Exotic Prey Research Articles

Exotic predators can sequester and use novel toxins from exotic non-coevolved prey.

Defensive chemicals of prey can be sequestered by some coevolved predators, which take advantage of prey toxins for their own defence. The increase in the number of invasive species in the Anthropocene has resulted in new interactions among non-coevolved predator and prey species. While novelty in chemical defence may provide a benefit for invasive prey against non-coevolved predators, resident predators with the right evolutionary pre-adaptations might benefit from sequestering these novel defences. Here, we chose a well-known system of invasive species to test whether non-coevolved predators can sequester and use toxins from exotic prey. Together with the invasive prickly pear plants, cochineal bugs (Dactylopius spp.) are spreading worldwide from their native range in the Americas. These insects produce carminic acid, a defensive anthraquinone that some specialized predators sequester for their own defence. Using this system, we first determined whether coccinellids that prey on cochineal bugs in the Mediterranean region tolerated, sequestered, and released carminic acid in reflex bleeding. Then, we quantified the deterrent effect of carminic acid against antagonistic ants. Our results demonstrate that the Australian coccinellid Cryptolaemus montrouzieri sequestered carminic acid, a substance absent in its coevolved prey, from exotic cochineal bugs. When attacked, the predator released this substance through reflex bleeding at concentrations that were deterrent against antagonistic ants. These findings reveal that non-coevolved predators can sequester and use novel toxins from exotic prey and highlights the surprising outcomes of novel interactions that arise from species invasions.

Salmon farming, overfishing and southern sea lion: Not so opportunistic responses of a top predator to human perturbations in the Patagonian Fjords

Pinnipeds are considered generalist predators that prey opportunistically on more abundant prey. Thus, their diet could be affected by natural and anthropogenic stressors, such as declines in native prey and increases in exotic prey such as escaped salmon. Using stable isotopes, we evaluated temporal and spatial variability in the diet of southern sea lion (Otaria flavescens), and assessed its response to seasonal and stochastic variability in native prey and escaped salmon. Demersal fishes (median contribution range = 50–79 %) and escaped salmon (6–44 %) were the most important prey, in all colonies and seasons examined. The median estimated contributions of caged salmon, Munida gregaria and Sprattus fuegensis were consistently lower than 10% in all colonies and seasons. Variability in the relative availability of stocked and escaped salmon, as well as in Merluccius australis and S. fuegensis, showed limited influence on the contribution of these prey to the diet. Thus, although a noticeable response was evident after a large-scale escape of farmed Atlantic salmon that occurred during the study period, the opportunistic behaviour of southern sea lion seems questionable. A better understanding of dietary responses to induced changes in prey availability may have management implications in marine habitats affected by overfishing and farming of exotic species.

Kleptoparasitism from condors to eagles mediated by an exotic prey

The presence of alien invasive species can enhance competitive interactions between native species. A common type of direct competition is kleptoparasitism, i.e., the theft of food. This foraging strategy is closely linked to scavenging and can represent a central source of food for some populations and species. Here, we describe novel observations of an obligate scavenger, the Andean condor (Vultur gryphus), stealing invasive European hares (Lepus europaeus) hunted by a large raptor, the Black-chested Buzzard eagle (Geranoaetus melanoleucus), in southern Argentina. We re-analyzed data on food habits of sympatric, obligate scavengers to show that Andean condors consume more hare than two smaller vultures. Our observations suggest that the prevalence of European hare in the diet of Andean condors is partially due to opportunistic kleptoparasitism of the Black-chested Buzzard eagle. We propose that condors kleptoparasite eagles regularly, with cascading consequences for the population dynamics of condors, eagles, and hares. Our observation illustrates how novel food resources generated by invasive species can lead to new context-dependent competitive interactions between obligate scavengers and apex predators.

