Variations in reproductive strategies between one invasive population and two native populations of Pseudorasbora parva

Reproductive traits of one invasive population in Lake Fuxian and two native populations in Lakes Chao and Dongting for Pseudorasbora parva were investigated to determine the variations in their reproductive strategies associated with the change of environmental conditions. Compared with the two native populations, P.parva markedly experienced the protraction in their spawning time and the decrease in mortality for adult individuals in Lake Fuxian. The three populations all got their first sexual maturity at the same age, but their total lengths at maturity were quite different for those in Lake Chao were significantly lower than in Lakes Fuxian and Dongting. Additionally, in spite that no significant difference occurred in their relative fecundities for P. parva in Lakes Fuxian and Dongting, the population in Lake Chao showed the markedly higher relative fecundity than the other two populations. These results were analyzed with the variations in water temperature, nutrient status, fishing stress among the three lakes. The relative decline in fecundity for the invasive population, which conflicted with the enemy release hypothesis, was disscussed with the context of the preponderance of another invasive fish, Neosalanx taihuensis, in Lake Fuxian.

A Systematic Review of Terrestrial Plant Invasion Mechanisms Mediated by Microbes and Restoration Implications

Terrestrial invasive plant species continue to wreak havoc on a global economic and ecological scale. With the advent of climate change and pending future catastrophes, the spread of resilient invasive plants will only increase exponentially. Here, the search continues for a better understanding of the below-ground microbially driven mechanisms involved in plant invasion where other above-ground mechanisms have been exhausted. Microbes govern the world around us and interact with every living and non-living facet of the world. To reinforce the important underpinnings of the role of microorganisms in plant invasion, a systematic review of recently published articles was undertaken. Using the ScienceDirect database, five (5) search queries were used to generate 1221 research articles. After a two-step reduction was made based on relevance of the articles, a final total of 59 articles were retrieved. An additional 18 relevant articles were also assessed through the PubMed database for analysis to account for other invasive plants. Thirty-seven (37) invasive species were investigated where soil physiochemical and microbial community structure changes were most prevalent (32% & 39% respectively) while enhanced mutualism, allelopathy and pathogen accumulation were reported less (16%, 10% & 3% respectively). In all invasive species assessed, the impact on plant invasion and inability of the native plants to compete was due to specific microbial associations of the invasive plant or disruption of the soil microbial community. This microbial community shift coincided with changes in physiochemical properties of the soil and the subsequent negative soil feedback for native plants. There is still an expanding potential for the use of biocontrol agents to aid restoration once the underpinnings of biotic resistance and enemy release are understood in a microbial and physiochemical context. The active and functional microbial community structure of the invasive plant rhizosphere and adjacent soil in its native and non-native region can offer a better inference of how they can be controlled using novel-below ground biocontrol methods.

Enemy release at range edges:do invasive species escape their herbivores as they expand into new areas?

Aims We test the hypothesis that invasive plant species at their range edges experience lower herbivory and allocate less to defense at the edge of an expanding range edge than from more central parts of their distribution,during secondary invasion in a new range.Invasive plants are often able to spread rapidly through new areas.The success of invasive species in new ranges is frequently attributed to enemy release in these new areas and associated evolutionary changes minimizing allocation to defense in favor of growth and reproduction.Enemy release could also explain rapid advances of invasive species upon arriving in new habitats.If invasive species accumulate enemies over time in a new location,then these species may experience a release from their enemies at expanding range fronts.Enemy release at these range fronts may accelerate range expansion.Methods We used populations of four woody invasive species within the invaded range,and four native control species.We quantified leaf herbivory and leaf physical defense traits at both range central and range edge locations,over two 1-month sampling periods,sampled 7 months apart.Important Findings Herbivory at the range edge did not differ to the range center but patterns were not consistent across species.There was a trend for lower herbivory at the range edge for Lantana camara,which was reflected in lower leaf toughness.Overall,leaf toughness was greater at the range edge location across invasive and control species.Physical defenses were different among range locations in a few species,though most species show the same trend,suggesting higher herbivory pressures at the range edge location or differences may be due to climatic factors.Leaves of L.camara were significantly less tough at range edges,suggesting that some species can potentially escape their enemies at range edges.However,our results overall do not support the hypothesis that plants at the edge of their ranges experience reduced impact from their enemies.

