- The impacts of nonnative species on UK biodiversity and the effectiveness of control
Manchester, SJ; Bullock, JM
Journal of Applied Ecology, [J. Appl. Ecol.], vol. 37, no. 5, pp. 845-864, 2000
1. The introduction of nonnative species continues to cause ecological concern globally, but there have been no published reviews of their effects in the UK. Impacts in the UK are therefore reviewed, along with current legislation and guidelines relating to the introduction and control of such species. 2. A large number of nonnative species have been introduced to the UK, both deliberately and accidentally, but only a small number have established and caused detrimental ecological impacts. However, general declines in UK biodiversity, and the potential effects of future climate change, may increase the susce ptibility of ecosystems to invasions. 3. Detrimental impacts of nonnative species on native biota have occurred through competition, predation, herbivory, habitat alteration, disease and genetic effects (i.e. hybridization). There are potential effects on genetic biodiversity as well as species biodiversity. 4. Several high profile examples highlight the technical difficulties, and financial implications, of removing an introduced species once it is established. Few UK control or eradication programmes have been successful. 5. Control might be more feasible if 'problem' species could be identified at an earlier stage of establishment. However, the poor success of attempts to characterize invasive species and predict which will have negative impacts highlight the individual and unpredictable nature of invasions. The difficulties of making general predictions suggest that every proposed species introduction should be subject to rigorous ecological characterization and risk assessment prior to introduction. 6. The plethora of UK legislation and guidelines developed to reduce impacts of nonnative species only go part of the way towards ameliorating impact. Many species already established in the wild might cause future problems. Illegal releases and escapes of nonnative species may augment feral populations or establish new colonies. While regulation of imports and releases is important, further enforcement of existing legislation and action against unlicensed releases is necessary.
- Zebra Mussel Destruction by a Lake Michigan Sponge: Populations, in Vivo super(31)P Nuclear Magnetic Resonance, and Phospholipid Profiling
Early, TA; Glonek, T
Environmental Science & Technology [Environ. Sci. Technol.], vol. 33, no. 12, pp. 1957-1962, 15 Jun 1999
The sponge Eunapius fragilis (Leidy), that has become abundant in southwestern Lake Michigan, overgrows zebra mussels, Dreissena polymorpha (Pallas). The overgrown mussels die. Population dynamics show that in the presence of zebra mussels, E. fragilis is the dominant species (61% of sponges), with 90% of these sponges being associated directly to the mussels. In vivo super(31)P NMR spectroscopy performed on overgrown mussels reveals that mussel ATP is depleted in a manner indicative of a tissue in anoxia. super(31)P NMR phospholipid profiles reveal that the phospholipids of such mussels have been degraded to their lyso-phospholipid forms. Phospholipid degradation may be the direct result of the lysosomal chemical action of the sponge or a secondary effect resulting from sponge-induced death by anoxia followed by microbial action on the weakened energy-depleted mussels.
- Current Distribution and Historical Range Expansion of Calosoma sycophanta (L.) (Coleoptera: Carabidae) in North America
Schaefer, PW; Fuester, RW; Taylor, PB; Barth, SE; Simons, EE; Blumenthal, EM; Handley, EM; Finn, TB; Elliott, EW
Journal of Entomological Science [J. Entomol. Sci.], vol. 34, no. 3, pp. 339-362, Jul 1999
Since the intentional introduction, release, and establishment of the lymantriid predator, Calosoma sycophanta (L.), in 1906-07 in the vicinity of Boston, MA, its range has continued to expand. Compilation of collection localities, all intentional releases in North America, and museum collection records permitted documentation of spread over time and a crude straight line estimate of the rate of dispersion, calculated at 6 km/year. Trapping and other collection records in recent years permitted an approximation of the current distribution, which now extends from southern Maine and all New England states south into Pennsylvania, Delaware, Maryland, and West Virginia. During 15 years of trapping at one New Jersey site and in the mid-Atlantic states, we collectively placed 3,792 traps in 253 locations. We captured 12,117 C. sycophanta, most of which were immediately released on location. Of those that were sexed (4,160), 74.3% were males. We recorded new state records for Delaware, Maryland, and West Virginia. Other species trapped include C. scrutator (200 specimens, most in New Jersey), C. wilcoxi (12, most in Delaware), C. frigidum (896, most in Pennsylvania) and C. calidum (22, most in Virginia).
