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1.
    
Human population migrations, as well as long‐distance trade activities, have been responsible for the spread of many invasive organisms. The black rat, Rattus rattus, has colonized most of the world following ship‐mediated trade. Owing to its tight association with human infrastructures, this species has been able to survive in unfavourable environments, such as Sahelian Africa. In this work, we combined interview‐based and population genetic surveys to investigate the processes underlying the ongoing invasion of south‐western Niger by black rats, with special emphasis on the capital city, Niamey. Our trapping and interview data are quite congruent, and all together point towards a patchy, but rather widespread, current distribution of R. rattus. Genetic data strongly suggest that road network development for truck‐based commercial flow from/to international harbours located in neighbouring countries (Benin, Togo, and Nigeria) facilitates the passive dispersal of black rats over a long distance through unfavourable landscapes. Another potentially, more ancient, invasion route may be associated with boat transport along the Niger River. Human‐mediated dispersal thus probably allows the foundation of persisting populations within highly anthropized areas while population dynamics may be more unstable in remote areas and mostly depends on propagule pressure.  相似文献   

2.
    
Species abundance is typically determined by the abiotic environment, but the extent to which such effects occur through the mediation of biotic interactions, including mutualisms, is unknown. We explored how light environment (open meadow vs. shaded understory) mediates the abundance and ant tending of the aphid Aphis helianthi feeding on the herb Ligusticum porteri. Yearly surveys consistently found aphids to be more than 17‐fold more abundant on open meadow plants than on shaded understory plants. Manipulations demonstrated that this abundance pattern was not due to the direct effects of light environment on aphid performance, or indirectly through host plant quality or the effects of predators. Instead, open meadows had higher ant abundance and per capita rates of aphid tending and, accordingly, ants increased aphid population growth in meadow but not understory environments. The abiotic environment thus drives the abundance of this herbivore exclusively through the mediation of a protection mutualism.  相似文献   

3.
    
The decline of amphibians has been of international concern for more than two decades, and the global spread of introduced fauna is a major factor in this decline. Conservation management decisions to implement control of introduced fauna are often based on diet studies. One of the most common metrics to report in diet studies is Frequency of Occurrence (FO), but this can be difficult to interpret, as it does not include a temporal perspective. Here, we examine the potential for FO data derived from molecular diet analysis to inform invasive species management, using invasive ship rats (Rattus rattus) and endemic frogs (Leiopelma spp.) in New Zealand as a case study. Only two endemic frog species persist on the mainland. One of these, Leiopelma archeyi, is Critically Endangered (IUCN 2017) and ranked as the world's most evolutionarily distinct and globally endangered amphibian (EDGE, 2018). Ship rat stomach contents were collected by kill‐trapping and subjected to three methods of diet analysis (one morphological and two DNA‐based). A new primer pair was developed targeting all anuran species that exhibits good coverage, high taxonomic resolution, and reasonable specificity. Incorporating a temporal parameter allowed us to calculate the minimum number of ingestion events per rat per night, providing a more intuitive metric than the more commonly reported FO. We are not aware of other DNA‐based diet studies that have incorporated a temporal parameter into FO data. The usefulness of such a metric will depend on the study system, in particular the feeding ecology of the predator. Ship rats are consuming both species of native frogs present on mainland New Zealand, and this study provides the first detections of remains of these species in mammalian stomach contents.  相似文献   

4.
    
