Micro-eukaryotic communities are highly sensitive to environmental changes, and their structure offers crucial insights into the impact of human activities on aquatic habitats. Despite their significance, the assembly...Micro-eukaryotic communities are highly sensitive to environmental changes, and their structure offers crucial insights into the impact of human activities on aquatic habitats. Despite their significance, the assembly mechanisms of micro-eukaryotic communities in lake ecosystems heavily influenced by human activities are not well understood. In this study, we utilized 18S rDNA amplicon sequencing to examine the biodiversity of micro-eukaryotes over a one-year period in Lake Weishan, one of the largest freshwater lakes in northern China. We analyzed the ecological processes governing community assembly among key ecological groups, specifically habitat generalists and specialists. Our findings revealed substantial temporal variation in microbial diversity and community composition, likely driven by water temperature, dissolved oxygen, and the concentrations of several ions (e.g., Ca^(2+) and F^(−)). Notably, community assembly in this canal-disturbed lake was predominantly influenced by stochastic processes (58.18%) rather than deterministic processes (20.46%). Habitat specialists (425 operational taxonomic units, OTUs) exhibited significantly greater diversity compared to habitat generalists (189 OTUs) and were predominantly shaped by stochastic processes (52.47%). In contrast, habitat generalists were less influenced by these processes (17.69%). Altogether, these results suggest that the ecological processes governing micro-eukaryotic community assembly differ markedly between habitat generalists and specialists, primarily due to their varied adaptability to environmental changes.展开更多
Foundational concepts of trait spaces, including phenotypic plasticity and function of traits, should be expanded and better integrated with ecological theory. This article addresses two areas where plasticity theory ...Foundational concepts of trait spaces, including phenotypic plasticity and function of traits, should be expanded and better integrated with ecological theory. This article addresses two areas where plasticity theory can become further integrated with ecological, evolutionary, and developmental thinking. First is the idea that not only trait means within environments and plasticity of trait means across environments is optimized by selection, but that the entire shape of phenotype distributions such as variance or skew should be optimized within and across environments. In order for trait distribution shape to evolve into adaptations, there must be a genetic basis for and selection upon variation in distribution shapes and their plasticities. I present published and new data demonstrating genetic control and selection for higher moments of phenotype distributions; though, plasticity in these values has not yet been tested. Genetic control of phenotype distribution moments is shown for Neurospora crassa ascospore size and shape. Selection on trait distribution moments is shown for Eurosta solidaginis gall size. Second, there is a tradition in modeling plasti- city as an adaptive strategy that pits it as an alternative to ecological specialization or generaliza- tion. However, these strategies need not be considered alternatives. Rather, with environmental fluctuation within generations plasticity may produce additive or non-additive intermediate （gener- alist） phenotypes, or something new altogether. I present published and new data on the snail Physa virgata and fish Gambusia affinis that show plasticity produces partly intermediate （general- ist） and partly unique phenotypic elements in mixed and fluctuating environments. Plasticity can thus be viewed in the context of a broader trait space and as having broader ecological roles than currently is conceived.展开更多
Black bean aphid, Aphis fabae (Homoptera;Aphididae) is a serious pest causing crop loss. Plant-aphid interaction is a dynamic system subjected to continual variation and changes. Host plants induce various biochemical...Black bean aphid, Aphis fabae (Homoptera;Aphididae) is a serious pest causing crop loss. Plant-aphid interaction is a dynamic system subjected to continual variation and changes. Host plants induce various biochemical and physical defense mechanisms due to aphid feeding. Aphids can overcome plant defenses by enzymatic adaptations and sequestering secondary metabolites produced by the plant within their bodies as a defense against their enemies. Many strategies were developed and evolved by aphids in order to overcome plant defense barriers which allowed them to feed, grow and reproduce on their host plants. This study aimed to aid in better understanding of the effect of altering host plant on specialist and generalist aphid fitness.The influence of plant defense on population development of Aphis fabae was also investigated. Analyses for insect enzymes were also demonstrated in addition to further biochemical studies on host plant defences. Generalists showed different ecological and enzymatic adaptations towards host plants than specialist Aphis fabae. The results were fully discussed in details.展开更多
Prey choice is often evaluated at the species or population level. Here, we analyzed the diet of octopuses of different populations with the aim to assess the importance of individual feeding habits as a factor affect...Prey choice is often evaluated at the species or population level. Here, we analyzed the diet of octopuses of different populations with the aim to assess the importance of individual feeding habits as a factor affecting prey choice. Two methods were used, an assessment of the extent to which an individual octopus made choices of species representative of those population （PSi and IS） and 25% cutoff values for number of choices and percentage intake of individual on their prey. In one population of Octopus cfvulgaris in Bermuda individuals were generalist by IS=0.77, but most chose many prey of the same species, and were specialists on it by 〉75% intake. Another population had a wider prey selection, still generalist with PSi=0.66, but two individuals specialized by choices. In Bonaire, there was a wide range of prey species chosen, and the population was specialists by IS=0.42. Individual choices revealed seven specialists and four generalists. A population of Octopus cyanea in Hawaii all had similar choices of crustaceans, so the population was generalist by IS with 0.74. But by individual choices, three were considered a spe-cialist. A population of Enteroctopus dofleini from Puget Sound had a wide range of preferences, in which seven were also spe-cialists, IS=0.53, By individual choices, thirteen were also specialists. Given the octopus specialty of learning during foraging, we hypothesize that both localized prey availability and individual personality differences could influence the exploration for prey and this translates into different prey choices across individuals and populations showed in this study.展开更多
Characterizing the diversity and structure of host–parasite communities is crucial to understandingtheir eco-evolutionary dynamics.Malaria and related haemosporidian parasites are responsible forfitness loss and mort...Characterizing the diversity and structure of host–parasite communities is crucial to understandingtheir eco-evolutionary dynamics.Malaria and related haemosporidian parasites are responsible forfitness loss and mortality in bird species worldwide.However,despite exhibiting the greatest ornithologicalbiodiversity,avian haemosporidians from Neotropical regions are quite unexplored.Here,we analyze the genetic diversity of bird haemosporidian parasites(Plasmodium andHaemoproteus)in 1,336 individuals belonging to 206 bird species to explore for differences in diversityof parasite lineages and bird species across 5 well-differentiated Peruvian ecoregions.Wedetected 70 different haemosporidian lineages infecting 74 bird species.We showed that 25 out ofthe 70 haplotypes had not been previously recorded.Moreover,we also identified 81 new host–parasite interactions representing new host records for these haemosporidian parasites.Our outcomesrevealed that the effective diversity(as well as the richness,abundance,and Shannon–Weaver index)for both birds and parasite lineages was higher in Amazon basin ecoregions.Furthermore,we also showed that ecoregions with greater diversity of bird species also had highparasite richness,hence suggesting that host community is crucial in explaining parasite richness.Generalist parasites were found in ecoregions with lower bird diversity,implying that the abundanceand richness of hosts may shape the exploitation strategy followed by haemosporidian parasites.These outcomes reveal that Neotropical region is a major reservoir of unidentified haemosporidianlineages.Further studies analyzing host distribution and specificity of these parasites inthe tropics will provide important knowledge about phylogenetic relationships,phylogeography,and patterns of evolution and distribution of haemosporidian parasites.展开更多
