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1.
In the framework of phenotypic plasticity, tolerance to browsing can be operationally defined as a norm of reaction comparing plant performance in undamaged and damaged conditions. Genetic variation in tolerance is then indicated by heterogeneity in the slopes of norms of reaction from a population. We investigated field gentian (Gentianella campestris) tolerance to damage in the framework of phenotypic plasticity using a sample of maternal lines from natural populations grown under common garden conditions and randomly split into either a control or an artificial clipping treatment. We found a diversity of tolerance norms of reaction at both the population and family level: the impacts of clipping ranged from poor tolerance (negative slope) to overcompensation (positive slope). We detected heterogeneity in tolerance norms of reaction in four populations. Similarly, we found a variety of plastic architectural responses to clipping and genetic variation in these responses in several populations. Overall, we found that the most tolerant populations were late flowering and also exhibit the greatest plastic increases in node (meristem) production in response to damage. We studied damage-imposed natural selection on plasticity in plant architecture in 10 of the sampled populations. In general, there was strong positive direct selection on final number of nodes for both control and clipped plants. However, the total selection on nodes (direct + indirect selection) within each treatment category depended heavily on the frequency of damage and cross-treatment genetic correlations in node production. In some cases, strong correlated responses to selection across the damage treatment led to total selection against nodes in the more rare environment. This could ultimately lead to the evolution of maladaptive phenotypes in one or both of the treatment categories. These results suggest that tolerance and a variety of architectural responses to damage may evolve by both direct and indirect responses to natural selection. While the present study demonstrates the potential importance of cross-treatment genetic correlations in directing the evolution of tolerance traits, such as branch or node production, we did not find any strong evidence of genetic trade-offs in candidate tolerance traits between undamaged and damaged conditions. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

2.
Numerous hypotheses suggest that natural enemies can influence the dynamics of biological invasions. Here, we use a group of 12 related native, invasive, and naturalized vines to test the relative importance of resistance and tolerance to herbivory in promoting biological invasions. In a field experiment in Long Island, New York, we excluded mammal and insect herbivores and examined plant growth and foliar damage over two growing seasons. This novel approach allowed us to compare the relative damage from mammal and insect herbivores and whether damage rates were related to invasion. In a greenhouse experiment, we simulated herbivory through clipping and measured growth response. After two seasons of excluding herbivores, there was no difference in relative growth rates among invasive, naturalized, and native woody vines, and all vines were susceptible to damage from mammal and insect herbivores. Thus, differential attack by herbivores and plant resistance to herbivory did not explain invasion success of these species. In the field, where damage rates were high, none of the vines were able to fully compensate for damage from mammals. However, in the greenhouse, we found that invasive vines were more tolerant of simulated herbivory than native and naturalized relatives. Our results indicate that invasive vines are not escaping herbivory in the novel range, rather they are persisting despite high rates of herbivore damage in the field. While most studies of invasive plants and natural enemies have focused on resistance, this work suggests that tolerance may also play a large role in facilitating invasions.  相似文献   

3.
Evidence from 10 studies comparing angiosperm trees and 5 studies comparing conifers of differing shade‐tolerance was analysed. The number of intraphyletic comparisons in which the more shade‐tolerant species showed the greater relative increase of biomass in elevated CO2 was significantly higher than would be expected by chance alone. It is suggested that more shade‐tolerant species are inherently better disposed, in terms of plant architecture and partitioning of biomass and nitrogen, to utilise resources (light, water, nutrients) that are potentially limiting in elevated CO2 and that these traits are responsible for the interaction between shade‐tolerance and CO2 concentration. Compared with less shade‐tolerant angiosperm trees, more shade‐tolerant angiosperm species generally have a lower leaf area ratio in ambient CO2 and show a smaller relative reduction in elevated CO2. Furthermore, leaf nitrogen content is usually lower in more shade‐tolerant angiosperm species and tends to be more strongly reduced by elevated CO2 in those species. Within angiosperm trees, more shade‐tolerant species showed a stronger stimulation of net leaf photosynthetic rate in most experiments, but this trend was not significant.  相似文献   

