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Woodland caribou (Rangifer tarandus caribou) are declining across much of their distribution in Canada in response to habitat alteration, leading to unsustainable predation, particularly by wolves (Canis lupus). Habitat alteration can benefit the primary prey species of wolves (moose [Alces alces] and deer [Odocoileus spp.]) by creating early seral conditions that contain more of their preferred food types. This increase in primary prey populations results in elevated wolf abundance and heightened predation pressure on caribou. In response to the elevated wolf populations and the risks to caribou, managers have reduced wolf abundance in key areas. Ecological theory suggests that reducing wolf abundance would release moose from the top‐down effects of wolf predation, potentially allowing moose populations to grow. Elevated moose abundance thus has the potential to cause wolf populations to rebound quickly each year following reductions, suggesting a possible link between moose abundance and the number of wolves killed for caribou conservation. To test this idea we used a unique management situation in British Columbia and Alberta, Canada, where lethal wolf removals were annually conducted across specific southern mountain caribou population ranges and, in some places, moose populations were concurrently reduced via liberalized hunting. We used indices of moose abundance and wolf removal data to test the hypothesis that reducing moose populations to a historical abundance target by hunting leads to fewer wolves killed for caribou conservation. After controlling for habitat quality, wolves removed per km2 was 3.2 times lower in areas with reduced moose density (x¯ $\bar{x}$ = 1.55 wolves/1,000 km2 ± 0.33 [SE]) than in those without reduced moose density (x¯ $\bar{x}$ = 5.02 wolves/1,000 km2 ± 0.52). However, the average number of wolves removed per year decreased under both conditions. After 9 years, there was a 35% reduction in the predicted difference in the annual removal between areas with and without moose reduction. Our results suggest that policies that do not reduce or stabilize moose abundance will result in the removal of more wolves to increase caribou abundance. Like wolf reductions, moose reductions can also be controversial and affect local harvesters. Thus, understanding the consequences of actions that support caribou recovery is essential to supporting evidence‐based policy discussions. [ABSTRACT FROM AUTHOR]

Consumers can influence the competitive outcomes of prey species in various ways. Modern coexistence theory predicts that consumers can promote prey coexistence by preferably targeting a competitively superior one, thereby reducing fitness differences. However, previous studies yielded mixed conclusions. In this study, we tested the hypothesis that a parasitic annual plant, Cuscuta campestris, facilitates the coexistence of two common annual plants. We performed field surveys and parasitism experiments to parameterize a plant competition dynamics model. The model suggested a competition–defence tradeoff: the legume Lespedeza striata was a better competitor than the grass Setaria faberi, while it was more susceptible to the parasite. Moreover, an empirical host–parasite dynamics model, extended from the plant competition model, predicted their coexistence within broad, biologically reasonable ranges of parameters. This work provides field evidence of the coexisting–promoting role of a parasitic plant, as caused by stabilising feedback between host and parasite densities. [ABSTRACT FROM AUTHOR]

As exotic plants invade into a new range, they can escape from specialist enemies. However, they may support generalist enemies, including both native and introduced fungal pathogens, which creates the potential for spillover and apparent competition from exotic to native plants in communities.To assess the potential for spillover of putatively pathogenic, root‐associated fungi (hereafter, 'pathogens') in communities invaded by exotic plants, we conducted a two‐phase plant–soil feedback experiment: a monoculture experiment with native and exotic plants grown alone and a multi‐species, community‐level experiment that ranged in the extent of exotic dominance. We used next‐generation sequencing to characterise sharing of pathogens between native and exotic plants in communities.Exotic plants outperformed natives in communities, despite harbouring higher relative abundance of generalist pathogens. The higher generalism of pathogens supported by exotic plants made them more prone to be shared with natives. The proportion of pathogens shared between exotic and native plants in communities correlated with reduced competitive ability of native compared with exotic plants.Synthesis: These data suggest that exotic plants host more generalist pathogens that are shared with native plants, which may confer an indirect benefit to exotic over native plants through apparent competition. [ABSTRACT FROM AUTHOR]

Understanding the composition and dynamics of ecological communities is challenging because of the large number of organisms present and their numerous interactions. Among agricultural systems, intercropping considerably increases the complexity of communities compared to monocultures and alternative host plants can influence insect pest damage. Using literature records, we construct and analyse connectance trophic webs of date palm (Phoenix dactylifera) agro-ecosystems, including and excluding intercrops. Estimates of connectance (community complexity) are relatively low and little affected by consideration of intercrops. Plant–herbivore overlap is relatively high, suggesting that herbivores are typically not specialists. Herbivore–natural enemy overlap is greater when intercrops are considered, suggesting that diffuse apparent competition regulates pest populations. We pay particular attention to how trophic web structure might affect Batrachedra amydraula (Lesser date moth), an important economic pest. Records indicate it having 15 species of natural enemies and sharing 9 of these with other herbivores; these may maintain populations of natural enemies when the moth is seasonally rare, contributing to pest suppression. The estimated potential for apparent competition between the lesser date moth and other herbivores is higher when intercrops are considered. The consequent expectation of less severe infestations in plantations that are intercropped compared to monocultures matches empirically derived reports. Further, comparing results obtained from the literature on one country (Oman) and from 15 Middle Eastern countries, we find that community metric estimates are relatively little affected by the geographical scale considered. Overall, our results suggest that literature-based trophic web construction can provide an efficient and robust alternative, or in addition, to direct empirical methodologies and that the presence of intercrops will contribute to major pest suppression via indirect apparent competition. [ABSTRACT FROM AUTHOR]

Abstract Modern humans widely shaped present ecosystems through intentional and unintentional geographical redistribution of wildlife, both in historical and pre‐historical times. However, the patterns of ancient human‐mediated indirect changes in wildlife range are largely unknown, and the mechanisms behind them remain obscure. We used a multidisciplinary approach to (a) reconstruct the process of colonization of the Mediterranean Basin by a long‐lived bird of prey, the Bonelli's eagle (Aquila fasciata), and (b) test the hypothesis that this colonization was unintentionally favoured by anatomically modern humans through a release of competition by dominant species, primarily golden eagles (A. chrysaetos). The fossil record of Bonelli's eagles in the Mediterranean Basin was restricted to the last c. 50 ky. This timing matches the period of modern human presence in Europe. Distribution modelling showed that Bonelli's eagles find more suitable conditions in interglacial periods, while glacial maxima are largely unfavourable unless in coastal refugia. In agreement with this, all Bonelli's eagle's fossils were found in coastal areas, and demographic inference from genetic data revealed a drop in the effective population size by around the last glacial maximum. In today's communities, we found a strongly asymmetric competitive relationship between (subordinate) Bonelli's and (dominant) golden eagles, with the former occupying far more humanized areas than the latter both at the landscape scale and the local (i.e. nesting cliff) scale. Moreover, the nesting habitat overlap analysis indicated that, in the absence of the other species, a notably higher population of Bonelli's eagle, but not of golden eagle, could be expected. Our findings are consistent with the human‐mediated competitor release hypothesis, by which anatomically modern humans could have unintentionally favoured the large‐scale colonization by Bonelli's eagles of a previously competitively hostile Mediterranean Basin. Reconstructing the role of ancient humans in shaping present ecosystems may help to understand the historical, current and future population trajectories of competing species of conservation concern under the ongoing scenario of global environmental change. It also illustrates how human‐mediated apparent competition may promote large‐scale redistribution and colonization of wildlife, including long‐lived species. Read the free Plain Language Summary for this article on the Journal blog.