Invasive oaks escape pre-dispersal insect seed predation and trap enemies in their seeds

Species introduced to habitats outside their native range often escape control by their natural enemies.Besides competing with native species,an alien species might also affect the native herbivores by introducing a new source of different quality food.Here,we describe the case of northern red oak(Quercus rubra)invasion in Europe.We collected data on insect(moth Cydia spp.and weevil Curculio spp.)seed predation of northern red oak in its native(USA,North America)and invasive(Poland,Europe)range,as well as for sessile oaks(Quercus petrea)in Europe.We also evaluated the quality of acorns as hosts for weevil larvae by collecting infested acorns and measuring weevil developmental success,and quantifying acorn traits such as seed mass,tannins,lipids and protein concentration.We used DNA barcoding to identify insects to the species level.The predation by moths was similar and very low in both species and in both ranges.However,red oaks escape pre-dispersal seed predation by weevils in Europe.Weevil infestation rates of northern red oak acorns in their invasive range were 10 times lower than that of sessile oaks,and also 10 times lower than that of red oaks in North America.Furthermore,even when weevils oviposited into northern red oaks,the larvae failed to develop,suggesting that the exotic host created a trap for the insect.This phenomenon might gradually decrease the local abundance of the seed predator,and further aid the invasion.

Responses of morphological and physiological traits to herbivory by snails of three invasive and native submerged plants

The submerged plant species Carolina fanwort(Cabomba caroliniana)has become a dominant invasive aquatic plant in the Lake Taihu Basin(LTB)in China.Introduced species may escape their original specialist enemies and encounter fewer enemies in their new environment.They were assumed to have suffered less herbivory than native species as they are relatively unpalatable(the enemy release hypothesis[ERH]).The objective of this study was to compare the responses of C.caroliniana with those of co-occurring native species to herbivory from native herbivores.We conducted a mesocosm experiment to record the responses of C.caroliniana and two commonly co-occurring native submerged plant counterparts,water thyme(Hydrilla verticillata)and Eurasian watermilfoil(Myriophyllum spicatum),to herbivory by two native generalist gastropod snails,Radix swinhoei and Sinotaia quadrata.Plant morphological traits(total biomass,shoot/root[S/R]biomass ratio and relative growth rate[RGR])and physiological traits(leaf total nonstructural carbohydrate[TNC],lignin,and cellulose)were recorded.The snail S.quadrata rarely influenced the plant traits of the three submerged plants.With the increasing numbers of R.swinhoei treatments,most of the plant traits of H.verticillata and M.spicatum changed,while those of C.caroliniana showed a relatively stable fluctuation.This result indicates that C.caroliniana is more resistant to herbivory by the snail R.swinhoei,which is consistent with the ERH hypothesis.This finding indicates that herbivorous snail species contributes to the invasion of C.caroliniana,which potentially alters the species composition of submerged plants in the plant community.

Invading from the garden？ A comparison of leaf herbivory for exotic and native plants in natural and ornamental settings

The enemies release hypothesis proposes that exotic species can become in- vasive by escaping from predators and parasites in their novel environment. Agrawal et al. （Enemy release？ An experiment with congeneric plant pairs and diverse above- and below-ground enemies. Ecology, 86, 2979-2989） proposed that areas or times in which damage to introduced species is low provide opportunities for the invasion of native habitat. We tested whether ornamental settings may provide areas with low levels of herbivory for trees and shrubs, potentially facilitating invasion success. First, we compared levels of leaf herbivory among native and exotic species in ornamental and natural settings in Cincinnati, Ohio, United States. In the second study, we compared levels of herbivory for invasive and noninvasive exotic species between natural and ornamental settings. We found lower levels of leaf damage for exotic species than for native species; however, we found no differences in the amount of leaf damage suffered in ornamental or natural settings. Our results do not provide any evidence that ornamental settings afford additional release from herbivory for exotic plant species.

An intercontinental comparison of insect seed predation between introduced and native oaks

Novel interactions between introduced oaks and their natural enemies across different continents provide an opportunity to test the enemy release hypothesis(ERH)at local and global scales.Based on the ERH,we assessed the impacts of native seed-feeding insects on introduced and native oaks within and among continents.We combined a common-garden experiment in China and biogeographic literature surveys to measure seed predation by insects and the proportion of acorn embryos surviving after insect infestation among 4 oak species with different geographical origins:Quercus mongolica origin from China,Q.robur and Q.petraea from Europe,and Q.rubra from North America.Mostly supporting the ERH,oaks in introduced continents escaped seed predation compared to those in native continents and compared to other native oaks in introduced continents.Common-garden comparisons showed that total acorn infestation rate of introduced Q.rubra(section Lobatae)was considerably lower than that of native oaks(section Quercus)in China and Europe,likely because of the differences in seed traits associated with different oak sections.Literature surveys showed that seed predation of introduced oaks was lower in the introduced continent than in the native continent.Embryo survival was higher in introduced Q.rubra than native oaks in China and Poland.However,insect seed predation of recently introduced Q.rubra in China was similar to that in Europe,which is not consistent with the ERH.Our results suggest that reduced acorn attack by native insects and higher embryo survival after acorn damage could increase the establishment success or invasion risk of introduced oaks in non-native continents.