- Influence of Non-native Trout and Geomorphology on Distributions of Indigenous Trout in the Yellowstone River Drainage of Wyoming
Dissertation Abstracts International Part B: Science and Engineering [Diss. Abst. Int. Pt. B - Sci. & Eng.], Jul 1999, vol. 60, no. 1, p. 6
Yellowstone cutthroat trout Oncorhynchus clarki bouvieri (YSC) are declining throughout their historic range in Wyoming due to anthropogenic influences. I intensively studied three watersheds (Greybull River, North, and South Forks of the Shoshone River) in the Yellowstone River drainage in Wyoming that were likely to contain genetically pure YSC in order to define factors limiting their persistence. Native YSC have been extirpated by hybridizing rainbow trout O. mykiss and competing brook trout Salvelinus fontinalis and brown trout Salmo trutta from 70% of the perennial streams which currently support a trout. Exotic trout and YSC used similar habitats throughout these watersheds indicating that introduced trout have the ability to invade and displace YSC. Rainbow trout genes were found in the highest elevation sites, evidence that YSC are not biologically isolated from rainbow trout. Four remaining populations of genetically pure cutthroat trout in the study area appear demographically and genetically viable, but genes from Snake River cutthroat trout occur in these fish and they are threatened by exotic salmonids in the watersheds. The YSC has declined primarily due to hybridization and competition with exotic salmonids. Conservation of this native fish will require re-establishment of large, connected populations in relatively large watersheds void of non-native trout.
- Effect of Introduced Mosquitofish on Pacific Treefrogs and the Role of Alternative Prey
Goodsell, JA; Kats, LB
Conservation Biology [Conserv. Biol.], vol. 13, no. 4, pp. 921-924, Aug 1999
Mosquitofish (Gambusia affinis) are distributed by many mosquito control programs because of their broad habitat tolerance and because they are considered by some to be effective mosquito predators. As a result, mosquitofish have become established as an exotic species in numerous perennial streams in the Santa Monica Mountains within the last 10-15 years. Previous studies have found that mosquitofish prey heavily on California newt (Taricha torosa) larvae that inhabit mountain streams. We found Pacific treefrog (Hyla regilla) tadpoles in the stomachs of 65% of stream-caught mosquitofish. In both laboratory and field experiments, we found that mosquitofish preyed heavily on treefrog tadpoles, even when high densities of mosquito larvae were presented as alternative prey. Thus, despite apparent high densities of Pacific treefrog populations, our experiments suggest that introduced mosquitofish may negatively affect stream-breeding H. regilla in the Santa Monica Mountains.
- A Remarkable Disjunct Introduction of Conchopus borealis Takagi to the New World (Diptera: Dolichopodidae)
Masunaga, Kazuhiro; Saigusa, Toyohei; Woodley, NE
Entomological Science [Entomol. Sci.], vol. 2, no. 3, pp. 399-404, 25 Sep 1999
A Japanese marine shore dolichopodid, Conchopus borealis Takagi, is recorded from California and Alabama, USA, the first record of this genus from the New World. The male ventral lobe of this species is illustrated for specimens from North America and seven localities in Japan. No geographical variation is detected and it is considered that the Nearctic populations of this species were recently introduced from Japan through commerce.
