Effects of invasive wetland macrophytes on habitat selection and movement by freshwater turtles

Abstract

Invasive species can significantly impact native wildlife by structurally altering habitats and access to resources. Understanding how native species respond to habitat modification by invasive species can inform effective habitat restoration, avoiding inadvertent harm to species at risk. The invasive graminoids Phragmites australis australis (hereafter Phragmites) and Typha × glauca are increasingly dominating Nearctic wetlands, often outcompeting native vegetation. Previous research suggests that turtles may avoid invasive Phragmites when moving through their home ranges, but the mechanisms driving avoidance are unclear. We tested two hypotheses that could explain avoidance of invaded habitat: (1) that stands of invasive macrophytes (Phragmites and Typha x glauca) impede movement, and (2) that they provide inadequate thermal conditions for turtles. We quantified active-season movements of E. blandingii (n = 14, 1328 relocations) and spotted turtles (Clemmys guttata; n = 12, 2295 relocations) in a coastal wetland in the Laurentian Great Lakes. Neither hypothesis was supported by the data. Phragmites and mixed-species Typha stands occurred within the home ranges of mature, active E. blandingii and C. guttata, and were used similarly to most other available habitats, regardless of macrophyte stem density. Turtles using stands of invasive macrophytes did not experience restricted movements or cooler shell temperatures compared to other wetland habitat types. Control of invasive macrophytes can restore habitat heterogeneity and benefit native wetland species. However, such restoration work should be informed by the presence of at-risk turtles, as heavy machinery used for control or removal may injure turtles that use these stands as habitat.

Spatial and thermal ecology of juvenile head‐started Blanding's turtles Emydoidea blandingii

“…Starking‐Szymanski et al (2018) also showed larger home ranges when their juveniles were released in non‐preferred habitat, and smaller home ranges when released in preferred habitat. Similar to our observation of juveniles avoiding open water, a study by Angoh et al (2021) found Blanding's turtles avoided landscape features of their habitat that were open land, forest and open water. Therefore, it is also plausible our SMAs were small due to multiple factors.…”

Effects of release method on the survival, somatic growth, and body condition of headstarted turtles

“…Although we considered season as a covariate in our analysis, the lack of data from wild populations in late summer made it challenging to accurately estimate the effect of season on body condition. In addition, the ecology and demography of Blanding's turtle populations vary geographically (Edge et al 2010, Paterson et al 2012, Ritchie 2017, Angoh et al 2021), so our results should be interpreted with caution because individual‐ (e.g., maternal effects), population‐ (e.g., density), and landscape‐level (e.g., land cover type) processes can affect conservation success of headstarted turtles.…”

“…Average daily temperature (1981-2010) ranges from −3.6°C in January to 22.6°C in July, whereas the mean annual precipitation ranges from 750-900 mm (Environment and Natural Resources 2023). Additional information about the study site can be found in Angoh et al (2021).…”

“…The weight of the transmitter and epoxy did not exceed 5% of the turtle's body mass, and thus, was unlikely to decrease fitness. We have not observed decreased fitness in previous use of these methods (Edge et al 2010, Rasmussen and Litzgus 2010, Angoh et al 2021. We tracked a variable number of hard-or delayed-release turtles for 1-6 additional years (Table S1, available in Supporting Information).…”

Baseline Invasive Species Community Mapping at Lower Klamath Wetland, Oregon-California (USA)

“…The result of these drought periods has been an significant reduction of previously productive wetlands areas that are now colonized by invasive species such as perennial pepperweed (Lepidium latifolium), poison hemlock (Conium maculatum), kochia (Kochia scoparia) and quackgrass (Elymus repens), which now dominate wetland management units and considerably reducing the energetic carrying capacity and the quality of nesting habitats [2]. Invasive species are altering the structure of the vegetation of these habitats and its functionality [3] e.g., by reducing the number of breeding ducks. Among the flood management practices to restore wetland vegetation communities are flood management rotations that include intensive grazing, mowing and chemical treatments to facilitate the restoration of wetland vegetation communities and adjacent upland habitats [4].…”