Competition is known in biology through various mechanisms and species often compete for resources indirectly. We consider a system consisting of a predator, prey, which is not fully consumed and converts to a secondary resource (carcasses), and scavengers, which feed on the carcasses. Such an ecosystem is a simplified sketch of interactions in the savannah between lions and spotted hyenas, with lions killing herbivore prey, especially ungulates, whose leftovers serve as primary food for the hyenas. We perform an analytic and numerical study of the possible bifurcations which the model presents between states where one or more species are absent and the coexistence state. [ABSTRACT FROM AUTHOR]

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We present a mechanistic model of coexistence among a mycorrhizal fungus and one or two plant species that compete for a single nutrient. Plant–fungal coexistence is more likely if the fungus is better at extracting the environmental nutrient than the plant and the fungus acquires carbon from the plant above a minimum rate. When they coexist, their interaction can shift from mutualistic to parasitic at high nutrient availability. The fungus is a second nutrient source for plants and can promote the coexistence of two plant competitors if one is better at environmental nutrient extraction and the other is better at acquiring the nutrient from the fungus. Because it extracts carbon from both plants, the fungus also serves as a conduit of apparent competition between the plants. Consequently, the plant with the lower environmental nutrient extraction rate can drive the plant with the higher environmental nutrient extraction rate extinct at high carbon supply rates. This model illustrates mechanisms to explain several observed patterns, including shifts in plant–mycorrhizal growth responses and coexistence along nutrient gradients, equivocal results among experiments testing the effect of mycorrhizal fungi on plant diversity, and differences in plant diversity among ecosystems dominated by different mycorrhizal groups. [ABSTRACT FROM AUTHOR]

Predation risk is a function of spatiotemporal overlap between predator and prey, as well as behavioural responses during encounters. Dynamic factors (e.g. group size, prey availability and animal movement or state) affect risk, but rarely are integrated in risk assessments. Our work targets a system where predation risk is fundamentally linked to temporal patterns in prey abundance and behaviour. For neonatal ungulate prey, risk is defined within a short temporal window during which the pulse in parturition, increasing movement capacity with age and antipredation tactics have the potential to mediate risk.In our coyote–mule deer (Canis latrans–Odocoileus hemionus) system, leveraging GPS data collected from both predator and prey, we tested expectations of shared enemy and reproductive risk hypotheses. We asked two questions regarding risk: (A) How does primary and alternative prey habitat, predator and prey activity, and reproductive tactics (e.g. birth synchrony and maternal defence) influence the vulnerability of a neonate encountering a predator? (B) How do the same factors affect behaviour by predators relative to the time before and after an encounter?Despite increased selection for mule deer and intensified search behaviour by coyotes during the peak in mule deer parturition, mule deer were afforded protection from predation via predator swamping, experiencing reduced per‐capita encounter risk when most neonates were born. Mule deer occupying rabbit habitat (Sylvilagus spp.; coyote's primary prey) experienced the greatest risk of encounter but the availability of rabbit habitat did not affect predator behaviour during encounters. Encounter risk increased in areas with greater availability of mule deer habitat: coyotes shifted their behaviour relative to deer habitat, and the pulse in mule deer parturition and movement of neonatal deer during encounters elicited increased speed and tortuosity by coyotes.In addition to the spatial distribution of prey, temporal patterns in prey availability and animal behavioural state were fundamental in defining risk. Our work reveals the nuanced consequences of pulsed availability on predation risk for alternative prey, whereby responses by predators to sudden resource availability, the lasting effects of diversionary prey and inherent antipredation tactics ultimately dictate risk. [ABSTRACT FROM AUTHOR]

Aim: Intraspecific variation in species relative abundance is shaped by a complex interplay of abiotic and biotic factors, making it both necessary and challenging to assess their combined relative importance in explaining variations across space and time. We used two congeneric butterfly species for which extensive count data and a deep understanding of their natural history is available to test three hypotheses explaining intraspecific variation in their abundance: (H1) seasonal dispersal behaviour driven by climate, (H2) resource availability and (H3) apparent competition mediated via shared parasitoids. Taxon: Gonepteryx rhamni (Brimstone) and G. cleopatra (Cleopatra). Location: NE Iberian Peninsula, where both species coexist, and a nearby archipelago (Balearic Islands), where only Cleopatra occurs. Methods: We analysed spatial abundance variations for both species in the mainland and island–mainland differences in the abundance of Cleopatra. Abiotic and biotic factors, including temperature, host plant and overwintering habitat availability, larval parasitism and density dependence, were tested to explain the observed variations. Results: H1 can explain variation in butterfly abundance between mainland regions since in warmer summers populations increased in cooler areas but decreased in warmer areas. H2 explains the variation within mainland climate regions with a strong positive relationship between resource availability and abundance but is unlikely to explain the island–mainland variation in the abundance of Cleopatra. H3 could neither explain biogeographical variation in abundance because although richer parasitoid communities were found on the mainland, larval mortality rates were similar or lower on the mainland than in the islands. Main Conclusions: Climate and resource availability jointly account for variation in butterfly abundance across the mainland, but neither these factors nor parasitism can explain island–mainland differences. Both coexisting butterfly species and their larval parasitoids may have undergone evolutionary processes, resulting in spatial segregation that promotes the coexistence of the two butterfly species on the mainland. [ABSTRACT FROM AUTHOR]

Introduced herbivores often alter predator–prey dynamics between native organisms. We investigated whether the exotic mite Raoiella indica can interfere in the predation relationships between the predator Amblyseius largoensis and the native herbivorous mite Oligonychus pratensis and be favored as a result. Populations of A. largoensis were established in laboratory, one reared with exotic prey and another with native prey. For each population, of A. largoensis were evaluated for: egg-to-adult developmental time, oviposition rate, and feed conversion efficiency (FCE) of females. Also, to observe the interaction with prey, behavioral tests were conducted, evaluating the time to the first attack, oviposition site preference, and prey preference consumption. Regardless of prey offered, there was no prey effect on immature developmental time or female oviposition rate. However, A. largoensis showed superior FCE feed on exotic (11.4%) over native prey (3.9%). Both A. largoensis populations preferred to prey on eggs of native species and also tended to choose oviposition sites containing native prey eggs. Those reared on exotic prey attacked their first prey in less time than those reared on native prey. Therefore, the presence of R. indica affects both predator population growth and the feeding preference for native prey, which causes a risk of displacement of O. pratensis. [ABSTRACT FROM AUTHOR]

For species primarily regulated by a common predator, the P* rule of Holt & Lawton (Holt & Lawton, 1993. Am. Nat. 142, 623-645. (doi:10.1086/285561)) predicts that the prey species that supports the highest mean predator density (P*) excludes the other prey species. This prediction is re-examined in the presence of temporal fluctuations in the vital rates of the interacting species including predator attack rates. When the fluctuations in predator attack rates are temporally uncorrelated, the P* rule still holds even when the other vital rates are temporally auto-correlated. However, when temporal auto-correlations in attack rates are positive but not too strong, the prey species can coexist due to the emergence of a positive covariance between predator density and prey vulnerability. This coexistence mechanism is similar to the storage effect for species regulated by a common resource. Negative or strongly positive auto-correlations in attack rates generate a negative covariance between predator density and prey vulnerability and a stochastic priority effect can emerge: with non-zero probability either prey species is excluded. These results highlight how temporally auto-correlated species' interaction rates impact the structure and dynamics of ecological communities.

Sexual dimorphism is a ubiquitous source of within-species variation, yet the community-level consequences of sex differences remain poorly understood. Here, we analyse a bitrophic model of two competing resource species and a sexually reproducing consumer species. We show that consumer sex differences in resource acquisition can have striking consequences for consumer-resource coexistence, abundance and dynamics. Under both direct interspecific competition and apparent competition between two resource species, sexual dimorphism in consumers attack rates can mediate coexistence of the resource species, while in other cases can lead to exclusion when stable coexistence is typically expected. Slight sex differences in total resource acquisition also can reverse competitive outcomes and lead to density cycles. These effects are expected whenever both consumer sexes require different amounts or types of resources to reproduce. Our results suggest that consumer sexual dimorphism, which is common, has wide-reaching implications for the assembly and dynamics of natural communities.