Background: Harvesting of forest products is a widespread driver of disturbance in developing nations, where policies are increasingly aimed at managing natural forests for sustainable use. There is thus need for rese...Background: Harvesting of forest products is a widespread driver of disturbance in developing nations, where policies are increasingly aimed at managing natural forests for sustainable use. There is thus need for research aimed at understanding the impact of resource use on forest habitats and concomitant effects on biodiversity.Afromontane forests in the Eastern Cape, South Africa are harvested informally for poles and medicinal bark and occur along elevational gradients of 800–1600 m above sea level. Patterns of spatial diversity and human disturbance are expected to be affected by elevation. Furthermore, species’ responses to disturbance are expected to vary depending on their level of habitat specialisation. Understanding harvest impacts on forest biodiversity thus requires disentangling the separate effects of elevation and disturbance, and considering forest-specialist and forest-generalist species separately. This study comprises two components. First, harvest activities, resultant harvestmediated habitat heterogeneity, and avifaunal species richness, composition and beta-diversity were compared across two elevational zones in a harvested forest. Second, the role of harvest-mediated habitat heterogeneity in driving patterns of avifaunal diversity were assessed, while controlling for elevation, and considering forest-specialist and forest-generalist species separately.Results: Harvest rates were higher, and activities more varied in the lower elevation zone, with significant impacts of harvesting on habitat features resulting in higher harvest-mediated habitat heterogeneity at lower elevations.Harvest-mediated increases in habitat heterogeneity positively affected forest-generalist species richness, while forest-specialist richness was negatively affected. While species composition of both groups differed across elevational zones, variation in harvest-mediated habitat heterogeneity did not fully account for this, suggesting that factors other than disturbance shape avifaunal communities along the elevation gradient. However, variation in harvest-mediated habitat heterogeneity accounted for the amount of beta-diversity attributed to species turnover in the forest-specialist assemblage, indicating that harvest disturbances affect the mechanisms driving beta-diversity of this group.Conclusion: Spatial patterns of avifaunal diversity are affected by elevation over a 300-m gradient. Harvesting results in increased habitat heterogeneity, which variably affects avifaunal communities at the forest-scale, with positive effects for forest generalists and negative effects for forest-specialists.展开更多
There are five species of parasitic cowbirds (Molothrus) and the Brown-headed Cowbird (M. ater) is the only widespread species in North America. The Brown-headed Cowbird is a host generalist and is typically found in ...There are five species of parasitic cowbirds (Molothrus) and the Brown-headed Cowbird (M. ater) is the only widespread species in North America. The Brown-headed Cowbird is a host generalist and is typically found in open habitats and forest edges. The cowbirds are of a more recent origin than many other brood parasites and perhaps as a result, cowbird adaptations for parasitism and their hosts’ counter-adaptations to thwart parasitism do not appear as sophisticated as those of other brood parasite-host systems. Because of its generalist nature, the cowbird has the potential to negatively impact endangered host species whose populations are limited due to anthropogenic habitat loss. As a consequence, the Brown-headed Cowbird is one of the few brood parasitic species that is the subject of control programs to limit its effects on such hosts.展开更多
Glucosinolates and their hydrolysis products, found in plants of the order Brassicales, are well-known for their defensive properties against insect herbivores. Arabidopsis thaliana (Col-0) genetic lines with mutation...Glucosinolates and their hydrolysis products, found in plants of the order Brassicales, are well-known for their defensive properties against insect herbivores. Arabidopsis thaliana (Col-0) genetic lines with mutations that modify the type of glucosinolates (i.e. myb28myb29 and cyp79B2cyp79B3 are deficient in the production of aliphatic and indolyl glucosinolates, respectively) make it possible to test for the specific effects of these secondary chemicals on insect herbivores. The Pad3 mutant (deficient in camalexin), which has a role in resistance to pathogens, was also tested. Likewise, the effects of different glucosinolate hydrolysis products can be evaluated using genetically modified (GM) lines of the wild type Col-0 ecotype, which naturally produces isothiocyanates. These GM lines include the nitrile-producing 35S: ESP and the double knockout tgg1tgg2, which virtually lacks hydrolysis products. In both no-choice and choice experiments, the crucifer specialist Pieris rapae was virtually unaffected by differences in the type of glucosinolates or hydrolysis products. In contrast, the generalist insect Spodoptera exigua had statistically significant increases in pupae/adult weight and faster developmental times when reared on mutants deficient in the production of aliphatic and indolyl glucosinolates and their hydrolysis products. There were no differences in the performance of either insect species when reared on wild type Col-0 or Pad3. Results from feeding choice trials showed that Pieris rapae had no statistically significant preference for any of the genetic lines. In contrast, Spodoptera exigua had a significant feeding preference for the double mutant tgg1tgg2. This study provides evidence that variation in the type of glucosinolates and their hydrolysis products can influence insect performance and feeding choices, and that responses are species-specific.展开更多
Microorganisms are essential contributors to the forest ecosystems of the Qinghai-Xizang Plateau,encompassing generalists,intermediates,and specialists.Investigating the characteristics and drivers of these microbial ...Microorganisms are essential contributors to the forest ecosystems of the Qinghai-Xizang Plateau,encompassing generalists,intermediates,and specialists.Investigating the characteristics and drivers of these microbial sub-communities across varying elevations is essential for understanding their ecological functions in high-altitude forest soils.This study examines the diversity patterns,assembly processes,environmental adaptations,and potential functions of bacterial and fungal subcommunities along an elevation gradient from 3900 m to the timberline on Shergyla Mountain,China.The findings revealed notable differences between low and high elevations in the diversity and composition of microbial sub-communities.According to neutral and null models,generalists,characterized by the widest niche width and highest migration rates,were primarily influenced by stochastic processes(71.9%).In contrast,deterministic factors,including homogeneous and variable selection,exerted a stronger effect on the assembly of specialists(51.0%).Elevation and nutrient availability emerged as key environmental drivers shaping microbial sub-communities,particularly for specialists,while generalists experienced fewer constraints from environmental factors.Network analysis further demonstrated that habitat specialists occupy central positions within microbial networks,playing a pivotal role in maintaining network stability.Additionally,nitrogen cycling genes—specifically nifH,amoA,nirS and nosZ—exhibited a U-shaped distribution across the elevation gradient and showed a substantial correlation(p<0.05)with the Chao1 and Shannon indices of bacterial specialists.The results enhance our knowledge of microbial community dynamics and underscore the crucial ecological role of microbial specialists in the ecosystems of high-altitude forests.展开更多
