Interspecific competition in small rodents: from populations to individuals

The role of interspecific competition in shaping animal and plant communities has formed one of the major issues in ecology for decades. Small mammals, mainly rodents, have been among the model systems used for research on interspecific competition. Most studies within small mammal systems in the past have examined effects of competition on population attributes such as on population size, habitat use, or population dynamics. Population-level responses are the cumulative effects of individual responses, however, the influence of competition on individual life-history traits has rarely been studied. Research on life-histories may bridge gaps between population biology and effects of competition on individual behaviour. In this paper, we review recent research approaches to interspecific competition in rodents based on census data and species assemblages, that use regression analysis, time series analysis, removal and exclusion experiments, and showcase our own experimental research on the effects of interspecific competition on individual life-history traits in boreal voles.     

Soil modification by invasive plants: effects on native and invasive species of mixed-grass prairies

Invasive plants are capable of modifying attributes of soil to facilitate further invasion by conspecifics and other invasive species. We assessed this capability in three important plant invaders of grasslands in the Great Plains region of North America: leafy spurge (Euphorbia esula), smooth brome (Bromus inermis) and crested wheatgrass (Agropyron cristatum). In a glasshouse, these three invasives or a group of native species were grown separately through three cycles of growth and soil conditioning in both steam-pasteurized and non-pasteurized soils, after which we assessed seedling growth in these soils. Two of the three invasive species, Bromus and Agropyron, exhibited significant self-facilitation via soil modification. Bromus and Agropyron also had significant facilitative effects on other invasives via soil modification, while Euphorbia had significant antagonistic effects on the other invasives. Both Agropyron and Euphorbia consistently suppressed growth of two of three native forbs, while three native grasses were generally less affected. Almost all intra- and interspecific effects of invasive soil conditioning were dependent upon presence of soil biota from field sites where these species were successful invaders. Overall, these results suggest that that invasive modification of soil microbiota can facilitate plant invasion directly or via ‘cross-facilitation’ of other invasive species, and moreover has potential to impede restoration of native communities after removal of an invasive species. However, certain native species that are relatively insensitive to altered soil biota (as we observed in the case of the forb Linum lewisii and the native grasses), may be valuable as ‘nurse’species in restoration efforts.     

Springtime in the city: exotic shrubs promote earlier greenup in urban forests

Despite the widespread recognition that urban areas are frequently dominated by exotic and invasive plants, the consequences of these changes in community structure have not been explicitly considered as an explanation for the pattern of advanced leaf phenology, or early greenup, reported in many urban areas. As such, we evaluated two hypotheses that could account for advanced greenup in forests along an urban to rural gradient: advanced phenology within individual species or differences in woody plant community. We monitored the spring leafing phenology of Aesculus glabra (Ohio buckeye), Lonicera maackii (Amur honeysuckle), and Acer negundo (box elder) in 11 forests spanning an urban to rural gradient in central Ohio, USA. From February to April 2006, we monitored these species, recorded woody plant composition, and documented daily minimum and maximum temperatures at each site. We found a weak but general trend of advanced phenology within species in more urban landscapes. Monthly average minimum temperatures were higher with increasing urbanization while monthly average maximum temperatures were similar across the urban to rural gradient. We also found evidence for shifts in woody plant communities along the urbanization gradient, mainly driven by the abundance of L. maackii, an invasive exotic species, in the more urban forests. Because L. maackii leafs out weeks earlier than native woody species and is very abundant in urban forests, we suggest that the invasion of forests by this species can generate earlier greenup of urban forests.     

The invasive plant species Centaurea maculosa alters arbuscular mycorrhizal fungal communities in the field

While several recent studies have described changes in microbial communities associated with exotic plant invasion, how arbuscular mycorrhizal fungi (AMF) communities respond to exotic plant invasion is not well known, despite the salient role of this group in plant interactions. Here, we use molecular methods (terminal restriction fragment length polymorphism analyses based on the large subunit of the rRNA gene) to examine AMF community structure in sites dominated by the invasive mycorrhizal forb, Centaurea maculosa Lam. (spotted knapweed), and in adjacent native grassland sites. Our results indicate that significant AMF community alteration occurs following C. maculosa invasion. Moreover, a significant reduction in the number of restriction fragment sizes was found for samples collected in C. maculosa-dominated areas, suggesting reduced AMF diversity. Extraradical hyphal lengths exhibited a significant, on average 24%, reduction in C. maculosa-versus native grass-dominated sites. As both AMF community composition and abundance were altered by C.maculosa invasion, these data are strongly suggestive of potential impacts on AMF-mediated ecosystem processes. Given that the composition of AMF communities has the potential to differentially influence different plant species, our results may have important implications for site restoration after weed invasion.     