The native and exotic prey community of two invasive paper wasps (Hymenoptera: Vespidae) in New Zealand as determined by DNA barcoding

Social wasps are invasive in many regions around the world. In their new communities, introduced predators such as these wasps may be beneficial as consumers of exotic pests, but they will also consume native species. Here, we examined the diet of the exotic European paper wasp (Polistes dominula) and the closely related congener, Polistes chinensis, in a region of New Zealand where they co-occur. DNA barcoding was used to analyse their diet. The diet of both wasp species was largely Lepidopteran but other orders such as Hemiptera, Diptera and Coleoptera were also represented. Our analysis showed substantial site-to-site variation in diet. The two wasps differed significantly in their prey, although these differences appear to be driven by taxa identified from a small number of DNA reads in a small number of samples. Native and introduced fauna were represented in the diets of both wasps and included important agricultural pests. Of the 92 prey taxa able to be identified to species level, 81 were identified as exotic or introduced to New Zealand. The remaining 11 were species native to New Zealand. However, our estimates suggest over 50% of the prey DNA in the wasp diet is derived from native species. These wasps are abundant in some coastal and urban habitats, where they are likely to consume pest species as well as native species of conservation importance. The ecosystem services or costs and benefits provided by these invasive species are likely to be contingent on the prey communities and habitats they occupy.

Poisoned chalice: Use of transformed landscapes associated with increased persistent organic pollutant concentrations and potential immune effects for an adaptable carnivore

Wildlife around cities bioaccumulate multiple harmful environmental pollutants associated with human activities. Exposure severity can vary based on foraging behaviour and habitat use, which can be examined to elucidate exposure pathways. Carnivores can play vital roles in ecosystem stability but are particularly vulnerable to bioaccumulation of pollutants. Understanding the spatial and dietary predictors of these contaminants can inform pollutant control, and carnivores, at the top of food webs, can act as useful indicator species. We test for exposure to toxic organochlorines (OCs), including dichloro-diphenyl-trichloroethane (DDT) and polychlorinated biphenyls (PCBs), in a medium-sized felid, the caracal (Caracal caracal), across the peri-urban and agricultural landscapes of the city of Cape Town, South Africa. Concentrations in both blood (n = 69) and adipose tissue (n = 25) were analysed along with detailed spatial, dietary, demographic, and physiological data to assess OC sources and exposure risk. The analysis revealed widespread exposure of Cape Town's caracals to organochlorines: detection rate was 100% for PCBs and 83% for DDTs in blood, and 100% for both compounds in adipose. Caracals using human-transformed areas, such as vineyards and areas with higher human population and electrical transformer density, as well as wetland areas, had higher organochlorine burdens. These landscapes were also highly selected foraging areas, suggesting caracals are drawn into areas that co-incidentally increase their risk of exposure to these pollutants. Further, biomagnification potential was higher in individuals feeding on higher trophic level prey and on exotic prey. These findings point to bioaccumulation of OC toxicants and widespread exposure across local food webs. Additionally, we report possible physiological effects of exposure, including elevated white blood cell and platelet count, suggesting a degree of immunological response that may increase disease susceptibility. Cape Town's urban fringes likely represent a source of toxic chemicals for wildlife and require focused attention and action to ensure persistence of this adaptable mesocarnivore.

Exotic Prey Facilitate Coexistence between Pumas and Culpeo Foxes in the Andes of Central Chile

Coexistence between species with similar ecological niches implies species must segregate along one or more niche axes to survive. Space, time, and trophic resources are regarded as the principal axes upon which species segregate. We examined segregation along these niche axes to determine mechanisms underlying coexistence between the two main predators, puma (Puma concolor) and culpeo foxes (Lycalopex culpaeus) in the Andes of Central Chile. We used occupancy modeling to examine space use and overlap, Kernel Density Estimation to determine temporal activity patterns and overlap, and analysis of prey remains in feces to assess diet breadth and similarity. We found high spatial overlap and positive associations between detection of the carnivores lending little support for spatial segregation. Similarly, we found high nocturnal, temporal overlap between pumas and foxes that matched peaks in activity of prey. In contrast, we found relatively low dietary overlap indicating niche segregation likely occurs along the dietary axis. The Puma diet was dominated by introduced, exotic hares and foxes appeared to shift away from hares to rabbits, small mammals, and seeds. Given that lagomorphs are the main dietary resource for pumas in particular, management decisions regarding the control or eradication of such exotic species could negatively affected puma survival.