In this paper,we investigate the influence of the nonlocal prey competition on the spatiotemporal dynamics for a generalist predator-prey system.The condition of stability and bifurcations is clearly determined.Our re...In this paper,we investigate the influence of the nonlocal prey competition on the spatiotemporal dynamics for a generalist predator-prey system.The condition of stability and bifurcations is clearly determined.Our results show that when the prey spreads quickly,the nonlocal intraspecific competition of the prey does not affect the dynamics,however,when the prey spreads slowly,it can affect the dynamics.Besides,no Hopf bifurcation occurs if the ratio of the growth rate of the predator to prey is larger,otherwise,system has Hopf bifurcation and Hopf Bogdanov-Takens bifurcation and so on.It is surprised that the system only with the nonlocal prey competition has more rich dynamics than the system with the nonlocal competitions in both the prey and the predator.The coexistence of bistable spatially inhomogeneous steady states is also found.展开更多
Aims Forest fragmentation and the associated augmentation of forest edge zones are increasing worldwide.Forest edges are characterized by altered plant species richness and community composition.As the tree layer and ...Aims Forest fragmentation and the associated augmentation of forest edge zones are increasing worldwide.Forest edges are characterized by altered plant species richness and community composition.As the tree layer and its species composition has been shown to influence herb layer composition,changes in tree species composition or richness may weaken or strengthen edge effects in forest ecosystems.We studied effects of the edge-center transition,tree species composition and their potential interaction on the understory vegetation in the Hainich National Park,Germany’s largest connected deciduous forest,allowing to cover large edge-center transects.Methods We established 12 transects in an area of 75 km^(2) of continuous forest,6 beech-dominated and 6 in multispecies forest stands.Each transect reached from the forest edge up to 500 m into the forest interior.Vegetation relevés were conducted in regular,logarithmic distances along each transect.Important Findings Herb species richness was influenced by an interaction of edge effects and tree diversity level.With increasing distance from the forest edge,herb species richness remained constant in multispecies forest stands but rapidly decreased in beech-dominated forest stands.Further,herb richness was higher in the interior of multispecies forest stands.Percent forest specialists increased and percent generalists decreased with distance from the edge and this contrasting pattern was much more pronounced in beech-dominated transects.By using structural equation modeling,we identified litter depth mediated by tree species composition as the most important driver of herb layer plant species richness.展开更多
Aims Plant diversity has been linked to both increasing and decreasing levels of arthropod herbivore damage in different plant communities.So far,these links have mainly been studied in grasslands or in artificial tre...Aims Plant diversity has been linked to both increasing and decreasing levels of arthropod herbivore damage in different plant communities.So far,these links have mainly been studied in grasslands or in artificial tree plantations with low species richness.Furthermore,most studies provide results from newly established experimental plant communities where trophic links are not fully established or from stands of tree saplings that have not yet developed a canopy.Here,we test how tree diversity in a species-rich subtropical forest in China with fully developed tree canopy affects levels of herbivore damage caused by different arthropod feeding guilds.Methods We established 27 plots of 30×30 m area.The plots were selected randomly but with the constraint that they had to span a large range of tree diversity as required for comparative studies in contrast to sample surveys.We recorded herbivore damage caused by arthropod feeding guilds(leaf chewers,leaf skeletonizers and sap feeders)on canopy leaves of all major tree species.Important Findings Levels of herbivore damage increased with tree species richness and tree phylogenetic diversity.These effects were most pronounced for damage caused by leaf chewers.Although the two diversity measures were highly correlated,we additionally found a significant interaction between them,whereby species richness increased herbivory mostly at low levels of phylogenetic diversity.Tree species with the lowest proportion of canopy leaf biomass in a plot tended to suffer the highest levels of herbivore damage,which is in contrast to expectations based on the resource concentration hypothesis.Our results are in agreement with expectations of the dietary mixing hypothesis where generalist herbivores with a broad spectrum of food plants benefit from increased resource diversity in tree species-rich forest patches.展开更多
Aims The superior performance of many non-indigenous species in a new range can be attributed to different factors such as pre-adaptation to environmental conditions in new areas or to factors inherent to displacement...Aims The superior performance of many non-indigenous species in a new range can be attributed to different factors such as pre-adaptation to environmental conditions in new areas or to factors inherent to displacement mechanisms such as loss of co-evolved pathogens and herbivores that increase the speed of evolutionary change towards a shift in allocation from defence to growth and reproduction.To assess the importance of the different mechanisms governing the success of Conyza canadensis,a globally successful invader,we simultaneously tested several recent hypotheses potentially explaining the factors leading to biological invasion.Methods We tested(i)whether plants from the non-native range showed a higher fitness than plants from the native North American range,(ii)whether they differed in resistance against an invasive generalist herbivore,the slug Arion lusitanicus and against a recently established specialist aphid herbivore,Uroleucon erigeronense and(iii)experimentally assessed whether C.canadensis releases allelopathic chemicals that have harmful effects on competing species in the nonnative range.We compared populations along a similar latitudinal gradient both in the native North American and invasive European range and analysed patterns of adaptive clinal variation in biomass production.Important Findings The invasion success of C.canadensis in Europe cannot be attributed to a single trait,but to a combination of factors.Invasive plants benefited from increased growth and above all,increased reproduction(a key trait in an annual plant)and were less attacked by a co-migrated specialist enemy.The observed loss of defence against generalist slugs did not translate into a decreased fitness as invasive C.canadensis plants showed a high re-growth potential.In contrast to earlier in vitro studies,we detected no allelopathic effects on the competing flora in the non-native range.The latitudinal cline in vegetative biomass production in the non-native range observed in our common garden study indicates a high adaptive potential.However,only further genetic studies will provide conclusive evidence whether the differentiation in the non-native range is caused by pre-adaptation and sorting-out processes of putatively repeatedly introduced populations of this composite,long-distance disperser with highly volatile seeds or evolved de novo as a rapid response to new selection pressures in the nonnative range.展开更多
Successful invasions by exotic plants are often attributed to a loss of co-evolved specialists and a re-allocation of resources from defense to growth and reproduction. However, invasive plants are rarely completely r...Successful invasions by exotic plants are often attributed to a loss of co-evolved specialists and a re-allocation of resources from defense to growth and reproduction. However, invasive plants are rarely completely released from insect herbivory because they are frequently attacked by generalists in their introduced ranges. The novel generalist community may also affect the invasive plant＇s defensive strategies and resource allocation. Here, we tested this hypothesis using American pokeweed （Phytolacca americana L.）, a species that has become invasive in China, which is native to North America. We examined resistance, tolerance, growth and reproduction of plant populations from both China and the USA when plants were exposed to natural generalist herbivores in China. We found that leaf damage was greater for invasive populations than for native populations, indicating that plants from invasive ranges had lower resistance to herbivory than those from native ranges. A regression of the percentage of leaf damage against mass showed that there was no significant difference in tolerance between invasive and native populations, even though the shoot, root, fruit and total mass were larger for invasive populations than for native populations. These results suggest that generalist herbivores are important drivers mediating the defensive strategies and resource allocation of the invasive American pokeweed.展开更多
