Animal trade and non-indigenous species introduction: the world-wide spread of squirrels

Aim  In this study, a dataset on world-wide squirrel introductions has been used to locate the relative pathways and to determine the factors correlated with species establishment.
Location  The world.
Methods  The analysis includes a chronological table of introductions, a biogeographical analysis and an assessment of the likelihood of establishment according to species, propagule pressure, area of origin and characteristics of the recipient area.
Results  The main vector of such introductions was the intentional importation of live animals. Introductions increased in developed countries and proportionately to the volume of imported mammals. Moreover, areas characterized by higher numbers of native squirrels were more invaded. Squirrels were often introduced deliberately and only to a smaller extent escaped from captivity. The likelihood of their establishment increased proportionately to the number of animals released and decreased proportionately to the increase of the latitudinal distance between the recipient area and the native range of the species. The likelihood that the release of one pair of either Sciurus or Callosciurus species would establish a new population was higher than 50%.
Main conclusion  Squirrels proved to be successful invaders and their importation should be restricted so as to prevent further introductions.     

Comparison of methods for estimating the spread of a non-indigenous species

Aim  To compare different quantitative approaches for estimating rates of spread in the exotic species gypsy moth, Lymantria dispar L., using county-level presence/absence data and spatially extensive trapping grids.
Location  USA
Methods  We used county-level presence/absence records of the gypsy moth's distribution in the USA, which are available beginning in 1900, and extensive grids of pheromone-baited traps, which are available in selected areas beginning in 1981. We compared a regression approach and a boundary displacement approach for estimating gypsy moth spread based on these sources of data.
Results  We observed relative congruence between methods and data sources in estimating overall rates of gypsy moth spread through time, and among regions.
Main conclusions  The ability to estimate spread in exotic invasive species is a primary concern in management programmes and one for which there is a lack of information on the reliability of methods. Also, in most invading species, there is generally a lack of data to explore methods of estimating spread. Extensive data available on gypsy moth in the USA allowed for such a comparison. We show that, even with spatially crude records of presence/absence, overall rates of spread do not differ substantially from estimates obtained from the more costly deployment of extensive trapping grids. Moreover, these methods can also be applied to the general study of species distributional changes, such as range expansion or retraction, in response to climate change or other environmental effects.     

Differential effects of tributyltin and copper antifoulants on recruitment of non-indigenous species

Maritime transport is a primary vector for many marine invaders. For the past two decades, most commercial vessels have used tributyltin (TBT) antifouling (AF) paint, whereas recreational vessels have been restricted to alternatives, most commonly containing copper. Settlement plates painted with a collar of copper or TBT AF paint, and unpainted control plates, were deployed in commercial and recreational embayments in Port Jackson, Australia, and sampled photographically after 5 and 10 months. Copper enhanced early recruitment of several non-indigenous species (NIS), whereas recruitment of indigenous species was typically reduced by copper. TBT limited the recruitment of NIS for just 5 months and indigenous species, for the entire study. The results suggest that the use of toxic AF paints, and the possible accumulation of AF biocides in embayments, may be negatively affecting indigenous epibiota. Conversely, copper antifoulants on recreational vessels may be facilitating the transport and establishment of copper tolerant NIS into disturbed estuarine habitats.     

The unintended effects of prisoner reentry policy and the marginalization of urban communities

Despite the stated purpose of the Prisoner Reentry Industry, to effectively manage formerly incarcerated individuals’ transition back into the community, there is evidence to suggest that its policies may be counterproductive to this process. Drawing on personal experiences as a mentor to a formerly incarcerated African-American woman, this essay seeks to provide examples of how policy gridlock can impede the transition of individuals from prison, into the community, and how this contributes to the economic and social affliction of urban communities.     