Run rabbit run: spotted-tailed quoll diet reveals invasive prey is top of the menu

Information about the ecological functional roles of native predators may help inform the conservation of wildlife and pest management. If predators show preferences for certain prey, such as invasive species, this could potentially be used as a conservation tool to help restore degraded (e.g. overgrazed) ecosystems via the reintroduction of native predators and suppression of exotic prey (e.g. introduced herbivores). The diet of spotted-tailed quolls was studied in a fenced reserve in south-eastern Australia where native mammals have been reintroduced, foxes and cats removed, but invasive European rabbits still persist. A total of 80 scats were collected over 12 months and analysis of macroscopic prey remains was conducted to determine diet. Rabbits were by far the most commonly consumed prey species by volume (~76%) and frequency (~60%), followed by brushtail possums (~11% for both volume and frequency), and other small and medium-sized native mammals in much smaller amounts. Quoll scat analysis revealed 10 mammal species in total, eight of which were native. Bird, reptile and invertebrate remains were uncommon in quoll scats. This suggests that spotted-tailed quolls may show a preference for preying on invasive European rabbits in certain contexts, and this could potentially be used as part of quoll reintroductions to aid rabbit population suppression and ecosystem restoration.

Effects of a low-thiamine diet on reproductive traits in three populations of Atlantic salmon targeted for reintroduction into Lake Ontario

Exotic prey fishes that have high thiaminase levels are associated with a thiamine deficiency and reduced fitness in many salmonids. If sensitivity to low thiamine availability differs among the three Atlantic salmon (Salmo salar) populations targeted for reintroduction into Lake Ontario, this could substantially influence their performance. We quantified the effects of a low-thiamine diet and a control diet on tissue thiamine concentrations, survival, growth rate, and reproductive traits (sperm and egg quality) in Atlantic salmon from the three candidate source populations. Fish that consumed the low-thiamine diet had comparable growth rates but lower survival and lower muscle thiamine concentrations (26 nmol·g–1) than control fish (34 nmol·g–1). Sperm count, velocity, motility, and longevity did not differ based on diet. Embryo survival was lower for females fed the low-thiamine diet, and the low-thiamine diet was associated with significantly lower egg thiamine concentrations (11 versus 17 nmol·g–1). The effects of the low-thiamine diet did not differ among the tested populations, which suggests that source population selection is unlikely to fully overcome this potential challenge for re-establishing wild populations.

Mercury in the fish of New York's Great Lakes: A quarter century of near stability.

We collected 849 fish of 16 species from New York portions of Lake Erie, Lake Ontario and the intervening Niagara River and its tributary Cayuga Creek, and analyzed fillets from individual fish for total mercury. Concentrations ranged from 0.029 to 1.090 ppm wet weight, with 92% below the EPA tissue residue criterion of 0.3 ppm, and thus not posing an undue risk from human consumption. We compared these 2010-2017 results to historical data spanning 40 years to assess temporal changes. The temporal pattern was generally consistent among water bodies and species: Mercury concentrations differed little between the most recent collections and fish taken from 1999-2008 and 1988-1996, while concentrations in all three of these periods were generally lower than in 1970. Smallmouth Bass from Lake Ontario were an exception with a continued decline, likely due to diet change following the introduction of exotic prey. Overall, though, fish tissue mercury concentrations from these large water bodies, which integrate regional influences, appear to have changed little in the last quarter century. We also report a consistent spatial pattern for multiple species having lower mercury concentrations in Lake Erie than in Lake Ontario over the period of record.

Predation on endangered species by human-subsidized domestic cats on Tokunoshima Island

It is important to unravel how invasive species impact native ecosystems in order to control them effectively. The presence of abundant exotic prey promotes population growth of invasive predators, thereby enhancing the predation pressure on native prey (hyper-predation). Not only the exotic prey but also feeding by humans is likely to cause “hyper-predation”. However, the contribution of artificial resources to this was underestimated in previous studies. Here, we combined fecal and stable isotope analyses to reveal short- and long-term food habits of free-ranging cats on Tokunoshima Island. Although 20.1% of the feral cat feces contained evidence of forest-living species, stable isotope analysis suggested that the cats were mostly dependent on artificial resources. In addition, a general linear model analysis showed that their diet was strongly correlated with landscape variables. These results indicate that the invasive free-ranging cats are aided by anthropogenic feeding, and they move from the human habituated area to natural areas with high biodiversity. These findings suggest the possibility of human feeding indirectly accelerates the effect of cat predation, and call for a further study on their demography. Cat management mainly involves trapping, but our findings show that educating local residents to stop feeding free-ranging cats and keeping pet cats indoors are also important.

