外来树种对本地林业虫害的诱发作用

白蜡窄吉丁、萧氏松茎象、光肩星天牛、黄斑星天牛、云斑天牛和桑天牛等林业害虫均为我国本地林业生态系统中的昆虫种类,在北美白蜡树、北美松树和北美黑杨派杨树等外来树种引入和大量栽培之前,一直没有形成严重的危害,以至于白蜡窄吉丁和萧氏松茎象都没有引起人们的关注。这些重要林业害虫在我国的发生都是伴随着敏感外来树种的引进和大量不合理的种植而逐渐严重起来的。本文对外来树种的引进与本地林业虫害的发生之间的关系进行了分析,提出了外来树种的不合理引进可能诱发本地林业新虫害的观点,并对其发生机理以及相应的研究和治理对策进行了讨论。     

Adaptive management for eradication of exotic species

The problems of controlling exotic species have been acknowledged as serious threats to an indigenous ecosystem as well as to society. In response to these threats, various management programs of exotic species have been proposed for supporting eradication in many regions. Although eradication is regarded as the first-best solution, such attempts have been unsuccessful in reality due to mainly two factors: (1) stock-dependent catchability, and (2) uncertainties. This article demonstrates when to aim at eradication through addressing an optimal adaptive management strategy in the framework of a bio-economic model with the aforementioned factors. The study sets out that the sensitivity of catchability in response to a change in the existing stock determines whether or not aiming at eradication is justified. The results also show that process uncertainty associated with stock growth significantly affects the timing of removal actions for eradication, and an increase in the degree of uncertainty could help achieve eradication in a cost–effective manner if we optimally adapt our removal actions to the uncertainty.     

A peculiar relationship between genetic diversity and adaptability in invasive exotic species: bluegill sunfish as a model species

A peculiar relationship exists between population genetics and invasion biology. Introduced populations often suffer a depletion of genetic variation, but they can persist and adapt to new environments. Here, we show that this relationship is observed in bluegill sunfish (Lepomis macrochirus), an invasive exotic fish in Japan. Genetic analysis using selectively neutral genetic markers reconfirmed that the bluegill introduced into Japan from the United States in 1960 had a single origin with only 15 founders. The analysis also shows that in the process of range expansion, the introduced bluegills experienced severe depletion of genetic diversity due to the founder effect and/or genetic drift. Despite such a decline in genetic diversity, the bluegill populations exhibited a divergent feeding morphology in response to the colonized environments. Such a morphological divergence can facilitate prey exploitation, thereby causing a greater negative impact on native prey resources. Further, in a trophically polymorphic bluegill population in Lake Biwa, physiological characteristics and genetic structures of the intestinal bacterial communities were associated with the difference in diet among the trophic morphs in the host bluegill population. This empirical evidence suggests that despite the severe decline in genetic diversity, the introduced bluegill populations rapidly adapted to the new environment and formed diverse functional relationships with the native bacterial community. Thus, these findings suggest that genetic variation at selectively neutral markers does not always predict adaptability and invasiveness in introduced populations.     

Dynamics of some Western Australian ligneous formations with special reference to the invasion of exotic species

Invasion of natural vegetation in Australia by exotic species has become pronounced in the last 150 years of European settlement. Changes in the frequency and type of fire have been a major disturbance to the dynamics of natural vegetation, and this disturbance has allowed rapid spread of exotics, particularly in urban and semi-rural regions. Less obvious disturbances include changes in nutrient levels and hydrological regimes, which also allow exotic species to establish and spread, at the expense of native species. Permanent plots established in various vegetation types show a decline in diversity which is associated with an increase in invasion by exotic species. Possible management strategies, designed to maintain the natural vegetation, which can be postulated include control and change of fire regime, removal of exotic species before seed-set, and the active introduction of native plants adapted to disturbance.We gratefully acknowledge the assistance of R. Hume for cartography and Doreen Jones for typing. One of us (DJB) was in receipt of a Commonwealth of Australia postgraduate award during the course of this work.     