Economics of invasive species policy and management

This article examines the use of economic analysis to inform bioinvasion management, with particular focus on forest resources. Economics is key for understanding invasion processes, impacts, and decision-making. Biological invasions are driven by and affect economic activities at multiple scales and stages of an invasion. Bioeconomic modeling seeks to inform how resources can be optimally allocated across invasion management activities—including prevention, surveillance programs for early detection and management, and controlling invasion populations and spread—to minimize the long-term costs and damages. Economic analysis facilitates understanding of decisions by public and private decision-makers, gaps between these, and the design of policies to achieve socially desirable outcomes. Private decision-makers may undercontrol invasions relative to socially optimal levels, because they generally account for their own costs and benefits of control but less often for broader ecosystem impacts or future spread across the landscape. Economic analysis considers approaches for increasing private invasion management and evaluates feedbacks between ecological and economic systems that can affect policy outcomes. Future research should continue evaluation and design of control strategies across the biosecurity continuum and across species to enhance cost-effectiveness, better incorporate uncertainty into policy design, increase focus on incentives and behavioral tools to influence private behaviors that affect invasion spread, and incorporate invasive species consideration within broader systems-focused science. In addition, challenges in valuing biodiversity and ecosystem service impacts and the costs and effectiveness of control measures are key data gaps. Greater collaboration between decision-makers and researchers will facilitate development and communication of usable economic research.     

The prevalence of non-indigenous species in southern California embayments and their effects on benthic macroinvertebrate communities

The prevalence of non-indigenous species (NIS) in southern California embayments was assessed from 123 Van Veen grab samples collected in nine bays and harbors during the summer of 1998. NIS occurred in all but two samples. They accounted for only 4.3% of the 633 taxa but contributed 27.5% of the abundance. There was no significant difference in the proportion of NIS abundance among ports harboring large vessels, small boat marinas, and areas where boats were not moored. Three species accounted for 92% of the NIS abundance: a spionid polychaete worm Pseudopolydora paucibranchiata, a mytilid bivalve Musculista senhousia, and a semelid bivalve Theora ubrica. The NIS did not appear to have a negative impact at the overall community level since NIS abundance was positively correlated with the abundance and richness of other species. This may be due to biogenic structures built by P. paucibranchiata and M. senhousia that enhance the abundances of other macrofauna.     

Biocontrol without borders: the unintended spread of introduced weed biological control agents

An underlying assumption of classical biological control implies that intentionally introduced natural enemies will remain within the boundaries that delineate the program’s area of implementation. A weed biological control program targeting Melaleuca quinquenervia in Florida, USA has resulted in the release and establishment of Oxyops vitiosa and Boreioglycaspis melaleucae. An international survey of M. quinquenervia populations in 13 other states or countries where the insects have not been intentionally introduced was initiated to monitor the long range dispersal of O. vitiosa and B. melaleucae beyond the herbivores’ intended geographic range (Florida). Surveys in 2006 resulted in the discovery of B. melaleucae within the canopies of several M. quinquenervia trees near San Juan, Puerto Rico. In 2007, O. vitiosa was observed on the island of New Providence in the Bahamas but neither herbivore was detected on nearby Grand Bahama or Andros islands. In 2009, B. melaleucae was observed attacking M. quinquenervia trees in Los Angeles, California (USA). The herbivores have not been detected on other surveyed M. quinquenervia populations in Cuba, Jamaica, Texas (USA), Costa Rica, Brazil, Hawaii (USA) or South Africa. There is no evidence to suggest that herbivore colonization of New Providence, Puerto Rico, or California was influenced by linear distance between Florida and the recipient M. quinquenervia stand. While the dispersal pathway(s) remains unknown, biological control agents were detected from 200 to >3500 km from their original release location (Florida) and at locations that have strong links via tourism and trade as indicated by the number of airline flights connecting south Florida with colonized tree populations. Implications of this unintended spread are discussed in relation to permeability of biogeographical barriers and risk assessment of biological control agents.     

The role of regulatory decision-making on non-indigenous species introductions

Introduction is a critical stage in vertebrates’ invasion process; once imported, they have a high probability of establishment and spread. While there is a consensus that trade is a primary conduit for non-indigenous species (NIS) introductions, and a key locus for preventive regulation, few policies have been evaluated by scientists for effectiveness. A science-based quantitative assessment of regulatory performance could significantly decrease invasion risk. We carried out a quantitative analysis of data on importation permits of terrestrial vertebrates and the reporting system, using the Israeli regulatory system as a model. This regulatory system is based on long-established wildlife protection legislation, now being used to control NIS vertebrates, much as is the case in many other countries. Ecological risk assessment for NIS was sometimes carried out, but it is not mandatory within the regulatory process, and no legally-binding criteria for assessment exist. We found a significant decrease in number of permits issued over the years, but this decrease does not reflect perception of ecological risk. We found permit quotas of much wider volumes than those actually used, indicating that trade volumes are dictated by retailers rather than by regulators. Actual imports are frequently not reported, hindering efforts to assess propagule pressure and to monitor and analyze effects of introductions. We conclude that the regulatory system should be more science-based, that the import database should be formulated to allow future ecological research and mitigation, and that legally-binding ecological risk assessment would contribute significantly to the strength of NIS regulation.     

