Importation dynamics as proxies for propagule pressure are necessary but not sufficient to explain establishment success in non-native herpetofauna

Florida is a major entry point for global wildlife trade, creating a high risk of introducing non-native reptiles and amphibians. Using Law Enforcement Management Information System records of reptiles and amphibians imported into Florida from 1999 to 2018, we examined temporal trends in live imports, particularly for legally regulated species, and assessed whether import volumes were associated with establishment probability using a probabilistic model. During the study period, 12.74 million reptiles (1,162 species) and 4.59 million amphibians (350 species) entered through the three main Florida ports. Annual imports decreased significantly over time (Reptiles: 32,731 individuals per year; Amphibians: 10,155 individuals per year), particularly among regulated species, with the reductions occurring gradually. Logistic regression models revealed a strong positive relationship between import numbers and establishment success; for reptiles, import numbers explained 26.4% of the variation in establishment outcomes, while for amphibians, import numbers explained 8.26% of the variation, values expected given that establishment is influenced by multiple unmeasured biological and environmental factors beyond propagule pressure. For reptiles, establishment probability reached 10% at 6,000 imported individuals, 25% at 46,000, and 50% at 369,000. Amphibians did not exceed the establishment‐probability thresholds. Using updated bibliographic sources, a total of 61 reptiles and five amphibians have been reported as being established in Florida. However, our models predict that around 99 reptiles (95% CI: 71.06–147.32) and 6 amphibians (95% CI: 5.41–9.15) could be established in the state based on import volumes alone. Our findings highlight the relevance of integrating predictive modeling, law enforcement data, and decision-making to conduct risk assessments to guide prevention, control, and vigilance efforts. Although the observed patterns are not causal and explain only part of the variation, they provide a basis for identifying broad trends and guiding future research and monitoring efforts.

Controlling propagule pressure is essential to reducing the risk of establishing non-native species, due to its strong influence on the likelihood that introduced individuals survive, reproduce, and overcome demographic and environmental challenges in novel habitats (Simberloff, 2009; Von Holle and Simberloff, 2005). Non-native species can arrive in new areas through various natural pathways, such as animal vectors, wind dispersal, and extreme weather events like hurricanes (Censky et al., 1998; Viana et al., 2016). However, non-natural pathways, like the legal and illegal trade of wildlife and ornamental plants, remain the most significant drivers of non-native species establishment (Bradie et al., 2013; Copp et al., 2010; Pyšek et al., 2015). These pathways pose a serious threat to native biodiversity, often due to intentional or accidental releases by sellers or consumers. Such releases, and their success at establishment, are frequently influenced by the economic and biological characteristics of the traded species (Stringham and Lockwood, 2018). Thus, mitigating propagule pressure, especially from human-mediated pathways, is important for preventing biological invasions and protecting native biodiversity.

In the context of wildlife, various factors such as native range size, dietary breadth, reproductive rate, tolerance to environmental change, and a prior history of establishment elsewhere may predict the successful establishment of non-native species (Duncan et al., 2001; Forsyth et al., 2004); however, the number of individuals introduced has been identified as one of the most powerful predictors of establishment success, because higher numbers of released individuals increase the probability of population establishment (García-Díaz et al., 2015). Still, estimating the risk of biological invasions presents challenges as risk assessments are multidimensional, often with many data gaps, and changes in trade dynamics affect precision (Catford et al., 2009; Hulme, 2009). For that reason, it is necessary to apply new methodologies to predict stages of invasion and to manage them effectively, particularly those focused on identifying patterns (Kueffer et al., 2013). While many studies highlight propagule pressure as an important factor for estimating invasion potential, its predictive power increases when it is analyzed alongside other contextual factors, such as species traits and ecosystem characteristics (Novoa et al., 2020).

This is particularly important because the relationship between propagule pressure and establishment success is not linear, and the same level of pressure can lead to establishment in some species and failure in others (Duncan et al., 2014). Nevertheless, quantitative data on animal introductions, such as the number of individuals entering new environments, are not always available, limiting the estimation potential of propagules (Novoa et al., 2020). It is essential to develop projects specifically focused on gathering and analyzing this type of information, particularly in regions severely affected by invasive animals. Such efforts could improve our understanding of introduction dynamics and facilitate the identification of patterns that underlie successful invasions.