Higher biodiversity is often assumed to be a more desirable scenario for maintaining the functioning of ecosystems,but whether species-richer communities are also more disturbance-tolerant remains controversial.In thi...Higher biodiversity is often assumed to be a more desirable scenario for maintaining the functioning of ecosystems,but whether species-richer communities are also more disturbance-tolerant remains controversial.In this study,we investigated the bacterial communities based on 472 soil samples from 28 forests across China with associated edaphic and climatic properties.We developed two indexes(i.e.,community mean tolerance breadth[CMTB]and community mean response asynchrony[CMRA])to explore the relationship between diversity and community resistance potential.Moreover,we examined this resistance potential along the climatic and latitudinal gradients.We revealed that CMTB was significantly and negatively related to species richness,resulting from the changes in balance between relative abundances of putative specialists and generalists.In comparison,we found a unimodal relationship between CMRA and richness,suggesting that higher biodiversity might not always lead to higher community resistance.Moreover,our results showed differential local patterns along latitude.In particular,local patterns in the northern region mainly followed general relationships rather than those for the southern forests,which may be attributed to the differences in annual means and annual variations of climate conditions.Our findings highlight that the community resistance potential depends on the composition of diverse species with differential environmental tolerance and responses.This study provides a new,testable evaluation by considering tolerance breadth and response asynchrony at the community level,which will be helpful in assessing the influence of disturbance under rapid shifts in biodiversity and species composition as a result of global environmental change.展开更多
We investigated the performance trade-offs of fleas(Siphonaptera)while adapting to a novel host using two host generalists(Xenopsylla conformis and Xenopsylla ramesis)and one host specialist(Parapulex chephrenis)maint...We investigated the performance trade-offs of fleas(Siphonaptera)while adapting to a novel host using two host generalists(Xenopsylla conformis and Xenopsylla ramesis)and one host specialist(Parapulex chephrenis)maintained on their principal hosts(Meriones crassus for Xenopsylla and Acomys cahirinus for P.chephrenis).We asked whether,over generations,(i)a host generalist may become a specialist by evolving the ability to exploit a novel host and losing the ability to exploit an original host and(ii)a host specialist can become a generalist by evolving the ability to exploit a novel host without losing the ability to exploit an original host.We established an experimental line of each species on a novel host(Acomys russatus for Xenopsylla and M.crassus for P.chephrenis)and maintained this line on this host during 23 generations.We compared reproductive performance of progenitors of each line and their descendants when they exploited either original or novel host in terms of egg number and size,hatching success,offspring production,and offspring size.We found changes in performance over generations in female offspring size only.Xenopsylla conformis demonstrated a tendency to become a host specialist(increased performance on the novel host with a concomitant decreased performance on the original host),whereas P.chephrenis demonstrated a tendency to become a host generalist(increased performance on the novel host without a concomitant decreased performance on the original host).We conclude that the probability of generalist to specialist transition,and vice versa,is context-dependent and varies between species.展开更多
Nothapodytes nimmoniana(Family Icacinaceae)is a deciduous tree species distributed in Asia facing severe population decline.Wood chips from the tree are a source of camptothecin,a globally soughtafter alkaloid with ca...Nothapodytes nimmoniana(Family Icacinaceae)is a deciduous tree species distributed in Asia facing severe population decline.Wood chips from the tree are a source of camptothecin,a globally soughtafter alkaloid with cancer-treating properties,and are harvested unsustainably in natural forests.We studied the pollination ecology of the species and asked if there are constraints in pollination and fruiting success in its natural populations.We also discuss the potential effects of wood extraction on pollinators and reproductive success in the population.Methods The study was carried out during the flowering season in two populations with varying exploitation levels,both located in the Protected Area Network in the Western Ghats of Karnataka State.We assessed floral resource availability and measured pollinator diversity and activity in the canopy from the perspective of the biology of the species.We quantified pollinator abundance and percent fruit set as a function of population density.Important Findings Flowers belong to the fly pollination syndrome and are open to visits by generalists such as Apis dorsata and Trigona iridipennis.Fruiting success did not vary between exploited and unexploited sites,but there was a significant difference in pollinator assemblage.In a lean male flowering year,fruit set was low,suggesting pollen limitation in the population.No fruiting was recorded in the second year at the site where trees were felled soon after the flowering period.We argue that when male floral resources are altered in exploited populations,pollinators of generalist nature may show a shift in foraging pattern.Also,generalist plants may be as susceptible to pollination loss as are specialist plants.The need for outcrossing in the species would probably exacerbate this vulnerability.展开更多
Current evidence suggests that pollen is both chemically and structurally protected. Despite increasing interest in studying bee-flower networks, the constraints for bee development related to pollen nutritional conte...Current evidence suggests that pollen is both chemically and structurally protected. Despite increasing interest in studying bee-flower networks, the constraints for bee development related to pollen nutritional content, toxicity and digestibility as well as their role in the shaping of bee-flower interactions have been poorly studied. In this study we combined bioassays of the generalist bee Bombus terrestris on pollen of Cirsium, Trifolium, Salix, and Cistus genera with an assessment of nutritional content, toxicity, and digestibility of pollen. Microcolonies showed significant differences in their development, non-host pollen of Cirsium being the most unfavorable. This pollen was characterized by the presence of quite rare 37-sterols and a low digestibility. Cirsium consumption seemed increase syrup collection, which is probably related to a detoxification mixing behavior. These results strongly suggest that pollen traits may act as drivers of plant selection by bees and partly explain why Asteraceae pollen is rare in bee generalist diet.展开更多
This paper studies the dynamics of the generalist predator–prey systems modeled in[E.Alexandra,F.Lutscher and G.Seo,Bistability and limit cycles in generalist predator–prey dynamics,Ecol.Complex.14(2013)48–55].When...This paper studies the dynamics of the generalist predator–prey systems modeled in[E.Alexandra,F.Lutscher and G.Seo,Bistability and limit cycles in generalist predator–prey dynamics,Ecol.Complex.14(2013)48–55].When prey reproduces much faster than predator,by combining the normal form theory of slow-fast systems,the geometric singular perturbation theory and the results near non-hyperbolic points developed by Krupa and Szmolyan[Relaxation oscillation and canard explosion,J.Differential Equations174(2)(2001)312–368;Extending geometric singular perturbation theory to nonhyperbolic points—fold and canard points in two dimensions,SIAM J.Math.Anal.33(2)(2001)286–314],we provide a detailed mathematical analysis to show the existence of homoclinic orbits,heteroclinic orbits and canard limit cycles and relaxation oscillations bifurcating from the singular homoclinic cycles.Moreover,on global stability of the unique positive equilibrium,we provide some new results.Numerical simulations are also carried out to support the theoretical results.展开更多
基金supported by the National Natural Science Foundation of China(No.32030015,32470545)Science&Technology Fundamental Resources Investigation Program(Grant No.2022FY100400)+1 种基金the Key Projects of Science and Technology Research from the Education Department of Hubei Province(D20221002)the Project(No:RSP2025R7)of the King Saud University,Saudi Arabia.