When predators consume prey, they risk becoming infected with their prey's parasites, which can then establish the predator as a secondary host. A predator population's diet therefore influences what parasites it is exposed to, as has been repeatedly shown in many species such as threespine stickleback (Gasterosteus aculeatus) (more benthic-feeding individuals obtain nematodes from oligocheate prey, whereas limnetic-feeding individuals catch cestodes from copepod prey). These differing parasite encounters, in turn, determine how natural selection acts on the predator's immune system. We might therefore expect that ecoevolutionary dynamics of a predator's diet (as determined by its ecomorphology) should drive correlated evolution of its immune traits. Conversely, the predator's immunity to certain parasites might alter the relative costs and benefits of different prey, driving evolution of its ecomorphology. To evaluate the potential for ecological morphology to drive evolution of immunity, and vice versa, we use a quantitative genetics framework coupled with an ecological model of a predator and two prey species (the diet options). Our analysis reveals fundamental asymmetries in the evolution of ecomorphology and immunity. When ecomorphology rapidly evolves, it determines how immunity evolves, but not vice versa. Weak trade-offs in ecological morphology select for diet generalists despite strong immunological trade-offs, but not vice versa. Only weak immunological trade-offs can explain negative diet-infection correlations across populations. The analysis also reveals that eco-evo-immuno feedbacks destabilize population dynamics when trade-offs are sufficiently weak and heritability is sufficiently high. Collectively, these results highlight the delicate interplay between multivariate trait evolution and the dynamics of ecological communities.

Indirect interactions are widespread among prey species that share a common predator, but the underlying mechanisms driving these interactions are often unclear, and our ability to predict their outcome is limited.Changes in behavioural traits that impact predator space use could be a key proximal mechanism mediating indirect interactions, but there is little empirical evidence of the causes and consequences of such behavioural‐numerical response in multispecies systems.Here, we investigate the complex ecological relationships between seven prey species sharing a common predator. We used a path analysis approach on a comprehensive 9‐year data set simultaneously tracking predator space use, prey densities and prey mortality rate on key species of a simplified Arctic food web.We show that high availability of a clumped and spatially predictable prey (goose eggs) leads to a twofold reduction in predator (arctic fox) home range size, which increases local predator density and strongly decreases nest survival of an incidental prey (American golden plover). On the contrary, a scattered cyclic prey with potentially lower spatial predictability (lemming) had a weaker effect on fox space use and an overall positive impact on the survival of incidental prey.These contrasting effects underline the importance of studying behavioural responses of predators in multiprey systems and to explicitly integrate behavioural‐numerical responses in multispecies predator–prey models. [ABSTRACT FROM AUTHOR]

Conservation biological control of crop pests by natural enemies relies on management strategies to favour their trophic interactions. In agricultural landscapes, natural enemies acting across habitat boundaries may feed on non-pest prey, resulting in apparent competition between non-pest prey and pests. Such communities, including pests, non-pest prey, and natural enemies have been shown to be affected by landscape heterogeneity depending on the dispersal capacity of the interacting organisms. Nonetheless, a mechanistic understanding of how natural enemies’ dispersal capacity interacts with landscape heterogeneity affecting conservation biological control is, however, lacking. Here, we contribute to such mechanistic understanding through modelling. We simulated the consequences of differences in landscape heterogeneity defined by the contrast of plant resource distribution in a semi-natural habitat compared to a crop and variation in natural enemy dispersal capacity on biological control of a pest. Our model showed that variation in plant resource distribution resulted in bottom-up effects that led to shifts in the dominant mechanism underlying biological control. At high landscape heterogeneity when resources differ strongly between crop and the semi-natural habitat, non-pest prey benefitted from the plant resources available, promoting apparent-competition-mediated biocontrol for high-dispersing natural enemies. At low landscape heterogeneity, pests benefitted mostly from plant resources available, promoting direct plant-pest-enemy mediated biocontrol. Interestingly, intermediate levels of landscape heterogeneity resulted in the lowest levels of biocontrol. Our results highlight the importance of potential bottom-up effects that the matching between plant resources available in a habitat and the resource preference of herbivores can induce on conservation biological control.

Sexual reproduction is the primary mode of reproduction in eukaryotes, but some organisms have evolved deviations from classical sex and switched to asexuality. These asexual lineages have sometimes been viewed as evolutionary dead ends, but recent research has revealed their importance in many areas of general biology. Our review explores the understudied, yet important mechanisms by which sperm‐dependent asexuals that produce non‐recombined gametes but rely on their fertilization, can have a significant impact on the evolution of coexisting sexual species and ecosystems. These impacts are concentrated around three major fields. Firstly, sperm‐dependent asexuals can potentially impact the gene pool of coexisting sexual species by either restricting their population sizes or by providing bridges for interspecific gene flow whose type and consequences substantially differ from gene flow mechanisms expected under sexual reproduction. Secondly, they may impact on sexuals' diversification rates either directly, by serving as stepping‐stones in speciation, or indirectly, by promoting the formation of pre‐ and postzygotic reproduction barriers among nascent species. Thirdly, they can potentially impact on spatial distribution of species, via direct or indirect (apparent) types of competition and Allee effects. For each such mechanism, we provide empirical examples of how natural sperm‐dependent asexuals impact the evolution of their sexual counterparts. In particular, we highlight that these broad effects may last beyond the tenure of the individual asexual lineages causing them, which challenges the traditional perception that asexual lineages are short‐lived evolutionary dead ends and minor sideshows. Our review also proposes new research directions to incorporate the aforementioned impacts of sperm‐dependent asexuals. These research directions will ultimately enhance our understanding of the evolution of genomes and biological interactions in general. [ABSTRACT FROM AUTHOR]

Scatter-hoarding rodents play important roles in seed dispersal and predation in many forest ecosystems. Existing studies have shown that the seed foraging preference of rodents is directly affected by seed traits and indirectly affected by the traits of other co-existing seeds nearby (i.e., neighbor effect). Plant seeds exhibit a combination of diverse seed traits, including seed size, chemical defense, and nutrient content. Therefore, it is difficult to evaluate the influence of each single seed trait on such neighbor effects. Here, by using artificial seeds, we investigated the impacts of contrasts in seed size, tannin content, and nutrient content on neighbor effects. We tracked 9000 tagged artificial seeds from 30 seed-seed paired treatments in a subtropical forest in southwest China. The contrast in seed size between paired seeds created obvious neighbor effects measured through three seed dispersal related indicators: the proportion of seeds being removed, the proportion of seeds cached, and the distance transported by rodents. However, the magnitudes and the signs of the neighbor effects differed among pairs, including both apparent mutualism and apparent competition, depending on the contrast in seed size between paired seeds. The contrasts of tannin and nutrient content between paired seeds showed relatively few neighbor effects. Our results suggest that the contrast in seed traits between the target seed and its neighboring seeds should be considered when studying rodent-seed interactions. Furthermore, we expect that similar complex neighbor effects may also exist in other plant-animal interactions, such as pollination and herbivory. [ABSTRACT FROM AUTHOR]