Florida hosts the greatest number of established non-native herpetofauna species globally (Fujisaki et al., 2015; Krysko et al., 2016; Liu et al., 2025). A total of 180 reptiles and amphibians had been reported as introduced by 2016, of which 63 had become established (Krysko et al., 2016). This pattern is largely driven by the state’s tropical climate, ecological heterogeneity, land cover, and the large pet trade industry, which have facilitated the establishment of numerous species (Fujisaki et al., 2010, Fujisaki et al., 2015). These non-native species are causing severe impacts on native biodiversity (Dorcas et al., 2012; Mazzotti et al., 2015; Tennessen et al., 2016), as well as on agricultural production and private property (Claunch et al., 2025; Searcy et al., 2023). As a result, the economic costs associated with their mitigation, prevention, and control are substantial (Alvarez and Solís, 2018). Thus, it is crucial to invest more resources in preventive strategies focused on introduction pathways and risk profiling, which are generally more cost-effective and efficient than the eradication of established species (Lieurance et al., 2023).

In this study, we treated importation data as proxies for propagule pressure because direct data on release or escape events are unavailable for most wildlife trade. Specifically, we analyzed the spatiotemporal dynamics of reptile and amphibian imports in Florida using data from the United States Fish and Wildlife Service’s (USFWS) Law Enforcement Management Information System (LEMIS) from 1999 to 2018. To do so, we assessed whether the number of traded individuals has declined in recent years, particularly for species with a high potential for establishment or those subject to possession prohibitions. Then, we evaluated whether import volumes are associated with species establishment and estimated species-specific establishment probabilities using a probabilistic model over the study period. Our findings offer valuable insights into how trade intensity interacts to shape the likelihood of establishment, highlighting the critical role of propagule pressure as a predictor of invasion success. These results underscore the need for early detection strategies and proactive interventions, particularly in regions facing high introduction pressure, to enhance the effectiveness of invasive species management.

Data from 1999 to 2018 related to importations of animals coming across commercial ports in Florida were provided by the USFWS LEMIS database (Figure 1). Which records international wildlife movements through any official point of entry or exit of the country, including sea, air, and land ports. Also, it can include seizures made by USFWS Office of Law Enforcement’s special agents (Goodman and Kolby, 2024). In this study, we retained only records corresponding to live-animal imports and excluded shipments coded as seizures or confiscations. Because all live international herpetofauna imported into Florida entered by air, we restricted the dataset to international airports. For reptiles, Miami International Airport accounted for 99.90% of records, followed by Tampa (0.09%) and Orlando (0.0001%); for amphibians, Tampa accounted for 50.90%, Miami for 49.09%, and Orlando for 0.0004%. It is important to note that although LEMIS records the number of live animals imported through Florida’s ports of entry, these data do not necessarily represent the number of individuals that ultimately remained within the state.

We included all live imports, regardless of whether shipments originated in native-range countries or involved specimens previously exported from the United States and subsequently re-imported through international trade. Such records reflect secondary trade flows rather than primary introductions from native ranges but nonetheless represent individuals entering Florida’s commercial system and thus potential sources of release or escape. Species native to Florida and broadly distributed across the state were removed from the import database. Although most taxa in the LEMIS database were identified only to the species level, Trachemys scripta was consistently reported at the subspecies level (T. s. elegans and T. s. scripta). We kept these two subspecies as separate analytical units because this distinction is biologically relevant in Central and South Florida, where neither species is native, and may reflect different introduction pathways into local ecosystems.

Since this dataset includes multiple taxonomic groups, we first filtered the records to retain only amphibians and reptiles. All subsequent analyses were applied within R software version 4.3.2 (R Core Team, 2023). Statistical significance levels were categorized as very strong (p < 0.001), strong (p < 0.01), moderate (p < 0.05), weak (p < 0.10), or none (p > 0.10). These categories were interpreted in conjunction with effect sizes, confidence intervals, and sample size, following the criteria for their interpretation (Muff et al., 2022c, 2022a, 2022b).

Updated taxonomic classifications were retrieved using the name_backbone() function from the rgbif package (Chamberlain et al., 2025). We employed the ggplot2 package (Wickham, 2016) to visualize data for different taxonomic categories for both groups, and temporal importation dynamics across the years analyzed. An Ordinary Least Square linear regression model was used to determine the trend in importation across years. We consulted the official regulations in Florida that govern the possession, importation, transportation, sale, and release of non-native species within the state (Chapter 68-5, F.A.C.) to obtain the list of reptiles and amphibians prohibited during the analyzed years. We only used species with prohibitions between 1999 and 2018 to understand whether regulations affected trade dynamics into the state. It is important to note that the following analyses were conducted separately for amphibians and reptiles.

