The role of aggression in range expansion and biological invasions

Traits that aid in the invasion process should exhibit a gradient across the expansion range in response to changing selection pressures. Aggression has been repeatedly associated with invasion success in many taxa, as it may help invaders to wrestle the resources from other species which enhances their success in a novel environment. However, aggression primarily al lows individuals to overcome conspecific rivals, providing advantages in competition over resources. Agonistic prowess could therefore increase fitness at both ends of the expansion gradient. Here we review the role of aggression in range expansion of in vasive species, and its potential role as a driver of range expansion. We analyze how these different mechanisms could affect trait variation in expanding and invasive populations. Specifically, we look at how aggression could help dilate the edges of a popula tion through niche competition, as well as lead to exclusion from the center （Le. areas of high population density） by the conspe cities. Both of these processes will result in a characteristic spatial distribution of phenotypes related to aggression that could provide insights into the ecological pressures and dynamics of expanding populations, potentially providing clues to their success as niche competitors and invasive species     

Invasion triangle: an organizational framework for species invasion

Species invasion is a complex, multifactor process. To encapsulate this complexity into an intuitively appealing, simple, and straightforward manner, we present an organizational framework in the form of an invasion triangle. The invasion triangle is an adaptation of the disease triangle used by plant pathologists to help envision and evaluate interactions among a host, a pathogen, and an environment. Our modification of this framework for invasive species incorporates the major processes that result in invasion as the three sides of the triangle: (1) attributes of the potential invader; (2) biotic characteristics of a potentially invaded site; and (3) environmental conditions of the site. The invasion triangle also includes the impact of external influences on each side of the triangle, such as climate and land use change. This paper introduces the invasion triangle, discusses how accepted invasion hypotheses are integrated in this framework, describes how the invasion triangle can be used to focus research and management, and provides examples of application. The framework provided by the invasion triangle is easy to use by both researchers and managers and also applicable at any level of data intensity, from expert opinion to highly controlled experiments. The organizational framework provided by the invasion triangle is beneficial for understanding and predicting why species are invasive in specific environments, for identifying knowledge gaps, for facilitating communication, and for directing management in regard to invasive species.     

Trends in marine biological invasions at local and regional scales: the Northeast Pacific Ocean as a model system

Introduced species are an increasing agent of global change. Biogeographic comparisons of introduced biotas at regional and global scales can clarify trends in source regions, invasion pathways, sink regions, and survey effort. We identify the Northeast Pacific Ocean (NEP; northern California to British Columbia) as a model system for analyzing patterns of marine invasion success in cool temperate waters. We review literature and field surveys, documenting 123 introduced invertebrate, algal, fish, and vascular plant species in the NEP. Major invasion pathways were shipping (hull fouling, solid and water ballast; 1500s-present) and shellfish (particularly oysters) and finfish imports (commonest from the 1870s to mid-1900s). The cumulative number of successful invasions over time increased at linear, quadratic, and exponential rates for different taxa, pathways, and regions within the NEP. Regional analysis of four major NEP estuaries showed that Puget Sound and the contiguous Straits had the most introduced species, followed by Humboldt Bay, Coos Bay and Willapa Bay. Data on cumulative shipping volumes predicted smaller-scale, but not larger-scale spatial patterns in the number of shipping-mediated invasions. We identify the major challenges in scaling up from regional to global invasion analysis in cool temperate regions. Retrospective analyses for distinct biogeographic regions such as the NEP provide insight into vector dynamics and regional invasibility, and are a necessary foundation for monitoring and managing global change caused by biotic invasions.     

A unifying probabilistic framework for analyzing residual dipolar couplings

Residual dipolar couplings provide complementary information to the nuclear Overhauser effect measurements that are traditionally used in biomolecular structure determination by NMR. In a de novo structure determination, however, lack of knowledge about the degree and orientation of molecular alignment complicates the analysis of dipolar coupling data. We present a probabilistic framework for analyzing residual dipolar couplings and demonstrate that it is possible to estimate the atomic coordinates, the complete molecular alignment tensor, and the error of the couplings simultaneously. As a by-product, we also obtain estimates of the uncertainty in the coordinates and the alignment tensor. We show that our approach encompasses existing methods for determining the alignment tensor as special cases, including least squares estimation, histogram fitting, and elimination of an explicit alignment tensor in the restraint energy.     

