae), cabbage aphid (Brevicorynebrassicae), black bean aphid (Aphis craccivora), spirea aphid (Aphis spiraecola) of agriculture importance and compared with eggs of Corcyracephalonica (Stainton). Lacewing larvae preferred Myzus persicae most followed by Brevicorynebrassicae. The highest growth index (8.31), larval survival (94.50 %), larval weight (10.45 mg), pupal weight (8.78 mg), faster multiplication rate (0.051) and fecundity (183.4 per gravid female) of the predator were recorded on M. persicae. However, the chrysopid reared on Corcyra eggs performed best in all biological parameters and fitness, than on aphid preys. This study explores the possibilities of selecting the most suitable prey aphid species for its exploitation as supplement for mass multiplication of chrysopid during off-season or unavailability of Corcyra eggs.     

Elevated temperature and periodic water stress alter growth and quality of common milkweed (<Emphasis Type="Italic">Asclepias syriaca</Emphasis>) and monarch (<Emphasis Type="Italic">Danaus plexippus</Emphasis>) larval performance

In this study, we examined the independent and interactive effects of temperature and water availability on the growth and foliar traits of common milkweed (Asclepias syriaca) and performance of a specialist herbivore, larvae of the monarch butterfly (Danaus plexippus). Milkweed from multiple population sources collected across a latitudinal gradient in Wisconsin, USA, were grown under all combinations of ambient or elevated temperature and the presence or absence of periodic water stress. Elevated temperature marginally increased, while water stress decreased plant growth. Milkweed from more northerly latitudes experienced larger growth responses to elevated temperature and were more resistant to water stress, especially under higher temperatures. Elevated temperature and water stress also altered milkweed composite foliar trait profiles. Elevated temperature generally increased leaf nitrogen and structural compounds, and decreased leaf mass per area. Water stress also elevated foliar nitrogen, but reduced defensive traits. Monarch larvae performed well on milkweed under elevated temperature and water stress, but gained the most mass on plants exposed to both treatments in combination. Our findings suggest that milkweed populations from more northerly latitudes in the upper Midwest may benefit more from rising temperatures than those in southerly locations, but that these beneficial effects depend on water availability. Monarch larvae grew larger on plants from all experimental treatments relative to ambient condition controls, indicating that future changes in milkweed presence on the landscape will likely influence monarch populations more than the effects of future changes in plant quality on larval performance.     

Natural enemy composition rather than richness determines pest suppression

Natural enemy (NE) biodiversity is thought to play an important role in agricultural pest suppression. However, the relative importance of the number of NE species (species richness), versus the particular combinations of species (species composition), in determining aphid suppression and ultimately crop yields, remains poorly understood. We tested the effects of NE richness and composition on pea aphids Acyrthosiphon pisum (Harris) and broad bean plants Vicia faba (Linn.). We used the larvae of two predator species, the ladybird Adalia bipunctata (Linn.) and the green lacewing Chrysopa carnea (Stephens), and the parasitic wasp Aphidius ervi (Haliday) as enemies. NEs generally reduced aphid density but did not increase final plant biomass, despite a significant negative correlation between aphid density and plant biomass. Among NE treatments, species richness had an inconsistent effect on aphid density. The composition of NEs within richness levels also affected final aphid density: the ladybird was a key species among the treatments in controlling aphid density and was especially effective in combination with the parasitoid. This ladybird/parasitoid combination also appeared to drive the higher level of suppression observed at the two, relative to three, species richness levels. Although these three species of aphid NEs are commonly used in aphid control, this is the first study, to our knowledge, that simultaneously examined these three species and highlighted the composition effect between the A. bipunctata and A. ervi. In conclusion, increasing NE species richness had an inconsistent effect on aphid density. Meanwhile, the presence of a key species (the ladybird) and its combination with a parasitoid was an important determinant of aphid biological control.     