- The impacts of introduced poeciliid fish and Odonata on the endemic Megalagrion (Odonata) damselflies of Oahu Island, Hawaii
Journal of Insect Conservation [J. Insect Conserv.], vol. 3, no. 3, pp. 225-243, Sep 1999
Since the beginning of this century there have been substantial declines in the distribution and abundance of native Megalagrion damselies on the Hawaiian Island of Oahu. Native damselies have also vanished from most low elevation areas on other Hawaiian Islands, although historically, lotic and wetland dwelling damsely species were once common throughout the archipelago. It is hypothesized that poeciliid species introduced for biological control have caused the decline of four stream-breeding damsely species on Oahu, and the extinction or near-extinction of two other species in Hawaii. This study documents the presence of remnant Megalagrion populations in Oahu streams, wetlands and estuaries, and records the elevational distributions of introduced species in each waterbody surveyed. The distributions of introduced Odonata are also recorded, because the seven species of damselies and dragonies introduced to Oahu since 1936 present another potential threat to native Hawaiian damselies. Native damsely and introduced poeciliid sh distributions were mutually exclusive on Oahu, and it is concluded that this is probably due to predation by the introduced sh. By contrast, even the rarest native Megalagrion damselies were found in areas containing introduced damselies and dragonies.
- Effects of Habitat Structure on Predator-prey Interactions Between Introduced White Bass and Endangered June Suckers
Dissertation Abstracts International Part B: Science and Engineering [Diss. Abst. Int. Pt. B - Sci. & Eng.], Oct 1999, vol. 60, no. 4, p. 1405
The June sucker (Chasmistes liorus) is an endangered lake sucker endemic to Utah Lake, Utah. The habitat of Utah Lake has been changed from a clear lake with a large littoral zone containing aquatic vegetation, to a very turbid lake which lacks a littoral zone and aquatic vegetation. The most recent decline in abundance of June sucker has been attributed to the introduction of white bass (Morone chrysops) and walleye (Stizostedion vitreum vitreum). The effects of increasing plant stem density on the behavior and habitat use of juvenile June sucker, and on the foraging success of white bass were examined in a series of laboratory and field experiments. As habitat complexity increased the foraging success of white bass decreased. The behavior of juvenile June sucker was modified by the presence of white bass and vegetation. Suckers always schooled when no vegetation or low levels of vegetation were present. Additionally, suckers were more dispersed in vegetation beds containing high levels of complexity when white bass were present. Laboratory experiments were performed to determine how different turbidity levels affected the survivorship and foraging success of juvenile June sucker. Four levels of turbidity were used in each of the experiments. White bass were used as the predator in the survivorship experiment. No significant differences in June sucker survivorship were found for any of the turbidity levels.
- Ecological Effects of Non-native Fish Species in Low Elevation Streams of the Central Valley, California
Dissertation Abstracts International Part B: Science and Engineering [Diss. Abst. Int. Pt. B - Sci. & Eng.], Oct 1999, vol. 60, no. 4, 1400
Three separate studies are described which examine the effects of non-native fish species on Central Valley California streams. The first is an experimental study of competition between a California native centrarchid, the Sacramento perch (Archoplites interruptus) and an ubiquitous non-native, the bluegill (Lepomis macrochirus). The experiments indicate that (1) Sacramento perch gain less weight and show reduced growth when placed with bluegill, (2) Sacramento perch demonstrate less aggressive behavior than bluegill, (3) Sacramento perch shift their habitat use in the presence of bluegill. Overall the results imply that Sacramento perch and bluegill exhibit interspecific competition. The second work is an investigation into the larval ecology of stream fish in Putah Creek, a Central Valley stream. Native larvae occurred both earlier in the year and in higher abundance than introduced species. Both native larvae and overall numbers of larvae were more abundant at the upstream site. Larval fish abundance was not a good indicator of juvenile abundance at the same sites later in the year. The two methods of collection utilized tended to select for different species. At both locations larval fish were collected in significantly greater numbers at night. It is suggested that the difference between the sites is due to habitat changes resulting from an upstream dam that has created a refuge for native taxa.