Down under the southeastern Pacific: marine non-indigenous species in Chile

This article presents the first compilation of marine non-indigenous species (NIS) of algae and macro-invertebrates invading Chilean waters. A total of 32 cosmopolitan and non-cosmopolitan species are reported. Among them there are six species considered as extending their southern range of distribution in connection with El Niño events. The article highlights negative and positive impacts caused by marine NIS invasions. Among the first are Codium fragile var. tomentosoide, considered as a pest in Gracilaria chilensis aquaculture facilities in northern Chile, and Ciona intestinalis, a pest in scallop aquaculture installations. Among the second are bio-engineers species, such as the ascidian Pyura praeputialis and the sea grass Heterozostera tasmanica, which have caused an increase in local biodiversity and enhancement of nursery grounds via the creation of new habitats. Further more, invaders such as the algae Mastocarpus papillosus, Porphyra linearis and P. pseudolinearis represent new exploitable resources, extracted by coastal food gatherers along the coast (M. papillosus) or potential species to develop aquaculture. Additional information is presented on the anemone Anemonia alicemartinae, which appears to be a native species (?), having shown in the past 40–50 years, a geographical southward range extension of approximately 1900 km. The number of NIS reported for Chile is compared with those published for the southwestern Atlantic, South Africa, North America (Atlantic and Pacific coasts) and New Zealand. It is suggested that probably the low number of Chilean NIS is due to the fact that the Chilean coasts are environmentally less stressed than other coasts in the world, due to the scarcity of estuaries, gulfs, enclosed bays, lagoons and low human populations. These kinds of sheltered areas have been suggested as centers for bio-invasions, due to the high rate of human-mediated transfer and increase of pollutants. Furthermore, none of NIS reported from Chile show a fast geographical expansion rate (exception of A. alicemartinae), nor invading strategies such as those described for marine NIS in other latitudes, where notorious ecological unbalances following invasions have been observed. An alternative hypothesis is that the low number of marine NIS invading Chile is underestimated, since the modern list of species generated through specific taxonomically intensive port and harbor surveys is still lacking. Fifteen species (five invertebrate and 10 fish) have been deliberately imported to Chile for aquaculture. The invertebrates appear to be controlled within aquaculture facilities and have not established naturalized populations or caused direct ecological impacts on local communities. On the contrary, several millions of salmoniforms (and rainbow trout) have escaped from farming facilities in southern Chile and established naturalized populations. Studies on ecological impacts are lacking. These escapees are also playing a role in the enhancement of artisanal and sport fishery activities.     

Selectivity in vector management: an investigation of the effectiveness of measures used to prevent transport of non-indigenous species

Measures taken to control the spread of non-indigenous species by human vectors may act selectively by providing effective protection against some (but not all) species. Toxic antifouling paints are used by boat owners to prevent the development of fouling assemblages on the hulls of their boats, which reduce vessel speed and maneuverability. By reducing fouling, these paints also prevent transport of non-indigenous species. Using experimental surfaces mimicking boat hulls, we evaluated the effectiveness and selectivity of (1) antifouling paints, and (2) manual, in-water hull cleaning for preventing the transport of marine sessile invertebrates by recreational vessels. Different types of antifouling paints provided effective protection only against barnacles and bivalves. Other fouling taxa occurred on experimental surfaces after a period of only 2 months. Manual hull cleaning did not remove fouling completely, and even enhanced the risk of subsequent recruitment by some fouling organisms. Up to six times more individuals and colonies recruited to boat surfaces from which the existing fouling organisms had been removed manually than to surfaces that had been sterilized or contained intact fouling assemblages. Bivalves, colonial and solitary ascidians, encrusting bryozoans, hydroids, tubiculous polychaetes, and sponges consistently recruited in greatest abundance to manually cleaned surfaces. Individual taxa responded in complex, but predictable ways to the biogenic cues left by manual cleaning, so that different suites of organisms colonized surfaces that had originally contained fouling assemblages of local or non-local origin. Our study shows that widely adopted measures to control the spread of non-indigenous species by human vectors are often highly selective and, while effective for some taxa, do not prevent the transport of others.     