Genetic structure of the populations of <Emphasis Type="Italic">Dactylorhiza ochroleuca</Emphasis> and <Emphasis Type="Italic">D. incarnata</Emphasis> (Orchidaceae) in the area of their joint growth in Russia and Belarus

We carried out an allozyme analysis to investigate polymorphism and genetic structure of the populations of D. incarnata and D. ochroleuca in regions of their joint growth in Russia and Belarus. We found that D. ochroleuca individuals in the populations of the Urals and Siberia, which are distant fragments from the main range of the species, do not differ significantly from individuals within the main part of the area (Belarus) on the basis of the allelic composition of eight gene loci. We revealed that D. ochroleuca and D. incarnata are differentiated by different alleles of the GDH locus. Thus, we established a genetic marker suitable to distinguish these closely related taxa. In addition to the GDH locus, D. ochroleuca and D. incarnata in the places of their joint growth, differ in the allelic structure of the PGI and NADHD loci. D. incarnata from the Urals and Siberia were polymorphic for both loci, and individuals from Belarus were polymorphic for one locus (PGI). In contrast, all D. ochroleuca individuals growing in sympatric populations with polymorphic D. incarnata were homozygous for the same alleles. Thus, comparison of the genetic structure of D. ochroleuca and D. incarnata points to the existence of a genetic isolation and a functioning isolation mechanism even under conditions of their joint growth. We found that the GDH locus in D. incarnata is polymorphic only in populations which grow together with D. ochroleuca, with exception a few examples. Thus, we conclude that variability of the GDH locus in D. incarnata is associated with hybridization with D. ochroleuca.     

Examination of dogbane beetle (<Emphasis Type="Italic">Chrysochus auratus</Emphasis>) feeding and phenology on spreading dogbane,and considerations for biological control

We carried out experiments that considered the feeding, phenology, and biocontrol potential of dogbane beetle, Chrysochus auratus, on spreading dogbane, Apocynum androsaemifolium, a native perennial weed in lowbush blueberry (Vaccinium angustifolium). In no-choice host-feeding experiments, adult beetles did not feed upon common milkweed (Asclepias syriaca), periwinkle (Vinca minor), wild raisin (Viburnum cassenoides), and lowbush blueberry, all plants related to spreading dogbane or found around lowbush blueberry fields. In a field experiment, significant decreases in spreading dogbane total and foliar weight occurred at a density of 16 beetles per ramet, but not at lower beetle densities. In our Nova Scotia (NS) field sites, beetles were present for 8–12 weeks, beginning in late June or early July (225–335 growing degree days, GDD). Beetle abundance peaked at 4–7 beetles/m² and occurred at 357–577 GDD, which temporally coincides with the incidence of mature spreading dogbane plants in the field. The results suggest that although inundations of C. auratus could cause significant defoliation of spreading dogbane, natural populations of the beetle probably could not satisfactorily suppress development of this weed as a stand-alone control tactic. Conservation and augmentation of C. auratus populations should nonetheless be encouraged in integrated management programs for spreading dogbane.     

A mixture of herbivore-induced plant volatiles from multiple host plant species enhances the attraction of a predatory bug under field-cage conditions

Plants respond to herbivore attack by emitting a blend of volatiles called herbivore-induced plant volatiles (HIPVs), which attract arthropod natural enemies. Under natural conditions and multiple cropping agriculture systems, natural enemies are thought to encounter a mixture of HIPVs emanating from multiple plant species. The effect of such a mixture of HIPVs on the responses of natural enemies under field conditions has not been explored. Our study assessed whether a mixture of HIPVs from multiple host plant species influenced predator responses in field-cage conditions. We investigated (1) foraging behaviors of a predatory bug, Orius strigicollis, on cotton bollworm (Helicoverpa armigera) larvae-infested multiple host plant species, and (2) the attractiveness of a mixture of reconstituted HIPVs from multiple plant species to O. strigicollis in outdoor cages. Significantly, greater numbers of predators were attracted to H. armigera-infested multiple plant species. The predators exterminated significantly greater numbers of H. armigera larvae with the multiple versus single plant species treatments. Significantly, greater numbers of O. strigicollis were captured on traps baited with the mixture of reconstituted HIPVs from multiple versus single plant species. The enhanced attractiveness of a mixture of HIPVs from multiple plant species to O. strigicollis might be the result of an additive effect of HIPVs from the three plant species when combined in a mixture.     