4.
Aims Early models of plant defense conceived resistance and tolerance to herbivore damage as mutually exclusive strategies. Support for this idea has been equivocal and studies on these two strategies are still needed to understand the evolution of defenses in natural populations. In Arabidopsis lyrata, the production of trichomes, a documented resistance trait, has been associated with a fitness cost in the absence of herbivores. We examined whether trichome production is also associated with reduced tolerance to simulated herbivore damage.Methods We conducted a field experiment in a natural Swedish population of A. lyrata where we inflicted leaf (0 vs. 50% of the area of each leaf removed) and inflorescence damage (0 vs. 50% of inflorescences removed) to trichome-producing and glabrous plants in a factorial design. We examined the response (survival, growth and reproduction) of the plants to the imposed damage over 2 years.Important findings Trichome-producing plants were not less tolerant than glabrous plants to simulated herbivore damage (no significant morph × leaf damage or morph × inflorescence damage interactions). Inflorescence and leaf damage had independent negative effects on the performance of damaged plants. Leaf damage reduced rosette size the year of damage, but effects on reproductive output in the year of damage, and on survival and reproductive performance the following year were weak and not statistically significant. Inflorescence damage significantly reduced the number of flowers, fruits and seeds the year of damage, but not in the following year. Irrespective of morph, the study population was more tolerant to leaf than to inflorescence damage. The results indicated no trade-off between trichome production and tolerance, suggesting that these two defense mechanisms have the potential to evolve independently in this A. lyrata population.  相似文献   

5.
When entering a new community, introduced species leave behind members of their native community while simultaneously forming novel biotic interactions. Escape from enemies during the process of introduction has long been hypothesized to drive the increased performance of invasive species. However, recent studies and quantitative syntheses find that invaders often receive similar, or even more, damage from enemies than do native species. Therefore, invasives may be those more tolerant to enemy damage, or those able to maintain competitive ability in light of enemy damage. Here, we investigate whether tolerance and competitive ability could contribute to invasive plant success. We determined whether invasive plants were more competitive than native or noninvasive exotic species in both the presence and absence of simulated herbivory. We found competition and herbivory additively reduced individual performance, and affected the performance of native, invasive, and noninvasive exotic species’ to the same degree. However, invasives exerted stronger competitive effects on an abundant native species (Elymus canadensis) in both the presence and absence of herbivory. Therefore, while invasive species responded similarly to competition and simulated herbivory, their competitive effects on natives may contribute to their success in their introduced range.  相似文献   

6.
Temperate plants are at risk of being exposed to late spring freezes. These freeze events—often called false springs—are one of the strongest factors determining temperate plants species range limits and can impose high ecological and economic damage. As climate change may alter the prevalence and severity of false springs, our ability to forecast such events has become more critical, and it has led to a growing body of research. Many false spring studies largely simplify the myriad complexities involved in assessing false spring risks and damage. While these studies have helped advance the field and may provide useful estimates at large scales, studies at the individual to community levels must integrate more complexity for accurate predictions of plant damage from late spring freezes. Here, we review current metrics of false spring, and how, when, and where plants are most at risk of freeze damage. We highlight how life stage, functional group, species differences in morphology and phenology, and regional climatic differences contribute to the damage potential of false springs. More studies aimed at understanding relationships among species tolerance and avoidance strategies, climatic regimes, and the environmental cues that underlie spring phenology would improve predictions at all biological levels. An integrated approach to assessing past and future spring freeze damage would provide novel insights into fundamental plant biology and offer more robust predictions as climate change progresses, which are essential for mitigating the adverse ecological and economic effects of false springs.  相似文献   

7.
Tolerance to herbivory is an adaptation that promotes regrowth and maintains fitness in plants after herbivore damage. Here, we hypothesized that the effect of competition on tolerance can be different for different genotypes within a species and we tested how tolerance is affected by competitive regime and damage type. We inflicted apical or leaf damage in siblings of 29 families of an annual plant Raphanus raphanistrum (Brassicaceae) grown at high or low competition. There was a negative correlation of family tolerance levels between competition treatments: plant families with high tolerance to apical damage in the low competition treatment had low tolerance to apical damage in the high competition treatment and vice versa. We found no costs of tolerance, in terms of a trade‐off between tolerance to apical and leaf damage or between tolerance and competitive ability, or an allocation cost in terms of reduced fitness of highly tolerant families in the undamaged state. High tolerance bound to a specific competitive regime may entail a cost in terms of low tolerance if competitive regime changes. This could act as a factor maintaining genetic variation for tolerance.  相似文献   