Direct predation upon parasites has the potential to reduce infection in host populations. For example, the fungal parasite of amphibians, Batrachochytrium dendrobatidis (Bd), is commonly transmitted through a free‐swimming zoospore stage that may be vulnerable to predation. Potential predators of Bd include freshwater zooplankton that graze on organisms in the water column. We tested the ability of two species of freshwater crustacean (Daphnia magna and D. dentifera) to consume Bd and to reduce Bd density in water and infection in tadpoles. In a series of laboratory experiments, we allowed Daphnia to graze in water containing Bd while manipulating Daphnia densities, Daphnia species identity, grazing periods and concentrations of suspended algae (Ankistrodesmus falcatus). We then exposed tadpoles to the grazed water. We found that high densities of D. magna reduced the amount of Bd detected in water, leading to a reduction in the proportion of tadpoles that became infected. Daphnia dentifera, a smaller species of Daphnia, also reduced Bd in water samples, but did not have an effect on tadpole infection. We also found that algae affected Bd in complex ways. When Daphnia were absent, less Bd was detected in water and tadpole samples when concentrations of algae were higher, indicating a direct negative effect of algae on Bd. When Daphnia were present, however, the amount of Bd detected in water samples showed the opposite trend, with less Bd when densities of algae were lower. Our results indicate that Daphnia can reduce Bd levels in water and infection in tadpoles, but these effects vary with species, algal concentration, and Daphnia density. Therefore, the ability of predators to consume parasites and reduce infection is likely to vary depending on ecological context.  相似文献   

5.
    
Parasite transmission is determined by the rate of contact between a susceptible host and an infective stage and susceptibility to infection given an exposure event. Attempts to measure levels of variation in exposure in natural populations can be especially challenging. The level of exposure to a major class of parasites, trophically transmitted parasites, can be estimated by investigating the host's feeding behaviour. Since the parasites rely on the ingestion of infective intermediate hosts for transmission, the potential for exposure to infection is inherently linked to the definitive host's feeding ecology. Here, we combined epidemiological data and molecular analyses (polymerase chain reaction) of the diet of the definitive host, the white‐footed mouse (Peromyscus leucopus), to investigate temporal and individual heterogeneities in exposure to infection. Our results show that the consumption of cricket intermediate hosts accounted for much of the variation in infection; mice that had consumed crickets were four times more likely to become infected than animals that tested negative for cricket DNA. In particular, pregnant female hosts were three times more likely to consume crickets, which corresponded to a threefold increase in infection compared with nonpregnant females. Interestingly, males in breeding condition had a higher rate of infection even though breeding males were just as likely to test positive for cricket consumption as nonbreeding males. These results suggest that while heterogeneity in host diet served as a strong predictor of exposure risk, differential susceptibility to infection may also play a key role, particularly among male hosts. By combining PCR analyses with epidemiological data, we revealed temporal variation in exposure through prey consumption and identified potentially important individual heterogeneities in parasite transmission.  相似文献   

6.
    
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7.
    
A major goal in the study of mutualism is to understand how co‐operation is maintained when mutualism may potentially turn into parasitism. Although certain mechanisms facilitate the persistence of mutualism, parasitic species have repeatedly evolved from mutualistic ancestors. However, documented examples of mutualism reversals are still rare. Leafflowers (Phyllantheae; Phyllanthaceae) include approximately 500 species that engage in obligate mutualism with leafflower moths (Epicephala; Gracillariidae), which actively pollinate flowers, and whose larvae feed on the resulting seeds. We found that the Taiwanese population of the Phyllanthus reticulatus species complex was associated with six sympatric Epicephala species, of which three were derived parasites that induced gall formation on flowers/buds and produced no seeds. Notably, two parasitic species have retained mutualistic pollination behaviour, suggesting that the parasitism was likely not selected for to reduce the cost of mutualism. We propose that the galling habit evolved as an adaptation to escape parasitism by a specialized braconid wasp. The tough gall produced by one species was almost free of braconid parasitism, and the swollen gall induced by the other species probably prevents attack as a result of the larger airspace inside the gall. Our findings suggest that the presence of a third‐party partner can greatly influence the evolutionary fate of mutualisms, regardless of whether the pairwise interaction continues to favour co‐operation.  相似文献   

8.
    