Arthropod diversity of exotic vs. native Robinia species in northern Arizona

1 Arthropods were collected on native locust, Robinia neomexicana A. Gray, and exotic Robinia pseudoacacia L. in northern Arizona over a 2‐year period to determine the number of arthropod species and number of individuals present. 2 More arthropod species were found on the native (251) than on the exotic Robinia (174). 3 Greater species diversity was likewise found on the native than the exotic. The five most numerous insects collected each year accounted for 81% to 91% of the total number collected on the exotic and native Robinia in 1997 and 1998. Only 12 species occurred on both the native and exotic Robinia in both years. 4 These findings are discussed in the context of using exotic trees in plantations and ecological theory regarding rates of arthropod species accumulation on exotic hosts.     

本地种与外来种水生植物在不同基质营养下的生长比较

近年来,生物入侵由于其对生态系统,环境,经济等多方面造成的后果日益严重,逐渐成为目前全球普遍关注的生态问题。对于植物而言,外来入侵种不仅会大大降低本地物种的存活率,而且对本地物种的分布也会造成很大程度的负面影响。不仅如此,外来入侵种还会对本地水生或陆生生态系统造成十分严重的影响和破坏。随着国内外专家学者对外来种研究的深入,许多有关外来种入侵机制的假说和理论不断被提出。其中以资源假说(Resource Hypothesis,Davis 等 2000)研究的最为广泛和深入。在资源假说中,Davis等提出:伴随着一定数量繁殖体,外来物种的入侵会随着资源(例如光,营养和水份)的增加而加剧。为了验证(1)外来种和本地种的表现是否存在差异,如果存在,这种是否也会随着资源的增加而增强?(2)外来种与本地种的差异是否对我们预测和防治入侵有帮助?本文在此基础上,采用4种水生外来种,水鳖科(Hydrocharitaceae)两种,小二仙草科(Haloragidaceae)狐尾藻属(Myriophyllum)两种,与本地同科或同属且形态相似的3种水生植物为实验材料。分别配制两种不同营养级别的基质环境,比较了在高、低营养基质环境中外来种和本地种与生长相关的参数指标。结果显示:在高营养基质和低营养基质环境中,本地种较外来种更大地积累其生物量并且拥有更高的相对生长速率(relative growth rate)。结果还显示:在侧枝的生物量分配方面,外来种较本地种显著增高。由于断枝是水生植物无性繁殖的重要手段之一,并且断枝由侧枝或主茎受到生物或非生物的扰动产生。我们使用侧枝生物量的分配这一指标来间接反映水生植物的无性繁殖能力。结果表明,本地种较外来种能较好适应当地不同的基质营养环境;但是在无性繁殖体的传播方面,外来种较本地种占有一定的优势。因此,我们尝试提出:对外来水生植物的防治应继续以管理本地水生植物的栖息地和保护本地水生植物多样性为主,并且应加大对外来水生植物无性繁殖体特别是断枝传播的管理和控制力度。     

A model describing the effect of sex-reversed YY fish in an established wild population: The use of a Trojan Y chromosome to cause extinction of an introduced exotic species

A novel means of inducing extinction of an exotic fish population is proposed using a genetic approach to shift the ratio of male to females within a population. In the proposed strategy, sex-reversed fish containing two Y chromosomes are introduced into a normal fish population. These YY fish result in the production of a disproportionate number of male fish in subsequent generations. Mathematical modeling of the system following introduction of YY fish at a constant rate reveals that female fish decline in numbers over time, leading to eventual extinction of the population.     

Effects of exotic and translocated fish species in the inland waters of Turkey

Throughout the world a number of problems have arisen following the introduction of new fish species; impacts of introductions are not limited to biological and ecological effects but may also have socioeconomic implications. Exotic and translocated fish species have become established in various parts of the inland waters of Turkey since the 1950s. The present paper reviewed ecological and economical effects of introduced freshwater fish of Turkey.     

California native and exotic perennial grasses differ in their response to soil nitrogen,exotic annual grass density,and order of emergence