8.
Northeast (NE) China covers three climatic zones and contains all the major forest types of NE Asia. We sampled 108 forest plots in six nature reserves across NE China to examine the influence of climate and local factors (canopy seasonality, successional stage, topography and forest structure) on geographic patterns of plant richness. We analyzed the relative effects of different factors at two spatial scales: the regional scale (across both latitude and altitude) and the local scale (along the altitudinal gradient within site). Our results showed that the relative importance of climate vs local factors differed remarkably depending on scale and functional group. While total and tree species richness were mainly limited by climate, herb and shrub richness was more related to local factors (especially at the local scale). In the climatic factors, heat sum was the major correlate of tree, shrub and total species richness, while herb richness was more associated with winter coldness. Precipitation was not a limiting factor for forest plant richness in NE China. Climate accounted for 34–76% of variation in richness at the regional scale, but explained only 0–44% at the local scale. Among the local factors, shrub species richness was sensitive to seasonal canopy openness, with higher richness in deciduous forests than in the evergreen needle-leaf forest. On the other hand, herb richness was sensitive to forest successional stage, with higher richness in middle- successional forests than in the early and late-sucessional forests. Local topography (aspect and position on slope) and forest structure (tree density) also showed remarkable influence on species richness. Our results suggest the importance of including local factors when examining large scale diversity gradient (especially for understory species), and the necessity of comparing diversity patterns among functional groups at different spatial scales.  相似文献   

9.
Negative frequency‐dependent selection (FDS), where rare genotypes are favoured by selection, is commonly invoked as a mechanism explaining the maintenance of genetic variation in plant defences. However, empirical tests of FDS in plant–herbivore interactions are lacking. We evaluated whether the oviposition preference of the specialist herbivore Lema daturaphila is a mechanism through which this herbivore can exert FDS on its host plant Datura stramonium. The frequency of contrasting resistance–tolerance strategies was manipulated within experimental plots, and the plants were exposed to a similar initial density of their natural herbivore. Herbivore oviposition preference and final density, as well as plant damage and seed production, were estimated. Overall, we found that the high‐resistant–low‐tolerant genotypes produced four times more seeds when common than when rare, whereas the high‐tolerant–low‐resistant genotypes achieved twice its fitness when rare than when common. This pattern was the result of differential oviposition preferences. In addition, when the high‐resistant–low‐tolerant genotypes were common, there was a three‐fold decreased in herbivore final density which led to a decrease in damage level by 10%. Thus, in our experiment positive FDS seems to favour resistance over tolerance. We discuss how this result would change if the extent of herbivore local adaptation and damage modify the pattern of positive FDS acting on resistance and the optimal allocation to tolerance.  相似文献   

10.
Bermudagrass (Cynodon dactylon) is a widely used warm-season turfgrass and one of the most drought tolerant species. Dissecting the natural variation in drought tolerance and physiological responses will bring us powerful basis and novel insight for plant breeding. In the present study, we evaluated the natural variation of drought tolerance among nine bermudagrass varieties by measuring physiological responses after drought stress treatment through withholding water. Three groups differing in drought tolerance were identified, including two tolerant, five moderately tolerant and two susceptible varieties. Under drought stress condition, drought sensitive variety (Yukon) showed relative higher water loss, more severe cell membrane damage (EL), and more accumulation of hydrogen peroxide (H2O2) and malondialdehyde (MDA), while drought tolerant variety (Tifgreen) exhibited significantly higher antioxidant enzymes activities. Further results indicated that drought induced cell injury in different varieties (Yukon, SR9554 and Tifgreen) exhibited liner correlation with leaf water content (LWC), H2O2 content, MDA content and antioxidant enzyme activities. Additionally, Tifgreen plants had significantly higher levels of osmolytes (proline level and soluble sugars) when compared with Yukon and SR9554 under drought stress condition. Taken together, our results indicated that natural variation of drought stress tolerance in bermudagrass varieties might be largely related to the induced changes of water status, osmolyte accumulation and antioxidant defense system.  相似文献   