Theories involving niche diversification to explain high levels of tropical diversity propose that species are more likely to co‐occur if they partition at least one dimension of their ecological niche space. Yet, numerous species appear to have widely overlapping niches based upon broad categorizations of resource use or functional traits. In particular, the extent to which food partitioning contributes to species coexistence in hyperdiverse tropical ecosystems remains unresolved. Here, we use a molecular approach to investigate inter‐ and intraspecific dietary partitioning between two species of damselfish (Dascyllus flavicaudus, Chromis viridis) that commonly co‐occur in branching corals. Species‐level identification of their diverse zooplankton prey revealed significant differences in diet composition between species despite their seemingly similar feeding strategies. Dascyllus exhibited a more diverse diet than Chromis, whereas Chromis tended to select larger prey items. A large calanoid copepod, Labidocera sp., found in low density and higher in the water column during the day, explained more than 19% of the variation in dietary composition between Dascyllus and Chromis. Dascyllus did not significantly shift its diet in the presence of Chromis, which suggests intrinsic differences in feeding behaviour. Finally, prey composition significantly shifted during the ontogeny of both fish species. Our findings show that levels of dietary specialization among coral reef associated species have likely been underestimated, and they underscore the importance of characterizing trophic webs in tropical ecosystems at higher levels of taxonomic resolution. They also suggest that niche redundancy may not be as common as previously thought.  相似文献   

9.
    
Plants are exposed to microbial pathogens as well as herbivorous insects and their natural enemies. Here, we examined the effects of inoculation of potato plants, Solanum tuberosum L. (Solanaceae), with the late blight pathogen Phytophthora infestans (Mont.) de Bary (Peronosporales: Pythiaceae) on an aphid species commonly infesting potato crops and one of the aphid's major parasitoids. We observed the peach‐potato aphid, Myzus persicae Sulzer (Hemiptera: Aphididae), and its natural enemy, the biocontrol agent Aphidius colemani Viereck (Hymenoptera: Braconidae), on potato either inoculated with water or P. infestans. Population growth of the aphid, parasitism rate of its natural enemy, and other insect life‐history traits were compared on several potato genotypes, the susceptible cultivar Désirée and genetically modified (GM) isogenic lines carrying genes conferring resistance to P. infestans. Effects of P. infestans inoculation on the intrinsic rate of aphid population increase and the performance of the parasitoid were only found on the susceptible cultivar. Insect traits were similar when comparing inoculated with non‐inoculated resistant GM genotypes. We also tested how GM‐plant characteristics such as location of gene insertion and number of R genes could influence non‐target insects by comparing insect performance among GM events. Different transformation events leading to different positions of R‐gene insertion in the genome influenced aphids either with or without P. infestans infection, whereas effects of position of R‐gene insertion on the parasitoid A. colemani were evident only in the presence of inoculation with P. infestans. We conclude that it is important to study different transformation events before continuing with further stages of risk assessment of this GM crop. This provides important information on the effects of plant resistance to a phytopathogen on non‐target insects at various trophic levels.  相似文献   

10.
    
Invasive species pose one of the greatest threats to biodiversity. This study investigates the extent to which human disturbance to natural ecosystems facilitates the spread of non‐native species, focusing on a small mammal community in selectively logged rain forest, Sabah, Borneo. The microhabitat preferences of the invasive Rattus rattus and three native species of small mammal were examined in three‐dimensional space by combining the spool‐and‐line technique with a novel method for quantifying fine‐scale habitat selection. These methods allowed the detection of significant differences for each species between the microhabitats used compared with alternative, available microhabitats that were avoided. Rattus rattus showed the greatest preference for heavily disturbed habitats, and in contrast to two native small mammals of the genus Maxomys, R. rattus showed high levels of arboreal behavior, frequently leaving the forest floor and traveling through the understory and midstory forest strata. This behavior may enable R. rattus to effectively utilize the complex three‐dimensional space of the lower strata in degraded forests, which is characterized by dense vegetation. The behavioral flexibility of R. rattus to operate in both terrestrial and arboreal space may facilitate its invasion into degraded forests. Human activities that generate heavily disturbed habitats preferred by R. rattus may promote the establishment of this invasive species in tropical forests in Borneo, and possibly elsewhere. We present this as an example of a synergistic effect, whereby forest disturbance directly threatens biodiversity and indirectly increases the threat posed by invasive species, creating habitat conditions that facilitate the establishment of non‐native fauna.  相似文献   

11.
    