Early emergence of plant seedlings can offer strong competitive advantages over later-germinating neighbors through the preemption of limiting resources. This phenomenon may have contributed to the persistent dominance of European annual grasses over native perennial grasses in California grasslands, since the former species typically germinate earlier in the growing season than the latter and grow rapidly after establishing. Recently, European perennial grasses have been spreading into both non-native annual and native perennial coastal grass stands in California. These exotic perennials appear to be less affected by the priority effects arising from earlier germination by European annual grasses. In addition, these species interactions in California grasslands may be mediated by increasing anthropogenic or natural soil nitrogen inputs. We conducted a greenhouse experiment to test the effects of order of emergence and annual grass seedling density on native and exotic perennial grass seedling performance across different levels of nitrogen availability. We manipulated the order of emergence and density of an exotic annual grass (Bromus diandrus) grown with either Nassella pulchra (native perennial grass), Festuca rubra (native perennial grass), or Holcus lanatus (exotic perennial grass), with and without added nitrogen. Earlier B. diandrus emergence and higher B. diandrus density resulted in greater reduction in the aboveground productivity of the perennial grasses. However, B. diandrus suppressed both native perennials to a greater extent than it did H. lanatus. Nitrogen addition had no effect on the productivity of native perennials, but greatly increased the growth of the exotic perennial H. lanatus, grown with B. diandrus. These results suggest that the order of emergence of exotic annual versus native perennial grass seedlings could play an important role in the continued dominance of exotic annual grasses in California. The expansion of the exotic perennial grass H. lanatus in coastal California may be linked to its higher tolerance of earlier-emerging annual grasses and its ability to access soil resources amidst high densities of annual grasses.     

A testcross procedure for selecting exotic strains to improve pure-line cultivars in predominantly self-fertilizing species

Methods for identifying germplasm carrying alleles with the potential to improve a particular single-cross hybrid have been proposed and discussed in recent years. There is a need for similar methods to be used in breeding crops for which pure-line cultivars, rather than hybrids, are the goal. The objective of this research was to develop a method to identify germplasm lines with the potential to contribute favorable alleles not present in a specified pure line or set of pure lines. Given a set of adapted pure lines (A ₁, A ₂ ..., A _m) to be improved and a set of germplasm lines (P ₁ P ₂ ..., P _f), the procedure consists of producing all f x m possible hybrids and evaluating them along with the parents. The testcross statistic T _ij is defined by T _ij=(F _ij–A _j)+(1–) (F _ij–P _i), where A _j, P _i, and F _ij represent the performance of thej ^th adapted line, the i ^th germplasm line, and their hybrid, respectively. The statistic is the mean value of T _ij over all adapted parents A _j. If =(1/2)(1+d), where d = the mean degree of dominance, then T _ij measures the potential for alleles from P _i to improve A _j and measures the potential for alleles from P _i to improve the set A ₁, A ₂ ..., A _m. Use of data on soybean and peanut hybrids published by other researchers suggests that the value assumed for d has little effect on the P _i chosen. The ability of the T _ij and statistics to identify germplasm strains carrying rare favorable alleles should be assessed in empirical studies.Joint contribution: OARDC (Journal Articale No. 161-94), USDAARS, Iowa Agriculture and Home Economics Expriment Station (Journal Paper No. J-16109; Project 2985), and Agreculture and Agri-Food Canada. Salaries and research support for S. K. St. Martin Provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, Ohio State University     

Nutrient requirements of exotic tree species in Zimbabwe

Pot and field experiments were conducted in the greenhouse and at three field sites (Marondera, Domboshawa and Makoholi) in Zimbabwe to examine the effects of soils and fertilizers on nutrient uptake and growth of 6 exotic tree species (Eucalyptus camaldulensis, E. grandis, E. tereticornis, Leucaena leucocephala, Casuarina cunninghamiana, and Acacia holosericea). Plant growth, N and P contents of all species were increased by the application of N, P, K and micronutrient fertilizers. The effect of individual nutrients (N, P, K and micronutrients) and their combination on Eucalyptus species was further investigated in a pot experiment using soil from Domboshawa. Eucalyptus species responded only to N application and no significant interactions were found between N and the other elements. Nutrient uptake results showed that E. camaldulensis and E. tereticornis removed more cations than the N-fixing trees but only in the fertilized treatments. L. leucocephala and C. cunninghamiana were higher in P, but no clear trends were observed for N. Plant growth and nutrient uptake by E. camaldulensis. C. cunninghamiana and A. holosericea were assessed in the field at the three sites. Plant species grown in the Marondera site had greater height and diameter at breast height (DBH) than those in the two other sites. These results followed trends in soil nutrient contents. The analysis of foliage revealed differences in the nutrient concentration of leaves from different trees, but no effect of site was found. The interrelationships between plant characteristics, soil and foliage nutrients were examined. In a pot experiment, mineral N was the only variable correlated with growth response and nutrient uptake, while in the field the only significant correlation was obtained with soil pH.     