Established species

We conducted a bibliographic review using multiple online scientific search platforms and digital libraries, including Google Scholar, ScienceDirect, Scopus, SciELO, and Semantic Scholar. The search included terms such as “invasive species,” “established species,” “non-native species,” and “alien species” combined with “Florida” using the Boolean operator “AND”. This review was supplemented with citizen science and expert reports on invasive species, particularly from EDDMapS (2025). The goal was to determine which species from our dataset are currently established in Florida, allowing us to check the relationship between propagule pressure and establishment success. Although some species are reported as established in different years in literature, these records may reflect separate establishment events, distinct introduction pathways, or uncertainty in historical records. However, because available data do not allow us to analyze every independent event, we treat them as established or not established. Non-parametric Wilcoxon tests were performed to compare the total number of imported individuals reported per species between established and non-established species.

We fitted logistic regression models (binomial family, logit link) with establishment status as the binary response variable (1 = established, 0 = not established) and propagule pressure (number of imported individuals per species) as the predictor. This modeling approach served two purposes. First, to evaluate and validate whether propagule pressure is a reliable predictor of establishment probability, model fit was assessed using discrimination (Area Under the Curve, AUC), calibration regression (intercept and slope), and DHARMa residual diagnostics (uniformity and outlier tests), all performed with the DHARMa package (Hartig, 2016). Second, the logistic regression models were used to provide a management-oriented visualization. For the latter, we used a log10-transformation of the predictor to stabilize the scale and plot predicted probabilities across the observed range of import volumes. Horizontal reference lines were added at 10%, 25%, and 50%, and the corresponding propagule thresholds were calculated by inverting the fitted link function.

Establishment probability

We applied the probabilistic approach developed by Leung et al. (2004), and extended by Wonham et al. (2013) to multi-specific systems. We included only data from individuals identified to the species level to avoid overestimating establishment probabilities. This model incorporates the number of individuals imported into the state, the frequency of each importation event, and the biological susceptibility of each species to establishment. We assumed independence between these importation events, each one acts as a potential establishment unit. The probability of establishment per species (P E,s) should be interpreted as cumulative over the study period rather than as time‐varying annual estimates, and was modeled following:

Where:

R s: Number of importation events recorded for the species s.

N r,s: Number of individuals of species s imported in event r.

p s: Probability of establishment of a single individual of the species s.

c: Coefficient of Allee effect.

The probability that a single individual contributes to establishment (p) after importation was modeled under three scenarios: low (0.0001), medium (0.001), and high (0.01). These values represent the probability that any given individual contributes to establishment after importation, corresponding to approximately 0.01%, 0.1%, and 1% per individual, respectively. Although species are expected to differ considerably in per capita establishment probabilities due to variation in ecology, behavior, habitat suitability, and introduction dynamics, we used a general range of hypothetical values to conduct sensitivity analyses. This approach follows common practice when species-specific estimates are unavailable, exploring ranges of plausible parameters rather than fixed empirical values (Wonham et al., 2013). Also, the Allee effect occurs when a population is small because its growth or survival depends on the density of other individuals with which to reproduce; without sufficient numbers, the population cannot increase (Stephens et al., 1999). In this case, the value of the Allee effect represents the positive density dependence of the minimum density for reproduction and establishment. This effect was modeled using the following approaches, according to Leung et al. (2004): Without Allee effect (1), moderate Allee effect (1.5), and strong Allee effect (2). These scenarios allow establishment probability to vary across propagule sizes, with small propagules having a reduced chance of overcoming Allee effects and large propagules being more likely to establish. We ran the formula to explore all possible combinations between the probability of establishment and the coefficient of the Allee effect, considering a probability of establishment ≥ 0.5 as the threshold for classifying species as potential invaders and as a filter to include only those species with a moderate to high likelihood of establishment in the estimation analyses (Table 1).

Where:

E SE: Expected number of established species.

S: Total number of imported species analyzed.

P E,s: Probability of establishment of the species s.

Then, based on the expected number of established species obtained from the different parameter combinations, we determine the risk of being established by averaging the results of all models. To evaluate the predictive power of each model, we again fitted binomial logistic regression with a logistic link, using species establishment status as the response variable and the mean establishment probabilities for each scenario as predictors (Table 2). We defined the best model using the Akaike Information Criterion (AIC). Since some models showed low AIC values with differences less than 5 (AIC < 5), this difference suggests moderate support that the performance of the models is not different (Burnham et al., 2011; Burnham and Anderson, 2004). Thus, we compared the AUC applying the DeLong test to calculate whether the difference between their areas under the curve was statistically significant among models, using the package pROC (Robin et al., 2011). We chose this analysis because it helps to compare the predictive ability of two models, and we comply with the usage criteria by not applying them to nested models (Delong et al., 1988; Demler et al., 2012).