11.
The role of competition for light among plants has long been recognised at local scales, but its importance for plant species distributions at larger spatial scales has generally been ignored. Tree cover modifies the local abiotic conditions below the canopy, notably by reducing light availability, and thus, also the performance of species that are not adapted to low‐light conditions. However, this local effect may propagate to coarser spatial grains, by affecting colonisation probabilities and local extinction risks of herbs and shrubs. To assess the effect of tree cover at both the plot‐ and landscape‐grain sizes (approximately 10‐m and 1‐km), we fit generalised linear models (GLMs) for the plot‐level distributions of 960 species of herbs and shrubs using 6935 vegetation plots across the European Alps. We ran four models with different combinations of variables (climate, soil and tree cover) at both spatial grains for each species. We used partial regressions to evaluate the independent effects of plot‐ and landscape‐grain tree cover on plot‐level plant communities. Finally, the effects on species‐specific elevational range limits were assessed by simulating a removal experiment comparing the species distributions under high and low tree cover. Accounting for tree cover improved the model performance, with the probability of the presence of shade‐tolerant species increasing with increasing tree cover, whereas shade‐intolerant species showed the opposite pattern. The tree cover effect occurred consistently at both the plot and landscape spatial grains, albeit most strongly at the former. Importantly, tree cover at the two grain sizes had partially independent effects on plot‐level plant communities. With high tree cover, shade‐intolerant species exhibited narrower elevational ranges than with low tree cover whereas shade‐tolerant species showed wider elevational ranges. These findings suggest that forecasts of climate‐related range shifts for herb and shrub species may be modified by tree cover dynamics.  相似文献   

12.
Salt tolerance and heavy metal hyperaccumulation are two rare plant abilities that are heavily studied for their potential to contribute to agricultural sustainability and phytoremediation in response to anthropogenic environmental change. Several observations suggest that it is worth investigating the link between the abilities to tolerate high levels of soil salinity or accumulate more of a particular heavy metal from the soil than most plants. Firstly, several angiosperm families are known to contain both salt tolerant plants (halophytes) and heavy metal hyperaccumulators. Secondly, some halophytes can also accumulate heavy metals. Thirdly, although salinity tolerance and heavy metal hyperaccumulation typically require many physiological or anatomical changes, both have apparently evolved many times in angiosperms and among closely related species. We test for a significant relationship between halophytes and hyperaccumulators in angiosperms using taxonomic and phylogenetic analyses. We test whether there are more angiosperm families with both halophytes and hyperaccumulators than expected by chance, and whether there are more species identified as both halophyte and hyperaccumulator than if the abilities were unconnected. We also test whether halophytes and hyperaccumulators are phylogenetically clustered among species in seven angiosperm families. We find a significant association between halophytes and hyperaccumulators among angiosperm families and that there are significantly more species identified as both halophytes and hyperaccumulators than expected. Halophytes and hyperaccumulators each show low phylogenetic clustering, suggesting these abilities can vary among closely related species. In Asteraceae, Amaranthaceae, Fabaceae, and Poaceae, halophytes and hyperaccumulators are more closely related than if the two traits evolved independently.  相似文献   

13.
We quantified the variation and plasticity in cold tolerance among four larval stages of four laboratory strains of Drosophila melanogaster in response to both acute (<2 h of cold exposure) and chronic (7 h of cold exposure) cold exposure. We observed significant differences in basal cold tolerance between the strains and among larval stages. Early larval instars were generally more tolerant of acute cold exposures than third-instar larvae. However, wandering larvae were more tolerant of chronic cold exposures than the other stages. Early stages also displayed a more pronounced rapid cold-hardening response than the later stages. Heat pre-treatment did not confer a significant increase in cold tolerance to any of the strains at any stage, pointing to different mechanisms being involved in resolving heat- and cold-elicited damage. However, when heat pre-treatment was combined with rapid cold-hardening as sequential pre-treatments, both positive (heat first) and negative (heat second) effects on cold tolerance were observed. We discuss possible mechanisms underlying cold-hardening and the effects of acute and chronic cold exposures.  相似文献   