外来入侵植物与人工林下层植被结构的关联性

为有效防控外来入侵植物,在广西陆川县人工林区进行植被嵌套样方调查,分析群落物种组成与植被结构和环境因子之间的相关性。Mantel检验表明样方物种组成与样方植被结构的相关性(r=0.208, P=0.002)高于其与环境因子相关性(r=0.084, P=0.051)。MRPP分析表明,有入侵植物阔叶丰花草(Spermacoce alata)、假臭草(Praxelis clematidea)和胜红蓟(Ageratum conyzoides)样方的植被结构与无这3种植物样方的有极显著不同(P 0.01),而有无薇甘菊(Mikainamicrantha)样方的植被结构相似。t检验表明林冠盖度(3.0 m)与这4种植物入侵均无显著相关性(P0.073)。通过增加垂直高度1.5 m以下的植被密度,可以减少阔叶丰花草、假臭草和胜红蓟的入侵,但对抑制薇甘菊入侵无效。因此,植被结构作为过滤器,可能主要作用于植物的种子产生时间、萌发周期和生长习性;以种子方式繁殖的入侵植物能否定植相对更依赖干扰、暴露的裸地;兼具无性和有性繁殖且能攀援和匍匐生长使得薇甘菊能够在不同植被结构的群落中相对随机地定植。     

Traditional Knowledge and Management of <Emphasis Type="Italic">Feijoa (Acca sellowiana)</Emphasis> in Southern Brazil

Traditional Knowledge and Management of Feijoa (Acca sellowiana) in Southern Brazil. This paper investigates traditional knowledge of the use and management of Acca sellowiana in southern Brazil. Fifty-six informants from three rural communities were assigned to one of four subgroups (“maintainers,” “managers,” “cultivators,” or “users”) based on their responses regarding management and use of A. sellowiana. Traditional knowledge related to use of this species is widespread among rural residents, but traditional knowledge related to management is fragmented depending on whether one uses, manages, or cultivates the species. Knowledge held in rural communities suggests that A. sellowiana could play an expanded role in local economies as well as biodiversity conservation. We suggest that participatory research could stimulate greater local use as well as on-farm conservation of A. sellowiana.     

The role of trematode parasites in larval anuran communities: an aquatic ecologist’s guide to the major players

Conservation strategies depend on our understanding of the ecosystem and community dynamics. To date, such understanding has focused mostly on predator–prey and competitor interactions. It is increasingly clear, however, that parasite–host interactions may represent a large, and important, component of natural communities. The need to consider multiple factors and their synergistic interactions if we are to elucidate the contribution of anthropogenic factors to loss in biodiversity is exemplified by research into present-day amphibian declines. Only recently has the role of factors such as trematode parasite infections been incorporated into studies of the population and community dynamics of aquatic systems. We argue that this is due, at least in part, to difficulties faced by aquatic ecologists in sifting through the complex systematics that pervade the parasite literature. We note that two trematode species are of dominant importance with regard to North American larval anuran communities, and provide in this review a clear explanation of how to distinguish between the infective stages of these two parasites. We describe the general biology and life history of these parasites, as well as what is known about their effect on larval anurans, and the interactive effects of environmental stressors (typically anthropogenic in nature) and parasites on larval anurans. We hope that this review will convince the reader of the potential importance of these parasites to aquatic communities in general, and to amphibian communities specifically, and will also provide the information necessary for aquatic ecologists to more frequently consider the role of these parasites in their studies of aquatic ecology.     

互花米草入侵对鸟类的生态影响

生物入侵威胁本地物种生存,破坏生态系统的结构和功能,是导致全球生物多样性丧失的重要原因之一。外来植物是入侵生物中的重要一类,可以显著改变本地植被群落,并影响其他生物类群。鸟类作为生态系统中的较高营养级,对由入侵植物引起的栖息地变化十分敏感。互花米草自引入中国沿海以来,其分布区域不断扩散,多数研究认为互花米草入侵造成本地生物多样性降低和生态系统退化。系统梳理了互花米草入侵对鸟类栖息地、食物资源、繁殖、群落等方面的生态影响。主要负面影响有:(1)植被群落结构不利于鸟类栖息、筑巢、觅食;(2)鸟类食物资源丰度和多样性下降;(3)本地鸟类种群数量和物种多样性显著下降。在我国东部沿海湿地,互花米草入侵已经显著改变了植被与鸟类分布格局。但随着入侵历史的增长,少数小型雀形目鸟类却可以逐渐适应互花米草生境。互花米草入侵为某些非本地鸟类提供了空白生态位,在一定程度上丰富了本地物种多样性,对互花米草的快速清除反而可能不利于已适应并依赖互花米草生境的鸟类。综上,认为互花米草入侵对鸟类群落甚至整个生态系统的影响可能需要更多研究进行综合评价,应开展长期、大尺度、多因子的监测研究和多物种比较研究,建立生态评价模型并制定科学有效的互花米草管理对策。     