Assessing the risk effects of native predators on the exotic American bullfrog (Lithobates catesbeianus) and their indirect consequences to ecosystem function

Understanding the factors and mechanisms that affect the impacts of invasive species in invaded environments has been widely debated among researchers. However, few studies about invasive species have explored the effects of predation risks by native predators on exotic prey. Herein, the traditional invasive predator-native prey framework was reversed. We tested if tadpoles, of the worldwide invasive American Bullfrog Lithobates catesbeianus, were affected by the predation risk imposed by native predators. We used two different species of belostomatid predators and tested whether and how predation-induced phenotypic plasticity on L. catesbeianus reverberated in morphological, physiological, and ecosystem-level processes. Individuals of L. catesbeianus modified their morphological (tail muscle width), behavioral (activity and foraging), and physiological (growth and growth efficiency) traits in the presence of predation risk. Based on the observed morphological changes, our results suggest that prey may recognize predator-specific cues. In addition, we observed that L. catesbeianus' responses to predation risk can affect ecosystem-level properties, by inducing trophic cascades and reducing animal-mediated nutrient recycling rates. In summary, our study supports that exotic prey species who are subjected to native predators may display anti-predator responses, with implications for their development, as well as possible ecosystem-level effects.

Naïve, bold, or just hungry? An invasive exotic prey species recognises but does not respond to its predators

Alien species experience both costs and benefits in invaded environments, through naivete of potential prey species, but also predation pressure from native predators. The question of whether alien prey recognise and respond to native predators has been relatively understudied, despite the hypothesised potential for native predators to provide biotic resistance to invasion. There are two main hypotheses about whether exotic prey should recognise native and exotic predators in their new ranges: (1) naivete—predicting recognition of evolutionarily familiar predators only, and (2) pre-adaptation—predicting recognition of all predators through a generalist recognition template. With regards to antipredator responses, (3) naivete theory presumes that exotic prey will respond to the predators they recognise, but we suggest that (4) a bold behavioural syndrome, and/or a high marginal value of food in invaded environments might result in weak or absent responses, even to recognised predators. Here we combine the giving-up density framework with behavioural analysis of remote camera footage to experimentally test these ideas in a disturbed, peri-urban, Australian ecosystem, where alien black rats are predated on by alien dogs, foxes, cats, and native quolls. Black rats recognised dogs and foxes, but appear naive towards quolls. However, they showed no antipredator responses at all, consistent with a bold behavioural syndrome, elevated predation risk, and/or a high marginal value of food in invaded environments.

Experimental Test of Preferences for an Invasive Prey by an Endangered Predator: Implications for Conservation.

Identifying impacts of exotic species on native populations is central to ecology and conservation. Although the effects of exotic predators on native prey have received much attention, the role of exotic prey on native predators is poorly understood. Determining if native predators actively prefer invasive prey over native prey has implications for interpreting invasion impacts, identifying the presence of evolutionary traps, and predator persistence. One of the world’s most invasive species, Pomacea maculata, has recently established in portions of the endangered Everglade snail kite’s (Rostrhamus sociabilis plumbeus) geographic range. Although these exotic snails could provide additional prey resources, they are typically much larger than the native snail, which can lead to lower foraging success and the potential for diminished energetic benefits in comparison to native snails. Nonetheless, snail kites frequently forage on exotic snails. We used choice experiments to evaluate snail kite foraging preference in relation to exotic species and snail size. We found that snail kites do not show a preference for native or exotic snails. Rather, snail kites generally showed a preference for medium-sized snails, the sizes reflective of large native snails. These results suggest that while snail kites frequently forage on exotic snails in the wild, this behavior is likely driven simply by the abundance of exotic snails rather than snail kites preferring exotics. This lack of preference offers insights to hypotheses regarding effects of exotic species, guidance regarding habitat and invasive species management, and illustrates how native-exotic relationships can be misleading in the absence of experimental tests of such interactions.

Medium-sized exotic prey create novel food webs: the case of predators and scavengers consuming lagomorphs.

