Perceptual Range, Targeting Ability, and Visual Habitat Detection by Greater Fritillary Butterflies Speyeria cybele (Lepidoptera: Nymphalidae) and Speyeria atlantis

Abstract

Butterflies are widely invoked as model organisms in studies of metapopulation and dispersal processes. Integral to such investigations are understandings of perceptual range; the maximum distance at which organisms are able to detect patches of suitable habitat. To infer perceptual range, researchers have released butterflies at varying distances from habitat patches and observed their subsequent flight behaviors. It is often assumed that butterflies rely on visual senses for habitat detection; however, this assumption has not been explicitly investigated. Here, we assess the extent and sensory determinants of perceptual range for the great spangled fritillary (Speyeria cybele (Fabricius, 1775)) and Atlantis fritillary (Speyeria atlantis (W.H. Edwards, 1862)). This was achieved by experimentally releasing butterflies over open water at various distances from a lake island, representing an isolated habitat patch in a dichotomous habitat-matrix landscape. To infer whether butterflies rely on vision for habitat detection, we exposed a subset of butterflies to a series of intense light flashes before release to induce flash blindness (bleaching of photoreceptive rhodopsins) without affecting olfaction. Flashed individuals were 30.1 times less likely to successfully navigate to the target island after release, suggesting butterflies rely primarily on visual senses to navigate fragmented landscapes. For unflashed butterflies, the likelihood of successful navigation decreased by a factor of 2.1 for every 10 m increase in release distance. However, no specific distance threshold for perceptual range was observed. We therefore suggest that perceptual range is best viewed as a continuum of probabilities (targeting ability), reflecting the likelihood of habitat detection across a range of distances.

Distinguishing effects of area per se and isolation from the sample‐area effect for true islands and habitat fragments

“…Most interestingly, our modelling framework simultaneously resolved that effects of area per se on species' abundances and occurrences varied significantly with species‐specific functional traits, suggesting that mechanisms outlined by the theory of island biogeography are not neutral with respect to species identity. Whether species' sensitivity to fragmentation varies predictably with functional traits is a long‐standing and pertinent question in conservation biology (Roland and Taylor 1997, Lens et al 2002, Gehring and Swihart 2003, Henle et al 2004, Tscharntke and Brandl 2004, Thies et al 2005, Ewers and Didham 2006, Prugh et al 2008, Barbaro and Van Halder 2009, Öckinger et al 2009, Hanski 2015, Warzecha et al 2016, MacDonald et al 2018a, 2019). In this study, effects of area per se were significantly greater for butterfly species with smaller wingspans.…”

“…The presence/absence of preferred larval host plants (compiled from Hall et al 2014, Acorn and Sheldon 2017) for each species on each island was included as a binary variable. We included species' wingspan (mm; as reported in Burke et al 2011) in models as a functional trait variable, serving as a measure of both body size and mobility/dispersal ability (Roland and Taylor 1997, Lens et al 2002, Ewers and Didham 2006, Öckinger et al 2009, MacDonald et al 2018a, 2019). Other functional traits predicted to relate to species' sensitivity to fragmentation (e.g.…”

“…Indeed, area per se and isolation effects have been inferred to vary widely among species, even within single landscapes and taxa (Henle et al 2004, Ewers and Didham 2006, Nowicki et al 2007, Öckinger et al 2009, Hanski 2015, Hillebrand et al 2018, MacDonald et al 2018a). Functional traits, including body size (Gehring and Swihart 2003, Henle et al 2004, Larsen et al 2008, Prugh et al 2008, Barbaro and Van Halder 2009, Warzecha et al 2016), mobility/dispersal ability (Roland and Taylor 1997, Lens et al 2002, Ewers and Didham 2006, Öckinger et al 2009, MacDonald et al 2018a, 2019), degree of ecological specialization (Tscharntke and Brandl 2004), rarity/conservation status (Ewers and Didham 2006) and trophic position (Tscharntke et al 2002, Thies et al 2005, Ewers and Didham 2006) are hypothesized to relate species' sensitivity to area per se and isolation. Still, relatively few empirical studies have investigated how functional traits relate to interspecific variation in responses to area per se and isolation or how this interspecific variation scales to emergent patterns of species richness, such as those reflected in ISARs (Melbourne et al 2004, but see Barbaro and Van Halder 2009, Öckinger et al 2009).…”

Morphometric criteria to differentiate Drosophila suzukii (Diptera: Drosophilidae) seasonal morphs

“…A classification and regression tree analysis were used to determine the best discriminatory criteria to classify D. suzukii morphs. A classification and regression tree analysis is a nonparametric modeling approach that creates tree models by continuously splitting the data into homogenous groups based on categorical or continuous predictor variables [52,53].…”

“…We used a classification tree model because the interpretation is straightforward relative to other analytical approaches [52,59]. Decision trees have been used previously in entomological research for determining predictor variables in both field and systematic studies [60][61][62].…”