Vulnerability of riparian zones to invasion by exotic vascular plants

We compared the invasibility of riparian plant communities high on river banks with those on floodplain floors for four South African rivers. Analyses of abundant and significant riparian species showed that the floors have 3.1 times more exotic plants than the banks. The percent exotics ranges from 5% to 11% of total species richness for the banks, and from 20% to 30% for the floors. Species richness and percent exotics are negatively correlated for the banks, but not correlated for the floors.Despite great differences in climate, species richness, and landuse history, the percentages of exotic plants in three rivers in the Pacific Northwest of the USA and one river in southwestern France are similar to those in South Africa (24-30% vs. 20-30%, respectively). Furthermore, the high proportions of exotic species in these riparian plant communities are comparable to those reported for vascular plant communities on islands. We conclude that the macro-channel floor regions of the riparian zones of South African rivers are highly vulnerable to invasion by exotic vascular plants.     

Deposition of exotic bird-dispersed seeds into three habitats of a fragmented landscape in the northeastern United States

Dispersal by frugivorous birds facilitates invasion by many exotic plants. We measured the seed rain of ornithochorous native and exotic plants at three habitats of a fragmented landscape of the northeastern United States for 1 year. We studied maple-beech forests, old fields, and abandoned conifer plantations. Across all sites we collected 2,196 ornithochorous seeds, including seeds from six exotic species and 10 native species. The majority (90%) of collected seeds were from exotic species. Seed dispersal was broadly similar among habitats, though seed rain of exotic species was higher in old fields than forested habitats. Seed rain was not strongly influenced by artificial perches for most species. However, seeds of exotic species were more commonly found in traps under an artificial perch in old fields. Seed rains for the exotic Elaeagnus umbellata, Rhamnus cathartica, and Rosa multiflora were positively associated with local density of mature plants. Seed rain of R. cathartica was positively associated with abundance of seedlings but not saplings, suggesting that post-dispersal mortality was important. Seed dispersal of the exotic Lonicera spp. was high in all habitats, accounting for 66% of all seeds collected. With the exception of Lonicera spp., seed rain of common exotic invaders was affected by the abundance of seed sources, and these species might be effectively controlled by elimination of local fruiting plants. Fruits of Lonicera morrowii, which has extensively invaded our area, are apparently a common component in the diet of frugivores.     

Probability models to facilitate a declaration that an exotic insect species has not yet invaded an area

A procedure is presented to facilitate a declaration that an area has not yet been invaded by a specific exotic insect pest following a trapping campaign to detect the pest species. For this we use a probability model to assess null trapping results and also a growth model to help verify that pests were not present at a given time in the past. The probability model is developed to calculate the probability of negative trapping results if in fact there were insects present, and then the hypothesis that insects are present can be rejected. The model depends on knowledge of the efficiency of the traps and also the area of attractiveness of the traps. If an incipient and undetected population does become established, then natural growth should eventually make it apparent. Using a growth model, the rate of increase of an insect population starting from one gravid female insect is calculated. For both the probability model and the growth model, the conclusion that no invaders were present relates to some period in the past, the lag being defined by the time interval during the trapping activity or the time taken for one fertilized female to produce a population detectable by trapping. If no insects are observed after a suitable waiting period, then a conclusion can be drawn that none were present. The methodology is applied to hypothetical insects with discrete or continuous reproduction.     

Effects of experimental manipulation of light and nutrients on establishment of seedlings of native and invasive woody species in Long Island,NY forests

While earlier studies on the process of invasion often focused on single factors or on the general explanation of ‘disturbance,’ recent work has attempted to move towards a more mechanistic understanding of the factors that promote plant community invasion. Manipulative experiments provide a means for discerning causal relationships and interactive effects of environmental factors in promoting invasion; such experiments have been conducted in a number of grassland and shrub ecosystems. This study extends multifactor manipulative experiments into forest communities to compare factors influencing early seedling establishment for native and invasive woody plants. In Long Island, NY, invasion patterns are correlated with forest community type (pine barrens or hardwood), light availability, and soil N and Ca. We conducted manipulative field experiments in two different years to determine the relative importance and interaction of experimental gaps and N and Ca addition in pine barrens and hardwood forests in promoting invasion. We used seedlings of seven common native and invasive species in the first experiment, and 16 native and invasive species paired phylogenetically in the second experiment. Light had the strongest effect on plant growth; all plants grew more in gaps. We found no difference in the average growth rates of native and invasive species. Invasives responded more to high resources than did natives, with highest relative growth rates in gaps in the more fertile soils of the hardwood forests. Opportunities for invasion may differ from year to year, with differential success of invaders only in some years and under some environmental conditions. Clearly, to understand the complex interactions between resources and invasion in forests will require many manipulative experiments across a range of environments and using suites of invasive and native species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Land use history, hurricane disturbance, and the fate of introduced species in a subtropical wet forest in Puerto Rico

