Patterns of niche filling and expansion across the invaded ranges of an Australian lizard

Abstract

Studies of realized niche shifts in alien species typically ignore the potential effects of intraspecific niche variation and different invaded‐range environments on niche lability. We incorporate our detailed knowledge of the native‐range source populations and global introduction history of the delicate skink Lampropholis delicata to examine intraspecific variation in realized niche expansion and unfilling, and investigate how alternative niche modelling approaches are affected by that variation. We analyzed the realized niche dynamics of L. delicata using an ordination method, ecological niche models (ENMs), and occurrence records from 1) Australia (native range), 2) New Zealand, 3) Hawaii, 4) the two distinct native‐range clades that were the sources for the New Zealand and Hawaii introductions, and 5) the species’ global range (including Lord Howe Island, Australia). We found a gradient of realized niche change across the invaded ranges of L. delicata: niche stasis on Lord Howe Island, niche unfilling in New Zealand (16%), and niche unfilling (87%) and expansion (14%) in Hawaii. ENMs fitted to native‐range data generally identified suitable climatic conditions at sites where the species has established non‐native populations, whereas ENMs based on native‐range source clades and non‐native populations had lower spatial transferability. Our results suggest that the extent to which realized niches are maintained during invasion does not depend on species‐level traits. When realized niche shifts are predominately due to niche unfilling, fully capturing species’ responses along climatic gradients by basing ENMs on native distributions may be more important for accurate invasion forecasts than incorporating phylogenetic differentiation, or integrating niche changes in the invaded range.

Sex‐specific shifts in morphology and colour pattern polymorphism during range expansion of an invasive lizard

“…Furthermore, these morphological changes were driven by a different sex in each invasive population (males in Hawaii, females in New Zealand). As predicted, shifts in morphology were limited to the invasive populations (Hawaii, New Zealand) that had experienced niche shifts, either via niche expansion or unfilling, relative to the native range (Tingley et al., ). This suggests that selective processes (e.g.…”

“…However, the temporal shift in colour pattern in the Hawaiian delicate skink population appears to be slightly different in that the relative morph frequencies currently observed (98% in females, 6% in males; this study) have overshot those evident at an equivalent latitude in the native range (Townsville: 19°S, 83% in females, 34% in males; Forsman & Shine, ). Thus, the divergent selection on colour pattern has intensified in the Hawaiian population, and might be a result of niche evolution in Hawaii (Tingley et al., ) or differences in microhabitat or predation pressure in the Hawaiian Islands. In contrast, contrary to our predication, no shift in colour morph frequency was observed in New Zealand, and only minor shifts (presumably due to genetic admixture of source clades with differing colour morph frequencies) were observed on Lord Howe Island.…”

“…The most substantial phenotypic shifts are expected in the Hawaiian Islands, where both niche expansion (i.e. when a species colonizes environmental conditions in its invaded range that are present, but unoccupied, in its native range) and unfilling have been demonstrated (Tingley et al., ). As sexual dimorphism in lizards is primarily driven by selection related to environmental factors (Bonneaud et al., ; Herrel et al., , ), the potential for sex‐specific shifts in morphology will be highest in populations that experience the largest changes in their realized niche (i.e. most likely to occur in Hawaii and New Zealand). As the relative presence of the mid‐lateral stripe appears to be closely linked to latitude (Forsman & Shine, ), we predict that post‐introduction shifts in this colour pattern polymorphism will only be evident where there are substantial differences in the latitude of the source and introduced population (i.e.…”

“… The magnitude of phenotypic change during range expansion will be related to the degree of realized niche shift between each source population(s) and invasive population. For instance, as niche conservatism is evident on Lord Howe Island (Tingley, Thompson, Hartley, & Chapple, ), the potential for phenotypic shifts is expected to be minor. Any changes that are present will most likely be the result of the genetic admixture among four native‐range source populations that is present on the island (Chaplin, ).…”

“…The most substantial phenotypic shifts are expected in the Hawaiian Islands, where both niche expansion (i.e. when a species colonizes environmental conditions in its invaded range that are present, but unoccupied, in its native range) and unfilling have been demonstrated (Tingley et al, 2016).…”