Between 1999 and 2018, a total of 12,738,179 reptiles were imported through commercial ports in Florida. Of these, 10.63% were identified only to genus level, 0.006% to family, and 0.0002% to order, whereas the remaining 89.36% were identified to species level. Also, the order Squamata accounted for the vast majority (94.5%), followed by Testudines (5.2%), and Crocodylia (0.27%). Taxonomically, Squamata exhibited the highest diversity, comprising 55 families, 389 genera, and 1,098 species. Testudines included 11 families, 71 genera, and 151 species of turtles, while Crocodylia was represented by two families, three genera, and seven species. The most frequently reported species were green iguana (Iguana iguana; 27.1%), ball python (Python regius; 9.7%), Chinese water dragon (Physignathus cocincinus; 5.8%), central bearded dragon (Pogona vitticeps; 5.1%), and Asian grass lizard (Takydromus sexlineatus; 4.3%). A typographical error was also identified in the name Seymoviua margaritiferus (10 individuals), whose taxonomic identity could not be confirmed.

A total of 4,585,986 individual amphibians were reported. Of these, 23.23% were identified only to genus level and 0.02% to family, whereas the remaining 76.75% were identified to species level. The order Anura represented the majority of the imports (80.8%), followed by Caudata (17.6%), and Gymnophiona (0.05%). Anura included 30 families, 107 genera, and 266 species. Caudata comprised six families, 19 genera, and 40 species, while Gymnophiona was represented by three families, four genera, and five species. The most frequently imported taxa were African dwarf frog (Hymenochirus boettgeri; 12.1% of the total), African clawed frog (Xenopus laevis; 10.9%), red-eyed tree frog (Agalychnis callidryas; 7.1%), Australian green tree frog (Litoria caerulea; 5.6%), and oriental fire-bellied toad (Bombina orientalis; 4.5%). An additional 1.5% were only identified at the class level as amphibians, with no further taxonomic identification.

Importation trend

We detected significant negative trends in the number of imported individuals for both reptiles and amphibians between 1999 and 2018 (Figure 2A). For reptiles, the linear regression model showed evidence of a very strong negative effect of time on the number of individuals imported (SE = 4,163; t = –7.863; p < 0.001, R 2 = 0.7745), decreasing by 32,731 individuals per year. In the case of amphibians, the annual decline showed strong evidence of a negative temporal trend (SE = 3,214; t = –3.160; p = 0.005, R 2 = 0.3568), but the yearly decrease in the number of animals was lower (10,155 individuals), and the proportion of variance explained was 42% lower.

We found significant negative annual trends in the importation of six prohibited species (Figure 2B). Reticulated python (P. reticulatus) exhibited a reduction of approximately 1,739 individuals per year with very strong evidence of a decline (SE = 0.36; t = –4.78; p = 0.0002; R 2 = 0.588). Similarly, the Nile monitor (Varanus niloticus), showed an annual decrease of 1,505 individuals (SE = 0.34; t = –4.39; p = 0.0004; R 2 = 0.517). The green anaconda (Eunectes murinus) experienced a strong evidence of a decline, averaging 3,456 fewer individuals per year (SE = 0.92; t = –3.75; p = 0.0019; R 2 = 0.484). In contrast, the amethystine python (Morelia amethystinus; SE = 0.13; t = –2.47; p = 0.024; R 2 = 0.264) and the North African rock python (P. sebae; SE = 0.30; t = –2.25; p = 0.044; R 2 = 0.296) showed moderate evidence of decline, with yearly reductions of 329 and 666 individuals, respectively. Finally, the Indian python (P. molurus) exhibited weak evidence of a decline, corresponding to 1,082 fewer individuals per year (SE = 0.55; t = –1.98; p = 0.073; R 2 = 0.263). It is important to note that imports of the amethystine python, the reticulated python, and the Nile monitor were still occurring in 2018, despite being prohibited since 2010.

Established species

We identified a total of 66 non-native amphibian and reptile species established in Florida based on the bibliographic review, comprising five amphibians and 61 reptiles (Supplementary Table 1). Most of the data came from a crucial review of established species present in Florida published in 2016 (Krysko et al., 2016), except for the rainbow boa (Epicrates cenchria), the western clawed frog (Xenopus tropicalis), and the Rio Cauca caecilian (Typhlonectes natans) which were reported as established later (Sheehy et al., 2025; Asher and Krysko, 2024; Goodman et al., 2021). Allison’s anole (Anolis allisoni) is a special case, although it was first reported as introduced in Florida by Krysko et al. (2015) and was included in the review of non-native species by Krysko et al. (2016), it wasn’t until later studies that its status as an established species in the state was confirmed (Morris et al., 2021). Among reptiles, the list spans three orders (Crocodylia, Testudines, and Squamata), 24 families, 41 genera, and 61 species. The established amphibians include the greenhouse frog (Eleutherodactylus planirostris), the Cuban treefrog (Osteopilus septentrionalis), the cane toad (Rhinella marina), the West African clawed frog (X. tropicalis), and the Rio Cauca caecilian (T. natans). Of these, only the cane toad was reported in the LEMIS database, and the Rio Cauca caecilian was not reported directly. However, only 442 records were identified at the family level and 221 at the genus level.

