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1.
Indirect interactions between populations of different species can be important in structuring natural communities. Indirect effects are either mediated by changes in population densities (trophic or density-mediated effects) or by changes in the behavior of species that are not trophically connected (behavioral or trait-mediated effects). We reviewed the literature on aphids and their parasitoids to explore the various possible indirect interactions that can occur in such communities. The review was motivated by our study of a particular aphid–parasitoid community in a natural (i.e., nonagricultural) habitat, and by the wealth of information that exists about aphid–parasitoid systems in agricultural settings. We focused our review on aphid–parasitoid interactions, but considered how these were influenced by the other aphid natural enemies and also by aphid mutualists and host plants. We conclude that indirect effects are likely to have a major effect in structuring aphid–parasitoid communities, and that the latter are a valuable model system for testing ideas about community interactions. Received: December 20, 1998 / Accepted: January 12, 1999  相似文献   

2.
Beck  Jared J. 《Plant Ecology》2021,222(11):1225-1238
Plant Ecology - Antagonistic interactions between plants and soil biota promote species diversity in many plant communities but little is known about how these plant–soil interactions...  相似文献   

3.
Wilkinson EB  Feener DH 《Oecologia》2007,152(1):151-161
Species must balance effective competition with avoidance of mortality imposed by predators or parasites to coexist within a local ecological community. Attributes of the habitat in which species interact, such as structural complexity, have the potential to affect how species balance competition and mortality by providing refuge from predators or parasites. Disturbance events such as fire can drastically alter habitat complexity and may be important modifiers of species interactions in communities. This study investigates whether the presence of habitat complexity in the form of leaf litter can alter interactions between the behaviorally dominant host ants Pheidole diversipilosa and Pheidole bicarinata, their respective specialist dipteran parasitoids (Phoridae: Apocephalus sp. 8 and Apocephalus sp. 25) and a single species of ant competitor (Dorymyrmex insanus). We used a factorial design to manipulate competition (presence/absence of competitors), mortality risk (presence/absence of parasitoids) and habitat complexity (presence/absence of leaf litter). Parasitoid presence reduced soldier caste foraging, but refuge from habitat complexity allowed increased soldier foraging in comparison to treatments in which no refuge was available. Variation in soldier foraging behavior correlated strongly with foraging success, a proxy for colony fitness. Habitat complexity allowed both host species to balance competitive success with mortality avoidance. The effect of fire on habitat complexity was also studied, and demonstrated that the immediate negative impact of fire on habitat complexity can persist for multiple years. Our findings indicate that habitat complexity can increase dominant host competitive success even in the presence of parasitoids, which may have consequences for coexistence of subordinate competitors and community diversity in general.  相似文献   

4.
Species coexistence involving trophic interactions has been investigated under two theoretical frameworks—partitioning shared resources and accessing exclusive resources. The influence of body size on coexistence is well studied under the exclusive resources framework, but has received less attention under the shared-resources framework. We investigate body-size-dependent allometric extensions of a classical MacArthur-type model where two consumers compete for two shared resources. The equilibrium coexistence criteria are compared against the general predictions of the alternative framework over exclusive resources. From the asymmetry in body size allometry of resource encounter versus demand our model shows, counterintuitively, and contrary to the exclusive resource framework, that a smaller consumer should be competitively superior across a wide range of supplies of the two resource types. Experimental studies are reviewed to resolve this difference among the two frameworks that arise from their respective assumptions over resource distribution. Another prediction is that the smaller consumer may have relatively stronger control over equilibrium resource abundance, and the loss of smaller consumers from a community may induce relatively stronger trophic cascades. Finally, from satiating consumers’ functional response, our model predicts that greater difference among resource sizes can allow a broader range of consumer body sizes to coexist, and this is consistent with the predictions of the alternative framework over exclusive resources. Overall, this analysis provides an objective comparison of the two alternative approaches to understand species coexistence that have heretofore developed in relative isolation. It advances classical consumer–resource theory to show how body size can be an important factor in resource competition and coexistence.  相似文献   

5.
Mechanisms that affect a host plant’s ability to face herbivory are subjects of ongoing interest. Plant reproductive phenology plays a key role in the dynamics of communities in many ways. In ant–plant–herbivore interactions, host-plant phenology affects traits of its herbivores which in turn determine what traits ants must have to benefit the host-plant. Diversity of plant phenological traits could influence the ecological diversity of coevolved ant–plant mutualisms.  相似文献   