Foragers must balance the costs and gains inherent in the pursuit of their next meal. Classical functional response formulations describe consumption rates driven by prey density and are naive to predator foraging costs. Here, we integrated foraging costs into functional responses to add mechanism and precision to foundational ideas. Specifically, using a model system with a single predator and two prey, we express a functional response emerging from variable energy and time costs of each predation phase: searching, attacking, or consuming prey. The utility of our model is explored through a focused example where prey can exert variable influence on predator foraging costs through antipredator traits. Dissimilarity between prey in their foraging costs influence the energy gain rate of the predator through optimal prey switching. We found that a small subset of prey antipredator traits and density conditions generated a stabilizing Type III (sigmoidal) functional response—the pattern often thought to typify a generalist predator switching between prey species. The sigmoid functional response occurred for highly profitable prey only when the costly prey (1) were at a high density and (2) their antipredator traits increased energy or time costs following an encounter. We outline testable predictions regarding foraging costs from our model. We provide guidance on how to apply optimal foraging theory to empirical scenarios where predator foraging costs vary due to prey type, predator type, or environmental conditions. Our framework represents a synergy of foundational and contemporary theory across disciplines, facilitating the discovery of shared principles and context‐dependent variation across varied predator–prey systems. [ABSTRACT FROM AUTHOR]

In the long‐term absence of disturbance, ecosystems often enter a decline or retrogressive phase which leads to reductions in primary productivity, plant biomass, nutrient cycling and foliar quality. However, the consequences of ecosystem retrogression for higher trophic levels such as herbivores and predators, are less clear. Using a post‐fire forested island‐chronosequence across which retrogression occurs, we provide evidence that nutrient availability strongly controls invertebrate herbivore biomass when predators are few, but that there is a switch from bottom‐up to top‐down control when predators are common. This trophic flip in herbivore control probably arises because invertebrate predators respond to alternative energy channels from the adjacent aquatic matrix, which were independent of terrestrial plant biomass. Our results suggest that effects of nutrient limitation resulting from ecosystem retrogression on trophic cascades are modified by nutrient‐independent variation in predator abundance, and this calls for a more holistic approach to trophic ecology to better understand herbivore effects on plant communities. [ABSTRACT FROM AUTHOR]

Invasive alien species are among the most important threats to biodiversity, with invasive plants ranking among the highest. Classical weed biological control—or biocontrol—reunites exotic plants with host-specific natural enemies from their native range with the aim of controlling the invasive plant. We reviewed the attention classical weed biocontrol has received from scientific publications for the last 30 years, classified according to the area of academia and applied sciences, as well as the region of the world. Biological control journals were excluded from the analyses to avoid bias. This process allowed us to evaluate the support classical weed biocontrol has among the scientific community. We also recorded the number of weed biocontrol agents released from 1900 to date, where they were collected, and where they were released as a way to analyze the evolution of classical weed biocontrol policies in different parts of the world. Classical weed biocontrol releases peaked between 1990 and 1999, but have declined since, probably due to funding issues, increases in regulations, and bad publicity. Researchers in theoretical ecology appear to be more skeptical toward weed biocontrol than scientists in applied and experimental biology. Our synthesis also suggests that despite resistance to classical weed biocontrol in some quarters of the scientific community, the general scientific perception of the discipline has been consistently favorable. This means that the general scientific perception of classical weed biocontrol contradicts its level of current application. The five main objections against classical weed biocontrol—direct nontarget effects, indirect and hidden nontarget effects, evolution of host shifts in biocontrol agents, dispersion to unwanted areas, and disagreements on its level of success in the field—are summarized and analyzed in terms of their relevance and probability of occurrence. We also describe the way classical weed biocontrol practitioners deal with them at present to ensure safety and sustainability. Our analysis suggests the potential of classical weed biocontrol is undervalued in some areas of science and management due to objections that are plausible in theory, although their likelihood is very low and on-ground evidence scant. [ABSTRACT FROM AUTHOR]

Although global change can reshape ecosystems by triggering cascading effects on food webs, indirect interactions remain largely overlooked. Climate‐ and land‐use‐induced changes in landscape cause shifts in vegetation composition, which affect entire food webs. We used simulations of forest dynamics and movements of interacting species, parameterized by empirical observations, to predict the outcomes of global change on a large‐mammal food web in the boreal forest. We demonstrate that climate‐ and land‐use‐induced changes in forest landscapes exacerbate asymmetrical apparent competition between moose and threatened caribou populations through wolf predation. Although increased prey mortalities came from both behavioral and numerical responses, indirect effects from numerical responses had an overwhelming effect. The increase in caribou mortalities was exacerbated by the cumulating effects of land use over the short term and climate change impacts over the long term, with higher impact of land use. Indirect trophic interactions will be key to understanding community dynamics under global change. [ABSTRACT FROM AUTHOR]

The use of alternative food for arthropod predators in augmentative and conservation biological pest control has increased considerably during the last two decades. Dozens of studies on this topic have been published, showing mixed effects. There are theoretical arguments to expect positive as well as negative effects of alternative food on pest control. In this review, we first discuss these arguments, resulting in a list of factors that potentially affect augmentative and conservation biocontrol with alternative food. We subsequently perform a meta-analysis of selected literature, which is mainly on control of various species of spider mites, thrips, whiteflies and chrysomelids, but also includes some studies on aphids, psyllids and mealybugs. The analysis reveals three factors that have significant effects on the way alternative food affects pest control. First, supplying alternative food should result in increases in the predator densities. Hence, there should be sufficient time for the predators to produce future generations during the cropping season. In the absence of such a numerical response, supplying alternative food can result in lower predation due to satiation of the predators, resulting in decreased pest control. Second, biocontrol is better when predators are released and provided with alternative food before pest invasion, allowing them to build up a population of predators that protects the crop. Third, when the alternative food consists of prey, it should not be of higher quality than the pest, otherwise predators may preferentially feed on the alternative prey, releasing the pest from predation. We furthermore analysed data on biocontrol of thrips, spider mite pests, whiteflies and chrysomelids for which enough data were available to disentangle effects of the various factors mentioned above. These analyses confirmed general results, from which guidelines for improvement of biocontrol of these specific pest groups can be derived. We also argue that the effects of alternative food on biocontrol should be studied by repeatedly assessing densities of pests and predators through time, preferably throughout a growing season. [ABSTRACT FROM AUTHOR]

Competition is a driving factor in shaping ecological communities and may act directly or indirectly through apparent competition. We examined a classic example of parasite-mediated competition between northern (Glaucomys sabrinus) and southern flying squirrels (G. volans) via the intestinal nematode, Strongyloides robustus, and tested whether it could act as a species barrier in a flying squirrel hybrid zone. We live-trapped flying squirrels (G. sabrinus and G. volans), grey squirrels (Sciurus carolinensis), red squirrels (Tamiasciurus hudsonicus), and chipmunks (Tamias striatus) from June–September 2019 at 30 woodlots in Ontario, Canada. Fecal samples from squirrels were collected and analyzed for the presence of endoparasite eggs. For each individual, we calculated Scaled Mass Index (SMI) as a measure of body condition to assess the effect of S. robustus on squirrels. We found eggs of S. robustus in all species except chipmunks. Infection with S. robustus did not appear to affect body condition of southern flying squirrels and grey squirrels, but we did find a weak negative effect on northern flying squirrels and red squirrels. Despite a weak asymmetric effect of S. robustus on flying squirrels, we did not find any evidence that parasite-mediated competition could lead to competitive exclusion from woodlots. Furthermore, S. robustus eggs were common in feces of the red squirrel, a species largely sympatric with northern flying squirrel.