- Life History Variation in Introduced Populations of the Mayan Cichlid, Cichlasoma urophthalmus, in the Everglades
Dissertation Abstracts International Part B: Science and Engineering [Diss. Abst. Int. Pt. B - Sci. & Eng.], Dec 1999, vol. 60, no. 6, p. 2471
Life history strategies were described for three introduced populations of the Mayan cichlid, "Cichlasoma" urophthalmus in the Florida Everglades. The three populations represented three distinct habitat types recently invaded by the Mayan cichlid: freshwater sawgrass wetland, freshwater flooded cypress forest, and brackish mangrove canal. Fish were collected monthly using cast-nets over an 18 month period in 1996-7. Somatic growth rates, condition, and female reproductive allocation were compared across the three populations, and to published data from Mexican studies. Somatic growth rates of adult size fish were compared using otolith mass-body length relations. These results suggest that cypress forest fish exhibited faster growth. Abiotic and biotic factors were evaluated as potential explanations for the observed differences in growth rate. The differences among the populations could not be explained by geographic proximity, hydrologic similarity, water temperature, salinity, length-frequency distributions, or age composition. Although dietary differences could not be excluded, higher growth rates in the cypress forest population were attributed to either a life history strategy of reduced gonad investment, or a new population effect of intra-specific competitive release. Fulton's K condition factor was used to determine somatic condition for each adult fish sampled. Condition factor varied seasonally both within and across sites, and increased with rising water levels. Overall, condition was highest in the cypress forest population. The brackish mangrove population showed the least seasonal fluctuations, but exhibited markedly lower condition than the other populations. Condition factor was also calculated for fish collected in an earlier Mexican study at Celestun Lagoon, Yucatan. Condition factor of Mexican fish was about 20% higher than that of the Florida fish. Female reproductive allocation strategy was compared using fecundity counts and oocyte size measurements. Fecundity varied across sites, with higher fecundity at the cypress and mangrove populations. Comparisons were complicated by the lack of linear length- fecundity relations at the sawgrass and mangrove sites. Oocyte diameter was highest for the sawgrass population. Thus, there appears to be a trade- off between oocyte size and number, with the sawgrass females allocating their resources differently from the other populations.
- Species introductions and their ecological consequences: An example with congeneric sunfish
Huckins, CJF; Osenberg, CW; Mittelbach, GG
Ecological Applications [Ecol. Appl.], vol. 10, no. 2, pp. 612-625, 2000
Pumpkinseed (Lepomis gibbosus) and redear sunfish (L. microlophus) are sister species with largely allopatric native ranges. For purposes of sport fishery enhancement, redear have been introduced into lakes of southern Michigan, and as a result, a large zone of artificial sympatry of pumpkinseed and redear has been created. Redear and, to a lesser extent, pumpkinseed are morphologically and behaviorally specialized molluscivores, and we hypothesized that introduced redear would have strong negative effects on pumpkinseed due to competition for snails, which are each species' main adult resource. Specifically, we predicted that redear would reduce snail availability, alter pumpkinseed diet, and reduce pumpkinseed growth and density. To examine these predictions, we surveyed pumpkinseed diets, growth, and densities, as well as snail availability in lakes with and without introduced redear. We also conducted a controlled field experiment (target-neighbor design) in which relative neighbor densities of each species were manipulated and the effects on target individuals of each species were measured. This experiment was designed to explore mechanisms underlying the competitive interactions suggested by the longer-term field study. Together, the field patterns and short-term experimental results demonstrate that the introduction of redear negatively affected the native pumpkinseed: (1) In lakes where redear had been introduced, the abundance of pumpkinseed declined an average of 56%, while average pumpkinseed abundance increased 60% in lakes without introduced redear. (2) In the presence of redear, pumpkinseed had fewer snails in their diets and showed only a weak ontogenetic niche shift to feeding on snails. (3) Snail biomass was similar to 69% lower in lakes where redear had been introduced, and snail biomass was similar to 50% lower in experimental treatments containing redear instead of pumpkinseed. In the experiment, pumpkinseed growth was reduced in the presence of redear. However, contrary to our predictions, pumpkinseed growth rates did not differ between lakes with redear vs. those without redear. We suggest that a reduction in pumpkinseed growth rate is an expected short-term response to redear introduction, whereas the long-term response is a reduction in pumpkinseed density.
