Long‐term drivers of persistence and colonization dynamics in spatially structured amphibian populations

Abstract

Many organisms live in networks of local populations connected by dispersing individuals, called spatially structured populations (SSPs), where the long-term persistence of the entire network is determined by the balance between two processes acting at the scale of local populations: extinction and colonization. When multiple threats act on an SSP, a comparison of the different factors determining local extinctions and colonizations is essential to plan sound conservation actions. Here we assessed the drivers of long-term population dynamics of multiple amphibian species at the regional scale. We used dynamic occupancy models within a Bayesian framework to identify the factors determining persistence and colonization of local populations. Since connectivity among patches is fundamental for SSPs dynamics, we considered two measures of connectivity acting on each focal patch: incidence of the focal species and incidence of invasive crayfish. We used meta-analysis to summarize the effect of different drivers at the community level. Persistence and colonization of local populations were jointly determined by factors acting at different scales. Persistence probability was positively related to the area and the permanence of wetlands, while it showed a negative relationship with the occurrence of fish. Colonization probability was highest in semipermanent wetlands and in sites with a high incidence of the focal species in nearby sites, while it showed a negative relationship with the incidence of invasive crayfish in the landscape. By analyzing long-term data on amphibian population dynamics, we found a strong effect of some classic features commonly used in SSP studies, such as patch area and focal species incidence. The presence of an invasive alien species at the landscape-scale emerged as one of the strongest drivers of colonization dynamics, suggesting that studies on SSPs should consider different connectivity measures more frequently, such as the incidence of predators, especially when dealing with biological invasions.

Similar species, different fates: Abundance dynamics in spatially structured populations of common and threatened frogs

“…The crayfish showed its stronger effects at the SSP scale (Figure 3c), in agreement with previous studies on amphibian population dynamics (Falaschi et al, 2021; Manenti et al, 2020). The strong relationship between crayfish incidence and abundance confirms that this invasive species can alter SSP dynamics across the landscape and possibly reduce the number of immigrants from nearby wetlands (Manenti et al, 2020).…”

“…The red swamp crayfish has a great potential to negatively affect frog populations: it has a generalist diet, can feed on tadpoles and egg masses, and can modify habitats through the consumption of macrophytes and burrowing (Cruz et al, 2006;Lo Parrino et al, 2020). Previous analyses on the presence/absence of R. dalmatina revealed no site-level effect of invasive crayfish (Bélouard et al, 2019;Falaschi et al, 2021). Still, our results indicate lower abundance in wetlands occupied by this invasive species (Figure 3c), even if the crayfish was only found in a few sites (max.…”

Visual recognition and coevolutionary history drive responses of amphibians to an invasive predator

“…Few studies have investigated behavioral responses of amphibian larvae to this invasive crayfish, and to our knowledge only one of them showed that behavioral shifts can improve the survival of larvae (Polo-Cavia and Gomez-Mestre 2014), while others suggested that reduction of activity and/or altered microhabitat use do not necessarily reduce vulnerability (Rebelo and Cruz 2005). In fact, multiple native amphibians underwent rapid declines and local extinctions after the invasion of the American crayfish (Gamradt and Kats 1996, Cruz et al 2008, Ficetola et al 2011, Liu et al 2018, Falaschi et al 2021, suggesting that the responses of native amphibians can be insufficient to withstand the predatory pressure posed by this voracious crayfish, at least for some species.…”

Invasive predators induce plastic and adaptive responses during embryo development in a threatened frog

“…Nowadays Procambarus clarkii is widespread in Italy and it invaded the study area between (Lo Parrino et al 2020). Landscape-level analyses have shown that the crayfish has strong effects on frog populations, reducing tadpole survival in the wild and affecting the dynamics of population networks (Ficetola et al 2012, Falaschi et al 2021.…”

“…Despite the strong predatory pressure imposed by Procambarus clarkii, so far, the total abundance of clutches in invaded populations by the crayfish does not seem to have undergone a significant decrease (Manenti et al 2020). Frog persistence is certainly due to the immigration of frog individuals from source populations , Falaschi et al 2021), but it is also possible that plastic and adaptive responses to this predator help to counteract the heavy predator pressure, allowing a sufficient number of tadpoles to attain metamorphosis.…”