For reptiles, established species had a significantly higher number of recorded individuals in the import dataset compared to non-established species, where the difference showed very strong evidence (Wilcoxon rank-sum test, W = 7650.5, p < 2.2 × 10 -16), while for amphibians, the difference was no evidence (W = 53, p = 0.256). Reptiles had a strong positive association between import numbers and establishment (β Number = 1.22 ± 0.141; z = 8.66; P < 0.001). The model explained 26.42% of the variation (Nagelkerke’s pseudo-R 2). Performance was good (AUC = 0.871), DHARMa diagnostics indicated no issues with uniformity, dispersion, or outliers (KS p = 0.602; dispersion p = 0.864; outliers p = 0.210). For amphibians, logistic regression showed no association between import numbers and establishment (β Number = 0.84 ± 0.83; z = 1.013; P = 0.311), explaining 8.26% of the variation (Nagelkerke’s pseudo-R 2). Discrimination was high (ROC-AUC = 0.83), and residual diagnostics indicated no departures: DHARMa uniformity (KS test p = 0.94), dispersion (p = 0.87), and outliers (p = 0.5).

The reptile model indicated that the probability of establishment reached approximately 10% at ~6,000 individuals, 25% at ~46,000 individuals, and 50% at ~369,000 individuals imported per species (Figure 3A). In contrast, amphibians did not exceed the establishment‐probability thresholds across the observed range of importation volumes. The only established amphibian represented in the regression is the cane toad, as it was the only species recorded in the LEMIS dataset (Figure 3B).

Establishment probability

Based on the mean probability of establishment calculated across all models, the reptiles with the highest establishment risk in Florida were the Amazon lava lizard (Tropidurus occipitalis, 77.28%), the Chapa mountain dragon (Diploderma chapaense; 65.93%), the green iguana (63.54%), the Hispaniolan masked curlytail lizard (Leiocephalus personatus; 62.63%), the northern grass lizard (Takydromus septentrionalis; 62.60%), the steppe runner (Eremias arguta; 62.55%), the northern curlytail lizard (Leiocephalus carinatus; 61.35%), the banded sea krait (Laticauda semifasciata; 58.24%), and the Chinese water dragon (Physignathus cocincinus; 57.22%; Supplementary Table 2). Among these, only the green iguana and the northern curlytail lizard are currently established in Florida. In the case of amphibians, the Boulenger’s dwarf clawed frog (Hymenochirus boulengeri; 74.64%), the African dwarf frog (Hymenochirus boettgeri; 71.30%), the Hong Kong warty newt (Paramesotriton hongkongensis, 65.13%), the red-bellied toad (Melanophryniscus stelzneri; 62.58%), the American bullfrog (Lithobates catesbeianus; 61.92%), the African clawed frog (Xenopus laevis; 60.51%), the Congo dwarf clawed frog (Hymenochirus curtipes; 59.86%), the oriental fire-bellied toad (Bombina orientalis; 59.76%), the Chinese fire-bellied newt (Cynops orientalis; 58.64%), and the Andean toad (Rhinella spinulosa; 54.40%) showed the highest probabilities of establishment in the state (Supplementary Table 3). However, the American bullfrog occurs naturally in northern and central Florida. In contrast, the African clawed frog is not currently considered established in the state; for many years, some Florida records attributed to this species were confused with the West African clawed frog, which is the species documented as established.

The estimated number of potential established species in Florida varied substantially (Table 1). For reptiles, predictions ranged from 0 species under the most conservative scenario (Model 1) to 182.23 species under the most permissive scenario (Model 9). Models 7, 8, and 9 showed lower AIC values (350.19, 346.96, and 345.45, respectively). DeLong’s test showed that model 7 had a significantly higher AUC than model 8 (ΔAUC = 0.00349; Z = 2.28; p = 0.0226) and model 9 (ΔAUC = 0.00631; z-value = 2.33; p-value = 0.0196). This model estimates 99.56 established species in Florida (95% confidence interval: 71.01-146.83). The DHARMA residuals showed a good fit (KS test p=0.798, Dispersion test p=0.8, Outlier test p=0.34).

