Exotic invasive plants alter thermal regimes: implications for management using a case study of a native ectotherm

Abstract

Summary1. Exotic invasive plants can alter ecosystem structure and function, yet there is a paucity of evidence regarding broadly applicable mechanisms. We hypothesized that denser growth patterns characteristic of exotic invasive plants lead to a common effect of reduction and homogenization of environmental temperatures and that these alterations compromise thermal quality of habitat for ectotherms. 2. We quantified thermal regimes within native and exotic plant-dominated habitats, including monocultures of 11 exotic species as well as stratified mixed-exotic habitats in a temperate forest landscape in the eastern US. 3. Exotic plant-dominated habitats exhibited reduced and less variable temperature compared to their native counterparts, with stratified mixed-exotic habitats exhibiting the lowest temperatures overall and exotic shrubs (six species) the lowest as a structural group. Thermal effects were extended beyond the growing season of native vegetation owing to extended leaf phenology of exotic woody species. 4. To demonstrate that these effects can alter environmental cues and adversely impact native species, we used a 4-year radiotelemetry study and laboratory thermal preference trials to relate habitat thermal quality to multiscale resource selection by a native snake, Agkistrodon contortrix. To further test the effect of vegetation structure and the efficacy of targeted management, we removed exotic foliar cover from eight 400 m 2 plots.5. Radio-tagged snakes avoided exotic vegetation at multiple spatial scales. In contrast to previous studies of A. contortrix, snakes exhibited preference for sites composed of higher native vegetation density and height. Response to exotic foliage removal was also rapid -including use of sites during gestation and parturition. 6. Together with other recent studies, our results suggest a direct, non-trophic effect that is common to a broad range of exotic invasive plant species in a variety of ecological contexts. We further offer a mitigation technique that may be implemented when large-scale control or eradication is not cost-effective or ecologically sound.

A spatial genomic approach identifies time lags and historical barriers to gene flow in a rapidly fragmenting Appalachian landscape

“…Copperheads rely on rocky overwintering hibernacula located high on steep‐sided and often south‐facing slopes (Maigret & Cox, ), sites disproportionately destroyed by surface mining (Maigret et al, ). Copperheads are also generally intolerant of dense, invasive vegetation common to many reclaimed surface mines (Carter, Eads, Ravesi, & Kingsbury, ; Carter, Ravesi, Eads, & Kingsbury, ). Additionally, herpetofauna generally, and pit vipers in particular, have been shown to be especially vulnerable to vehicular traffic (Andrews & Gibbons, ; Shepard, Dreslik, Jellen, & Phillips, ), and elevated genetic differentiation associated with highways has been detected using microsatellite markers (Clark, Brown, Stechert, & Zamudio, ; DiLeo, Rouse, Dávila, & Lougheed, ).…”

“…Copperheads rely on rocky overwintering hibernacula located high on steep-sided and often south-facing slopes (Maigret & Cox, 2018), sites disproportionately destroyed by surface mining . Copperheads are also generally intolerant of dense, invasive vegetation common to many reclaimed surface mines (Carter, Eads, Ravesi, & Kingsbury, 2015;Carter, Ravesi, Eads, & Kingsbury, 2017). Additionally, herpetofauna generally, and pit vipers in particular, have been shown to be especially vulnerable to vehicular traffic (Andrews & Gibbons, 2005;Shepard, Dreslik, Jellen, & Phillips, 2008), and elevated genetic differentiation associated with highways has been detected using microsatellite markers (Clark, Brown, Stechert, & Zamudio, 2010;DiLeo, Rouse, Dávila, & Lougheed, 2013 Using RADseq data and nonspatial and spatially informed analyses, we investigated the potential for recently formed population structure across A. contortrix in eastern Kentucky as a result of this landscape change, with a particular focus on the effects of habitat fragmentation via surface coal mining and through the network of historical (c. 1920) and more recently constructed (c. 1975) high-traffic roads.…”

Thermal landscape change as a driver of ectotherm responses to plant invasions

“…Changes in thermal quality caused by plant invasions are expected to be largest when the alien plants present novel growth forms or structural features relative to the dominant native vegetation [9,26]. For example, larger size and faster-growing alien trees can cause reductions in light and temperature in shrubland habitats [27,28], and those with extended phenology can lengthen thermal effects beyond the growing season of native vegetation [29].…”

“…Using radio-tracking, field observations and experimental trials, several studies in this review showed that invaded areas were actively avoided by individuals, including females selecting incubation sites (e.g. [27,29,45]). The responses of ectothermic individuals using invaded areas were also assessed.…”

To forage, mate, or thermoregulate: Influence of resource manipulation on male rattlesnake behavior

“…We placed 10 physical models of massasaugas throughout the study site to collect hourly operative environmental temperatures (T e ) that approximate T b s of snakes in the absence of clear behavioral or physiological thermoregulation (i.e., thermoconformity) (Blouin-Demers & Weatherhead, 2001;Carter, Eads, Ravesi, & Kingsbury, 2015;Harvey & Weatherhead, 2011). The models were 10-cm-long and 2.54-cm-diameter copper tubes which we painted dark brown to mimic the thermal properties of a massasauga.…”