Evaluating spatially explicit management alternatives for an invasive species in a riverine network

Brielle K. Thompson; Julian D. Olden; Sarah J. Converse

doi:10.3897/neobiota.96.132363

Home/Archive/USGS

USGS · 70267760

Evaluating spatially explicit management alternatives for an invasive species in a riverine network

Brielle K. Thompson·Julian D. Olden·Sarah J. Converse

View original source ↗Export metadata ↓

Abstract

Invasive species have substantial ecological and economic costs and removing them can require large investments by management agencies. Optimal spatial allocation of removal effort is critical for efficient and effective management of invasive species. Using a series of ecologically informed model simulations, we evaluated and compared different spatially explicit removal strategies for invasive rusty crayfish ( Faxonius rusticus ) in the John Day River, USA. We assessed strategies in terms of their performance on three likely management objectives: suppression (minimise overall population abundance), containment (minimise the spatial extent of invasion) and prevention (minimise spread into a specific area). We developed five spatial removal strategies to achieve those objectives, denoted as: Target Abundance (removal at locations with the highest population abundance), Target Growth (removal at locations with the highest population growth), Target Edges (removal at the most distant locations in the river), Target Downstream (removal at the most downstream invaded segments on the Mainstem), and Target Random (removal at randomly selected locations). Each strategy was assessed at various effort levels, referring to the number of spatial segments in the river in which removals were conducted, after seven years of management. We identified the alternative that best achieved each objective, based on decision criteria for risk-neutral and risk-averse decision-makers and further evaluated strategies based on Pareto efficiency, which identifies the set of alternatives for which an improvement on one objective cannot be had without a decline in performance on another. We found that Target Abundance and Target Growth strategies best achieved the suppression objective, for risk neutral and risk averse decision-makers, respectively and Target Downstream was always best in achieving the prevention objective across both types of decision-makers. No single strategy consistently performed best in terms of the containment objective. In terms of all three objectives, Target Downstream was consistently Pareto efficient across all levels of management effort and both decision criteria. The modelling framework we provided is adaptable to a variety of riverine invasive species to help assess and compare spatial management strategies.

Explore related subjects

NeoBiota Article

Source-reported bounding extent: 44.11199343230538° to 45.69676723476786° latitude; -120.88724466132285° to -118.7532889941624° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Brielle K. Thompson, Julian D. Olden, Sarah J. Converse. 2024-11-14. Evaluating spatially explicit management alternatives for an invasive species in a riverine network. https://doi.org/10.3897/neobiota.96.132363

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Designing biosurveillance using target analysis for a cryptic invasive species, the brown treesnake (Boiga irregularis)

Biosurveillance is especially important for invasive species that are difficult to control or remove once established. Target analysis, or the strategic evaluation of factors that affect or improve detection of organisms, is one approach to improve biosurveillance over time. Due to their ecologically and economically devastating effects, brown treesnakes ( Boiga irregularis ), an invasive snake in the United States territory of Guam, have a dedicated biosecurity program to prevent their spread. Guam has been occupied by brown treesnakes since the 1940s, and they are distributed throughout the island. The neighboring Saipan Island, otherwise known as Saipan, participates in biosecurity programs designed to prevent their establishment. We evaluated biosurveillance protocols within rapid response and detection exercises for brown treesnakes. Our goal was to identify, account for, and reduce potential error when inferring absence from lack of detection using data collected in Guam and Saipan. We evaluated 1) whether brown treesnake detection probability was density dependent; 2) whether using terrestrial environmental DNA ( eDNA ) sampling detected snakes in occupied areas; 3) the likelihood brown treesnakes would have been detected in Saipan, given sampling effort during a biosurveillance exercise, and whether lizards could be used as a proxy on snake-free islands for estimating factors that affect detection; 4) the effect of transect design on pacing and subsequently pacing on lizard counts; and 5) the importance of observer training in surveying for cryptic reptiles and completing broad versus targeted bioinventories. We found that brown treesnake detection probability was density dependent when using visual surveys and declined with abundance in Guam, supporting that greater effort was required to have high confidence that lack of detection supported absence in areas with low snake densities. The terrestrial eDNA sampling protocol we developed was effective at detecting snakes in occupied locations in Guam and may be a complementary tool. However, further validation of eDNA protocols would still be required for early detection application. We also found that among trained observers, the ability to detect lizards was positively predictive of the number of snakes they detected at the standard snake densities in Guam. Thus, lizard detection appeared to be a reasonable proxy for evaluating visual search protocols for snakes on snake-free islands. Overall, creating easy pace-setting relationships between time and distance (i.e., 10 m per min), with flagging that clearly marked location on a transect, greatly reduced variability in search pace across survey nights. Observers that were continuously trained to maintain brown treesnake search profiles detected twice as many, on average, cryptic reptiles compared to individuals who had never received training, which was not true for the non-reptiles (birds and small mammals). Additionally, conducting broad bioinventories with many target species reduced detection of the target species, and this was increasingly true as years since the observer completed training for the target species increased. We thus found that designing biosurveillance exercises to evaluate search protocols can help improve or refine survey methods to reduce noise in the data, and accounting for that can improve the estimated confidence that failure to detect an invasive species infers absence.

NeoBiota↗

USGS2025

Reproductive condition of an invasive snake in urban, savanna, and forest habitats

Predation by Brown Treesnakes ( Boiga irregularis ) has caused the decline or extinction of all native forest vertebrates on Guam, including birds, lizards, and bats. Loss of the highest-quality prey has caused shifts in Brown Treesnake size and life history. We sought to understand how reproductive condition varies among habitats island-wide, particularly comparing urban and savanna habitats (where some primarily non-native large prey remain) with prey-depauperate forest habitats. We dissected 100 snakes from each of 18 sites stratified by 6 habitat types and calculated a body condition index, relative follicle size (for females; N = 817) and relative testes size (for males; N = 992) for each. Low detection of reproductive females continues to hamper research on their biology, as only 11% of females had secondary vitellogenic follicles (N = 89). Although variation among sites within habitats was high, above-average reproductive development of both males and females was most frequently observed in urban and savanna habitats, emphasizing the potential for prey subsidies in these habitats to fuel population growth and affect invasive snake management objectives. Furthermore, the trade-off between body condition and reproductive condition appeared to be more severe in forested habitats and less severe in urban habitats for both males and females. There were few obvious seasonal patterns, although there was a slightly lower probability of females having secondary vitellogenic follicles in the wet season compared to the dry season.

NeoBiota↗

USGS2025

Coelomic foreign bodies in wild-caught Python spp. in the Greater Everglades Ecosystem, Florida, USA

Burmese pythons ( Python molurus bivittatus ) and African rock pythons ( Python sebae ) have established invasive populations in southern Florida, severely disrupting local ecosystems. We analysed necropsy data from 2,179 pythons captured between 2006 and 2022, revealing nine cases of coelomic foreign bodies, primarily consisting of bird beaks, which presumably entered the coelom following gastrointestinal perforations during prey consumption. Despite the presence of foreign bodies, most examined pythons exhibited no obvious health issues. These findings indicate that the consumption of prey with sharp morphological features, such as wading birds, may not impede the pythons’ survival or health significantly, thereby underscoring their adaptability as apex predators in the Greater Everglades Ecosystem.

Florida↗