Niche lability mitigates the impact of invasion but not urbanization

Abstract

Native species can coexist with invasive congeners by partitioning niche space; however, impacts from invasive species often occur alongside other disturbances. Native species' responses to the interactions of multiple disturbances remain poorly understood. Here we study the impacts of urbanization and an invasive congener on a native species. Using abundance (catch-per-unit effort) and vertical distribution of native green anoles (Anolis carolinensis) and invasive brown anoles (Anolis sagrei) across a gradient of natural-to-urban forests, we ask if niche shifting (lability) is occurring, and if it can mitigate impacts from one or both disturbances. We use generalized linear models to relate species abundances across the landscape to urbanization, forest structural complexity, and congener abundances (i.e., A. sagrei); and test for an interaction between urbanization and congener abundance. Our data show that A. sagrei presence results in a 17-fold upward shift in vertical niche of A. carolinensis-an 8.3 m shift in median perch height, and models reveal urbanization also drives an increase in A. carolinensis perch height. A. carolinensis and A. sagrei abundances negatively and positively correlate with urbanization, respectively, and neither species' abundance correlate with congener abundance. Despite a positive correlation between A. sagrei abundance and urbanization, our results do not show evidence of this interaction affecting A. carolinensis. Instead, niche lability appears to enable the native species to mitigate the impact of one driver of decline (invasive competition) while our data suggest it declines with the second (urbanization).

Ecological patterns and processes in the vertical dimension of terrestrial ecosystems

“…• Niche plasticity/lability hypothesis: Species can adjust their vertical niche in pursuit of optimal conditions (microclimatic and/or resource; Basham et al, 2022) or as a compensatory response to disturbance (Borden et al, 2022;Neilly et al, 2018) • Arboreal trait syndrome: The amalgamation of physiological, behavioural and morphological adaptations to living above-ground generates a syndrome of traits (Scheffers & Williams, 2018). A similar hypothesis by Scheffers et al (2017) proposes that, as a consequence of this syndrome, arboreal species should also have higher dispersal potential which would increase resistance and resilience to both current and historical environmental instability, respectively.…”

“…Novel competitive interactions can also trigger shifts in vertical niche preferences. In northern Florida, USA, the brown anole Anolis sagrei , a non‐native, aggressive and understorey dwelling species, caused an 8.3 m shift in median perch height in the native green anole Anolis carolinensis (Borden et al, 2022). Overall competition likely plays an important role in forest diversity dynamics, particularly when there are strong similarities in food and habitat preferences.…”

“…Species living towards the canopy experience higher rates of evaporative water loss; hence, stronger desiccation resistance (often combined with other adaptations such as larger body size/mass) could be an advantage (Bujan et al, 2016; Hood & Tschinkel, 1990; Tracy et al, 2010). Niche plasticity/lability hypothesis : Species can adjust their vertical niche in pursuit of optimal conditions (microclimatic and/or resource; Basham et al, 2022) or as a compensatory response to disturbance (Borden et al, 2022; Neilly et al, 2018). Here, two traits are prerequisite for a niche shift—suitable morphology to expand into a new niche (e.g.…”

Rapid introgression of invasive alleles following hybridization between a native Anolis lizard species and a cryptic invader across an urban landscape

“…To investigate the relationship between anthropogenic habitat disturbance and the genotypes of hybrid green anoles, canopy cover and impervious surface area were selected as quantitative proxies of urbanization. These variables are commonly used as metrics of urbanization (Borden et al, 2022), are expected to be negatively correlated (i.e., canopy cover will be low and impervious surface area will be high in distinctly urban habitats), and are related to environmental temperatures relevant for lizards (Ackley et al, 2015;Battles & Kolbe, 2019;Kolbe et al, 2016). Using GPS coordinates for the site of capture of each hybrid individual, values for both variables were extracted from the 2016 US Forest Service Tree Canopy Cover and 2016 Percent Developed Imperviousness GIS layers produced by the National Land Cover Database (Yang et al, 2018).…”

Rapid morphological shifts in a co-invaded assemblage of lizards

“…Anecdotally, local Hawaiians frequently told us that the brown anoles were displacing green anoles, despite the layman's inability to distinguish between a brown A. carolinensis and an A. sagrei may limit the reliability of these observations. Furthermore, if A. sagrei were displacing A. carolinensis to higher perches, as seen in the southeastern United States (Edwards and Lailvaux 2012; Stuart et al 2014;Borden et al 2022), this may cause A. carolinensis to be less visible to the casual observer even if they remained present at unchanging density. Experimental studies have also demonstrated that A. carolinensis' ability to colonize novel islands is apparently inhibited (if not prevented) by a co-invasion of A. sagrei (Losos and Spiller 1999) but given A. carolinensis' earlier colonization of Hawai'i, these phenomena may not be relevant in this system.…”