For amphibians, estimates ranged from 0 (Model 1) to 116.52 established species (Model 9) across models (Table 1). Differences in AIC among models were less than two, and pairwise DeLong tests showed no significant differences for all models (p-value > 0.1). Therefore, model 4, which estimated 5.99 established species (95% confidence interval: 5.40-9.19), was selected because it offered a good balance between AIC (25.583), AUC (0.671), and Nagelkerke’s pseudo-R 2 (11.2%) compared to other models. The DHARMA residuals indicated a good fit (KS test p= 0.946; Dispersion test p= 0.952; Outlier test p= 0.91).

Florida plays a vital role as a central hub for the importation and redistribution of exotic wildlife across the United States (Sinclair et al., 2021), mainly because it is home to major ports of entry into the United States and supports a thriving captive wildlife industry (Mazzotti and Harvey, 2012). According to our results, Squamata was the most heavily traded reptile order, consistent with its position as the most species‐rich reptile group globally, and between 1999 and 2018, the state received 10.73% of all reptile species in the world (Uetz et al., 2025), and accounted for 33.86% of the global trade in reptiles (Marshall et al., 2020). Regarding amphibians, Anura dominated imports, coinciding with its status as the most diverse amphibian order worldwide, and 4.68% of all species traded worldwide entered Florida (Frost, 2024). Given the established link between import volumes and propagule pressure (García-Díaz et al., 2015), Florida represents a hotspot for potential future invasions, driven by the high biodiversity and substantial proportions of exotic animals entering the state each year. These broad patterns also provide a framework for examining how individual species and market dynamics shape invasion risk within the state.

One example is the green iguana, a foundational species in the Florida wildlife trade, accounting for 27% of all reptiles traded in the state. Trade in this exotic species has declined, possibly because of reduced demand (Jones, 2025; Robinson et al., 2015). However, as mentioned by these same researchers, the overall decrease in reptile imports, including the green iguana, may also be linked to broader factors, including stricter international regulations, especially for those species within the CITES Appendix II, and the growth of captive breeding in consumer countries, with the United States maintaining particularly high levels of captive breeding. Florida’s long-standing role as one of the nation’s primary hubs for commercial harvest, trade, and importation of herpetofauna, supported by numerous dealers, breeders, and major ports of entry (Enge, 2005), offers more options to get exotic animals without the need to import individuals from other countries.

This situation also applies to amphibians, mainly because their transport requirements are more stringent than those of other taxa. Historically, the amphibian trade was susceptible to even slight fluctuations in trip duration, temperature, humidity, ventilation, and animal density, which can quickly lead to mortality, stress, and disease (Mendyk, 2023). In this context, a greater availability of local breeders, wholesalers, and holding facilities could facilitate supply and reduce transportation costs by minimizing transit times and environmental fluctuations. Nevertheless, a more comprehensive analysis is needed to fully understand the underlying causes driving the recent overall decline in exotic wildlife importations to Florida for amphibians and reptiles.

The consistent declines in importations observed for six species restricted under Chapter 68-5, F.A.C. in 2010 indicate the possible impact that targeted legislation can have in reducing the influx of high-risk non-native reptiles into Florida. The significant negative trends suggest that regulatory prohibitions, when effectively implemented and enforced, can quickly reduce legal import volumes of these species on commercial channels. Such reductions are directly relevant to propagule pressure theory, as decreasing the number of individuals entering the state is expected to lower the likelihood of establishment and any subsequent ecological impacts. Additionally, preventing the introduction of new individuals into already established populations can limit genetic diversity and, as a result, reduce the adaptive potential and expansion ability of invasive species (Dlugosch and Parker, 2008; Lockwood et al., 2005; Rius and Darling, 2014). However, declines in imports could also reflect shifts toward in-state captive breeding, increased reliance on undocumented imports, and stricter international regulations (Jones, 2025; Robinson et al., 2015). Moreover, the weaker responses observed in some species suggest that the effectiveness of such measures can vary among different taxa, possibly due to differences in pre-ban trade volumes, the availability of special possession permits (Conditional/Prohibited/Nonnative Species Permit – CSP), alternative sourcing pathways, or the presence of established captive populations within the state. Although these patterns are promising, they should be interpreted cautiously, given remaining information gaps that prevent attributing the observed declines to any single factor or set of mechanisms driving changes in propagule pressure.

