Network analysis for species management in rivers networks: Application to the Loire River

Abstract

Forecasting the colonization process is important for wildlife managers who supervise the reintroduction of endangered species or control the spread of invasive species. Patch connectivity is thus critical to predicting the fates of expanding populations. Connectivity in river networks results from river dendritic structure and dispersal modality of organisms. Both factors may strongly affect the colonization process and the efficiency of conservation action plans. Based on empirical data, we simulated, using a simplified model with limited number of parameters, the colonization of a large river network, the Loire River, by the native Eurasian beaver and the invasive African clawed frog. For each species, we inferred model parameters (dispersal behavior and distances) by comparing the simulated and the observed distributions. Using network theory, we evaluated the efficiency of alternative conservation strategies to prevent or promote colonization of the river network. Network robustness to fragmentation and disturbance was also assessed. The model accurately predicted more than 70% of the observed species ranges. Conservation strategies that selectively protect habitat patches with the highest connectivity values provide a weak advantage at preventing connectivity loss compared to random protection strategies. In contrast, the targeted destruction of highly connected patches had a much stronger effect on the fragmentation of the network than the random removal of habitat patches. Spatial network topology strongly contributes to determining colonization patterns of large river watersheds. Network theory allows tests for robustness of rivers to fragmentation and disturbance, and identification of strategies for conservation planning.

Assessing the effect of landscape features on pond colonisation by an elusive amphibian invader using environmental DNA

“…Contrary to our expectations, the density of the hydrographic network around the ponds did not significantly affect the colonisation process at all buffer sizes. This seems to contradict previously published works, which hypothesised that lotic systems may facilitate dispersal between ponds (Chaput- Bardy et al, 2017;Fouquet & Measey, 2006;Measey, 2016;Vimercati et al, 2017), and the observation that X. laevis successfully breeds in streams in Portugal (Moreira, Marques, Sousa, & Rebelo, 2017). The density of the hydrographic network might thus not be a good predictor of connectivity, if, for example, a straight stream flowing between ponds facilitates the dispersal of individuals.…”

“…This seems to contradict previously published works, which hypothesised that lotic systems may facilitate dispersal between ponds (Chaput- Bardy et al, 2017;Fouquet & Measey, 2006;Measey, 2016;Vimercati et al, 2017), and the observation that X. laevis successfully breeds in streams in Portugal (Moreira, Marques, Sousa, & Rebelo, 2017). This seems to contradict previously published works, which hypothesised that lotic systems may facilitate dispersal between ponds (Chaput- Bardy et al, 2017;Fouquet & Measey, 2006;Measey, 2016;Vimercati et al, 2017), and the observation that X. laevis successfully breeds in streams in Portugal (Moreira, Marques, Sousa, & Rebelo, 2017).…”

“…This figure corresponds to the dispersal distance which best predicted the colonisation of the Loire river drainage by X. laevis according to Chaput-Bardy et al (2017). We included all ponds where the species was detected.…”

“…For absences, we selected only ponds within 4 km from a colonised pond. This figure corresponds to the dispersal distance which best predicted the colonisation of the Loire river drainage by X. laevis according to Chaput-Bardy et al (2017). We therefore selected ponds that can be theoretically reached from a colonised pond.…”

“…Breeding calls are emitted underwater and are only detected using hydrophones, which severely limits species detection in water (Measey et al, 2012;Vimercati, Davies, Hui, & Measey, 2017). Nevertheless, the species has been reported to use hydrographic networks to disperse overland between ponds (Chaput-Bardy, Alcala, Secondi, & Vuilleumier, 2017;Fouquet & Measey, 2006;Measey, 2016), at the juvenile and adult stages (Courant, 2017;De Villiers & Measey, 2017;Measey, 2016). Similarly to what has been observed in other invasive species characterised by high elusiveness (Jarić et al, 2019), an established alien population of X. laevis can remain undetected for years before any control action is undertaken (Measey et al, 2012;Sousa, Maurício, & Rebelo, 2018;Wang, Hong, & Measey, 2019).…”