Dynamic economic analysis on invasive species management: Some policy implications of catchability

The problem of controlling invasive species has emerged as a global issue. In response to invasive species threats, governments often propose eradication. This article challenges the eradication view by studying optimal strategies for controlling invasive species in a simple dynamic model. The analysis mainly focuses on deriving policy implications of catchability in a situation where a series of controlling actions incurs operational costs that derive from the fact that catchability depends on the current stock size of invasive species. We analytically demonstrate that the optimal policy changes drastically, depending on the sensitivity of catchability in response to a change in the stock size, as well as on the initial stock. If the sensitivity of catchability is sufficiently high, the constant escapement policy with some interior target level is optimal. In contrast, if the sensitivity of catchability is sufficiently low, there could exist a threshold of the initial stock which differentiates the optimal action between immediate eradication and giving-up without any control. In the intermediate range, immediate eradication, giving-up without any control, or more complex policies may be optimal. Numerical analysis is employed to present economic intuitions and insights in both analytically tractable and intractable cases.     

Feeding ecology of indigenous and non-indigenous fish species within the family Sphyraenidae

The feeding ecology of two common indigenous (Sphyraena viridensis and Sphyraena sphyraena) and one abundant non-indigenous sphyraenid species, Sphyraena chrysotaenia, of Indo-Pacific Ocean origin, was investigated in an area of the eastern Mediterranean Sea. The stomach contents of 738 individuals of varying size, collected during the period December 2008 to August 2009, were examined. The dietary analyses revealed that all three species were specialized piscivores with a diet consisting of >90% fish, both by number and mass. Concurrent sampling of the fish assemblage made it possible to calculate selectivity as well as diet breadth and overlap of these strict piscivores. Even though several prey species were found in the stomachs of the three predators examined, selectivity towards Atherina boyeri was highly significant. For all species examined, >70% of the diet by mass was made up by three indigenous species of commercial value: Spicara smaris, Boops boops and A. boyeri. Diet breadth and size of prey increased with increasing body size for all predators. With increased body size, the diet overlap between indigenous and non-indigenous species decreased. This could be attributed to increased diet breadth and the specific life-history characteristics of indigenous species developing into larger individuals. During winter, the condition factor of the non-indigenous species was significantly lower than that of the indigenous, indicating that winter conditions in the Mediterranean Sea may limit its further expansion north and westward. With this study, the gap in knowledge of the feeding preferences of the most abundant piscivorous species found in coastal areas of the study region is filled. Additionally, the results indicate that non-indigenous species familial affiliation to indigenous ones does not facilitate invasion success.     

Impact of non-indigenous species on natives enhanced by anthropogenic alteration of selection regimes

Changes in environmental conditions often reverse outcomes of competitive interactions among species. Such context dependency implies that the speed, persistence, and ubiquity of anthropogenic habitat alterations may suddenly put even previously well-adapted native species at a competitive disadvantage with non-native species. That is, anthropogenic disturbance may so drastically alter environments that a native species finds itself in an environment that in key ways is just as novel as it is to a non-indigenous species. Extreme disturbances may thereby erase a native species' prior advantage of local environmental adaptation accrued during its long-term incumbency over evolutionary time. I document examples from two areas of dramatic human alteration of selection regimes – eutrophication and the selective removal of top predators – that support this mechanism. Additionally, I highlight ways in which this mechanism is experimentally testable. Alteration of selection regimes may prove to be a powerful explanation for the enhanced success and impact of biological invasions in our globally disturbed biosphere.     