Biological invasions provide a framework for reintroductions: selecting areas in England for pine marten releases

We suggest that reintroductions, like biological invasions, have two phases: establishment when a new population becomes self-sustaining, and spread when a population increases its distribution. Stochastic effects on mortality and sex ratios are most likely to determine whether a population becomes established, while factors influencing birth rates will probably most influence spread. Using this establishment-spread structure, we evaluate the autecological suitability of regions in England for pine marten Martes martes reintroductions. Risks of mortality from predator control, traffic accidents and predation by foxes were used to evaluate suitability for establishment. Mortality risk was higher in all potential release regions in England (selected as having 25% or more woodland cover) than in regions of current pine marten distribution in Scotland; risk of predation was higher in the latter. Indices of prey abundance were used to evaluate suitability for populations to spread. Prey indices in potential release regions were generally higher than in regions of current distribution. A relation between prey, woodland cover, and known pine marten densities suggested that potential release regions are capable of supporting relatively high densities of pine martens, though these might be reduced by higher mortality. We concluded that all potential release regions are suitable for pine marten populations to spread. However, reintroductions should first be to regions with lower risk of mortality, in case higher levels of the latter prevent establishment. The suitability of relict regions of distribution in northern England was low until post-war afforestation, suggesting that habitat suitability constrained recovery of relict populations. These regions remain less suitable for reintroductions.     

Reconstructing past biological invasions: niche shifts in response to invasive predators and competitors

Studying historic invasions can provide insight into the ongoing invasions that threaten global biodiversity. In this study, we reconsider the impacts of Littorina littorea and Carcinus maenas on the rocky intertidal community of the Gulf of Maine. Past research using invader-removal experiments demonstrated strong top-down effects of L. littorea on algal community structure; however, such removal experiments may overlook the long-term effects of niche shifts and local extinctions caused by invasive species. We considered how a niche-shift in the native littorine, Littorina saxatilis, may change the interpretation of L. littorea impacts. Using a factorial experiment crossing predator presence/absence with L. littorea presence/absence, we found that L. saxatilis is able to exert top-down control on ephemeral algae similar to that exerted by L.␣littorea and that both competition by L. littorea and predation by C. maenas have strong, negative impacts on L. saxatilis. We also found higher predation rates on protected shores and at lower tidal heights and preferential predation on L.␣saxatilis compared to L. littorea. While movement experiments demonstrate that behavioral response to tidal height is the proximate cause of L. saxatilis exclusion from the lower intertidal, our study suggests that the ultimate causes are the additive effects of competition from and predation by invasive species.     

Invasion of the southern Gulf of St. Lawrence by the clubbed tunicate (Styela clava Herdman): Potential mechanisms for invasions of Prince Edward Island estuaries

All but one of the nine non-native marine species that established populations in the southern Gulf of St. Lawrence (sGSL) in the past decade initially invaded the sGSL via coastal and estuarine waters of Prince Edward Island (PEI). Almost half of these species are tunicates, and all but one still occur only in PEI. Recent introductions include Styela clava Herdman in 1997, Botryllus schlosseri (Pallas) in 2001, Botrylloides violaceus Oka in 2002, and Ciona intestinalis (Linnaeus) in 2004. The goal of this paper was to investigate which characteristics of PEI estuaries may have resulted in their being more susceptible to tunicate invasions than estuaries elsewhere in the sGSL. At least one genus that recently established viable populations in PEI was previously introduced to the Gulf of St. Lawrence, apparently without establishing permanent populations. This implies that either propagule pressure has increased or environmental factors are more conducive to establishment now than they were previously. The fluctuating resource availability model predicts increased invasibility of environments that experience pulses of resources such as space or nutrients. Intense development of both agriculture and aquaculture in PEI, and high population density compared to other areas of the sGSL, are associated with high and fluctuating estuarine nutrient levels and a large surface area of artificial substrates (mussel socks) that is kept relatively free of competitors, and is replaced regularly. Changes in nutrient loading and the development of aquaculture have also occurred within the past two to three decades. The provision of artificial structure is likely a critical factor in the successful establishment of tunicates in PEI, because natural hard substrates are scarce. Facilitation by green crabs (Carcinus maenas L.) may be a contributing factor in the spread of Styela. Only one estuary lacking green crabs has an established population of Styela, and at least two known inoculations of Styela into estuaries without green crabs have failed. A likely mechanism for facilitation is the consumption by green crab of the snail Astyris lunata, a known Styela predator.     