Tropical forests are suffering from increasing intensities and frequency of disturbances. As a result, non-native species accidentally introduced or intentionally planted for farming, plantations, and ornamental purposes may spread and potentially invade undisturbed native forest. It is not known if these introduced species will become invasive, as a result of recurrent natural disturbances such as hurricanes. Using data from three censuses (spanning 15 years) of a 16-ha subtropical wet forest plot, we investigated the impact of two hurricanes on populations of plant species that were planted in farms and plantations that were then abandoned and from the natural spread of species introduced into Puerto Rico in the past. The populations of four species (Citrus paradis, Mangifera indica, Musa sp., and Simarouba glauca) changed little over time. Six species (Artocarpus altilis, Calophyllum calaba, Genipa americana, Hibiscus pernambucensis, Syzygium jambos, and Swietenia macrophylla) declined between the first two censuses after Hurricane Hugo, then increased again in Census 3 after Hurricane Georges. Spathodea campanulata gradually increased from census to census, while Coffea arabica declined. These introduced species represent only a small part of the forest basal area and few show signs of increasing over time. The number of stems per plant, new recruits, and the growth rates of these introduced species were within the ranges of those for native plant species. The mortality rates over both census intervals were significantly lower for introduced species (<5% year⁻¹) than for native ones (15% year⁻¹). Many new recruits established after Hurricane Hugo (prior to this study) had opened the forest canopy and these high mortality rates reflect their death as the canopy recovered. Only Swietenia macrophylla and Syzygium jambos showed an increase in stem numbers in the closed canopy area of forest that had suffered limited human disturbance in the past. A future increase in frequency of disturbance may enable greater stem numbers of introduced species to establish, while lower-mortality rates compared to native species, may allow them to persist during inter-hurricane intervals. An increase in the population of introduced species, especially for those that grow into large trees, may have an impact on this tropical forest in the future.     

The effect of soil nitrogen on competition between native and exotic perennial grasses from northern coastal California

The invasion of European perennial grasses represents a new threat to the native coastal prairie of northern California. Many coastal prairie sites also experience anthropogenic nitrogen (N) deposition or increased N availability as a result of invasion by N-fixing shrubs. We tested the hypothesis that greater seedling competitive ability and greater responsiveness to high N availability of exotic perennial grasses facilitates their invasion in coastal prairie. We evaluated pairwise competitive responses and effects, and the occurrence of asymmetrical competition, among three common native perennial grasses (Agrostis oregonensis, Festuca rubra, and Nassella pulchra) and three exotic perennial grasses (Holcus lanatus, Phalaris aquatica, and Festuca arundinacea), at two levels of soil N. We also compared the root and shoot biomass and response to fertilization of singly-grown plants, so we could evaluate how performance in competition related to innate plant traits. Competitive effects and responses were negatively correlated and in general varied continuously across native and exotic species. Two exceptions were the exotic species Holcus, which had large effects on neighbors and small responses to them, and competed asymmetrically with all other species in the experiment, and the native grass Nassella, which had strong responses to but little effect on neighbors, and was out-competed by all but one other species in the experiment. High allocation to roots and high early relative growth rate appear to explain Holcus’s competitive dominance, but its shoot biomass when grown alone was not significantly greater than those of the species it out-competed. Competitive dynamics were unaffected by fertilization. Therefore, we conclude that seedling competitive ability alone does not explain the increasing dominance of exotic perennial grasses in California coastal prairie. Furthermore, since native and exotic species responded individualistically, grouping species as ‘natives’ and ‘exotics’ obscured underlying variation within the two categories. Finally, elevated soil N does not appear to influence competition among the native and exotic perennial grasses studied, so reducing soil N pools may not be a critical step for the restoration of California coastal prairie.