Providing scientifically defensible evidence and correct calibrated thresholds for risk screening non-native species with second-generation Weed Risk Assessment-type decision-support tools

Abstract

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Risk of invasiveness of non-native fishes can dramatically increase in a changing climate: The case of a tropical caldera lake of conservation value (Lake Taal, Philippines)

“…To date, the calibrated threshold value of 34.5 recorded in this screening of non-native fishes with regard to a tropical volcanic lake of high conservation value is the highest found globally for identifying potentially invasive freshwater fishes (Vilizzi et al 2022b). This large variation in threshold values for different risk assessment areas (Vilizzi et al 2022b) may be attributed to factors such as number of translocated species, hydrological characteristics and climate conditions.…”

“…To date, the calibrated threshold value of 34.5 recorded in this screening of non-native fishes with regard to a tropical volcanic lake of high conservation value is the highest found globally for identifying potentially invasive freshwater fishes (Vilizzi et al 2022b). This large variation in threshold values for different risk assessment areas (Vilizzi et al 2022b) may be attributed to factors such as number of translocated species, hydrological characteristics and climate conditions. Additionally, the dramatic increase in the number of high-risk, and especially very high-risk species, under predicted climate change conditions (Table 2) is a warning sign of the high susceptibility of Lake Taal to further invasions by non-native fishes.…”

“…As a final note, this risk screening study for Lake Taal using the AS-ISK decision-support tool is to be regarded as the most currently valid for the Philippines. In this respect, the recent paper by To et al (2022), which aimed to evaluate the potential invasiveness of Siluriform species in the same risk assessment area using the AS-ISK, has some inconsistencies regarding the implementation of standard analytical protocols, which are discussed in Vilizzi & Piria (2022). The present “correction” is important, therefore, in setting the standard for the risk screening/assessment process of non-native (invasive) species in the Philippines.…”

“…To achieve a valid screening, a standard protocol was followed (Vilizzi et al 2022a) whereby the assessor must provide for each question a response, confidence level and justification (e.g. Vilizzi & Piria 2022), with two score outcomes (BRA and BRA+CCA). Scores < 1 suggest a “low risk” of the species being or becoming invasive in the risk assessment area, whereas scores ≥ 1 indicate a “medium risk” or a “high risk”.…”

“…Scores < 1 suggest a “low risk” of the species being or becoming invasive in the risk assessment area, whereas scores ≥ 1 indicate a “medium risk” or a “high risk”. The distinction between medium and high risk is defined using a calibrated threshold obtained by Receiver Operating Characteristic (ROC) curve analysis (Vilizzi et al 2022a, b). An additional ad hoc threshold was used to distinguish a “very high risk” category within fishes classified as high risk (as per Britton et al 2011) to help prioritise allocation of resources for comprehensive (follow-up) risk assessment (Copp et al 2016a, Vilizzi et al 2022a).…”