14.
Plants can defend themselves against the damaging effects of herbivory in at least two ways. Resistant plants avoid or deter herbivores and are therefore fed upon less than susceptible plants. Tolerant plants are not eaten less than plants with little tolerance, but the effects of herbivore damage are not so detrimental to a tolerant plant as they are to a less tolerant plant. Biologists have suggested that these two strategies might represent two alternative and redundant defenses against herbivory since they appear to serve the same function for plants. I explore the relationship between resistance and tolerance, particularly with regards to how the joint evolution of these two traits will influence the evolution of plant defense. Although I briefly review some of the contributions of theory to the study of tolerance, I concentrate on an empirical, ecological genetic approach to the study of the evolution of these characters and the coevolution of tolerance and herbivores. In order to understand the evolution of any trait, we must understand the evolutionary forces acting on the trait. Specifically, we must understand how natural selection acts on tolerance. I review several studies that have specifically measured the form of selection acting on tolerance and tested the hypothesis that resistance and tolerance are alternative strategies. I also present a statistical analysis that does not support the hypothesis that herbivores are selective agents on tolerance. Finally, I consider a variety of constraints that possibly restrict the evolution of tolerance. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
In European dry grasslands land-use changes affect plant species performance and frequency. Potential driving forces are eutrophication and habitat fragmentation. The importance of these factors is presumably scale dependent. We used a functional trait approach to detect processes that influence species frequency and endangerment on different spatial scales. We tested for associations between functional traits and (1) frequency and (2) degree of endangerment on local, regional and national scales. We focussed on five selected traits that describe the life-history of plant species and that are related to competition, dispersal ability and habitat specificity. Trait data on plant height, SLA, plant coverage, peak of flowering and diaspore mass were measured for 28 perennials from common to rare and endangered to non-endangered on 59 dry grassland sites in north-eastern Germany. Multiple regression models revealed that species frequency is positively and species endangerment negatively related to plant height, plant coverage and SLA on more than one spatial scale. On the local scale, diaspore mass has a negative effect on species frequency. More frequent and less endangered species show a later peak of flowering on nationwide and regional scales. We concluded that competition traits are more important on larger scales, whereas dispersal traits are more important for species frequency on the smaller scale. On national and regional scales, eutrophication and habitat loss may be the main drivers of species threat, whereas on the local scale fragmentation plays a crucial role for the performance of dry grassland species.  相似文献   

16.
Biogeography and metacommunity ecology provide two different perspectives on species diversity. Both are spatial in nature but their spatial scales do not necessarily match. With recent boom of metacommunity studies, we see an increasing need for clear discrimination of spatial scales relevant for both perspectives. This discrimination is a necessary prerequisite for improved understanding of ecological phenomena across scales. Here we provide a case study to illustrate some spatial scale-dependent concepts in recent metacommunity studies and identify potential pitfalls. We presented here the diversity patterns of Neotropical lepidopterans and spiders viewed both from metacommunity and biogeographical perspectives. Specifically, we investigated how the relative importance of niche- and dispersal-based processes for community assembly change at two spatial scales: metacommunity scale, i.e. within a locality, and biogeographical scale, i.e. among localities widely scattered along a macroclimatic gradient. As expected, niche-based processes dominated the community assembly at metacommunity scale, while dispersal-based processes played a major role at biogeographical scale for both taxonomical groups. However, we also observed small but significant spatial effects at metacommunity scale and environmental effects at biogeographical scale. We also observed differences in diversity patterns between the two taxonomical groups corresponding to differences in their dispersal modes. Our results thus support the idea of continuity of processes interactively shaping diversity patterns across scales and emphasize the necessity of integration of metacommunity and biogeographical perspectives.  相似文献   