Non-native species pose a threat to native organisms. When non-native and native species are closely related, the former can often competitively exclude the latter. Many studies have focused on competitive exclusion of native insect species by non-native eusocial hymenopterans, including ants, hornets, paper wasps and bees. Although solitary species of wasps have been introduced in many regions, few studies have investigated the effects of these insects on their native congeners. We investigated competitive interactions between native and non-native solitary wasps belonging to the same genus (Hymenoptera: Vespidae: Eumeninae: Anterhynchium). Specifically, we compared resource use and natural enemies of the native Anterhynchium flavomarginatum and supposedly non-native A. gibbifrons at a forest edge in Takasago, Hyogo, Japan, in June-October 2019, using trap nests (bamboo canes). Of 950 bamboo canes, 70 (7.4%) and 50 (5.3%) were used as nests by A. flavomarginatum and A. gibbifrons, respectively. Anterhynchium flavomarginatum produced two generations over the period studied, whereas A. gibbifrons produced only one. Although A. gibbifrons began nesting two weeks after A. flavomarginatum, the nesting period of A. gibbifrons overlapped that of the first nesting period of A. flavomarginatum. Nest architecture and the inner diameter of the canes used by both species were similar, suggesting potential competition for nesting resources. Anterhynchium flavomarginatum used larvae of 14 species of moths (Lepidoptera: Crambidae, Pyralidae, Tortricidae) as food for their larval offspring, whereas A. gibbifrons used only a single species, Demobotys pervulgalis (Lepidoptera: Crambidae). Prey species were exclusive to each wasp species, indicating no competition for this resource. Three parasitoid species, Macrosiagon nasutum (Coleoptera: Ripiphoridae), Amobia distorta (Diptera: Sarcophagidae) and Megaselia sp. (Diptera: Phoridae), attacked both Anterhynchium species. The percentage parasitism by Amobia distorta was higher for the native A. flavomarginatum. Anterhynchium gibbifrons may indirectly affect A. flavomarginatum via shared parasitoids.

Abstract Although global change can reshape ecosystems by triggering cascading effects on food webs, indirect interactions remain largely overlooked. Climate‐ and land‐use‐induced changes in landscape cause shifts in vegetation composition, which affect entire food webs. We used simulations of forest dynamics and movements of interacting species, parameterized by empirical observations, to predict the outcomes of global change on a large‐mammal food web in the boreal forest. We demonstrate that climate‐ and land‐use‐induced changes in forest landscapes exacerbate asymmetrical apparent competition between moose and threatened caribou populations through wolf predation. Although increased prey mortalities came from both behavioral and numerical responses, indirect effects from numerical responses had an overwhelming effect. The increase in caribou mortalities was exacerbated by the cumulating effects of land use over the short term and climate change impacts over the long term, with higher impact of land use. Indirect trophic interactions will be key to understanding community dynamics under global change.

The eastern gray squirrel (Sciurus carolinensis) has been labeled as one of the 100 worst invasive alien species by the IUCN. In Europe, the species has been introduced to Britain, Ireland and Italy, and its subsequent spread has resulted in wide-scale extinction of native Eurasian red squirrels (Sciurus vulgaris) from the areas colonized by the gray squirrel. This replacement of a native by an alien competitor is one of the best documented cases of the devastating effects of biological invasions on native fauna. To understand how this replacement occurs, we present a systematic review of the literature on competition and interactions between red and gray squirrels. We describe the patterns of red and gray squirrel distribution in those parts of Europe where gray squirrels occur and summarize the evidence on the different processes and mechanisms determining the outcome of competition between the native and alien species including the influence of predators and pathogens. Some of the drivers behind the demise of the red squirrel have been intensively studied and documented in the past 30 years, but recent field studies and mathematical models revealed that the mechanisms underlying the red-gray paradigm are more complex than previously thought and affected by landscape-level processes. Therefore, we consider habitat type and multi-species interactions, including host-parasite and predator-prey relationships, to determine the outcome of the interaction between the two species and to better address gray squirrel control efforts.

Organisms from higher tropical levels (e.g., herbivores) can mediate indirect competitive interactions between two target plant species, but such apparent competition may also be mediated by a third plant species and thus may vary depending on the size and competitive ability of the target plant species and the third plant species. We set up an outdoor experiment with four aquatic plant species with similar niches but differing greatly in size, i.e., Lemna minor (the smallest), Spirodela polyrhiza (the second smallest), Salvinia natans (the second largest) and Pistia stratiotes (the largest). We grew L. minor and S. polyrhiza alone or in mixture and in the absence of any third plant species, in the presence of a small, third species S. natans or in the presence of a large, third species P. stratiotes. In the absence of the third species or in the presence of S. natans, the growth of L. minor was greatly inhibited by S. polyrhiza, but in the presence of P. stratiotes, the inhibiting effects of S. polyrhiza disappeared completely and the growth of L. minor greatly increased. By contrast, the presence of L. minor had no effect on the growth of S. polyrhiza, and this effect did not depend on the presence or absence of the third plant species, although the presence of the third species, particularly P. stratiotes, decreased its growth. We conclude that the presence of a third plant species can regulate plant-plant interactions, but such an impact depends on the size and competitive ability of the competing species as well as the third species. Our findings highlight the role of complexity in plant-plant interactions, and suggest that apparent competition between plants can also occur at the same trophic level. These results have important implications for the explanations of species coexistence and biodiversity maintenance.

Sea otters (Enhydra lutris) and wolves (Canis lupus) are two apex predators with strong and cascading effects on ecosystem structure and function. After decades of recovery from near extirpation, their ranges now overlap, allowing sea otters and wolves to interact for the first time in the scientific record. We intensively studied wolves during 2015 to 2021 in an island system colonized by sea otters in the 2000s and by wolves in 2013. After wolf colonization, we quantified shifts in foraging behavior with DNA metabarcoding of 689 wolf scats and stable isotope analyses, both revealing a dietary switch from Sitka black-tailed deer (Odocoileus hemionus), the terrestrial in situ primary prey, to sea otters. Here we show an unexpected result of the reintroduction and restoration of sea otters, which became an abundant marine subsidy for wolves following population recovery. The availability of sea otters allowed wolves to persist and continue to reproduce, subsequently nearly eliminating deer. Genotypes from 390 wolf scats and telemetry data from 13 wolves confirmed island fidelity constituting one of the highest known wolf population densities and upending standardly accepted wolf density predictions based on ungulate abundance. Whereas marine subsidies in other systems are generally derived from lower trophic levels, here an apex nearshore predator became a key prey species and linked nearshore and terrestrial food webs in a recently deglaciated and rapidly changing ecosystem. These results underscore that species restoration may serve as an unanticipated nutrient pathway for recipient ecosystems even resulting in cross-boundary subsidy cascades. [ABSTRACT FROM AUTHOR]

Changes in primary productivity have the potential to substantially alter food webs, with positive outcomes for some species and negative outcomes for others. Understanding the environmental context and species traits that give rise to these divergent outcomes is a major challenge to the generality of both theoretical and applied ecology. In aquatic systems, nutrient-mediated eutrophication has led to major declines in species diversity, motivating us to seek terrestrial analogues using a large-mammal system across 598 000 km2 of the Canadian boreal forest. These forests are undergoing some of the most rapid rates of land-use change on Earth and are home to declining caribou (Rangifer tarandus caribou) populations. Using satellite-derived estimates of primary productivity, coupled with estimates of moose (Alces alces) and wolf (Canis lupus) abundance, we used path analyses to discriminate among hypotheses explaining how habitat alteration can affect caribou population growth. Hypotheses included food limitation, resource dominance by moose over caribou, and apparent competition with predators shared between moose and caribou. Results support apparent competition and yield estimates of wolf densities (1.8 individuals 1000 km−2) above which caribou populations decline. Our multi-trophic analysis provides insight into the cascading effects of habitat alteration from forest cutting that destabilize terrestrial predator–prey dynamics. Finally, the path analysis highlights why conservation actions directed at the proximate cause of caribou decline have been more successful in the near term than those directed further along the trophic chain. [ABSTRACT FROM AUTHOR]

