Comparable temperature-dependent predatory impacts of two invasive crayfish, Pontastacus leptodactylus and Pacifastacus leniusculus

“Invasive species are a major driver of biodiversity loss worldwide (Bellard et al. 2016; Doherty et al. 2016; Blackburn et al. 2019; IPBES 2019), particularly within freshwaters (Sala et al. 2000; Cox and Lima 2006) which are typically heavily invaded (Strayer 2010).”

“…than terrestrial and marine realms (Darwall et al. 2018; Tickner et al. 2020) as a result of multiple threats including invasive non-native species, climate-change, over-exploitation, destruction/alteration of habitat and pollution (Strayer and Dudgeon 2010; Reid et al. 2019; Tickner et al. 2020).”

“Invasive species are a major driver of biodiversity loss worldwide (Bellard et al. 2016; Doherty et al. 2016; Blackburn et al. 2019; IPBES 2019), particularly within freshwaters (Sala et al. 2000; Cox and Lima 2006) which are typically heavily invaded (Strayer 2010).”

“Both categorical and flexible models were fitted to the data using the Lambert W function (Bolker 2008).”

“…than terrestrial and marine realms (Darwall et al. 2018; Tickner et al. 2020) as a result of multiple threats including invasive non-native species, climate-change, over-exploitation, destruction/alteration of habitat and pollution (Strayer and Dudgeon 2010; Reid et al. 2019; Tickner et al. 2020).”

“Functional responses were modelled using maximum likelihood estimation (MLE, v.1.0.25.1; Bolker 2023) and Rogers’ (1972) Random Predator Equation to account for prey depletion: In which, N E represents the number of prey eaten, N 0 is the initial density of prey, a is the attack parameter, h is the…”

“As well as consumer response to different contexts like temperature, prey response should also be incorporated into impact assessments for more accurate impact predictions (Kumschick et al. 2015; Urban et al. 2016; South et al. 2022).”

“Thus, to reduce future invasive impact, an emphasis should be on pre-emptively identifying potential new damaging invaders and implementing proactive policy to prevent invasions (Strayer 2010).”

“Invasive species are a major driver of biodiversity loss worldwide (Bellard et al. 2016; Doherty et al. 2016; Blackburn et al. 2019; IPBES 2019), particularly within freshwaters (Sala et al. 2000; Cox and Lima 2006) which are typically heavily invaded (Strayer 2010).”

“Frustratingly, invasive species impacts are typically observed after invasions are successful (Crooks 2005; Strayer et al. 2006), and eradication of established invasive crayfish remains challenging (Peay 2001; Gherardi et al. 2011; Simberloff 2021).”

“It holds that, invasive species have greater per-capita consumptive effects on resources than natives, and that greater impact is associated with greater per-capita effects (Ricciardi et al. 2013; Dick et al. 2014).”

“Frustratingly, invasive species impacts are typically observed after invasions are successful (Crooks 2005; Strayer et al. 2006), and eradication of established invasive crayfish remains challenging (Peay 2001; Gherardi et al. 2011; Simberloff 2021).”

“This is due to the wide range of introduction sources: aquaculture, ornamental trade, and ballast water release, and relatively low barriers to dispersal within freshwaters (Padilla and Williams 2004; Moorhouse and Macdon-ald 2015; Faria et al. 2025).”

“Invasive species are a major driver of biodiversity loss worldwide (Bellard et al. 2016; Doherty et al. 2016; Blackburn et al. 2019; IPBES 2019), particularly within freshwaters (Sala et al. 2000; Cox and Lima 2006) which are typically heavily invaded (Strayer 2010).”

“Where categorical functional response models (Type II or III) could not be fitted (i.e. P. leniuscu-lus at 9 °C), a flexible model was fitted (Real 1977; Vucic-Pestic et al. 2010b; Pritchard et al. 2017).”

“Invasive species are a major driver of biodiversity loss worldwide (Bellard et al. 2016; Doherty et al. 2016; Blackburn et al. 2019; IPBES 2019), particularly within freshwaters (Sala et al. 2000; Cox and Lima 2006) which are typically heavily invaded (Strayer 2010).”

“As well as consumer response to different contexts like temperature, prey response should also be incorporated into impact assessments for more accurate impact predictions (Kumschick et al. 2015; Urban et al. 2016; South et al. 2022).”

“Frustratingly, invasive species impacts are typically observed after invasions are successful (Crooks 2005; Strayer et al. 2006), and eradication of established invasive crayfish remains challenging (Peay 2001; Gherardi et al. 2011; Simberloff 2021).”