A 10-year study of changes in forest vegetation on Silhouette island, Seychelles

A 10 year study of forest communities on Silhouette island, Seychelles demonstrates stability of forest composition in most areas over this time-scale. Areas with heavy invasion by alien species were found to be regenerating, particularly with the rapid loss of Clidemia hirta. This is attributed to the abundance of well-adapted native plants allowing competitive exclusion to take place, throughout competition for light. It was noted that invasive plant species tend to be unstable on the rocky slopes covered by native high forest. A high rate of tree fall and limited seed dispersal may reduce the impact of the invasive tree Paraserianthes falcataria in the future. Other species such as Cinnamomum verum and Psidium cattleianum may persist as major invaders due to wider seed dispersal.     

Aspects of population dynamics in Halimione portulacoides communities

Summary Studies on sample plots inHalimione portulacoides communities show that environmental disturbances, either natural or induced by man, start a sequence of partly overlapping density maxima inSuaeda maritima, Aster tripolium andPuccinellia maritima successively, before the originalHalimione community totally recovers. When succession time before recovering is long enough, there are tendencies in redundancy of this sequence stressing the unilinear character of the succession. Minor environmental impacts induce a longer time-lag period of theSuaeda density maximum, suggesting threshold values of these impacts for the species to maintain minimal population densities or to become locally extinct. This sequence of interim species starting after an environmental disturbance, suggests also a gradient character in various biological attributes, for instance in life-time, propagation, nutrient and genetic plasticity strategies. The mechanism described can therefore be interpreted as a complex of mostly well-adapted and well-integrated inherent species strategies capable of absorbing environmental shocks. It is suggested that in the salt-marsh ccosystem the pattern of spatial variation in densities and that of temporal variation in fluctuations of the three species populations under natural conditions reflect corresponding patterns of environmental disturbances in the vegetation taking into account a timelag associated with the magnitude of the impact concerned.Contribution to the Symposium on Plant species and plant communities held at Nijmegen, 11–12 November 1976, on the occasion of the 60th birthday of Professor Victor Westhoff.Nomenclature follows Heukels-van Ooststroom. Flora van Nederland, 18e druk, 1975. Wolters-Noodhoff, Groningen.The authors are greatly indebted to Dr K.F. Vaas (Yerseke) for reviewing the English text.Communication Nr. 160.     

Pocket gophers (Geomys bursarius), vegetation,and soil nitrogen along a successional sere in east central Minnesota

Summary Insect size tactics or developmental strategies are discussed in relation to decisions individuals make about when to mature. Such decisions carry with them costs and benefits in terms of that individual's reproductive success. Whenever size affects fitness, selection should act such that individuals evaluate the costs and benefits due to changes in size and should mature when the ratio of benefit to cost is maximized.Predictions about seasonal changes in adult sizes within a population are tested on two species of mole cricket, Scapteriscus acletus and vicinus. Specifically, individuals maturing in the fall should be larger than average because there is no cost associated with delayed reproduction since reproduction occurs only during spring months. Smaller than average individuals should remain in juvenile stages and get larger before reproducing. Also it is predicted that as the spring reproductive season progresses a greater proportion of smaller individuals should mature because the costs due to delaying reproduction increase. The changes in seasonal distribution of adult sizes of mole crickets support the predictions and suggest that individuals make decisions about when to mature based on costs and benefits associated with changes in size.     

Competing for crevices: interspecific conflict influences retreat-site selection in montane lizards

Direct interference competition between sympatric taxa affects habitat use and shelter-site selection in species within most major vertebrate lineages. However, studies on interspecific social interference in reptiles largely have been confined to research on interactions between non-native (invasive) species and native fauna. Does interspecific interference also influence habitat use within natural assemblages of reptiles? We studied five broadly sympatric species of viviparous montane skinks within the genera Egernia and Eulamprus in southeastern Australia. Previous work has shown strong interspecific overlap in abiotic attributes of shelter-sites for these taxa, but no joint occupancy of retreats. Laboratory trials in which we manipulated the identity of co-occurring lizards revealed frequent displacement from “preferred” (hotter) shelters, with interspecific interactions more intense than intraspecific conflicts. The five species displayed a linear interspecific dominance hierarchy, with larger species displacing smaller taxa. Field manipulations confirmed that interspecific interactions between these species affect shelter-site use. We conclude that direct agonistic encounters between individuals of different species strongly influence habitat use by lizards within this assemblage.     