Chemical information is used in a variety of contexts including habitat recognition, foraging and predator avoidance, and a plethora of studies have shown that an individual's distinct chemical profile can mediate interactions with conspecifics. Interestingly, recent work has revealed that diet alone is sufficient to change the chemical profile of individuals, and with it, the way other individuals perceive and interact with them. Free amino acids are known to be utilised across species in a range of contexts, including during predator–prey and host–parasite interactions, and have been widely postulated to underpin diet‐mediated social interactions, especially in fish. However, so far no empirical evidence has been presented to support this suggestion. Using an established behavioural assay in three‐spined sticklebacks (Gasterosteus aculeatus), we aimed to assess association preferences in groups of fish fed experimental diets which differed by a single free amino acid. Our results demonstrate that free amino acids alone are sufficient to mediate interindividual association preferences, raising the possibility that such a mechanism may be widespread among aquatic animals.  相似文献   

12.
    
  1. The importance of terrestrial carbon in aquatic ecosystems is widely recognised, but patterns of terrestrial reliance can be variable. Fish often act as important links between terrestrial and aquatic ecosystems, but little is known about how resource seasonality and fish density influence fish reliance on terrestrial energy in lakes.
  2. We sampled a high‐latitude subarctic lake in Finnish Lapland during the open‐water season over three consecutive years to assess both patterns of terrestrial reliance and trophic niche structure of introduced brown trout (Salmo trutta), the only resident fish species. The small size of the study lake made it possible to sample the whole population by conducting a complete fish removal, allowing for a direct assessment of size structure and changes in brown trout density over time.
  3. We hypothesised that annual and seasonal shifts in the dietary niches of brown trout would directly track the availability of pulsed resources such as aquatic and terrestrial insects as well as rodents. We further expected that dietary niche shifts would be correlated with population density, leading to a smaller trophic niche size at lower densities. We therefore investigated the annual and seasonal patterns of resource use using measures of dietary niche and in particular of terrestrial reliance, derived from stomach content analysis and stable‐isotope analyses (SIA) of liver and muscle, along a temporal gradient of declining fish density.
  4. According to stomach content, terrestrial reliance in brown trout was the highest in each year at mid‐to‐late summer, evidently following the peak abundance of terrestrial invertebrates and rodents. Surprisingly, we could not detect annual or seasonal shifts in terrestrial reliance from estimates provided by isotope ratios in muscle or liver. Furthermore, fish density did not appear to influence either terrestrial reliance or trophic niche size. However, trophic position derived from SIA of liver tissue decreased with decreasing densities, while fish condition increased.
  5. Large, consistent pulses of terrestrial invertebrates in mid‐summer (or rodents during their peak years) are likely important for brown trout in the long term and could explain the lack of density‐dependent correlation in terrestrial reliance. However, further studies are needed to link the abundance of pulsed resources to resource use by fish across wider gradients of lake size, productivity and fish density.
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13.
    
Anthropophilic species (“commensal” species) that are completely dependent upon anthropic habitats experience different selective pressures particularly in terms of food than their noncommensal counterparts. Using a next‐generation sequencing approach, we characterized and compared the gut microflora community of 53 commensal Rattus rattus and 59 noncommensal Rattus satarae captured in 10 locations in the Western Ghats, India. We observed that, while species identity was important in characterizing the microflora communities of the two Rattus hosts, environmental factors also had a significant effect. While there was significant geographic variation in the microflora of the noncommensal R. satarae, there was no effect of geographic distance on gut microflora of the commensal R. rattus. Interestingly, host genetic distance did not significantly influence the community in either Rattus hosts. Collectively, these results indicate that a shift in habitat is likely to result in a change in the gut microflora community and imply that the gut microflora is a complex trait, influenced by various parameters in different habitats.  相似文献   

14.
    