In this study, the integration of useful statistical methods from different disciplines for analyzing the forest community of the Lienhuachih area of central Taiwan was attempted. We employed a seriated heat map to confirm the presence of multiple community patterns in the area and used the gap statistics and a clustplot to confirm the number and structure of the patterns, respectively. A minimum spanning tree was used to display a succession series among the quadrats, and Renyi diversity was used to indicate the species composition of these patterns. The results confirmed the existence of six patterns with different biodiversity structures in which pattern C was the succession prototype of the local community patterns. Next, we used the patterns as nodes of a social network to perform bipartite network analysis. The results showed that a community network consisted of 108 taxa and six syntaxa. The syntaxa were highly vulnerable to extinction; therefore, the optimal conservation strategy for local species would be to first protect the syntaxa. The random forest method and bipartite modularity were used to analyze the dominant characteristic species of the six syntaxa. The results showed that these two methods are useful for detecting characteristic species of the syntaxa. Therefore, this study proposed a new nomenclature system, namely the Mathematic Code of Syntaxonomic Nomenclature, to support the results of numerical vegetation analysis. Finally, the potential for an apparently competitive network was examined, the role of an apparently competitive network in the local structuring community was explored, and six new associations in the Lienhuachih area were described. [ABSTRACT FROM AUTHOR]

The alternative prey hypothesis supposes that predators supported by a primary prey species will shift to consume alternative prey during a decrease in primary prey abundance. The hypothesis implies that during declines of one prey species, a predator modifies their behavior to exploit a secondary, or alternative, species. Despite occurring in many systems, the behavioral mechanisms (e.g., habitat selection) allowing predators to shift toward alternative prey during declines in the abundance of their primary prey are poorly understood. We evaluated habitat selection and use by a generalist predator with respect to two prey species during a dramatic decrease in the abundance of primary prey. Further, we evaluated how spatial variation in access to primary prey affected habitat selection, and assessed similarity and overlap between habitats used by each prey species. Coyotes (Canis latrans) exhibited decreasing selection for cottontail rabbits (Sylvilagus spp.; primary prey) during population decreases but did not shift habitat selection toward neonate mule deer (Odocoileus hemionus; alternative prey). Use of rabbit habitat remained high even during historically low rabbit abundance, while mule deer habitat was used in proportion to its availability. Coyotes seemingly do not make large shifts in habitat selection toward alternative prey following spatial and temporal decreases in the abundance of primary prey, but instead, take advantage of habitat overlap to facilitate prey‐switching behavior. Our work extends previous research conducted under the alternative prey hypothesis by explicitly evaluating the influence of habitat overlap between prey species and variation in access to prey habitat as factors affecting prey‐switching behaviors in predators. [ABSTRACT FROM AUTHOR]

Banker plant systems have the advantages of introducing natural enemies preventively and maintaining by providing alternative prey, thus controlling the pests sustainably. Banker plant systems are usually composed of three factors: a banker (secondary) plant, an alternative prey, and a shared predator (attacking an alternative prey on the secondary plant, and the targeted pest on the crop). However, for most banker plant systems, there is a lack of understanding regarding the dynamic relationship among these elements, with detrimental effects on practical applications. Therefore, in this study, the control of Myzus persicae on Capsicum annum by the Coccinella septempunctata–Megoura japonica–Vicia faba banker plant system was used as the research system. The effects of different release time of predators, different initial numbers of alternative prey (Me. japonica) and different initial ratios of target pests/alternative prey on the indirect interaction of two aphids and the biological control effect of shared predators were tested. The occurrence of indirect interactions between the two aphid preys, the impact on population dynamics, and biological control effectiveness of the shared predator C. septempunctata were investigated. When the initial numbers of both species of aphids were equal (200 each), the delay between aphid and C. septempunctata introduction in the cage had no effect on My. persicae, but Me. japonica showed lower numbers when testing the least time between predatory introductions. When the numbers of the two aphids were manipulated, the My. persicae population was significantly reduced by the predator only at a ratio of My. persicae to Me. japonica < 1, while initial ratios ≥ 1 enabled My. persicae population growth. In 1–6 days, the control effect of C. septempunctata was the best. Principal component analysis showed that the experimental time, initial numbers of Me. japonica, and relative numbers of Me. japonica affected the predation of My. persicae by C. septempunctata. In addition, when the initial aphid ratio was greater than 1/4, C. septempunctata was able to effectively control My. persicae. Overall, our study confirmed the number-mediated indirect interaction (apparent competition) relationship and its impact on prey population dynamics. We provide useful information for optimizing banker plant systems, to boost biocontrol of aphid pests. [ABSTRACT FROM AUTHOR]

Species exhibit various trade‐offs that can result in stable coexistence of competitors. The gleaner–opportunist trade‐off to fluctuations in resource abundance is one of the most intuitive, yet also misunderstood, coexistence‐promoting trade‐offs. Here, we review its history as an ecological concept, discuss extensions to the classical theory and outline opportunities to advance its understanding.The mechanism of coexistence between species that grow relatively faster than their competitors in a low‐resource environment (i.e. a gleaner) versus a high‐resource environment (i.e. an opportunist) was first proposed in the 1970s. Stable coexistence could emerge between gleaners and opportunists if the opportunist species (dominant in unstable environments) dampens resource fluctuations via relatively convex functional responses, while the gleaner species (dominant in stable environments) promotes fluctuations, or diminishes them less than the opportunist does, via relatively saturating functional responses.This fluctuation‐dependent coexistence mechanism has since been referred to by various names, including the Armstrong–McGehee mechanism and relative nonlinearity of competition. Several researchers have argued this mechanism likely plays a relatively minor role in species coexistence owing in part to the restricted range of conditions that allow it to operate. More recent theoretical research, however, suggests that relative nonlinearity can operate over wider conditions than previously thought.Here, we identify several novel, or little explored, extensions to the gleaner–opportunist trade‐off that can yield species coexistence under phenomena as diverse as fluctuations in predation/pathogen pressure, multiple resources, phenotypic plasticity and rapid evolution, amongst other phenomena.While the original definition of the gleaner–opportunist trade‐off may be imperfect as a collective for these extensions, we argue that a subtle reframing of the trade‐off focusing on species' performance in equilibrium versus fluctuating conditions (irrespective of preferences for high or low resources, predation pressure or other competitive factors) reveals their fundamental commonality in stable coexistence via relative nonlinearity. An extended framing shines a light on the potential ubiquity of this canonical trade‐off in nature and on the breadth of theoretical and empirical terrain that remains to be trodden. [ABSTRACT FROM AUTHOR]

Abstract The alternative prey hypothesis supposes that predators supported by a primary prey species will shift to consume alternative prey during a decrease in primary prey abundance. The hypothesis implies that during declines of one prey species, a predator modifies their behavior to exploit a secondary, or alternative, species. Despite occurring in many systems, the behavioral mechanisms (e.g., habitat selection) allowing predators to shift toward alternative prey during declines in the abundance of their primary prey are poorly understood. We evaluated habitat selection and use by a generalist predator with respect to two prey species during a dramatic decrease in the abundance of primary prey. Further, we evaluated how spatial variation in access to primary prey affected habitat selection, and assessed similarity and overlap between habitats used by each prey species. Coyotes (Canis latrans) exhibited decreasing selection for cottontail rabbits (Sylvilagus spp.; primary prey) during population decreases but did not shift habitat selection toward neonate mule deer (Odocoileus hemionus; alternative prey). Use of rabbit habitat remained high even during historically low rabbit abundance, while mule deer habitat was used in proportion to its availability. Coyotes seemingly do not make large shifts in habitat selection toward alternative prey following spatial and temporal decreases in the abundance of primary prey, but instead, take advantage of habitat overlap to facilitate prey‐switching behavior. Our work extends previous research conducted under the alternative prey hypothesis by explicitly evaluating the influence of habitat overlap between prey species and variation in access to prey habitat as factors affecting prey‐switching behaviors in predators.