“However, freshwater biodiversity is declining faster than terrestrial and marine realms (Darwall et al. 2018; Tickner et al. 2020) as a result of multiple threats including invasive non-native species, climate-change, over-exploitation, destruction/alteration of habitat and pollution (Strayer and…”

“…and widely introduced in Central Europe through the aquaculture pathway, is data deficient in terms of impact assessment compared to widely distributed invasive species like the Signal crayfish P. leniusculus or Red swamp crayfish Procambarus clarkii (Holdich et al. 2008; Twardochleb et al. 2013).”

“…prey abundance changes with temperature using a resource reproductive qualifier (RRQ) based on the average number of eggs per oviger-ous females at different temperatures as observed by Hynes (1955), whereby: Temperatures observed by Hynes (1955) did not exactly match our temperature treatments.”

“Where categorical functional response models (Type II or III) could not be fitted (i.e. P. leniuscu-lus at 9 °C), a flexible model was fitted (Real 1977; Vucic-Pestic et al. 2010b; Pritchard et al. 2017).”

“Comparative Functional response (FR), which captures density dependent consumption by an invader and compares it to other species, is a commonly used impact assessment (Dick et al. 2017; Faria et al. 2025).”

“Impact was comparable between P. leptodactylus and P. leniusculus at all temperatures as indicated by broadly overlapping Type II FR curves (Bollache et al. 2007; Alexander et al. 2014).”

“Gammarus pulex were used as prey as they are ubiquitous, omnivo-rous keystone species which alter nutrient cycling through leaf shredding and structuring of macro-invertebrate assemblages (Kelly et al. 2002; Navel et al. 2010).”

“Concerningly, non-native P. leptodactylus have been shown to have greater impact on gatherer and shredder invertebrates than P. leniusculus (Jackson et al. 2014).”

“Impact was comparable between P. leptodactylus and P. leniusculus at all temperatures as indicated by broadly overlapping Type II FR curves (Bollache et al. 2007; Alexander et al. 2014).”

“Coupled with the high thermal tolerance of P. leptodactylus (Kir et al. 2025) this suggests a predator–prey asymmetry in thermal responses, which may alter impact (Öhlund et al. 2015; Pinta-nel et al. 2021; Meehan and Lindo 2023).”

“British or cold-adapted Gam-marus pulex populations show reduced reproductive functioning from 10–20 ℃ , and reductions in survival from 15–30 ℃ (Welton and Clarke 1980; Foucreau et al. 2014).”

“Frustratingly, invasive species impacts are typically observed after invasions are successful (Crooks 2005; Strayer et al. 2006), and eradication of established invasive crayfish remains challenging (Peay 2001; Gherardi et al. 2011; Simberloff 2021).”

“The greater impact at 12–17 ℃ is consistent with previous research finding highest FRs at intermediate temperatures (Uiterwaal and DeLong 2020).”

“This can be combined with observed abundances of invaders in different contexts, to give a Relative Impact Potential (RIP), which provides a field contextualised impact assessment with greater predictive power (Laverty et al. 2017; Dickey et al. 2020).”

“Furthermore, at 12 and 17 ℃ FRR values of P. leptodactylus are similar or greater than mean FRR benchmark values for invaders with known high ecological impact (83.36) reported by (Cuthbert et al. 2019).”

“Whilst our study was simplistic and based on arenas without structural complexity which can tend to Type II FR’s (Vucic-Pestic et al. 2010a), we consider impact relative to a known damaging invader thus similar results can be viewed as a proxy for high impact.”

“Gammarus pulex were used as prey as they are ubiquitous, omnivo-rous keystone species which alter nutrient cycling through leaf shredding and structuring of macro-invertebrate assemblages (Kelly et al. 2002; Navel et al. 2010).”

“RIPq was also generated and visualised for Gammarus fossarum using a different measure of reproductive output i.e. the fecundity index (Number of eggs/wet weight of female) provided by (Pöckl 1993) to test broader applications (Figure SI4a).”

“…must also consider temperature-dependent prey response, given asymmetry in predator and prey responses to temperature can alter impact (Öhlund et al. 2015; Pintanel et al. 2021; Meehan and Lindo 2023) for a more holistic, accurate impact assessment (Dickey et al. 2020; South et al. 2022).”

“British or cold-adapted Gam-marus pulex populations show reduced reproductive functioning from 10–20 ℃ , and reductions in survival from 15–30 ℃ (Welton and Clarke 1980; Foucreau et al. 2014).”

“For example, as temperatures increases from 5–15 ℃ , G. pulex show an increase in motility (Vellinger et al. 2012).”

“Consequently, P. leptodactylus will likely be an impactful invader, particularly within lentic European freshwaters, over-predating G. pulex and destabilising broader fresh-water systems and communities in a similar fashion to P. leniusculus (Dunoyer et al. 2014; Galib 2020; Mathers et al. 2020b).”