文摘Micro-eukaryotic communities are highly sensitive to environmental changes, and their structure offers crucial insights into the impact of human activities on aquatic habitats. Despite their significance, the assembly mechanisms of micro-eukaryotic communities in lake ecosystems heavily influenced by human activities are not well understood. In this study, we utilized 18S rDNA amplicon sequencing to examine the biodiversity of micro-eukaryotes over a one-year period in Lake Weishan, one of the largest freshwater lakes in northern China. We analyzed the ecological processes governing community assembly among key ecological groups, specifically habitat generalists and specialists. Our findings revealed substantial temporal variation in microbial diversity and community composition, likely driven by water temperature, dissolved oxygen, and the concentrations of several ions (e.g., Ca^(2+) and F^(−)). Notably, community assembly in this canal-disturbed lake was predominantly influenced by stochastic processes (58.18%) rather than deterministic processes (20.46%). Habitat specialists (425 operational taxonomic units, OTUs) exhibited significantly greater diversity compared to habitat generalists (189 OTUs) and were predominantly shaped by stochastic processes (52.47%). In contrast, habitat generalists were less influenced by these processes (17.69%). Altogether, these results suggest that the ecological processes governing micro-eukaryotic community assembly differ markedly between habitat generalists and specialists, primarily due to their varied adaptability to environmental changes.
文摘Foundational concepts of trait spaces, including phenotypic plasticity and function of traits, should be expanded and better integrated with ecological theory. This article addresses two areas where plasticity theory can become further integrated with ecological, evolutionary, and developmental thinking. First is the idea that not only trait means within environments and plasticity of trait means across environments is optimized by selection, but that the entire shape of phenotype distributions such as variance or skew should be optimized within and across environments. In order for trait distribution shape to evolve into adaptations, there must be a genetic basis for and selection upon variation in distribution shapes and their plasticities. I present published and new data demonstrating genetic control and selection for higher moments of phenotype distributions; though, plasticity in these values has not yet been tested. Genetic control of phenotype distribution moments is shown for Neurospora crassa ascospore size and shape. Selection on trait distribution moments is shown for Eurosta solidaginis gall size. Second, there is a tradition in modeling plasti- city as an adaptive strategy that pits it as an alternative to ecological specialization or generaliza- tion. However, these strategies need not be considered alternatives. Rather, with environmental fluctuation within generations plasticity may produce additive or non-additive intermediate （gener- alist） phenotypes, or something new altogether. I present published and new data on the snail Physa virgata and fish Gambusia affinis that show plasticity produces partly intermediate （general- ist） and partly unique phenotypic elements in mixed and fluctuating environments. Plasticity can thus be viewed in the context of a broader trait space and as having broader ecological roles than currently is conceived.
文摘Black bean aphid, Aphis fabae (Homoptera;Aphididae) is a serious pest causing crop loss. Plant-aphid interaction is a dynamic system subjected to continual variation and changes. Host plants induce various biochemical and physical defense mechanisms due to aphid feeding. Aphids can overcome plant defenses by enzymatic adaptations and sequestering secondary metabolites produced by the plant within their bodies as a defense against their enemies. Many strategies were developed and evolved by aphids in order to overcome plant defense barriers which allowed them to feed, grow and reproduce on their host plants. This study aimed to aid in better understanding of the effect of altering host plant on specialist and generalist aphid fitness.The influence of plant defense on population development of Aphis fabae was also investigated. Analyses for insect enzymes were also demonstrated in addition to further biochemical studies on host plant defences. Generalists showed different ecological and enzymatic adaptations towards host plants than specialist Aphis fabae. The results were fully discussed in details.
文摘Prey choice is often evaluated at the species or population level. Here, we analyzed the diet of octopuses of different populations with the aim to assess the importance of individual feeding habits as a factor affecting prey choice. Two methods were used, an assessment of the extent to which an individual octopus made choices of species representative of those population （PSi and IS） and 25% cutoff values for number of choices and percentage intake of individual on their prey. In one population of Octopus cfvulgaris in Bermuda individuals were generalist by IS=0.77, but most chose many prey of the same species, and were specialists on it by 〉75% intake. Another population had a wider prey selection, still generalist with PSi=0.66, but two individuals specialized by choices. In Bonaire, there was a wide range of prey species chosen, and the population was specialists by IS=0.42. Individual choices revealed seven specialists and four generalists. A population of Octopus cyanea in Hawaii all had similar choices of crustaceans, so the population was generalist by IS with 0.74. But by individual choices, three were considered a spe-cialist. A population of Enteroctopus dofleini from Puget Sound had a wide range of preferences, in which seven were also spe-cialists, IS=0.53, By individual choices, thirteen were also specialists. Given the octopus specialty of learning during foraging, we hypothesize that both localized prey availability and individual personality differences could influence the exploration for prey and this translates into different prey choices across individuals and populations showed in this study.
基金This study was funded in part by the US National Science Foundation sponsored Research Coordination Network for Haemosporida of Terrestrial Vertebrates(malariarch.org,NSF 0954891)the Spanish Ministry of Economy and Competitiveness(CGL2015-64650P)+3 种基金Junta de Extremadura(Consejerıa de Economıa e Infraestructuras),FEDER(IB16121).S.M.and A.M.R were supported by a PhD grant from the Ministry of Economy and Competition of Spain and a mobility grant of Junta de Extremadura(129/2015)respectively.L.G.-L.was supported by the Junta de Extremadura(PO17024,Post-Doc grant)J.M.was supported by a postdoctoral contract from the University of Extremadura(Junta de Extremadura—IB16121)a postdoctoral grant from the Juan de la Cierva Subprogram(FJCI-2017-34109),with the financial sponsorship of the MICINN.