6.
Habitat conservation for threatened temperate insect species is often guided by one of two paradigms: a metapopulation approach focusing on patch area, isolation and number; or a habitat approach focusing on maintaining high quality habitat for the focal species. Recent research has identified the additive and interacting importance of both approaches for maintaining populations of threatened butterflies. For specialised host-parasitoid interactions, understanding the consequences of habitat characteristics for the interacting species is important, because (1) specialised parasitoids are particularly vulnerable to the consequences of fragmentation, and (2) altered interaction frequencies resulting from changes to habitat management or the spatial configuration of habitat are likely to have consequences for host dynamics. The spatial ecology of Cotesia bignellii, a specialist parasitoid of the threatened butterfly Euphydryas aurinia, was investigated at two spatial scales: within habitat patches (at the scale of individual aggregations of larvae, or ‘webs’) and among habitat patches (the scale of local populations). Parasitism rates were investigated in relation to larval web size, vegetation sward height and host density. Within patches, the probability of a larval webs being parasitized increased significantly with increasing number of larvae in the web, and parasitism rates increased significantly with increasing web isolation. The proportion of webs parasitized was significantly and negatively correlated with cluster density. Among habitat patches the proportion of parasitized webs decreased as cluster density increased. Clusters with a high proportion of larval webs parasitized tended to have lower parasitism rates per larval web. These results support the call for relatively large and continuous habitat patches to maintain stable parasitoid and host populations. Conservation efforts directed towards maintenance of high host plant density could allow E. aurinia to reduce parasitism risk, while providing C. bignellii with sufficient larval webs to allow population persistence.  相似文献   

7.
The relationship between plants and ants is often mediated by the presence of extrafloral nectaries (EFNs) that attract ants and provide rewards by protecting plants from herbivores or parasites. Ficus trees (Moraceae) and their pollinators (Hymenoptera: Agaonidae) are parasitized by many nonpollinating fig wasp species (Hymenoptera: Chalcidoidea) that decrease the reproductive output of the mutualistic partners. Previous studies have shown that ants living on and patrolling Ficus species can efficiently deter parasitic wasps. The aim of this study was to verify the presence of EFNs on figs of Ficus benguetensis and test the hypothetical protection service provided by ants. Figs in different developmental stages were collected from Fu-Yang Eco Park, Taipei, Taiwan. Sugars on the fig surface were collected and analyzed through high-performance anion-exchange chromatography. Moreover, ants were excluded from the figs to determine the effect of ants on the nonpollinating fig wasps. We identified three oligosaccharides whose relative proportions varied with the fig developmental phase. In addition, results showed that the ant-excluded figs were heavily parasitized and produced three times less pollinators than did the control figs. Finally, the specific interactions of Ficus benguetensis with ants and the relationship between figs and ants in general are discussed.  相似文献   

8.
Food web dynamics are well known to vary with indirect interactions, classic examples including apparent competition, intraguild predation, exploitative competition, and trophic cascades of food chains. Such food web modules entailing predation and competition have been the focus of much theory, whereas modules involving mutualism have received far less attention. We examined an empirically common food web module involving mutualistic (N 2) and parasitic (N 3) consumers exploiting a resource of a basal mutualist (N 1), as illustrated by plants, pollinators, and nectar robbers. This mutualism–parasitism food web module is structurally similar to exploitative competition, suggesting that the module of two consumers exploiting a resource is unstable. Rather than parasitic consumers destabilizing the module through (?,?) indirect interactions, two mechanisms associated with the mutualism can actually enhance the persistence of the module. First, the positive feedback of mutualism favors coexistence in stable limit cycles, whereby (+,?) indirect interactions emerge in which increases in N 2 have positive effects on N 3 and increases in N 3 have negative effects on N 2. This (+,?) indirect interaction arising from the saturating positive feedback of mutualism has broad feasibility across many types of food web modules entailing mutualism. Second, optimization of resource exploitation by the mutualistic consumer can lead to persistence of the food web module in a stable equilibrium. The mutualism–parasitism food web module is a basic unit of food webs in which mutualism favors its persistence simply through density-dependent population dynamics, rather than parasitism destabilizing the module.  相似文献   