Exploitation of a single species by a threshold management policy

Continuous time models of single exploited populations usually generate outcomes expressing a dependence of yield and economic items on harvest intensity. In this work it is shown that a known threshold policy is able to generate yield and related economic items that do not depend on harvest intensity, but rather on the values of the population threshold itself and the species intrinsic parameters. It is argued that since this result can be carried over to other models of single species dynamics, it may have significant implications in the management and conservation of exploited populations.     

The potential role of an unregulated coastal anthropogenic activity in facilitating the spread of a non-indigenous biofoulant

Despite an exponential rise in anthropogenically-mediated transfers of non-indigenous species during the last 150 years, several coastal anthropogenic activities remain unregulated under current legislation frameworks. This study investigates the potential role of commercial periwinkle (Littorina littorea) harvesting as an unregulated facilitator of both small- and large-scale geographic range expansion of an invasive oyster epibiont (Ostrea chilensis) within the Menai Strait (North Wales, UK) and beyond. The frequency of oyster-fouled periwinkles was greatest in areas of high adult oyster abundance and restricted to large, market-sized periwinkles (>20 mm) inhabiting the low shore. Active efforts by commercial collectors to reject oyster-fouled periwinkles were found to be inadequate, with oysters of all sizes observed within collected hauls. Whilst the survival of fouled and unfouled periwinkles was comparable under post-collection refrigerated conditions, a significant decrease in both mobility and flesh content was associated with the presence of oyster epibionts. Survival of all but the smallest oyster epibionts under post-collection refrigerated conditions enhances the possibility of accidental non-indigenous oyster transfers. Better interventions during both initial visual inspection and post-griddling stages are recommended, as well as the development of techniques that kill off all non-indigenous epibionts, whilst leaving the freshness and marketability of the periwinkles uncompromised.     

Burrower bugs (Heteroptera: Cydnidae) in peanut: seasonal species abundance, tillage effects, grade reduction effects, insecticide efficacy, and management

Pitfall traps placed in South Carolina peanut, Arachis hypogaea (L.), fields collected three species of burrower bugs (Cydnidae): Cyrtomenus ciliatus (Palisot de Beauvois), Sehirus cinctus cinctus (Palisot de Beauvois), and Pangaeus bilineatus (Say). Cyrtomenus ciliatus was rarely collected. Sehirus cinctus produced a nymphal cohort in peanut during May and June, probably because of abundant henbit seeds, Lamium amplexicaule L., in strip-till production systems. No S. cinctus were present during peanut pod formation. Pangaeus bilineatus was the most abundant species collected and the only species associated with peanut kernel feeding injury. Overwintering P. bilineatus adults were present in a conservation tillage peanut field before planting and two to three subsequent generations were observed. Few nymphs were collected until the R6 (full seed) growth stage. Tillage and choice of cover crop affected P. bilineatus populations. Peanuts strip-tilled into corn or wheat residue had greater P. bilineatus populations and kernel-feeding than conventional tillage or strip-tillage into rye residue. Fall tillage before planting a wheat cover crop also reduced burrower bug feeding on peanut. At-pegging (early July) granular chlorpyrifos treatments were most consistent in suppressing kernel feeding. Kernels fed on by P. bilineatus were on average 10% lighter than unfed on kernels. Pangaeus bilineatus feeding reduced peanut grade by reducing individual kernel weight, and increasing the percentage damaged kernels. Each 10% increase in kernels fed on by P. bilineatus was associated with a 1.7% decrease in total sound mature kernels, and kernel feeding levels above 30% increase the risk of damaged kernel grade penalties.     

Community context and the influence of non-indigenous species on juvenile salmon survival in a Columbia River reservoir

Non-indigenous species (NIS) have been called biological pollutants, which implies that reducing their numbers should reduce negative impacts. To test this hypothesis, we used food web models, parameterized with data from field studies, to ask how reducing the number of NIS co-occurring with endangered salmon would affect salmon mortality. Our analyses indicate that predation on Upper Columbia River spring chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss juveniles was affected very little by NIS reduction. The effects of removing NIS were partly or totally offset by indirect food web interactions, and were subtle compared to effects of native predator management. We predict that the most effective way of reducing predation on salmon smolts will involve managing native predators and targeted removals of specific NIS. Minimizing impact of established NIS thus entails not only reducing NIS prevalence, but also considering background management practices and community context.