  1. Climatic warming has induced marked shifts in the geographical distribution and seasonal phenology of many species, although the impacts of climatic changes on the interactions between species across trophic levels are far less well known.
  2. Freshwater microcosms were used to test the effect of temperature on the life history traits of a prey species, the fairy shrimp Chirocephalus diaphanus (Anostraca), the abundance of a predator, the microcrustacean Heterocypris incongruens (Ostracoda), and on the interaction between them.
  3. When reared in the absence of predators, C. diaphanus survival was low at the highest temperature (25 °C) and greatly reduced at the lowest temperature (5 °C). It was reproductively most successful at an intermediate temperature (20 °C), suggesting that it may benefit from the increase in temperature predicted under future climate change scenarios. In the absence of other species, temperature would have to increase dramatically to affect C. diaphanus adversely.
  4. Heterocypris incongruens was more abundant and its predation on C. diaphanus greatest at higher temperatures, partially offsetting the positive effect of raised temperature on prey observed when the predator was absent. The net effect was that the optimal temperature for C. diaphanus when coexisting with its predator was lower than when it was in isolation. This means that currently predicted increases in temperature ultimately may be detrimental to C. diaphanus.
  5. Predation rates were generally enhanced by high temperature, prey size and prey density, with significant interaction between them. Thus, the positive effects of raised temperature on predation rate were additionally dependent upon prey characteristics, being strongest when prey were large and at high density and weakest when prey were small and at low density.
  6. Interactions with a natural enemy, in this case a predator, may alter how species respond to raised temperatures; prey size and density further modify the outcome of this interaction. This context dependency in the response of both predators and prey to temperature suggests that the ecological impacts of future climate change on trophic interactions may be difficult to predict.
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15.
    
Recently, several species of aerial‐hawking bats have been found to prey on migrating songbirds, but details on this behaviour and its relevance for bird migration are still unclear. We sequenced avian DNA in feather‐containing scats of the bird‐feeding bat Nyctalus lasiopterus from Spain collected during bird migration seasons. We found very high prey diversity, with 31 bird species from eight families of Passeriformes, almost all of which were nocturnally flying sub‐Saharan migrants. Moreover, species using tree hollows or nest boxes in the study area during migration periods were not present in the bats’ diet, indicating that birds are solely captured on the wing during night‐time passage. Additional to a generalist feeding strategy, we found that bats selected medium‐sized bird species, thereby assumingly optimizing their energetic cost‐benefit balance and injury risk. Surprisingly, bats preyed upon birds half their own body mass. This shows that the 5% prey to predator body mass ratio traditionally assumed for aerial hunting bats does not apply to this hunting strategy or even underestimates these animals’ behavioural and mechanical abilities. Considering the bats’ generalist feeding strategy and their large prey size range, we suggest that nocturnal bat predation may have influenced the evolution of bird migration strategies and behaviour.  相似文献   

16.
    
The northward expansion of round sardinella (Sardinella aurita) in the Mediterranean Sea, together with declines and fluctuations in biomass and landings of European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) observed in recent decades, may suggest potential inter‐specific competition in the pelagic domain. The coexistence of sympatric zooplanktivorous fish species might therefore be exposed in part to trophic niche overlap and competition for food. Combining visual diet characterization under the microscope with DNA metabarcoding from stomach contents of fish collected in spring results show that predation on relatively large krill is equally important for sardinella than for the other two niche overlapping species. Furthermore, an important overlap is found in their isotopic niche, especially with anchovy, using nitrogen (δ15N) and carbon (δ13C) stable isotopes in muscle tissue. In fact, the three fish species are able to feed effectively in the whole prey size spectrum available during the sampled season, from the smallest diatoms and copepods to the larger prey (i.e., decapods and euphausiids), including fish larvae. Moreover, effective predation upon other large prey like siphonophores, which is observed only when multi‐proxy analyses in stomach contents are applied, might also be relevant in the diet of sardinella. The overlapping diet composition in spring, together with the effective use of food resource by sardinella, can be of special interest in potential future scenarios with warmer water temperature leading to lower zooplankton and/or higher jellyfish availability, where sardinella may take advantage over other species due to its feeding plasticity.  相似文献   

17.
    
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18.
    