9.
Resource regulation occurs when herbivory maintains or increases plant susceptibility to further herbivory by the same species. A review of the literature indicates it is a widespread plant–animal interaction involving a diverse array of herbivores. At least three mechanisms can produce this positive feedback cycle. First, phytophagous insect and mammalian herbivore damage can stimulate dormant buds to produce vigorous juvenile growth, which is preferred for further attack. Juvenilization cycles may have repeatedly evolved because herbivores are able to take advantage of a generalized plant compensatory response to any type of damage. Second, herbivores can manipulate plant source–sink relationships to attain more resources, and this alteration of plant growth may benefit subsequent herbivore generations. Third, herbivory can alter plant nutrition or defensive chemistry in a way that makes a plant susceptible to more herbivory. Resource regulation probably occurs because damage to resources preferred by the herbivores induces a generalized plant response that produces more preferred resources. Alternatively, manipulation of plant resources to induce resource regulation may have evolved in herbivores with a high degree of philopatry due to selection to alter plant resources to benefit their offspring. Resource regulation can stabilize insect population dynamics by maintaining a supply of high-quality plant resources. It can also increase the heterogeneity of host-plant resources for herbivores by altering the physiological age structure and the distribution of resources within plants. Resource regulation may have strong plant-mediated effects on other organisms that use that host plant, but these effects have not yet been explored.  相似文献   

10.
《Fungal biology》2023,127(5):1005-1009
Research on bacterial-fungal interactions (BFIs) has revealed that fungi and bacteria frequently interact with one another within diverse ecosystems and microbiomes. Assessing the current state of knowledge within the field of BFI research, particularly with respect to what interactions between bacteria and fungi have been previously described, is very challenging and time consuming. This is largely due to a lack of any centralized resource, with reports of BFIs being spread across publications in numerous journals using non-standardized text to describe the relationships. To address this issue, we have developed the BFI Research Portal, a publicly accessible database of previously reported interactions between bacterial and fungal taxa to serve as a centralized resource for the field. Users can query bacterial or fungal taxa to see what members from the other kingdom have been observed as interaction partners. Search results are accompanied by interactive and intuitive visual outputs, and the database is a dynamic resource that will be updated as new BFIs are reported.  相似文献   

11.
Human–wildlife interactions are often associated with a myriad of stakeholder groups, intense political scrutiny, and limited biological data, creating complex decision-making situations for wildlife management agencies. Limited research exists on the development and testing of tools (e.g., models to predict the spatial distribution of interactions) to reduce human–black bear (Ursus americanus) interactions (HBI). Available models predicting spatial distribution of HBI are usually developed at scales too large to predict across urban areas, are rarely tested against independent data sets, and usually do not incorporate both landscape and anthropogenic variables. Our objective was to develop a predictive modeling tool that could identify areas of high conflict potential across urban landscapes. We compared locations of HBI in Missoula, MT, recorded by Montana Fish, Wildlife & Parks from 2003 to 2008, to random locations using logistic regression. The final model discriminated the relative spatial probability of HBI within Missoula well, and a second study area moderately. The probability of HBI in Missoula increased when residents lived close to forested patches and major rivers and streams and in intermediate housing densities (approx. 6.59 houses/ha). Our results provide a wildlife management tool and a repeatable statistical framework that predicts spatial distribution of HBI using only a small set of variables. © 2011 The Wildlife Society.  相似文献   

12.
Hydrobiologia - Natural enemies are known to modify competitive hierarchies among terrestrial plants. Here we examine whether the same applies to freshwater systems. Lagarosiphon major...  相似文献   

13.
Capsule Changes in return date coincided with marked changes in population size that probably resulted in fluctuating competition for nest-sites.

Aims To document the changes in return dates over a 44-year period and to identify the factors associated with these changes.

Methods We compared changes in return date at Shetland colonies with those for the Isle of May, southeast Scotland, and with the available information on population size, the abundance of some fish species eaten by Common Guillemots and large-scale changes in the oceanography and climate of the eastern Atlantic as reflected by the winter index of the North Atlantic Oscillation (NAO).

Results Common Guillemots normally return to colonies in Shetland in late winter. However, during the 1960s return dates became gradually earlier with birds present from early October. Autumn return remained the norm for about ten years after which return dates gradually reverted back to late winter. In contrast, Common Guillemots on the Isle of May, 400 km south of Shetland, showed no marked shift, returning in October each year. There was a strong negative correlation between date of return of Shetland birds and population size, whereas on the Isle of May birds came back earlier when there was a large positive winter NAO index. There was no convincing evidence that changes in wintering areas or fish abundance influenced when birds returned to the colonies, although the fish data may not have been collected on the correct spatial scale.