Functional convergence and phenotypic divergence in two specialist species of pine-associated ladybirds

Traditionally, convergent evolution has been considered to produce phenotypic similarity in independently evolved species. By contrast, recent studies have detected morphological divergence between species even in similar selective environments when different morphological traits combine to produce a specific functional output. However, it is still unclear whether a complex combination of non-morphological phenotypic traits, such as behavioural and life-history traits, can produce a similar performance in different species. In this study, I examined prey capture performance and related phenotypes in two sympatric ladybird species, Sospita oblongoguttata and Harmonia yedoensis, which specialize on the giant pine aphid, which is known to be elusive for ladybird hatchlings. In particular, I focused on egg size and proportion of trophic eggs in the clutch, since the amount of maternal investment per offspring can contribute to prey capture performance of ladybird hatchlings. Predation success of hatchlings against the giant pine aphid was higher in both S. oblongoguttata and H. yedoensis than in Harmonia axyridis, a generalist ladybird species that feeds on various kinds of aphid species in nature. Sospita oblongoguttata females, however, produced relatively larger eggs and in most clutches provided no trophic eggs, whereas H. yedoensis females produced smaller eggs and provided more trophic eggs per clutch. Moreover, hatchling morphology in H. yedoensis more closely resembled that of its congener, H. axyridis, than that of the more distantly related S. oblongoguttata, although like H. yedoensis, S. oblongoguttata predates on the elusive pine aphid. These results in two pine-associated specialist ladybirds indicate that divergent phenotypes can nonetheless have similar prey capture performance. In conclusion, this work demonstrates that the general ultimate function can be achieved by various mechanisms through convergence that operates at different level of life.     

Responses of a predatory bug to a mixture of herbivore-induced plant volatiles from multiple plant species

The attractiveness of herbivore-induced plant volatiles (HIPVs) from a specific plant species to natural enemies has been well established. However, under natural conditions and polycultural agriculture systems, the interactions among trophic levels are thought to be more complex. For instance, complex mixtures of volatiles emitted from diverse host plant species infested by polyphagous herbivores might affect responses of natural enemies. In this study, we investigated whether a mixture of HIPVs emitted from herbivore-damaged multiple host plant species affect responses of a predatory bug. Therefore, we report (1) olfactory responses of the predatory bug (Orius strigicollis) to volatiles emitted from cotton bollworm (Helicoverpa armigera) first instar larvae-damaged multiple plant species (tomato, French bean and sweet corn), (2) chemical analyses of volatiles emitted from the three plant species exposed to different treatments and (3) olfactory responses of the predators to a reconstituted HIPV blend from multiple plant species based on chemical analyses. O. strigicollis significantly preferred volatiles emanating from H. armigera-damaged multiple plant species to volatiles emanating from a single plant species. In all the three plant species, H. armigera-damaged seedlings emitted significantly a greater amount of volatiles as well as a larger number of volatile compounds than an undamaged or a mechanically injured seedling. The predators preferred the reconstituted HIPVs from multiple plant species to the reconstituted HIPVs from a single plant species. Thus, the mixture of HIPVs from multiple plant species enhanced the attractiveness to the predators.     

Genetic structure of populations and natural hybridization between <Emphasis Type="Italic">Dactylorhiza salina</Emphasis> and <Emphasis Type="Italic">D. incarnata</Emphasis> (Orchidaceae)

The results of studying the polymorphism and genetic structure of populations of D. salina and D. incarnata growing in Zabaykalsky krai and Buryatia are represented according to the data of allozyme analysis of eight genetic loci (PGI, NADHD, SKDH, GDH, PGM, DIA, ADH, and IDH). The specificity of the allelic structure of loci SKDH, PGM, and IDH is established, for which D. salina and D. incarnata reliably differ from each other. It is shown that interspecies introgressive hybrid complexes with different genetic structures were formed in Transbaikalia. Places of mass growth of D. incarnata were observed to have single plants of D. salina, the interspecies hybrids of the first and subsequent generations. Places of mass growth of D. salina were observed to contain only the hybrids that are not hybrids of the first generation. They were heterozygous not for three loci with differentiating alleles of both parents, SKDH, PGM, and IDH, but for only one of them. The degree of genetic differentiation among five populations of D. salina was on average 7.5% and that of D. incarnata was 7.1%, which in accordance with Wright’s estimation relates to mean values. The average value of FST for all studied populations of the two related species of the genus Dactylorhiza was 0.478, indicating a very high degree of genetic differentiation between D. salina and D. incarnata growing in Transbaikalia. The greatest differences between the species are for the allelic structure of loci SKDH, PGM, and IDH (FST was equal to 0.705, 0.976, and 0.762, respectively). Analysis of molecular variance (AMOVA) showed that populations of D. salina and D. incarnata in the zone where their ranges in Zabaykalsky krai and Buryatya overlap have essential differences both for the variation of alleles frequencies of eight loci (71%, d.f. = 9) and for the variability of genotypes (61%, d.f. = 9). Despite the fact that D. salina and D. incarnata explicitly share a gene flow as a result of interspecies hybridization, the genetic differentiation of populations of these related species remains at a high level.     

