Invasive snake causes massive reduction of all endemic herpetofauna on Gran Canaria

Quantifying the importance of ontogeny and prey type in modeling top-down and bottom-up effects of an ectothermic predator

Dietary decisions by predators can affect prey abundance and overall food web dynamics. Many predators do not forage on the same prey at the same frequency throughout their lives. Ontogenetic shifts in prey preference are not, however, often accounted for when modeling food web relationships, despite growing literature that suggests that stage specific dietary relationships may be an important consideration when modeling trophic interactions. We investigated the importance of considering size-structure of a predator population with ontogenetic diet shifts in evaluating relationships with prey response using a manipulative experiment with the brown treesnake (Boiga irregularis) in Guam. After removing ~ 40% of the snake population via toxic mammal carrion, we measured the strength of the relationship between snake density and the response of two types of prey (lizards and mammals). We evaluated these relationships based on total population size or division of the population into stage specific size categories based on diet preference predictions. We hypothesized that the density of juvenile snakes would correlate more strongly with lizard detections, while adult snakes would better correlate to rodent detections. We also measured reproductive output following changes in rates of prey detection. As expected by known ontogenetic shifts in dietary preference, explicit stage-based models better predicted shifts in rates of observed prey items than did total predator density for both lizards and mammals. Additionally, rodent detections were predictive of one reproductive pulse from snakes, while lizard detections were not predictive or correlated. Our findings support that consideration of predatory species stage-based dietary preference can be meaningful for understanding food web dynamics, particularly when a predator has a broad diet or one that changes through time.

Morphology, Behaviour and Evolution of Gallotia Lizards from the Canary Islands

We summarize, here, the results from several studies conducted over many years on several endemic species of lizards (genus Gallotia) from the Canary Islands. Quantitative analyses show clear differences both among the species of every island and populations within each species. Sexual dimorphism exists in all analysed species, and a phylogenetic analysis shows that the degree of dimorphism did not change along the evolutionary history of the Canary Islands: species with large and small body sizes have a similar degree of sexual dimorphism, with male body size changes closely following those undergone by females. In G. caesaris (from El Hierro and La Gomera islands) and in G. stehlini (from Gran Canaria), longer hind limb length was correlated with more open habitats. Within most species, males are more conspicuous than females, mainly in terms of body size, behaviour and coloration pattern. Lateral colour spots are blue in most species and green in others. In G. galloti from Tenerife, male lateral spots have larger spot areas and percentage of reflectance in the ultraviolet/blue part of the spectrum than females. This trait shows a monthly variation along April to July, both in males and females, its magnitude being larger in May-June. Behaviour analysis, especially in the last species, shows a great diversity in behaviour patterns, and analysis of intrasexual male competition revealed that contest outcome depends on several morphological and colouration characteristics but mainly on the individual's behaviour. Detailed behavioural analyses were useful for managing a few captive individuals of the highly endangered G. bravoana from La Gomera island. Experimental analyses of some behaviours in the endemic Hierro island lizard (G. simonyi, in danger of extinction) show that individuals may learn to recognize predator models and increase their running speeds with training.

One Health Approach: Invasive California Kingsnake (Lampropeltis californiae) as an Important Source of Antimicrobial Drug-Resistant Salmonella Clones on Gran Canaria Island

The increase in the reptile population has led to a rise in the number of zoonotic infections due to close contact with reptiles, with reptile-associated salmonellosis being particularly relevant. California kingsnake invasion not only threatens the endemic reptile population of the island of Gran Canaria (Spain) but also poses serious public health problems by spreading zoonotic pathogens and their antimicrobial resistance (AMR) to the environment. Thus, the aim of this study was to assess the occurrence, genetic diversity, and AMR among Salmonella spp. strains isolated from California kingsnakes in Gran Canaria Island (Spain). Of 73 invasive individuals captured, 20.5% carried Salmonella spp., belonging to different subspecies and serovars, with subsp. salamae as the most abundant. Pulsed-field electrophoresis showed high genetic diversity among subsp. salamae isolates, and among these, 73.3% showed resistance to at least one of the antimicrobials tested. In conclusion, the present study revealed the importance of wild invasive California kingsnakes as reservoirs of drug-resistant Salmonella spp. that could pose a direct threat to livestock and humans. Identification of drug-resistant Salmonella strains in wildlife provides valuable information on potential routes of transmission that involve risks to public and animal health.