Food web interactions are key to community structure. The introduction of species can be seen as an uncontrolled experiment of the addition of species. Introduced species lead to multiple changes, frequently threatening the native biodiversity. However, little is known about their direct effect on the upper level of the food web. In this study we review empirical data on the predator–prey relationship between the introduced lagomorphs and their consumers, and use meta-analytical tools to quantify the strength of their interactions. We expect that exotic lagomorphs will destabilize food webs, affect ecological processes and compromise the conservation of the invaded regions. We found 156 studies on the diet of 43 species of predators that consume lagomorphs as exotic preys in South America and Oceania. We found an average exotic lagomorphs-predator link of 20% which indicates a strong interaction, given that the average for the strongest links with native prey (when lagomorphs are not included in the predator diet) is about 24%. Additionally, this last link decreases to 17% when lagomorphs are present. When lagomorphs arrive in a new environment they may become the most important resource for predators, producing an unstable equilibrium in the novel food web. Any disruption of this interaction could have catastrophic consequences for the native diversity by directly impacting predators or indirectly impacting native preys by apparent competition. Eradication or any change in their abundances should be carefully considered in conservation actions since those will have great impacts on predator populations and ultimately in the whole communities.

Presence of Native Prey Does Not Divert Predation on Exotic Pests by Harmonia axyridis in Its Indigenous Range.

In China, two invasive pests, Bemisia tabaci MEAM1 (Gennadius) and Frankliniella occidentalis (Pergande), often co-occur with the native pest, Aphis gossypii (Glover), on plants of Malvaceae and Cucurbitaceae. All three are preyed on by the native ladybird, Harmonia axyridis (Pallas); however, the native predator might be expected to prefer native prey to the exotic ones due to a shared evolutionary past. In order to clarify whether the presence of native prey affected the consumption of these two invasive species by the native predator, field-cage experiments were conducted. A duplex qPCR was used to simultaneously detect both non-native pests within the gut of the predator. H. axyridis readily accepted both invasive prey species, but preferred B. tabaci. With all three prey species available, H. axyridis consumption of B. tabaci was 39.3±2.2% greater than consumption of F. occidentalis. The presence of A. gossypii reduced (by 59.9% on B. tabaci, and by 60.6% on F. occidentalis), but did not stop predation on the two exotic prey when all three were present. The consumption of B. tabaci was similar whether it was alone or together with A. gossypii. However, the presence of aphids reduced predation on the invasive thrips. Thus, some invasive prey may be incorporated into the prey range of a native generalist predator even in the presence of preferred native prey.

A native top predator relies on exotic prey inside a protected area: The puma and the introduced ungulates in Central Argentina

Top predators play an important role to preserving healthy and functional ecosystems. Predatory interactions among generalist predators and native prey may be altered due to occurrence and availability of introduced prey species. These interactions seldom receive attention in biodiversity conservation, particularly when establishing protected area management guidelines. In this study we described puma (Puma concolor) diet in a protected area from central Argentina, where red deer (Cervus elaphus) and wild boar (Sus scrofa) were regionally introduced for game a hundred years ago. We aimed to evaluate if the puma effectively bases its diet on native prey species maintaining natural ecological interactions despite the occurrence and availability of these introduced prey species. We analyzed 83 puma scats in a landscape containing both native and introduced species susceptible to predation. Results indicate that puma diet was composed mostly by introduced species, which represented 80.8% of the total biomass consumed (Cervus elaphus 40.6%, Sus scrofa 39.4%, and Ovis aries 0.8%). Pumas mainly preyed on introduced ungulates in the protected area, where management guidelines do not account for puma-native prey interactions. We suggest implementation of management actions to reduce densities of these introduced ungulates to restore natural ecological interactions between the puma and native prey.

Long‐term monitoring reveals declines in an endemic predator following invasion by an exotic prey species

AbstractInvasive predators can cause population declines in native prey species, but empirical evidence linking declines of native predators to invasive prey is relatively rare. Here, we document declines in an Australian freshwater crocodile Crocodylus johnstoni population following invasion of a toxic prey species, the cane toad Rhinella marina. Thirty‐five years of standardized spotlight surveys of four segments of a large river in northern Australia revealed that the density of freshwater crocodiles decreased following toad invasion and continued to decline thereafter. Overall, intermediate‐sized freshwater crocodiles (0.6–1.2 m) were most severely impacted. Densities of saltwater crocodiles Crocodylus porosus increased over time and were generally less affected by toad arrival, although toad impacts were inconsistent across survey sections and size classes. Across the entire river, total freshwater crocodile densities declined by 69.5% between 1997 and 2013. Assessments of the status of this species within other large river systems in northern Australia, where baseline data are available from before the toads arrived, should be prioritized. Our findings highlight the importance of long‐term monitoring programmes for quantifying the impacts of novel and unforeseen threats.