Conclusion Competition for high quality nest-sites is the most likely reason for Common Guillemots returning to the colonies during the autumn and winter.  相似文献   

14.
Body size is a major factor constraining the trophic structure and functioning of ecological communities. Food webs are known to respond to changes in basal resource abundance, and climate change can initiate compounding bottom-up effects on food-web structure through altered resource availability and quality. However, the effects of climate and co-occurring global changes, such as nitrogen deposition, on the density and size relationships between resources and consumers are unknown, particularly in host–parasitoid food webs, where size structuring is less apparent. We use a Bayesian modelling approach to explore the role of consumer and resource density and body size on host–parasitoid food webs assembled from a field experiment with factorial warming and nitrogen treatments. We show that the treatments increased resource (host) availability and quality (size), leading to measureable changes in parasitoid feeding behaviour. Parasitoids interacted less evenly within their host range and increasingly focused on abundant and high-quality (i.e. larger) hosts. In summary, we present evidence that climate-mediated bottom-up effects can significantly alter food-web structure through both density- and trait-mediated effects.  相似文献   

15.
Resource competition theory suggests that the nature of diversity–resource–invasibility interactions will vary along fertility gradients, concurrent with changes in the relative availability of limiting above- versus below-ground resources. Experimental support for this contingency is lacking. Here, we manipulated resident diversity, baseline fertility, and the availabilities of light and soil nitrogen in grassland communities invaded by two functionally distinct non-native plant species (Lolium arundinaceum and Melilotus alba). We tested the hypotheses that increased resident diversity reduces community invasibility and dampens the effects of light and soil nitrogen pulses, and that the relative effects of light versus soil nitrogen additions on diversity–invasibility relationships depend on the baseline fertility of the study system. Our results reveal an overall weak negative effect of resident diversity on Lolium performance, but in contrast to our expectations, this diversity effect did not vary with light or soil nitrogen additions or with baseline fertility. However, the relative effects of above- versus below-ground resource additions on invader performance varied with baseline fertility as expected: Lolium responded most strongly to soil nitrogen additions in low-fertility mesocosms and most strongly to increased light availability in high-fertility mesocosms. In contrast to Lolium, nitrogen-fixing Melilotus was overall less responsive to diversity and resource manipulations. Together, these patterns do not lend support for the dependence of diversity–resource–invasibility relationships on either baseline fertility or invasive species identity, but they do highlight the dominant role of resources over diversity in determining invader performance, as well as the manner in which fertility alters the relative importance of above- versus below-ground resource pulses in promoting invasions.  相似文献   

16.
Life zones and their changes in distribution in north-east China were studied based on climate–vegetation relationships. The warmth index (WI) and aridity index (the ratio of evaporation [evaporation rate, ER] to precipitation) were used to represent the site condition. The typical site condition of each vegetation type was determined as the classification criterion. The boundaries of the four potential vegetation zones were estimated based on the combinations of WI and ER in relation to vegetation (i.e. cold-temperate conifer forest zone, temperate broad-leaved conifer mixed forest zone, warm-temperate deciduous forest zone, and temperate steppe zone). The distribution changes in vegetation zone caused by human activities were estimated by comparing the potential vegetation with the actual one. The percentage cover of forest has shrunk from about 70% to the present 27%. About 23% of the study area was replaced by agricultural vegetation and industrial use. Nearly half of the region could have been covered by broad-leaved conifer mixed forest which was shrunk to a small area, less than 5% of the region. The broad-leaved deciduous forest zone in the southern part could have occupied about 7% of the area, and had almost no virgin stand.  相似文献   

17.
Global changes, such as climate and urbanization, are strongly entwined and aggravated by the development of human activities, which also intensifies the human-mediated dispersal of species. However, few studies have explicitly considered the combined influence of urbanization and climate on species expansion. We investigated the combined roles of climate, urbanization and human-mediated dispersal in the expansion of Tetramorium immigrans (an invasive pavement ant in North America) in urban areas of South-eastern France. A total of 544 T. immigrans individuals were sampled from 16 urban gradients and genotyped at 14 microsatellite markers. Based on molecular ecology methods and statistical modelling, we evaluated the impact of climate and urbanization on its distribution patterns. Through the combined study of the occurrence probabilities of T. immigrans, its genetic structure and the founder effects within its populations, the effect of climate–urbanization interaction on species distribution was clearly evidenced, suggesting that in the north of its range, T. immigrans subsists under harsher climate by colonizing the most urbanized areas. Many taxa may conform to such pattern, making the combined study of climate and urbanization a necessary challenge for future studies. Distribution patterns concurred with similar observations in the American invasive range of T. immigrans, making it likely that it may not be native to the northernmost part of its European range. Cryptic invasions or discreet range shifts in response to increasing urbanization are likely to occur in many taxa, especially in ants, and deserve increased attention from researchers and managers alike.  相似文献   