Spatial ecology to strengthen invasive snake management on islands

Knowledge on the spatial ecology of invasive predators positively contributes to optimizing their management, especially when involving cryptic and secretive species, such as snakes. However, this information is lacking for most invasive snakes, particularly on islands, where they are known to cause severe ecological and socio-economic impacts. This research is focused on assessing the spatial ecology of the California kingsnake (Lampropeltis californiae) on Gran Canaria to strengthen management actions. We monitored 15 radio-tagged individuals once per day on 9-11 days per month from July 2020 to June 2021 to calculate the species' home range and describe annual activity patterns in the invaded range. To account for the species' diel activity during the emergence period, we additionally monitored snakes from January to May 2021 during three consecutive days per month in four different time intervals each day. We detected movement (consecutive detections at least 6 m apart) in 31.68% of the 1146 detections during the whole monitoring period. Movements most frequently detected were shorter than 100 m (82.24%), and among them the range 0-20 m was the most recurrent (27.03%). The mean distance of movement was 62.57 ± 62.62 m in 1-2 days. Average home range was 4.27 ± 5.35 ha-calculated with the Autocorrelated Kernel Density Estimator (AKDE) at 95%-and did not significantly vary with SVL nor sex. We detected an extremely low value of motion variance (0.76 ± 2.62 σ²m) compared to other studies, with a general inactivity period from November to February, January being the less active month of the year. Diel activity was higher during central and evening hours than during early morning and night. Our results should be useful to improve control programs for this invasive snake (e.g., trap placement and visual survey guidance) on Gran Canaria. Our research highlights the importance of gathering spatial information on invasive snakes to enhance control actions, which can contribute to the management of secretive invasive snakes worldwide.

Burmese pythons in Florida: A synthesis of biology, impacts, and management tools

Burmese pythons (Python molurus bivittatus) are native to southeastern Asia, however, there is an established invasive population inhabiting much of southern Florida throughout the Greater Everglades Ecosystem. Pythons have severely impacted native species and ecosystems in Florida and represent one of the most intractable invasive-species management issues across the globe. The difficulty stems from a unique combination of inaccessible habitat and the cryptic and resilient nature of pythons that thrive in the subtropical environment of southern Florida, rendering them extremely challenging to detect. Here we provide a comprehensive review and synthesis of the science relevant to managing invasive Burmese pythons. We describe existing control tools and review challenges to productive research, identifying key knowledge gaps that would improve future research and decision making for python control.

Coupling phenotypic changes to extinction and survival in an endemic prey community threatened by an invasive snake

When facing novel invasive predators, native prey can either go extinct or survive through exaptation or phenotypic shifts (either plastic or adaptive). Native prey can also reflect stress-mediated responses against invasive predators, affecting their body condition. Although multiple native prey are likely to present both types of responses against a single invader, community-level studies are infrequent. The invasive California kingsnake (Lampropeltis californiae) a good example to explore invasive predators' effects on morphology and body condition at a community level, as this invader is known to locally extinct the Gran Canaria giant lizard (Gallotia stehlini) and to notably reduce the numbers of the Gran Canaria skink (Chalcides sexlineatus) and the Boettger's gecko (Tarentola boettgeri). By comparing a set of morphological traits and body condition (i.e. body index and ectoparasite load) between invaded and uninvaded areas for the three squamates, we found clear evidence of a link between a lack of phenotypic change and extinction, as G. stehlini was the single native prey that did not show morphological shifts. On the other side, surviving C. sexlineatus and T. boettgeri exhibited phenotypic differences in several morphological traits that could reflect plastic responses that contribute to their capacity to cope with the snake. Body condition responses varied among species, indicating the potential existence of simultaneous consumptive and non-consumptive effects at a community level. Our study further highlights the importance addressing the impact of invasive predators from a community perspective in order to gain a deeper understanding of their effect in native ecosystems.