Regarding the probability of establishment, results should be interpreted with caution as well. Although propagule pressure was defined as one of the best variables for estimating herpetofauna establishment probability in Florida (Van Wilgen and Richardson, 2012), we used data on importation volume and frequency as proxies for propagule pressure, and these metrics do not directly capture release or escape events, and simulations parameterized with those inputs can still carry nontrivial uncertainty; knowing both components, such as propagule size and introduction frequency, tends to reduce, but not eliminate, uncertainty (Stringham and Lockwood, 2021). Moreover, estimating establishment probability from historical data has several limitations. Firstly, importation data can be biased due to misidentification by authorities, mistyped numbers, incorrect code selections, or multiple identical declarations of the same importation (Goodman and Kolby, 2024; Weissgold, 2024). Secondly, apparent associations between predictors and invasion success often reflect unmeasured confounding variables, including human‐mediated release probabilities and market dynamics in the pet trade, factors that have been shown to covary with import volume and retail prices (Stringham and Lockwood, 2018). Thirdly, failing to incorporate the spatial distribution of suitable habitat climatic matching, time lags between introduction and detection, interstate redistribution after importation, or accidental introductions via stowaways can obscure key dimensions of the invasion process. Fourthly, even below the Allee-effect threshold, stochasticity in introduction events can yield a slight but real chance of persistence and growth (Wittmann et al., 2014).

Another point is that Florida is a hub for the exotic pet trade in the country (Sinclair et al., 2021). Thus, our predictions may be overestimated because the exact number of animals sent on to other states remains unclear. Therefore, it is necessary to connect our database with data from pet stores and other local distributors of exotic wildlife to estimate the actual number of animals present in Florida during the years analyzed. Given this situation, one opportunity is to confirm how the regional dynamics of the exotic wildlife trade vary across different regions of the state and how the local demand for exotic pets correlates with the number of established species, as those non-native animals tend to be concentrated more intensely in specific areas (Searcy et al., 2023).

At the same time, parameters show that establishment predictions are highly sensitive to assumptions about per-individual establishment probability and Allee effects, with the expected number of established species spanning two orders of magnitude across model combinations and the best logistic fits occurring under higher p-values and stronger Allee coefficients. This pattern is consistent with the theory: establishment risk rises steeply with propagule pressure once release sizes and event frequency overcome demographic stochasticity and Allee thresholds, the essence of the risk–release relationship (Duncan et al., 2014; Leung et al., 2004; Stringham and Lockwood, 2021). Yet mismatches between high predicted risk and observed establishment for several taxa underscore that propagule pressure is necessary but not sufficient; integrating species traits and recipient-environment filters improves inference (Cassey et al., 2018; García-Díaz et al., 2015). From a management perspective, the strong sensitivity in the number of established species reinforces that reducing import volumes and event frequency (e.g., via trade restrictions and enforcement) should yield disproportionate risk reductions, especially before populations surpass Allee thresholds; this aligns with evidence that prevention is generally more cost-effective than post-establishment control (Epanchin-Niell, 2017) and with documented ecological impacts when introductions are not curtailed, such as the green iguana (Claunch et al., 2025; Krysko et al., 2007) or the Burmese python in Florida (Dorcas et al., 2012).

The species included in the import dataset have different ecological requirements, allowing some species to have a greater opportunity to establish in the state, even when the overall probability of establishment is low. Our results support this idea: for established reptiles, probabilities ranged from the highest average value for I. iguana (63.54%) to the lowest, Anolis cristatellus (1.09%), and more than 1,100 species have probabilities above the lowest estimated for an already-established species. For amphibians, R. marina (9.40%) ranks 221st among species likely to establish themselves. These extremes reflect the variability in establishment potential among species within each group. Moreover, when we compare the number of species predicted to be established by the best-performing model with the number currently documented as established, the gap is significant for reptiles, where the lower confidence interval is 10 species above the actual number of established reptiles as of 2025.

Part of this discrepancy may reflect misidentifications; mistaken identity has been confirmed for at least one cryptic taxon in Florida (Goodman et al., 2021), raising the possibility that additional imported or established species are misreported, as in the case of the cane toads (Rhinella spp.), whose Florida populations were historically referred to as Rhinella marina (Krysko et al., 2016), but some historical records suggest that founders may have originated from regions occupied by Rhinella marina and R. horribilis (King and Krakauer, 1966). Also, genetic lineages of some established species, such as Caiman crocodilus, have only recently begun to be reported accurately in Florida (Parks et al., 2024), and some genetic lineages have been elevated to the taxonomic status of new species, such as the case of Boa constrictor and B. imperator (Hynková et al., 2009), leaving us in doubt about the genetic and morphological identity of several non-native species in Florida. Strengthening verification through routine genetic barcoding or genomic assays, rigorous morphological diagnostics, and deposition of voucher specimens is essential to confirm the identity of non-native populations.