“…freshwater invaders (Mathers et al. 2020b; O’Hea Miller et al. 2024), for example Signal crayfish ( Pontastacus leni-usculus ) alter aquatic community structure through reduction of benthic fish, salmonid fry and macro-invertebrate abundance (Edmonds et al. 2011; Hold-ich et al. 2014; Galib 2020).”

“It is also important to note that these abundance estimates were based on CPUE which, driven by life history or climatic variables other than temperature, can vary substantially seasonally (Richards et al. 1996; Zimmerman and Palo 2012; Harwood et al. 2025) which could bias our impact estimates.”

“Crayfish are particularly damaging freshwater invaders (Mathers et al. 2020b; O’Hea Miller et al. 2024), for example Signal crayfish ( Pontastacus leni-usculus ) alter aquatic community structure through reduction of benthic fish, salmonid fry and macro-invertebrate abundance (Edmonds et al. 2011;…”

“Crayfish are particularly damaging freshwater invaders (Mathers et al. 2020b; O’Hea Miller et al. 2024), for example Signal crayfish ( Pontastacus leni-usculus ) alter aquatic community structure through reduction of benthic fish, salmonid fry and macro-invertebrate abundance (Edmonds et al. 2011;…”

“…must also consider temperature-dependent prey response, given asymmetry in predator and prey responses to temperature can alter impact (Öhlund et al. 2015; Pintanel et al. 2021; Meehan and Lindo 2023) for a more holistic, accurate impact assessment (Dickey et al. 2020; South et al. 2022).”

“South et al. 2019).”

“…observations of population specific functional responses for freshwater invaders like Faxonius limosus , Faxonius rusticus and Pseudorasbora parva (Boets et al. 2019; Grimm et al. 2020; Chicatun et al. 2024) and suggests, if possible, impact assessments be carried out at the population not…”

“Comparative Functional response (FR), which captures density dependent consumption by an invader and compares it to other species, is a commonly used impact assessment (Dick et al. 2017; Faria et al. 2025).”

“This could be exacerbated by climate change and associated temperature increases, which can increase abundance or feeding rates of invasive species (Cuthbert and Briski 2021; Teesalu et al. 2025).”

“P. leptodactylus ’ higher abundance is surprising given P. leniusculus are typically more fecund (Chybowski 2013; Cìlbìz 2020) but likely reflects that P. leptodactylus were only sampled from lentic environments in which they had high abundance (Harwood et al. 2025), and P. leniusculus from lotic,…”

“…of population specific functional responses for freshwater invaders like Faxonius limosus , Faxonius rusticus and Pseudorasbora parva (Boets et al. 2019; Grimm et al. 2020; Chicatun et al. 2024) and suggests, if possible, impact assessments be carried out at the population not species level.”

“It is also important to note that these abundance estimates were based on CPUE which, driven by life history or climatic variables other than temperature, can vary substantially seasonally (Richards et al. 1996; Zimmerman and Palo 2012; Harwood et al. 2025) which could bias our impact estimates.”

“It is also important to note that these abundance estimates were based on CPUE which, driven by life history or climatic variables other than temperature, can vary substantially seasonally (Richards et al. 1996; Zimmerman and Palo 2012; Harwood et al. 2025) which could bias our impact estimates.”

“Furthermore, based on current P. leptodactylus distribution and predicted suitable invasion range there is potential for range expansion into northern Europe in 2050 (Hodson et al. 2024).”

“P. leptodactylus ’ higher abundance is surprising given P. leniusculus are typically more fecund (Chybowski 2013; Cìlbìz 2020) but likely reflects that P. leptodactylus were only sampled from lentic environments in which they had high abundance (Harwood et al. 2025), and P. leniusculus from lotic,…”

“Coupled with the high thermal tolerance of P. leptodactylus (Kir et al. 2025) this suggests a predator–prey asymmetry in thermal responses, which may alter impact (Öhlund et al. 2015; Pinta-nel et al. 2021; Meehan and Lindo 2023).”

“As well as consumer response to different contexts like temperature, prey response should also be incorporated into impact assessments for more accurate impact predictions (Kumschick et al. 2015; Urban et al. 2016; South et al. 2022).”

“This could be exacerbated by climate change and associated temperature increases, which can increase abundance or feeding rates of invasive species (Cuthbert and Briski 2021; Teesalu et al. 2025).”

“…of population specific functional responses for freshwater invaders like Faxonius limosus , Faxonius rusticus and Pseudorasbora parva (Boets et al. 2019; Grimm et al. 2020; Chicatun et al. 2024) and suggests, if possible, impact assessments be carried out at the population not species level.”

“Experiments were carried out in the dark, to mimic natural crayfish feeding conditions, and reduce the chance of limited activity due to light exposure (Boyle et al. 2025).”