The predator discrimination of prey can affect predation intensity and the prey density dependence of predators, which has the potential to alter the coexistence of prey species. We used a predator–prey population dynamics model accounting for the predator's adaptive diet choice and predator discrimination of prey to investigate how the latter influences prey coexistence. The model revealed that (i) prey species that are perceived as belonging to the same species by a predator are attacked in the same manner, and it is more difficult for them to coexist than those that are recognized as different prey species, and (ii) prey species that are not discriminated by a predator—and therefore cannot coexist—may coexist in the presence of an alternative predator that does discriminate between them. These results suggest that prey diversity, which favours the predator discrimination of prey, and the different capabilities of predators to identify prey species both enhance prey coexistence.

Apparent competition is one mechanism that can contribute to the complex dynamics observed in natural systems, yet it remains understudied in empirical systems. Understanding the dynamics that shape the outcome of processes like apparent competition is vital for appreciating how they influence natural systems.We empirically evaluated the role of indirect trophic interactions in driving apparent competition in a model laboratory system. Our experimental system was designed to let us evaluate combined direct and indirect interactions among species.Here we describe the results of a factorial experiment using two noncompeting prey (Colpidium kleini, a heterotroph, and Chlamydomonas reinhardtii, an autotroph) consumed by a generalist predator Euplotes eurystomus to explore the dynamics of apparent competition. To gain intuition into the potential mechanism driving the asymmetry in the observed results, we further explored the system using structural equation modelling.Our results show an important role of positive interactions and indirect effects contributing to apparent competition in this system with a marked asymmetrical outcome favouring one prey, Chlamydomonas. The selected structural equation supports a role of indirect facilitation; although Chlamydomonas (a photoautotroph) and Colpidium (a bacterivore) use different resources and therefor do not directly compete, Colpidium reduces bacteria that may compete with Chlamydomonas. In addition, formation of colonies by Chlamydomonas in response to predation by Euplotes provides an antipredator defence not available to Colpidium.Asymmetric apparent competition may be more common in natural systems than the symmetric interaction originally proposed in classic theory, suggesting that exploration of the mechanisms driving the asymmetry of the interaction can be a fruitful area of further research to better our understanding of interspecific interactions and community dynamics. [ABSTRACT FROM AUTHOR]

Climate change is altering interspecific interactions globally, yet community‐level responses are difficult to predict due to both the direct and indirect effects of changing abiotic and biotic conditions. Snowshoe hares (Lepus americanus) are particularly vulnerable to decreasing snow cover and resultant camouflage mismatch. This species shares a suite of predators with alternative prey species including porcupines (Erethizon dorsatum) and ruffed grouse (Bonasa umbellus), and all three species historically exhibited synchronized population dynamics. Recently, the community has become partially disassembled, notably with the loss of snowshoe hares and associated enemy‐mediated indirect interactions resulting from declining snow duration. Specifically, we hypothesized that the extirpation of hares in the early 1990s indirectly increased predation pressure on ruffed grouse and porcupines. To test our hypothesis, we experimentally translocated 96 snowshoe hares to a site within a regional ecotone between northern and southern forests where snowshoe hares were recently extirpated and monitored community members before, during, and after translocation. Ruffed grouse were only loosely associated with the biotic interactions that linked porcupines and snowshoe hares, likely due to predation occurring from avian predators and strong negative direct effects of declining winter snow depths. In contrast, predation of neonate porcupines was virtually non‐existent following repatriation, compared with periods without hares. This abrupt attenuation of predation did not increase overall survival due to increased non‐predation mortality from cold, early spring weather. Porcupines directly benefited from warming winters: decreased snow cover increased adult survival and warmer temperatures around parturition increased maternal condition and reduced non‐predation causes of mortality for neonates. Our experimental manipulation suggests that enemy‐mediated indirect interactions were likely to be important features of this community; however, climate change has disrupted these interactions, resulting in extirpation of a central prey species (snowshoe hare) and increased predation of an alternative prey species (porcupine). We show complex effects from climate change with some species directly and negatively affected, while others benefited from direct effects of warming winters, but suffered negative effects from indirect interactions. Due to absent snowshoe hares and associated biotic interactions, continued persistence of this community module is unlikely, potentially resulting in altered no‐analog communities along trailing edge distributions. [ABSTRACT FROM AUTHOR]

Parasites are viewed as a major threat to wild pollinator health. While this may be true for epidemics driven by parasite spillover from managed or invasive species, the picture is more complex for endemic parasites. Wild pollinator species host and share a species-rich, generalist parasite community. In contrast to the negative health impacts that these parasites impose on individual hosts, at a community level they may act to reduce competition from common and abundant pollinator species. By providing rare species with space in which to exist, this will act to support and maintain a diverse and thus healthier pollinator community. At this level, and perhaps paraxodically, parasites may be good for pollinators. This stands in clear contrast to the obvious negative impacts of epidemic and spillover parasites on wild pollinator communities. Research into floral resources that control parasites could be best employed to help design landscapes that provide pollinators with the opportunity to moderate their parasite community, rather than attempting to eliminate specific parasites from wild pollinator communities. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'. [ABSTRACT FROM AUTHOR]

Prudent predators catch sufficient prey to sustain their populations but not as much as to undermine their populations' survival. The idea that predators evolve to be prudent has been dismissed in the 1970s, but the arguments invoked then are untenable in the light of modern evolution theory. The evolution of prudent predation has repeatedly been demonstrated in two‐species predator–prey metacommunity models. However, the vigorous population fluctuations that these models predict are not widely observed. Here we show that in complex model food webs prudent predation evolves as a result of consumer‐mediated ('apparent') competitive exclusion of resources, which disadvantages aggressive consumers and does not generate such fluctuations. We make testable predictions for empirical signatures of this mechanism and its outcomes. Then we discuss how these predictions are borne out across freshwater, marine and terrestrial ecosystems. Demonstrating explanatory power of evolved prudent predation well beyond the question of predator–prey coexistence, the predicted signatures explain unexpected declines of invasive alien species, the shape of stock–recruitment relations of fish, and the clearance rates of pelagic consumers across the latitudinal gradient and 15 orders of magnitude in body mass. Specific research to further test this theory is proposed. [ABSTRACT FROM AUTHOR]

Omnivory is ubiquitous in ecological communities. Yet, we lack a consensus of how plant alternative resources impact the ability of omnivores to suppress prey populations. Previous work suggests that plant alternative resources can increase, decrease, or have no effect on the magnitude of omnivore−prey interactions. This discrepancy may arise from (1) the ability of omnivore populations to respond to plant alternative resources and (2) identity‐specific effects of plant alternative resources. We used a meta‐analysis to examine how omnivore population responses and the identity of plant alternative resources affect (1) omnivore predation rates (mainly reported as per capita predation rate) and (2) omnivore impacts on prey population density. Plant alternative resources reduced omnivore predation rate regardless of identity. The suppression of the predation rate by flowers and flowering plants was magnified when pollen alone was tested as the alternative resource. Surprisingly, plant alternative resource availability reduced prey density, suggesting that omnivore predation increased with plant alternative resources. This discrepancy (plant alternative resources not only decreased omnivore predation rates but also decreased prey density) resulted from experimental differences in the ability of omnivore populations to respond to plant alternative resources. In the presence of plant alternative resources, allowing omnivore population responses decreased prey density, while not allowing population responses increased prey density. Because omnivores commonly suppress prey density in the presence of plant alternative resources when population responses of omnivores are allowed, the effectiveness of biological control may depend upon the availability of such resources and the facilitation of population responses. [ABSTRACT FROM AUTHOR]

Trophic interaction modifications occur in food webs when the direct or indirect interaction between two species is affected by a third species. These behavioral modification effects are often referred to as associational effects. Changes in focal resource availability and consumption by a generalist herbivore can affect a range of outcomes from resource exclusion to multiple resources coexisting with the focal plant species. Here, we investigate the indirect interaction between a focal and alternative resource mediated by a generalist consumer. Using theoretical approaches we analyse the conceptual link between associational effects (both resistance and susceptibility) and the theory of apparent competition and resource switching. We find that changes in focal resource traits have the potential to affect the long-term outcome of indirect interactions. Inclusion of density-dependence expands generalist life-histories and broadens the range where, through associational effects, the availability of alternative resources positively influence a focal resource. We conclude that different forms of associational effects could, in the long-term, lead to a range of indirect interaction dynamics, including apparent competition and apparent mutualism. Our work aims to connects the theoretical body of work on indirect interactions to the concepts of associational effects. The indirect interactions between multiple resources need more thorough investigation to appreciate the range of associational effects that could result from the dynamical interaction between a generalist consumers and its focal and alternative resources.