The blacklegged tick Ixodes scapularis is the primary vector for the bacterium causing Lyme disease in eastern North America and for other medically important pathogens. This species is vulnerable to attack by fungal pathogens and arthropod predators, but the impacts of interactions between biocontrol agents have not been examined. The biocontrol agent Met52®, containing the entomopathogenic fungus Metarhizium brunneum (=M. anisopliae), controls blacklegged ticks with efficacy comparable to chemical acaricides. The brush‐legged wolf spider Schizocosa ocreata is a predator of I. scapularis that reduces their survival under field conditions. We conducted a field microcosm experiment to assess the compatibility of Met52 and S. ocreata as tick biocontrol agents. We compared the fits of alternative models in predicting survival of unfed (flat) and blood‐fed (engorged) nymphs. We found the strongest support for a model that included negative effects of Met52 and S. ocreata on flat nymph survival. We found evidence for interference between biocontrol agents, with Met52 reducing spider survival, but we did not find a significant interaction effect between the two agents on nymph survival. For engorged nymphs, low recovery rates resulted in low statistical power to detect possible effects of biocontrol agents. We found that nymph questing activity was lower when the spider was active above the leaf litter than when the spider was unobserved. This provides the first evidence that predation cues might affect behavior important for tick fitness and pathogen transmission. This study presents field microcosm evidence that the biopesticide Met52 and spider Schizocosa ocreata each reduced survival of blacklegged ticks Ixodes scapularis. Met52 reduced spider survival. Potential interference between Met52 and the spider should be examined at larger scales, where overlap patterns may differ. Ticks were more likely to quest when the spider was inactive, suggesting the ticks changed their behavior to reduce danger.  相似文献   

19.
    
Invasive species have led to precipitous declines in biodiversity, especially in island systems. Brown (Rattus norvegicus) and black rats (R. rattus) are among the most invasive animals on the planet, with eradication being the primary tool for established island populations. The need for increased research for defining eradication units and monitoring outcomes has been highlighted as a means to maximize success. Haida Gwaii is an archipelago ~100 km off the northern coast of British Columbia, Canada, that hosts globally significant breeding populations of seabirds that are at risk due to invasive rats. Here, we paired sampling of brown (n = 287) and black (n = 291) rats across the Haida Gwaii archipelago with genotyping by sequencing (10,770–27,686 SNPs) to investigate patterns of population connectivity and infer levels/direction of gene flow among invasive rat populations in Haida Gwaii. We reconstructed three regional clusters for both species (north, central and south), with proximate populations within regions being largely more related than those that were more distant, consistent with predictions from island biogeography theory. Population assignment of recently detected individuals post‐eradication on Faraday, Murchison and the Bischof Islands revealed all were re‐invaders from Lyell Island, rather than being on‐island survivors. Based on these results, we identified six eradication units constituting single or clusters of islands that would limit the potential for reinvasion, some of which will need to be combined with biosecurity measures. Overall, our results highlight the importance of targeted research prior to conducting eradications and demonstrate a framework for applying population genomics for guiding invasive species management in island systems.  相似文献   

20.
    
Juvenile survival is a highly variable life‐history trait that is critical to population growth. Antipredator tactics, including an animal's use of its physical and social environment, are critical to juvenile survival. Here, we tested the hypothesis that habitat and social characteristics influence coyote (Canis latrans) predation on white‐tailed deer (Odocoileus virginianus) and mule deer (O. hemionus) fawns in similar ways during the neonatal period. This would contrast to winter when the habitat and social characteristics that provide the most safety for each species differ. We monitored seven cohorts of white‐tailed deer and mule deer fawns at a grassland study site in Alberta, Canada. We used logistic regression and a model selection procedure to determine how habitat characteristics, climatic conditions, and female density influenced fawn survival during the first 8 weeks of life. Fawn survival improved after springs with productive vegetation (high integrated Normalized Difference Vegetation Index values). Fawns that used steeper terrain were more likely to survive. Fawns of both species had improved survival in years with higher densities of mule deer females, but not with higher densities of white‐tailed deer females, as predicted if they benefit from protection by mule deer. Our results suggest that topographical variation is a critical resource for neonates of many ungulate species, even species like white‐tailed deer that use more gentle terrain when older. Further, our results raise the possibility that neonatal white‐tailed fawns may benefit from associating with mule deer females, which may contribute to the expansion of white‐tailed deer into areas occupied by mule deer.  相似文献   

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