Microsatellite loci for Ponto-Caspian gobies: markers for assessing exotic invasions

We developed and tested eight polymorphic microsatellite loci for Ponto‐Caspian ‘neogobiin’ gobies, many of which are invasive in Eurasia and North America, whose study will aid understanding of the population genetics underlying their success. We tested samples from one to two locations from 12 taxa in the recently revised genera Babka, Benthophilus, Mesogobius, Neogobius = Apollonia, Ponticola and Proterorhinus; including the bighead, Caspian, knout, monkey, racer, round, tadpole and tubenose gobies; and taxa from introduced vs. native populations, those diverging between fresh and marine waters, and those differentiated between the Black and Caspian Seas. Populations conformed to Hardy–Weinberg equilibrium expectations, averaging five to 15 alleles per locus and 0.11 to 0.67 mean heterozygosity. Allelic variation significantly differentiated among all taxa and populations.     

Ecological consequences of biological invasions: three invertebrate case studies in the north-eastern Baltic Sea

Population dynamics and ecological impacts of the cirriped Balanus improvisus, the polychaete Marenzelleria neglecta and the cladoceran Cercopagis pengoi were investigated in the north-eastern Baltic Sea. After an increase during the first decade of invasion, the density of M. neglecta and C. pengoi declined afterwards. The studied abiotic environmental variables did not explain the interannual variability in the seasonal cycles of M. neglecta and C. pengoi indicating that the species are at their initial phase of invasion. The population dynamics of B. improvisus was best described by water temperature. B. improvisus promoted the growth of the green alga Enteromorpha intestinalis. M. neglecta enhanced the content of sediment chlorophyll a and reduced growth and survival of the polychaete Hediste diversicolor and growth of the amphipod Monoporeia affinis. Concurrent with the invasion of C. pengoi the abundance of small-sized cladocerans declined, especially above the thermocline. C. pengoi had become an important food for nine-spined stickleback, bleak, herring and smelt.     

Regulation of female reproduction in mites: A unifying model for the Acari

It is well established in the literature that circulating high levels of juvenile hormone (JH) are responsible for the initiation of vitellogenesis and female reproduction in most insects studied so far. Exceptions include some Diptera, Lepidoptera and Hymenoptera. The current view is that JH also regulates yolk protein (vitellogenin, Vg) synthesis and female reproduction in mites. However, there is no published evidence that mites have the common insect JHs at any stage of their development. Also, research on the effects of exogenous applications of JH and JH analogs on the reproduction of mites is contradictory. Significant information is available on the life history of mite reproduction, and new information has become available on mite storage proteins including Vg. Although initial studies suggested that ticks may respond to exogenously applied juvenile hormone or anti-JHs, current research shows that ticks cannot synthesize the common insect JHs and have no detectable levels of these hormones in their hemolymph during female reproduction. In ticks, it appears that ecdysteroids, and not JH, regulate expression of the Vg gene and the synthesis and release of Vg protein into the hemolymph. In fact within the Arthropoda, JH has been found only in insects. Methyl farnesoate and not JH regulates Vg synthesis in the Crustacea, the sister group to the insects. Based on this evidence, a new working hypothesis is proposed, i.e., that ecdysteroids and not the JHs regulate vitellogenesis in the Acari including both ticks and mites. To the present, the role of neuropeptides in the regulation of female reproduction in mites is not known.     

Saving camels from straws: how propagule pressure-based prevention policies can reduce the risk of biological invasion

Nonnative species that harm or have the potential to cause harm to the environment, economy, or human health are known as invasive species. Propagule pressure may be the most important factor in establishment success of nonnative species of various taxa in a variety of ecosystems worldwide, and strong evidence is emerging that propagule pressure determines both the scale of invasion extent and impact. In a limited way, the US government is applying a “propagule pressure approach” in a variety of prevention policy contexts aimed at minimizing the impact of harmful organisms. However, there are also readily apparent opportunities for enacting propagule pressure-based measures to fill current gaps in invasive species prevention and control at national, state, and local levels. An explicit focus on propagule pressure-based policies could substantially increase the effectiveness of US efforts to prevent the introduction of invasive species through by intentional and unintentional introductions. The views expressed in this paper are solely those of the authors and do not necessarily reflect those of the US government. “As the last straw breaks the laden camel’s back...” -Charles Dickens, Dombey and Son     

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.     