- A Provisional Model for Smooth Brome Management in Degraded Tallgrass Prairie
Willson, GD; Stubbendieck, J
Ecological Restoration [Ecol. Restor.], vol. 18, no. 1, pp. 34-38, 2000
In this article, we present a provisional model for managers who choose to control smooth brome through the use of prescribed burns. We developed the model following research on smooth brome management at the University of Nebraska Agricultural Research and Development Center near Mead, Nebraska, and at Pipestone National Monument near Pipestone, Minnesota. We begin, however, by reviewing the literature on smooth brome tiller morphology, especially its use of carbohydrate reserves, and by discussing management practices for the control of smooth brome.
- The relative importance of species invasions and sediment disturbance in regulating chemical dynamics in western Lake Erie
Morrison, HA; Whittle, DM; Haffner, GD
Ecological Modelling [Ecol. Model.], vol. 125, no. 2-3, pp. 279-294, 15 Jan 2000
PCB congener concentrations were measured in aquatic biota and sediment from the western basin of Lake Erie during 1993-1994 and 1996-1997. Between these time periods the round goby (Neogobius melanostomus) invaded and proliferated in the basin and mean annual particulate organic carbon (POC), dissolved organic carbon (DOC) and PCB congener concentrations in sediment changed. The objectives of this study were to use a food web bioaccumulation model and field data to quantify the relative importance of the round goby, POC, DOC and chemical concentration in sediment, to PCB congener levels in aquatic biota prior to (1993-1994) and since (1996-1997) the invasion of the basin by round gobies. The predicted effects of round gobies on PCB congener transfer, mediated through alterations in food web structure, were small increases (range 2-6%) in PCB burdens of pelagic fish species such as alewife and walleye. Larger increases (range 8-19%) in PCB burdens were predicted for benthic feeding sport fish species such as yellow perch and largemouth bass. Small decreases (range 1-5%) in PCB congener concentrations in fish were predicted to result from decreases in bioavailable concentrations of PCBs in water. Bioavailable concentrations of PCBs in water were predicted to decrease as a result of observed changes in POC and DOC concentrations. However, in all cases predicted changes in PCB concentrations in fish, resulting from changes in food web structure and POC and DOC, were smaller than those predicted from measured increases in PCB congener concentrations in sediment between 1993 and 1994 and 1996-1997. Increased concentrations of PCBs in sediment were attributed to exposure of older and more heavily contaminanted sediments from turbulence caused by higher wind speeds in 1996-1997 compared to 1993-1994.
- Introduced Chrysomya (Diptera: Calliphoridae) Flies in Northcentral Alabama
Journal of Entomological Science [J. Entomol. Sci.], vol. 35, no. 1, pp. 91-92, Jan 2000
- Environmental and Economic Costs of Nonindigenous Species in the United States
Pimentel, D; Lach, L; Zuniga, R; Morrison, D
Bioscience, vol. 50, no. 1, pp. 53-64, Jan 2000
Estimating the economic impacts that are associated with nonindigenous species is difficult; nevertheless, enough data are available to quantify some of the impacts on agriculture, forestry, and public health in the United States. In this article, we assess the magnitude of the environmental impacts and economic costs associated with the diverse nonindigenous species that have become established within the United States. Although species translocated within the United States can also have significant impacts, our assessment is limited to nonindigenous species that did not originate within the United States or its territories.
- Role of Light Availability and Dispersal in Exotic Plant Invasion along Roads and Streams in the H. J. Andrews Experimental Forest, Oregon
Parendes, AL; Jones, AJ
Conservation Biology [Conserv. Biol.], vol. 14, no. 1, pp. 64-75, Feb 2000
We examined the roles of dispersal mechanism, a biological barrier; light availability, an environmental barrier; and level of disturbance, a physical barrier, in explaining the spatial patterns of exotic plant species along road and stream segments in a forest landscape in the western Cascade Range of Oregon (U.S.A). The presence or absence of 21 selected exotic plant species and light levels were observed along 0.3- to 0-km transects within four habitat types. Each habitat represented a different level of disturbance: high-use roads, low-use roads, abandoned roads, and streams in the H. J. Andrews Experimental Forest. Nearly 300 50 x 2-m sampling units were surveyed along five transects in each habitat type. We used ordination (nonmetric multidimensional scaling) and logistic regression to analyze data. All of the nearly 200 sampling units along roads with high and low levels of vehicle traffic contained at least one exotic plant species, and some contained as many as 14. Streams that were most recently disturbed by floods 20-30 years ago and abandoned spur roads with no traffic for 20-40 years also had numerous exotic species. Roads and streams apparently serve multiple functions that enhance exotic species invasion in this landscape: they act as corridors or agents for dispersal, provide suitable habitat, and contain reservoirs of propagules for future episodes of invasion. Species-specific dispersal mechanisms, habitat characteristics, and disturbance history each explain some, but not all, of the patterns of exotic species invasion observed in this study.