18.
While studying breeding systems and pollination ecology of nine Gentiana species (G. lutea, G. punctata, G. asclepiadea, G. pneumonanthe, G. cruciata, G. pyrenaica, G. verna, G. utriculosa, and G. nivalis) in the Bulgarian mountains, we recorded number of insects that feed on their maturing seeds. In addition, parasitoid wasps in connection to these seed predators were detected. Insects are identified and the impact on the seed set of afore mentioned Gentiana species is estimated. Fruit capsules of Gentiana spp. from different populations in the mountains in Bulgaria were investigated for the presence or absence of damage by larvae during the period of 16 years. The seed destruction varies among the nine investigated Gentiana species. The insects whose larvae damaged the seed/fruit set belonged mainly to Coleoptera and Diptera. The larvae of lycaenid butterflies, Maculinea spp. (Lepidoptera), were recorded only in seeds of G. asclepiadea, G. pneumonanthe and G. cruciata. Parasitoid wasps from the families Ichneumonidae, Braconidae, and Pteromalidae were identified, some of them new for the fauna of Bulgaria.  相似文献   

19.
Interactions between species of different trophic levels have long been recognized as fundamental processes in ecology. Although mounting evidence indicates that plant species diversity (PSD) or plant genetic diversity (PGD) can influence the plant-associated arthropod community, these two fundamental levels of biodiversity are not often manipulated simultaneously to assess their effects on species interactions. We used a large tree diversity experiment (BEF-China), which manipulates PSD and PGD in a crossed design to test individual and combined effects of PSD and PGD on multitrophic interaction networks and interaction partner species richness and occurrence. We focused on two tree species, on which sap-sucking Hemiptera and interacting ant species commonly occur. This tri-trophic interaction can be divided into the antagonistic plant–Hemiptera interaction and the mutualistic Hemiptera–ant interaction, known as trophobioses. Qualitative evaluation of tri-trophic interaction networks at different PSD and PGD combinations showed increased interaction partner redundancy at high PSD and PGD. This was supported by increased Hemiptera species richness at high PSD and PGD. Furthermore, the data indicate higher occurrence of Hemiptera and trophobioses and higher trophobiotic ant species richness with increasing PSD and PGD. As no plant diversity component alone caused an effect we conclude that the combined effect of high PGD and high PSD might be additive. In summary, as plant genetic diversity, especially at low species richness, seems to increase the interaction partner redundancy in interaction networks and the diversity of interacting communities, we suggest that genetic diversity should be considered in forest conservation and restoration programs.  相似文献   

20.
Krill plays a significant role in the Barents Sea ecosystem, providing energy transport between different trophic levels. The current paper presents the results of a long-term study (1980–2009) based on pelagic trawl catches from August to September. Our investigations show that the krill species were distributed widely in the Barents Sea and that the largest krill concentrations were restricted to the west-central and eastern parts of the Barents Sea. The current paper presents the relative biomass indices, and the estimates must be interpreted as minimum biomass. The mean annual krill biomass was estimated to be 22 million tonnes in wet weight, with the highest values being as much as 48 million tonnes. Capelin is the largest pelagic stock, and in some years, their biomass can amount to 4–7 million tonnes, which can impose high predation pressure on krill. When their biomass is high, capelin may consume close to 26 million tonnes annually. The predation from pelagic (herring and blue whiting) and bottom (cod and haddock) fish species was much lower, being 9 and 1 million tonnes, respectively. A negative relationship between krill biomass and capelin stock size above 74°N was observed during the study period. However, during the last decade, the krill biomass has increased despite heavy predation from capelin in some years. A positive significant linear relationship between the mean annual Kola temperature and the krill biomass seems to indicate that the recent warming conditions have favourable impacts on the krill populations in the Barents Sea.  相似文献   

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