Interspecific primate associations in Amazonian flooded and unflooded forests

Stable associations between two or more primate species are a prominent feature of neotropical forest vertebrate communities and many studies have addressed their prevalence, and their costs and benefits. However, little is known about the influence of different habitat types on the frequency, seasonality, and composition of mixed-species groups in Amazonian forest primates. Here we examine the features of interspecific primate groups in a large mosaic of flooded (várzea and igapó) and unflooded (terra firme) forest in central Amazonia. In total, 12 primate species occurred in the study area, nine of which were observed in mixed-species associations. Primates were more than twice as likely to form associations in várzea forest than in terra firme forest. Squirrel monkeys were most frequently found in mixed-species groups in all forest types, most commonly in association with brown capuchins. Another frequent member of interspecific associations was the buffy saki, which often formed mixed-species groups with tamarins or brown capuchins. There was no seasonality in the frequency of associations in terra firme forest whereas associations in várzea forest were twice as frequent during the late-dry and early-wet seasons than in the late-wet and early-dry seasons. Interspecific primate associations were common in all forest types, but the degrees to which different species associate varied between these environments. We suggest that the temporal variation of várzea forest associations is connected with seasonal changes in habitat structure and resource abundance. However, more work is needed to pinpoint the underlying causes of mixed-species associations in all forest types and their strong seasonality in várzea forest.     

Extreme habitats as refuge from parasite infections? Evidence from an extremophile fish

Living in extreme habitats typically requires costly adaptations of any organism tolerating these conditions, but very little is known about potential benefits that trade off these costs. We suggest that extreme habitats may function as refuge from parasite infections, since parasites can become locally extinct either directly, through selection by an extreme environmental parameter on free-living parasite stages, or indirectly, through selection on other host species involved in its life cycle. We tested this hypothesis in a small freshwater fish, the Atlantic molly (Poecilia mexicana) that inhabits normal freshwaters as well as extreme habitats containing high concentrations of toxic hydrogen sulfide. Populations from such extreme habitats are significantly less parasitized by the trematode Uvulifer sp. than a population from a non-sulfidic habitat. We suggest that reduced parasite prevalence may be a benefit of living in sulfidic habitats.     

Incorporating uncertainty and social values in managing invasive alien species: a deliberative multi-criteria evaluation approach

The management of Invasive Alien Species (IAS) is stymied by complex social values and severe levels of uncertainty. However, these two challenges are often hidden in the conventional model of management by “value-free” analyses and probability-based estimates of risk. As a result, diverse social values and wide margins of error in risk assessment carry zero weights in the decision-making process, leaving IAS risk decisions to be made in the wake of political pressure and the crisis atmosphere of incursion. We propose to use a Deliberative Multi-Criteria Evaluation (DMCE) to incorporate multiple social values and profound uncertainty into decision-making processes. The DMCE process combines the advantages of conventional multi-criteria decision analysis methods with the benefits of stakeholder participation to provide an analytical structure to assess complex multi-dimensional objectives. It, therefore, offers an opportunity for diverse views to enter the decision-making process, and for the negotiation of consensus positions. The DMCE process can also function as a platform for risk communication in which scientists, stakeholders, and decision-makers can interact and discuss the uncertainty associated with biological invasions. We examine two case studies that demonstrate how DMCE provides scientific rigor and transparency in the decision-making process of invasion risk management. The first case regards pre-border priority ranking for potential invasive species and the second relates to selecting the most desirable policy option for managing a post-border invader.     

Seed predation of two alien Opuntia species invading Mediterranean communities

Invasibility depends on the interaction of the introduced species with the abiotic and biotic factors of the recipient community. In particular, the biotic resistance posed by native herbivores has been claimed to be of great importance in controlling plant invasion. We investigated fruit and seed predation of two exotic Opuntia species within and between Mediterranean communities in order to determine how patterns of predation matched patterns of invasion. Predators were small mammals, presumably mice, which could consume more than 50% of the seeds produced. Predators could be equally effective in consuming fruit and single seeds. O. maxima fruits were slightly preferred to O. stricta fruits, but predators did not distinguish between seeds. Seed predation was more intense in invaded than in non-invaded communities. However, there was a high spatial variation in seed predation that did not always match patterns of invasion, suggesting that seed predation alone is not a good predictor of community invasibility to Opuntia. According to these results invasibility to Opuntia is limited in some (but not all) communities by native mice. Seed losses by predation were high for both species. However, we estimated that more than 75% of seeds dispersed by birds to non-invaded areas are not predated.     