文摘Characterizing the diversity and structure of host–parasite communities is crucial to understandingtheir eco-evolutionary dynamics.Malaria and related haemosporidian parasites are responsible forfitness loss and mortality in bird species worldwide.However,despite exhibiting the greatest ornithologicalbiodiversity,avian haemosporidians from Neotropical regions are quite unexplored.Here,we analyze the genetic diversity of bird haemosporidian parasites(Plasmodium andHaemoproteus)in 1,336 individuals belonging to 206 bird species to explore for differences in diversityof parasite lineages and bird species across 5 well-differentiated Peruvian ecoregions.Wedetected 70 different haemosporidian lineages infecting 74 bird species.We showed that 25 out ofthe 70 haplotypes had not been previously recorded.Moreover,we also identified 81 new host–parasite interactions representing new host records for these haemosporidian parasites.Our outcomesrevealed that the effective diversity(as well as the richness,abundance,and Shannon–Weaver index)for both birds and parasite lineages was higher in Amazon basin ecoregions.Furthermore,we also showed that ecoregions with greater diversity of bird species also had highparasite richness,hence suggesting that host community is crucial in explaining parasite richness.Generalist parasites were found in ecoregions with lower bird diversity,implying that the abundanceand richness of hosts may shape the exploitation strategy followed by haemosporidian parasites.These outcomes reveal that Neotropical region is a major reservoir of unidentified haemosporidianlineages.Further studies analyzing host distribution and specificity of these parasites inthe tropics will provide important knowledge about phylogenetic relationships,phylogeography,and patterns of evolution and distribution of haemosporidian parasites.
基金supported by the National Research Foundation(NRF)South Africa(FBIP 98871)
文摘Background: Harvesting of forest products is a widespread driver of disturbance in developing nations, where policies are increasingly aimed at managing natural forests for sustainable use. There is thus need for research aimed at understanding the impact of resource use on forest habitats and concomitant effects on biodiversity.Afromontane forests in the Eastern Cape, South Africa are harvested informally for poles and medicinal bark and occur along elevational gradients of 800–1600 m above sea level. Patterns of spatial diversity and human disturbance are expected to be affected by elevation. Furthermore, species’ responses to disturbance are expected to vary depending on their level of habitat specialisation. Understanding harvest impacts on forest biodiversity thus requires disentangling the separate effects of elevation and disturbance, and considering forest-specialist and forest-generalist species separately. This study comprises two components. First, harvest activities, resultant harvestmediated habitat heterogeneity, and avifaunal species richness, composition and beta-diversity were compared across two elevational zones in a harvested forest. Second, the role of harvest-mediated habitat heterogeneity in driving patterns of avifaunal diversity were assessed, while controlling for elevation, and considering forest-specialist and forest-generalist species separately.Results: Harvest rates were higher, and activities more varied in the lower elevation zone, with significant impacts of harvesting on habitat features resulting in higher harvest-mediated habitat heterogeneity at lower elevations.Harvest-mediated increases in habitat heterogeneity positively affected forest-generalist species richness, while forest-specialist richness was negatively affected. While species composition of both groups differed across elevational zones, variation in harvest-mediated habitat heterogeneity did not fully account for this, suggesting that factors other than disturbance shape avifaunal communities along the elevation gradient. However, variation in harvest-mediated habitat heterogeneity accounted for the amount of beta-diversity attributed to species turnover in the forest-specialist assemblage, indicating that harvest disturbances affect the mechanisms driving beta-diversity of this group.Conclusion: Spatial patterns of avifaunal diversity are affected by elevation over a 300-m gradient. Harvesting results in increased habitat heterogeneity, which variably affects avifaunal communities at the forest-scale, with positive effects for forest generalists and negative effects for forest-specialists.
文摘There are five species of parasitic cowbirds (Molothrus) and the Brown-headed Cowbird (M. ater) is the only widespread species in North America. The Brown-headed Cowbird is a host generalist and is typically found in open habitats and forest edges. The cowbirds are of a more recent origin than many other brood parasites and perhaps as a result, cowbird adaptations for parasitism and their hosts’ counter-adaptations to thwart parasitism do not appear as sophisticated as those of other brood parasite-host systems. Because of its generalist nature, the cowbird has the potential to negatively impact endangered host species whose populations are limited due to anthropogenic habitat loss. As a consequence, the Brown-headed Cowbird is one of the few brood parasitic species that is the subject of control programs to limit its effects on such hosts.
文摘Glucosinolates and their hydrolysis products, found in plants of the order Brassicales, are well-known for their defensive properties against insect herbivores. Arabidopsis thaliana (Col-0) genetic lines with mutations that modify the type of glucosinolates (i.e. myb28myb29 and cyp79B2cyp79B3 are deficient in the production of aliphatic and indolyl glucosinolates, respectively) make it possible to test for the specific effects of these secondary chemicals on insect herbivores. The Pad3 mutant (deficient in camalexin), which has a role in resistance to pathogens, was also tested. Likewise, the effects of different glucosinolate hydrolysis products can be evaluated using genetically modified (GM) lines of the wild type Col-0 ecotype, which naturally produces isothiocyanates. These GM lines include the nitrile-producing 35S: ESP and the double knockout tgg1tgg2, which virtually lacks hydrolysis products. In both no-choice and choice experiments, the crucifer specialist Pieris rapae was virtually unaffected by differences in the type of glucosinolates or hydrolysis products. In contrast, the generalist insect Spodoptera exigua had statistically significant increases in pupae/adult weight and faster developmental times when reared on mutants deficient in the production of aliphatic and indolyl glucosinolates and their hydrolysis products. There were no differences in the performance of either insect species when reared on wild type Col-0 or Pad3. Results from feeding choice trials showed that Pieris rapae had no statistically significant preference for any of the genetic lines. In contrast, Spodoptera exigua had a significant feeding preference for the double mutant tgg1tgg2. This study provides evidence that variation in the type of glucosinolates and their hydrolysis products can influence insect performance and feeding choices, and that responses are species-specific.
基金supported by the Fundamental Research Funds for the Central Universities(China)(No.B240201049)the China Postdoctoral Science Foundation(No.376371)the Six Talent Peaks Project in Jiangsu Province(China)(No.2016-JNHB-007).
文摘Microorganisms are essential contributors to the forest ecosystems of the Qinghai-Xizang Plateau,encompassing generalists,intermediates,and specialists.Investigating the characteristics and drivers of these microbial sub-communities across varying elevations is essential for understanding their ecological functions in high-altitude forest soils.This study examines the diversity patterns,assembly processes,environmental adaptations,and potential functions of bacterial and fungal subcommunities along an elevation gradient from 3900 m to the timberline on Shergyla Mountain,China.The findings revealed notable differences between low and high elevations in the diversity and composition of microbial sub-communities.According to neutral and null models,generalists,characterized by the widest niche width and highest migration rates,were primarily influenced by stochastic processes(71.9%).In contrast,deterministic factors,including homogeneous and variable selection,exerted a stronger effect on the assembly of specialists(51.0%).Elevation and nutrient availability emerged as key environmental drivers shaping microbial sub-communities,particularly for specialists,while generalists experienced fewer constraints from environmental factors.Network analysis further demonstrated that habitat specialists occupy central positions within microbial networks,playing a pivotal role in maintaining network stability.Additionally,nitrogen cycling genes—specifically nifH,amoA,nirS and nosZ—exhibited a U-shaped distribution across the elevation gradient and showed a substantial correlation(p<0.05)with the Chao1 and Shannon indices of bacterial specialists.The results enhance our knowledge of microbial community dynamics and underscore the crucial ecological role of microbial specialists in the ecosystems of high-altitude forests.