17.
Drought has significant effect on wheat production by decreasing grain yield. Phenotyping the populations is a useful tool for understanding the interactions between phenotype and genotype. 135 doubled haploid (DH) genotypes and their parental varieties Plainsman (Pl) and Cappelle Desprez (CD) were phenotyped in glasshouse under well-watered (WW) and drought-stress (DS) conditions. The response of plant height, heading time, aboveground biomass, grain yield, root dry mass harvest index (HI) under both conditions, and stress tolerance index (STI) and water consumption in WW conditions was studied. We found 20% decrease in the plant growth, 66% decrease in the aboveground biomass, and 77% decrease in the grain yield. Under WW conditions, high water consumption was not related to high yields, STI, and HI. The tolerant and the sensitive genotypes were selected. In the WW and water consumption treatment, the sensitive genotype group had better grain yield performance, but under DS, the tolerant group had higher grain yield. The average yield loss was 59% in the tolerant group compared to the WW treatment, and the sensitive yield loss was 68%. Correlation was found between the grain yield and root dry mass in the tolerant group. There was significant difference between the tolerant and sensitive groups on water consumption, as the sensitive genotypes had higher water need. We found strong positive correlation between the water consumption and the grain yield in the tolerant group. This study showed that the tolerant genotypes had improved water regulating efficiency.  相似文献   

18.
While evolutionary ecologists emphasize different ways in which plants can evolutionarily respond to herbivory, such as resistance or tolerance, community ecology has lagged in its understanding of how these different plant traits can influence interactions, abundance, composition, and diversity within more complex food webs. In this paper, we present a series of models comparing community level outcomes when plants either resist or tolerate herbivory. We show that resistance and tolerance can lead to very different outcomes. A particularly important result is that resistant species should often coexist locally with other, less resistant competitors, whereas tolerant species should not be able to coexist locally with less tolerant competitors, although priority effects allow them to coexist regionally. We also use these models to suggest some insights into the evolution of these traits within more complex communities. We emphasize how understanding the differential effects of plant tolerance and resistance in food webs provides greater appreciation of a variety of empirical patterns that heretofore have appeared enigmatic. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
Understanding stability across ecological hierarchies is critical for landscape management in a changing world. Recent studies showed that synchrony among lower‐level components is key to scaling temporal stability across two hierarchical levels, whether spatial or organizational. But an extended framework that integrates both spatial scale and organizational level simultaneously is required to clarify the sources of ecosystem stability at large scales. However, such an extension is far from trivial when taking into account the spatial heterogeneities in real‐world ecosystems. In this paper, we develop a partitioning framework that bridges variability and synchrony measures across spatial scales and organizational levels in heterogeneous metacommunities. In this framework, metacommunity variability is expressed as the product of local‐scale population variability and two synchrony indices that capture the temporal coherence across species and space, respectively. We develop an R function ‘var.partition’ and apply it to five types of desert plant communities to illustrate our framework and test how diversity shapes synchrony and variability at different hierarchical levels. As the observation scale increased from local populations to metacommunities, the temporal variability of plant productivity was reduced mainly by factors that decreased species synchrony. Species synchrony decreased from local to regional scales, and spatial synchrony decreased from species to community levels. Local and regional species diversity were key factors that reduced species synchrony at the two scales. Moreover, beta diversity contributed to decreasing spatial synchrony among communities. We conclude that our new framework offers a valuable toolbox for future empirical studies to disentangle the mechanisms and pathways by which ecological factors influence stability at large scales.  相似文献   

20.
The factors shaping the ways in which animals use resources are a key element of conservation biology, but ecological studies on resource use typically neglect to consider how the study’s spatial scale may have affected the outcomes. We used the dryad butterfly, inhabiting xerothermic grassland and wet meadow, to test for differences in its resource use at two scales–habitat patch and landscape. Based on records of plant species composition from random points within four habitat patches and from points in 53 patches along surveyed transects, we compared the microhabitat preferences of the butterfly on the patch scale, and species occurrence and abundance patterns on the landscape scale. We distinguished four main groups of factors related to vegetation structure which affected the butterfly’s resource use—factors having similar effects on both spatial scales, factors operating primarily on one of the scales considered, factors relevant only on a single spatial scale, and factors operating on both scales but with effects differing between the two habitat types. We suggest that invertebrates may respond on two spatial levels or on only one, and conclude that larger-scale studies can meet the challenges of a sophisticated metapopulation approach and can give insight into the habitat characteristics affecting the persistence of species in landscapes. We stress the value of large-scale studies on species’ habitat preferences when planning conservation strategies, while pointing out that small-scale studies provide useful information about species ecology and behavior, especially if conducted in multiple habitats.  相似文献   

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