Altered trophic pathway and parasitism in a native predator (Lepomis gibbosus) feeding on introduced prey (Dreissena polymorpha)

Populations of invasive species tend to have fewer parasites in their introduced ranges than in their native ranges and are also thought to have fewer parasites than native prey. This 'release' from parasites has unstudied implications for native predators feeding on exotic prey. In particular, shifts from native to exotic prey should reduce levels of trophically transmitted parasites. We tested this hypothesis in native populations of pumpkinseed sunfish (Lepomis gibbosus) in Lake Opinicon, where fish stomach contents were studied intensively in the 1970s, prior to the appearance of exotic zebra mussels (Dreissena polymorpha) in the mid-1990s. Zebra mussels were common in stomachs of present-day pumpkinseeds, and stable isotopes of carbon and nitrogen confirmed their importance in long-term diets. Because historical parasite data were not available in Lake Opinicon, we also surveyed stomach contents and parasites in pumpkinseed in both Lake Opinicon and an ecologically similar, neighboring lake where zebra mussels were absent. Stomach contents of pumpkinseed in the companion lake did not differ from those of pre-invasion fish from Lake Opinicon. The companion lake, therefore, served as a surrogate "pre-invasion" reference to assess effects of zebra mussel consumption on parasites in pumpkinseed. Trophically transmitted parasites were less species-rich and abundant in Lake Opinicon, where fish fed on zebra mussels, although factors other than zebra mussel consumption may contribute to these differences. Predation on zebra mussels has clearly contributed to a novel trophic coupling between littoral and pelagic food webs in Lake Opinicon.

Trophic interactions between puma and endemic culpeo fox after livestock removal in the high mountains of central Argentina

Abstract This study presents the first data on the diet of the puma (Puma concolor) and an endemic culpeo fox (Pseudalopex culpaeus smithersi) in the high mountains of central Argentina, based on scat analysis. Trophic interactions of both carnivores were examined from 2003 to 2008 inside a protected area after livestock removal. A total of 604 scats were analyzed. Native species (small cavids and cricetine rodents) were most frequently consumed (58%–100%) by both carnivores. Exotic prey were consumed more in 2003 than in other years by both carnivores. Culpeo foxes consumed a higher number of prey items and a lower mean weight of mammalian prey than pumas. Niche breadth was high for pumas in 2003 and for culpeo foxes in 2004, decreasing in subsequent years with the same tendency in both carnivores. Diet overlap was high in all years. Pumas seemed to prey on available prey items, suggesting a trend toward diet specialization in small prey in both carnivores. Native prey are the most important food items for both carnivores inside the park; these results are encouraging in terms of the resilience of at least some components of the predator-prey assemblage in the high mountains of central Argentina.

Invasion by a non-native ecosystem engineer alters distribution of a native predator

Aim Shifts in diet composition, abundance or distribution of native predators can occur as a result of exotic prey introductions. We examined effects of non-native earthworms and anthropogenic landscape disturbance on habitat selection by the American robin (Turdus migratorius), a generalist predator, at landscape and local levels. We also investigated whether robins could act as vectors of spread for earthworm cocoons (egg cases). Location Boreal forest of Alberta, Canada. Methods We conducted robin and earthworm surveys at campgrounds, well pads, roads, pipelines, seismic lines and forest interiors across northern Alberta. At a subset of paired locations that had similar habitats and anthropogenic disturbance levels, we sampled both robins and earthworms. Results Both groups were most likely to occur at campgrounds, well pads and roads. Furthermore, robins were more likely to occur at locations where earthworms were present in our paired local-level surveys. This correlation between robin and earthworm distributions could be due to robins acting as a vector for earthworm spread, rather than robins’ use of earthworms as prey. However, in tests using captive robins, earthworm cocoons did not survive digestion. Main conclusions Robin and earthworm distributions were correlated, likely due to robins’ use of earthworms as prey. These results suggest exotic prey can strongly influence native predators at both landscape and local levels, with shifts in native predator distributions occurring as a result of spatial variability in exotic prey distributions. Although the impacts of ecosystem engineering by earthworms have been previously demonstrated, our study provides evidence that effects of earthworms can also cascade upwards via trophic interactions.