- The Invasion of the Shimofuri Goby (Tridentiger bifasciatus) into California: Establishment, Potential for Spread, and Likely Effects
Dissertation Abstracts International Part B: Science and Engineering [Diss. Abst. Int. Pt. B - Sci. & Eng.], Feb 2000, vol. 60, no. 8, p. 3687
The San Francisco Bay/Delta estuary is dominated by nonindigenous species at nearly every taxonomic level. One of the most recent fish invaders is the shimofuri goby (Tridentiger bifasciatus), native to Asian estuaries. To predict the success and impact of the goby's continuing invasion, I examined its physiology, feeding ecology, and behavioral interactions with potential competitors. Shimofuri gobies have higher temperature tolerances than most fishes in the estuary (critical thermal maximum = 37 degree C when acclimated to 20 degree C). Although they cannot survive in undiluted seawater, shimofuri gobies tolerate wide fluctuations in salinity and can reproduce in fresh water. Thus, while they are capable of inland range expansion, a marine route of expansion is not possible. Shimofuri gobies are non-selective predators on benthic invertebrates, mainly amphipods, hydroids, and barnacle cirri. Hydroids are rare, and barnacle cirri are absent from the stomachs of other resident fishes. The goby's ability to specialize on seasonally abundant prey and to exploit two novel food sources makes it well-suited to the estuary and partially explains its impressive success relative to many resident species. In behavioral experiments with three ecologically similar resident fishes, shimofuri gobies were rarely submissive. Prickly sculpins (Cottus asper) and yellowfin gobies (Acanthogobius flavimanus) were rarely aggressive toward shimofuri gobies despite considerable size advantages. Sculpins and tidewater gobies (Eucyclogobius newberryi) were more submissive toward shimofuri gobies than toward conspecifics. Shimofuri gobies were more aggressive toward other gobies than toward sculpins. The invasion of the shimofuri goby is unlikely to be curbed by behavioral interactions with these species. However, if the shimofuri goby becomes sympatric with the endangered tidewater goby, populations of tidewater gobies may be eliminated through competition or predation. In laboratory experiments shimofuri gobies outcompeted a resident nonindigenous crab (Rhithropanopeus harrisii) for shelters. This was most pronounced during the day, when predators are active, and during the spawning season, when shelters are in short supply. The goby's invasion is unlikely to be affected by shelter competition with the crab, but the crab may suffer increased predation due to competitive exclusion from shelters.
- Effects of Long-Term Ungulate Exclusion and Recent Alien Species Control on the Preservation and Restoration of a Hawaiian Tropical Dry Forest
Cabin, JR; Weller, GS; Lorence, HD; Flynn, WT; Sakai, KA; Sandquist, D; Hadway, JL
Conservation Biology [Conserv. Biol.], vol. 14, no. 2, pp. 439-453, Apr 2000
Although the destruction of tropical rain forests receives much attention, tropical dry forests are in general far more threatened and endangered. Eliminating grazing ungulates is often considered a key first step toward protecting these ecosystems, but few studies have investigated the long-term effects of this technique. We examined the effects of ungulate exclusion from a 2.3-ha native dry-forest preserve on the island of Hawaii by comparing its present flora to the flora of an adjacent area subjected to continuous grazing since the preserve was fenced over 40 years ago. Relative to this adjacent area, the fenced preserve contained a more diverse flora with substantially greater coverage of native overstory and understory species. Until recently, however, regeneration of native canopy trees within the preserve appears to have been thwarted by a dominant herbaceous cover of alien fountain grass ( Pennisetum setaceum) and predation by alien rodent species. Our results indicate that although ungulate exclusion may be a necessary and critical first step, it is not sufficient to adequately preserve and maintain Hawaii's remaining tropical dry forest remnants. Our recent efforts to control the dominant alien species within the fenced preserve suggest that this practice may facilitate both the regeneration of native species and the colonization and potential invasion of new alien plants. Comparisons of seedlings of the dominant native canopy tree Diospyros sandwicensis growing in sites both dominated by and free of fountain grass suggested that fountain grass inhibits Diospyros seedling growth and photosynthesis but may increase survival if seedlings are protected from ungulates.