At the same time, this discrepancy may indicate that additional non-native species are already present in ecosystems but have not yet been reported, an opportunity to strengthen Early Detection and Rapid Response (EDRR) efforts. Online platforms developed to track and map invasive species, such as EDDMapS (EDDMapS, 2025), show that new introduced species, such as Antaresia maculosa, Pelusios castaneus, Gongylophis colubrinus, Chlamydosaurus kingii, and Python breitensteini, have been reported during the last 10 years, indicating that new non-native species are still being introduced and potentially could become established in Florida. EDRR can improve public engagement and materially aid invasive-species control. Sustained proactive management, coupled with outreach to improve identification and reporting, will be critical to mitigate ecological impacts and limit spread within Florida and into other suitable regions.

On the other hand, differences in estimated establishment probability between established and non-established species for both amphibians and reptiles were primarily driven by variation in propagule size and introduction frequency, underscoring the key role of propagule pressure in invasion success (Cassey et al., 2018; García-Díaz et al., 2015; Van Wilgen and Richardson, 2012). However, the significance level was much lower for amphibians, likely due to the small number of established species in this group. Additionally, the modest pseudo-R 2 values suggest that, while wildlife importations as propagule pressure is necessary, it alone do not fully explain the results; life history, introduction pathways, ecological traits, and ecosystem characteristics are also crucial factors (Blackburn et al., 2016; Mahoney et al., 2015; Catford et al., 2009).

In Florida, previous work has shown that introduction effort, measured as the number of release events, is a strong predictor of establishment success (Van Wilgen and Richardson, 2012), a pattern also reported across multiple taxa and regions worldwide (Hayes and Barry, 2008). Although this information is crucial for managing introduced species, no information was available on how to control or prevent these release events. Thus, our results can be used as a practical decision-support tool to anticipate which species may exceed critical thresholds of establishment risk in the future, thereby providing taxon-specific benchmarks that directly inform risk assessment and management strategies. This type of information is particularly valuable for prioritizing high-risk species, enabling early control or eradication efforts before invasions fully materialize (Rouget et al., 2016). This is particularly relevant in major commercial ports, where responsible authorities must act as critical filters, determining which species and in what quantities are allowed to enter the state. Nevertheless, improving these assessments will require the incorporation of more detailed information on introduction pathways and dispersal routes, as these factors strongly modulate invasion risk (Blackburn et al., 2009; Wilson et al., 2009).

From a management perspective for both taxonomic groups, it is necessary to integrate variables related to climate suitability, together with import data. Specifically, considering habitats within both the native and introduced range to identify a greater number of limiting factors present in recipient habitats that are crucial for the survival of newly introduced species (Romer et al., 2025). In the case of amphibians, the relatively low number of established species analyzed limits the precision of these results, as they may be overestimating the importance of these factors, which, although potentially critical, would likely have a lower degree of influence if the number of species were increased.

Many variables have been used as risk profiles to determine which species are more likely to establish in Florida conditions (Bomford et al., 2009; Fujisaki et al., 2010, Fujisaki et al., 2015; Mazzotti and Briggs-Gonzalez, 2015; Reed, 2005). These variables are generally used to assess and predict their influence on the establishment of non-native species, and they could be analyzed alongside import data in order to increase predictive power. However, despite their broad applicability across taxonomic groups, their effects on establishment probability can vary, with the influence of specific variables often shifting as the taxonomic level or habitat scope narrows. Therefore, while these risk classification variables provide an initial overview of potential risks across taxa, once particular species are identified, it becomes necessary to refine the analysis at a finer scale. Trait-based classification can serve not only as a screening tool but also as a guide for locating non-native populations. When combined with propagule pressure, environmental suitability, and pathway-specific information, trait-based approaches enable a more spatially explicit assessment of invasion risk, helping identify habitats and regions within Florida where establishment is most likely. This, in turn, improves the effectiveness of Early Detection and Rapid Response programs. The approach also enables a more accurate evaluation of each species’ individual risk and the real impact of the variables involved.

Our two complementary approaches offer a more integrated understanding of the invasion risk from the herpetofauna trade in Florida. First, detecting significant declines in import volumes, especially for regulated species, indicates that targeted legislation can effectively reduce imports that are directly or indirectly linked to propagule pressure, although its success varies across taxa. Second, probabilistic establishment models highlight that propagule pressure, measured by both event frequency and shipment size, is a key but not the only factor influencing establishment success; it also stresses the importance of biological thresholds like the Allee effect in predicting invasion outcomes. Overall, these findings emphasize that limiting importations, enhancing predictive models, and integrating these tools into policy and management of wildlife trade are crucial steps to reduce future invasions and their ecological and economic impacts in Florida.