基金supported by grants from the National Natural Science Foundation of China(Nos.11971143 and 12071105)the Natural Science Foundation of Zhejiang Province(No.LZ23A010001).
文摘In this paper,we investigate the influence of the nonlocal prey competition on the spatiotemporal dynamics for a generalist predator-prey system.The condition of stability and bifurcations is clearly determined.Our results show that when the prey spreads quickly,the nonlocal intraspecific competition of the prey does not affect the dynamics,however,when the prey spreads slowly,it can affect the dynamics.Besides,no Hopf bifurcation occurs if the ratio of the growth rate of the predator to prey is larger,otherwise,system has Hopf bifurcation and Hopf Bogdanov-Takens bifurcation and so on.It is surprised that the system only with the nonlocal prey competition has more rich dynamics than the system with the nonlocal competitions in both the prey and the predator.The coexistence of bistable spatially inhomogeneous steady states is also found.
基金German Research Foundation within the framework of the Research Training Group(GRK 1086:‘The role of biodiversity for biogeochemical cycles and biotic interactions in temperate deciduous forests’).
文摘Aims Forest fragmentation and the associated augmentation of forest edge zones are increasing worldwide.Forest edges are characterized by altered plant species richness and community composition.As the tree layer and its species composition has been shown to influence herb layer composition,changes in tree species composition or richness may weaken or strengthen edge effects in forest ecosystems.We studied effects of the edge-center transition,tree species composition and their potential interaction on the understory vegetation in the Hainich National Park,Germany’s largest connected deciduous forest,allowing to cover large edge-center transects.Methods We established 12 transects in an area of 75 km^(2) of continuous forest,6 beech-dominated and 6 in multispecies forest stands.Each transect reached from the forest edge up to 500 m into the forest interior.Vegetation relevés were conducted in regular,logarithmic distances along each transect.Important Findings Herb species richness was influenced by an interaction of edge effects and tree diversity level.With increasing distance from the forest edge,herb species richness remained constant in multispecies forest stands but rapidly decreased in beech-dominated forest stands.Further,herb richness was higher in the interior of multispecies forest stands.Percent forest specialists increased and percent generalists decreased with distance from the edge and this contrasting pattern was much more pronounced in beech-dominated transects.By using structural equation modeling,we identified litter depth mediated by tree species composition as the most important driver of herb layer plant species richness.
基金the European project BACCARA funded by the European Commission’s Seventh Framework Program(FP7/2007-2013 under Grant Agreement No.226299)for financial supportthe administration of the Gutianshan National Nature Reserve and to the members of the BEF-China consortium for logistic and intellectual support+1 种基金the National Science Foundation of China(NSFC 30710103907 and 30930005)the German Research Foundation(DFG FOR 891)that granted and permitted the establishment of the experiment.
文摘Aims Plant diversity has been linked to both increasing and decreasing levels of arthropod herbivore damage in different plant communities.So far,these links have mainly been studied in grasslands or in artificial tree plantations with low species richness.Furthermore,most studies provide results from newly established experimental plant communities where trophic links are not fully established or from stands of tree saplings that have not yet developed a canopy.Here,we test how tree diversity in a species-rich subtropical forest in China with fully developed tree canopy affects levels of herbivore damage caused by different arthropod feeding guilds.Methods We established 27 plots of 30×30 m area.The plots were selected randomly but with the constraint that they had to span a large range of tree diversity as required for comparative studies in contrast to sample surveys.We recorded herbivore damage caused by arthropod feeding guilds(leaf chewers,leaf skeletonizers and sap feeders)on canopy leaves of all major tree species.Important Findings Levels of herbivore damage increased with tree species richness and tree phylogenetic diversity.These effects were most pronounced for damage caused by leaf chewers.Although the two diversity measures were highly correlated,we additionally found a significant interaction between them,whereby species richness increased herbivory mostly at low levels of phylogenetic diversity.Tree species with the lowest proportion of canopy leaf biomass in a plot tended to suffer the highest levels of herbivore damage,which is in contrast to expectations based on the resource concentration hypothesis.Our results are in agreement with expectations of the dietary mixing hypothesis where generalist herbivores with a broad spectrum of food plants benefit from increased resource diversity in tree species-rich forest patches.
基金This work was supported by a grant from the Swiss National Science Foundation to J.J.(nr.3100AO-104006).
文摘Aims The superior performance of many non-indigenous species in a new range can be attributed to different factors such as pre-adaptation to environmental conditions in new areas or to factors inherent to displacement mechanisms such as loss of co-evolved pathogens and herbivores that increase the speed of evolutionary change towards a shift in allocation from defence to growth and reproduction.To assess the importance of the different mechanisms governing the success of Conyza canadensis,a globally successful invader,we simultaneously tested several recent hypotheses potentially explaining the factors leading to biological invasion.Methods We tested(i)whether plants from the non-native range showed a higher fitness than plants from the native North American range,(ii)whether they differed in resistance against an invasive generalist herbivore,the slug Arion lusitanicus and against a recently established specialist aphid herbivore,Uroleucon erigeronense and(iii)experimentally assessed whether C.canadensis releases allelopathic chemicals that have harmful effects on competing species in the nonnative range.We compared populations along a similar latitudinal gradient both in the native North American and invasive European range and analysed patterns of adaptive clinal variation in biomass production.Important Findings The invasion success of C.canadensis in Europe cannot be attributed to a single trait,but to a combination of factors.Invasive plants benefited from increased growth and above all,increased reproduction(a key trait in an annual plant)and were less attacked by a co-migrated specialist enemy.The observed loss of defence against generalist slugs did not translate into a decreased fitness as invasive C.canadensis plants showed a high re-growth potential.In contrast to earlier in vitro studies,we detected no allelopathic effects on the competing flora in the non-native range.The latitudinal cline in vegetative biomass production in the non-native range observed in our common garden study indicates a high adaptive potential.However,only further genetic studies will provide conclusive evidence whether the differentiation in the non-native range is caused by pre-adaptation and sorting-out processes of putatively repeatedly introduced populations of this composite,long-distance disperser with highly volatile seeds or evolved de novo as a rapid response to new selection pressures in the nonnative range.
基金We would like to thank Xue-Fang Yang and Shun-Liang Feng for plant harvests. We also thank English editing by Van Driesche Scientific Editing. This work was sup- ported by the National Natural Science Foundation of China （31470447 and 31200286 to W. Huang, 31370404 to J. Ding）.