Biotic resistance of impact: a native predator (<Emphasis Type="Italic">Chaoborus</Emphasis>) influences the impact of an invasive predator (<Emphasis Type="Italic">Bythotrephes</Emphasis>) in temperate lakes

Introduced predators have caused some of the largest documented impacts of non-native species. Interactions among predators can have complex effects, leading to both synergistic and antagonistic outcomes. Complex interactions with native predators could play an important role in mediating the impact of non-native predators. We explore the role of the native predator context on the effect of the introduced predatory cladoceran Bythotrephes longimanus. While post-invasion impacts have been well described, studies have largely ignored the role of native predators. We used a field mesocosm experiment to determine whether Bythotrephes’ impact on prey communities is influenced by the presence of the ubiquitous native predatory insect larvae Chaoborus. The two predators exhibited niche complementarity as no change in total zooplankton prey abundance was detected across predator treatments. Rather, copepod abundances increased with decreasing abundances of Chaoborus, while cladocerans decreased with increasing abundances of Bythotrephes. Thus, the replacement of Chaoborus with Bythotrephes led to changes in the overall community structure of the zooplankton prey, but had little effect on prey total abundance. More interestingly, we found evidence of biotic resistance of impact, that is, the impact of Bythotrephes on the cladoceran community was altered when the two predators co-occurred. Specifically, the predation effect of Bythotrephes was more restricted to the shallower regions of the water column in the presence of Chaoborus, leading to a reduced impact on deeper dwelling prey taxa. Overall, our results demonstrate that the native predator context is important when trying to understand the effect of non-native predators and that variation in native predator abundances and assemblages could explain variation in impact across invaded habitats.     

Network topology of stable isotope interactions in a sub-arctic raptor guild

Predation is an ecologically important process, and intra-guild interactions may substantially influence the ecological effects of predator species. Despite a rapid expansion in the use of mathematical graph theory to describe trophic relations, network approaches have rarely been used to study interactions within predator assemblages. Assemblages of diurnal raptors are subject to substantial intra- and interspecific competition. Here we used the novel approach of applying analyzes based on network topology to species-specific data on the stable isotopes ¹³C and ¹⁵N in feathers to evaluate patterns of relative resource utilization within a guild of diurnal raptors in northern Sweden. Our guild consisted of the golden eagle (Aquila chrysaetos), the gyrfalcon (Falco rusticolus), the peregrine falcon (Falco peregrinus) and the rough-legged buzzard (Buteo lagopus). We found a modular trophic interaction structure within the guild, but the interactions were less nested than expected by chance. These results suggest low redundancy and hence a strong ecological importance of individual species. Our data also suggested that species were less connected through intra-guild interactions than expected by chance. We interpret our results as a convergence on specific isotope niches, and that body size and different hunting behaviour may mediate competition within these niches. We finally highlight that generalist predators could be ecologically important by linking specialist predator species with disparate dietary niches.     

Persistence in Stochastic Lotka–Volterra Food Chains with Intraspecific Competition

This paper is devoted to the analysis of a simple Lotka–Volterra food chain evolving in a stochastic environment. It can be seen as the companion paper of Hening and Nguyen (J Math Biol 76:697–754, 2018b) where we have characterized the persistence and extinction of such a food chain under the assumption that there is no intraspecific competition among predators. In the current paper, we focus on the case when all the species experience intracompetition. The food chain we analyze consists of one prey and \(n-1\) predators. The jth predator eats the \(j-1\)st species and is eaten by the \(j+1\)st predator; this way each species only interacts with at most two other species—the ones that are immediately above or below it in the trophic chain. We show that one can classify, based on the invasion rates of the predators (which we can determine from the interaction coefficients of the system via an algorithm), which species go extinct and which converge to their unique invariant probability measure. We obtain stronger results than in the case with no intraspecific competition because in this setting we can make use of the general results of Hening and Nguyen (Ann Appl Probab 28:1893–1942, 2018a). Unlike most of the results available in the literature, we provide an in-depth analysis for both non-degenerate and degenerate noise. We exhibit our general results by analyzing trophic cascades in a plant–herbivore–predator system and providing persistence/extinction criteria for food chains of length \(n\le 4\).     