- Homogenization of fish faunas across the United States
Science (Washington) [Science (Wash.)], vol. 288, no. 5467, pp. 854-856, 5 May 2000
Fish faunas across the continental United States have become more similar through time because of widespread introductions of a group of cosmopolitan species intended to enhance food and sport fisheries. On average, pairs of states have 15.4 more species in common now than before European settlement of North America. The 89 pairs of states that formerly had no species in common now share an average of 25.2 species. Introductions have played a larger role than extirpations in homogenizing fish faunas. Western and New England states have received the most introductions, which is a reflection of the small number of native fishes in these areas considered desirable gamefish by settlers.
- Species diversity and biological invasions: Relating local process to community pattern
Science (Washington) [Science (Wash.)], vol. 288, no. 5467, pp. 852-854, 5 May 2000
In a California riparian system, the most diverse natural assemblages are the most invaded by exotic plants. A direct in situ manipulation of local diversity and a seed addition experiment showed that these patterns emerge despite the intrinsic negative effects of diversity on invasions. The results suggest that species loss at small scales may reduce invasion resistance. At community-wide scales, the overwhelming effects of ecological factors spatially covarying with diversity, such as propagule supply, make the most diverse communities most likely to be invaded.
- Biological control of invading species--risk and reform
Strong, DR; Pemberton, RW
Science (Washington) [Science (Wash.)], vol. 288, no. 5473, pp. 1969-1970, 16 Jun 2000
Biological control (BC), the science and technology of controlling pests with natural enemies, has had several recent successes, including suppression in Africa of invading mealybug and whitefly pests of cassava by means of introduced wasps. Increasingly, BC is used to suppress weeds in natural areas, such as the ecosystems of South African Cape Fynbos, the Australian Kakadu National Park, and the Florida Everglades, U.S.A.. The everglades BC projects include control of the Old World climbing fern Lygodium microphyllum. Biological control is also contemplated against insects invading natural areas and even against invasive marine species. However, BC is not a panacea, and without careful use, it can misfire. Ecologists, conservation groups, and others have raised questions about the safety, rationale, and even the need for some projects. Safeguards to exclude importation of enemies dangerous to the native fauna are in place on very few borders of the world. In the United States, oversight of BC is based on a hodge-podge of old legislation meant for other purposes. Protection of native plants from foreign herbivores imported and disseminated for weed BC has been problematic; meanwhile, native insects and other invertebrates have little protection under the current structure. We suggest reforms that will reduce ecological risk and reinforce the public trust in this powerful technique.
- Host-area specific climatic-matching: similarity breeds exotics
Biological Conservation [Biol. Conserv.], vol. 94, no. 3, pp. 341-351, Jul 2000
Non-indigenous species invasions carry a high price in economic and ecological terms. Preventing the establishment of nonindigenous species is preferable to post-establishment control and eradication. Predicting where the next nonindigenous species will come from can help in deterring the introduction and establishment of potential invasive species. Discriminant analyses were performed to determine the relationship between plant species distributions and 16 climatic variables for south Florida and Australia. The discriminant functions correctly identified half-degree blocks in Australia that held high numbers of species (both native and non-indigenous) shared by south Florida and Australia. Climate data for Africa and the Americas was applied to the discriminant function to predict regions with potentially high numbers of plant species that are climatically pre-adapted to south Florida. The results of these analyses will be used to focus research on areas that have the greatest potential for contributing species to the already severely invaded natural areas of south Florida. The results also suggest a mechanism to control the introduction of nonindigenous species to any host area of interest.