Competition is a driving factor in shaping ecological communities and may act directly or indirectly through apparent competition. We examined a classic example of parasite-mediated competition between northern (Glaucomys sabrinus) and southern flying squirrels (G. volans) via the intestinal nematode, Strongyloides robustus, and tested whether it could act as a species barrier in a flying squirrel hybrid zone. We live-trapped flying squirrels (G. sabrinus and G. volans), grey squirrels (Sciurus carolinensis), red squirrels (Tamiasciurus hudsonicus), and chipmunks (Tamias striatus) from June–September 2019 at 30 woodlots in Ontario, Canada. Fecal samples from squirrels were collected and analyzed for the presence of endoparasite eggs. For each individual, we calculated Scaled Mass Index (SMI) as a measure of body condition to assess the effect of S. robustus on squirrels. We found eggs of S. robustus in all species except chipmunks. Infection with S. robustus did not appear to affect body condition of southern flying squirrels and grey squirrels, but we did find a weak negative effect on northern flying squirrels and red squirrels. Despite a weak asymmetric effect of S. robustus on flying squirrels, we did not find any evidence that parasite-mediated competition could lead to competitive exclusion from woodlots. Furthermore, S. robustus eggs were common in feces of the red squirrel, a species largely sympatric with northern flying squirrel. [Display omitted] • Strongyloides robustus was detected in 4 squirrel species. • The highest prevalence of S. robustus was found in red squirrels and northern flying squirrels. • Body condition was lowest in red squirrels and northern flying squirrels infected with S. robustus. • No evidence of parasite-mediated competition between sympatric flying squirrels leading to competitive exclusion. [ABSTRACT FROM AUTHOR]

Documenting trophic niche partitioning and resource use within a community is critical to evaluate underlying mechanisms of coexistence, competition, or predation. Detailed knowledge about foraging is essential as it may influence the vital rates, which, in turn, can affect trophic relationships between species, and population dynamics. The aims of this study were to evaluate resource and trophic niche partitioning in summer/autumn between the endangered Atlantic‐Gaspésie caribou (Rangifer tarandus caribou) population, moose (Alces americanus) and their incidental predators, the black bear (Ursus americanus) and coyote (Canis latrans), and to quantify the extent to which these predators consumed caribou. Bayesian isotopic analysis showed a small overlap in trophic niche for the two sympatric ungulates suggesting a low potential for resource competition. Our results also revealed that caribou occupied a larger isotopic niche area than moose, suggesting a greater diversity of resources used by caribou. Not surprisingly, coyotes consumed mainly deer (Odocoileus virginianus), moose, snowshoe hare (Lepus americanus), and occasionally caribou, while bears consumed mainly vegetation and, to a lesser extent, moose and caribou. As coyotes and bears also feed on plant species, we documented trophic niche overlap between caribou and their predators, as searching for similar resources can force them to use the same habitats and thus increase the encounter rate and, ultimately, mortality risk for caribou. Although the decline in the Gaspésie caribou population is mostly driven by habitat‐mediated predation, we found evidence that the low level of resource competition with moose, added to the shared resources with incidental predators, mainly bears, may contribute to jeopardize the recovery of this endangered caribou population. Highlighting the trophic interaction between species is needed to establish efficient conservation and management strategies to insure the persistence of endangered populations. The comparison of trophic niches of species sharing the same habitat or resources is fundamental to evaluate the mechanisms of coexistence or competition and eventually predict the consequences of ecosystem changes in the community. [ABSTRACT FROM AUTHOR]

Understanding Batesian mimicry is a classic problem in evolutionary biology. In Batesian mimicry, a defended species (the model) is mimicked by an undefended species (the mimic). Prior theories have emphasized the role of predator behavior and learning as well as evolution in model-mimic complexes but have not examined the role of population dynamics in potentially governing the relative abundances and even persistence of model-mimic systems. Here, we examined the effect of the population dynamics of predators and alternative prey on the prevalence of warning-signaling prey composed of models and mimics. Using optimal foraging theory and signal detection theory, we found that the inclusion of predator and alternative prey population dynamics could reverse traditional theoretical predictions: as alternative prey increase in numbers, mimics suffer because larger populations of predators are maintained, resulting in apparent competition. Under some circumstances, apparent competition affects model populations as well, although not as severely as it affects mimics. Our results bear on the intriguing puzzle that in nature warning signals are relatively scarce, yet experiments suggest that such signals can be highly advantageous. The availability of alternative prey and numerical responses by predators can overwhelm advantages observed in experiments to keep warning signals in model-mimic systems relatively scarce. [ABSTRACT FROM AUTHOR]

Many insect herbivores engage in apparent competition whereby two species interact through shared natural enemies. Upon insect attack, plants release volatile blends that attract natural enemies, but whether these volatiles mediate apparent competition between herbivores is not yet known. We investigate the role of volatiles that are emitted by bean plants upon infestation by Acyrthosiphon pisum aphids on the population dynamics and fitness of Sitobion avenae aphids, and on wheat phloem sap metabolites. In a field experiment, the dynamics of S. avenae aphids on wheat were studied by crossing two treatments: exposure of aphid colonies to A. pisum-induced bean volatiles and exclusion of natural enemies. Glasshouse experiments and analyses of primary metabolites in wheat phloem exudates were performed to better understand the results from the field experiment. In the field, bean volatiles did not affect S. avenae dynamics or survival when aphids were exposed to natural enemies. When protected from them, however, volatiles led to larger aphid colonies. In agreement with this observation, in glasshouse experiments, aphid-induced bean volatiles increased the survival of S. avenae aphids on wheat plants, but not on an artificial diet. This suggests that volatiles may benefit S. avenae colonies via metabolic changes in wheat plants, although we did not find any effect on wheat phloem exudate composition. We report a potential case of associational susceptibility whereby plant volatiles weaken the defences of receiving plants, thus leading to increased herbivore performance. [ABSTRACT FROM AUTHOR]

Ecosystems are linked through spatial flows of organisms and nutrients that impact their biodiversity and regulation. Theory has predominantly studied passive nutrient flows that occur independently of organism movement. Mobile organisms, however, commonly drive nutrient flows across ecosystems through nutrient recycling. Using a meta‐ecosystem model where consumers move between ecosystems, we study how consumer recycling and traits related to feeding and sheltering preferences affect species diversity and trophic regulation. We show local effects of recycling can cascade across space, yielding spatially heterogeneous top‐down and bottom‐up effects. Consumer traits impact the direction and magnitude of these effects by enabling recycling to favour a single ecosystem. Recycling further modifies outcomes of competition between consumer species by creating a positive feedback on the production of one competitor. Our findings suggest spatial interactions between feeding and recycling activities of organisms are key to predicting biodiversity and ecosystem functioning across spatial scales. [ABSTRACT FROM AUTHOR]