Multitrophic interactions mediate the effects of climate change on herbivore abundance

Climate change can influence the abundance of insect herbivores through direct and indirect mechanisms. In this study, we evaluated multitrophic drivers of herbivore abundance for an aphid species (Aphis helianthi) in a subalpine food web consisting of a host plant (Ligusticum porteri), mutualist ants and predatory lygus bugs (Lygus spp.). We used a model-selection approach to determine which climate and host plant cues best predict year-to-year variation in insect phenology and abundance observed over 6 years. We complemented this observational study with experiments that determined how elevated temperature interacts with (1) host plant phenology and (2) the ant-aphid mutualism to determine aphid abundance. We found date of snowmelt to be the best predictor of yearly abundance of aphid and lygus bug abundance but the direction of this effect differed. Aphids achieved lower abundances in early snowmelt years likely due to increased abundance of lygus bug predators in these years. Elevating temperature of L. porteri flowering stalks reduced their quality as hosts for aphid populations. However, warming aphid colonies on host plants of similar quality increased population growth rates. Importantly, this effect was apparent even in the absence of ants. While we observed fewer ants tending colonies at elevated temperatures, these colonies also had reduced numbers of lygus bug predators. This suggests that mutualism with ants becomes less significant as temperature increases, which contrasts other ant-hemipteran systems. Our observational and experimental results show the importance of multitrophic species interactions for predicting the effect of climate change on the abundances of herbivores.     

Predation on crown-of-thorns starfish larvae by damselfishes

Examining the functional response of predators can provide insight into the role of predation in structuring prey populations and ecological communities. This study explored feeding behaviour and functional responses of planktivorous damselfishes when offered captive reared larvae of crown-of-thorns starfish, Acanthaster sp., with the aim of determining whether these predators could ever play a role in moderating outbreaks of Acanthaster sp. We examined predatory behaviour of 11 species of planktivorous damselfish, testing: (1) the relationship between predator size and predation rate, both within and among fish species; (2) consumption rates on larvae of Acanthaster sp. versus larvae of a common, co-occurring coral reef asteroid Linckia laevigata; (3) maximal feeding rates upon both Acanthaster sp. and L. laevigata; and (4) functional responses of planktivorous fishes to increasing densities of Acanthaster sp. Consumption rates of crown-of-thorns larvae by damselfishes were independent of predator size; however, there was a significant negative relationship between predator size and consumption rate of L. laevigata, when pooling across all predatory species. Some damselfishes, including Acanthochromis polyacanthus and Amblyglyphidodon curacao, consumed larval Acanthaster sp. at a greater rate than for L. laevigata. Most predatory species (all except A. curacao and Pomacentrus amboinensis) exhibited a Type II functional response whereby the increasing feeding rate decelerated with increasing prey density. In addition to revealing that a wide range of planktivorous fishes can prey upon larvae of Acanthaster sp., these data suggest that planktivorous damselfishes may have the capacity to buffer against population fluctuations of Acanthaster sp. Importantly, predators with Type II functional responses often contribute to stability of prey populations, though planktivorous fishes may be swamped by an abnormally high influx of larvae, potentially contributing to the characteristic population fluctuations of Acanthaster sp.     

Continuing influences of introduced hedgehogs <Emphasis Type="Italic">Erinaceus europaeus</Emphasis> as a predator of wader (Charadrii) eggs four decades after their release on the Outer Hebrides,Scotland

Non-native predators can cause major declines or even localised extinctions in prey populations across the globe, especially on islands. The removal of non-native predators can, therefore, be a crucial conservation management tool but there can be challenges when they are viewed as charismatic in their own right. Four decades after their introduction to islands in the Outer Hebrides, Scotland, European hedgehogs Erinaceus europaeus continue to be an important nest predator for a declining population of breeding waders. Where hedgehogs were rare, clutch survival rates (assessed using nest temperature loggers) of five species of waders (dunlin Calidris alpina, lapwing Vanellus vanellus, redshank Tringa totanus, snipe Gallinago gallinago and ringed plover Charadrius hiaticula) were higher than where hedgehogs were relatively more abundant. Hedgehogs were the most frequent nest predator identified using cameras. However, factors influencing population sizes of breeding waders are complex and unlikely to be attributable to a single species of predator. The interactions between predation, land use, habitat and the changes in each deserve further attention.