文摘Successful invasions by exotic plants are often attributed to a loss of co-evolved specialists and a re-allocation of resources from defense to growth and reproduction. However, invasive plants are rarely completely released from insect herbivory because they are frequently attacked by generalists in their introduced ranges. The novel generalist community may also affect the invasive plant＇s defensive strategies and resource allocation. Here, we tested this hypothesis using American pokeweed （Phytolacca americana L.）, a species that has become invasive in China, which is native to North America. We examined resistance, tolerance, growth and reproduction of plant populations from both China and the USA when plants were exposed to natural generalist herbivores in China. We found that leaf damage was greater for invasive populations than for native populations, indicating that plants from invasive ranges had lower resistance to herbivory than those from native ranges. A regression of the percentage of leaf damage against mass showed that there was no significant difference in tolerance between invasive and native populations, even though the shoot, root, fruit and total mass were larger for invasive populations than for native populations. These results suggest that generalist herbivores are important drivers mediating the defensive strategies and resource allocation of the invasive American pokeweed.
基金the National Natural Science Foundation of China(Nos.31600403,31800422,41673111,U1501232,41622106,31971553,and 31700470)the Natural Science Foundation of Guangdong Province,China(No.2016A030312003)+1 种基金the Natural Science Foundation of Guangxi Province,China(No.2017GXNSFBA198099)the U.S.National Science Foundation(NSF A22-0042).
文摘Higher biodiversity is often assumed to be a more desirable scenario for maintaining the functioning of ecosystems,but whether species-richer communities are also more disturbance-tolerant remains controversial.In this study,we investigated the bacterial communities based on 472 soil samples from 28 forests across China with associated edaphic and climatic properties.We developed two indexes(i.e.,community mean tolerance breadth[CMTB]and community mean response asynchrony[CMRA])to explore the relationship between diversity and community resistance potential.Moreover,we examined this resistance potential along the climatic and latitudinal gradients.We revealed that CMTB was significantly and negatively related to species richness,resulting from the changes in balance between relative abundances of putative specialists and generalists.In comparison,we found a unimodal relationship between CMRA and richness,suggesting that higher biodiversity might not always lead to higher community resistance.Moreover,our results showed differential local patterns along latitude.In particular,local patterns in the northern region mainly followed general relationships rather than those for the southern forests,which may be attributed to the differences in annual means and annual variations of climate conditions.Our findings highlight that the community resistance potential depends on the composition of diverse species with differential environmental tolerance and responses.This study provides a new,testable evaluation by considering tolerance breadth and response asynchrony at the community level,which will be helpful in assessing the influence of disturbance under rapid shifts in biodiversity and species composition as a result of global environmental change.
基金supported by Israel Science Foundation(grant 149/17 to ISK and BRK).
文摘We investigated the performance trade-offs of fleas(Siphonaptera)while adapting to a novel host using two host generalists(Xenopsylla conformis and Xenopsylla ramesis)and one host specialist(Parapulex chephrenis)maintained on their principal hosts(Meriones crassus for Xenopsylla and Acomys cahirinus for P.chephrenis).We asked whether,over generations,(i)a host generalist may become a specialist by evolving the ability to exploit a novel host and losing the ability to exploit an original host and(ii)a host specialist can become a generalist by evolving the ability to exploit a novel host without losing the ability to exploit an original host.We established an experimental line of each species on a novel host(Acomys russatus for Xenopsylla and M.crassus for P.chephrenis)and maintained this line on this host during 23 generations.We compared reproductive performance of progenitors of each line and their descendants when they exploited either original or novel host in terms of egg number and size,hatching success,offspring production,and offspring size.We found changes in performance over generations in female offspring size only.Xenopsylla conformis demonstrated a tendency to become a host specialist(increased performance on the novel host with a concomitant decreased performance on the original host),whereas P.chephrenis demonstrated a tendency to become a host generalist(increased performance on the novel host without a concomitant decreased performance on the original host).We conclude that the probability of generalist to specialist transition,and vice versa,is context-dependent and varies between species.
文摘Nothapodytes nimmoniana(Family Icacinaceae)is a deciduous tree species distributed in Asia facing severe population decline.Wood chips from the tree are a source of camptothecin,a globally soughtafter alkaloid with cancer-treating properties,and are harvested unsustainably in natural forests.We studied the pollination ecology of the species and asked if there are constraints in pollination and fruiting success in its natural populations.We also discuss the potential effects of wood extraction on pollinators and reproductive success in the population.Methods The study was carried out during the flowering season in two populations with varying exploitation levels,both located in the Protected Area Network in the Western Ghats of Karnataka State.We assessed floral resource availability and measured pollinator diversity and activity in the canopy from the perspective of the biology of the species.We quantified pollinator abundance and percent fruit set as a function of population density.Important Findings Flowers belong to the fly pollination syndrome and are open to visits by generalists such as Apis dorsata and Trigona iridipennis.Fruiting success did not vary between exploited and unexploited sites,but there was a significant difference in pollinator assemblage.In a lean male flowering year,fruit set was low,suggesting pollen limitation in the population.No fruiting was recorded in the second year at the site where trees were felled soon after the flowering period.We argue that when male floral resources are altered in exploited populations,pollinators of generalist nature may show a shift in foraging pattern.Also,generalist plants may be as susceptible to pollination loss as are specialist plants.The need for outcrossing in the species would probably exacerbate this vulnerability.
文摘Current evidence suggests that pollen is both chemically and structurally protected. Despite increasing interest in studying bee-flower networks, the constraints for bee development related to pollen nutritional content, toxicity and digestibility as well as their role in the shaping of bee-flower interactions have been poorly studied. In this study we combined bioassays of the generalist bee Bombus terrestris on pollen of Cirsium, Trifolium, Salix, and Cistus genera with an assessment of nutritional content, toxicity, and digestibility of pollen. Microcolonies showed significant differences in their development, non-host pollen of Cirsium being the most unfavorable. This pollen was characterized by the presence of quite rare 37-sterols and a low digestibility. Cirsium consumption seemed increase syrup collection, which is probably related to a detoxification mixing behavior. These results strongly suggest that pollen traits may act as drivers of plant selection by bees and partly explain why Asteraceae pollen is rare in bee generalist diet.
文摘This paper studies the dynamics of the generalist predator–prey systems modeled in[E.Alexandra,F.Lutscher and G.Seo,Bistability and limit cycles in generalist predator–prey dynamics,Ecol.Complex.14(2013)48–55].When prey reproduces much faster than predator,by combining the normal form theory of slow-fast systems,the geometric singular perturbation theory and the results near non-hyperbolic points developed by Krupa and Szmolyan[Relaxation oscillation and canard explosion,J.Differential Equations174(2)(2001)312–368;Extending geometric singular perturbation theory to nonhyperbolic points—fold and canard points in two dimensions,SIAM J.Math.Anal.33(2)(2001)286–314],we provide a detailed mathematical analysis to show the existence of homoclinic orbits,heteroclinic orbits and canard limit cycles and relaxation oscillations bifurcating from the singular homoclinic cycles.Moreover,on global stability of the unique positive equilibrium,we provide some new results.Numerical simulations are also carried out to support the theoretical results.