Positive feedbacks between plant invasions and fire regimes: <Emphasis Type=Italic>Teline monspessulana</Emphasis> (L.) K. Koch (Fabaceae) in central Chile

Invasive species can increase fire frequency and intensity, generating favorable conditions for their self-perpetuation. Mediterranean south-central Chile may be especially prone to the effects of invasive species on fire regimes because it is less adapted to fire and it contains a highly endemic flora. Teline monspessulana (L.) K. Koch (syn. Cytisus monspessulanus L.; Genista monspessulana (L.) L.A.S. Johnson) is an introduced shrub that forms monotypic stands or is present as an understory species in native forests as well as in forestry plantations. Dense T. monspessulana stands are completely destroyed by fire, generating the conditions for it seeds to germinate and establish an abundant regeneration, with up to 900 plants/m². We report key evidence on abundance and biomass in adult stands, and patterns of seed bank and regeneration after fire in stands of T. monspessulana around the city of Concepción, Chile. We estimated living biomass in pure stands and underneath Eucalyptus plantations. In burned areas, we assessed T. monspessulana seed bank and studied regeneration patterns. We found that T. monspessulana densities reaches 52,778 plants/ha and 8.92 ton/ha in pure stands and 34,223 plants/ha and 2.31 ton/ha underneath Eucalyptus plantations. T. monspessulana generates small caliper fuel and acts as a ladder-fuel. Large soil seed banks allow for abundant regeneration after fire, with mean densities of 877,111 plants/ha, but an overall mortality of 37.2% in the first year after the fire. The high values of regeneration compared to final densities in adult stands suggest that density-dependent mortality. Our results indicate that T. monspessulana regeneration is not only favored by fires, but also that the species creates favorable conditions for intense and continuous fires, both under pure conditions, but also associated to exotic tree plantations. To understand the implications of positive feedbacks between invaders and fire, we recommend focusing in the mechanisms by which they increases fuel accumulation and fuel flammability, and how higher fire frequency and intensity favors invasive species recruitment over native species. Comprehension of this dynamics will allow for better management and control of these invasions which have major ecological, economical and social implications.     

Review of the biology and ecology of a ragweed leaf beetle,Ophraella communa (Coleoptera: Chrysomelidae), which is a biological control agent of an invasive common ragweed,Ambrosia artemisiifolia (Asterales: Asteraceae)

A ragweed leaf beetle, Ophraella communa (Coleoptera: Chrysomelidae), has been highlighted as a potential biological control agent of Ambrosia artemisiifolia. O. communa and A. artemisiifolia are native in North America and alien species in East Asia and Europe. As an invasive weed, A. artemisiifolia causes severe economic losses as reducing agricultural production as well as producing severe allergenic pollen. As an herbivore insect, O. communa has strong host preference on A. artemisiifolia. All the developmental stages of O. communa can be found on A. artemisiifolia and it attacks a single plant in repeated and extended manners. With few individuals on A. artemisiifolia, O. communa can completely defoliate before pollen production. Therefore, O. communa had been focused as a biological control of this invasive weed, but its introduction was denied because of possible damage on an important crop, Helianthus annuus. O. communa was accidentally introduced in East Asia and Europe in 1990s and 2010s, respectively. Fortunately, O. communa population was well established to suppress A. artemisiifolia in the introduced areas. Following detailed field surveys and host specificity tests of O. communa were conducted and proved a strong potential of O. communa as a biological control agent of A. artemisiifolia. Moreover, O. communa has been investigated in physiological and evolutionary studies. In this study, the potential of O. communa as a biological control agent and a study organism are reviewed.     

The multiple decrement life table: a unifying framework for cause-of-death analysis in ecology

Summary The multiple decrement life table is used widely in the human actuarial literature and provides statistical expressions for mortality in three different forms: i) the life table from all causes-of-death combined; ii) the life table disaggregated into selected cause-of-death categories; and iii) the life table with particular causes and combinations of causes eliminated. The purpose of this paper is to introduce the multiple decrement life table to the ecological literature by applying the methods to published death-by-cause information on Rhagoletis pomonella. Interrelations between the current approach and conventional tools used in basic and applied ecology are discussed including the conventional life table, Key Factor Analysis and Abbott's Correction used in toxicological bioassay.