Mysids in toxicity testing — a review

The use of mysid shrimp, particularly the genusMysidopsis, along with specific testing procedures, has become accepted in aquatic toxicology. Investigators have developed methodologies for both culture and testing of these organisms. Acute and chronic (life cycle) toxicity tests in addition to dredge spoil and effluent tests with mysids are now becoming common. Attempts have been made to use mysids as test organisms in behavioral, physiological, nutritional, and food-chain studies. In general,Mysidopsis spp. have been shown to be as sensitive or more sensitive to toxic substances than other marine species tested. The ease of handling and culture, relative sensitivity to toxicants, short life cycle, small size and direct larval development make these organisms desirable for research purposes. Continued research using mysid species will probably demonstrate even greater usefulness of these organisms in assessment of pollutant impacts on estuarine or marine communities.     

On community structure in high alpine grasslands

Previously published data on production biology, energy use efficiency, nutrient availability and vulnerability were reinterpreted for the explanation of community processing and structure in high altitude grasslands of the Alps. The final goal of the approach was to present a characterization of these plant communities in generalized terms.The keystone-concept was applied, and the alpine grasslands then defined as plant communities with one or a few keystone species. Associated species show a varying degree of interdependence from these keystones. They form guilds exploiting resources not needed by the latter. As many of these species belong to these groups, and alpine grasslands are commonly species rich, a high functional redundancy is typical for these communities.     

Evolutionary Processes Associated with Biological Invasions in the Brassicaceae

This review highlights evolutionary processes in the Brassicaceae which cause, accompany or are a consequence of biological invasions. Case studies in Capsella and Diplotaxis address the genetics of colonising species. The greatest colonising ability in Capsella bursa-pastoris is associated with polyploidy, predominant selfing, and high genetic diversity. Success of colonial populations seems to be due to the introduction of preadapted genotypes. Colonising species in Diplotaxis reveal contrasting evolutionary patterns. Genetic attributes in D. muralis include annuality, polyploidy, and predominant selfing. Very different from Capsella, D. muralis is nearly devoid of genetic diversity as revealed by molecular markers. In contrast to D. muralis, the colonising D. tenuifolia is perennial, diploid, self-incompatible, and displays high genetic diversity. Hybrid speciation, establishment of the hybrids in man-made habitats, stabilisation of their reproductive system, and reproductive isolation from the parent populations were analysed in Cardamine. The Nasturtium example highlights the importance of hybridisation for the evolution of invasiveness. The last case study concentrates on the evolutionary consequences of hybridisation between native and invading Rorippa species. Introgressive hybridisation between the invasive Rorippa austriaca and native Rorippa species is common and widespread in central Europe, and interspecific gene transfer has led to the formation of a new invasive genotype. Each successful invasion presents new aspects and sound case studies are needed in order to understand the ecology and evolution of the colonisation process and to enable us to assess the evolutionary consequences of biological invasions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Have the Harmful Effects of Introduced Rats on Islands been Exaggerated?

Introduced rats are now being eradicated from many islands. Increasingly, these eradications are contested by activists claiming moral, legal, cultural, historic or scientific reasons and poorly documented evidence of effects. We reviewed the global literature on the effects of rats on island flora and fauna. We then used New Zealand as a case study because of its four-decade history of rat eradications and many detailed and innovative studies of how rats affect native species. These include use of exclosures, local manipulations of rat populations, video surveillance, and measurements of responses following eradications. The most intensive studies have been on the Pacific rat (Rattus exulans), a small South-East Asian species spread by Polynesians throughout the Pacific. These and the more recently introduced Norway rat (R. norvegicus) and ship (roof) rat (R. rattus) suppress some forest plants, and are associated with extinctions or declines of flightless invertebrates, ground-dwelling reptiles, land birds, and burrowing seabirds. On islands off France, Norway rats are also implicated in declines of shrews. Globally, ship rats were associated with declines or extinctions of the largest number of indigenous vertebrate species (60), including small mammals such as deer mice and bats. Effects of rats on forest trees and seabird populations are sufficiently pervasive to affect ecosystem structure and function. However, the data are patchy. Deficiencies in our knowledge would be reduced by documenting distribution and abundance of indigenous species before and after eradications. Comprehensive measurements of the responses of indigenous species to rat eradications would enable the development of testable models of rat invasion effects.