- Invasive plants versus their new and old neighbors: A mechanism for exotic invasion
Callaway, RM; Aschehoug, ET
Science (Washington) [Science (Wash.)], vol. 290, no. 5491, pp. 521-523, 20 Oct 2000
Invading exotic plants are thought to suceed primarily because they have escaped their natural enemies, not because of novel interactions with their new neighbors. However, we find that Centaurea diffusa, a noxious weed in North America, has much stronger negative effects on grass species from North America than on closely related grass species from communities to which Centaurea is native. Centaurea's advantage against North American species appears to be due to differences in the effects of its root exudates and how these root exudates affect competition for resources. Our results may help to explain why some exotic species so successfully invade natural plant communities.
- Elevated CO sub(2) increases productivity and invasive species success in an arid ecosystem
Smith, SD; Huxman, TE; Zitzer, SF; Charlet, TN; Housman, DC; Coleman, JS; Fenstermaker, LK; Seemann, JR; Nowak, RS
Nature, vol. 408, no. 6808, pp. 79-82, 2 Nov 2000
Arid ecosystems, which occupy about 20% of the earth's terrestrial surface area, have been predicted to be one of the most responsive ecosystem types to elevated atmospheric CO sub(2) and associated global climate change. Here we show, using free-air CO sub(2) enrichment (FACE) technology in an intact Mojave Desert ecosystem, that new shoot production of a dominant perennial shrub is doubled by a 50% increase in atmospheric CO sub(2) concentration in a high rainfall year. However, elevated CO sub(2) does not enhance production in a drought year. We also found that above-ground production and seed rain of an invasive annual grass increases more at elevated CO sub(2) than in several species of native annuals. Consequently, elevated CO sub(2) might enhance the long-term success and dominance of exotic annual grasses in the region. This shift in species composition in favour of exotic annual grasses, driven by global change, has the potential to accelerate the fire cycle, reduce biodiversity and alter ecosystem function in the deserts of western North America.
- Global spread of microorganisms by ships
Ruiz, GM; Rawlings, TK; Dobbs, FC; Drake, LA; Mullady, T; Huq, A; Colwell, RR
Nature, vol. 408, no. 6808, pp. 49-50, 2 Nov 2000
Commercial ships have spread many species around the world, but little is known of the extent and potential significance of ship-mediated transfer of microorganisms. Here we show that the global movement of ballast water by ships creates a long-distance dispersal mechanism for human pathogens and may be important in the worldwide distribution of microorganisms, as well as for the epidemiology of waterborne diseases affecting plants and animals. We measured the concentrations of total bacteria, virus-like particles (VLPs) and the bacteria Vibrio cholerae O1 and O139, which cause human epidemic cholera, in the ballast water of vessels arriving to Chesapeake Bay from foreign ports. We collected water samples to estimate the abundance of total bacteria and VLPs, and also took both water and plankton samples to measure the concentration of V. cholerae, as the bacterium forms associations with plankton. We predict that coastal ecosystems are frequently invaded by microorganisms from ballast water. First concentrations of bacteria and viruses exceed those reported for other taxonomic groups in ballast water by 6-8 orders or magnitude, and the probability of successful invasion should increase with inoculation concentration. Second, the biology of many microorganisms may facilitate invasion, combining a high capacity for increase, asexual reproduction, and the ability to form dorman resting stages. Such flexibility in life history can broaden the opportunity for successful colonization, allowing rapid population growth when suitable environmental conditions occur. Third, many microorganisms can tolerate a broad range of environmental conditions, such as salinity or temperature, so many sites may be suitable for colonization. This suite of factors may yield a high rate of invasion for microorganisms compared to invertebrates, which are already known to invade coastal habitats from ballast water.